62 Comments

1. DCM on January 8, 2016 at 13:18

   It’s what we need to be doing.

2. Al Globus on January 8, 2016 at 14:29

   Thanks for the reference! I thought perhaps that it might be good for us to be in contact.

   I was a little disappointed that you didn’t mention what I think is the most important part of our study: that at 500 km ELEO you may not need any radiation shielding at all. This means a two to three orders of magnitude mass reduction vs deep space settlements. The mass calculations may be found at http://space.alglobus.net/papers/Easy.pdf with a pointer to the online excel implementation.

   I stated a small informal email group to discuss ELEO (equatorial low earth orbit) settlements that perhaps you might like to join. Our first project is a survey to see if people might be willing to live in 4 rpm cylinders 110 m in length, which should be starting in a day or two.

3. Michael on January 8, 2016 at 14:40

   It may be better to have a water jacket between the outer and inner structure with the ability to move a large amount of the water to a smaller inner radiation shelter when the Sun flares up as added protection. I am of the opinion that unless we resolve the ‘infrastructure’ problem we will never build interstellar craft.

   I once though of the idea of using as much of a single stage rocket to orbit as possible to be used as building materials to expand into space instead of returning to earth. For instance the rocket motors are removed and reused for deep space missions, the aluminium material is ground down into particles that can be used as rocket fuel, extruding materials as well as vapour deposition materials. Any remaining fuel is stored for power and propellant. It seems a bit of waste to even bring back the rocket components for reuse on earth when we want to expand into space. We could simply have a very small return vehicle instead.

   Any good?

4. J. Jason Wentworth on January 8, 2016 at 14:48

   This is an excellent and timely article! The soft, carbon-rich habitat envelopes also–unlike metal modules–*don’t* produce health-harming showers of secondary cosmic rays from the impacts of the primaries. This makes inflatable habitats desirable for spaceships, too. Below is information on a reusable manned lunar and planetary spaceship concept that would dovetail perfectly with Greg’s inflatable “proto-colony” proposal–in fact, his idea would enable it, because it would use concepts that he covers in his article:

   Here (see: http://www.oldrocketforum.com/showthread.php?t=9464&highlight=S-IVC and http://www.oldrocketforum.com/showthread.php?t=9167&highlight=S-IVC ) are two links to reports on existing (but not used) 1960s-vintage technologies that we could use today to create “DIY” (Do-It-Yourself) reusable manned lunar and planetary spaceships which could be *launched directly from the Earth’s surface*. These reports cover work that NASA and its contractors did in the mid-to-late 1960s in preparation for chemically-propelled manned flyby missions to Venus and/or Mars (some trajectories allowed for close flybys of *both* planets in a single mission), using modified Apollo/Saturn hardware. Astonishingly, they found that long-term storage of liquid oxygen and liquid hydrogen propellant was possible in a modified (better insulated) Saturn S-IVB stage, which they designated the S-IVC. With today’s more advanced insulating materials, current LOX/kerosene and LOX/LH2 rocket stages (Falcon 9, Atlas V, Delta IV, H-2, and Ariane 5 first stages [or lowest core stages]) could be used as the main elements of such spaceships. Now:

   All of these first stages or core stages are probably capable of lofting themselves into Low Earth Orbit (as SSTO vehicles) without assistance. (The Ariane 5’s LOX/LH2-powered core stage–it has a mass fraction of 0.912–definitely can; it’s listed in G. Harry Stine’s 1996 SSTO book “Halfway to Anywhere: Achieving America’s Destiny in Space,” and I’ve listed the other SSTO-capable rocket stages below, as a reference.) Such a rocket stage, after having boosted itself into orbit, could be outfitted as a spaceship. The additions (which would be launched separately) include an inflatable crew module (with a life support system) mounted in front, extra insulation for the stage’s propellant tanks (although this might be able to be applied to the stage before its SSTO launch), a guidance and attitude control system, communications equipment, and a docking system (for manned landers, for docking the spaceship with a space station, etc.) at the front end of the crew module (the docking system [with an airlock, if desired] could be integrated into the inflatable module when it was built). Also:

   Since the inflatable modules have a rigid central core structure, it might not be necessary to rigidize the envelope by pre-impregnating its fabric outer layer with a vacuum-hardening (or UV-hardening) resin. The inflatable module’s central framework–if one was included in the spaceship’s inflatable crew module–could probably handle the structural loads imposed by docking operations. Also, most rockets’ first stages have rocket engines whose nozzles aren’t optimized for peak efficiency in a vacuum, since they operate in the Earth’s atmosphere (the engine nozzles of some lowest core stages, which operate longer at high altitudes, may be vacuum-optimized). The non-vacuum-optimized nozzles of first stage engines could easily be made so (after the stage had lofted itself into orbit) by adding nozzle skirt extensions (made of niobium or other high-temperature, refractory metals) to the existing nozzles, so that the engines would operate in space at maximum efficiency. In addition:

   Some historic and existing rocket upper stages were/are also capable of SSTO performance, and these (after being suitably outfitted in orbit) could also serve as spaceships (or as space tugs, interorbital shuttles, or–with the addition of removable landing gear “kits”–as Moon or asteroid landing/ascent vehicles). These small spacecraft would make excellent lunar surface-to lunar orbit (and back down to the Moon) short-range shuttles, which could ferry personnel and supplies between the Moon’s surface and lunar orbit (or Lagrangian point) space stations (as well as interplanetary spaceships orbiting the Moon to refuel and pick up supplies on departure or arrival from/to the Earth-Moon system), and vice-versa. Plus:

   If a Lunatron–an electromagnetic launching track (proposed by Arthur C. Clarke, refined by Neil P. Ruzic, and studied in detail by William Escher at the NASA Marshall space Flight Center in 1962 [see: http://arc.aiaa.org/doi/abs/10.2514/6.1963-1508 ; he coined the name “lunatron”])–was set up at a lunar base, these upper stage-based lunar shuttle spacecraft would be even more attractive, because they could be launched into lunar orbit and beyond using virtually *no* rocket propellant (for reaching an orbit around the Moon, they would only have to conduct a very brief “perilune-raising” burn, to raise the perilune point of the orbit above the Moon’s surface [the perilune point would be *at* the surface otherwise, since the launching track is on the surface]). Below are references on SSTO-capable existing and historic rocket stages:

   The SSTO-capable rocket stages (listed on page 42 of Stine’s book “Halfway to Anywhere: Achieving America’s Destiny in Space”–I got my copy from AbeBooks.com http://www.abebooks.com ) are the Titan II Stage 1 (mass fraction 0.966), Black Arrow Stage 1 (mass fraction 0.922), Saturn V Stage 1 (mass fraction 0.941), Titan III Stage 1 (mass fraction 0.948), Titan IV Stage 1 (mass fraction 0.947), Delta 6925 Stage 1 (mass fraction 0.944), Atlas E (mass fraction 0.933), Saturn V Stage 2 (mass fraction 0.927), Zenit Stage 1 (mass fraction 0.903), Titan III Stage 2 (mass fraction 0.923), Saturn IB Stage 2 (mass fraction 0.913), Titan II Stage 2 (mass fraction 0.908), Saturn IB Stage 1 (mass fraction 0.907), Ariane 5 Stage 1 (mass fraction 0.912), Saturn V Stage 3 (mass fraction 0.905), and Energia core (mass fraction 0.907).

5. J. Jason Wentworth on January 8, 2016 at 15:03

   Greg Matloff’s inflatable rotating space station “proto-colony” design could also be set up in a crater on Phobos and/or Deimos so that the body of each satellite would protect the stations from GCRs and solar wind particles, requiring radiation shielding *only* on the upward (space-facing) sides of the modules. A pressurized corridor/station support beam running from one edge of a crater to the other would permit access to the station’s axis in the center, and it would support the rotating station at that point as well. Also:

   Since the Martian moons’ gravity is negligible, this would confer two important benefits: [1] the corridor/station support beam wouldn’t need to be strongly (heavily) built, and [2] the artificial local gravity vector inside the modules would be virtually perpendicular to each module’s deck (floor), since the deviation in the “centrifugal gravity’s” direction of ‘local down’ caused by either moon’s gravity (acting at a right angle to the “centrifugal gravity) would be virtually zero. This would enable visitors to stay there indefinitely without long-term low-gravity health risks, since they could live in a 1 G environment inside the moons’ rotating surface stations (rotating stations in Mars orbit could provide 1 G environments too, of course, but they would require much more radiation shielding, on *all* sides). In addition:

   Such crater-(radiation) shielded, rotating inflatable stations could also be set up on asteroids (and on other small moons), even Vesta and Ceres. (Angling the modules’ floors to compensate for the greater deviation of the local gravity [on the larger asteroids] pulling at a right angle to the surface stations’ “centrifugal gravity” would ensure that ‘local down’ is perpendicular to the floor in each module.) Having the residents spend most of their time inside the 1 G rotating surface stations should prevent fractional-G health problems, so that the “gravitational segregation” of humanity (which Arthur C. Clarke, Patrick Moore, and others feared would render native-born Lunarian and Martian colonists unable to visit their ancestors’ home planet) could be avoided.

6. TLDR on January 8, 2016 at 15:09

   I would place the ISS Centrifuge demo first in priority. In order to achieve long-distance human exploration in space (e.g., Mars), humanity needs to master the technology of artificial gravity.

7. Hop David on January 8, 2016 at 15:37

   ” the habitat should consist of two modules arranged in dumbbell configuration connected by a variable-length spar with a hollow, pressurized interior. The rotation rate of the modules around the center could be adjusted to provide various levels of artificial gravity. ”

   That’s an exciting notion. As you say, we could determine if Mars or even Lunar gravity are sufficient to maintain health. We could also see how well humans adapt to high ?, angular velocity. We used to think 1 rpm was the ceiling but theres’s some indication we could adjust to 4 rpm, even higher.

   Since spin gravity scales with ?^2 * r, a four-fold increase in ? could translate to a 16 fold decrease in hab radius.

   If small spin habs suffice to keep workers healthy, asteroid mines become more doable. I talk about that at http://hopsblog-hop.blogspot.com/2013/12/whats-minimum-spin-hab.html

8. Andrew Palfreyman on January 8, 2016 at 15:50

   Now we’re starting to get serious about launching lots of mass in short order, why not build a maglev launcher up the side of a mountain? Something like StarTram Phase I at least?

   I also wonder if Skylon/SABRE will be able to compete with reusable rockets.

9. RobFlores on January 8, 2016 at 15:57

   TLDR,
   Is the operational lifetime of the ISS inherently limited or not?
   Are there core elements to the ISS that cannot be replaced/repaired
   and when they become unsafe will the station need to be De-orbited?
   This is one hesitation about, counting the ISS for future additons/alterations.

   Overall Your idea seems like a good testbed.
   Even better, a fairly scaled down (in terms of volume, Not length)
   would tells us much, before committing large resources to this type
   of space architecture. All logic/models says it should work nicely.
   But that’s what the models for the NIF laser fusion said too.

10. FrankH on January 8, 2016 at 16:06

    @TLDR – I agree; without artificial gravity (even just a test) it’s all pointless re-treading of where we’ve been before and where we’ll stay – Earth Orbit.

    Add room for experiments with radiation shielding methods, from station wall construction/materials to magnetic shielding.

11. Alex Tolley on January 8, 2016 at 16:06

    I think this has bit almost every item on my wish list.

    Regarding radiation. Looking at the Globus abd Strout table 4, it seems that there is a low point for exposure, after which radiation levels increase a little with extra shielding, a result of increasing 2ndaries. While polythene is a good shield, water is close as an effective shield, more flexible in application as it is liquid, and can be sourced more easily, either from earth or possbly from space resources. It is also more multi-use, as the H2 and O2 can be separated and used as chemical fuels or a massive O2 reserve. This makes it a better material IMO.

    While we don’t have good anti-radiation drugs, I think we should be exploring approaches to increase the human cellular response to damagedDNA, by more aggressive responses to cancer cells and by better DNA repair approaches. These fruits of biomedical research might well offer a way to reduce shielding requirements for deep space.

    I would certainly like to see the use of the tether to test various fractional g levels, so that we could understand the consequences of fractional g before we make plans for colonizing other bodies. It may prove necessary to either live in a 1 g environment or use cheap acceleration methods to compensate. We need to study this as soon as possible, as this will influence designs for habitats.

12. Stan Erickson on January 8, 2016 at 16:26

    Instead of all this stuff about keeping humans alive in space, why not just solve the problems of growing humans from eggs or stem cells autonomously, and send the equipment to Mars? No need for humans to travel in space to have a colony.

    stanericksonsblog.blogger.com

13. Alex Tolley on January 8, 2016 at 16:44

    With SpaceX showing that it can recover 1st stage boosters, we can hope that launching heavy payloads, like water, with moderate reliability will reduce the cost of shielding for these habitats, making them more economic to launch and resupply.

    George Dyson in a recent Edge.org piece also suggested we need to separate the propellant from its energy source, making launches much safer, especially for passengers. If we use water as the propellant, and microwaves as the power source, we might just make launches extremely cheap as the flight frequency should increase. Throwing up large payloads cheaply will make all the difference in realizing how to live in space.

14. Hop David on January 8, 2016 at 19:45

    Andrew Palfreyman, for years one of my favorite daydreams was a west to east magrail up Mount Chimborazo, a tall mountain near the equator.

    Atmospheric density is a show stopper. Max Q for the space shuttle was about 35 kilopascals (if I remember right). Even at the thin air at the top of Mount Chimborazo, dynamic pressure would make it hard to exceed .5 km/s. .25 km/s is a more realistic figure. This doesn’t help a whole lot to achieve the ~100 altitude where air is tenuous enough to do the major horizontal burn to achieve orbital velocity.

    This would be major infrastructure built over difficult terrain with only minor benefits.

    At this time this my once favored day dream is in the discard bin.

    We discussed this at Nasa Spaceflight: http://forum.nasaspaceflight.com/index.php?topic=24169.msg1308624#msg1308624

15. Greg Matloff on January 8, 2016 at 20:59

    Thanks to all my colleagues for their responses. And thanks for pointing out uncertainties, improvements and applications. I think that interest in such ideas among members of the technical community can lead to a human breakout from LEO into deep space. In my opinion, the deep-space Earth-independent habitats that might grow out of such a venture are infinitely more important than a publicity sprint to Mars.

16. Astronist on January 8, 2016 at 21:13

    “To address these issues we might require a dedicated facility in Earth orbit.” Only one? I think you’re still thinking in terms of one-off space agency missions. The way I see manned spaceflight evolving, before any sustainable human presence on the Moon or Mars begins, there’ll be a space economy with a number of stations in various Earth orbits owned and operated by a variety of companies and governments.

    You are presumably aware of John S. Lewis’s point that highly eccentric Earth orbits are optimal as the Earth terminus for robotic asteroid mining flights? And of my point (published in Spaceflight magazine a year or two ago) that highly eccentric orbits lead naturally on to Earth-Moon cycler stations for safe lunar access? (As also described in my novel The Moonstormers, a link to which appears on my website front page.)

    Stephen

17. Marcel Williams on January 8, 2016 at 23:41

    SLS derived pressurized habitats would provide a lot more volume per mass than Bigelow and ISS derived habitats.

    Deep Space Habitats (NASA) Smitherman

    http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150016185.pdf

    The orbits with the lowest station keeping requirements would be at EML3, EML4, and EML5 (less than 1 m/s delta-v per year)

    Maintaining a Safe, Stable, and Human Accessible Parking Orbit
    David C. Folta NASA / Goddard Space Flight Center (anyone who needs a pdf copy of this paper should email since its no longer posted on the internet).

    I recently wrote about the issue of living on low gravity moons and planets on my blog:

    Living and Reproducing on Low Gravity Worlds

    http://newpapyrusmagazine.blogspot.com/2014/09/living-and-reproducing-on-low-gravity.html

    Marcel

18. Larry Kennedy on January 8, 2016 at 23:45

    TLDR
    I’m with you! I’ve long been a champion of a short arm centrifuge experiment in orbit. Work/exercise stations could be set up to avoid troublesome head movements. No one knows if a limited time in such stations would eliminate low gravity health effects. The experiment is long overdue.

19. DCM on January 9, 2016 at 4:45

    “Stan Erickson January 8, 2016 at 16:26

    Instead of all this stuff about keeping humans alive in space, why not just solve the problems of growing humans from eggs or stem cells autonomously, and send the equipment to Mars? No need for humans to travel in space to have a colony.

    stanericksonsblog.blogger.com”

    So you’d have a bunch of babies crawling about that, at best, will be without examples of human behavior, relating only to machines?

20. Brett on January 9, 2016 at 4:51

    @Andrew Palfreyman

    I think it would be much easier just to redirect a Near Earth Asteroid than building a giant non-rocket launch system on Earth. Even a small NEA might have tens of thousands of tons of material to work.

21. Antonio on January 9, 2016 at 6:57

    I don’t see the need at all of this kind of space habitat to go to Mars. If you want to go to Mars, go to Mars! What’s the point of studying human health in an environment much harder and dangerous than Mars in order to know the human body would react in Mars? It’s totally non-sense!

22. J. Jason Wentworth on January 9, 2016 at 9:01

    I’m gratified to see the interest that Greg’s proposal has elicited here, and there are numerous comments that deserve amplification!

    Al Globus: Thank you for pointing out that possible 500 km ELEO “favorable [from the radiation standpoint] microenvironment,” and I’m interested in your survey.

    Michael, TDLR, Hop David, and Alex Tolley: Water could serve a dual function in a centrifugal artificial gravity space station or colony. The classic 1950s rotating wheel designs used water, pumped automatically as needed along the periphery, to maintain the spinning stations’ balance as people and/or equipment moved around inside. (A wobble in the spin would make docking operations at the hub trickier, as well as possibly making the artificial gravity vary enough to be nausea-inducing. A slight amount of intermittent wobble, as the automated pumps restored balance as people walked around inside, would likely be pleasant, like the gentle rocking of a boat on a calm lake. A large-amplitude or long-duration wobble might–like the heaving of a ship on a stormy sea–make the station’s occupants feel as if they were seasick.) BUT:

    Since these are still unknowns, this is just one of many excellent reasons why Greg’s inflatable, centrifugal artificial gravity “proto-colony” idea should be tried, at 1 G and at fractions of 1 G (simulating the surface gravities of the Moon, Mars, and asteroids). All of these G levels could even be tested concurrently using a single station of Greg’s design, simply by “stringing” opposing module sets at the appropriate distances from the “proto-colony’s” spin axis. The water could serve both as radiation shielding and as movable balance ballast for such rotating stations. Also:

    The ISS Centrifuge should be tried as well. How wonderful it would be if the health benefits of Earth-surface gravity (or some percentage of it) turned out to be achievable–*without* unpleasant side effects–with such a relatively small device! It may very well be, but there’s no way to know for sure without actual in-space tests of long-radius and short-radius centrifugal artificial gravity systems. The maddening paucity of medical data (after nearly six decades of human space travel!) on this crucial requirement for solar system exploration and settlement is, sadly, largely due to a late 1960s-vintage political and economic influence which still affects us today:

    As I read in “Homesteading Space: The Skylab Story” by David Hitt, Owen Garriot, and Joe Kerwin (University of Nebraska Press, published 2008), when NASA was planning Skylab, the Congress was suspicious that NASA would use it to prepare for a Mars expedition, which most of the legislators were dead-set against funding in the social/political/economic circumstances of those times. Skylab was deliberately designed so that it couldn’t be re-supplied (and thus couldn’t be used to simulate a full-duration Mars round trip), in order to assuage Congressional suspicions that it was a Mars mission “stalking horse.” Wernher von Braun’s creative insubordination, by which he’d quietly developed the means to launch the Jupiter-C (Juno I) lofted Explorer satellites despite orders to the contrary, made NASA wary of *him* with regard to Skylab, since he had wanted a Mars expedition for most of his life. This led to an interesting (but rigged) artificial gravity demonstration that was arranged to persuade von Braun that it would be ineffective for a space station (and thus also for a Mars expedition):

    Von Braun and several top NASA officials (Low and Mueller, if memory serves–unfortunately, my copy of the book is packed away right now, so I’m going by memory here) took a ride in a centrifuge “room” that simulated 1 G, or a significant fraction of it. Because the centrifuge was operating on the Earth’s surface (and because it *wasn’t* generating multiples of 1 G inside like the centrifuges used to train the astronauts [which made those centrifuges’ “gravity vectors” predominant to their riders]), their balance mechanisms were adversely affected (“down” changed direction, and was at an angle to the floor). The ride was intentionally made long enough to cause von Braun to become queasy. After it was over they said, “You see, Wernher? Spinning space stations would make their crews sick!” Von Braun–who by then was nearing his retirement from NASA–didn’t fight them over this, and Skylab flew as a microgravity station. But that “test” didn’t truly simulate how centrifugal artificial gravity would feel inside a rotating space station because in free fall, the station’s “gravity” vector would be the *only* one that the crew members’ balance mechanisms would detect, and “down” would always–comfortably–be perpendicular to the floor. (The Coriolis Force, which is more apparent in smaller rotating stations than in larger ones, would be a novel “twist” as far as the human balance system is concerned, but since it would be constant at any given radius from the axis, I suspect that the human balance system would quickly adapt to its presence [the residents would learn to pour their coffee at a slight angle, to ensure “hitting” the cup].) This is yet another reason for building the ISS Centrifuge and Greg’s “proto-colony”–to discover the “limits of comfort” in rotating structures of various sizes and rotational speeds!)

    Alex Tolley: I heartily agree with George Dyson and you regarding separating propellant and energy source (and I “like the cut of your and Brian McConnell’s Spacecoach’s jib!”) As well as microwaves, electrothermal (arc-jet and resisto-jet) thrusters–using water as the propellant fluid–could be used to power lunar and interplanetary spaceships, with the thrusters’ electricity being supplied by thin-film solar cell arrays or (for trips beyond Mars) by Topaz-type nuclear reactors. And:

    Arc-jet propulsion (see: https://www.google.com/search?hl=en&source=hp&biw=&bih=&q=arc-jet+propulsion&gbv=2&oq=arc-jet+propulsion&gs_l=heirloom-hp.12…113914.123227.0.125100.18.18.0.0.0.0.0.0..0.0….0…1ac.1.34.heirloom-hp..18.0.0.dAGEarh_xWI ) may be *better* than nuclear thermal rocket propulsion for manned spaceships. The arc is hotter than a solid-core nuclear thermal rocket’s reactor, and the arc-jet’s exhaust isn’t radioactive. The arc also–as described in the 1964 (revised in 1968) Time-LIFE book “Man and Space” by Arthur C. Clarke–creates a “plasma pinch effect” that further accelerates the super-heated propellant out through the engine’s nozzle. While not as high-thrust as a nuclear rocket engine (by a large margin), arc-jet and resisto-jet thrusters can be clustered to provide significant thrust levels (tens of pounds of thrust) for spaceship propulsion. The relatively high thrust (compared to an ion or Hall Effect thruster’s) of an arc-jet rocket, combined with its *lower* specific impulse than that of an ion or Hall Effect thruster, actually makes them more desirable for propelling lunar and planetary spaceships, and here is why:

    An aircraft turbojet (pure jet) engine accelerates a smaller mass of air to a higher velocity (for the same amount of fuel burned) than does a turbofan (fanjet) engine–that is, a turbofan has a higher thrust but a lower specific impulse (a lower exhaust velocity) than a turbojet that burns the same amount of fuel. Yet the turbofan is much more efficient than the turbojet, because its exhaust velocity is a better match for the aircraft’s desired velocity (a turbofan can also use afterburning to power supersonic aircraft, while still burning less fuel for the same performance as an afterburning turbojet–rather similarly, an arc-jet or resisto-jet thruster could use an electrostatic or electromagnetic “afterburner” to further accelerate its exhaust, if desired). Now:

    For this same reason (which Bob Forward found to be true for antimatter rockets, too), an arc-jet rocket (or a cluster of them, to provide the desired thrust) is a better match for the velocity of a lunar or planetary spaceship than is an ion thruster or a Hall Effect thruster, both of which have very high exhaust velocities but have microscopic thrusts, which results in long trip times. The exhaust velocities of ion and Hall Effect thrusters are 40,000 mph and up, but no interplanetary spaceship will reach such velocities–or be wanted to–unless it’s going way out into the Kuiper Belt or beyond; for trips to the planets and back, the ships’ characteristic mission velocities will be much lower, and will thus be better matched to the exhaust velocities of arc-jets. Plus, the greater acceleration of an arc-jet or resisto-jet powered spaceship would enable it to avoid “loitering” in the Earth’s Van Allen radiation belts while climbing away from Earth, unlike an ion or Hall Effect propelled ship. Also:

    As Bob Forward found for antimatter rockets, they are most efficient–regardless of the desired mission–when the engine’s exhaust velocity is 63% of the characteristic mission velocity. To put it colloquially, “the higher exhaust velocities are wasted” when the ship won’t reach–and isn’t desired to reach–the velocity of a very high-speed exhaust, just as with the early, turbojet-powered airliners. Plus, arc-jet and resisto-jet rockets are very simple and durable, and they can use any working fluid (including ones that are readily obtainable on other celestial bodies, such as ammonia, methane, and water). As well, arc-jet propelled spaceships could produce rather small but useful fractional G constant accelerations, which would reduce trip times, reduce long-term zero G health problems, and make possible normal–although slower than on Earth, in our 1 G gravity–plumbing and handling of foods, drinks, and wastes onboard.

    Hop David: The mountainside launch tracks (the “Save A Stage” folks http://g2mil.com/stage.htm cover them) might be worthwhile for another reason–being able to use captive boosters (which would never leave the ground) that could be reused, to lower launch costs. (The Sanger-Bredt World War II Antipodal Bomber design and the 1960s Junkers Raumtransporter [Space Transporter] design both utilized captive boosters and launching tracks, and Dr. Sanger found that steam rockets [for maximum economy] were feasible for the Junkers design, on which he was a consultant.) Depending on the vehicle, the captive booster need not have its own rocket engines, but could simply be a “drop tank sled” from which the flight vehicle’s engines would draw propellant during the high-speed run across the valley and up the mountain. Philip Bono’s Hyperion SSTO (Single-Stage-To-Orbit) spaceship (which could also have operated as an intercontinental ballistic transport) was designed to ride on such a sled; this feature enabled this “cheater ‘almost-SSTO'” vehicle to be smaller and lighter than one that had to carry all of its propellant in internal tanks.

23. J. Jason Wentworth on January 9, 2016 at 9:41

    ADDENDUM: Here (see: http://g2mil.com/skyramp.htm ) is a link to the Sky Ramp Technology website, which contains information (and links to papers and other sites) concerning rail launchers, launch tracks, captive boosters, and mountainside launch tracks (and space vehicles to make use of them) of various kinds. Our current space infrastructure, as it exists, will never be able to support interplanetary–much less interstellar–expeditions (or even starprobes), and certainly not affordable ventures of these kinds. New and better ways of getting into and returning from space, and of living there (that’s where proposals like Greg’s come in), must be developed unless we want to forever consider LEO the Ultima Thule of space–and perish THAT thought! Also:

    There is no *one* “right” space infrastructure that will make interplanetary and interstellar expeditions technologically possible and affordable; as in shipping and aviation, such a space infrastructure will have vehicles and facilities (on Earth, in space, and then also on other worlds) of many different types, sizes, and capabilities, to enable the vigorous–and profitable–space activities upon which future voyages to the planets and other stars will depend. Columbus’ and Magellan’s ships weren’t specially developed for their missions, but used the knowledge and industrial capabilities that had already been developed for cargo vessels and warships; so shall it be in our–and our children’s–time, for the exploration vessels of *our* beckoning, mysterious ocean.

24. Michael on January 10, 2016 at 2:41

    A way to build large torus’s in space would be to inflate a torus made of rubber or flexible tube and around its thickness have a metal vaporising ring unit. After the tubes inflation this ring moves around the torus spraying metals to a required thickness, then the air is removed from the inner tube and the inner side metalized and plastics for insulation applied. Hubs and connections can then be added later.

    I was thinking years ago of having a manufacturing station in space that would disassemble a complete rocket, the tanks and contents used for various things with the rocket motors and turbines (some of them) returning to earth in a shuttle type re-entry vehicle. We throw an incredible amount of material away going into space that could be reused effectively even if we use a little more energy to get them there it would be worth it.

    @J. Jason Wentworth

    There is also the sea cannon, a better design me thinks.

    http://phys.org/news/2010-01-space-cannon-payloads-orbit-video.html

25. Greg Matloff on January 10, 2016 at 7:40

    Dear Jason
    Thank you again for the very thoughtful further development of this concept.

    Dear Marcel Williams
    You are correct about SLS vs. Falcon Heavy. But SLS is expensive and politics-dependent. At most, there can be only one launch every year or two. That is not the (projected) case for Falcon Heavy.

    Regards, Greg

26. J. Jason Wentworth on January 10, 2016 at 11:50

    Astronist: Thank you for mentioning Dr. John S. Lewis’ concept of HEEO (Highly-Eccentric Earth Orbit) space stations for lower Delta-V lunar access (his book “Mining the Sky” covers this concept in detail). “Swing Stations” in figure-8 Earth-Moon orbits also have possibilities (they’re discussed in “Frontiers of Space” by Philip Bono and Kenneth Gatland), although I haven’t seen an analysis of the Delta-V costs of getting up to and down from such stations at the Earth and Moon ends. Such orbits are pretty stable, though, because the Soviet Luna 3 probe (which took the first photographs of the Moon’s far side) followed its figure-8 orbit for about six months after it died, until it finally re-entered the Earth’s atmosphere and burned up. This suggests that a Swing Station would need little impulse–and not very often–to maintain its figure-8 orbit (a solar sail, of the heliogyro or disc type for a rotating station, might be sufficient), and Greg’s inflatable, centrifugal artificial gravity design would lend itself well to a figure-8 orbit or HEEO type lunar/terrestrial access station. Also:

    I agree that *stations* (emphatically plural) must be built if we’re to get anywhere, and government space agencies will never do this–only private industry can, or even wants to. As rocket and SSTO (Single-Stage-To-Orbit) spaceship designer Gary Hudson pointed out, NASA, being a government agency, thrives by taking small, incremental steps toward ill-defined goals. This shields them from failure (one can’t be blamed for failing if one never announces specific goals, and later fails to achieve them), and taking small steps doesn’t raise the ire of the Congress, which would usually balk at large funding requests. And since this status–or stasis–keeps their workforce level constant and keeps all of NASA’s facilities running, everyone (except those who want to see more done in and with space) is happy. NASA initially resisted President Kennedy’s specific-timeline manned Moon landing proposal because it *was* a specific goal, and because it had an end, after which greater things might–but might not–come, whereas lunar mission design studies and component testing could go on indefinitely. NASA had been, along with their contractors, conducting manned lunar mission studies for some years before JFK’s famous May 25, 1961 speech calling for a Moon landing “before this decade is out,” but they had no particular first mission date in mind, stating only that it “should be feasible in 1970 or later.” Having the first manned Mars expedition always 30 years in the future, and conducting inexpensive unmanned Mars missions to prepare for it, is a stable and desirable situation from NASA’s point of view, which is why I’m glad that Elon Musk, Geoff Bezos, and other “apple cart upsetters” of space have arrived on the scene…

    Marcel Williams: You are correct about the SLS and its inflatable habitat-lofting capabilities, but the SLS is a fragile thread upon which to hang such hopes. Due to its great cost, very low projected launch rate (these two factors reinforce each other), and large payload capability (which results in a low launch rate, because such large payloads are very expensive and thus rare), the giant rocket may be cancelled before its first flight. Even if it does fly successfully (a failure of the first one would be a huge blow to NASA, monetarily as well as politically), its very high unit cost may result in it being abandoned after only a few flights. Its continued availability depends on the continued existence of the ambitious (and expensive) manned cislunar missions that it is intended to support, and their continuation in the current fiscal climate is by no means assured–no cislunar missions, no SLS. Also, its much lower-priced competitor, SpaceX’s Falcon Heavy, may–particularly if its early test flights go well–result in the SLS’s demise (the Falcon Heavy may not be able to orbit as much mass as the SLS [I don’t have their respective payload figures handy–this old computer doesn’t travel the “interwire” easily], but their payload capabilities aren’t incomparable).

    DCM: I like your mental picture–“Romper Room” on Mars! The Star Trek (original series) episode “Charlie X” didn’t exactly instill confidence in what to expect of a computer-reared child… :-) But seriously, all of the ideas about sending humans to other planets–or to the planets of other stars–as eggs or stem cells would require multiple technologies whose realization (and successful integration, so that they’d all work together properly to conceive, gestate, birth, rear, and teach the children) is probably so far off that we might have Alcubierre’s warp drive before then. But I oppose such schemes on moral grounds; I would not want to have been deprived of real, loving, living parents, and I therefore could not support having other, future children deprived of parents, either. Just because humans -can- do some thing, it does not automatically follow that they *should* do it.

    Brett: I agree with you in principle (the shallower the gravity well that one is trying to lift material out of, the cheaper it is), but other factors make it prudent to examine all potential shielding material sources, even our Earth, on a case-by-case basis. For example, an O’Neill mass driver (essentially a smaller, specialized version of William Escher’s Lunatron, which could launch manned spacecraft as well as bulk cargoes off the Moon electromagnetically) could launch pellets of compacted lunar regolith to a station or “proto-colony” construction site near the Earth using trivial–in terms of cost–amounts of electricity, which could be generated by solar arrays or nuclear reactors on the Moon’s surface. I personally favor such plans because the transport (launcher) costs will be low, once the system is set up. But setting up the system–which must include a catcher–will be quite expensive (even for Neil P. Ruzic’s very simple Lunatron, which he described in his book “Where the Winds Sleep”). The size of the station also influences the shielding cost, which in turn influences the source choice. A giant O’Neill colony would require so much shielding that the mass driver on the Moon would be worth the cost of setting it up. For a quite small “proto-colony” like Greg Matloff’s, however, bringing the much smaller required mass of shielding material up from Earth might–depending on how it was shipped (perhaps as secondary payload on satellite launches to similar orbits)–actually be cheaper, despite the Earth’s much deeper gravity well. (With a capable tug [one is under private development for lunar applications; I forget the firm’s name, but they’re at the Cape], your idea of bringing back small NEAs to use for shielding may well be the cheapest option.)

    Antonio: A Mars expedition using current propulsion technologies will have to utilize minimum-energy, Hohmann transfer orbits for both legs of the voyage. Because both the departure and return legs require the crew to wait for suitable Earth/Mars planetary alignments, the mission will last about 970 days, more than 2-1/2 years. No one has ever spent such long periods of time in free fall, and getting that experience (which might contain some nasty medical surprises) would be a dangerous thing to do during a Mars voyage, millions of miles from help on Earth. In addition to consisting of *two* 260-day periods of weightlessness (one outbound, one inbound), the crew would have to spend the other 450 days either on Mars or in orbit around Mars, while waiting for the second (Mars departure) planetary alignment. If a portion of the crew remained in orbit to survey the planet, as many Mars expedition plans call for, they would spend the whole ~970 day mission (except during the brief rocket burns) in free fall. Also:

    If the surface exploration party remained on Mars for the 450 days, no one knows if the Martian gravity–3/8 of Earth’s–would be sufficient for them to remain healthy and strong. This is why Earth-orbit experiments with centrifugal artificial gravity stations, spinning to produce 1 G, 1/6 G (lunar gravity), 3/8 G (Martian gravity), and still-smaller fractions of 1 G (various asteroids’ gravities) are so important, both to train astronauts how to function effectively on those worlds and to learn what the minimum healthy “sub-1 G” exposure durations are. This information could also be useful for minimizing the costs of space stations and spaceships. For example:

    It might be found that humans can live indefinitely in, say, a 1/2 G environment and–after an exercise program–return to Earth’s 1 G environment with no ill effects. If so, this would enable rotating space stations and spaceships (including those for Mars expeditions) to be built more lightly (since they wouldn’t have to spin as rapidly to produce 1/2 G as they would to generate 1 G, for the same-size vehicles), which would reduce their costs. Another important factor, about which little is yet known, is what rotational speeds–for vehicles of given sizes–might cause vertigo and nausea in humans (from seeing the stars, Earth, Moon, and Sun whirling around outside the windows), and if the “rotation tolerance” varies among the population (as susceptibility to free fall space sickness–called Space Adaptation Syndrome–does). We can also learn how long 1/6 G lunar gravity and 3/8 G Martian gravity can be withstood without possibly making humans unable to return safely to Earth’s 1 G environment. Our ignorance of all of these things is almost total, and only by experimenting with centrifugal artificial gravity in near-Earth stations and “proto-colonies” can we replace our ignorance with knowledge.

27. Hop David on January 10, 2016 at 13:03

    J. Jason Wentworth writes: “ADDENDUM: Here (see: http://g2mil.com/skyramp.htm ) is …”

    Going to that site they note the space shuttle burns 40% of it’s propellent in the first minute to achieve 1000 mph and back this up with a link to http://spaceflight.nasa.gov/shuttle/reference/basics/launch.html

    What they don’t mention is the shuttle’s altitude after a minute. That’d be a little more than 7 miles (11 kilometers). About twice the altitude of Mt Chimborazo. And it is just short of the minute mark the shuttle achieves max Q. http://spaceflightnow.com/shuttle/sts124/fdf/124ascentdata.html

    As I already mentioned, the shuttle’s max Q was about 35 kilopascals. Something traveling 1000 mph at the top of Mt Chimborazo would be subjected to about 75 kilo pascals dynamic pressure.

    Naive space enthusiasts regularly bring up this notion at Nasa Space Flight Forum or Space Stack Exchange. And it is regularly debunked by the seasoned aerospace engineers. Earth’s atmosphere is a show stopper.

    Such a scheme would work well on an airless world like Luna, Mercury or Ceres. It would even work on Olympus Mons of Mars. But not on earth.

    Jason, I agree with most of the other stuff you’ve written. However I also differ with your notion of HEOs. When it comes to delta V to various destinations, EML2 is the best spot (in my opinion) http://hopsblog-hop.blogspot.com/2015/05/eml2.html

28. Alex Tolley on January 10, 2016 at 16:23

    @Hop David
    While a ramp launch up a mountain won’t work, what about the 20 mile tower as proposed by Neil Stephenson (Hieroglyph project) that is being worked on at the University of Arizona. It is an ambitious project, but the idea is to build a steel tower to that height. One proposal is to launch spacecraft from it. If the loads are tolerable, it could support a vertical electromagnetic launcher that could be used for cargo launches, and possible crew.

    Have you looked at that proposal at all? The Tall Tower

29. Alex Tolley on January 10, 2016 at 16:30

    @Michael. Rather than spraying metal to form the torus, why not print it instead? That way, instead of just having a continuous, smooth torus, you could build in all sorts of sophisticated structural functionality right into the hull. Additive printing also allows not just one metal, but a range of materials to increase the strength of the hull and also to improve the functionality of some of the built-in functional parts, e.g. electrical wiring.

30. ole burde on January 10, 2016 at 16:54

    The advance of space exploration is consistently slowed down by wasting money on giant bigger-than-life enormously complex projects such as the spaceshuttle , ISS , the James Webb Telescope and several others . On the other hand we have relatively cheap projects like Kepler or the mars rovers who were designed to do a single well defined thing , and did so perfectly .
    This lesson should be used when we think about how to design a space habitat capable of variable gravity . The cheapest way to experiment on the subject must be to use to ANIMALS (as in most other biological related experiments ) ,such as rats and rabbits who are very close to humans . Such a habitat would only need a human aboard for limited periods and could be positioned close to the or even connected to the ISS . The human visitor would access the modules by cabledrive along the tether , and he could perhabs stay long enough to get a first impression of what the minimum spin rate for a real habitat might be , but the basic parameters and generation-long effects of variable gravity could be determined very cheaply first by using small short lived mammals . The whole thing , two identical modules connected by a tether ,could weigh less than than two ton if designed around resupply and maintenance from the ISS . It might be possible to do the whole thing for a small fraction of the cost of other , much less focused plans …

31. Sean Robert Meaney on January 10, 2016 at 23:57

    All I know is that thirty two billion cubic feet of hydrogen is sufficient to lift a million tons to the edge of space where the motors can burn rocket fuel to lift an O’Neil cylinder to orbit.

32. Michael on January 11, 2016 at 3:06

    @Alex Tolley

    ‘Rather than spraying metal to form the torus, why not print it instead? That way, instead of just having a continuous, smooth torus, you could build in all sorts of sophisticated structural functionality right into the hull…’

    Printing is a way to go but it is much slower than vapour disposition, I think a compromise would be better. The bulk of the non complex torus via vapour techniques with the hub, spokes and complex shapes via printing.

    @Hop David

    The aerodynamic pressure limit may actually help us if say we use the ‘cannon’ to achieve air scramjet speeds, it would allow a lot of savings in fuel and complexity.

33. DCM on January 11, 2016 at 5:08

    “J. Jason Wentworth January 10, 2016 at 11:50
    ………..
    DCM: I like your mental picture–“Romper Room” on Mars! The Star Trek (original series) episode “Charlie X” didn’t exactly instill confidence in what to expect of a computer-reared child… :-) But seriously, all of the ideas about sending humans to other planets–or to the planets of other stars–as eggs or stem cells would require multiple technologies whose realization (and successful integration, so that they’d all work together properly to conceive, gestate, birth, rear, and teach the children) is probably so far off that we might have Alcubierre’s warp drive before then. But I oppose such schemes on moral grounds; I would not want to have been deprived of real, loving, living parents, and I therefore could not support having other, future children deprived of parents, either. Just because humans -can- do some thing, it does not automatically follow that they *should* do it.”

    Right. This will be a slow, methodical development likely taking at least a century in which environments are designed and tested by robots but intended for humans. No doubt there will be some disasters, but the survival of humans, if not of life in general depends on it.
    The same experiments should be done designing space habitats beginning with bacteria and algae, working gradually up to more complex ones for complex life.
    It will be a huge project employing millions and yielding developments valuable on Earth as well.

34. Antonio on January 11, 2016 at 5:21

    J. Jason Wentworth:

    “A Mars expedition using current propulsion technologies will have to utilize minimum-energy, Hohmann transfer orbits for both legs of the voyage.”

    Nope. With chemical propulsion there are several trajectories available. For security reasons, the best one is a 6 month free-return trajectory, that will put the spacecraft back on Earth if something fails after the initial burns.

    “Because both the departure and return legs require the crew to wait for suitable Earth/Mars planetary alignments, the mission will last about 970 days, more than 2-1/2 years. No one has ever spent such long periods of time in free fall”

    Huh? First, each one-way trip is only 6 months (the mean stay period in the Mir and the ISS) and in Mars they will have 40% Earth gravity. And second, there is absolutly no need to make the trip in free fall. The ship and the third stage of the rocket can be connected by a tether and they can spin to create artificial gravity.

    “If a portion of the crew remained in orbit to survey the planet, as many Mars expedition plans call for, they would spend the whole ~970 day mission (except during the brief rocket burns) in free fall.”

    There is absolutly no need to remain in Mars orbit.

    “If the surface exploration party remained on Mars for the 450 days, no one knows if the Martian gravity–3/8 of Earth’s–would be sufficient for them to remain healthy and strong.”

    For two 6-month one-way trips, the stay on Mars will be around 500 days. Valeri Polyakov stayed in the Mir for 437 days and 18 hours and, after landing on Earth, he walked outside the capsule without help. And he stayed all that time in 0 g, not 40% g!

    (BTW, G is a different constant.)

35. J. Jason Wentworth on January 11, 2016 at 6:00

    Michael: Inflatable structures can also be designed to harden in space (via exposure to UV light or perhaps to vacuum). The June 1962 issue of Popular Science magazine reported on pre-peg (resin pre-impregnated) inflatable space structures that would be launched into orbit, inflate themselves, and then become self-rigid when the resin cured (see: http://books.google.com/books?id=yCADAAAAMBAJ&pg=PA92&lpg=PA92&dq=Popular+Science+balloons+that+harden+in+space&source=bl&ots=RCSPMXTv-s&sig=vK-J9f3iMoLxXVO4efk-QZpQCCA&hl=en&sa=X&ei=VlclVPrnDYO4ogSsyIGgDQ&ved=0CBQQ6AEwAA#v=onepage&q=Popular%20Science%20balloons%20that%20harden%20in%20space&f=false ). This technology was developed for planned-but-never-flown follow-ons to the Echo balloon passive communications satellites. In addition to being useful for large space colonies (particularly for creating an initial form on which epoxy cement could be applied), smaller rotating and non-rotating (microgravity) inflatable space stations (and Moon and Mars habitat modules) could also be made self-rigid in this way. Also:

    Goodyear actually built a 30′ diameter prototype inflatable wheel space station (complete with an airlock at its hub), and NASA built a 24′ diameter, hubless inflatable space station test article; in fact, the 30′ Goodyear space station needed only solar cell panels, thrusters, and a life support system to be flight-ready. The article, “Inside Our First Space Station” in the December 1962 issue of Popular Science magazine (see: http://books.google.com/books?id=ISEDAAAAMBAJ&pg=PA96&lpg=PA96&dq=Inside+Our+First+Space+Station+Popular+Science+December+1962&source=bl&ots=ghhVG7LMgL&sig=BqF9EKJ9pe0R_tiWOo1qNIhxo8c&hl=en&sa=X&ei=2lQlVO2_KNPqoATfnoDABA&ved=0CB4Q6AEwAg#v=onepage&q=Inside%20Our%20First%20Space%20Station%20Popular%20Science%20December%201962&f=false ) covered the 30′ and 24′ space stations, and it also covered a much larger (150 feet in diameter) proposed inflatable wheel space station (at the time of writing, Goodyear was building a 45′ diameter test version). Here is a link to several websites that contain information on early NASA and aerospace industry work on inflatable wheel space stations (see: https://www.google.com/search?hl=en&source=hp&q=1962+Goodyear+inflatable+space+station&gbv=2&oq=1962+Goodyear+inflatable+space+station&gs_l=heirloom-hp.12…392134.405624.0.407266.38.29.0.0.0.0.0.0..0.0….0…1ac.1.34.heirloom-hp..38.0.0.RCDAefyiueE ). Such inflatable stations, if made with self-rigidizing pre-peg envelopes, could dispense with sprayed-on or printed-on (as Alex Tolley mentioned) metal coatings if desired, because metal structures facilitate the creation of showers of secondary particles from primary cosmic ray impacts. Speaking of radiation (and meteoroid & space debris) shielding:

    Pykrete (see: http://search.lycos.com/web/?q=Pykrete&keyvol=00ede1be03019b97f1ec ) could be a very cheap but effective radiation and impact shielding option; it’s a highly melting-resistant water ice developed by Geoffrey Pyke in Great Britain during World War II, for building aircraft carriers up to a mile long entirely out of ice! Pykrete, which is also used to make “ice hotel” buildings at some northern ski resorts (including here in Alaska), is made by mixing wood pulp with water. It would provide very good radiation shielding (due to the water *and* the carbon in the wood pulp) as well as be an excellent thermal insulation (covered with reflective foil or metallized Kapton or mylar, it would be essentially permanent in space, resisting sublimation). It could be made as thick as needed, and it would be easy to repair–just add more Pykrete and place a new layer of foil or metallized Kapton over it! Also:

    A 60′ long test vessel made of Pykrete survived a summer test in Jamaica. Pykrete is very strong, too–during a demonstration before the British Admiralty, an axe swung at a block of Pykrete merely glanced off, barely scratching it (moments before, the same man had easily split a “control block” of ordinary sea ice). One naval officer produced a pistol and fired at both blocks; the ordinary sea ice was “holed,” but his second bullet ricocheted off the block of Pykrete, nearly striking another official who was present! It could be applied over the structure of the “proto-colony” or station, probably with a thin liner of some kind between it and the Pykrete.

    I’ve seen articles on the sea cannon before. Its engineering problems (in the earlier articles I read) sounded slightly fantastic, but it would enable all-azimuth launches. (Gerald Bull had designed a very small, ruggedized multi-stage satellite launch vehicle that could be fired from a large gun; for small, acceleration-hardened payloads, it could have provided inexpensive, short-notice launches; had he not gone to work for Saddam Hussein and not been “neutralized” as a result, Canada might be a satellite launch provider today.)

    Hop David: I don’t dispute your performance gain figures. The possible advantage of mountainside launchers, especially if reusable captive boosters or “drop-tank sleds” are used, could be cost savings. (For example, OTRAG’s simplified, pressure-fed nitric acid/diesel-powered MCD [Minimum Cost Design] launch vehicles weren’t the lightest or the most efficient by a large margin, but they were cheap. They made the ultimately-fatal mistake–which Wernher von Braun had warned them against–of setting up shop in rogue nations, which resulted in their demise due to political pressure from the U.S. and West Germany.) If private space firms want to try mountainside launch tracks (especially with private capital), let ’em try. They might fall flat on their faces, but they might not.

    Ditto for HEO and figure-8 orbit stations (other, now unforeseen operational or commercial factors could make them desirable, despite their Delta-V costs). The history of aviation, particularly commercial aviation, is replete with similar confidently-stated limits on engine power, range, payload, and speed that were broken, often soon after the pronouncements were made. As Arthur C. Clarke chronicled (as a caution against accepting premature limits on space travel), these aviation breakthroughs were achieved via increased sophistication in, and straightforward extensions of, existing aeronautical technology–they required no scientific or engineering breakthroughs.

    Alex Tolley: I’ve read about that Tall Tower launcher project. Its initial cost might be eye-popping, but it doesn’t exceed the limits of known materials or engineering practices.

    ole burde: The Mars Society has done this (on Earth) with a rotating mouse “space station.” The mice soon learned how to move properly in the “circular floor is down” environment, and they even reproduced successfully during the long test run.

36. Hop David on January 11, 2016 at 12:34

    J. Jason Wentworth wrote “If private space firms want to try mountainside launch tracks (especially with private capital), let ‘em try. They might fall flat on their faces, but they might not.”

    If the private entrepreneurs are competent and numerate (as Musk and Bezos seem to be) I wouldn’t expect them to try. I expect others to try but would be surprised if they had the capital.

    “Ditto for HEO and figure-8 orbit stations (other, now unforeseen operational or commercial factors could make them desirable, despite their Delta-V costs). The history of aviation, particularly commercial aviation, is replete with similar confidently-stated limits on engine power, range, payload, and speed that were broken, often soon after the pronouncements were made. ”

    What pronouncements are you talking about?

    I said EML2 is the best location I know of. From EML2 is takes .4 km/s to enter a 384,400 x 6678 km HEO using the Farquhar route and 0 km/s using WSBs such as Belbruno and Shane Ross promote. For a given HEO, it is unlikely perigee will be in the right place when a launch window occurs. On the other hand, EML2 makes a full circuit each 4 weeks so perigee can be any longitude within two weeks of a given launch window. Using the Farquhar route EML2 is 3.4 km/s from LEO, takes 9 days to reach. Using WSBs, EML2 is 3.1 km/s from LEO and takes a few months to reach.

    There are no “confidently stated limits on engine power” in my article on EML2. If you don’t have time to read the article, that’s okay. But until you read the article don’t confidently try to stick words in my mouth.

37. Michael on January 11, 2016 at 13:03

    @J. Jason Wentworth

    The evaporating inflatable torus is a sound idea but I wanted to use as much of the materials from a rocket as possible, the two concepts could in fact be used together. My only concern is with the degradability of the chemicals used over time, resins also don’t like it to cold or to hot as well.

    As for the Pykrete I used hemp string and found it to be much better than wood pulp, first at impacts and second if enough of the fluffy material is near the surface the shards are caught in the tangled fibres limiting mass loss. Ice will firstly make a very good radiation and impact protection due to the hydrogen component and secondly when an impact blows out some ice it will sublime in space and prevent secondary projectiles in orbits that could impact the original or other structures.

    As for the sea/mountain or tower launch we only need to get to scramjet velocities and we are away, 99% of all material that we send into space can survive thousands of G’s so why not use their strengths to an advantage.

38. Alex Tolley on January 11, 2016 at 14:10

    @Jason – I agree that we are better off using plastics rather than metal where appropriate. Despite recurrent fads for inflatable anything, there seems a distrust of such approaches. Only non-rigid airships, which have never exactly taken off, have this as the preferred structure. In space the rules are very different, and inflatables seem much more suited. With the new plastics, we can build structures with far better performance than rubber, both lighter and stronger.

    Bigelow’s 2 scale test vehicles have shown the way, and the inflatable test structure for the ISS will finally give us some more data especially with respect to human interaction.

    I tend to think that at the moment, building anything but the simplest structures is best dome on Earth, and then shipped to space. Inflatable structures that can expand to large volumes seems a very appropriate approach to me.

39. Alex Tolley on January 11, 2016 at 14:18

    Re: Shipping embryos to Mars.

    Again we seem to be caught up in a binary scenario. Either humans OR embryos + technology. I see no reason why some humans cannot be sent up with the embryos, which will then become the bulk of the population. It is not hard to see that a colony of “quiverfull” believers could pop out a large population quite quickly. Sending prefertilized eggs or embryos for implantation might be an option that avoids radiation damage, although I tend to think that sending a well shielded colonist is better way to go – then create the population. For planets around Sol, there is no need to try to invent artilect technology to replace human parents.

    The embryo approach only makes sense for long journeys in time – interstellar voyages or even storage on Earth to mitigate extinction events.

40. Alex Tolley on January 11, 2016 at 14:27

    Brian and I are fans of Pykrete. It is surprising how little work has been done on this material. It seems to me that today we might use plastics rather than wood as the material to prevent crack propagation, much like the reinforcements for concrete.

    When we can grow plants successfully in space, they might well become the raw material for all sorts of articles, including the reinforcement of ice structures. For Mars and outwards, reinforced ice structures might be a relatively easily worked material. Suitably insulated on the inside, human habitation should be possible.

    Water transformed to ice seems very analogous to spray form or printed structures. With the abundance of water, this should be a useful material for space construction as well as life support and propellant.

41. DCM on January 11, 2016 at 19:17

    “Alex Tolley January 11, 2016 at 14:18

    Re: Shipping embryos to Mars. ”

    Yes. A dozen adults contain all that’s needed to create a population of millions.
    Extra fertilized eggs or even eggs and sperm are fine to send along with them.

42. Marcel Williams on January 12, 2016 at 3:39

    @J. Jason Wentworth

    I doubt if Congress will cancel their own creation. If anything, they appear to be increasing their support for the SLS. There are tons of things you can use the SLS for. A water producing lunar outpost program would require heavy use of the SLS.

    The Falcon heavy and the ULA’s future Vulcan Heavy will be able to place nearly 60 tonnes into orbit but within a very confined fairing size . The SLS, on the other hand will be able to deploy objects over 100 tonnes with large diameters possibly as large as 1o meters. The SLS would be the only vehicle capable of deploying Bigelows largest space habitat, the Olympus 2100.

    The launch cost of the SLS will depend on the frequency of its use. But even if NASA doesn’t launch a single mission a year, the annual fixed cost for the SLS will probably be around $3 billion a year. Since the SLS is basically a Space Shuttle derived system, I doubt if the flexible cost per each launch will exceed $250 million per launch. So four SLS launches plus the annual fixed cost per year would probably come out to be about $4 billion (about a $1 billion per launch). With four launches per year and a $3 billion dollar budget, the Space Shuttle cost were about $750 per launch. Since NASA currently has a human spaceflight related budget of over $9 billion a year, $4 billion a year for about four SLS launches per year seems quite affordable.

    NASA , on the other hand, is talking about the SLS costing around $500 million per launch. They’d have to launch at least 12 rockets per year to reach that goal:-)

    Marcel

43. J. Jason Wentworth on January 13, 2016 at 9:12

    Antonio: The 970 day Mars mission is the reference minimum-energy, Hohmann transfer round-trip one. It is, of course, possible to reach Mars faster, even using chemical propulsion (Mariner 4 made a one-way trip in 227 days rather than the optimum 260). But Mariner 4’s mission was only to encounter Mars in a fly-by, not to rendezvous with the planet and enter orbit, much less return to Earth. All of these additional steps are very expensive in terms of rocket propellant, and when a human crew is involved, their radiation shielding, life-support system, and food (all of which are quite massive) require even more impulse to accelerate and decelerate, on both legs of the trip. (Aerocapture at Mars can help here, but careful trade-offs must be made to ensure that the heat shield’s mass doesn’t equal or exceed that of the propellant it’s meant to replace.)

    A six-month free-return trajectory could certainly be utilized, but the size and cost of a chemical propulsion spaceship that could do it might be prohibitive. (Going inward toward Venus and using its gravity to assist the Mars transfer could reduce the propellant requirements; there was a December 1978 Venus/Mars launch window [for proposed modified Apollo manned planetary flyby ships], with a 625 day total mission duration, but entering Mars orbit–and even more so, landing and taking off, followed by a return to Earth–were far beyond the capabilities of such vehicles.)

    There are multiple good reasons why the entire crew of a Mars expedition should not land on the planet. A spacecraft that could land on Mars, then later take off and return to Earth, would have to be enormous, even if it were a multi-stage vehicle. (Such an “all-in-one” direct ascent vehicle is possible for lunar missions [it was studied as an Apollo candidate, to be sent to the Moon by a huge Nova launch vehicle], but it was a very large and expensive spaceship, even for carrying only three people to the Moon and back.) With Mars’ higher gravity, plus the higher Delta-V requirements to get there and escape, such a vessel wouldn’t be practical, which is why Mars mission proposals envision one or more inter-orbital spaceships that dispatch smaller, lighter landing craft to the surface. Having part of the crew remain in Mars orbit is a prudent safety precaution (in case something broke down aboard the main ship, or if the returning landing craft couldn’t maneuver to dock with it due to some problem [this was a feared possibility during the Apollo missions–the CSM had the ability to maneuver to and dock with a “passive” LEM ascent stage for this reason]). Also, the crew members in Mars orbit could explore Phobos and Deimos, operate real-time-controlled rovers landed in more dangerous areas away from the manned landing site (Valles Marineris, Olympus Mons, etc.), as well as survey the planet from orbit.

    You’re assuming that fractional-G (I use “G” because not every online platform will reproduce the italicized lowercase “g,” and because in the context of astronautics, everyone knows which G is being referred to) onboard centrifugal artificial gravity is sufficient for long missions. I think you *are* right, but no one knows for sure, because it’s never been tried. The minimum required gravity for health may also–which again, no one knows–vary among the population, and it, too, may depend on the duration spent in the reduced-gravity environment. Some people might thrive at 1/3 G for a year, while others might require at least 2/3 G for an eight-month mission; until we have been able to subject a large sample of people to different sub-1 G levels for different durations, we can’t know, and I wouldn’t want to see such lessons learned for the first time–possibly with tragic results–during a Mars mission. The old aviators’ saying, “There are old pilots, and there are bold pilots, but there are no old, bold pilots” applies even more forcefully to space flight.

    We know more about human adaptation to free fall conditions, but even Valeri Polyakov’s impressive 437 day, 18 hour stay aboard Mir doesn’t indicate whether most people–or even most astronauts, cosmonauts, spacionauts, or taikonauts–would do as well as he did. It is dangerous to generalize from a sample of one. This *isn’t* to say that he is the only person who could emerge hale and hearty from 437+ days in free fall, but how rare–or common–is his ability? We don’t know. (After John Glenn’s Space Shuttle flight, there was much discussion in the medical field that his flight did not necessarily indicate that the average elderly person could endure the conditions of acceleration, deceleration, and free fall as well as he did, because he was a very exceptionally physically-fit example of a man of his age.)

44. J. Jason Wentworth on January 13, 2016 at 11:32

    Hop David: You infer things that I did not say, or even imply; I don’t consider a person’s disagreement with something I say to be a personal attack, and I hope you would not think so of me. The pronouncements and the “confidently-stated limits on engine power” that I mentioned were made by aviation experts in that field’s early days–not by me against your article or ideas–which Arthur C. Clarke used to caution against disregarding possibilities, even ones that seem remote or highly impractical, simply because they appear to be so at any given moment in time.

    You and I really have only one difference, where such things are concerned: You look at figures and decide, based on them, whether a particular device or process is practical or not. I don’t disregard figures, but I also recognize–as the whole history of science and technology, and their application by industry have shown–that other factors often determine what is and isn’t practical, and that these factors are often impossible to foresee. If something is physically possible, and it is needed (or even wanted) badly enough, it is usually developed, no matter how impractical it may be when its development is started (the great advances in liquid propellant rocket propulsion and inertial guidance technologies during World War II are just one example of this).

    In other cases, discoveries or developments in another field make some heretofore-impractical (or believed to be so) device practical. (German wartime missile development provides a good example of this as well. Wernher von Braun recorded his surprise at discovering that an ordinary firefighting pump, with suitable modifications, could easily fulfill the V-2’s demanding LOX and alcohol-water pumping requirements.) Similarly, the microelectronics revolution and the maser–both of which were unforeseen–made communications satellites practical (even Arthur C. Clarke had assumed that they’d have to be large, manned structures, with servicing engineers on the spot!). :-) So I always regard statements that a thing is impossible with caution, and statements that a thing is impractical as provisional, *even when the doubts against something’s possibility or practicality are my own*. Now:

    Maybe mountainside launch tracks utilizing reusable captive boosters and “drop-tank sleds” are impractical or uneconomical, but maybe they aren’t. You have one conclusion about them, and Eugene Sanger and Philip Bono had a different conclusion about them. The engineers at Junkers were also sufficiently confident in the concept to incorporate it into their 1960s Raumtransporter (Space Transporter) proposal, a reusable two-stage, winged vehicle accelerated on a track by a captive booster. The only way we’ll ever know which side is right is for someone to try it. Also:

    I have no doubt that you’re right about the high economy (its cheapness in terms of Delta-V) of EML-2, as compared with figure-8 Earth-Moon orbits and HEEOs (Highly-Eccentric Earth Orbits). But when (I hope it is not *if*) lunar settlement gets going, the cheapest orbits may not always be the most desirable ones, for reasons that have nothing to do with engineering or fuel economy. Sometimes *time* is the figure of merit (the less required, the better, as in most business situations), and there are other urgent needs, such as the rapid delivery of organs for transplant, in which “one is prepared to waste everything but time.” (Even in terrestrial transportation, the need for same-day air delivery–despite its great cost–is large enough that many courier companies provide it.) But even for ordinary lunar/terrestrial transportation needs, the higher Delta-V costs of figure-8 orbits and HEEOs may be of little importance one day:

    If electromagnetic launchers are established on the Moon, lunar launch costs will be trivial (once the capital costs of building the launchers are paid back through their use). The amount of energy required to lift an average-mass man to the Moon is about 1,000 kilowatt-hours, which if purchased from an electric power utility company would cost about $10 (in 1968–this cost figure is from Arthur C. Clarke’s 1968 book “The Promise of Space”–even at today’s electricity rates, it’s still a bargain). Since escaping from the Moon is much easier (requiring only about 1/24 as much work as escaping from Earth requires), the energy costs to reach those faster but more Delta-V-demanding orbits would be minor factors. Sending electromagnetically-launched Moon-made products directly to Earth might cost even less than transporting cargoes of the same mass between continents (in the 1960s, Clarke looked into the economics of such a Moon-Earth transportation system, using a simple, standard cargo nose cone that would parachute to the ground–today parafoils, improved inertial guidance systems, and GPS guidance would make such a system even more versatile).

45. Brett Bellmore on January 13, 2016 at 13:27

    It appears to me that, in the case of Mars, there’s a very strong case for starting out from the beginning with a cycler. The long duration trip there and back inherently involves heavy hardware that you’re not taking to the surface, might as well get more than one use out of it.

    In that vein, couldn’t a fractional G research facility be built in orbit, and at the appropriate time outfitted with better thrusters, and used as that cycler?

46. Antonio on January 13, 2016 at 13:47

    J. Jason Wentworth:

    The delta-V is not so expensive. Compared to the 258 days of a Hohmann transfer, a faster, 180 days conjunction-class free-return trajectory will cost a delta-V of 4.5 km/s from LEO to Mars surface. It will be followed by a 550 days stay in Mars and another 180 days return trip. This is the Mars Direct architecture by Robert Zubrin. It uses aerocapture for Mars orbit insertion (it spends 6 km/s from LEO to a highly elliptical Mars orbit and then uses aerobraking to circularize the orbit). And it uses aerobraking for landing on Mars surface (and some rocket propulsion at the end). Finally, it uses ISRU to produce the methane and oxygen for the return trip.

    In detail, the 4.5 km/s are the sum of 4 km/s for trans-Mars injection, 0.1 km/s for post-aerocapture orbit adjustment, and 0.4 km/s to land after using the aeroshield (but no parachute).

    Compare this to the 6 km/s from LEO to Moon surface (3.2 km/s for translunar injection, 0.9 km/s to capture into low lunar orbit, and 1.9 km/s to land on the Moon).

    How big the ship can be? Assuming we use a Saturn-V class, 140 tonnes to LEO, rocket and a H2/O2 upper stage for trans-Mars injection, we obtain a trans-Mars throw capability of 40.6 tonnes and a payload delivered to Mars surface of 25.2 tonnes.

    There is no need for an opposition-class Venus-flyby mission. That kind of mission only minimizes Mars stay, maximizes in-space stay and requires more propellant than the conjunction-class mission.

    Now, the radiation… It’s a HUGELY overstimated danger. Radiation in interplanetary space, as measured by the MARIE instrument onboard Mars Odyssey and the RAD instrument onboard Curiosity (on its trip to Mars) is ONLY DOUBLE than in ISS’s orbit. Radiation on Mars surface, if no additional countermeasures are taken, like putting sand bags on the roof of the habitat, would be around half of that in the ISS. Taking countermeasures during the trip like those in the ISS, with a shelter in the ship for solar storms surrounded by water and food supplies (35 grams per square centimeter of shielding), astronauts would receive around 520 mSv of radiation in the 910 days of the mission.

    Now, the food… No, we don’t need huge amounts. NASA standards for human consumption in space are 0.63 kg/day of dehydrated food, 1 kg/day of oxygen, 4 kg/day of potable water and 26 kg/day of wash water. Now, we assume the same figures but replace the 0.63 kg/day of dehydrated food by 1 kg/day of whole food and 0.5 kg/day of dehydrated food (better for morale on a long trip). We also assume a low efficiency life support system that recycles 80% of oxygen and drinking water and 90% of wash water. We assume too that we use ISRU to produce additional oxygen and water after landing on Mars. We obtain the following amounts per astronaut that need to be transported by the ship: 160 kg of oxygen, 1,600 kg of dry food, 3,200 kg of whole food, and 2,080 kg of water. Total: 7,040 kg per astronaut.

    “There are multiple good reasons why the entire crew of a Mars expedition should not land on the planet. A spacecraft that could land on Mars, then later take off and return to Earth, would have to be enormous, even if it were a multi-stage vehicle.”

    Nope. As I showed, the ship for the outbound trip doesn’t need to be huge. In the Mars Direct plan, the dry mass and payload of the ship (that serves also as surface habitat) is 25.2 tonnes. For the return trip, an Earth Return Vehicle (ERV) is sent beforehand to Mars and produces methane/oxygen there and also water for the astronauts. The dry mass and payload of the ERV is 28.6 tonnes (including 6.3 tonnes of hydrogen used for ISRU).

    Also, the safest place for the crew, apart from Earth, is Mars surface, not Mars orbit. They have gravity, radiation protection (by the atmosphere, sand, etc.), an unlimited oxygen supply and huge amounts of water, a power plant, a chemical plant (both provided by the ERV), etc.

    “I think you *are* right, but no one knows for sure, because it’s never been tried. The minimum required gravity for health may also–which again, no one knows–vary among the population, and it, too, may depend on the duration spent in the reduced-gravity environment.”

    Huh?? As I said, Poliakov stayed at 0 g (certainly much worse than the 40% g of Mars) for more than 14 months and he could walk in Earth gravity (worse than Mars gravity). And Poliakov was a random cosmonaut, not specially chosen for such a long stay (it was only its second mission) nor to walk just after landing (it was his decision to do so, he wanted to prove that Mars missions are possible). And the one-way trip time to Mars is the same as the mean stay on the ISS and the Mir. If artificial gravity where worse than 0 g (highly unlikely) they could simply detach the theter and stay in free fall. How can you say that no one knows??

47. Michael on January 13, 2016 at 16:42

    If we managed to get a complete rocket into orbit just the space in the tank would be enormous, for example the LH part of the space shuttle is 1,514.6 m^3. This tank could be re-enforced by spraying aluminium retrieved from the O2 tank onto it to thicken the walls for added strength and protection. Now add insulation and you would have quite a volume of working space, add say 6 together and rotated them then you could generate 1 g with each tank having 1 g at the outer part. We just throw to much away when for a little extra energy we could have much more usable materials in space.

    https://en.wikipedia.org/wiki/Space_Shuttle_external_tank#/media/File:Space_Shuttle_external_tank_assembly_01.jpg

48. J. Jason Wentworth on January 14, 2016 at 6:44

    Alex Tolley and Michael: I’m glad to hear that Pykrete research is ongoing! Another idea I have is for a large, thin-walled, pre-peg dome-ended cylinder that would inflate in orbit and harden, like the proposed Echo balloon follow-on satellites (self-hardening subscale models were tested successfully in vacuum chambers). Once this was done, epoxy concrete (which has been studied for some space colony designs) could be applied to or “printed” onto the shell, perhaps on the inside. Pykrete could be applied to the outside, to provide radiation and impact shielding, with one or more layers of metallized Kapton or foil being applied atop the Pykrete to protect it from sublimation in sunlight. Metals obtained from the launching rocket could be processed in orbit for use in the large colony, and they could be cast or forged into needed items inside the colony once it was spun up to provide artificial gravity.

    Michael, your mountain track (or tower) launched scramjet idea is intriguing. It could provide an alternative source (Earth) for raw materials that would be needed for large-scale construction in orbit. The vehicles could “be their own payloads,” with their bodies supplying the raw materials. The Russian space pioneer Fridrikh Tsander proposed a rather similar idea, where no-longer-needed parts of a space vehicle (once it had reached space) could be broken down, melted, and ejected as propellant. (If gaseous-core nuclear fission rockets are ever developed, such a thing could in principle be done, although its realization would require a lot of work.) But since your idea could use concave solar mirrors to melt the desired metals (the sunlight could also be admitted to the interior of a rotating colony, as in O’Neill’s and others’ colony designs), the metal processing could be conducted in the centrifugal artificial gravity, which would greatly simplify the processing.

    Marcel Williams: I’m gunshy about accepting cost and flight-rate figures given for the SLS, after such figures published by NASA for the Space Shuttle later turned out to have been doctored or made up out of thin air. Ditto for the SLS’s schedule. The last I read, the SLS was officially still on schedule, but in a SpaceFlightNow article, sources working in the program admitted that the official schedule depended on no snags or bad surprises turning up, which they–based on their Shuttle experience–conceded was unlikely. If its cost overruns become large enough, especially in this worsening economic environment, the next Congress (whose members may differ significantly, as some of the SLS’s most influential backers are retiring) might cancel it. A failure of the first one would further increase the pressure to cut losses on it. But as Michael wrote (using Shuttle External Tank figures, and the SLS uses–if memory serves–the same tankage diameter), the SLS’s first core stage, launched into orbit “as its own payload” (which it likely could do–many historic and existing rocket stages [including the Ariane 5’s lowest core stage] were/are capable of SSTO performance), would make one *big* honking “wet workshop” space station! As with the original Saturn IB-launched S-IVB “wet workshop” proposal, an SLS wet-workshop could have the grid floors installed before the stage was fueled and launched.

    Brett Bellmore: Greg Matloff’s inflatable “proto-colony” would likely make an excellent cycler. I think one originally built as an Earth orbit fractional G research facility could be re-purposed as a cycler. (The Bigelow Aerospace Genesis I and II inflatable test modules have borne the near-Earth environmental stresses–frequent day/night temperature cycles, and possibly [at their altitudes] monatomic oxygen exposure–well for several years.) Such inflatable, centrifugal artificial gravity Earth-Mars cyclers could also be enlarged over time if desired, by adding more modules and solar arrays.

    Antonio: ISRU technology (and the specific flight hardware using it) will have to be well-proved and “de-bugged” before it can be trusted to return a crew from millions of miles (and months of travel) away. Several sub-scale tests, conducted during robotic Mars sample return missions, would be highly advisable. Aerocapture into Mars orbit (which will require more precise guidance and control than aerobraking landings) will likewise require this before human crews can be entrusted to it.

    Yes, it requires less Delta-V to reach the surface of Mars from Earth than it does to reach the lunar surface from Earth (because decelerating into orbit around the Moon–or directly to a landing on the Moon–can only be done propulsively [tether technology might provide an alternative one day]), even without aerobraking. The Apollo CSM (Command/Service Module) even had ample impulse for a flyby mission around Mars or Venus. But food and air requirements for such missions, as well as tolerably large living space (even the most dedicated astronauts could hardly be expected to endure Apollo-sized quarters for 367 days [the shortest proposed Venus flyby; the longest mission, around Mars, was 686 days]), made a large–and heavy–habitation module necessary for the three-man crew. The S-IVB (with its permanently-attached hab), after the CSM separated, turned around, and docked with the hab, would have re-started in the Earth parking orbit, accelerating the stack into the Venus or Mars flyby trajectory, and that was all the “stock” Saturn V could do. Rendezvous (planetary orbit) or landing missions were out of the question. Radiation shielding would have further increased the hab module’s mass (solar flares could be deadly).

    I’ve read Robert Zubrin’s Mars Direct proposal. It depends on two technologies (ISRU and aerocapture) that sound promising, but haven’t yet been flight-qualified (I think they should be), and on whose successful implementation the mission–and the crew’s survival–depend. Just because something works in principle or even in a technology demonstrator project, it does not necessarily follow that its operational realization will be easy. The AEC/NASA experience with developing nuclear rocket engines showed, to both agencies’ surprise, that nuclear rockets were much harder to develop into flightworthy hardware than they’d thought. Ion main propulsion for space probes also took longer than expected, not for any fundamental scientific reasons, but because sufficiently long-life components had to be developed and flight-qualified through long-term vacuum chamber testing before such engines could be depended on to operate continuously for years.

    It’s easy to forget that Apollo achieved its goal of a Moon landing within the decade–at the cost of three lives–only because it was supported like a wartime crash program, with enormous amounts of money and talented manpower being thrown into the effort. A Mars expedition will not enjoy that situation, which is why I don’t share Robert Zubrin’s optimism that it can be done so relatively easily. Elon Musk’s effort to colonize Mars will require a sustained effort (and spending) for even longer, but I do hope he succeeds. On Mars (as on the Moon), regolith will provide excellent radiation shielding, but solar flares that occur enroute could incapacitate or kill a crew unless they were adequately shielded, and shielding is heavy. Regarding adaptation to free fall or fractional-G conditions for long periods:

    Can you guarantee that an entire crew could endure free fall as well as Valeri Polyakov did for 437+ days? You cannot, and neither can any physician, for the simple reason that he is a statistical sample of one. Until many more people have spent comparable periods in weightless conditions, we have no way of knowing whether he is typical or atypical. Perhaps 90% of all currently-qualified space travelers could do what he did, or maybe 70% of them could, but without much more testing, we can only guess, and no responsible space agency will take such a gamble on an interplanetary mission, where even one incapacitated crew member could jeopardize the mission or even the crew’s chances of survival. Fractional-G conditions are a complete unknown, as regards how long people can remain healthy under such conditions. There may be considerable variation among people, and finding out on distant Mars is not something that NASA will want to do. I’m not trying to throw cold water on interplanetary ambitions (or interstellar ones), but space is a very unforgiving environment, where small errors or oversights–that are inconsequential on Earth–can have deadly consequences. There is no way to make it 100% risk-free, but taking risks in deep space with unknowns that (with a little patience and near-Earth testing) would no longer be unknowns is inviting disaster.

49. Michael on January 14, 2016 at 15:06

    @J. Jason Wentworth

    ‘Michael, your mountain track (or tower) launched scramjet idea is intriguing.’

    I was advocating the sea launch concept, I found that the mountain and tower concept would have ice buildup and construction issues, although a sea launch would have a greater density of air to move through. (see the imbedded video), Dr Hunter also mentions scramjets in the video. The scramjets would be ejected after attaining a maximum speed and returned to earth or even used as raw materials in space for construction if powered into orbit.

    http://phys.org/news/2010-01-space-cannon-payloads-orbit-video.html

    ‘It could provide an alternative source (Earth) for raw materials that would be needed for large-scale construction in orbit. The vehicles could “be their own payloads,” with their bodies supplying the raw materials.’

    Yes that is correct, nothing stops us from kitting out the tanks internally ‘ready for fixtures’ AND using them as fuel tanks as well. Nothing stops us using old satellites in orbit either. And aluminum makes a great solid booster fuel and shielding, powdering it in space for use would be much easier as there is no oxygen to interfere.