Both Tau Zero Foundation founder Marc Millis and JPL’s recently retired Robert Frisbee appear in an article in the Smithsonian’s Air & Space, where voyages to distant places indeed are discussed. Nothing is further from Earth, the article notes, than Voyager 1, which travels at a speed (almost 17 kilometers per second) that would get it across the US in a little under four minutes. Point that spacecraft toward Proxima Centauri and the journey at this speed would take 73,000 years. Clearly, something has to give, and writer Michael Klesius runs through the options.
From Ideas to Engineering
Voyager is actually headed in the vague direction of the constallation Camelopardalis, and won’t come near anything stellar in several hundred thousand years. We’d like to get mission times to a nearby star down to decades so that scientists and engineers working on the project could live to see its outcome.
How to achieve that is a question that has been at the back of Bob Frisbee’s mind for a long time now. To Alpha Centauri in just decades? Years? “We can see the theoretical possibilities of these things happening, but we just can’t get the engineering there,” Frisbee notes in the article, but he points out that this kind of brainstorming was what we used to do when thinking about a moon voyage, and that was a journey we made. It may take several generations of brainstorming but the ideas continue to fly.
Building a Breakthrough Concept
Let’s hope the Air & Space article provokes public discussion as it runs through the background of advanced propulsion studies in the 1990s, when wormholes were seriously tackled and warp drive began to be written up in scientific journals. Miguel Alcubierre’s concept of a spacecraft riding what is essentially a wave in spacetime kicked off a resurgence in breakthrough propulsion that led materially to projects like NASA’s Breakthrough Propulsion Physics, run by Millis until its termination in 2002. Funding issues are always problematic, but Tau Zero continues to probe these matters, and Frontiers of Propulsion Science, co-edited by Millis and Eric Davis, shows that the ongoing conversation is robust indeed.
Says Millis:
“I think back to the era of Dirac and Schrödinger and Einstein. When they were having their pivotal meetings and sometimes heated debates, they weren’t being funded for that work. They were just doing it because that’s what they did. And they made significant advances… And I’m thinking to myself, Well, it would be great if we got funding, but even if we don’t, when we talk amongst ourselves and debate things and encourage each other to write papers, we’re going to make progress.”
That kind of progress is what Tau Zero is about. Not that robust funding is out of the picture — we are building a philanthropic model for the foundation that should be able to tap private sector sources (with all the good things that follow from not being channeled through endless layers of bureaucracy). But keeping an eye on the issues and encouraging debate is bound to produce good outcomes, if only in the synergies that result from putting propulsion theorists with good ideas in continuing contact.
Options for Infrastructure
But before we go to the stars, we’ve got to build up our capabilities right here in the system. On that score, the article is also noteworthy for its examination of NERVA, a nuclear thermal rocket design that Klesius describes this way:
It would produce thrust the way chemical rockets do: by heating a propellant—in this case, hydrogen—and ejecting the expanded gas through a nozzle. Instead of heating hydrogen through combustion, however, the nuclear rocket vaporizes it through the controlled fission, or splitting of atomic nuclei, of uranium. Because nuclear fuel has a greater energy density, it lasts a lot longer than chemicals, so you can keep the engine running and continue to accelerate for half the trip. Then, with the speedometer clicking off about 15 miles per second — twice the speed reached by returning Apollo astronauts — you’d swing the ship around to point the other way and use the engine’s thrust to decelerate for the rest of the trip. Even when factoring in the weight of the reactor, a nuclear engine would cut the transit time in half.
NERVA was a promising technology that delivered 850 seconds of thrust — twice the efficiency of chemical rockets — in 1960s-era tests, but the program faded in the 1970s. You’ll find more on NERVA, and on Franklin Chang-Díaz’ work on VASIMR, in Klesius’ article. Neither NERVA nor VASIMR has interstellar potential, but in terms of opening up the Solar System for exploration and infrastructure building, these are solid options to investigate.
An Insurance Plan for Human Survival
I like the Chang-Díaz quote that ends the piece:
“The space program began the day humans chose to walk out of their caves. By exploring space we are doing nothing less than insuring our own survival.”
Indeed. And all the technologies described here point to ways of making the insurance policy pay big dividends. Klesius writes about a fusion-powered 180-day trip to Jupiter, one dependent on breakthroughs in fusion itself and in materials science. Build the infrastructure here in the Solar System and gradually push the envelope outwards. It’s a plan that could pay off one day in making that journey to Proxima Centauri via fusion, antimatter or other means, and crossing the gulf in a single human lifetime.
mark,i agree 100% with what you have said above.as long as we keep talking and thinking there is always the possibility of someone having that aaah ha moment and then we will be “off to the races”! i just hope and pray that i will be lucky enough to be that “comment maker”! just recently i have spoken to friends both here in n.j. and on line about the importance of spreading ourselves through the solar system as a,if you will,practice for starflight! respectfully your friend george
Barring some fundamental theoretical breakthrough in physics, what is the best we can hope to do with propulsion systems? How quickly could we get to Centauri using a propellant-based drive, presuming the issues were just ones of engineering? For example, I presume that the most efficient, power-dense energy source for a propellant-based system would be antimatter, and while there are vast engineering challenges in such a system, including producing enough of the fuel itself, these challenges don’t seem to require any fundamental change to the theoretical foundation of physics. As such, this approach seems to anchor the top-end of possible propulsion systems given our current understanding. Presuming there aren’t any theoretical advances, what’s the best we could do with such systems? (And is there anything better based on current physics, such as beamed power?)
NERVA and VASIMR appear to be intended for manned planetary flight, but wouldn’t they also be useful for unmanned exploration of near interstellar space? Proposed missions like the Innovative Interstellar Explorer with 30+ year travel times are already pushing the limits of what ion engines can do. It seems to me that using NERVA or VASIMR on a mission like that would be the most scientifically useful (as well as quickest, cheapest, and safest) way of demonstrating these technologies.
I’m re-reading Matloff & Mallove’s “The Starflight Handbook” and they make a strong case for the feasibility of long-term starflight – centuries long – but are less sanguine about shorter duration missions. The energy costs are incredible for relativistic speeds – not a show-stopper but enough to delay the first mission by a couple of centuries while we build enough energy infrastructure. Self-constructing technology, for exponential growth, seem a necessity unless we make a physics breakthrough, like macroscopic sphalerons or some other means of turning mass into energy directly, without the mess and waste of antimatter.
For scientific purposes I’m more hopeful about the potential of gravity-lensing telescopes sent out to 580 AU or so. The lure of such incredible enhancement of signal that the Sun naturally provides is pretty strong IMHO.
Without a physics breakthough, there is anti-matter and fusion. Anti-matter propulsion has enormous technical hurtles, including manufacture of the anti-matter itself. Fusion really cannot get you to relativistic speeds. All of which means that you are left with the upload/download transhumanist option where you go to the stars in a coke can sized space craft.
By this, I don’t mean the whole fantasy about living as software in a simulation. Rather, I am talking about mapping out the constituents of your mind and storing that data inactively in some kind of molecular-scale memory. Once you get to the target system, you use your nanotechnology to build the industrial infrastructure and then the biotech to grow yourself a new body with the brain’s neuro-connections being made to the same specification as that in the molecular memory, thus “downloading” you into your new body in your new solar system.
At least this is how I see going to the stars without any physics developments.
Hi NS
VASIMR could launch an IIE mission, but NERVA? It’s performance isn’t much better than chemical rockets with its Isp typically quoted as being just 850 seconds. The only way for a NERVA to match an ion-drive or VASIMR for terminal velocity is a solar fry-by trajectory with a perihelion boost. But NERVA specifically isn’t right for such a mission. A DUMBO style heat exchanger is needed to get a sufficient thrust-to-mass ratio. Plus-Ultra Technologies did a study on such a mission using their MITEE NTR, but it’s a pretty marginal performance.
Thanks for the reply, Adam. I wasn’t aware of NERVA’s unsuitability for a near-interstellar mission.
My main concern is that we not tie advanced propulsion too closely to manned missions. So many additional technology developments (besides engines) are needed for long-term manned spaceflight that it seems best to focus first on propulsion types suitable for unmanned probes.
Hi kurt9
I think there’s something to the idea you’re advocating. If such an upload/download scenario was achieveable then the high-speed solar sail designs discussed by Mallove & Matloff would be ideal choices, able to reach ~0.015 c via free sunlight alone. If such take a millennium to reach at system 15 ly away, then a millennium to replicate and relaunch a new wave, the colonization wave would reach the otherside of the galaxy (75,000 ly) in just 10 billennia. Does kind of make the Fermi Paradox so very puzzling. Of course if a species is able to upload/download then maybe it’s past the urge to exponential growth. Matloff, and Chris Boyce, independently suggested the Kuiper Belt is probably settled by ETIs from a whole range of colonization waves, as it is sufficiently rich to entice and sufficiently isolated for ‘privacy’ from the locals.
Thus any advancement in propulsion makes the Paradox even more acute IMHO, at least in a technological sense. Really boils down to the motivation that consistently propels a species across billennia and that’s something we have yet to discover for ourselves. If starflight is difficult forever, then each new ‘colony’ is essentially independent of its parent and the overall progress of a species through the galaxy will be more like Landis’ Percolation paper describes – potentially a spati0-temporal pattern with a lot of untouched ‘voids’ within it. We could just be in an ‘untouched’ part of the galaxy, not yet lucky enough to have stumbled upon space-junk.
Wonder what a space equivalent of the Pacific Gyre garbage patch would be like?
I would propose an entirely different approach. Minimize the mass to be accelerated and build all of the propulsion equipment in near-solar orbit. An array of powerful solar-powered LASER’s, all of which are focused at a “sail” attached to the vehicle. To try and carry all of the fuel, engines and control equipment with you is inefficient and potentially fatal in the event of an equipment failure.
Use the KISS principle.
Now, how the craft would decelerate once it had reached the “target” is the major problem. It would work for a “slingshot” out-and-back mission, however, as the LASERs could be used to decelerate the returning vehicle just as efficiently (if you even decided to return it, there’s really no valid reason to if it’s unmanned).
The time consumed doing these probe missions would not be wasted, either, as we could well have developed a better solution for manned flight prior to their completion.
Realistically, we wouldn’t want to send humans until we had a close-up look at the conditions by robotic probe first, in any case.
We have the technology to perform a mission like I’m describing right now, there’s nothing “uninvented”, like antimatter or fusion drives, involved.
Just my uneducated view on the subject.
If someone thinks NERVA is not good enough, what about these three
http://en.wikipedia.org/wiki/Nuclear_lightbulb
http://en.wikipedia.org/wiki/Nuclear_salt-water_rocket
http://www.rbsp.info/rbs/RbS/PDF/aiaa05.pdf
( I would also note, that with better materials and a little more engineering, NERVA type reactor could easily reach ISP ~1500 )
Adam September 4, 2009 at 6:53:
“For scientific purposes I’m more hopeful about the potential of gravity-lensing telescopes sent out to 580 AU or so. The lure of such incredible enhancement of signal that the Sun naturally provides is pretty strong IMHO”
I think this says very much indeed.
First of all, because such powerful telescopic capacity could and would substitute for much if not most of what interstellar probes could do at a minute fraction of the cost (also because we could aim such a telescope at an unlimited number of targets), it would partly or largely make those probes redundant. In fact this may *partly* explain the Fermi Paradox: if you can spy on the neighbors as much as you like, why bother to go there? Related issue: since the development of telescopic capacity is so vastly much easier and cheaper than physical space travel (we will probably get a more or less complete inventory of planetary systems in our MW galaxy and maybe even neighboring galaxies in the course of this century, maybe next one, ourselves) this imlies that, IF there is another techno civilization in the MW, even at comparable level or only slightly more advanced, they will definitely know that we are here. Not in every detail, but as a living planet with a techno civilization, maybe even some of the major infrastructure.
Secondly, open door, only the discovery and description of a living (or at least terraformable earthlike) planet would provide the public and political incentive and support for eventual interstellar travel.
Paul: are you also going to do an update on the ongoing ‘anti-gravity’ research ref. Heim, Dröscher/Häuser, Tajmar, Chiao, … (and their differences)? I am usually down to earth realistic, but at times that I allow myself to dream a bit, I imagine that this avenue of research may be our only, or at least best, bet for breakthrough/FTL propulsion.
Again, such research would probably also get an enormous boost from the telescopic discovery of an earthlike planet.
The transhumanist upload scenario presumes a breakthrough in information technology every bit as radical as various physics breakthroughs. If we are going to need such technologies we might as well stop discussing space travel because space travel with such technologies is going to be operating under a completely different set of constraints. It’s just invoking yet another “fantasy” scenario to duck the limitations imposed by the universe.
“What if we had magic pixie dust, how would we build a spacecraft then?” – this not a particularly interesting question, because we don’t have magic pixie dust, and it doesn’t seem particularly likely that we’ll ever have magic pixie dust, and even if we did have magic pixie dust any suggestions we make in the pre-magic pixie dust era will be hopelessly outdated when we have magic pixie dust to play around with.
Ronald asks:
Ronald, Martin Tajmar was in Cleveland recently for a meeting with Marc Millis and several others. I had hoped to be there but could not work out the travel time. And yes, I do plan to keep up with this work, especially since Martin publishes actively in the peer-reviewed journals and is running laboratory work to test out his ideas. If I hear of further developments re Heim et al., I’ll be looking at them as well, though so far this work seems to be entirely theoretical and it may be premature to comment. Eric Davis made much the same point in Frontiers of Propulsion Science.
“we could aim such a telescope at an unlimited number of targets”
That’s true in principle, but in practice changing the aim of a gravitational lens telescope to a target in a different part of the sky would require the device moving a vast amount of distance. Since the Sun is the lens, and the probe needs to be around 500-1000 AU away from it, the ability to shift targets is extremely limited, so much so that unless the target is very close (in terms of line of sight) to the original, it is probably much more practical to send a new scope. My guess is that gravitational lensing telescopes will be missioned for specific targets, rather than working like Hubble.
Paul, thanks!
I presume you are also aware of similarly interesting work, the superconducting gravitational mirror of Raymond Chiao from the University of California, Merced.
Otherwise search arXiv.org for his name, he has recent (2009) articles and I think also peer reviewed publications.
On the current advanced propulsion theme, Brian Wang has posted an interview with a researcher, Paul March, working on James Woodward’s Machian inertia effects…
http://nextbigfuture.com/2009/09/mach-effect-interview-with-paul-march.html
…would be an incredible breakthrough if it can be verified and then scaled up. The solar system would become as accessible as the planet, and the stars would follow. But there’s a lot of experimental confirmation work to be done yet.
Woodward hopes wormholes might follow. Negative mass densities mean wormhole stabilisation might be possible with all that implies. Whether Alcubierre warps are then possible at FTL speeds might be irrelevant if they can be combined with wormholes for high-gamma sub-light transit – the relativistic time compression means the wormhole provides a quasi-FTL linkage once it reaches its destination.
Brian Wang has a description of Woodward’s Mach effect work over on his website at: http://nextbigfuture.com/2009/09/mach-effect-interview-with-paul-march.html
Andy,
You misunderstand my previous point. I was not referring to the upload and live as software emulation that the transhumanists are always yakking about. I was referring to something much less radical, which is the mapping of the brain at the molecular or at least the synaptic level and storing that brain map INACTIVELY, then using that information to recreate the person’s brain (along with the body) using the kind of bionanotech that will certainly be in vogue in the latter half of this century.
I share your skepticism of the whole upload scenario (in fact, I don’t think its possible at all). However, you should note that this is not the same thing. Such brain mapping will certainly be possible in the next 2-3 decades and bionano will come into its own in the same timeframe.
Ronald wrote:
Yes, and we also covered Chiao in the Frontiers book, so I’ll be keeping a eye out for further developments on that front as well.
Laboratory-Scale Superconducting Mirrors for Gravitational Microwaves
http://arxiv.org/abs/0903.3280
1. Major breakthroughs in physics:
Some people hope such breakthroughs will show, that we can travel through space “better” than today.
(As history tells, the opposite could happen as well. As long as we had only Newtonian physics, we would have concluded, that there is no upper limit for velocity, and if we wanted to send a probe to Alpha Centauri in a certain short time, we would just increase the probe’s speed as much as necessary. But then came Einstein with his major breakthrough in physics, and now we know, that such an unlimited increase of speed is not possible. Bad luck! If bad luck continues another breakthrough in the future leads to another restriction.)
My recommendation is not to base something on major breakthroughs in physics. We can not use something like that in reasonable way. Making an assumption, which is not true according to current physics — the only one we have –, and proceeding — even in a logically correct way — to a certain conclusion leads to nothing useful in science and technology.
And some people should realize, that it does not help objecting “but you can’t prove the opposite” or, even better, “you can’t know”. This is at best childish, and does especially not help achieving a reputation in a discussion.
2. Preconditions of space exploration:
It is plausible for me, that the Tau Zero Foundation and many people in this news forum prefer talking about the physical and technical aspects of space exploration. This is very fascinating for me too.
But looking at history we can see manmade factors of a rather different kind, which cause a substantial delay of progress, and which are rivals for resources.
Space exploration is expensive, but currently the money — and this time really much money — goes into handling an unexpected economic crisis. As soon as mankind has recovered from the current crisis — when the next generation is where I am today — there will be other problems, e.g. war — war will be there for a long time –, or producing food, energy, etc. for the world population, or environmental pollution, or another economic crisis, or …
I hope space exploration can be of some substantial help with these other problems, and that we can communicate this to the people involved.
kurt9: in which case the “magic pixie dust” is the technology to recreate someone’s brain+body from information stored in a coke-can sized probe. Recreating an entire organism from scratch is extremely difficult! A living organism is not a static system, but a dynamic one. Incidentally this is why all these “lifeboat” ideas to store the DNA of various species are pointless: that’s like storing your information on CDs but not bothering about the CD player. Situation is worse with DNA because a CD player can play many different CDs, but you can’t produce a rat by using its DNA in a mouse.
Plus there’s the issue of getting something which has such high information density unscathed through a decades-to-centuries-long journey through interstellar space, at the mercies of particle collisions…
Regarding the funding situation for advanced propulsion mechanisms (or the lack thereof), I think we are on the cusp of some major gains. As soon as access to suborbital space becomes affordable to the general public and many people (including philanthropists) begin making the journey, I think some will be so fascinated by the experience that they will either donate their own money or become potent fundraisers themselves to help find the money needed to support and further develop these technologies.
Hi Folks;
We have the where-with-all to travel ever farther out into the universe, the argument for which I present below.
My hope is that both the ARES I and ARES V vehicles will come to fruition on time.
These systems would be a shame to abandon given all of the money that has already gone into them.
We definitely need and can have a medium duty lift vehicle like the ARES 1 to get us and our mid-range mass equipment to LEO. It is a potential national security issue to let several years go by without a good mid-range vehicle to lift both humans and heavy equipment into LEO orbit on a regular basis.
As for the ARES V, with the ability to lift some 275 metric tons into LEO, this baby can be used to lift components of a Mars bound or Asteroid Belt bound manned craft into LEO where-upon the components can be assembled. Just five ARES V vehicle launches could be used to assemble a 1,375 metric ton dry weight manned Mars Ship or other interplanetary ship into LEO.
Given that we have not yet fielded plasma or ion rockets for vehicles with the mass range of manned interplanetary craft yet, and we seem to be stuck in the rut of using chemical rockets for propulsion of such craft, the ARES I and the ARES V vehicles can open up a new era of manned interplanetary travel and perhaps off world colonies.
What comes next? Hopefully journeys out into the Kuiper Belt, the Oort cloud, and then to our stellar neighbors. But that will take more capable forms of propulsion unless we develop colony ships or World zondes that are energy efficient and can maintain civilizations for periods of tens to hundreds of thousands of years. Either way, I see humanity spreading ever further out into the Cosmos if only because of our wanderlust to explore and go beyond the next proverbial ridge or hill top.
Chemical Rockets can enable us to achieve velocities on the order of perhaps 1,000 kilometers per second using the most exothermic of known chemical reaction and a large enough but still plausible fueled mass to dry weight vehicle mass ratio, and 1,000 kilometers per second is greater than the escape velocity of just about every if not ever galaxy super-cluster, and so even with chemical rocket technology on steroids, we do in theory have the propulsion technical concepts to build huge interstellar colony ships or world zondes to enable use to travel and populate other galaxies.
If the rate of expansion of our universe levels off at some future time, all the better since in such a case, we can in theory go galaxy hopping or super galactic cluster hopping using such world zondes and ordinary chemical rockets.
Think of it, 1,000 km/sec is about 0.0033 C. In 10 EXP 15 years or the theoretical lifetime of the stelleriferous era in our universe, a world zonde could travel 3.33 trillion light years from Earth not taking into account the expansion of the universe. Taking such expansion into account, the actual distance traveled from the Milky Way Galaxy would be several orders of magnitude greater still, and the recessional velocity of the craft from the Milky Way would be several orders of magnitude greater that C or several orders of magnitude greater than the speed of light, once again assuming that the rate of expansion roughly stays the same or increases slightly over the next 10 EXP 15 years.
Even if exotic space time topology altering techniques prove untenable, and the shield requirements and collision avoidance requirement for relativistic manned space travel prove to hard to manage, we can and I feel it is our duty to work toward a colonization of our universe.
I pray and hope the space time topology altering technologies will enable us to one day zip about over cosmic spatial distances, and extreme gamma factor technology will be able to send humans far into the future, but in the event that we cannot due to any limits imposed by mother nature, we can still populate our universe, and we must do so.
The Ares I and Ares V vehicles offer a great hope for mankind. Let us not squander the possibilities by canceling these important programs. Since we know how to do rocket powered gravity assists, using such mechanisms around ordinary stars can definately enable chemical rocket powered world zondes to reach 1,000 km/sec or greater with repeated stellar gravity assists.
In short, we can and must aim for the stars.
jim yes we can and must aim for the stars you will not get any arguement from me on that but how and when are the questions! maybe the more intelligent use of launch vehicles we already have in the inventory would be a great first step.respectfully your friend george
in which case the “magic pixie dust” is the technology to recreate someone’s brain+body from information stored in a coke-can sized probe.
This is likely to be an advanced form of stem-cell regeneration. Regeneration and synthetic biology are rapidly growing fields right now. I see no reason why bionano will not give us the capability to grow us from scratch. After all, we do grow from scratch with the sperm and egg. We’re just creating a synthetic version of this. This is the same kind of technology that will be used to reanimate those in cryonic suspension.
BTW, the SENS 4 conferences is occurring this weekend. All of you do realize that if SENS does not work out, that you will need cryonic suspension to have any chance of getting to the stars, regardless of physics breakthroughs.
Here is another propulsion method that we could in theory implement in a crash course Manhattan Project like Herculean effort. The idea centers aroung Karl Schroeder’s brilliant idea of Stellar Cyclers, an idea I wish I had come up with. Accordingly, to the extent that we can charge the space craft so that the Lorentz turning force keeps the space craft in an interstellar orbital or cyclical motion, thus the name Cycler, a solar dive and fry sail or PV powered electrical rocket system could keep coming back to the sun or any star for powered gravity assists, thus amplifying the effects of an electrical rocket propulsion system. If we can rely on the extremely Doppler blue shifted light for each inbound cycle to power photo-electric systems that perhaps operate somehow at ultra-violet or x-ray frequencies (requiring some exotic yet to be developed or invented PV or PE materials) to power electrical propulsion systems such as, while on the outward bound legs of each cycle, the light sail would be deployed in full form thus givng the craft repeated incremental kinetic energy boosts wherein each boost would instill a relativistic scale quantity of kinetic energy to the craft, such a craft could reach outstandingly high gamma factors in principle.
Assuming that some way is found to protect the ship from ionizing radiation, debris, and interstellar and interplanetary dust, and to mitigate astro-dynamic drag, there is no reason why the ship could not be commensurately electrically charged so that it can continue to repeat the accelerative cycling essentially for periods of cosmic time duration thus reaching commensurately outstanding relativistic gamma factors.
Now, within a given galaxy such as the Milky Way, a Stellar Cycler could in theory orbit the galaxy with ever greater relativistic velocities while at the same time receiving a boost from the electromagnetic emission of stars, mid range blackholes, and even the centrally located supermassive black-holes which in the Milky Way have a mass on the order of 1 million to 10 million solar masses.
As long as the craft could maintain the requisite electrical charge and synchrotron radiation emissions by the craft could be kept at a level where the kinetic energy input to the craft is higher than synchrotron radiation and astrodynamic drag based losses, the craft should continue to accelerate essentially forever or at least over truly cosmic time intervals and achieve increadibly high gamma factors.
The use of photon, electron, proton, ion, neutrino and/or perhaps even tachyon rocket propulsion (if tachyons exist) could be made in space craft that would make powered gravity assists around stars, mid-range, and super massive backhoes all the while that craft was using the Stellar Cycler type Lorentz turning force to keep it glued to its energy source, the electromagnetic and gravitational fields of the Milky Way Galaxy or other host galaxies.
Note that given vector and scalar potentials A and ?,
F = dP/dTau = q{1/{[1 – [(v/C) EXP 2]] EXP (1/2)}}{( – dell phi) – dA/dt + [v X (dell X A)]} where v is the ship’s velocity, C is the speed of light, dell is the dell operator A and phi are the vector and scalar potentials of the interacting fields, q is the net ship’s electrical charge, and X represents the cross product operation.
dP/Tau expresses a relativistic form of the Lorentz force when no other forces are present. One can see that as gamma = 1/{[1 – [(v/C) EXP 2]] EXP (1/2)} grows, the Lorentz force grows. In the limit that C is reached, gamma goes to infinity and so does the Lorentz turning force even with a small but finite electrical charge of Q.
It is possible that the Lorentz force type of Stellar Cycler could take advantage of the Cosmic Microwave Background Radiation of CMBR where only the back side of a CMBR sail is reflective to CMBR and where additionally, the forward side of the sail is photo-electric to CMBR and which thus could absorb relativistic blue shifted CMBR and use the electrical energy produced to power photon, ion, proton, electron, neutrino, or perhaps even tachyon rockets, as well as electrodynamic hydrodynamic-plasma drive craft that utilize magnetic, electric, and/or electromagnetic fields as the field effect reaction mechanism to react against the interstellar and intergalactic plasma.
The same CMBR capture mechanisms could be utilized for CMBR blue-shifted to visible light, and ultraviolet light frequencies via the deployment of monolithic PV sails or perhaps mass saving PV grid type sails that are composed of PV electrically conducting materials in the form of a thread like weave or net comprised on PV nano-fibers separated by 0.05 to 0.1 microns. Such a sail could permit a mass savings of about 25 to 50 times that of a monolithic weave for hard ultraviolet photons. Such systems could also be used to collect solar or stellar energy to power electrical propulsion systems in Stellar Cycler dive fry runs as the relativistic gamma factor mounted.
I was reluctant to include such a long winded post and will not ordinarilly do so in the future, but I think that Karl Schroeder’s Stellar Cycler is a great idea based on completely known and well established physics. It can most probably be implemented this verycentury, financial resources pending.
James,
Chemical rockets aren’t that energetic. The most extreme chemical rockets imagined involve ionized helium recombination, with an exhaust velocity of ~30 km/s. With ridiculous levels of staging we might push such a vehicle up to ~x10 its exhaust velocity, a mere 300 km/s. Why? We have much more plentiful energy sources from the Sun and nuclear reactions.
Much easier to use solar-sails or nuclear pulse if you want low speed World-Ships. According to Matloff’s work a manned World-Ship should be able to get up to ~1,000 km/s via solar-sail with tolerable acceleration levels. Automated probes would achieve ~0.015c, as I’ve already noted. If we wait for the Sun to hit its Red Giant Tip then speeds of 0.05 c are straightforward – and there’s no reason why civilizations escaping from their star’s Red Giant phase can’t do the same.
Tulse September 5, 2009 at 9:11
(…) in practice changing the aim of a gravitational lens telescope to a target in a different part of the sky would require the device moving a vast amount of distance.
Yes, very true, I am aware of that. Therefore, I expect that such an instrument would be most worthwhile to use for a relatively densely packed cluster of targets, such as, in particular, (planet searches in) the Andromeda galaxy.
Hi Adam;
There remains the possibility that some forms of hydrogen that are compressed to the state at which they would exist as a solid stable metal might have an energy storage density as great as ~ 10,000 x that of TNT per unit of mass.
Mono-atomic hydrogen, if it could be safely stored might have an energy density several times greater than that of the potential energy of diatomic or normal hydrogen.
If hydrogen might perhaps be so compressed, why not other elemental gases.
However, I completely agree that nuclear energy is a much much better option.
Regarding Dive and Fry solar sail, assuming dragless operation and a somehow quickly fully deplyable nano-grid or net type reflector the following calculations might be of use.
Assuming fraction f of the starlight is reflected straight back and the sail moves radially outward,
the equation of motion is for a dive and fry stellar sail is essentially;
B[(1 + (B EXP 2)]dB/[(1 ? B)EXP 2] {[1 ? (B EXP2)] EXP 3/2} = p [(R0/x) EXP 2](dx/Ro),
where B = v/c, v is the speed of the sail, x is the distance from the star, R0 is the initial distance from the star,
P = 2fA(u0)R0/[Mo(C EXP 2)]
Where;
A is the area of the sail, m0 is its rest mass, and u0 is the energy density of starlight at x = R0; thus, u(x) = (u0)[(R0/x) EXP 2]
Adopting f = 1, a value of M0/A = (10 EXP ?8) kg/(meter EXP 2) = the effective mass specific reflecting area of the sail craft, and u0 ~ L/[4(pi)(Ro EXP 2)C] with L the Sun’s luminosity and R0 = 0.03AU, I find p ~ 5 × (10 EXP ?2).
Note also that the equation of motion can be integrated analytically to find the terminal speed.
Just integrate from zero to its terminal value and x from R0 to infinity.
This yields for the terminal velocity:
{[(1 ? (B EXP 2)] EXP (1/2)} [7 ? 14B + 11 (B EXP 2) + 2(B EXP 3)]/[(1 ? B ) EXP3](1 + B) = 7 + 15p,
With p = 5 × (10 EXP ?2), the terminal velocity = 0.251 C.
FTL scenarios are bedridden by a physics type “Fermi paradox” that lays them out cold.
If FTL was possible, we could build computers that beat NP problems. If NP problems were beatable, all physical (algorithmic) problems were easy. If all problems wer easy, we would already know everything.
But we don’t, so they aren’t, so it isn’t. Possible with FTL, that is.
[From research by computer scientist Scott Aaronson, see arxiv.]
Btw, Alcubierre’s drive is an especially easy example to put down on specifics. Even if it was constructible (and it isn’t because of energy/exotic matter requirements) it would only be another tachyon body equivalent, except an extremely contrived and expensive one. (Yes, well, we will recognize the passengers afterwards, at least.)
The problem is to get to the FTL tachyon state in the first place. Alcubierre doesn’t tell us anything on this.
torbjorn,thank you that was an interesting and well thought out arguement you just made.as you may know,i am one of the people who hopes that the next major breakthrough to allow warp drive,worm hole travel,etc etc might be closer than we suppose.you can never tell.after all alot of things where “impossible” just 100 years ago in 1909!!! today we take them for granted. respectfully your friend george
It might be possible to get thousands of gravitational assists from objects in the Kuiper Belt or Oort cloud. Those might build a craft up to a substantial speed if there were enough of them.
To Torbjorn Larsson, could you identify the specific paper by Scott Aaronson (he has several in arxiv). Thanks.
Not sure I’ll be able to understand it anyway though…
I stand by my point that unless we get a physics advance, that the human future is space will be mostly limited to this solar system and will be based on some sort of O’neill style space colonies. Of course, there is a considerable amount of resources in our solar system and it is considerably bigger in both size and resource limits than believed in the time of the L-5 society. The Kuiper belt was discovered as recently as 1992 and the objects beyond it more recent than that.
The key technology for space is not propulsion (although this is important). It is synthetic biology (AKA “wet” nanotechnology), necessary to create the habitats and the bio-systems inside them (like Dyson’s Trees). Such technology would be necessary for any kind of planetary surface colonization once we have the means to travel to other star systems.
The Adventures of the Rocketeer: Accelerated Motion Under the Influence of Expanding Space
Authors: Juliana Kwan, Geraint F. Lewis, J. Berian James
(Submitted on 8 Sep 2009 (v1), last revised 9 Sep 2009 (this version, v2))
Abstract: It is well known that interstellar travel is bounded by the finite speed of light, but on very large scales any rocketeer would also need to consider the influence of cosmological expansion on their journey.
This paper examines accelerated journeys within the framework of Friedmann- Lemaitre-Robertson-Walker universes, illustrating how the duration of a fixed acceleration sharply divides exploration over interstellar and intergalactic distances.
Furthermore, we show how the universal expansion increases the difficulty of intergalactic navigation, with small uncertainties in cosmological parameters resulting in significantly large deviations.
This paper also shows that, contrary to simplistic ideas, the motion of any rocketeer is indistinguishable from Newtonian gravity if the acceleration is kept small.
Comments: 9 pages, 7 figures, accepted for publication in PASA
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)
Cite as: arXiv:0909.1551v2 [astro-ph.CO]
Submission history
From: Juliana Kwan [view email]
[v1] Tue, 8 Sep 2009 19:51:31 GMT (316kb)
[v2] Wed, 9 Sep 2009 01:17:45 GMT (145kb)
http://arxiv.org/abs/0909.1551
observer,i like your idea about thousands of gravitational assists from the oort cloud.seems to make alot of sense. kurt 9 i sure hope that we do make considerable breakthroughs in propulsion! not too long ago i was guessing out loud that if we never saw a starfleet type of organization…then at the very “least” we would have a space force of some kind spread out all over the solar system flying ships that would be powered by fusion engines! and extensive bases on the moon mars asteroids etc! but just between us,i have little doubt that something very advanced for propulsion WILL happen along. thank you gentlemen,your friend george
george scaglione: “after all alot of things where “impossible” just 100 years ago in 1909!!! today we take them for granted.”
A little bit more than 100 years ago it was “impossible” that there is an upper limit to the velocity of material things. Today we take it for granted that there is one. Well, I said “we”, but I have to exclude some people who still don’t realize, that by the general theory of relativity we are able to explain a lot — and I mean: really a lot — of phenomena, whereas assuming the opposite contradicts substantial parts of reality. *These* facts are important and relevant for what we will be able to do today and in the future.
By the way, the theory of relativity is even used for everyday business. The Global Positioning System (GPS), as an example, works correctly only because the influence of the gravitational field of the earth on the GPS satellites is taken into account just the way the theory of relativity says. Go ahead and buy yourself some of these smart phones, and *use* the theory of relativity.
According to all what we know, travelling faster than light is a pipe dream. And — I beg your pardon? — “the next major breakthrough to allow warp drive,worm hole travel,etc etc might be closer than we suppose” — there are no reasons and there is no evidence. Over and above that, a major breakthrough in physics may, as I already said, as well and again lead to realizing, that there are even more restrictions — than only an upper limit to velocity. Be careful with your wishes! ;-)
duncan, i dream and will continue to do so however,yes,you may be ,i realize 100% correct! that is why i am very happy that few people doubt that fusion drives are not all that impossile.but respectfully to you sir,after we have used them for quite a while i would be suprised at the very least if they where not considerably improved.lol i should live so long! but thank you for your thoughts i appreciated hearing them .respectfully again your friend george
Hi George;
I share your dreams.
We might also find that the physics of special relativity breaks down as super high gamma factors.
Even if FTL travel is not possible, then at the very least we can in theory still approach C arbitrarilly closely. Say we could reach a gamma factor of a whopping {[5.3 x (10 EXP – 44)] EXP – 1}(3.1 x 10 EXP 7), then in one Planck Time Unit ship time or in tp = {[(h/(2 pi)) G]/[c EXP 5]} EXP (1/2) = 5.3 x (10 EXP – 44) second, the craft would travel one light year. The craft would travel about 2 x (10 EXP 43) light years in one year ship time neglecting the expansion of space time. In actuality, the recessional velocity of the craft after having traveled one year ship time at such a velocity would be much, much greater than [2 x (10 EXP 43)] C from what is left of the Milky Way and the distance traveled from the Milkway would be many orders of magnitude greater than 2 x (10 EXP 43) LY.
As for wormholes, warp drive, multiply connected space time regions, fTL travel, Einstein Rosen Bridges, electromagnetic field based teleporation, negative drive, inertial mass modification, anti-gravity, electrogravatic propulsion, gravity drive, and light speed travel, I will continue to dream the dream that perhaps these technologies can become viable at some future point in time.
If we can medically enhance our lifetime to essentially unlimited durations, and develop a virtually accident free lifestyle or some type of Era of Peace Utopia, then perhaps we can live for as long as 2 x (10 EXP 43) years or longer, which is long enough to see human space flight reach destinations of truely cosmic spatial and temporally future destination even if FTL travel is impossible.
So continue to Dream the Dreams, and I hope and pray they will come true.
Your Friend Jim
Hi Jim
Such speeds would be attained only by travelling just as far at 1 gee, since gamma increments by 1.0323 per light-year of displacement at 1 gee acceleration. Ship travel time would be ~0.97*ln(2(2E+43)) = 97.4 years. Of course it could all be crammed into 1 year tau by accelerating at 100 gee.
I do wonder what would happen once every particle making up the ship had a Planck energy worth of kinetic energy. But it’s unlikely to ever be attained since there’s no physical way of accelerating a vehicle to such speeds that I can think of, aside from massive amounts of handwavium…
James,
I always love and admire your big numbers. And share the dream.
I am just a simple man and would be very content just to travel the Milky Way ;-)
James M. Essig: “We might also find that the physics of special relativity breaks down as super high gamma factors.”
Well, James, I share your — and George Scaglione’s — ability to dream (I have kept this from my childhood on much more than most people around me, I think). But, as the Tau Zero Foundation’s website tells, the participants “have agreed to work together toward practical interstellar flight”. Please, pay particular attention to the word “practical”. There are many statements made by Paul Gilster and others, which show, I think, that they do not want fantasy physics and fantasy spaceships, but real, applicable physics and spaceships that will really travel to other stars, — and this not in the very far future.
It does not “help with this ambition” (and here comes a different side of me: I’m a rather down to earth person too), if you and others mention again and again science fiction dreams of what “might” be possible, but is not supported by any evidence, and if you and others make useless conclusions based on these unsupported assumptions. Take your statement about the physics of special relativity perhaps not being correct when moving with a velocity very near to the speed of light. We might find this? Today’s physics — the only physics we have — says “no”, and this is in accordance with observations from particle accelerators, from cosmic radiation, and from high speed phenomena near super novae, neutron stars, black holes and such.
Your comments show, I think — and I have read many of them –, that you know something about science and technology. You should be able to apply your knowledge more in a way supporting the objectives of the Tau Zero Foundation and the Centauri Dreams website. Please, connect your dreams to reality!
Hi Adam;
Thanks for the insights.
Especially, many thanks for providing the value of “Ship travel time would be ~0.97*ln(2(2E+43)) = 97.4 years”. If we can figure out how to do 1 G for 97.4 years, then perhaps traveling such distances might somehow be possible. I won’t hold my breath on that happening anytime soon, though. In the spirit of what Ronald said above, I will be happy to start with ordinary carried along from the start of the mission, fuel fusion rockets that migth reach 0.1 C or perhaps 0.2 C for trips to our local interstellar neighboors perhaps this very century.
Perhaps some how depolarizing the vacuum energy field in such a manner that the sometimes calculated latent energy density of the ZPF of 120 orders of magnitude greater than that of the observable universe could be harnessed. Perhaps one method of harnessing such ZPFs would entail some sort of unbalancing of the Casimar force between appropriately reflective members.
One mechanism that might become operable for a craft that accelerated to the point at which it would become a black hole in the direction of its travel due to relativistic contraction and mass increase, is the onset of a state of some sort of black hole based ramjet action. The extremely blue shifted bosonic and fermionic mattergy waves relative to the craft impinging on the craft from the front might simply pull the craft in some form of runaway acceleration via gravitational suction or attraction. The photons, neutrinos, and gravity waves incident on the craft from the back and the side of the craft from a limited angular distribution in impinging velocity vectors would be extremely red shifted with the resulting imbalance causing the craft to experience runaway acceleration.
Perhaps since the relative motion of the particles of the ship at such a high gamma factor as might cause the particles to become blackholes relative to the interstellar gas, dust, stars, and planets, would be that associated with ordinary STP values, the ship would not experience a collapse into a black hole state with respect to its self, but perhaps would do such with respect to the interstellar medium, or intergalactic medium. Perhaps this apparent paradox can be alleviated by the ship leaving our universe altogether, traveling into hyper space or by undergoing some other exotic kinematical space time background decoupling effects.
duncan, in the last few days for good or ill i have been issued a wake up call . you do make alot of sense in the things you have said both to me and mr essig.yes just science fiction will not cut it! and yes we DO have to look for real doable means of space/star flight.i will indeed continue to dream but i am now,i confess,a little worried.hope alot more of us wil chime in on this subject.lol – help! your friend george scaglione
Hi Duncan Ivry;
I believe any form of manned space travel that is even remotely plausible should be open for consideration.
The truth is we cannot at this point in time rule out a breakdown is special relativity at extreme gamma factors of say 10 EXP 20 or greater if such can be obtained. This gamma factor is will beyond the range of what our particle accelerators and observed cosmic rays could obtain.
We cannot rule out any Doubly Special Relativity whereupon, the velocity of light is dependent of frequency, and where extremely hard gamma rays might be observed to travel faster than C, in the extreme possible limiting value of frequency, even speed of many times C, perhaps even infinite velocities as an upper bounding limit.
As for FTL, warp drive, wormhole travel, teleportation, antigravity, negative drive, extra-dimensional and/or higher dimensional travel and the like, I say the jury is still out.
I think the phase “fantasy physics and fantasy spaceships” is a little strong, however, in the interest of common dialogue I will take the spirit of your advice in all future comments I send to the moderation in box of Tau Zero and avoid comments involving highly speculative notions such as those which I typically post at Tau Zero.
For the recond, I don’t for a minute believe that we have even a remotely complete picture of the true nature of the cosmos, and natural laws.
James M. Essig: “… I don’t for a minute believe that we have even a remotely complete picture of the true nature of the cosmos, and natural laws.”
This is a remarkable point. Warning: The following is about theory of science — or, as some may say, is about philosophy and useless and boring. But I have studied this discipline among others, and I think, it’s relevant. Please, accept my apologies.
There are different opinions among scientists, theoreticians of science (yes, this special breed does exist), and lay persons. Some people think, there is something like the true nature of the cosmos, and that the natural laws of, say, physics are something we *discover* by observing natural phenomena.
Other people — including me — think, that the laws of physics are products *invented* by physicists in a sophisticated cultural process called “science”. An example is Galileo’s law of motion, which has been invented by the physicist Galileo, and has been written down using mathematics. Nobody has been able to show that there is something “out there” — a true law embedded in nature — for which Galileo’s law can be considered an approximation, and for which Newton and Einstein invented better approximations. Physical laws are not discovered like we discover stones, plants, animals, stars, light, etc, when we look outside.
Nobody has been able to show, that there — seriously — *exist* physical laws as part of nature independent of our science culture, or has suggested physical experiments in order to observe those entities. We may ask whether it makes any difference thinking this or that way. Physicists prefer those hypotheses for which they need a smaller amount of resources. Applied to the case of “physical laws — discovered versus invented” the result is: The science of physics just plain works without assuming a “true nature of the cosmos”; assuming the opposite *scientifically* includes the effort of making an additional assumption, publishing it, designing experiments, perhaps building machines, making experiments, presenting the results at conferences, — *discussing it on websites* –, etc., and paying money for all this.
Of course, outside of science (and technology) people may well think or assume or believe or what, that there is a “true nature of the cosmos”. You aren’t surprised, that I’m no follower of split thinking, are you?
Why is this relevant? Because if we want to travel to the stars we should not waste our resources — beginning with the basement.
george scaglione: “i will indeed continue to dream but i am now,i confess,a little worried”
I’m sorry, if my comments are the cause of you being worried. I think, you don’t have to. I can tell you: I have a lot of dreams myself. I think, I have said it before: I like science fiction literature very much.
The head up in the sky *and* the feet down on the ground! Yes we can — ouch ;-)
Hi Duncan Ivy;
Sorry, but I have made my points and will stick with them. For the record, I am a realist who believes in a God.
For every paper that has come out against the possibility of any subset of the following, FTL, warp drive, wormhole travel, teleportation, antigravity, negative drive, extra-dimensional and/or higher dimensional travel and the like, and I still say the jury is still out,, papers offering loopholes and ways around the re- buttles to warp drives, wormhole travel, teleportation, antigravity, negative drive, extra-dimensional and/or higher dimensional travel and the like, come out with new and improved rationale.