Tim Folger and Les Johnson (NASA MSFC) stood last summer in front of a nuclear rocket at Marshall Space Flight Center in Huntsville, Alabama. Johnson’s work in advanced propulsion concepts is well known to Centauri Dreams readers, but what he was talking to Folger about in an article for National Geographic was an older technology. NERVA, once conceived as part of the propulsion package that would send astronauts to Mars, had in its day the mantle of the next logical step beyond chemical propulsion. A snip from the story:
Johnson looks wistfully at the 40,000-pound engine in front of us… “If we’re going to send people to Mars, this should be considered again,” Johnson says. “You would only need half the propellant of a conventional rocket.” NASA is now designing a conventional rocket to replace the Saturn V, which was retired in 1973, not long after the last manned moon landing. It hasn’t decided where the new rocket will go. The NERVA project ended in 1973 too, without a flight test. Since then, during the space shuttle era, humans haven’t ventured more than 400 miles from Earth.
I’m looking forward to getting back to Huntsville and seeing Les, as well as a number of other friends in the interstellar community, at the 2nd Tennessee Valley Interstellar Workshop, coming up this February, where it may be that NERVA will have a place in the discussion of how we go about building a system-spanning civilization. You’ll want to give Folger’s article a look for comments not only from Les but Freeman Dyson and Andreas Tziolas (from the Icarus team), as well as Elon Musk, the 100 Year Starship’s Mae Jemison, and NASA’s Mason Peck.
Image: NERVA nuclear rocket being tested. (Smithsonian Institution Photo No. 75-13750).
In fact, there are a number of issues presented here that I’ll want to get back to later, but I can’t cover the rest of the story today. I’m all but out the door for a brief but intense period of Tau Zero work that will leave me no time to keep up regular posts here or even to moderate comments. More about this later, and more about Folger’s essay as well, and please bear with me through the temporary slowdown. Things should get back to normal by mid-day Thursday.
Speaking of NERVA, though, I’ll leave you with an interesting petition Gregory Benford alerted me to with regard to the development of nuclear thermal rockets, one that calls for an effort to:
Harness the full intellectual and industrial strength of our universities, national laboratories and private enterprise to rapidly develop and deploy a nuclear thermal rocket (NTR) adaptable to both manned and un-manned space missions. A NTR (which would only operate in outer space) will jump-start our manned space exploration program by reducing inner solar system flight times from months to weeks. This is not new technology; NTRs were tested in the 1960s (President Kennedy was a guest at one test). The physics and engineering are sound. In addition to inspiring young Americans to careers in science, technology, engineering and mathematics, a working NTR will herald a speedy and economical expansion of the human presence in the cosmos.
Going significantly beyond the Moon demands advances in propulsion of the kind that nuclear thermal rockets can deliver. Getting NERVA concepts out of mothballs and updating them with modern materials are necessary steps as we push out into the Solar System.
NERVA was killed because of cesium releases, the physics hasn’t changed.
The last serious nuclear reactor effort by NASA or DOE was the SP-100 program in the 1980’s which was never completed. Probably neither organization has the infrastructure or experienced staff to develop a power or propulsion reactor today. When the Synthesis Group study (NASA/DOE/DOD) on future space activity was done around 1990, they favored involving the Nuclear Navy program due to its knowledgeable staff, existing infrastructure and appropriate technology. It is interesting that discussions of future nuclear thermal space propulsion never discuss this option. NASA keeps recommending only its own NERVA technology. This looks suspiciously like bureaucratic self-interest. If we were to ever get serious about a new nuclear effort in space, then we should broaden our considerations about where we should place the program.
Do you know if someone has considered what would it take to improve the Zubrin nuclear salt rocket concept (http://path-2.narod.ru/design/base_e/nswr.pdf) to replace part of the water with deuterated water, and use the fission reaction to heat up the deuterium or some He3 dissolved mixture, to achieve fusion?
It might be a long shot, but since we know how to achieve catalysed fusion via fission reactions, i wonder if we can achieve catalysed fusion in a continuous reaction in a nuclear rocket, like the one proposed here
Are there existing numerical models implemented in publicly available codes for this kind of domain modelling?
It’s worth noting that NERVA was updated with the classified Timberwind program in the 1980-90 period. NASA Glenn is taking that further, as Geoff Landis will discuss in the forthcoming STARSHIP CENTURY anthology. The nuclear rockets now exceed by a factor of 4 the Isp of the Saturn era, ~250 to 300, so they attain ~1000.
This means you can go to Mars with a quarter of the fuel mass.
Excellent article. Thank you for the shout-out on my White House petition, too. We have nearly 1,700 signatures as of this morning.
BTW, I was pleased that you heard about it from Gregory Benford, as he is my all-time favorite sci-fi author.
If the NTR were to be used in order to achieve shorter trip times to and from Mars, then that would take the mission off of the free return trajectory. If anything goes wrong, the crew could find themselves driving out to the asteroid belt never to return to Earth.
The lack of gravity can be easily solved by tethering and spinning the habitat. Radiation from the sun can be shielded by a relatively small amount of shielding. It is the galactic cosmic rays which is the only justifiable reason for speeding the trip to Mars and hence the main justification for the NTR.
But, if enough water shielding were sent into an Aldrin Cycler orbit, then one would only need to launch it once and it could be used by repeated crews. You need about 500 tonnes of water and 500 tonnes of propellant to make that happen. That would take about 19 Falcon Heavy launches costing about $2.4 billion. $2.4 billion would be a modest percentage of the overall costs for ongoing Mars missions.
As for NTR being able to send more mass, this is true. However, bioregenerative systems would reduce the amount of supplies sent on the trip and Mars ISRU would greatly reduce the mass needed to be sent from Earth.
It only makes sense if you use a very light-atom propellant like Hydrogen gas or helium. For higher weight atoms, the exhaust velocit drops as the atomic mass goes up ( given constant temoperature0 . BothH2 and He are hard to store in a liquid form for long periods of time. I suppose you could use lithium atoms but even they are getting to be heavy. Compare that with chemical rockets like o2 “+ H2 or O2 plus methane. These also operate at high temperature near the high temperature material strength limits. Both nuclear and chemical rockets cannot exceed the temperature limits of materials they are made of. Compare these options with ion propulsion systems or even VASR. In these the ions can go much faster.
Frankly, I love the IDEA of nuclear Rockets. I just do not like their present reality much.
THANK YOU for bringing this to our attention! Developing Nuclear Thermal Rockets (NTRs) and, in fact, *any* in-space nuclear power systems–for electricity as well as for propulsion–will require a public education program as well as engineering work.
Sadly, with few exceptions most people react to the notion of in-space (and Earth-based) nuclear power systems this way: “Nuclear?! — YAAAAAH!!!” This even includes RTGs (Radioisotope Thermoelectric Generators, i.e. “atomic batteries”), as the “Chernobyl in the sky” protests over the launch of the Cassini spacecraft showed–even the physicist Dr. Michio Kaku, who should have known better, opposed the Cassini mission for this reason. (Not far from where I live in Alaska, an RTG-powered automated weather station had its RTG replaced by a diesel generator system after the locals became aware of it, even though the RTG had been working perfectly for years–in their uninformed minds, the mere fact that it was nuclear made it “bad” and “dangerous.”) Now:
This does not mean that I think the prospects for getting NTRs built are hopeless, but that we who favor them must keep in mind that ours is a two-front struggle–educational as well as financial (one could say “political” as well, but this is largely a result of the other two). NTR engines are well worth fighting for, because they can open up the solar system–the commercial opportunities they will enable via an enlarged (cislunar and eventually solar system-wide) economy are thrilling. Used in concert with other non-chemical rocket space propulsion systems (lunar electromagnetic spacecraft launcher tracks, space elevators on the Moon and other low-gravity worlds, space tethers, solar sails, and electrical propulsion [nuclear-electric systems are quite useful]), the “commerce of the heavens” that Arthur C. Clarke predicted in his book “The Promise of Space” will come to fruition. Also:
A very worthwhile side-benefit (“spin-off”) of such a public education program would be greater acceptance of the use of nuclear power *on Earth*. The people have to be taught that they were lied to twice about nuclear power, and that both lies (“It’ll be too cheap to meter” and “The China Syndrome”) are at the extreme ends, while the truth is between them. Like any energetic substance, fissionable materials must be handled and used with care, but as with gasoline and countless industrial chemicals, nuclear power can be–and is–used safely as long as appropriate safety procedures are followed.
I dont think we are going to get any nuclear propulsion without dealing with the political-ideological resistance to anything nuclear . It would be a tragic waste of time to develop a modern Minerva style motor only to have it scrapped again by the same politically correct stupidity that killed it 40 years ago . If anyboddy has noticed , the present administration in the US incorporates powerfull dummy-green elements . It looks as if it can only get worse …
*Here* is why starflight advocates *must* support the development of -commercial- cislunar–and eventually interplanetary–space travel. As the above-linked “National Geographic” article by Tim Folger says:
“To build a starship, you first have to build a future that converts fiction into fact, and that takes a lot more than rocket science. The task isn’t figuring out right now how to design a starship; it’s continuing to build the civilization that will one day build a starship. Framed like that, more expansively, it begins to seem less impossible. But it’s a 100-year project or maybe a 500-year project, depending on your craziness level. [Les] Johnson’s level is lowish.
“I don’t know what the world will be like in 500 years,” he says. “If we have fusion power plants, and space-based solar panels beaming energy down, and we’re mining the moon and have an industrial base in low Earth orbit—maybe a civilization like that could do it. We’ll have to be a civilization that spans the solar system before we can think about taking an interstellar voyage.”
Nuclear reactions are a million times more powerful than chemical propulsion; yet the ISP for NTR only doubles or triples at best. While metal can barely contain chemical reactions, nuclear energy can never be contained efficiently by any matter. Stan Ulam figured this out in the first half of the last century and proposed the only practical system. A system with no containment problems; bombs.
Nuclear Pulse Propulsion used outside the Earth’s magnetosphere is the “next logical step.” Nuclear Thermal Propulsion is a second best choice and for the incredible expense involved is not much better than chemical. It seems like the cheap way to get something better than chemical but when compared to the ISP of approximately 100,000 available from bombs it is a waste of money.
And the Japanese just happen to have 40 tons of plutonium sitting around waiting to be used on nuclear missions to the outer solar system.
http://lifeboat.com/blog/2012/12/forty-tons-of-plutonium-for-bomb-propulsion
I signed the petition and I hope everyone else reading this will do the same. Also, pass it along to everyone you know.
I’m a believer in NTRs. More consideration should be given to also using them as an upper stage for getting to orbit.
Paul, you make no mention of the restrictions imposed by int’l treaties on nuclear devices. I’m guessing then there is a solution for that, right?
The only way we will get Nerva restarted or Mini MagOrion developed is if the technology is licensed to China, Japan or South Korea. They are the only countries with the nerve to go for it and face the consequences if something goes wrong. The West is too risk averse and has had its day in the sun.
Let’s give the technology to civilisations that have the courage to use it.
This seems the logical choice for manned missions to the moon and Mars.
Imagine if Nixon did not cut this program. Perhaps we could have had a moon base and a Mars mission or two before 1980.
I’m afraid the issue today is the lack of political will. The technology and the costs aren’t really it. We blow a trillion here, a trillion there on all kinds of inane things, e.g. the stimulus in 2009/10 for “Shovel Ready projects.”
For all the inner solar system and up to Jupiter, NTR cannot compete with the new solar powered electric rocket. And they become radioactive after being used , and they are dangerous and need radiation protection and they need liquid hydrogen and they are complex and so on . . ..
So why bother with this antiquate technology ?
NERVA is one of my most favourite things of all time!
I’d love to see it fly!
NERVA – a technical possibility for 50 years and a political and economic impossibility for 40 years!
As far as I can remember from back in the day when I read some reports on the technology, there were problems with radioactive debris from the NERVA core ending up in the exhaust, and the reactor cores degraded pretty fast. This is generally known I suppose. I think that new materials and manufacture processes can help, but nobody has looked much into this for the past 40+ years. In that respect, petitions might help to get things going, and also some NIAC work is based on this I think. Unfortunately, (a great deal of) time will pass before we have a working engine, and it could have been much different story if this was not dropped way back then.
central core of falcon heavy as mars MTV;
add 4 GEM-solids to the Falcon heavy.
replace two Merlin engines with three pewee 25 klb NTR engines on the Falcon heavy core stage.
after GEM-60 jettison air lite the 25 klb NTR engines at altitude and well down range, would this satisfy nuclear engine safety concerns?
The Falcon heavy would not have a payload except a an additional tank of LH2, our goal is to bring the core stage to orbit empty.
refuel this core stage with just LH2 all tanks and re fire the PEWEE NTR engines to mars
http://spirit.as.utexas.edu/~fiso/telecon/Borowski_6-27-12/
I hate to be the one making this comment because I love everything about nuclear options in all aspects of human life…but society will not accept this technology. Just say the word radiation in any context and heads jerk, pupils narrow. Solar sails? Now you’re talking the right kind of radiation.
I hope your in-born optimism can slice right through the barriers of group think.
Reducing flight times from months to weeks bothers me. Orbital mechanics still rules the solar system. The jump in specific impulse isn’t that great.
“It is the galactic cosmic rays which is the only justifiable reason for speeding the trip to Mars and hence the main justification for the NTR.”
Hi John, good to here from you.
You know my views on NTR I think; bombs are the only viable option.
But there is an “unobtanium” that could do what everyone seems to think NTR will accomplish.
http://en.wikipedia.org/wiki/Fission-fragment_rocket
The Americium fission fragment concept is probably the most promising nuclear propulsion design except for one problem; Americium is hard to come by.
But even the huge amount of funding necessary to get an Americium program started would be far cheaper in the long run than fooling with Low isp NTR junk. There is no cheap.
NTR technology provides a relatively small gain vs. chemical. How much of the performance gain will be lost due to shielding, and economic viability due to extra costs to ensure no launch failures for the fissionable material?
Does the development of NTR lead to more powerful propulsion technologies, or is it a dead end?
GaryChurch
Good call. See also http://www.rbsp.info/rbs/RbS/PDF/aiaa05.pdf.
Except, where is it written that the fuel has to be Americium? The concepts I have seen generally appear to be planning for “regular” fuel, i.e. Uranium or Plutonium of one or the other isotope.
In my opinion nuclear power should only be used in space where it can’t harm the planet or anyone on it. Coal is being shut down in America by the oil/gas&nuclear interests who don’t like competition and who like artificial scarcity to ramp up prices. Coal is our most abundant energy resource and it can now be produced cleanly, with water vapor and CO2 being the only by-products released. Although it is somewhat expensive to clean to this extent, the price would go down with greater use. Instead, the “politically correct” are shutting it down while countries like China continue to build (dirty) coal production plants at a high rate — so the coal pollution argument is just rubbish.
Spent nuclear materials in space could be disposed of by simply chucking them into the sun. On Earth there’s really no place to put it that will not pose a future hazard due to leaching, earthquakes, tectonic shifts, enemy attack, tsunamis, etc.
Has there been any opposition to the treaties that ban this from outer space? That’s where we’d need to start IMO. As far as I know, nobody of significance has went public about the ban. If we really want go to mars and the asteroid belt, we need some type of nuclear power/propulsion system. VASIMR is overrated UNLESS its the nuclear electric version.
@TH
You do know that the major source of mercury pollution in the environment is coal burning? And we are not even concerning ourselves with AGW.
“Except, where is it written that the fuel has to be Americium?”
Oops. You got me Eniac. I read so much stuff I things confused sometimes. Americium is the transuranic that makes fission fragment propulsion very feasible. Unfortunately….there is no cheap. It is extremely expensive stuff.
In my survey of propulsion technologies there is only one that is 99 percent guaranteed to work right now; bombs. I love bomb propulsion. The problems with it are well known and solved by launching missions from the Moon.
Am 242 fission fragment propulsion and beam propulsion are ties for second place. Beam propulsion is the most exciting of the three because with Lunar Solar Power the amount of energy is huge; enough to begin talking about star travel.
Alex is right- coal is not clean. It will never be clean. “Clean Coal” is a prime example of the new industry of greenwashing- where even the nastiest industrial practice can be made to glow with green tree-hugginess. A good book to read about this is Green Illusions by Ozzie Zehner. I am anti-nuclear on Earth and totally pro-nuclear in space.
Alex Tolley: “NTR technology provides a relatively small gain vs. chemical.”
For H2 propellant the gain is a factor of 4 in Isp. Getting liquid H2 & O2 into orbit and using them throughout the solar system is a huge problem. They leak out and take lots of cooling gear.
More’s to the point, liquid H2 has density 0.08 that of water (gm/cm3). So it takes 12 times the volume to carry the same mass as water. This is a huge overlooked problem with using H2 in orbit generally. Using water in a nuke rocket lessens Isp by 0.33. But it’s far easier to handle and 1/12 the volume. So using steam from water in NTRs makes perfect sense–and on Mars it’ll be easy to find (look at the poles).
I want over this in some detail in THE MARTIAN RACE. I really believe NTRs are crucial to opening the solar system.
Sometimes a tiny error in the English can have huge impact if taken as the basis for calculation by others. Benford writes “Using water in a nuke rocket lessens Isp by 0.33”. He meant “lessens Isp to 0.33” or “multiplies Isp by 0.33”.
Or, perhaps best: “reduces by two thirds”. Is that really what he meant to say?
My opinion:
NTRs are not sufficiently better than chemical to make them worth the (nuclear) trouble. A reactor plus ion drive is superior, and more technology-ready, too. Ultimately, only a fission fragment rocket can truly get the benefit of nuclear and be credible as an interstellar drive.
Bombs might work, too, but I do not share Gary’s confidence in how easy it would be to make them work, or that the effective ISP would come out any better than with ion drives.
“A reactor plus ion drive is superior, and more technology-ready, too. Ultimately, only a fission fragment rocket can truly get the benefit of nuclear and be credible as an interstellar drive.”
H-bombs seem to work pretty good.
“Only” fission fragment?
Possible but H-bombs slowing down an originally beam driven Bernal sphere several miles in diameter from .1 C or higher is my best guess as the ultimate form of the first class of starship.
But that is this century- I think the 22nd century will see black hole propulsion and this method will provide the human race with a means to colonize the galaxy.
How fast these black hole starships will go is the question. Energy requirements go up in a steep curve after about .3 C so it may be that 3 or 4 years for every light year will be the rule for thousands of years to come.
Or the black hole drive may take us up to a high fraction of C where a trip anywhere- even to another galaxy- may take a couple years of onboard time.
The nuclear electric ion drive is a system with very little thrust and due to the massive cosmic ray shield and structural weight of artifical gravity and life support for a multi-year mission, I do not think it can compete with bombs at all.
The starships that are launched with beam propulsion and loaded with H-bombs for slowing down will probably, hopefully, be intercepted in space by faster ships a couple centuries down the road and the passengers and crew transferred. We should still launch these slower first class of craft as insurance against an extinction level event.
Yes, sorry, shoulda said “reduces Isp vs pure H2 by 2/3.” So compared with Saturn V you get 8/3 times that Isp=250.
Trouble with ion rockets is low thrust. Nobody proposes moving big masses with them, and that’s what industrial space use needs. So ok for exploring, but not transport of ores, big comm sats etc.
GaryChurch:
Really? I must have missed that. Which mission were they flown on?
I keep hearing people say “Orion would have opened the solar system”, “Orion can get us to the stars”, but when you check the sources, you find there is little more than wishful thinking behind these claims. The more I listen to it the more it sounds like “Tesla had wireless power transmission working” to me.
It has never been tried, and as far as I know even if all works exceedingly well the Isp is not at all up to interstellar travel. There are a few issues like neutrons and incomplete burn-up keeping that much lower than we would want.
Eniac: “…it sounds like “Tesla had wireless power transmission working” to me. ”
And it works, too! It’s shining on me right this very moment.
The discussion I would like to see is about launching an NTR.
I am assuming that all construction would take place on earth (fanciful ideas of doing this off planet being uneconomic in teh extreme).
I also assume that launchers will continue to have a small failure rate.
So what happens under different failure modes? What are the problems and safety issues associated with various recovery scenarios?
If NTRs are to be widely used, then we will have to deal with these launch failures.
“Which mission were they flown on?”
Rockets never fly without ground runs.
1000 bombs exploded and trillions in classified research make bombs ideal for propulsion applications. They work.
http://nuclearweaponarchive.org/Usa/Tests/index.html
excerpt:
“Between 16 July 1945 and 23 September 1992 the United States of America conducted (by official count) 1054 nuclear tests, and two nuclear attacks. The number of actual nuclear devices (aka “bombs”) tested, and nuclear explosions is larger than this, but harder to establish precisely. Some devices that were tested failed to produce any noticeable explosion (some by design, some not), other “tests” (by official definition) were actually multiple device detonations. It is not clear whether all multiple device tests have yet been identified, and enumerated.”
The first H-bomb test released more energy- millions of times more energy- then anything you are proposing.
“I am assuming that all construction would take place on earth (fanciful ideas of doing this off planet being uneconomic in the extreme).”
There is no cheap Alex.
Plutonium and enriched Uranium are pretty hazardous materials. The best way is to use a human-rated launcher with a powerful escape system and capsule. Further packaging the “pits” of fissionable material to survive a launch failure would allow several hundred pounds to be sent to the Moon per launch.
Once the fissionables are soft landed on the Moon they can then be unpackaged and used for propulsion. Any type of accidental release in Earth orbit will reenter the atmosphere- anywhere in the magnetosphere will eventually reenter. Just being careful is not going to be acceptable- we know this from the shuttle program, chernobyl, fukushima, etc. We have to launch any nuclear missions from the Moon outside of the magnetosphere.
The given is that chemical propulsion is appropriate and desirable for lifting fissionables from the Earth and transporting them to the Moon. The other given is that chemical propulsion is useless for human space flight other than this small crossing. Which is why we have to transport nuclear material to the Moon in the first place- for nuclear propulsion to allow interplanetary travel.
My question is not about transporting nukes- it is about NTR vs. NPP.
Nuclear thermal is just not good enough. IMO bombs are all we have to work with for a long time to come.
@GaryChurch – you still need to explain what happens in the event of various failures when launching your packed fissile materials. For your bombs you are talking about U235 or Pu239. This is just the scenario for a villain to acquire processed fissile material, even if a simple launch failure did not contaminate the ground. For an Orion type vehicle, launch failures mean losing quite a few bomb cores.
Even if the Outer Space Treaty did not ban weapons in space blocking the building of bombs on the moon, the cost of a facility to construct bombs on the moon is not something that could be countenanced anytime soon, however wonderful the performance of the vehicle.
Now if you could breed the fissile material from relatively inert materials (that could be launched) in a low cost orbital facility, then you might be able to avoid the launch failure issue.
GaryChurch:
They work, alright, but not for propulsion applications. Not by a long shot.
Dynamite has a lot of energy, too. It is good for blowing up things, but rather impractical to propel a car or train. For that, we had to invent the steam and internal combustion engines, neither of which has anything in it remotely resembling dynamite.
“Even if the Outer Space Treaty did not ban weapons in space blocking the building of bombs on the moon, the cost of a facility to construct bombs on the moon is not something that could be countenanced”
Hi Alex
As George Dyson corrected me when I first posted my essay on bomb propulsion, the outer space treaty only requires signatories agree on the use of nuclear energy. It does not ban it. The “bombs” become pulse units when reconfigured and while they can certainly be used to destroy, they are designed to project a high speed cloud of plasma at a metal plate momentarily.
As for the cost; in my view the vast treasure we expend on defense makes any wailing and gnashing of teeth over space exploration hypocriticial. Two penultimate security threats- impacts and engineered pathogens- can only be answered by going into space. Going into space first means a Moon base because as I have explained so many times, chemical propulsion is useless for human interplanetary travel and nuclear materials can only be used outside the magnetosphere.
“This is just the scenario for a villain to acquire processed fissile material, even if a simple launch failure did not contaminate the ground. For an Orion type vehicle, launch failures mean losing quite a few bomb cores.”
The Orion capsule has a very powerful solid rocket abort system. Being specially packaged at the top of the stack with a heat shield interposed between the pits and a launch failure explosion, the fissionables should survive intact to be recovered from any failure. Considering the tremendous explosion the Challenger crew probably survived and subsequent 200 plus flawless SRB firings I believe the SLS is the best we can do for transporting fissionables to the Moon.
“They work, alright, but not for propulsion applications. Not by a long shot.”
Well, according to Freeman Dyson, Werner Von Braun, Arthur C. Clarke, Carl Sagan, Michio Kaku, and various other less famous authorities, bomb propulsion will work.
I will take their recommendation and several decades of “directed energy” weapons development over your casual dismissal.
I will not go to the trouble of finding an equally impressive list of famous authorities who are sceptical, although I think it is not difficult.
The question here is not who has the smarter thoughts about it. The fact is that thoughts is all we have. There is zero practical experience with bomb propulsion, which, for me, settles the question of technological readiness: There is none.
@GaryChurch
I will stand corrected if your Dyson anecdote is correct. However the placing of bombs in space, even if they are classified as propulsion units, seems fraught with legal implications.
I find your argument to guard against launch failure a little glib. Even assuming the escape tower approach is 100% reliable, how can you guarantee the payload will land in US/allied controlled territory? What if it falls into the ocean, especially on the continental shelves? Admittedly ancient history, but the US took over 2 months to find a nuclear bomb on the sea near Palomares in 1966 after an bomber accident. Unexpected failures happen, and because of the frequency of flights needed in your scenario, probably will happen, including failure of the emergency system. Obviously we cannot, nor should, have riskless systems. But who bears the risks is important.
With the size of program you suggest, a launch failure that did cause a problem might well be ignored simply because the project was “too big to fail”, or conversely the project would fail with a huge sunk cost. Yes, huge military projects fails (or apparently don’t), but while the electorate doesn’t get much say in these programs, failure doesn’t have much more than a cost impact.
“-an equally impressive list of famous authorities who are sceptical”
I have to throw the B.S. flag on that one.
You will not find skeptics among anyone who understands the principle of a directed energy weapon being used to project a plasma cloud. The exhaust velocity is…..astronomical. That is above all things the most impressive predictor of performance.
You might want to consider those thousands of nuclear weapons ready for use on this very planet. And the hundreds of tons of plutonium- enough for thousands of missions to the outer solar system- sitting unprocessed in nuclear power plants all over the world. 45 tons in Japan alone.
I think you are the one who is not ready Eniac.
Actually, this is a good place to mention that Freeman Dyson, when I interviewed him some years back, said he did not believe that Orion-style propulsion or any other nuclear method was suitable for interstellar flight. His views had changed since the energetic years of Project Orion and he was emphatic about the change. One of the problems he mentioned was that with nuclear methods, fission or fusion, you get such a small percentage of the energy available through matter. At one point, he said this:
“Nuclear energy doesn’t cut it. Nuclear energy is too small. You’re using only less than one percent of the mass with any kind of nuclear reaction whether its fission or fusion. So it means the velocities you get with nuclear energy are limited to much less than a tenth of lightspeed. So its not very interesting. Its great inside the Solar System but not outside.”
Dyson told me he was much more interested these days in propulsion methods he considered realistic, and that these involved leaving the propellant behind. In an essay to be published later this spring, he argues for laser, microwave and particle-beaming as conceivable interstellar systems that could work.
Thank you Paul.
I do not believe I ever mentioned bomb propulsion as being practical for starflight- just to slow down centuries later upon arrival after originally being beamed up to a certain fraction of the speed of light.