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A few years ago, I wrote several letters to NASA urging them to reactivate the NERVA nuclear rocket program as a safer, cleaner, and most cost-effective way to fly to Mars than chemical rockets. About a week ago, I saw on the Baton Rouge local news an update which stated that NASA has indeed determined to reactivate the NERVA program, apparently because they've come to agree with me, that it simply costs too much time and resource to fly to mars using chemical rockets. What do you think about this change in NASA's approach to solar system exploration?
Updates
+1 y
I've also tweeted to Elon Musk about this, asking his opinion and whether he'd use nuclear rockets if Congress allowed him to do so.
Updates
+1 y
Elon Musk replied to me that Nuclear is fine.
What Girls & Guys Said
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3Opinion
Nuclear thermal has some advantages, and some disadvantages. The high specific impulse ~1000 seconds is great - but the reactor is heavy, and hydrogen is very low density so you need very large tanks. (which may require a very different design launch vehicle) Hydrogen is also difficult to store so if you want deceleration fuel at Mars, you need a big refrigeration system.
Overall its a win over chemical, but not as much as the specific impulse different (1000 vs ~450) might imply.
So I think its worth a careful study, but I'm not convinced its a net win. If it is, I'm happy to support it
Electric drives (in particular plasma drives) can have higher ISP. I think this may be a better long term technology (solar / electric for inner solar system and nuclear / electric for deep space). The acceleration is very low, but I think its still plausibly competitive for mars and a big win for Jupiter.
Ion drive thrust is too low for the inner solar system but there are plasma drive concepts with more thrust (needing more power of course).
In-situ fuel production is also a nice possibility anywhere with water. There a relatively low power reactor (or solar) can be used to split water - but you still get the advantages of a chemical rocket's high thrust.
Still, if it were a vote, I'd be in favor of making Nerva work. There are some safety issues though - unless it can survive reentry you might want to only activate the reactor when you are on an escape trajectory, and that greatly reduces its usefulness.
It uses Uranium as a primer for a breeder reaction with LIthium 6 to produce Tritium then fuse Deuterium with Tritium, just like the Hydrogen Bomb. It can keep accelerating a spacecraft for 15 days or more, so you can literally burn the thruster for 10 or 15 days, then turn the spacecraft around and brake with the thruster for another 15 days to set orbital parameters for Mars.
Remember, you need to descend safely to Mars surface and then launch from Mars surface again later. Propellant is built into the reaction, I think, and the only byproduct is inert Helium 4, a free Neutron, and some water vapor.
And yes, I'm aware of the incredible efficiency of electric solar sails, at least theoretically for solar tractors to haul payloads around in the inner solar system. It can accelerate to several tens of kilometers per second velocities. Essentially have a "free" engine from the Sun on the outbound direction anyway.
NEVRVA is pure fission, no fusion. There are no practical fusion reactor designs yet, not even for ground based (which is much easier than space). People have barely reached "scientific" breakeven on fusion practical is decades away
Some people have talked about fusion for space travel , but there is nothing like a realistic design yet. (A workign fusion reactor would be worth a trllion $ but no one is close).
NERVA is just a fission reactor that gets hot, heats hydrogen which is used as propellant
(I can find references if you want - but this is something I know quite a bit about).
You sure? I thought NERVA used Lithium Hydroxide as the propellant and Uranium fission as the primer. That should produce both fission and fusion reactions in the nozzle.
I know the Daedalus concept definitely uses fusion, but I've never heard of a prototype of it being made. They had working prototypes of NERVA for both military and commercial use, and congress shut them down for no real reason.
As far as I know, NERVA is a pure fission reactor (Plutonium or Uranium - not sure which) that get to about 1000C. Then liquid hydrogen is heated and exhausted through nozzle. So sort of like a chemical rocket, but with the heat coming from nuclear reactions. Its actually not as hot as a chemical rocket, but hydrogen molecules are so much lighter than water that they end up with a higher exhaust velocity than you can get with any chemical rocket.
Dadalus is completely different ant purely speculative. NERVA was real, they ran a flight-ready test rocket in Nevada for something like an hour. Daedalus is so far just a fantasy, we simply do not know how to build fusion reactors that provide net energy output. Maybe we will figure it out, but not so far.
There was another concept "Orion" that used thermonuclear bombs for propulsion en.wikipedia.org/.../Project_Orion_(nuclear_propulsion)
That might have worked, but was a bit extreme - and would have to be so large that getting it into orbit would have been a trick (no sane person would suggest an orion rocket for earth takeoff).
i'm familliar with Orion. It's intended to colonize other stars, not Mars. It's way too dangerous and produces too much space debris to be used inside the Solar System. It's also the size of a very large building and has a huge ablation plate, etc. Not really interested in Orion because it's not safe at all.
Agree!. Just a fun concept (sort of like project Pluto / SLAM).
I would like to see advanced propulsion for space.
Update:
A couple days ago, MSN ran an article announcing European Space Agency has already FULLY DESIGNED a FUSION Rocket, and is in the process of building the thing.
So even if you are correct about NERVA not achieving Fusion, it looks like ESA has just solved the problem in recent years, and is already building the prototype of a true FUSION rocket.
If this test rocket works correctly, it will THEORETICALLY lead to human space flight up to around 30% of the speed of light at theoretical maximum. The biggest problem we'll have now is navigating inter-stellar space to avoid collisions with micro-meteors, since at speeds above 10% of C, even a grain of sand in space could cause noticeable damage to the spacecraft.
Maybe we'll eventually develop some sort of plasma shield or magnetic shielding to deflect micrometeorites in space in real time.
Sorry, I am not ranked high enough to post this type of link yet, but if you search for British or ESA building Fusion Rocket, you can find the article, which was published July 18 on MSN news homepage.
Maybe this www.esa.int/.../Nuclear_fusion_space_propulsion
and "Pulsar fusion"
Sigh. I really really wish ESA wouldn't have sites like this. If you read carefully it says "A fusion space propulsion system for powering humans to Mars and beyond, one of the 47 ideas selected from over 200 submitted."
You don't know who I am, have no reason to believe me, but I am familiar with the state of the art in fusion research. we are no where close to a working fusion reactor. Livermore's NIF project reached "scientific" breakeven - got more fusion energy out than laser energy in - but is still a factor of 100 away from overall power gain - and the machine is several football fields long to produce about enough energy to run a hair dryer. ITER (the giant multi-national Tokamak project) is aiming for 2035 for first fusion reactions.
Again, no reason for you to believe me, and I can't fault you for trusting an ESA site. (this is as bad as the NASA EM drive) Try reading the wikipeda articles on fusion power and see the current state of the art. Look at the curve that shows how well actual projects have done. Read up on what the Lawson criteria is. It says how much pressure you need for how long to get net positive fusion power.
There are a lot of fraudulent fusion power companies.
I wish I didn't need to be anonymous here.
Because of site rules and them demoting me several times for no fair reason, I am not yet allowed to post a direct link to the article on MSN, but they claimed a British company is already building the darn thing in that particular article.
You're probably right, but what the heck do I know. I'm only an amateur when it comes to rocket science.
Hey I'm not questioning you guys' opinions and stuff, since I did check on NERVA and it's true that the original design does not use any "by design" fusion products, so unless something unknown happens it must be pure fission in its original version.
I do maintain that the articl eaobut the British company, not necessary jointly with ESA as I may have erroneously confused GB with ESA in this case, but they claimed to already be constructing a "Fusion Rocket".
one possibility is that a Rocket need not be as precisely controlled as a Laser Implosion or Magnetic Confinement implosion experiment, because a rocket could still use Fissile material as a primer as I incorrectly thought NERVA did. I'm not saying that's the case, but what else could the GB company be claiming to be making?
Surely, they must be aware that if they are committing "Science Fraud" they are going to get caught relatively quickly in this case. Fission and Fusion each produce a little over a third of a million times more energy per unit mass fuel than does chemical burning of hydroge in the pressence of Oxygen, so surely they must realize any attempt at a hoax is going to get called out right away?
Hey. I think it's Great Britain, not necessarily the entire ESA, who has a company claiming to be building a Fusion Rocket.
If it's a hoax, we'll find out soon enough. Otherwise they evidently are claiming to know something nobody else knows about sustained Fusion propulsion.
Have you ever heard of Daedalus?
Its' a hypothetical Fusion Rocket concept which primarily uses off-board fuel in the form of Hydrogen clouds sparesely distributed in deep space or among local nebulae, etc. It works simialr to the fictional "Warp Nacelles" of Star Trek or similar ot a SCRAMJET except it uses Fusion Hydrogen-hydrogen and other reactions, instead of chemical burning of air and jet fuel.
Once it gets moving through a "thick enough" cloud of Hydrogen in space, it can presumably keep accelerating ot about 0.3C in one human lifetime. You evidently onnly need like one Hydrogen atom per cubic meter average to keep the reaction going, because the power of Fusion is so high once it starts. Because it is "offboard" fuel, it would have a nearly liimitless range, provided you can plot a course through a dense enough cloud of hydrogen to keep the reaction going.
One problem as i see it is shielding a rocket while moving that fast. Even colliding with a grain of sand at that velocity could prove catastrophic.
Also, I don't know what the Hypothetical Primer is for the Daedalus Fusion Rocket concept.
If NASA's "Heavy Electron Capture" technique ever evolves into producing a USEABLE net energy gain, something like that might be useful to Prime a true Fusion Reaction, at least I think anyway. This is the only LENR I'm aware of which has been proven to produce a net gain, but even it has never been shown to produce an economically significant gain. In other words, you do apparently gain some energy from this reaction, but not enough to do anything profitable at the moment.
Anybody realize how Star Trek Starships in the Series used Anti-matter ot react with ordinary hydrogen, but in the movies the Starships ran on pure collected Gamma Ray Photons stored in Depleted Deuterium Crystals?
In reality, we are light years away from ever synthesizing enough antimatter to get a net gain in a Rocket Ship, if that is even hypothetically possible. We do know how to temporarily trap and store photons in some situations, but prolonged storage, particular of the higher energy frequencies is pretty well out of the question. I've heard of infrared and visible laser lights being "trapped" in certain clouds of gases in the laboratory, but we'd be hard pressed to produce any rocketry with this technique too.
And then there's the Holy Grail of Energy Production, which is Zero Point Energy. I'm not aware of anyone provably doing anything useful with ZPE... yet, but it has been shown to be detectable in some laboratory experiments involving the Casimir Force, I think, between two charged polished plates. Under the right circumstances Zero Point Energy in a measurable but otherwise useless quantity is produced.
I've seen some people grasp at straws, offering the conjecture that a scaled up experiment might be able to produce macroscopic thrust or macroscopic amounts of other useful work, but I think that is purely speculative at best for now.
NASA has proven on a purely theoretical basis that if GR is True or mostly true, as is apparently the case, then at least two different types of true "Warp Drives" should be possible ot construct, but I don't know of anyone who even remotely claims to know how to draw such a schematic yet. If it is possible such a machine, present day humans are about as ignorant as a maggot looking at a chemical rocket schematic today.
For people who don't know this, due to Mass relativity in SR and GR, even with anti-matter rocketry, but assuming no warp drive, you cannot travel any faster than about 0.8C even in the most optimistic theories of antimatter rocketry and assuming close to 100% efficiency. In a real world antimatter rocket, even if we could synthesize enough of the stuff, you have all sorts of overhead, including the wasted mass of the fuel containers and the mass of additional hydrogen used as primary propellant, etc.. Even to get moving that fast, you'd need to carry absurd amounts of Hydrogen and anti-hydrogen in magnetic fields in modular stages of your vehicle, and eject the spent fuel tanks as they are spent, which is quite unlike Star Wars or Star Trek's idealic notion of a Star Fighter or Capital Starship flying perfectly through space. Real "sub-luminal" flight would never, ever be that idealistic, and I doubt even Warp Drive could ever be that idealistic.
Again, I've never seen a NASA or other rocket scientist even remotely claim to know how to draw a schematic for a working warp drive. The best they did was prove that the most simplified versions of Einstein's Field Equations don't contradict the notion of warp drive. Some Scientists have argued that the energy level needed for warp drive is so high or nearly even infinite, so that it might not be worth trying anyway, because you may as well fly manually and coast to your destination at sub-luminal speeds, instead of spending "nearly infinite" energy to accelerate one spacecraft to Warp.
the Propellant tanks in any fusion or antimatter or fission rocket scenario are like as big as the entire Space Shuttle system or the entire Space Launch System. Presumably it is stored as Kryogenic Hydrogen (Liquid) and then injected into the Reactor in synchronized fashion, super-heated to just around 4000 kelvins, and then released in a controlled burn manner.
Ion Drives can be more efficient than this for unmanned probes, but for manned purposes ion drives would not be very useful, since they require several years to accelerate even to "Solar System Velocities". So for example the TIE fighters and Bombers of Star Wars are once again thwarted by real science. A real Ion Drive can't accelerate a manned spacecraft that quickly and effectively, and certainly could not out-maneuver Darth Vader's laser weapons while flying down an artificial canyon on the Death Star's surface near the exhaust ports.
I could see future humans perhaps still being "pre-warp" era, using Ion Drives to send very long term space probes to nearby Star Systems to explore before risking humans, but I don't see much other use for Ion drives except in unmanned spacecraft and for minor orbital corrections in space Satellites.
I saw a science paper on Anti-matter rocketry theory in which the Dean of Southeastern Louisiana University attempted to calculate a more realistic efficiency parameter for antimatter rockets, and tried to take into consideration the extra mass of the fuel tanks and electromagnets you'd need to store antimatter, etc, and he had a rocket around 3000 times more massive than the "Payload" required to accelerate ot 0.8C. Even in this scenario, he was actually ignoring the mass of the propellant hydrogen, and only considered the mass of the fuel hydrogen and the mass of the fuel antimatter. By the time you take propellant into consideration, the hypothetical rocket evidently scales to being as big as a large asteroid or maybe even a Dwarf Planet worth of mass. All of thise must be precisely atomically designed and go exaclty right, and you can only reach at most 0.8C by this mechanism, which means it would still take over 5 years to reach the nearest Star with such a rocket... assuming you don't die of radiation sickness or crash into a meteor or micrometeorite or something along the way.
anyway, the good news is I don't think humans need to fly faster than 0.1C to reach nearby stars in one human lifetime or even half of one human lifetime, so teh worst case scenario nuclear or antimatter rocket calculations of "reaching the other Star ASAP" are not necessarily valid.
Basically it makes more sense to accelerate to about 0.1C and just coast to proxima Centauri for the rest of th ejourney. Because of the way Rocket Fuel and rocket propellant scales with payload scale, then this much lower "coasting" velocity uses hundreds and hundreds of times less total fuel than attempting to achieve 0.8C.
One could imagine given enough time, future human civilizations could "Leap frog" from one Star System to another nearby star System, instead of trying to fly half-way across the galaxy in one go.
On the other hand, paradoxically, if we actually had both the Anti-matter energy and the production capability of building a true antimatter rocket big enough to reach 0.8C. we'd paradoxically have little or no reason to bother leaving the Solar System, as we'd evidently have solved something mind-numbingly mysterious in physics and probably wouldn't have very many remaining problems locally by then, short of the Sun experiencing its eventual demise as a Red Giant star. If it came to that, our genomes would be expected to mutate in any number of trillions of ways by then, and our descendants would probably be unrecognizable to modern humans by the time that became an issue for them to escape the Solar System at the last possible moment.
So generally speaking we don't actually need interstellar manned flight for at least a few more centuries, and possibly not even for the next few tens of millions of years, as long as we don't totally destroy the planet through AGW, our descendants should do just fine in terms of eventually solving interstellar travel.
I think we can imagine how to build a fission rocket that could get to 0.1C. Could even make the rocket structure out of fuel, so not a lot of wasted tank space. The acceleration would be slow because you have to get rid of the waste heat, but if you are patient, you can get there.
Fusion is not scientifically impossible, we just don't know how to make a reasonable sized fusion reactor. ITER is huge - the size of an apartment building, and even the upgrade to DEMO will only produce about 500MW. There are ideas to make it smaller, but its still incredibly hard. Its harder to do almost everything in space than in is on the ground.
I think well eventually see fusion rockets, but given that terrestrial practical fusion is at least 2050, its going to be a long time.
Antimatter could be the ultimate fuel but its fundamentally difficult to produce anti protons. Protons are made of 3 quarks, and they are far more likely to form 2-quark mesons that decay very quickly. At the moment there is no known way to change that probability - but it doesn't violate basic physics to do so, so maybe someone will figure it out.
Its also very difficult to store a signfiicant mass of antimatter, but again doesn't violate physics, so maybe.
Right now though we are having trouble getting people back to the moon...
Yeah, I know, right. Like I'm familiar with the gist of how Quarks and Anti-Quarks work. I derived an anti-neutron reaction in the core of the Crab Nebula Supernova, which I think helps explain the "missing mass" of that object and I think also takes place in the most powerful Hydrogen Bombs and may explain Castle Bravo and Tsar Bomba's excess yields. evidently, if you fuse Protium Hydrogen in the presence of the correct isotope of Iron, it releases an anti-neutron, which then annihilates with a normal neutron. This appears to explain what happened to the missing one third of the Crab's mass. I don't knwo whether this could be tested in a controlled environment somehow outside a hydrogen bomb, but whatever. I'm assuming a particle accelrator might be able to test it. Like if you had a certain probability of a Proton colliding with the correct Iron isotope, it releases sometimes an anti-particle.
I couldn't claim to know how you would ever capture enough of it and magnetically confine it to fuel a Starship though.
I know CERN has worked very hard at antimatter production and so far has only managed to make enough atoms that you could count them. I'd be surprised by anti neutron production - creation of anti-quarks needs enough energy that the atomic isotope doesn't really matter - at those energies a nucleus is just a bag of quarks and gluons (I think).
Hydrogen bombs are actually very low energy in a particle physics sense. There are a LOT of particles, but each one is no more than maybe 20MeV, compared to the 7 TeV available at LHC
Man, that's messed up. Maybe it works inside a core collapse Supernova, but not the bomb? I don't know.
Yeah, I don't see how we'll ever do this any time soon then, but like i said, over the long term 0.1C and just coast to the nearest star is much more efficient than trying to fly at 0.3 to 0.8C.
Conditions in a core collapse supernova can get to energies where you can create quark pairs or even baryons. I don't know if that actually happens, or if any of that matter escapes the final black hole, but its not crazy. I haven't heard of antimatter being detected around supernova but I'm not sure how clear a signal it would be. e+/e- is clean but lots of things make positrons. Proton / antiproton is a messy intercation, maybe not easy to see. I know antimatter in cosmic rays is rare (<1e-4 I think) but has been detected, so its being generated somewhere (but maybe just high energy cosmic ray interactions)
The fuel tanks would need to be huge; hydrogen is hardly what you'd call dense. Assuming an SSTO rocket to an orbital assembly yard, you COULD lower the need for the all-in-one designs we've been using historically- but then, that'd make chemical propellants more appealing, too.
I think the bigger issue, though, is that Mars isn't the moon; the gravity reduction isn't so large that you can get away with a casual design for the return trip- wait a second. What are they priming the reaction with? Public perception is still DECADES away from being able to get away with anything fissile.
Deuterium doesn't quantum tunnel as easily as protium, and the tritium is produced in the breeder reaction. It produces a collosal amount of energy, like I said, you'd need a few pounds of Uranium and probably only consume one or two pounds of the fuel supply in the entire round trip. It's as much energy as Tsar Bomba in the reaction, but it's more gradual instead of instantaneous.
Also, you're forgetting that Uranium Fission and Hydrogen (deuterium-tritium->Helium) fusion release about 300 THOUSAND times more energy per kilogram fuel than the chemical BURNING of chemical reocket fuel, such as liquid hydorgen with liquid oxygen.
You might still need many tons of propellant, but you actually only need a few pounds of Deuterium, a few pounds of uranium, and a few pounds of lithium 6 as the "fuel" supply.
I'm not forgetting, I'm REMEMBERING- the Challenger, on its next mission, was going to be carrying enough plutonium to kill every human being on the planet ten times over. Had THAT gone down with the vessel, tens of thousands of people and uncountable plants and animals would've died. Public acceptance will kill dead any plan to launch from the ground that has the potential to do the same. A chemical rocket explodes, it could take out the launch pad; a nuclear rocket explodes, it could take out Orlando.
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