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NASA Space

NASA Looking At Nuclear Thermal Rockets To Explore the Solar System 282

Posted by Soulskill from the i'll-order-a-dozen dept.
MarkWhittington writes: Officially, NASA has been charged with sending astronauts to Mars sometime in the 2030s. Toward that end, according to a story in Universe Today, space agency engineers at the Marshall Space Flight Center are looking at an old concept for interplanetary travel, nuclear thermal engines. "...according to the report (cached), an NTP rocket could generate 200 kWt of power using a single kilogram of uranium for a period of 13 years – which works out of to a fuel efficiency rating of about 45 grams per 1000 MW-hr. In addition, a nuclear-powered engine could also provide superior thrust relative to the amount of propellant used." However, some doubts have been expressed whether NASA will be granted the budget to develop such engines.
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NASA Looking At Nuclear Thermal Rockets To Explore the Solar System More

NASA Looking At Nuclear Thermal Rockets To Explore the Solar System

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  • I have been stumping for this since they decided to retire the shuttle. Stop building big rockets to toss things away from Earth. Get it in orbit and use prestationed nuclear rockets to move it to and from higher orbits. Would just need to refuel them occasionally.

    • "Getting into orbit" requires a big rocket. (Score:5, Interesting)

      by robbak ( 775424 ) on Saturday January 31, 2015 @10:37PM (#48949751) Homepage

      That big rocket is mostly just to put the payload into orbit. Once in a low earth orbit, it doesn't take that much more to take it from there to a different orbit.

      This xkcd is probably the best way to grasp the difficulties of 'getting into space".

      https://what-if.xkcd.com/58/ [xkcd.com]

      • Re: (Score:3)

        by ihtoit ( 3393327 )

        +1 informative, explains it really well for pretty much everybody, and +1 funny for the reference to the Proclaimers song. I really didn't know that about the "coincidence"...

      • Re:"Getting into orbit" requires a big rocket. (Score:5, Interesting)

        by Anonymous Coward on Sunday February 01, 2015 @06:28AM (#48950723)

        Once in a low earth orbit, it doesn't take that much more to take it from there to a different orbit.

        This isn't really true. Getting from Earth surface to low Earth orbit takes a delta-v of 9.4 km/s, and getting from there to geostationary orbit takes another 3.9 km/s (see this map [imgur.com]). So, in terms of delta-v, you need to go another 3.9/9.4 ~ 40% as far as you already have.

        Okay, that's not that much further. But that doesn't mean that the size of the rocket you need just goes up by 40%. The required rocket size is *exponential* as a function of delta-v. To launch 1 tonne into low Earth orbit, you need a rocket that weighs ~30 tonnes - so, to launch 1 tonne into geostationary orbit, you need a rocket that weighs 30^1.4 ~ 120 tonnes. That's four times as much rocket, just to go that little bit further from one Earth orbit to another.

        Most of that rocket is still for putting that payload into orbit, as you said. But instead of a 30-tonne rocket putting a 1-tonne payload in orbit, it's a 120-tonne rocket putting a 4-tonne rocket in orbit, and that 4-tonne rocket putting a 1-tonne payload in a higher orbit.

        This is why more fuel-efficient engines, like nuclear or ion rockets, would be a great help even if they didn't have enough thrust to launch directly from the ground. If you can get 1 tonne from low Earth orbit to geostationary orbit with a 2-tonne nuclear rocket instead of a 4-tonne chemical rocket, the chemical rocket that launches you from the ground only needs to be 60 tonnes instead of 120 tonnes. That's a big advantage.

        If you're just tooling about in low/medium Earth orbit, sure, chemical rockets are all you need. But if you want to go to geostationary orbit or the moon, nuclear/ion rockets can make it more efficient; and if you want to to Mars/Venus and back, they're almost essential.

    • Re: Finally (Score:4, Informative)

      by zeigerpuppy ( 607730 ) on Sunday February 01, 2015 @05:05AM (#48950601)
      Open cycle nuclear engines are a bad idea anywhere close to earth orbit. They are essentially an open system that expells nuclear fission byproducts as well as propellant. They are not permitted to operate in earth orbit for a good reason. They would leave significant trails of radioactive material in orbit. This has implications for the sensors on satellites and is still going to fall to earth eventually. So these open cycle reactors may be useful for longer missions but would still need to get a heavy reactor into orbit. They also run essentially unshielded so on a manned mission you'd need lead or water shielding. Nuclear power sources using decay heat are probably better suited due to low levels of gamma an neutron radiation. The idea of collecting propellant along the way is quite attractive too but beyond our current engineering. http://en.m.wikipedia.org/wiki... [wikipedia.org]

  • OMG (Score:2, Funny)

    by JamesA ( 164074 )

    OMG nu-cle-er radiashun in space! Think of the environmental damage!

    • OMG mushroom cloud on the launch pad. Think of all the downwind environmental protesters!

    • OMG nu-cle-er radiashun in space!

      At some point you have to get the uranium up there. If the rocket it's on explodes for some reason you've got a bit of a mess here on Earth. I think it's a valid concern.

      • Wrap the quarter liter of Uranium in a 20cm thick steel shell. That'll be about 400 kg of steel and uranium, and be pretty much immune to explosions that aren't directed energy booms (shaped charge would be bad, accidental boom, ignorable.).

      • Re:OMG (Score:5, Informative)

        by Anonymous Coward on Saturday January 31, 2015 @10:15PM (#48949645)

        If only someone had been launching small quantities of radioisotopes into space for many decades and perfected the containment vessels... Oh wait, they have. They're called RTGs and they're absolutely designed to survive the rocket exploding on launch pad or free-fall from space after a failed launch. There has never been an incident where an RTG has leaked radioactive material into the environment. Not that it would matter - the amount we're talking about here is equal to the amount of uranium released into the environment by a coal-fired power plant every two hours in normal operation.

      • There was, and probably still is, far more nuclear material airborne 24/7 in standby aircraft. That's in actual bombs, too, with all the many other components assembled to cause it to explode, whereas the thruster would be contained to provide protection as used in currently launched devices.

      • I would think that the 20 or so kilograms of uranium from a rocket may be overshadowed by the 4.5 billion tons [stanford.edu] of uranium already in the ocean.

        Not that it shouldn't be protected, but if we want long term propulsion in space, we'll need energy densities that can't be generated from chemical propulsion.

      • Re: (Score:3, Informative)

        by quenda ( 644621 )

        If the rocket it's on explodes for some reason you've got a bit of a mess here on Earth. I think it's a valid concern.

        No it isn't. A common mistake, but uranium is barely radioactive at all. Perhaps you are thinking of the plutonium RTGs in deep space probes or Mars rovers?
        Or reactor waste products? But no, the clean uranium fuel loaded into the reactor is quite harmless.

        If the reactor is run for a few years, then crashes into earth, you get a big mess. [wikipedia.org]

        • I doubt your body knows the difference between the radiation from uranium versus plutonium.

          You post is utter nonsense.

          Marie Curie died due to much radiation (not only from uranium, mainly likely from radium) her notebook is so highly contaminated that it is kept in a save and you can not read it with ordinary means.

          • Actually plutonium is mostly just a biological toxin. Its a heavy metal that gets drawn into your cells and hits you about the same as say, a dose of cadmium breathed into the lungs would.

            Radiation is a funny thing: alpha emitters are harmless outside the body, but incredibly toxic if absorbed. Gamma emitters are no trouble at all - they're no more dangerous (barring chemical toxicity) outside then inside since the radiation passes through all practical wearable shielding.

            • Same foro Uranium, the poisoning in Iraq etc. is manly based on its chemical properties, not on its radioactivity. Nevertheless the later is not to underestimate.

              Your idea about gamma radiation is wrong. A percentage is always absorbed.

              See: http://en.wikipedia.org/wiki/G... [wikipedia.org]
              Scroll down Shielding and Matter interaction.

          • Re: (Score:2)

            by quenda ( 644621 )

            I doubt your body knows the difference between the radiation from uranium versus plutonium.

            It knows magnitude. Would you rather be hit with the lead from a BB gun, or the lead from a 20mm gattling gun. Its all lead, eh? That analogy understates the difference. BTW, we are talking about plutonium RTGs which use a different isotope to bombs or breeder reactors. I'd quote half-lives, but is amazing how many people think a longer half-life is worse.

            Marie Curie died due to much radiation (not only from uranium, mainly likely from radium)

            Given that radium is about a million times more radioactive than uranium, and as an experiment she kept a sample of radium on her skin until it caused an

            • The point is if you sleep a few nights besides an unshielded 1kg bunch of Uranium, you likely die from it.

              So your claim Uranium is harmless: is wrong.

              Why should Radium be million times more radioactive than Uranium? The only difference I see is that Radium has a short half life and decays in a combination of Alpha and Gamma decay. Unfortunately I find no table in either becquerel or sievert.

      • Re: (Score:2)

        by tsotha ( 720379 )
        We've been launching plutonium into space for decades for RTGs. It's a small enough amount you can shield it such that it will survive a launch failure.
      • It's a concern that was addressed decades ago, nuclear batteries such as the one on Cassini are tested by shooting them out of an artillery gun directly into a block of steel several feet thick. The battery weighs about 35kg, the plutonium inside it weighs less than a kilo. Sure, nothing is truly indestructible, but you need more than an exploding rocket (or uncontrolled re-entry) to crack one of those things open.

    • Re: (Score:2)

      by ihtoit ( 3393327 )

      yeah, really can't believe they're even considering it, adding to the nuclear pollution the Sun's putting out.

    • nu-cle-er radiashun

      That's nu-cu-lar radiashun.

  • there's NASA's killer app: a Hybrid Rocket. distracts the anti-nuke/global warming crowd.

  • About time (Score:5, Interesting)

    by mbone ( 558574 ) on Saturday January 31, 2015 @08:34PM (#48949313)

    At the Europa day on the Hill last summer, I ran into a 90 yr old Harry Finger (the former head of NERVA [wikipedia.org]) who remains absolutely convinced that this technology (which was ready for flight tests back in the Apollo period) is essential for human travel to the planets, and needs to be revived.

    Looking at the delta-V requirements for a human Mars mission, I can't say I disagree with him.

  • what we really need is a booster that uses a nuclear pulse engine. Then weight limitations sort of, well, there are no weight limits.

  • The VASIMR is the likely candidate for inter planetary travel.

    Think of adding a microwave to an Ion engine super heating the plasma first. . It's claimed to increase an Ion engine by 100x (Claimed).
    http://en.wikipedia.org/wiki/V... [wikipedia.org]

    There is also a problem with launching a reactor into space, it not only breaks a few treaties, it's the possibility of it failing falling back to Earth; the reason sending very high level nuclear waste to the Sun isn't being considered.

    • The USSR was launching nuclear-powered RORSAT satellites as late as 1988 (http://en.wikipedia.org/wiki/US-A). I don't *think* there's any treaty that prohibits doing so again, and the only difference between a satellite and a spaceship is the ability to maneuver within and/or leave orbit. Orion (nuclear pulse rocket) is prohibited by treaty, because it involves intentionally detonating nuclear bombs in the atmosphere, but there's no reason you couldn't launch a contained reactor.

      As for VASIMR, it's a very c

  • The nuclear fuel we have on this planet is our entry-ticket for exploring and colonizing the solar system. The most stupid thing that can be done with it is using it to generate electricity, because that can be done in a number of other ways. At the same time, until fusion takes off (if ever...), fissionable material is irreplaceable and cannot be made artificially.

    • This makes about as much sense as worrying about deorbiting Jupiter with all the gravitational slingshots we do around it. The amount of uranium we consume is extremely extremely tiny. For example, we could power 100% of the entire world's energy for 10,000 years using only the depleted uranium sitting around unused in barrels at enrichment plants. We might be making very inefficient use of it now, but there's nothing to stop us from eventually digging up spent fuel and reprocessing it, for instance.

      • Peak uranium in 41328, we're running out of time people!

      • Actually we can not do _anything_ with the _depleted_ uranium as it is not useable in a fission reactor.

        Or what you think why it is "sitting around" at the first place?

        For a reactor you need the opposite: _enriched_ uranium!

        • Actually we can not do _anything_ with the _depleted_ uranium as it is not useable in a fission reactor.

          That is like saying we'll never get beyond the nuclear bronze age (thermal spectrum). We already have, fast breeders [wikipedia.org] can output enriched product even from low-yield inputs like depleted uranium [wikipedia.org], though the reactor is expensive and dangerous and fun to operate, like a fine sports car.

          But the GP poster was obviously referring not to depleted uranium, but spent irradiated fuel stockpiled from conventional reactors which contains significant amounts of unburned fissile. You probably knew that but forgot to po

          • Pfft ... if you or the parent want to talk about fast breeders mention that before hand.

            Now we only need to build a few more fast breeders, or?

            Actually there are not many running on the planet.

            So: the depleted uranium we have right now is useless.

            But thanx for pointing out the obvious ;D

        • Wrong, look it up, depleted uranium (definition, U-235 content 0.3%) can indeed be used SOLEY as a nuclear fuel in the proper type of reactor. So can natural uranium.

      • Re: (Score:2)

        by gweihir ( 88907 )

        Seriously? You do not even know what depleted Uranium is (hint: Uranium unsuitable for fission) and presume to make grand statements? Pathetic.

        • You are wrong, even depleted uranium can be used in the proper type of reactor as nuclear fuel, and to breed fissionables out of things like thorium. In short, the earth will not run out of fissionable fuel.

  • At the start, it talks about using reactors to generate thermal thrust and using reactor generated electricity for ion propulsion. Then everything is limited to advocating thermal thrust. That's because thermal thrust reactors make manned exploration of the solar system much more feasible. Using reactors for ion propulsion is more suited to robotic exploration, because ion thrust means longer travel time. So the point of the article is to justify nuclear propulsion in space for manned missions, but they nev
  • The UFOs have space drives. Hundreds of witness, some with scientific credentials, have seen UFOs make extremely high G turns. With nothing being shoved out the ass end of the craft. Total silence.

    Our physics if fucking wrong, and space drives are possible!

    Instead of fucking with rockets, NASA needs to figure out what is wrong with our physics, and build the fucking space drive!

    • those tabloids you see in the checkout lines don't actually report reality, neither do the tin-foil-hat websites you frequent. There are no UFOs piloted by aliens visiting our planet, never have been.

      • Re: (Score:2)

        by anwyn ( 266338 )
        You are living proof that we are too stupid to go into space.

        • I am an engineer; real spacecraft using real applied physics are made by people like me. What is made by people like you? Sci-fi comics for kids?

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