It’s a fusion rocket engine!


Maybe Mars Inspiration should hold off on their proposed flyby launching in 2018. A new grant by NASA will reportedly develop a revolutionary engine that could reduce time travel to the Red Planet and other celestial destinations to a few weeks within a decade:

Earthsky — Is a fusion-powered rocket feasible? These researchers say it is. They say they’ve conducted successful lab tests of all portions of the process and that their task now is to combine these isolated test into a final experiment that produces fusion. The team said in a press release issued April 4, 2013 that it hopes to have everything ready for a first test by the end of summer 2013.

NASA estimates that a round-trip human expedition to Mars would take more than four years using current technology. The large amount of chemical rocket fuel would be expensive; launch costs alone would be more than $12 billion, NASA says. In contrast, the team in Washington has published papers calculating the potential for 30- and 90-day expeditions to Mars, using a fusion rocket.


  1. Crip Dyke, Right Reverend Feminist FuckToy of Death & Her Handmaiden says

    Yeah, I read about that thing. It’s as hot as hot gets.

    see what i did there?

    No, but really, pulse-plasma propulsion with a stirling engine shuttling massive waste heat between the engines and the crew compartment while generating electricity to boot, *that* is the kind of engine that could really make interplantetary travel almost practical!

  2. says

    Has a sustainable, contained, fusion reaction suddenly become easy? I must have dozed off and missed that memo. The implications for energy production would be vastly more important to humanity than a trip to Mars.

    How does it work? Powerpoint?

  3. Lofty says

    Marcus Ranum, fusion, as always, is just around the corner, just needs a few more trillions thrown at it…

  4. Dunc says

    So what sort of accelerations are involved in a 30-day mission to Mars? I’m all out of envelopes here…

  5. sawells says

    @2-3 : we’re not talking about a _contained_ fusion reaction, which is difficult, we’re talking about a series of fusion explosions. You don’t try to contain the hot products : they go away that way and the ship goes the other direction.

  6. StevoR : Free West Papua, free Tibet, let the Chagossians return! says

    @ Lofty : Like a Mars landing or human Lunar return cheap and widespread nuclear fusion always seems to be about twenty years away and has been since the 1950’s or so.

    Still I do think its well worth investing in and the rewards for us all for getting it to work are, well, astronomical! Mars journey only being the start there.

    I also really like the idea of thorium and liquid salts reactors that are discussed here :

    among other places as one strand of the solution to our global energy woes. Such new & superior forms of nuclear power are not going to be the whole solution there (& consequently to global overheating as well.) – but they can certainly a good part of it.

  7. sawells says

    @4 : if your accelerations are continuous then they don’t have to be large. For example, a constant acceleration of one gravity maintained for one month gets you up to about 8% of the speed of light. To cover an earth-mars distance of say 100 million km in thirty days you’d need to average about 40,000 m/s which is about 0.01% of the speed of light.

    So a few hours of 1g acceleration, or a few days of much less than that.

  8. Johnny Vector says

    I’m not sure where you got the “within a decade” part. This is about as advanced as the technology for JWST was before Hubble was launched. Even if there are no surprises about the physics of it, unless you put a billion dollars a year into this there’s no way you’d have even a demonstration project ready for launch in a decade. And of course the real reason to continue this research is because we know there will be physics surprises!

  9. Dunc says

    @7: Cheers. I should have been able to work that out myself – clearly I’m not feeling very bright today…

  10. unbound says

    @Marcus Ranum – Keep in mind that this is being done in space, so the safety considerations and designs change drastically compared to doing anything of this nature on earth. Cooling, waste, etc are not typically a concern in space, but are a big deal here on earth (which remains a headache with fission reactors).

    It is very likely that such a ship would be launched into orbit via standard chemical rockets, and the fusion engine used after that.

  11. says

    Cooling, waste, etc are not typically a concern in space…

    Agreed. But aren’t nuclear explosions in space a violation of at least one nuclear test ban treaty? IIRC that’s why the original ORION project was scrapped.

    Or did the USSR’s sudden massive existence failure take those treaties down with it?

  12. sawells says

    @11 : I gather this one is using lithium/hydrogen fusion with no heavy radionucleides, the bans are about thermonuclear weapons, those have a fission bomb setting off the fusion part.

  13. says

    . . . reduce time travel . . .

    Time travel? COOL? But how can reduce something that doesn’t exist yet? Is this one of those temporal paradox thingies?

  14. says

    My understanding is that the principle bottleneck is not so much the propulsion system as it is the shielding system. Once you get beyond Earth’s magnetosphere, the sun’s radiation is HARD. As I recall, all of the moon landings occurred during lunar night specifically to minimize exposure to solar radiation; travelers going beyond the moon won’t have even that protection. A few weeks to Mars, a few weeks there, a few weeks back…. Without extraordinary shielding and protection, they will never return alive.

  15. Reginald Selkirk says

    a revolutionary engine that could reduce time travel to the Red Planet…

    I’m just going to assume you meant time of travel.

  16. steve oberski says

    @Raging Bee

    But aren’t nuclear explosions in space a violation of at least one nuclear test ban treaty?

    Our planet has been orbiting “nuclear explosions in space” for the last 4.5 billion years or so.

  17. cag says

    Half the trip would be spent decelerating. Any power output variance would make for some very complex navigation.

  18. Trebuchet says

    The large amount of chemical rocket fuel would be expensive…

    Seriously? The fuel, I think, is probably the cheapest part of the whole process. Often it’s nothing but deconstructed water, which we put back together to gain energy. Alternatively, it’s petroleum, which we think nothing of burning by the millions of gallons in running to the store.

  19. Ben P says

    Seriously? The fuel, I think, is probably the cheapest part of the whole process. Often it’s nothing but deconstructed water, which we put back together to gain energy. Alternatively, it’s petroleum, which we think nothing of burning by the millions of gallons in running to the store.

    Well for one, most spacecraft with rockets that are intended for acceleration as opposed to mere stationkeeping use something more energetic than hydrogen and oxygen. In the space shuttle for example, the booster tank carried on liftoff burned Liquid Oxygen and Hydrogen, but the fuel carried inside the orbiter itself was Monomethyl Hydrazine and DiNitrogen Tetroxide as an oxidizer. Those are much more energetic and have more reaction mass so less fuel is needed for the same thrust.

    More importantly, the problem with a chemical fueled rocket for a long journey is the cruel and implacable math of rocket science. If you want to bring enough fuel to accelerate a rocket to get to mars in a reasonable time, you have to double it to have enough to decelerate, then quadruple if there’s a return voyage. Then you have to figure out the weight of the additional fuel needed to boost all that fuel into space itself.

    The Saturn V rocket was 6.2 million pounds at launch, it’s empty weight is 391,000 pounds, It’s launch weight was roughly 95% fuel. Stated differently, it took 5.8 million pounds of fuel to get an approximately 100,000 pound payload to the moon.

    Even for a very cheap fuel, a method that can drastically reduce the fuel weight would save an exponential amount of mass.

  20. Trebuchet says

    @Ben P: I pretty much agree with what you say, but would maintain that even the exotic fuels are a pretty trivial portion of the cost of a shuttle flight, for instance. The cost of carrying all the unburned fuel around IS a big deal, and a legitimate reason to look for alternatives. But the quoted post doesn’t say that, it just refers to fuel being expensive. It pretty much destroys any credibility of the proposal for me.

  21. zekehoskin says

    @Ben P: I can’t believe that nobody has pointed out that H2-O2 is actually the highest-ISP fuel-oxidizer combination available. The only reason for using hydrazine/N2O4 is because the combination is hypergolic (self-igniting) and simplifies the restart problem. Saturn used kerosene in its first stage because there was no way to build a tank that would hold that much H2 or a turbopump that would pump it fast enough to provide the kind of thrust needed. And yes, there are tripropellant systems with still-higher ISP, but not enough higher to make it worth dealing with the toxicity of the fuels and the exhaust. Li-H-F comes to mind.

  22. zekehoskin says

    About the implacable math: you don’t have to quadruple the fuel for a return trip. You have to quadruple the log of the mass ratio. If getting up to speed takes 10 pounds of fuel per pound of payload, the return trip takes 10,000 pounds of fuel per pound of payload.

  23. sawells says

    @22 : I read “expensive” as meaning most demanding. If you’re reading it as referring strictly to the dollar cost of buying the propellant, that seems strange to me – given the context. For comparison in simulation work if we say a method is “expensive” we’re usually talking about the demand in CPU cycles, not the monetary cost of the computer.

  24. Trebuchet says

    @25: I agree. It’s really just a poor choice of words, probably by the publicist rather than the scientists. I actually find the proposed technology very interesting and hopeful. Leaves me wondering if you could apply it to earthbound power by using the thrust to spin a turbine plus capturing the excess heat to make steam.

    Here’s a really good take on the tyranny of the rocket equation:

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