Optimized Nuclear Thermal Rocket for 45 Days to Mars

Nuclear Thermal Propulsion (NTP) is the preferred propulsion technology for manned missions throughout the solar system. The state-of-the-art NTP cycle is based on solid core Nuclear Engine for Rocket Vehicle Application (NERVA) class technology that is envisioned to provide a specific impulse (Isp) of 900 seconds doubling chemical rocket performance (450 seconds). Even with this impressive increase, the NTP NERVA designs still have issues providing adequate initial to final mass fractions for high DeltaV missions. Nuclear Electric Propulsion (NEP) can provide extremely high Isp ( over 10,000 seconds) but with only low thrust and limits on mass to power ratios. The need for an electric power source also adds the issue of heat rejection in space where thermal energy conversion is at best 30-40% under ideal conditions.

This is a NASA Innovative Advanced concepts study. New Class of Bimodal NTP/NEP with a Wave Rotor Topping Cycle Enabling Fast Transit to Mars.

A novel Wave Rotor (WR) topping cycle is proposed that promises to deliver similar thrust as NERVA class NTP propulsion, but with Isp in the 1400-2000 second range. Coupled with an NEP cycle, the duty cycle Isp can further be increased (1800-4000 seconds) with minimal addition of dry mass.

The ISP can be over four times better than the NERVA class nuclear rocket and ten times better than chemical rockets.

This bimodal design enables the fast transit for manned missions (45 days to Mars) and revolutionizes the deep space exploration of our solar system. The current NASA chemical rocket missions need to take 180-270 days to get to Mars.

Full scale nuclear thermal rockets were built and ground tested.

NERVA was about a $10 billion program (in today’s dollars) from 1955-1972.

The Rover/NERVA program was canceled before a prototype flight was achieved, but achieved a TRL 6 for the design requirements set in the 1960’s and 1970’s.

Many lessons learned from the entire Rover/NERVA program will help the current NTP program develop faster and at a lower cost back up to TRL 6.

There is again a nuclear thermal program at NASA.

The BWX technology company has been funded to make a nuclear thermal rocket. DARPA has finalized an agreement with Lockheed Martin for the company to begin work on the fabrication and design of the experimental NTR vehicle (X-NTRV) and its engine.

9 thoughts on “Optimized Nuclear Thermal Rocket for 45 Days to Mars”

  1. NERVA lives! Yay!

    Its pretty clear from the infographics that the proponents of this combined NERVA / NTP / NEP propulsion system have some kinks to work out … as it would be with any as-yet-flight-untested scheme. So be it. Work out the kinks.

    But in summary of The Space Future:


    NUCLEAR FISSION fuel — is the lowest tech, ultra potent energy source that the near future space programs can launch and keep working. The amount of usable fission energy in a kilogram of ²³⁵U or ²³⁹Pu is absolutely gob-smacking. With enormous usable total production energy (and power) levels, it is pretty feasible to IN-efficiently convert the fissions to heat, to aid the NTP, NEP and NERVA propulsion cycles. Might only be 10% energy-to-propulsion efficient, but who cares? This energy source is potent, cheap, proven and plentiful.

    FUSION fuel — is also wickedly potent, but alas … promised breakthroughs notwithstanding, as yet is not a very convincing. Lots of press, lots of papers, lots of spin-off companies, lots of venture capital funding. Yet, not even a single commercial-grade power source. Not for want of trying. 58+ years along, and if we’re totally honest, well not much really to show for the nearly $200,000,000,000 (amortized, prorated 2023 dollars) investment.

    BOTH require a ‘reaction mass’ (see below) to heat up, which produces the thrust.

    BUT OK, we can project, since this whole article is about projections, not realities.

    CHEMICAL propulsion essentially is tapped out. We can utilize something flammable (hydrogen H₂, methane CH₄, hydrazine N₂H₄, kerosene C₁₂H₂₆, rubber (CH₃)ₓ) and something oxygen rich (oxygen O₂, hydrogen peroxide H₂O₂, dinitrogen tetraoxide N₂O₄, ammonium perchlorate NH₄ClO₄, …) to burn, to make heat and simultaneously be the reaction mass (exhaust) to push the rocket forward.

    Kind of convenient, the 2-in–1 relationship. So convenient, that it got us TO THE MOON in 1968. No nuclear nuthin.

    BEAMED ENERGY propulsion — the last kind really of any potential to push around people and significant support stuff — doesn’t rely on chemical reactions at all. Just intense heating of a beam absorber chock-full of stainless or other non-reacting tubes, which carry a bunch of cold hydrogen, heated to near incandescence and shot out the tail. ISPs of around 800 appear to be not-that-stretchy. You’d still carry the same reaction mass as a bipropellant, but we’d get about 2× the total delta-V out of it. Halving (or better) the trip time.


    So where does chemical propulsion have to go? Well … a long time ago a whole lot of theoretical-and-practical studies were done as to the limits of chemical propulsion. Basically without resorting to exotic chemical reactions that are insanely toxic and difficult to handle (for example, using fluorine as the oxidizer instead of oxygen, and nitro-hydrazine as the ‘fuel’), then the hydrogen-oxygen combo has the highest potential. About 475 seconds in the vacuum of space. And basically the Space Shuttle and STS have ‘done that’.

    Things like NASA’s Saturn V Lunar Mission were mostly lofted by oxygen and kerosene. Oxygen because its ubiquitous, not too hard to handle as a cryogenic liquid, cheap and essentially non-toxic. Kerosene for the same reasons, and additionally because it isn’t a cryogen. 98% of it is burned off just getting the whole contraption at the top to Lunar transfer orbit.

    This morning’s (failed, I’m sad to say) StarShip™ launch was CH₄ methane + oxygen O₂ based. The ISP isn’t as high (mid 300s) but the cryogenics aren’t as befuddling as the liquid-hydrogen better fuel. Its SO FLUFFY! Not very much energy per liter compared to liquid methane.

    IN A NUTSHELL then, there really is only NUCLEAR on the table for self-contained, not completely Science Fiction propulsion in the near-to-mid future. And in that regard, there really is only FISSION as well. At least for the next 50 years, since it is available today.

    THUS, some combination of NERVA thermal and possibly enhanced with electrical super-heating tech IF IT manages to overcome the thermal-to-electrical conversion machinery masses. I mean, it wouldn’t make much sense to get 2× the ISP out of one’s fuel by adding 5× the total dry mass of reactor-and-electrical shît. You know?

    ⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
    ⋅-=≡ GoatGuy ✓ ≡=-⋅

  2. This is a BIG reason why Old/New space are HORRIBLY screwing up.

    They are all focused on competing against Starship OR building metal modules for a space station.
    1) It will be another 10 years before another low-cost re-usable starship is developed by private industry. IOW, Starship owns major launch for the next 10 years.
    2) Starship can be used to transport cargo and ppl to the moon, mars and venus. HOWEVER, it will be slow and not hold that many ppl.
    3) A modified Starship will likely be used for a space station within several years.
    4) Along comes this tug and at this time, it would likely be used to push starship to remote locations.

    Now, why are old/new space screwing up?
    Because they should be focused on building Tugs, inflatable stations, and separate life support modules.

    Building tugs that use a common berthing/docking which allows for electricity and fluid transfers (fuel, O2, water, sewage, etc) would enable multiple companies to compete head on with Starship. Initially build Chemical ones, but then add in Ion as well as nuclear engines.

    Building a metal module that can be used as station, transport, or even surface housing must be contained within the rocket to carry it. There is SLS, but that is WAY too expensive to send a module up and will be much smaller than Starship itself. Using even the FH will mean that the module MUST be way smaller than starship’s volume. If the module fits Starship, it will still be smaller than Starship’s volume. The one that could do it within 1-2 years, is the BA-2200. The BA-330 was ready to go up, be tested and used for commercial space. But the folded BA-2200 would fit INSIDE of cargo starship, be around 100K lb, which was what the ORIGINAL starship was to carry (now it can carry more), and would provide more than 2200 m^3 space. IOW, more than double what the starship has. Not only that, but it is much lighter than starship and is 100% devoted to just being a living module.

    Why build life support as its own module? First there will need to be 2 types. One for Micro Gs, and another for G. The later is likely much easier and cheaper to make than the first. Secondly, this would allow stations, transport, surface living units to have extra life supports to act as back-up, and make sure of this.

    CONgress/NASA needs to push this, along with a standard berthing/docking port fully finished for sending those fluids/electricity/data around. Modularity is what is needed.

    • You’re a big thinker with big objectives. Bravo.

      I think that we need to embrace a whole ‘constellation’ of interdependent technologies to make zipping-around-space practically possible. The enterprise requires cheap, durable and reliable off-Earth launches at least for the next 50 years. Actually, for a hundred or more. JUST to get ‘stuff and people’ off Earth.

      The people are in a way the least important part of the off-Earth equation. Equipment, oxidizers, fuels, supplies, machines, tools, raw materials, intricate repair parts, air, food, water. That’s where the BIG mass fraction lies.

      Moreover, and I admit it is an opinion likely influenced by 2001 Space Odyssey and a huge library of 1950s thru 1970s Science Fiction book reading, but I cannot envision a healthy, bold, BIG and compelling interplanetary space program that doesn’t have multiple rotating orbital space stations. Depots, stop-overs, refueling stations, rocket transfer stations. They, and rather large (jaw-dropping) solar power stations. These big things are really the key to it all.

      Then there are the host of smaller (essentially Shuttle) type craft. A lot of those will be required. Standardized so that they have a lot of not-custom swappable parts. Got to fix em, you know. Even cannibalizing them like old VW busses of decades past.

      But, in addition, SPACE becomes its own massive research environment, I really believe. On this I am not timid: though kind of expensive to get stuff to-and-from space (energy wise, per kilogram), the remarkably clean vacuum environment would make some already critical tech like ‘chip-making’ spectacularly more effective. Apparently — tho i am no expert — apparently some kinds of pharmaceuticals manufacture could be equally revolutionized. Oh, yes … and exotic metals (alloys) making. (This could be THE cash cow of the space program). And of course already mentioned, big power, big solar power.

      ODDLY, this kind of summary isn’t often recounted in articles. I guess it is assumed that if the reader has an imagination, has read or watched a bunch of SciFi future stuff, and can kind of abstract the potential of Space exploitation in a holistic sort-of-way, well … no need. Yet I think the recounting needs be. There have to be concrete objectives, a paradigm of the spacey future that makes sense, and CAN be achieved without requiring magic pixie dust and dump-trucks of powdered unicorn horn.

      Anyway. NUCLEAR is clearly required. Nothing else in the short term comes anywhere near as close in terms of realizable energy, useful energy and intensity of power.

      ⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
      ⋅-=≡ GoatGuy ✓ ≡=-⋅

      • Can’t even build nuscale in Idaho and here y’all are spouting off about space tugs and six ton nuclear rocket motors. Nonsense.

          • That explains it.

            Maybe they could sell nuscale power at a premium, Like those volkswagen factories “powered by wind” or those phone solicitations asking metosecuure ‘green power’ for my home. There sure are a lot of fans on the internet that want expensive power. Maybe we could lock you in for the next twenty years at Australian electric prices, and you could feel good aboutt the cause. You might voluntarily do that, but that particular and relatively pronuclear, right-leaning area of Idaho ad Utah didn’t want it.

            Additionally with regards to the actual story at hand, a wave rotor is a compressor, so i’m not really sure that would go hand in hand with dumping LH2 through a $40M reactor the size of a dishwasher, it sure sounds cool and meets threshold for ‘woo-hoo space! Yeah!’ (dune reference here)

    • TV and Cinema have been promising sub-lightspeed ‘impulse’ rockets and super-lightspeed ‘warp’ engines.

      We not only don’t have these, but at least as far as this old Physics wiseguy knows, we’re not going to get these either.

      Quite simply, in my humble opinion, we CAN NOT BEAT the most fundamental physics: nothing can go faster (or slower) without incurring periods of acceleration (deceleration). And moreover, ‘every reaction requires an opposite and equal reaction’ means we can’t accelerate without likewise accelerating SOMETHING away from our ship in turn. And that requires expending mass. Mass which cannot realistically be scooped up along the way either.

      These very simple principles then require discussions like the article’s. Working within these realities. Because we simply cannot escape them.


      No WARP drives.
      No IMPULSE drives.
      No teleportation. No magic.

      Maybe Holodecks.
      Maybe cybernetics and machine-brain interfaces.

      ⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
      ⋅-=≡ GoatGuy ✓ ≡=-⋅

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