Only one US-built nuclear reactor has ever flown in space, and that was more than 60 years ago.
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Here is NASA’s plan for nuking Gateway and sending it to Mars
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Presumably you don't even blink about all the hydrazine and NTO being rocketed around in far greater quantities? That stuff is much nastier than very robust HALEU fuel pellets (unused) which are pretty harmless unless you chew on them on something. Uranium is a toxic heavy metal so you don't want it in drinking water any more than other similar contaminants but it's fairly mild compared to many substances in RoHS/SVHC/REACH.
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You realize that NASA has spent $60B on SLS/Orion without a moon landing, without even a manned mission.
Now we finally have a NASA administrator who seemingly has the skill to finesse actual moon base through Congress without requiring a massive spending increase, and repurpose existing hardware for a terribly useless project (Gateway) into a legit nuclear electric spacecraft that could be a precursor of faster and far more powerful deep space probes.
We should at least enjoy the glow until a real problem emerges.
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Interesting. It surprised me in the artist’s impression/preliminary layout sketch that the radiator array is co-located with the PPE (and its thruster array), nearly as far as possible from the reactor and the Brayton cycle generator. I would have assumed that the Brayton cycle generator would have the biggest need for heat sinking on the spacecraft.
The thermodynamic cycle efficiency is probably somewhere in the 40-60% range (according to Wikipedia article for Brayton cycle). The eVinci page says their ground-based reactor design is 5MWe from 15MWth, so only 33% efficient even if we assume it scales down to spacecraft size without losing any efficiency. The amount of waste heat that needs to be rejected from the generator is very likely to be more than the amount of waste heat that needs to be removed from the ion drives (which convert a lot of their power consumption into kinetic energy of the propellant which leaves the spacecraft), and the other electrical systems in the PPE are relatively low power.
Anyone got any insight into why the radiators would be located at the PPE end, instead of next to the reactor? Or split the radiator complex into two smaller systems at each end, to save on piping?
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I imagine since this is a tech demo spacecraft on a very tight schedule, and the safety case is easier to close if it never returns to Earth orbit after starting up the reactor, that they likely won’t be trying to make it possible to refill the propellant tanks. That would be obvious scope creep. Surely this spacecraft will be a one-and-done mission. I’d actually hazard a guess that they intend to have the launch vehicle put the spacecraft on an Earth-escape trajectory before the reactor is even started, to avoid any risk of a hot reactor getting stranded in Earth orbit due to a drive problem.
I wonder what launch strategy they’re planning on. The render is a physically very large vehicle. The PPE was originally going to be co-manifested with Orion on an SLS. The whole thing seems like it won’t fit in any existing or planned fairing in the rendered configuration. They can’t possibly be planning to do in-orbit rendezvous and assembly on that budget and schedule. I guess maybe the idea is that it telescopes out from a folded-up configuration after launch? That seems like a big source of tech risk.
Or maybe the render is just not very accurate.
I wonder what launch strategy they’re planning on. The render is a physically very large vehicle. The PPE was originally going to be co-manifested with Orion on an SLS. The whole thing seems like it won’t fit in any existing or planned fairing in the rendered configuration. They can’t possibly be planning to do in-orbit rendezvous and assembly on that budget and schedule. I guess maybe the idea is that it telescopes out from a folded-up configuration after launch? That seems like a big source of tech risk.
Or maybe the render is just not very accurate.
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On the other hand, the terrestrial version should be cost-effective and handle much higher power levels, interplanetary can prioritize efficiency for higher dollar cost, which would be still peanuts in Gateway budget. Let's assume the diagram is only mock-up to give sleek futuristic spaceship-py appearance instead of a jumble of heat sinks, solar panels, etc. The model doesn't even have cabling!
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This particular layout is a common feature seen in many other nuclear electric rocket concepts proposed over the years.
Per Human Exploration of Mars Design Reference Architecture 5.0 Addendum #2, it's simply for radiation shielding.
While the power conversion systems are small and can be fitted adjacent to and within the reactor's shielding, the radiators are far too large and must be place further afield as to remain in the shield's, "shadow". While you could simply create a wider shield, this would certainly require more mass than merely increasing distance.
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Ah, thank you. While I was aware that PV panels are sensitive to radiation damage I didn’t realise that the same was true for radiator systems.
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Sending stuff to Mars is well understood and "relatively" cheap.
All of the massive ballooning costs was in the bringing stuff back part.
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Voix des Airs
Ars Praefectus
Won't making a spacecraft out of gold and marble make it kinda heavy?
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Probably, and it would've been another abandoned study at NEP/NTP without Isaacman's enthusiasm for NEP - He actually said outright at the start that why are we wasting time with something like DRACO that's not going to do anything much except have a small demonstrator putter around Cislunar space at best, let's instead build a big NEP rocket and send it somewhere for real.
The reactor design, though, most likely comes from the Fission Surface Project. It doesn't say so in that page, but Westinghouse got continuation last year to develop the initial $5 mil concept proposal Nasa page mentions into a more serious project.
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It was named in a whitehouse ceremony where he directly dictated the name to his PR flunkies as the “Best, the very best, everyone agrees, that it’s the … what is it, oh nucleer, yes rocket ?”
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I was gonna downvote you but yea, we are unreliable. It’s not just Trump though he’s amped it up 10x, every president this century other than Biden has made NASA change course on some huge projects.
The benefit for Europe is it gets to piggyback on these huge projects and develop their space technology and keep their top engineers working in cutting edge space tech.
But maybe apply a little more analysis before jumping in. The Gateway never made sense, so probably would have been a good one for Europe to skip. Canada didn’t really have a choice as Canadarm installation opportunities are extremely rare so they had to take the risk.
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It’s not “permanent”. The initial Artemis plan is four astronauts for 4 week missions. So it’s going to be empty much of time, though it’s reasonable to expect as long as costs remain under control that it will be added to so that larger groups can have longer stays.
As far as the health effects of 1/6 gravity, we researched zero gravity’s effects on health by leaving astronauts in orbit for longer and longer stretches. We will do same on moon.
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"NASA isn’t sure what they will do with the SR-1 mothership after reaching Mars. They could try to maneuver it into orbit around the red planet, or slingshot the spacecraft past Mars to head to another planetary destination."
Hmm... I was wondering if (because of its high, if slow, delta-V capabilities) it was FIRST going to go into Mars orbit and THEN drop off the helicopters (that way if there was a dust storm or something, it could wait it out, like Viking).
Then, as another commenter mentioned, bring it back for another load. Another possibility would be as a pickup vehicle for the (cancelled) sample return mission, I know the Europeans were supposed to provide that but if, for whatever reason, they can't/won't/aren't allowed to, then (again because of this craft's large, if slow, delta-v) it could pick up the sample capsule in Mars orbit and slowly bring it home.
Any of these extended mission ideas presumes that it has (a lot) of extra propellant (xenon gas). Does anyone know if that's true? Would it be practical/easy/cheap to make the tanks bigger? If it (ever) returns to earth orbit could these tanks be designed to be refueled? (Ok, might need to be done robotically, the reactor might be hot!).
A working, tested nuclear reactor (and super high power ion thrusters!) in space would be a very valuable asset. It would be nice not to leave it in orbit around Mars or have it run out of fuel in deep interplanetary space (maybe have it put a probe on some trajectory and then turn around and get refueled, again and again). Ion space tug!
Hmm... I was wondering if (because of its high, if slow, delta-V capabilities) it was FIRST going to go into Mars orbit and THEN drop off the helicopters (that way if there was a dust storm or something, it could wait it out, like Viking).
Then, as another commenter mentioned, bring it back for another load. Another possibility would be as a pickup vehicle for the (cancelled) sample return mission, I know the Europeans were supposed to provide that but if, for whatever reason, they can't/won't/aren't allowed to, then (again because of this craft's large, if slow, delta-v) it could pick up the sample capsule in Mars orbit and slowly bring it home.
Any of these extended mission ideas presumes that it has (a lot) of extra propellant (xenon gas). Does anyone know if that's true? Would it be practical/easy/cheap to make the tanks bigger? If it (ever) returns to earth orbit could these tanks be designed to be refueled? (Ok, might need to be done robotically, the reactor might be hot!).
A working, tested nuclear reactor (and super high power ion thrusters!) in space would be a very valuable asset. It would be nice not to leave it in orbit around Mars or have it run out of fuel in deep interplanetary space (maybe have it put a probe on some trajectory and then turn around and get refueled, again and again). Ion space tug!
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Looking more closely at the render, it’s very clear that the main boom between the PPE/radiators and the reactor/conversion module is a four or five segment telescoping box truss. The cabling and pipes are not shown, but the preliminary plan definitely seems to be to have that truss extend after launch. It looks like the whole truss is stored in the interior volume between the radiator panels during launch, with the reactor probably sticking out the front end.
I still wonder what launch vehicle and fairing dimensions they are designing to. Even with that truss fully collapsed, it seems like a decent sized vehicle, with the total (packed) length maybe somewhere in the range of 2-3x as long as the PPE alone? Apparently there is an existing launch contract for the Falcon Heavy to launch the PPE + HALO together on a trajectory to the Moon - "Freedom" might be in the same general category of size, dimensions and target orbital energy as that package.
I might be wrong about refuelling intentions. I’d forgotten that the PPE was itself repurposed from the Asteroid Redirect Mission, and in its role for the Lunar Gateway it had been planned to be refuellable. Perhaps NASA will try to retain that capability in this spacecraft design? Still seems like the first thing I’d cut to reduce scope, though.
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The PPE that will be used in this spacecraft has already been built - it was originally designed for the Asteroid Redirect Mission as a Solar Electric Propulsion demonstrator, which is why it has 60kW of ion thrusters, and then repurposed for the Lunar Gateway when the ARM was cancelled.
I think the plan here is to replace the large high-power solar arrays with much smaller units capable of basic spacecraft operations and running the core systems when the reactor is not running, and then use the reactor to provide main power for the thrusters. There must be some electrical engineering work to do to integrate the additional power source, but I doubt they'll be changing the PPE's tankage or propellant valve arrangements, or the filling mechanisms. There's very little time for monkeying with the hardware that already exists - the announcement claims they want to launch this thing in December 2028, which is only 33 months or so away (NSF says "Systems must be built and ready for assembly, integration, and testing by January 2028", which is only 22-ish months away). Hell of a tight timeline. Is there a prototype reactor already partly or fully built? Surely it must be at least close to complete design-wise, for that schedule to be even slightly credible, given the amount of new integration work there is to do. Doesn't look like there's any slack in the budget for design iterations to solve issues that come up in testing. (I wonder how close to mature landing systems for the helicopters are? I don't think there's a lot of hardware sitting on the shelf for that...)
That said, I think the PPE was expected to be refueled for both the ARM mission and the Gateway space station mission. Depending on what changes are necessary for this spacecraft, maybe that capability will be retained. I don't know how much complexity that would add.
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The scale of the reactor seems about right (40 kW) but reading between the lines of the January 2025 announcement it doesn't look like they're close to the TRL required to be integrating this thing with a spacecraft and launching it in less than 2 years time.
If this is the reactor they're planning to use, it will be an impressive accomplishment to manage it on this timeline!
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I notice from NASA's Lunar Gateway info page (now obsolete) that the Gateway was planned to have two radiation-related scientific instruments on it:
I expect that IDA was going to be inside the HALO module, given its purpose. But according to this article, the ERSA instruments were going to be mounted on the PPE, which is now being integrated into this demonstration spacecraft. I wonder if they're already there, and if so, whether they'll still fly with the PPE, and if they'll yield any useful information about the effectiveness of the reactor shielding and/or the environmental conditions en route to Mars...
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It's less about protecting the radiator panels themselves but more about preventing them from scattering ionizing radiation emitted by the reactor. While there isn't a crew to protect in this particular context, sensitive electronics and scientific instruments could be potentially damaged. You also don't want neutron radiation reflected back into the reactor.
Radiation scattering is also why rendezvous and docking with nuclear powered spacecraft (such as for refueling) would be a more restrictive procedure than is true with normal spacecraft. Approaching vehicles must remain in the, "shadow" of the reactor's shield, lest they are exposed to radiation and scatter it again. This means that, within a certain minimum distance, there would only be a very narrow cone where other spacecraft can safely approach.
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I someone who once worked for Gateway (née, Gateway 2000)... it's the only way to be sure.
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A dirty bomb involves fission products which don’t exist until after the reactor has gone critical (which I assume they won’t do until the mission is on an earth escape orbit). It won’t even contain plutonium. Uranium is about as toxic as lead, not great, not worse than some of the stuff already flying on rockets today. The real problem is the uranium not desintegrating and being retrieved by a third party. You don’t want a significant amount of weapons grade uranium to land near Cuba for example.
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While conscious of scope creep and the tight timeframe, I remember there have been articles recently on a gap in communication relays at Mars - bolt something to this. With that much power, if they can get it into orbit around Mars…
Also with respect to the timelines. If they do miss the Mars window, and it’s purely a tech demo anyway, why not launch it in, say, 2029 outside the window anyway? Just point it somewhere in the solar system and let it roam!
Also with respect to the timelines. If they do miss the Mars window, and it’s purely a tech demo anyway, why not launch it in, say, 2029 outside the window anyway? Just point it somewhere in the solar system and let it roam!
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So does the animation. Three more would be a trivial cost in the larger scheme of things. Personally, I'd hoped they meant 3 aeroshells each with 6 copters, but I don't want to sound greedy.
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The operating cost of running a whole fleet might be a bit higher, depending on their operation tempo, I suppose.
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They should put it into Martian orbit with a high power data relay dish to take advantage of the nuclear generator. The Mars Reconnaissance Orbiter and Mars Odyssey are over twenty years old now and we desperately need new communications assets in deep space.
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Wrong
Space reactors run on Uranium (well, you could design a plutonium reactor, but why? And there is thorium…) - certainly all small reactor design do.
They use highly enriched Uranium, true - often weapons grade. But U235 is only mildly more radioactive than U238.
You can find on the web, plenty of images of people handling reactor fuel rods (unused) with gloves and masks - as I said. This is because Uranium is a toxic heavy metal - about as toxic as lead. You don’t want the dust in your lungs, but in a lump, it just sits there. The radioactivity is alphas - which are stoped by just about anything. And they aren’t intense.
https://www.ans.org/file/14961/History SNAP Collage.jpg
Shows the assembly of the Snap-10 core
It’s running a reactor that makes the core radioactive in a nasty way.
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Kosmos 954 had been run for a long, long time.
The problem was the fission products from being run, not the Uranium core.
Note that NASA launches RTGs full of nasty isotopes of Plutonium, on a moderately regular basis. Plutonium is vastly more toxic and the isotopes used in RTGs are fiercely radioactive from the start.
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Send that large probe to psyche, with a nuclear power source it can just cut the raw iron nickel into rods and melt the outer surface layer, and have reasonably strong high quality iron nickel alloy. Pysches gravity is low enough, about 1.3% of earth, you can just push off into orbit with an arm getting you height and a tiny burn. It sounds perfect for moving around and getting big 100 kilogram samples from low gravity moons and large asteroids, starting at Mars and then moving to psyche, and then bringing back samples to drop off at earth or the moon base.
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