Nuclear Powered Spacecraft

Byeman said:
Yep all.
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That is patently false. You bar is either 100% successful or complete failure. That is idiotic. Has Psyche, which you cited as a Frankensat failed? It's had difficulties but is that a failure? You cited Skylab, implying it was a failure. It was damaged in launch and yet I seem to recall that it was successfully crewed repeatedly.

Byeman said:
Wrong, now you are changing your tune. The ESMs were not leftover ATV hardware. It is not the same as new designed based on older ones, which is done all the time and does not meet the intent of a "Frankensat". There is no unique ATV hardware in it.
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I didn't say they were. Metal is not cursed, and doesn't have to be a virgin, so I doubt a modified unit is inevitably doomed to fail while new hardware will work. The essential ATV design works, the Gateway unit may have to be modified, though it's a fairly self-contained tug.

OK, let's go back to 'cursed metal': the SSMEs on the Artemis boosters. Failures?

Several X-planes that used components manufactured for other, different aircraft - engines, landing gear, canopies, avionics. The X-59 is proceeding through its tests well so far, despite being a flying anthology. Is doom inevitable? And there are others.

Or Frankenships. the Royal Navy ships Nelson and Rodney were fitted with triple 16" gun turrets that were long-lead items for the cancelled G3 battlecruisers - a different design. Both ships performed excellently.

HMS Vanguard was fitted with four 15" double turrets from the Queen Elizabeth class that predated WWI. They were modified to increase elevation. She arrived too late for active combat but trials also showed excellent performance. Her guns had excellent range and accuracy, superior actually to more recent designs. She did pretty well as a royal yacht too.

The main guns are obviously not trivial elements on battleships and usually their design proceeds in parallel with the ship itself. This is because ballistics is complicated by calculations of recoil, roll centre, and so on. These have major effects on accuracy, so in specifying and designing the gun and its associated computing hardware, there's usually a lot of give-and-take along the way. Not so here: the Nelsons' hulls weren't G3s and Vanguard wasn't anything like a Queen Elizabeth. While the characteristics of the guns could not be changed (though Vanguard's turrets were modified), there were known well and the new ships were designed to accommodate them. None of them failed: the Nelsons endured the rigours of the Battle of the Atlantic and Vanguard at least went through trials designed to ensure that she was ready for the same (tests indicated unparalleled seakeeping in fact).

HMS Warspite... where to begin? Virtually a ship of Theseus, two world wars.
 
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Brett Davidson said:
That is patently false. You bar is either 100% successful or complete failure. That is idiotic. Has Psyche, which you cited as a Frankensat failed? It's had difficulties but is that a failure? You cited Skylab, implying it was a failure. It was damaged in launch and yet I seem to recall that it was successfully crewed repeatedly.
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Wrong, Psyche delayed the Verista mission 4 years. That means it was a financial and schedule failure.

Brett Davidson said:
OK, let's go back to 'cursed metal': the SSMEs on the Artemis boosters. Failures?
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Irrelevant. They are engines and not a spacecraft. Same engines have flown on multiple launch vehicles.
Brett Davidson said:
Several X-planes that used components manufactured for other, different aircraft - engines, landing gear, canopies, avionics. The X-59 is proceeding through its tests well so far, despite being a flying anthology. Is doom inevitable? And there are others.

Or Frankenships. the Royal Navy ships Nelson and Rodney were fitted with triple 16" gun turrets that were long-lead items for the cancelled G3 battlecruisers - a different design. Both ships performed excellently.
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Different environments. Also, can be repeatedly tweaked, modified, serviced, etc until it works.
 
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Brett Davidson said:
I didn't say they were. Metal is not cursed, and doesn't have to be a virgin, so I doubt a modified unit is inevitably doomed to fail while new hardware will work. The essential ATV design works, the Gateway unit may have to be modified, though it's a fairly self-contained tug.
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Not the same design, just "based" on. Different tank shapes, thrusters placement, three decks vs two.
 

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Byeman said:
Wrong, Psyche delayed the Verista mission 4 years. That means it was a financial and schedule failure.
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It fails if it doesn't happen or if it's an expanding cloud of debris. Neither is the case. It appears that you're making up and adding definitions of failure as you go along so that whatever happens is a failure. State a definition and stick to it.

My definition of success is 'returning data.' Delay and cost overruns are a problem of variable severity. By your definition, Webb has failed, full stop. The delay and cost overruns were scandalous and the managers and accountants failed in their declared objectives, manufacture was a success and the mission is an ongoing success because the data returned is stupendous. It is in fact possible for multiple facts to be true and you look absurd deliberately ignoring one for the sake of whatever you prefer.

Byeman said:
Irrelevant. They are engines and not a spacecraft. Same engines have flown on multiple launch vehicles.
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You are being arbitrary. Again.

It's becoming clear to me that I'm chasing moving goalposts.

Byeman said:
Different environments. Also, can be repeatedly tweaked, modified, serviced, etc until it works.
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Seriously? Different environment, same principles. It's rather hard to tweak, modify, service, etc. in the middle of a naval battle. There tend to be a lot of distractions and supply lines are stretched.

As for aircraft, you might be aware that this doesn't happen.

View: https://www.youtube.com/watch?v=gCBH8XIEFhM
 
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Brett Davidson said:
By your definition, Webb has failed, full stop.
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I agree Webb failed. It set back space astronomy several years and even a decade.
SLS has also. Cost and schedule
Brett Davidson said:
You are being arbitrary. Again.
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Not at all
A. The topic is spacecraft
b. engines or launch vehicles. It is every rare that an engine is only suited for model of a conveyance. Jet, car, truck, ship, plane, rocket. locomotives engines are used in multiple models.
Brett Davidson said:
Seriously? Different environment, same principles. It's rather hard to tweak, modify, service, etc. in the middle of a naval battle.

As for aircraft, you might be aware that this doesn't happen.
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Seriously? What are sea trials and test flights? As I recall, they are opportunities to tweak, modify, service, etc. a vessel before going into use. No equivalent for a one of a kind Frankensats, because the environment can't be replicated on earth.

You are out of your element here, this is architecture or buildings.
 
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Byeman said:
I agree Webb failed. It set back space astronomy several years and even a decade.
SLS has also. Cost and schedule
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I've already commented on the deliberate and selective use and exclusion of facts to fit a predetermined result. You can guess what I'm implying with that.

Byeman said:
Not at all
A. The topic is spacecraft
b. engines or launch vehicles. It is every rare that an engine is only suited for model of a conveyance. Jet, car, truck, ship, plane, rocket. locomotives engines are used in multiple models.

Seriously? What are sea trials and test flights? As I recall, they are opportunities to tweak, modify, service, etc. a vessel before going into use. No equivalent for a one of a kind Frankensats.
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The topic of the forum is high-performance machines intended for extreme environments. Again, arbitrary exclusion. You're using pseudo-legalistic argument based on little more than semantics to exclude unwanted facts.

Vacuum chambers, hot and cold tests, flight of test components and experiments in earlier spacecraft. Different kinds of tests but as close to actual environment as possible. You know perfectly well that spacecraft aren't just thrown together and launched.

'One of a kind Frankensats?' Most space probes are one of a kind and therefore by your definition untested. You are being inconsistent.

You can compare this to wrestling with a pig if you like. You've assumed undignified positions and besmeared yourself (with bad faith arguments). I'll let you guess whether I've enjoyed it.

In any case, I will no longer engage with someone perpetually moving goalposts or arguing in bad faith according to a predetermined outcome.
 
My amateur ass very much likes the SR-1 proposal. Mars helicopters are a popular payload idea due to Ingenuity's success, and low enough mass to allow for a heavier LEU power source to be used, and for the vehicle to still be launched directly out of Earth's gravity. The propulsion module already exists. I didn't like the cost effectiveness of Gateway and I'm not sad to see it cannibalized. The compromises are clear, and seem really well considered. Asking NASA to not save where it can on this project while trying to run a Lunar base program along with a myriad of other projects in the future of uncertain funding that it faces seems like a particularly dead horse to beat.
 
publiusr said:
If Plutonium-238 for a smaller craft were placed near this nuclear battery---might that help keep it topped off?

The smaller craft might be a lander perhaps
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Wait, you want to engineer in a deliberate leak of radiation from one vehicle to another?

Radioactive decay doesn't work like what you're suggesting. Both the suggestions have alpha decay as a main source ending up mostly as heat, Hence the use for RTGs. One radiation source next to another just ups your overall radiation they don't "recharge" each other.

Randy
 
RanulfC said:
Wait, you want to engineer in a deliberate leak of radiation from one vehicle to another?

Radioactive decay doesn't work like what you're suggesting. Both the suggestions have alpha decay as a main source ending up mostly as heat, Hence the use for RTGs. One radiation source next to another just ups your overall radiation they don't "recharge" each other.

Randy
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Radiation decay from two sources is like a slow leaks in separate unconnected pressure vessels.
 
The nuclear "battery" is just an RTG with a different heat source.
 
Byeman said:
>>>The payload is one that the science community is really interested

Unsubstantiated.
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It's more than that--there's no indication the science community is interested in this at all. The science community has ways of indicating its interest in missions and science goals, and this is not on their list of missions and science goals.

That said, this is not a science mission. It is a technology demonstration mission. As long as it does not take from the science budget, the scientists have little to complain about.

However, technology demonstration programs should have a clear path to a future requirement. They should not be engineers playing in a sandbox. There is no clear future requirement for this technology.

What a lot of people seem to miss with Skyfall is that before it was announced, there was no discussion of this within the science or tech development communities. You cannot point to papers, reports, presentations where somebody laid this thing out and explained why it was a good idea. This mission has no pedigree because it came from the NASA administrator, who just thought it up. It is a kludge of different hardware and goals and objectives, which don't fit well together. And they're brought together with a totally unrealistic timeline (even simple spacecraft take longer than two years to build, and this one is not simple). If you think about it, this is not that much different than Trump's battleship idea--before he announced it, nobody was saying "We need to build battleships again." He announced it with a ridiculous timeline, and now people are pretending that it's real.

But ultimately, it does not matter what I think or say about this. We'll just wait and watch. By next year it will be clear that they cannot meet the launch date, and then we'll see how long it takes before they publicly admit that.
 
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I was including the tech demo value in the science value, I should have clarified. I was under the impression that many scientists are interested in a more scientific follow up to Ingenuity. Obviously a Mars copter swarm isn't suited for the exact same missions as more massive rovers, but their numbers and ability to cover far more ground enables new possibilities. We've been planning and doing science missions with ground rovers for decades, I don't expect the second ever Mars flyer mission to match that planetary science capacity. I think it's a worthwhile compromise to enable LEU use and a direct trajectory.

I don't like the current political landscape, but I admire this project's ability to fit into it. Space programs are molded and driven by politics, often seemingly petty. Leveraging the ambitions of politicians for scientific gain is the duty of a program administrator.
 
World B4 said:
That's the whole point of the mission
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My point was about the propulsion system. The fact that it is exists is meaningless since the power system is the long lead item.
 
World B4 said:
I was including the tech demo value in the science value, I should have clarified. I was under the impression that many scientists are interested in a more scientific follow up to Ingenuity. Obviously a Mars copter swarm isn't suited for the exact same missions as more massive rovers, but their numbers and ability to cover far more ground enables new possibilities. We've been planning and doing science missions with ground rovers for decades, I don't expect the second ever Mars flyer mission to match that planetary science capacity. I think it's a worthwhile compromise to enable LEU use and a direct trajectory.
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No. The Mars science community has been clear about what they want, and three helicopters flying around the surface a little bit is not it. (And to state the obvious: if you want to fly some helicopters around Mars, you don't need a nuclear reactor to take them there. Chemical propulsion will do just fine, and is cheaper.)

Again, it's not a science mission. It's a tech demo. And it was dreamed up by the NASA administrator, not a group of scientists or engineers.

And again, I'll make my prediction: it will get delayed, it will go over budget (whatever the budget is--we don't know yet), and it will eventually get canceled. That assumes that Congress doesn't nip this thing in the bud. Missions that don't have constituencies (meaning people who want them to happen) tend to have short lives.
 
Byeman said:
My point was about the propulsion system. The fact that it is exists is meaningless since the power system is the long lead item.
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It has been a long time since I did anything related to electric propulsion (from the policy side, not engineering), but one of the things I picked up on then was that a big issue is not just the electric thrusters themselves, but the power unit that controls them. The electricity provided by whatever (in this case, a nuclear reactor) has to be regulated/controlled for the electric thrusters. Apparently that is a bit complicated. It's not like plugging a lamp into a wall socket. So my guess is that the long lead items on this are going to be:

-the nuclear reactor (because the last time we did one was in 1965)
-the power unit
-the electric propulsion system

As for the entry vehicle and the helicopters, JPL knows how to do all that stuff. They're not inventing any new technology. But there is a question of how quickly they can build some of those things. Can they make a heatshield in under two years? Can they manufacture three helicopters in that time? A lot of people got fired at JPL, so maybe they don't even have the people who remember how to do those things.
 
Byeman said:
Meaningless, since the power source has never been built much less flown.
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World B4 said:
That's the whole point of the mission
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Byeman said:
My point was about the propulsion system. The fact that it is exists is meaningless since the power system is the long lead item.
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Big point here, that needs to be understood is that the propulsion we know, enough to get the job done at any rate, but THE main sticking point is the power which is the "heart" of the mission a nuclear reactor capable of operating over an extended period in space.

As blackstar notes, we haven't done anything like this outside of studies since the mid-60s and ramping that up from essentially zero in a short timeline is more likely to never get off the ground (pardon the pun) than it is to fly.

Trying to throw a bone to "science" as a payload is just that, it's not actually serious. IIRC the general rule is that it takes about two years JUST to define and refine the payload concept and general design, even from a "known" position. Worse in this case is that process can't even start until the parameters of the spacecraft itself are known to a high degree of certainty.
(A major problem with the idea of sending payloads on Starship)

Randy
 
blackstar said:
No. The Mars science community has been clear about what they want, and three helicopters flying around the surface a little bit is not it. (And to state the obvious: if you want to fly some helicopters around Mars, you don't need a nuclear reactor to take them there. Chemical propulsion will do just fine, and is cheaper.)

Again, it's not a science mission. It's a tech demo. And it was dreamed up by the NASA administrator, not a group of scientists or engineers.

And again, I'll make my prediction: it will get delayed, it will go over budget (whatever the budget is--we don't know yet), and it will eventually get canceled. That assumes that Congress doesn't nip this thing in the bud. Missions that don't have constituencies (meaning people who want them to happen) tend to have short lives.
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I think that the marriage of convenience with a tech demo was the best way to get a new Mars surface mission approved right now, yeah it's more of a NEP test than anything else but somehow I doubt MSR could make the mass constraints.

It seems like the mission itself is something of a stress test for NASA's ability to act boldly and quickly and you're probably right about how that'll turn out.
 
RanulfC said:
As blackstar notes, we haven't done anything like this outside of studies since the mid-60s and ramping that up from essentially zero in a short timeline is more likely to never get off the ground (pardon the pun) than it is to fly.
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There have been ground tests of the KRUSTY reactor. I don't know if that is the design that they are intending to use, but there is some knowledge base. That said, the KRUSTY test was back in 2018. They were hoping to do a flight test after that, and we're now almost a decade later.

Also, there's another factor here that I forgot about--how do you convert the heat energy from the reactor to electricity? There are several ways to do that (i.e. Sterling, Brayton), some more studied than others. If they choose the well-known path, they get there faster and with fewer problems, but if they want to go with the more promising method, that requires more work and will take longer and cost more.

Although I am really skeptical of this mission proposal, I am supportive of the technology. I just don't think this is the way to implement it. First, we don't need in-space nuclear reactors. There are no realistic near-term uses for them. A more realistic goal is a reactor for use on the lunar surface. Skyfall is supposed to develop Space Reactor-1 and they are working on Lunar Reactor-1 as well. I think the latter should be the focus of their work.

Second, even if you decide to develop SR-1, it should not be tied to any payload. Fly it as a tech demo mission. That makes the overall development easier, and it also frees up the testing. They can do more and not worry about wrecking the mission.
 
RanulfC said:
Trying to throw a bone to "science" as a payload is just that, it's not actually serious. IIRC the general rule is that it takes about two years JUST to define and refine the payload concept and general design, even from a "known" position. Worse in this case is that process can't even start until the parameters of the spacecraft itself are known to a high degree of certainty.
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What is really going on here is that JPL has no missions. They need something to keep them afloat, and that is where the helicopter mission comes from. In other words, it is infrastructure/workforce support and not an actual science or engineering requirement.

The administration does not want to fund the Mars Sample Return mission. But there are other Mars missions they could fund instead. They could send one of them to JPL to build. But that's not how they are conceiving this. What happened was that the president asked "When are we sending something to Mars? Is it happening by 2028?" and the NASA administrator pulled a rabbit out of his hat. But it's a FrankenRabbit.
 
edwest4 said:
The year is 1965. The satellite is SNAP-10A.
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Yes. There have been a lot of space nuclear reactor projects since then. I have a list somewhere, including the money spent on them. They include SP-100, SPAR, Prometheus, etc. None of those have actually flown, however.
 
blackstar said:
But it's a FrankenRabbit
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I liked Bunnicula when I was young! I like the potential of NEP for the outer solar system, but I really don't think SR-1 would reliably function all the way through a trip that far out, so dropping the science payload off at Mars seems smart. If we want the drones to take close-up pictures of extremely rough, steep, vast, and/or treacherous terrain that a ground rover simply can't, the landing site should be carefully chosen. I worry that I haven't seen Isaacman publicly ask the Mars science community for suggestions about that, especially during his ignition speech. It would hurt to see a mission planning failure waste this opportunity, even if the technical challenges are overcome.
 
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southwestforests said:
A copy of that arrived here yesterday.
Have only skimmed through it at this point.
Looks good.
Was published April 16, 2023; is print on demand and this copy was printed January 23 in the little burg of Monee, Illinois, just south of Chicago.

Just for fun, here's a 2009 NASA interview with the author,
https://historycollection.jsc.nasa....s/vonEhrenfriedMH/vonEhrenfriedMH_3-25-09.htm
Here's the beginning of it,



View attachment 757480View attachment 757481View attachment 757482View attachment 757483
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Very interesting discussion. Nuclear-electric propulsion still feels like one of the most promising technologies for deep-space missions, especially for long-duration exploration like Titan or Mars missions. The recent work on ion plume behavior and electron scattering also shows how even small efficiency improvements can have a huge impact on future spacecraft reliability and range.
 
FonHua Icho said:
Very interesting discussion. Nuclear-electric propulsion still feels like one of the most promising technologies for deep-space missions, especially for long-duration exploration like Titan or Mars missions. The recent work on ion plume behavior and electron scattering also shows how even small efficiency improvements can have a huge impact on future spacecraft reliability and range.
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Not needed for Mars. Not really needed for Titan either. If you want to go beyond Saturn, it might pay off. But then you're talking about long operating times, and how do we know that a nuclear reactor will work properly for 10+ years?

Besides, doesn't Starship solve all problems? It will provide infinite fuel to spaceships and they can fly anywhere. For free. Starship!
 
The current House budget has this amount:

Nuclear Electric Propulsion (NEP).—The recommendation includes $50,000,000 for the development of NEP and encourages NASA to provide $10,000,000 for the design of test articles to enable a flight demonstration. The Committee notes that NEP will play a critical role in advancing the Space Reactor–1 Freedom (SR–1), the first nuclear-powered interplanetary spacecraft, which NASA plans to fly to Mars before the end of 2028.


That is not a lot of money. $10 million won't buy much of a new space nuclear reactor, especially if the plan is to launch it in two years. I suspect that by the time this budget process is done, there will be very little money for this project, it will slip its schedule and cost more. Then it will be canceled.
 
This was originally a DARPA project which was cancelled in June, 2025. NASA is now developing the Space Reactor-1 (SR-1) Freedom. It may or may not launch by December, 2028. "The spacecraft uses a closed Brayton cycle fission reactor to produce electricity, powering four 6 kW and three 12 kW Hall-effect thrusters."
 
I have in the works a very long article about the history of space nuclear power and propulsion. An overview of the projects that have been studied and partially developed over nearly 70 years. There have been a lot of reactor projects. The problem has been a lack of a clear requirement for any of them. They have often been funded at a level of a few millions to tens of millions of dollars to perform basic design and development. But then they reached a point where the next step--prototype flight hardware (not even flight hardware) required tens of millions of dollars. At that point, the people in charge asked "What do we need this for? Do we have a spacecraft that we are going to fund and fly that requires a nuclear reactor?" The answer has always been "no." And so there has been no reason to spend those tens of millions to advance the reactor to the next step.

I do think that nuclear surface power makes the most sense to develop. But even that has an unclear need. If you look at NASA's likely plans for sending humans to the Moon, they could do most of the missions without a nuclear reactor. So the cost pressure will still be there.
 
He discusses JIMO, and then concludes by saying that Skyfall, which is much less ambitious and therefore cheaper, makes more sense. But that still misses the point that the planetary science community doesn't want or need this. They have stated what they want in planetary science, and the administration is not going to fund those things. So Skyfall is a self-licking ice cream cone that serves only itself.


View: https://youtu.be/eS8FYnq-ECI?si=mqfG7NfVRfPVz_pa
 
edwest4 said:
This was originally a DARPA project which was cancelled in June, 2025. NASA is now developing the Space Reactor-1 (SR-1) Freedom. It may or may not launch by December, 2028. "The spacecraft uses a closed Brayton cycle fission reactor to produce electricity, powering four 6 kW and three 12 kW Hall-effect thrusters."
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Pretty sure the DARPA project was a nuclear thermal propulsion (NTP) system, not a reactor or NEP?

blackstar said:
He discusses JIMO, and then concludes by saying that Skyfall, which is much less ambitious and therefore cheaper, makes more sense. But that still misses the point that the planetary science community doesn't want or need this. They have stated what they want in planetary science, and the administration is not going to fund those things. So Skyfall is a self-licking ice cream cone that serves only itself.


View: https://youtu.be/eS8FYnq-ECI?si=mqfG7NfVRfPVz_pa
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Specifically I have to point out that what "might" get more scientific interest is building an NEP spacecraft that is reusable and not a one-way mission to somewhere. Problem there is it is again going to cost more in the end and require an entire "program" approach rather than a one-and-done single use "research" vehicle. (Can't wait to see article :) )
Far more useful instead of just getting to Mars would be getting there and coming back. Preferably with some samples and then sending it back to Mars with another lander et-al.

The real promise of nuclear propulsion is going from a chemical system with staging and long flight times to a more consistent and constant propulsion system that can be used to base a transportation system on. That seems to keep getting lost as things progress.

Randy
 
RanulfC said:
Specifically I have to point out that what "might" get more scientific interest is building an NEP spacecraft that is reusable and not a one-way mission to somewhere. Problem there is it is again going to cost more in the end and require an entire
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What the science community wants is missions that can be built (they do specific science missions and don't cost too much). They have a list of them, and they don't require NEP. They want realistic missions that can fly in the next decade, not a tech demo that won't result in an operational mission for several decades.

Ultimately, I think that's one of the reasons that Skyfall will eventually be canceled--it does not have a community that supports it, it only has the NASA administrator. When he leaves, Congress will ask "does anybody else really want this thing?" and the answer will be silence.
 
Manned Mars missions require a way to get to mars that can return at any point in time (including the worst possible, when Mars is on the far side of the sun from Earth), not waiting 2 years for a periapsis.

That basically requires NEP. If not Fusion gas-core nuclear-thermal rockets.

It doesn't take much thrust on the traveling ship to go from Earth to Mars in a month. 10 centigees, 0.1m/s/s, will get you from Earth to Mars at average distance in 34 days. Worst case, 47 days in space under just enough acceleration to be really annoying.

However, note that this means a transit delta-v of 401km/s. That's a hell of a lot of reaction mass tankage to deal with, and that would likely require some setup to refuel at Mars orbit.
 

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