My concern as one of the commenters mentioned, is shielding the crew and the ISP gains exceeding lugging along the extra shielding and the other downsides.
Shielding would consist of the reaction mass tanks and and a radiation shield ‘shadowing’ the crew quarters. Note: shielding will be needed against solar flares anyway so why not plan on reorienting the engine and its shielding “sunwards” to protect the crew capsule?
My understanding of the issue is that solar flare type radiation ends up hitting the spacecraft from all directions. So you end up needing radiation shielding in all directions.
You can shield the crew module by placing it at a long distance from the propellant tank/reactor. That would be advantageous anyway, because you can then put the ship into an end-over-end tumble for artificial gravity. A long truss that can handle tension and whatever acceleration due to thrust would be sufficient, and can be pretty lightweight. This reduces the area of shielding you need in front of the reactor.
I suppose the best configuration:
Lander – Crew Quarters – Shielded “storm cellar” – Propellant tanks —– (long truss and plumbing) —- reactor/engines.
So the storm cellar can take advantage of the LH2 mass in the prop tanks.
In the mid-1980s, the Air Force Ballistic Missiles Office and TRW Ballistic Missiles Division (for which I worked) were engaged in the early phase of developing the Small Mobile ICBM. One day, we had a tech geek from Brookhaven come in to brief us on a single-stage SICBM concept using their pellet-bed fission reactor technology (what NASA has apparently re-invented). The pellet technology used multi-layer spherical pellets of U-235, carbon, zirconium carbide, and other materials, with varying material thicknesses, amounts of U-235, etc, distributed 3 dimensionally within the reactor chamber to optimize neutronics, and ensure close to 100% burnup by the end of action time. The propellant was to be liquid ammonia, serving as both reaction mass and moderator. It would have met the size and weight requirements of SICBM, with a single stage.
The pellets would contain the fission products indefinitely, no matter where they landed, allowing testing from any of the missile ranges. But someone in the Air Force objected that we couldn’t have missiles that emit radioactive products. The Brookhaven guy paused, flabbergasted, and finally said “You would use these in an environment where megatons worth of nuclear explosives are going off overhead, and you’re worried about a couple of milli-Curies of short-lived products are coming out of the nozzles?” That was about where the briefing ended.
In reality, I think the fact that it would have met the size and weight requirements of SICBM with a single stage was what killed it. That single stage would not have been built by Thiokol, Aerojet, or Hercules, each of which got a stage contract for SICBM.
Well, the Air Force officer may have made the right call when it comes to life cycle cost that include clean up. Just from conventional fuel, the toxic cleanup jobs at Huntsville means newly minted geologists can work there, handling cleanup, for life.
I would think test flights and engine tests would also be pretty problematic, especially as environmental standards kept tightening over time.
Hanford will never be finished and why would they when so many companies make a lot of money spinning their wheels?
The cleanup of conventional propellant sites is nightmarish. Aerojet Sacramento is so polluted that the site has a negative worth. The same was true of Norton AFB, the biggest EPA Superfund site of the 1990s – the main problem there was the Air Combat Camera facility, which disposed of its developing chemicals (including cyanides) by dumping them in the ground, and the MAC wings disposing of 100 octane leaded av gas in a similar fashion. (Norton also had a large number of nuke warhead bunkers, but they weren’t a problem.)
The fact that nuclear materials have ~1 million times the energy content of their chemical competitors means that the waste problem is actually 1 million times smaller. In fact, diverting the ~95% enriched uranium for a single nuclear submarine reactor would have provided enough fissile material for all of the development, flight proof, and operational SICBMs.
Again, the encapsulation of pellet-bed reactors is complete and permanent. Test vehicle reactors would sit on the sea floor forever, and never leak a pico-Curie of fission products.
It may have been an uphill battle to get the bonehead regulators to understand all of this, but the technical arguments of the environmental superiority of this technology was overwhelming.
100 octane leaded gasoline aviation fuel?
From which century?
I know about 100 “low lead” for general aviation aircraft, but WW-II combat aircraft used a highly leaded fuel of much higher octane than that.
short-lived & few milli-Curies
what’s not to understand here?
Interesting bit of history there. I wasn’t aware the idea of pebble bed reactors went back quite that far, but that is obviously what this new design is as well.
The fact that this new design would work using reprocessed civilian reactor fuel is also a major plus. Longstanding U.S. policy anent nuke fuel reprocessing is about as sensible as Democratic Party policy anent fracking. It would be good to see both buried face down with forked sticks up their nether regions during a second Trump administration.
Here’s hoping this new NTR concept finds some traction soon.
That sounds a bit like Zubrin’s nuclear salt water reactor. Dissolve fissile salts in water, at a very specific concentration, such that when the solution is pumped into a beryllium-lined chamber with a rocket nozzle at the bottom, a sustainable chain reaction takes place, blasting white-hot plasma out the rocket nozzle at about fifty kilometers per second. It’s an “atomic blast engine” just like something out of a Heinlein story from 1946. Mind the exhaust, which is a radioactive death ray. You probably shouldn’t run this engine within an atmosphere, or point the exhaust in the direction of inhabited planets.
If someone had had the idea seventy or eighty years ago, we’d have cities on Luna and Mars now, and prospectors in the asteroid belt. As a society we’re too PC, too effeminate, too cowardly, too squeamish about a bit of radiation and a bit of risk–look at the way all of Western Civilization are absolutely losing their minds about a virus that’s harmless and doesn’t even produce symptoms most of the time unless the patient is 80+ with multiple severe preexisting health conditions, and has less than a 1% fatality rate even for them.
In a nation where over two and a half million people die every year, fewer than ten thousand confirmed COVID19 deaths–as opposed to people decapitated in automobile accidents and found to have coronavirus antibodies in their system by means of tests already known to have a significant false positive rate–cause everyone to lose their minds and panic, running in circles and shrieking like terrified toddlers. Meanwhile, we react to news of 300,000 deaths per year in the US as direct results of obesity by shrugging and opening another bag of potato chips. As they say on the chans, doesn’t that activate your almonds?
This thing is using low-enriched uranium, meaning the reactor mass is going to be prohibitive.
One of my acquaintances at NASA Glenn, who has been an advocate of Nuclear Thermal Propulsion for years, was raging about a painful incoherent idiocracy-esque decision to take our stockpiles of enriched fuel for future NTP programs and down-mix it with U-238, wastefully destroying a national resource and sabotaging future NTP designs.
The stated reason for doing so is “proliferation risk”. IMO, if the worlds first space-pirates manage to hijack an NTP stage in orbit to steal its fuel for bomb material, they’ve earned it.
Unfortunately the public has no idea how reactors work. If you have to use low-enriched fuel, your critical mass must be on the order of tons. If you use highly enriched fuel, you can form a critical mass with only 10s of kg of fuel, something on the order of the size of a softball. For spacecraft propulsion, the dead-weight mass of the reactor is *important*.
The entire history of our malicious nuclear decisions in the name of “nonproliferation” and “proliferation risk” seem designed to keep nuclear weapons material out of the hands of the UNITED STATES military and government. The idea of foreign actors being impeded by these efforts would require some pretty outlandish heists.
Absolutely agree. The insistence for LEU is driven by State Department policy hacks. The D’s in the House were pushing for language in the 2020 Defense appropriations bill that would have directed the Navy to start down the path of limiting their reactors to LEU. HEU means smaller reactors with more operating hours between refuelings.
For those interested in such things, I can strongly recommend the hard-physics-based space warship (design) simulator, “Children of a Dead Earth”.
It’s a single-developer passion project, and the UI is only adequate, but it’s interesting for exploring spaceship design space even if you have no interest in the combat. And there’s certainly a consensus amongst the players there that using anything other than weapons-grade uranium for your reactors is for newbies… (well, OK, a giant RTG might be acceptable for a missile boat with a minimal crew and NTR thrusters.)
Well this is more promising than an upgraded version of the old NERVA rocket; maybe 900seconds specific impulse tops for said NERVA vs :
Howe Industries is investigating a Pulsed Plasma Rocket system that can produce 20,000 lbs of thrust with an Isp of 5,000 seconds. The Pulsed Plasma Rocket (PPR) is smaller, less complex, and more affordable.
The whole point of nuclear thermal is that the heat rejection of the thermodynamic cycle is in the reaction mass coming out of the rocket nozzle. The second someone wants a laser or an electromagnet, you require a power source that needs to radiatively reject its heat. A big clunky Stefan-Boltzmann space radiator.
But to explore the Solar System beyond Mars, you are probably forced to go to nuclear-electric propulsion. The radiator problem then needs an out-of-the-box solution like those shower or pellet radiators.
Well, that combines so many highly-violent things into one system that I’ll have to contemplate it for quite some time to remotely understand it.
My initial take is that they’re using a super high energy liquid repeating rail gun to fire a nuke down a barrel – that is also perhaps a nuke, and using a laser-triggered neutron pulse stream to detonate the atomic bullet as it goes down the barrel, heating it to such a ridiculous degree that the result should just be measured by the exponent of the Kelvin temperature. And then it’s expanded through a magnetic nozzle.
But I see one fatal flaw in the design concept, and it’s a biggie.
Transit times of 3 months to Mars with a water shielded ship are enabled with a single SLS launch.
Even if it works, that means they’ll probably never need to build more than one of them. ^_^
Once Starship is operational (rather than when and if), it would be worthwhile for someone or somethng to fund a monolithic nuclear-electric propulsion module at its maximum payload (100+ tons). Such a thing (fueled reactor plus thrusters) would be worth enough using an expendable Starkicker upper stage would probably be cost effective. Then you could combine them as needed. Think an extended mission NautilusX for starters.
If I were the grant-funding Godfather for this, I would support work on advanced-concept space radiators.
If one has a good way to reject heat in space for the thermodynamics cycle making electricity, any number of high specific impulse propulsion systems would benefit.
This might be the space travel analog of the old war maxim “Amateurs worry about tactics, professionals worry about logistics”; “Amateurs worry about thrusters, professionals worry about radiators.”
I don’t see that Nuclear Thermal Propulsion has great advantage.
The hard part of going to Mars, is leaving Earth and Nuclear Thermal Propulsion doesn’t get you off Earth.
To make leaving Earth easier, you go to LEO. And leaving from LEO is about 1/2 of delta-v of getting to LEO.
It seems if using Nuclear Thermal Propulsion, you going to go the LEO and then go to Mars. One might argue you don’t need to stage from LEO- though since have launch radioactive material, it seems that this argues against doing that.
I tend to think one stage from high earth orbit, to go to Mars quickly and staging from High earth orbit, provides about + 3 delta-v advantage vs staging from LEO. It costs more rocket power to get to high earth.
One argue that you use the Nuclear Thermal Propulsion to ferry from LEO to a high earth orbit, and leave from high earth orbit to get to Mars.
But seems to me that from high earth orbit, it’s better to use a chemical rocket. Or from High earth, you return a low perigee, quickly accelerate when there and get the Oberth effect.
So with Nuclear Thermal Propulsion the general “plan” is to stage in LEO and as compared to high Earth orbit, that starting from a -3 km/sec to delta-v. Also with Nuclear Thermal Propulsion you not expending all propellent at Low earth orbit, and so have less Oberth effect.
It seems how you get to Mars in 3 month or less, is you travel a shorter distance to Mars. A hohmann transfer is the most efficient in terms of delta-v to Mars, but it’s also a long distance to get to Mars.
So getting to mars from Earth in less 8 months in not a hohmann transfer. Getting to Mars in say 7 month is something similar to hohmann transfer + a patched conic.
And getting to Mars in 3 month or less is NOT similar to hohmann transfer though could something which is like a patched conic.
Or in terms delta-v used it’s not efficient like Hohmann transfer- but travels a shorter distance. It’s efficient in terms shorter distance traveled and thereby less time to get to Mars.
It’s not clear to me, how a Nuclear Thermal Propulsion gets to Mars in 3 months or less. But one could have hohmann solar escape trajectory which could intercept Mars and then use the Nuclear Thermal Propulsion to do something “like a patched conic” so one enter Mars orbit {rather than zoom by it at large difference in velocity]. And that seems like bad idea, but one might call it an option.
The other way could just head towards Mars. We call this the Starship Enterprise way going somewhere and you using the rocket thrust a long time- hours maybe days. And not vaguely like hohmann transfer. It’s sort of spiraling out like with ion engines.
But like Ion rockets {which don’t hohmann transfers] it’s inefficient like how Ion rockets {though have great rocket thrust velocities] are inefficient trajectories. It’s inefficient because constantly changing vector.
Now if using chemical rockets to get to Mars in 3 months or less, I would change to vector at one time {within 15 mins of time} now maybe Nuclear Thermal Propulsion rocket is likewise changing the vector at one time {but within an hour or so??}.
It does not seem like you want to send cargo to Mars fast- because it’s inefficient, instead you want to send the crew to Mars fast.
So other than using Nuclear Thermal Propulsion rocket as tug ferrying stuff from LEO to high orbit and sending crew fast somewhere, there not not use for it.
And probably only party who use them would be NASA and Military. So high cost to build and high cost to operate. Cost plus and vast stupidity and corruption
The reason why we want to build nuclear thermal stages is because interplanetary space travel is juuust barely possible with chemical rockets if you want to do one-way trips. If you want to build an orbit-to-orbit vehicle that can make a round-trip, you’re going to want something better than 350 sec Isp. Either you need a lot of stages, like Werner von Braun, or you need some sort of low MM nuclear-thermal or solar-thermal hydrogen stage. (Or you need an extremely high specific power reactor and a giant radiator sail for some sort of nuclear-electric, probably for cargo transfer.)
Elon Musk has juuust enough propellant to get his vehicle out of orbit and onto an Earth-Mars transfer ellipse, then his ship is *out of gas*. At that point, their crew depends on aerobraking in Mars’s atmosphere – they can’t go into orbit (they’d sail past if they missed) and scope out the situation, they can’t control when they hit.
Orbit may be “halfway to anywhere” but it’s only halfway, and that’s only for a one-way trip.
Earth escape is something like 3.2 km/sec
(that doesn’t get you to mars – it just gets you into a free solar orbit near earth.)
Getting onto an earth-mars transfer ellipse and getting off again at mars is something like 6 km/sec
Entering Mars’s orbit from infinity is something like 1.4 km/sec
That’s 10 km/sec one way. A two way orbit-to-orbit Mars mission for a mothership that has time to stop, drop off satellites, and check things out before a landing attempt is a ~20 km/sec delta-V mission.
If can’t make rocket fuel in space {such with the Moon} the only of value related to space, is using Earth orbits for satellites.
Or The End of the Space Age is correct. https://space.nss.org/the-end-of-the-space-age/
“Elon Musk has juuust enough propellant to get his vehicle out of orbit and onto an Earth-Mars transfer ellipse, then his ship is *out of gas*. ”
Idea of starship is to re-fuel in LEO. Once refueled the Starship can {or is planned} land 100 passengers on Mars surface.
If instead re-fuel starship in Earth high orbit, it might be able to send say 4 crew to Mars surface in 3 months.
The deal with nuclear/solar electric propulsion is that you have a much wider “launch window” and more flexibility in what sort of trajectories you can take. Figuring out what trajectories get you to your target requires some nonlinear-optimization – I wrote something to do this a while back.
True – you spend more delta-V on a low-thrust trajectory to get somewhere than an equivalent high-thrust trajectory. But it also doesn’t matter as much because your Isp can be 2000, 3000, 4000 sec as needed. (There is a tradeoff between thrust and Isp at a given power level.) You can actually perform much higher delta-V missions with only ~50%ish propellant masses.
If you could manage 1mm/sec^2 acceleration at initial mass, you can be very maneuverable in terms of the interplanetary portions of flight. (This is very ambitious though.)
–True – you spend more delta-V on a low-thrust trajectory to get somewhere than an equivalent high-thrust trajectory. But it also doesn’t matter as much because your Isp can be 2000, 3000, 4000 sec as needed. (There is a tradeoff between thrust and Isp at a given power level.) You can actually perform much higher delta-V missions with only ~50%ish propellant masses.–
If stage in high earth {say, gateway} you use Ion rocket engine which get higher Isp. Oberth effect doesn’t work very well with low thrust- so wouldn’t return to low perigee. So orbit moon and go wherever. Coupled beamed energy, one might get to Mars in 3 months. But it seems you would ion engines to send cargo to Mars high orbits, and ion engine can then return to earth high orbit without re-fueling at Mars.
“The deal with nuclear/solar electric propulsion is that you have a much wider “launch window” and more flexibility in what sort of trajectories you can take. ”
I think main problem is lack of market for nuclear propulsion.
And NASA made choice paying for development of SLS.
Doing SLS was mistake, if NASA had done nuclear/solar electric propulsion, instead, we could wasting 20 billion on it rather than SLS.
We don’t need SLS, or nuclear/solar electric propulsion to explore the Moon and explore Mars.
I think NASA should work towards getting crew to Mars in less than 90 days. And I think chemical rockets can do this.
If NASA needs more launch windows to Mars, they establish infrastructure in Venus Orbit- that could be done at lower cost as compared developing spacecraft with nuclear/solar electric propulsion.
So I favor containing with SLS and ISS. But NASA will end SLS and ISS, then then maybe it do development of nuclear/solar electric propulsion.
Or maybe after NASA has explored Mars {to determine whether and where there could settlements on Mars- or if have settlement on Mars, there might a market for nuclear/solar electric propulsion- and if NASA want explore moons of Jupiter or Mercury, it could need nuclear/solar electric propulsion.
Having spacecraft with nuclear/solar electric propulsion does make Mars settlement more viable. Commercial lunar rocket production on the Moon, makes the Moon viable, and Mars settlements more viable. And that is what NASA should be focused on.
I was looking for delta-v of Nuclear Thermal Propulsion spacecraft. And I found “something”: http://www.stocktonastro.org/resources/Documents/October-2017-Presentation.pdf
Something says:
“Takeaway Message:
Investing in rocket engine technology
to increase Ve is worth every penny!”
I was not convinced, Anyhow, “There were plans at one time to mount a NERVA rocket to a Centaur Upper Stage.”
Delta Vmax: 9.9 km/s vs Delta Vmax: 14.9 km/s.
There wasn’t much details, and wondered about the fuel pump- how does it pump- cause it would have pump a lot H2 to match the thrust normal Centaur which mostly power by dense LOX:
6 kg LOX to 1 kg H2: LOX: 17,821 kg and LH2: 3,009 kg (14%)
So seems have pump about 6 times more H2 than that Centaur for similar thrust. Not that this is particular problem- I guess one uses the heated H2 gas to power it? What more interesting:
“What if we want to get to Mars even quicker still?
We could abandon elliptical transfers altogether and go for a hyperbolic transfer. This one is a 93-day round trip with 17-day stay at Mars.”
Madness. Why anyone go to Mars for 17 day stay?? And using enormous amount of delta-v:
“Earth departure delta-v: 25.3 km/sec
Earth departure flight path angle 30 degrees
Mars arrival delta-v: 29.31 km/sec
Total outbound transfer delta-v: 54.81 km/sec
Outbound transfer time: 33:29 days ” **
Obviously chemical rocket can’t do this, but then again doing it would be crazy.
But what happens if that don’t stop at Mars. I am not sure, but one could perhaps be leaving the solar system. But say one slows it down a bit, or it doesn’t leave the solar, where is it’s perihelion?
Or it doesn’t return to Earth distance as it’s perihelion, instead it’s perihelion somewhere near the Sun {if it not escaping the Sun}.
So with chemical rockets, would do something with around same
“Earth departure flight path angle 30 degrees” but if don’t stop at Mars, the perihelion would be at Venus distance. And if you didn’t stop at Venus, it would then, return to Mars distance.
Or would have Earth departure flight path angle, so matches a hohmann transfer from Venus to Mars when crosses Earth orbit distance from the Sun
If going from Venus to Mars one could do hohmann type trajectory and use patched conic transfer to get to Mars quicker than compared to simple hohmann transfer. Such hohmann transfer if don’t do patched conic, would travel beyond Mars distance, but it also returns to Venus.
So chemical rocket power from Earth have going further than Mars distance [but return to Venus distance at perihelion} and also do patched conic to get to Mars.
So hohmann from Venus to Mars, “Cosmic Train Schedule”:
0.5954 Years [217.321 days or about 7.2 months http://clowder.net/hop/railroad/VMa.htm
And hohmann and patched could reduce it about 5 months, and going from Venus, one would cross Earth distance in about 2 months. So from Earth, and matching that trajectory, it should take about 3 months to get from Earth to Mars using patched conic . And to make less 3 months, have flight pathway which return at perihelion closer to Sun than Venus distance.
Now if matched simple hohmann from Venus to Mars, it arrive at Mars at slower velocity, than a simple hohmann from Earth to Mars. Or one could say, patched conics work “better” when going from Venus to Mars {one has less velocity in which you are changing it’s vector].
Anyhow with these hyperbolic transfer which Nuclear Thermal Propulsion spacecraft use they spending as much {or more in above example] braking as gets closer Mars. And what talking about is adding velocity {and altering vector} as you get nearer Mars {with a patched conic}. And starting from high earth orbit, and rocket power delta-v added at perigee is around 8 km/sec, and 3-4 km/sec added could be from rocket stage which doesn’t leave Earth’s gravity well {a re-usable tug which uses it’s remaining rocket fuel to returns to high Earth orbit to re-fuel}.
So talking about using a lot rocket fuel {hundreds of tons}, but such faster travel times to Mars are just used for crew getting to Mars.
** https://kb.osu.edu/bitstream/handle/1811/87426/1/Justin_Clark_Undergraduate_Thesis.pdf
This indicate 60 day to Mars require a less 30 Km/sec delta-V
and doing a similar thing, I guess less 15 km/sec to leave and less 15 km to brake at Mars starting at Earth 400 by 400 km and ending at 250 by 33,813 km Mars orbit.
If was {as wild guess} say, 25 degree. Where would perihelion be if didn’t stop at Mars?
My concern as one of the commenters mentioned, is shielding the crew and the ISP gains exceeding lugging along the extra shielding and the other downsides.
Shielding would consist of the reaction mass tanks and and a radiation shield ‘shadowing’ the crew quarters. Note: shielding will be needed against solar flares anyway so why not plan on reorienting the engine and its shielding “sunwards” to protect the crew capsule?
My understanding of the issue is that solar flare type radiation ends up hitting the spacecraft from all directions. So you end up needing radiation shielding in all directions.
You can shield the crew module by placing it at a long distance from the propellant tank/reactor. That would be advantageous anyway, because you can then put the ship into an end-over-end tumble for artificial gravity. A long truss that can handle tension and whatever acceleration due to thrust would be sufficient, and can be pretty lightweight. This reduces the area of shielding you need in front of the reactor.
I suppose the best configuration:
Lander – Crew Quarters – Shielded “storm cellar” – Propellant tanks —– (long truss and plumbing) —- reactor/engines.
So the storm cellar can take advantage of the LH2 mass in the prop tanks.
In the mid-1980s, the Air Force Ballistic Missiles Office and TRW Ballistic Missiles Division (for which I worked) were engaged in the early phase of developing the Small Mobile ICBM. One day, we had a tech geek from Brookhaven come in to brief us on a single-stage SICBM concept using their pellet-bed fission reactor technology (what NASA has apparently re-invented). The pellet technology used multi-layer spherical pellets of U-235, carbon, zirconium carbide, and other materials, with varying material thicknesses, amounts of U-235, etc, distributed 3 dimensionally within the reactor chamber to optimize neutronics, and ensure close to 100% burnup by the end of action time. The propellant was to be liquid ammonia, serving as both reaction mass and moderator. It would have met the size and weight requirements of SICBM, with a single stage.
The pellets would contain the fission products indefinitely, no matter where they landed, allowing testing from any of the missile ranges. But someone in the Air Force objected that we couldn’t have missiles that emit radioactive products. The Brookhaven guy paused, flabbergasted, and finally said “You would use these in an environment where megatons worth of nuclear explosives are going off overhead, and you’re worried about a couple of milli-Curies of short-lived products are coming out of the nozzles?” That was about where the briefing ended.
In reality, I think the fact that it would have met the size and weight requirements of SICBM with a single stage was what killed it. That single stage would not have been built by Thiokol, Aerojet, or Hercules, each of which got a stage contract for SICBM.
Well, the Air Force officer may have made the right call when it comes to life cycle cost that include clean up. Just from conventional fuel, the toxic cleanup jobs at Huntsville means newly minted geologists can work there, handling cleanup, for life.
I would think test flights and engine tests would also be pretty problematic, especially as environmental standards kept tightening over time.
Hanford will never be finished and why would they when so many companies make a lot of money spinning their wheels?
The cleanup of conventional propellant sites is nightmarish. Aerojet Sacramento is so polluted that the site has a negative worth. The same was true of Norton AFB, the biggest EPA Superfund site of the 1990s – the main problem there was the Air Combat Camera facility, which disposed of its developing chemicals (including cyanides) by dumping them in the ground, and the MAC wings disposing of 100 octane leaded av gas in a similar fashion. (Norton also had a large number of nuke warhead bunkers, but they weren’t a problem.)
The fact that nuclear materials have ~1 million times the energy content of their chemical competitors means that the waste problem is actually 1 million times smaller. In fact, diverting the ~95% enriched uranium for a single nuclear submarine reactor would have provided enough fissile material for all of the development, flight proof, and operational SICBMs.
Again, the encapsulation of pellet-bed reactors is complete and permanent. Test vehicle reactors would sit on the sea floor forever, and never leak a pico-Curie of fission products.
It may have been an uphill battle to get the bonehead regulators to understand all of this, but the technical arguments of the environmental superiority of this technology was overwhelming.
100 octane leaded gasoline aviation fuel?
From which century?
I know about 100 “low lead” for general aviation aircraft, but WW-II combat aircraft used a highly leaded fuel of much higher octane than that.
short-lived & few milli-Curies
what’s not to understand here?
Interesting bit of history there. I wasn’t aware the idea of pebble bed reactors went back quite that far, but that is obviously what this new design is as well.
The fact that this new design would work using reprocessed civilian reactor fuel is also a major plus. Longstanding U.S. policy anent nuke fuel reprocessing is about as sensible as Democratic Party policy anent fracking. It would be good to see both buried face down with forked sticks up their nether regions during a second Trump administration.
Here’s hoping this new NTR concept finds some traction soon.
That sounds a bit like Zubrin’s nuclear salt water reactor. Dissolve fissile salts in water, at a very specific concentration, such that when the solution is pumped into a beryllium-lined chamber with a rocket nozzle at the bottom, a sustainable chain reaction takes place, blasting white-hot plasma out the rocket nozzle at about fifty kilometers per second. It’s an “atomic blast engine” just like something out of a Heinlein story from 1946. Mind the exhaust, which is a radioactive death ray. You probably shouldn’t run this engine within an atmosphere, or point the exhaust in the direction of inhabited planets.
If someone had had the idea seventy or eighty years ago, we’d have cities on Luna and Mars now, and prospectors in the asteroid belt. As a society we’re too PC, too effeminate, too cowardly, too squeamish about a bit of radiation and a bit of risk–look at the way all of Western Civilization are absolutely losing their minds about a virus that’s harmless and doesn’t even produce symptoms most of the time unless the patient is 80+ with multiple severe preexisting health conditions, and has less than a 1% fatality rate even for them.
In a nation where over two and a half million people die every year, fewer than ten thousand confirmed COVID19 deaths–as opposed to people decapitated in automobile accidents and found to have coronavirus antibodies in their system by means of tests already known to have a significant false positive rate–cause everyone to lose their minds and panic, running in circles and shrieking like terrified toddlers. Meanwhile, we react to news of 300,000 deaths per year in the US as direct results of obesity by shrugging and opening another bag of potato chips. As they say on the chans, doesn’t that activate your almonds?
This thing is using low-enriched uranium, meaning the reactor mass is going to be prohibitive.
One of my acquaintances at NASA Glenn, who has been an advocate of Nuclear Thermal Propulsion for years, was raging about a painful incoherent idiocracy-esque decision to take our stockpiles of enriched fuel for future NTP programs and down-mix it with U-238, wastefully destroying a national resource and sabotaging future NTP designs.
The stated reason for doing so is “proliferation risk”. IMO, if the worlds first space-pirates manage to hijack an NTP stage in orbit to steal its fuel for bomb material, they’ve earned it.
Unfortunately the public has no idea how reactors work. If you have to use low-enriched fuel, your critical mass must be on the order of tons. If you use highly enriched fuel, you can form a critical mass with only 10s of kg of fuel, something on the order of the size of a softball. For spacecraft propulsion, the dead-weight mass of the reactor is *important*.
The entire history of our malicious nuclear decisions in the name of “nonproliferation” and “proliferation risk” seem designed to keep nuclear weapons material out of the hands of the UNITED STATES military and government. The idea of foreign actors being impeded by these efforts would require some pretty outlandish heists.
Absolutely agree. The insistence for LEU is driven by State Department policy hacks. The D’s in the House were pushing for language in the 2020 Defense appropriations bill that would have directed the Navy to start down the path of limiting their reactors to LEU. HEU means smaller reactors with more operating hours between refuelings.
For those interested in such things, I can strongly recommend the hard-physics-based space warship (design) simulator, “Children of a Dead Earth”.
It’s a single-developer passion project, and the UI is only adequate, but it’s interesting for exploring spaceship design space even if you have no interest in the combat. And there’s certainly a consensus amongst the players there that using anything other than weapons-grade uranium for your reactors is for newbies… (well, OK, a giant RTG might be acceptable for a missile boat with a minimal crew and NTR thrusters.)
Well this is more promising than an upgraded version of the old NERVA rocket; maybe 900seconds specific impulse tops for said NERVA vs :
Howe Industries is investigating a Pulsed Plasma Rocket system that can produce 20,000 lbs of thrust with an Isp of 5,000 seconds. The Pulsed Plasma Rocket (PPR) is smaller, less complex, and more affordable.
https://www.nextbigfuture.com/2020/09/pulsed-plasma-rocket.html
The whole point of nuclear thermal is that the heat rejection of the thermodynamic cycle is in the reaction mass coming out of the rocket nozzle. The second someone wants a laser or an electromagnet, you require a power source that needs to radiatively reject its heat. A big clunky Stefan-Boltzmann space radiator.
But to explore the Solar System beyond Mars, you are probably forced to go to nuclear-electric propulsion. The radiator problem then needs an out-of-the-box solution like those shower or pellet radiators.
Well, that combines so many highly-violent things into one system that I’ll have to contemplate it for quite some time to remotely understand it.
My initial take is that they’re using a super high energy liquid repeating rail gun to fire a nuke down a barrel – that is also perhaps a nuke, and using a laser-triggered neutron pulse stream to detonate the atomic bullet as it goes down the barrel, heating it to such a ridiculous degree that the result should just be measured by the exponent of the Kelvin temperature. And then it’s expanded through a magnetic nozzle.
But I see one fatal flaw in the design concept, and it’s a biggie.
Even if it works, that means they’ll probably never need to build more than one of them. ^_^
Once Starship is operational (rather than when and if), it would be worthwhile for someone or somethng to fund a monolithic nuclear-electric propulsion module at its maximum payload (100+ tons). Such a thing (fueled reactor plus thrusters) would be worth enough using an expendable Starkicker upper stage would probably be cost effective. Then you could combine them as needed. Think an extended mission NautilusX for starters.
If I were the grant-funding Godfather for this, I would support work on advanced-concept space radiators.
If one has a good way to reject heat in space for the thermodynamics cycle making electricity, any number of high specific impulse propulsion systems would benefit.
This might be the space travel analog of the old war maxim “Amateurs worry about tactics, professionals worry about logistics”; “Amateurs worry about thrusters, professionals worry about radiators.”
I don’t see that Nuclear Thermal Propulsion has great advantage.
The hard part of going to Mars, is leaving Earth and Nuclear Thermal Propulsion doesn’t get you off Earth.
To make leaving Earth easier, you go to LEO. And leaving from LEO is about 1/2 of delta-v of getting to LEO.
It seems if using Nuclear Thermal Propulsion, you going to go the LEO and then go to Mars. One might argue you don’t need to stage from LEO- though since have launch radioactive material, it seems that this argues against doing that.
I tend to think one stage from high earth orbit, to go to Mars quickly and staging from High earth orbit, provides about + 3 delta-v advantage vs staging from LEO. It costs more rocket power to get to high earth.
One argue that you use the Nuclear Thermal Propulsion to ferry from LEO to a high earth orbit, and leave from high earth orbit to get to Mars.
But seems to me that from high earth orbit, it’s better to use a chemical rocket. Or from High earth, you return a low perigee, quickly accelerate when there and get the Oberth effect.
So with Nuclear Thermal Propulsion the general “plan” is to stage in LEO and as compared to high Earth orbit, that starting from a -3 km/sec to delta-v. Also with Nuclear Thermal Propulsion you not expending all propellent at Low earth orbit, and so have less Oberth effect.
It seems how you get to Mars in 3 month or less, is you travel a shorter distance to Mars. A hohmann transfer is the most efficient in terms of delta-v to Mars, but it’s also a long distance to get to Mars.
So getting to mars from Earth in less 8 months in not a hohmann transfer. Getting to Mars in say 7 month is something similar to hohmann transfer + a patched conic.
And getting to Mars in 3 month or less is NOT similar to hohmann transfer though could something which is like a patched conic.
Or in terms delta-v used it’s not efficient like Hohmann transfer- but travels a shorter distance. It’s efficient in terms shorter distance traveled and thereby less time to get to Mars.
It’s not clear to me, how a Nuclear Thermal Propulsion gets to Mars in 3 months or less. But one could have hohmann solar escape trajectory which could intercept Mars and then use the Nuclear Thermal Propulsion to do something “like a patched conic” so one enter Mars orbit {rather than zoom by it at large difference in velocity]. And that seems like bad idea, but one might call it an option.
The other way could just head towards Mars. We call this the Starship Enterprise way going somewhere and you using the rocket thrust a long time- hours maybe days. And not vaguely like hohmann transfer. It’s sort of spiraling out like with ion engines.
But like Ion rockets {which don’t hohmann transfers] it’s inefficient like how Ion rockets {though have great rocket thrust velocities] are inefficient trajectories. It’s inefficient because constantly changing vector.
Now if using chemical rockets to get to Mars in 3 months or less, I would change to vector at one time {within 15 mins of time} now maybe Nuclear Thermal Propulsion rocket is likewise changing the vector at one time {but within an hour or so??}.
It does not seem like you want to send cargo to Mars fast- because it’s inefficient, instead you want to send the crew to Mars fast.
So other than using Nuclear Thermal Propulsion rocket as tug ferrying stuff from LEO to high orbit and sending crew fast somewhere, there not not use for it.
And probably only party who use them would be NASA and Military. So high cost to build and high cost to operate. Cost plus and vast stupidity and corruption
The reason why we want to build nuclear thermal stages is because interplanetary space travel is juuust barely possible with chemical rockets if you want to do one-way trips. If you want to build an orbit-to-orbit vehicle that can make a round-trip, you’re going to want something better than 350 sec Isp. Either you need a lot of stages, like Werner von Braun, or you need some sort of low MM nuclear-thermal or solar-thermal hydrogen stage. (Or you need an extremely high specific power reactor and a giant radiator sail for some sort of nuclear-electric, probably for cargo transfer.)
Elon Musk has juuust enough propellant to get his vehicle out of orbit and onto an Earth-Mars transfer ellipse, then his ship is *out of gas*. At that point, their crew depends on aerobraking in Mars’s atmosphere – they can’t go into orbit (they’d sail past if they missed) and scope out the situation, they can’t control when they hit.
Orbit may be “halfway to anywhere” but it’s only halfway, and that’s only for a one-way trip.
Earth escape is something like 3.2 km/sec
(that doesn’t get you to mars – it just gets you into a free solar orbit near earth.)
Getting onto an earth-mars transfer ellipse and getting off again at mars is something like 6 km/sec
Entering Mars’s orbit from infinity is something like 1.4 km/sec
That’s 10 km/sec one way. A two way orbit-to-orbit Mars mission for a mothership that has time to stop, drop off satellites, and check things out before a landing attempt is a ~20 km/sec delta-V mission.
If can’t make rocket fuel in space {such with the Moon} the only of value related to space, is using Earth orbits for satellites.
Or The End of the Space Age is correct.
https://space.nss.org/the-end-of-the-space-age/
“Elon Musk has juuust enough propellant to get his vehicle out of orbit and onto an Earth-Mars transfer ellipse, then his ship is *out of gas*. ”
Idea of starship is to re-fuel in LEO. Once refueled the Starship can {or is planned} land 100 passengers on Mars surface.
If instead re-fuel starship in Earth high orbit, it might be able to send say 4 crew to Mars surface in 3 months.
The deal with nuclear/solar electric propulsion is that you have a much wider “launch window” and more flexibility in what sort of trajectories you can take. Figuring out what trajectories get you to your target requires some nonlinear-optimization – I wrote something to do this a while back.
True – you spend more delta-V on a low-thrust trajectory to get somewhere than an equivalent high-thrust trajectory. But it also doesn’t matter as much because your Isp can be 2000, 3000, 4000 sec as needed. (There is a tradeoff between thrust and Isp at a given power level.) You can actually perform much higher delta-V missions with only ~50%ish propellant masses.
If you could manage 1mm/sec^2 acceleration at initial mass, you can be very maneuverable in terms of the interplanetary portions of flight. (This is very ambitious though.)
This is something I wrote about low-thrust optimization a while back:
https://www.amssolarempire.com/Programs/projectnavigator.html
–True – you spend more delta-V on a low-thrust trajectory to get somewhere than an equivalent high-thrust trajectory. But it also doesn’t matter as much because your Isp can be 2000, 3000, 4000 sec as needed. (There is a tradeoff between thrust and Isp at a given power level.) You can actually perform much higher delta-V missions with only ~50%ish propellant masses.–
If stage in high earth {say, gateway} you use Ion rocket engine which get higher Isp. Oberth effect doesn’t work very well with low thrust- so wouldn’t return to low perigee. So orbit moon and go wherever. Coupled beamed energy, one might get to Mars in 3 months. But it seems you would ion engines to send cargo to Mars high orbits, and ion engine can then return to earth high orbit without re-fueling at Mars.
“The deal with nuclear/solar electric propulsion is that you have a much wider “launch window” and more flexibility in what sort of trajectories you can take. ”
I think main problem is lack of market for nuclear propulsion.
And NASA made choice paying for development of SLS.
Doing SLS was mistake, if NASA had done nuclear/solar electric propulsion, instead, we could wasting 20 billion on it rather than SLS.
We don’t need SLS, or nuclear/solar electric propulsion to explore the Moon and explore Mars.
I think NASA should work towards getting crew to Mars in less than 90 days. And I think chemical rockets can do this.
If NASA needs more launch windows to Mars, they establish infrastructure in Venus Orbit- that could be done at lower cost as compared developing spacecraft with nuclear/solar electric propulsion.
So I favor containing with SLS and ISS. But NASA will end SLS and ISS, then then maybe it do development of nuclear/solar electric propulsion.
Or maybe after NASA has explored Mars {to determine whether and where there could settlements on Mars- or if have settlement on Mars, there might a market for nuclear/solar electric propulsion- and if NASA want explore moons of Jupiter or Mercury, it could need nuclear/solar electric propulsion.
Having spacecraft with nuclear/solar electric propulsion does make Mars settlement more viable. Commercial lunar rocket production on the Moon, makes the Moon viable, and Mars settlements more viable. And that is what NASA should be focused on.
I was looking for delta-v of Nuclear Thermal Propulsion spacecraft. And I found “something”:
http://www.stocktonastro.org/resources/Documents/October-2017-Presentation.pdf
Something says:
“Takeaway Message:
Investing in rocket engine technology
to increase Ve is worth every penny!”
I was not convinced, Anyhow, “There were plans at one time to mount a NERVA rocket to a Centaur Upper Stage.”
Delta Vmax: 9.9 km/s vs Delta Vmax: 14.9 km/s.
There wasn’t much details, and wondered about the fuel pump- how does it pump- cause it would have pump a lot H2 to match the thrust normal Centaur which mostly power by dense LOX:
6 kg LOX to 1 kg H2: LOX: 17,821 kg and LH2: 3,009 kg (14%)
So seems have pump about 6 times more H2 than that Centaur for similar thrust. Not that this is particular problem- I guess one uses the heated H2 gas to power it? What more interesting:
“What if we want to get to Mars even quicker still?
We could abandon elliptical transfers altogether and go for a hyperbolic transfer. This one is a 93-day round trip with 17-day stay at Mars.”
Madness. Why anyone go to Mars for 17 day stay?? And using enormous amount of delta-v:
“Earth departure delta-v: 25.3 km/sec
Earth departure flight path angle 30 degrees
Mars arrival delta-v: 29.31 km/sec
Total outbound transfer delta-v: 54.81 km/sec
Outbound transfer time: 33:29 days ” **
Obviously chemical rocket can’t do this, but then again doing it would be crazy.
But what happens if that don’t stop at Mars. I am not sure, but one could perhaps be leaving the solar system. But say one slows it down a bit, or it doesn’t leave the solar, where is it’s perihelion?
Or it doesn’t return to Earth distance as it’s perihelion, instead it’s perihelion somewhere near the Sun {if it not escaping the Sun}.
So with chemical rockets, would do something with around same
“Earth departure flight path angle 30 degrees” but if don’t stop at Mars, the perihelion would be at Venus distance. And if you didn’t stop at Venus, it would then, return to Mars distance.
Or would have Earth departure flight path angle, so matches a hohmann transfer from Venus to Mars when crosses Earth orbit distance from the Sun
If going from Venus to Mars one could do hohmann type trajectory and use patched conic transfer to get to Mars quicker than compared to simple hohmann transfer. Such hohmann transfer if don’t do patched conic, would travel beyond Mars distance, but it also returns to Venus.
So chemical rocket power from Earth have going further than Mars distance [but return to Venus distance at perihelion} and also do patched conic to get to Mars.
So hohmann from Venus to Mars, “Cosmic Train Schedule”:
0.5954 Years [217.321 days or about 7.2 months
http://clowder.net/hop/railroad/VMa.htm
And hohmann and patched could reduce it about 5 months, and going from Venus, one would cross Earth distance in about 2 months. So from Earth, and matching that trajectory, it should take about 3 months to get from Earth to Mars using patched conic . And to make less 3 months, have flight pathway which return at perihelion closer to Sun than Venus distance.
Now if matched simple hohmann from Venus to Mars, it arrive at Mars at slower velocity, than a simple hohmann from Earth to Mars. Or one could say, patched conics work “better” when going from Venus to Mars {one has less velocity in which you are changing it’s vector].
Anyhow with these hyperbolic transfer which Nuclear Thermal Propulsion spacecraft use they spending as much {or more in above example] braking as gets closer Mars. And what talking about is adding velocity {and altering vector} as you get nearer Mars {with a patched conic}. And starting from high earth orbit, and rocket power delta-v added at perigee is around 8 km/sec, and 3-4 km/sec added could be from rocket stage which doesn’t leave Earth’s gravity well {a re-usable tug which uses it’s remaining rocket fuel to returns to high Earth orbit to re-fuel}.
So talking about using a lot rocket fuel {hundreds of tons}, but such faster travel times to Mars are just used for crew getting to Mars.
** https://kb.osu.edu/bitstream/handle/1811/87426/1/Justin_Clark_Undergraduate_Thesis.pdf
This indicate 60 day to Mars require a less 30 Km/sec delta-V
and doing a similar thing, I guess less 15 km/sec to leave and less 15 km to brake at Mars starting at Earth 400 by 400 km and ending at 250 by 33,813 km Mars orbit.
If was {as wild guess} say, 25 degree. Where would perihelion be if didn’t stop at Mars?