The project, in concert with US government agency DARPA, aims to develop pioneering propulsion system for space travel as soon as 2027:
The project is intended to develop a pioneering propulsion system for space travel far different from the chemical systems prevalent since the modern era of rocketry dawned almost a century ago.
"Using a nuclear thermal rocket allows for faster transit time, reducing risk for astronauts," Nasa said in a press release.
[...] Using current technology, Nasa says, the 300m-mile journey to Mars would take about seven months. Engineers do not yet know how much time could be shaved off using nuclear technology, but Bill Nelson, the Nasa administrator, said it would allow spacecraft, and humans, to travel in deep space at record speed.
[...] Using low thrust efficiently, nuclear electric propulsion systems accelerate spacecraft for extended periods and can propel a Mars mission for a fraction of the propellant of high-thrust systems.
Also at CNN and Engadget. Link to Nasa press release.
(Score: 3, Informative) by takyon on Friday January 27 2023, @09:26AM
I don't see it becoming more relevant than in-orbit refueling/refilling in the 2030s. They are going to be very cautious with this demonstrator, which will be orbiting Earth for at least 300 years, by the way.
https://spacepolicyonline.com/news/nasa-darpa-plan-nuclear-thermal-propulsion-demo-in-2027/ [spacepolicyonline.com]
[SIG] 10/28/2017: Soylent Upgrade v14 [soylentnews.org]
(Score: 4, Interesting) by Rich on Friday January 27 2023, @09:55AM (6 children)
I discovered a new abbreviation by following through: "HALEU", which stands for "High-Assay Low Enriched Uranium", which is a weird way to say "5-20% enrichment". The Mars story is bullshit, Musk would be Emperor of Mars before they even have spaceship for their engine, and I suspect this is a means to funnel money into establishing a supply for that, because the "20 exciting startups developing small reactors" figured out they'd need more power per mass and less refueling cycles to even have a chance to be competitive.
But while this "HALEU" stuff might be a win-win for the startups and the military with their HEU reprocessing, and might be useful in space, it's not sustainable for the "20 startups". U-235 is a rather limited natural resource and they should be looking at plutonium fuel if they really mean to provide a somewhat sustainable concept. (Not that I personally think they could ever come close to renewables if they factor in long term safe waste storage, with an emphasis on safe).
(Score: 2) by gawdonblue on Friday January 27 2023, @10:07AM (5 children)
There's another new abbreviation: the m-mile.
With Mars being just 300 of them, should not take long to get there :)
(Score: 1) by BlueCoffee on Friday January 27 2023, @01:35PM (3 children)
The meter-mile? Is that metric or Imperial? :)
At least they stopped using the silly "a thousand-million" for billion, and "a thousand-thousand" for a million. Those were annoying popular AFYA.
(Score: 2) by Immerman on Friday January 27 2023, @03:05PM (2 children)
Is that a short-scale billion (10^9) or a long-scale billion (10^12)? Yeah, we've (mostly) laid the long scale to rest, thankfully.
(Score: 2) by maxwell demon on Saturday January 28 2023, @08:06AM (1 child)
Thankfully? Most of the world uses the long scale. You are the odd one out.
The Tao of math: The numbers you can count are not the real numbers.
(Score: 2) by Immerman on Saturday January 28 2023, @06:00PM
Have I been misinformed?
In that case I'm 100% in favor of thousand million and million million.
(Score: 2) by Rich on Friday January 27 2023, @05:56PM
Wouldn't a (small) m-mile be more like roughly 5 ft 3 23/64 in?
(Score: 1) by Runaway1956 on Friday January 27 2023, @10:39AM (9 children)
No matter the source of energy, the ships need reaction mass. TFA mentions that the nuclear rocket will use a fraction of the reaction mass that conventional rockets use, but doesn't offer details. Then TFA devolved into a personal attack on Musk, and I stopped reading. I'm suspicious that these rockets are so much vaporware.
(Score: 1, Disagree) by Anonymous Coward on Friday January 27 2023, @10:50AM (4 children)
(Score: 2, Informative) by Anonymous Coward on Friday January 27 2023, @01:37PM (2 children)
Acceleration is related to the change in momentum, which goes as the velocity of the ejecta, not the velocity squared.
(Score: 2) by HiThere on Friday January 27 2023, @02:28PM (1 child)
True, it's velocity that is related to the square of the speed of the ejecta. It's still a quite significant difference. (OK, momentum too. But for figuring transit time velocity is the relevant one.)
I'm not quite clear on the limitations of the "nuclear-electric rocket" that they're proposing, though. My first guess was some fancy development of the ion-rocket, in which case it could run for a long time, but wouldn't produce that much thrust. However if they're ejecting reactor mass, you likely wouldn't want to use it where the exhaust could enter an atmosphere.
Javascript is what you use to allow unknown third parties to run software you have no idea about on your computer.
(Score: 2) by crafoo on Friday January 27 2023, @02:50PM
well, the nuclear rocket project was pretty cool, but yeah I think it was a vacuum engine not designed for atmosphere use. https://www1.grc.nasa.gov/historic-facilities/rockets-systems-area/7911-2/ [nasa.gov]
Pretty sure this new project is something new, but we have tried to use nuclear power for rockets and we even prototyped it out many decades ago.
(Score: 1, Informative) by Anonymous Coward on Friday January 27 2023, @09:10PM
No it isn't. Momentum is linear. Kinetic energy is squared.
The relevant factor that makes this sort of nuclear rocket useful is that the exhaust velocity is determined by both the temperature of the exhaust and inversely by the molecular mass. H2 - O2 rockets are currently the best and they have an exhaust molecular mass of 18, giving a maximum Isp of about 420 before they melt the engine. Nuclear rockets can just heat up hydrogen and that has a mass of 2.
The NERVA rocket they developed back in the sixties and seventies had a tested Isp of 840 and was expected to reach about 1200 with further development.
https://en.wikipedia.org/wiki/NERVA [wikipedia.org]
(Score: 5, Interesting) by Immerman on Friday January 27 2023, @03:20PM (3 children)
Probably because the details are entirely context-dependent, the rocket equation is sort of messy.
As a rule, nuclear-thermal rockets to date have a specific impulse (Isp) in the 500-1000 second range, compared to the 250-400 seconds of chemical rockets. So probably safe to assume about twice the specific impulse. To put that in context the massive increase in engineering complexity for the Raptor full-flow staged combustion engine design gained, as I recall, less than a 10% increase, and that's considered a dramatic improvement.
The rocket equation is
delta_v = g*Isp*ln(m_initial/m_final)
or
m_initial/m_final = e^(delta_V/(g*Isp))
So twice the Isp means twice the delta-V from a given amount of propellant, but you don't usually care about "what will this get me?", you want to know "what do I need to get this?", and the change in propellant needed for the same delta-V depends entirely on where you started on the exponential curve.
(Score: 2) by Immerman on Friday January 27 2023, @03:36PM (2 children)
As a sample comparison, to get the ~11km/s delta-V to escape from Earth's surface into interplanetary space is
mi/mf @ 380seconds Isp (=SpaceX Raptor) = 19
mi/mf @ 800seconds Isp (some nuclear engine) = 4
So roughly a 5x reduction in propellant mass needed
On the other hand, I believe to get between LEO and Mars is closer to 4km/s, in which case the difference is
mi/mf @ 380seconds Isp (=SpaceX Raptor) = 2.9
mi/mf @ 800seconds Isp (some nuclear engine) = 1.7
Much less dramatic. However that's the minimum delta-V required - in practice the whole point is to get there faster, which means a bunch more delta-V added symmetrically at both ends (speeding up then slowing down)... and I suppose "what will this get me" really is the key question.
(Score: 2) by mcgrew on Saturday January 28 2023, @08:08PM (1 child)
Directly from Earth? Not likely! It would take off from Earth with a chemical rocket as its first stage. Once it's in space it can spew all the radioactivity it can, which is the very reason for using nukes in the first place, to have them in the gamma ray machine that is outer space in as short a time as possible.
You still have to do a hell of a lot more than just get there to be in any way useful.
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(Score: 2) by Immerman on Saturday January 28 2023, @09:38PM
I certainly hope so! I just grabbed a couple of the delta-V's I could recall offhand to demonstrate how the benefit is highly delta-V dependent
Though if I recall correctly some of the NTR designs should theoretically be safe for use in the atmosphere...so long as nothing goes wrong...
(Score: 3, Funny) by Anonymous Coward on Friday January 27 2023, @01:40PM (1 child)
If we use these thrusters, we'll fly astronauts to Mars faster than we've ever flown astronauts there!
(Score: 0) by Anonymous Coward on Friday January 27 2023, @09:12PM
They'll be able to fake Moon landings so much faster.
(Score: 5, Interesting) by VLM on Friday January 27 2023, @01:49PM (2 children)
http://orbit.medphys.ucl.ac.uk/ [ucl.ac.uk]
As per Orbiter game from the turn of the century, orbital mechanics is non-trivial and for various safety reasons they'll want a non-return orbit such that if the thrusters cut out at any point in the mission the craft won't impact the earth. Ironically the human safety people will want the opposite so if the main engine cuts out they can use the RCS thrusters to line up a re-entry so the crew doesn't end up lost in space.
The meta argument about this is its a waste of chemical fuel to haul supplies and too dangerous to use nuclear fuel to haul people, which means you'll "have to" have a much more complicated mission profile. And those usually don't have much of a time limit. So the engineers are confused about "how long it will take" because it'll probably haul something the size of the ISS to Mars "eventually" rather than breaking speed records with humans on board.
Then again, who knows what they'll end up doing.
(Score: 4, Informative) by Immerman on Friday January 27 2023, @03:55PM
Keep in mind that the primary use-case for nuclear engines is interplanetary flights: Where a safe return trajectory is not an option[1], and the desire for more speed is almost entirely because space radiation and microgravity are both slowly killing and crippling your passengers the entire time they're in transit.
We're going to be putting these on passenger craft just as soon as we're sure they're reliable - there's no reason not to.
They'll also be nice for more cheaply getting big payloads there "eventually", but the high-efficiency Hohmann Transfer Orbit route is locked at... I think it's around 9 months between Earth and Mars, regardless of engine type used.
[1] there's no trajectory between Earth and Mars that, if the "arrrival burn" at the other planet fails, will pass anywhere close to either planet again for a few years. At which point it's probably far to late to rescue anyone. And a fast trajectory will be even worse - it could be decades before it approaches either planet again.
It's easy for the moon, since any transfer orbit that's not stopped in lunar orbit is still in Earth orbit and will immediately loop back to Earth. But for interplanetary flights a "miss" will remain in orbit around the sun, with an orbital period that doesn't coincide with either Earth or Mars, so when it next passes either of the planet's orbits, the planets themselves will be nowhere remotely nearby.
(Score: 3, Informative) by Immerman on Friday January 27 2023, @04:03PM
Oh, and as for the danger of nuclear fuel in a spaceship... it doesn't really exist.
You're already flying through a radioactive hellscape filled with far higher energy cosmic rays
It's easy to shield the reactor from the passenger compartment by putting your water tanks between them - every ~7cm of water halves the radiation levels, and it's not going to take much to bring the reactor-sourced radiation down below the ambient background radiation of interplanetary space.
Finally, nuclear fuel isn't substantially radioactive (if it were it wouldn't still exist after 4.5 billion years in the ground), only the nuclear waste and the reactor itself are. So launching fuel into orbit is a non-issue - way less dangerous than launching a probe/rover with a standard RTG into orbit, which *is* highly radioative within its protective casing.