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The US military is getting serious about nuclear thermal propulsion:
[...] the US Defense Advanced Research Projects Agency announced its intent to have a flyable nuclear thermal propulsion system ready for a demonstration in 2025.
Through this Demonstration Rocket for Agile Cislunar Operations, or DRACO program, the defense agency seeks technology that will allow for more responsive control of spacecraft in Earth orbit, lunar orbit, and everywhere in between, giving the military greater operational freedom in these domains.
"Activity in cislunar space is expected to increase considerably in the coming years," Tabatha Thompson, a DARPA spokeswoman, told Ars. "An agile nuclear thermal propulsion vehicle enables the DOD to maintain Space Domain Awareness of the burgeoning activity within this vast volume."
In "Phase 1" of its solicitation, DARPA has asked industry for the designs of both a nuclear thermal reactor and an operational spacecraft upon which to demonstrate it. This initial phase of the program is to last 18 months. Subsequent phases will lead to detailed design, fabrication, ground tests, and an in-space demonstration. No contracts have yet been awarded, and award values will be determined by industry submissions.
The propulsion system is thought to make travel around the Solar System quicker.
(Score: 1, Funny) by Anonymous Coward on Tuesday June 16 2020, @01:43AM (23 children)
Flying military vehicles filled with plutonium. That sounds delightful!
(Score: 3, Touché) by Hartree on Tuesday June 16 2020, @01:58AM (14 children)
"Flying military vehicles filled with plutonium. That sounds delightful!"
We already have them. They're called B-52, B-2 and B-1 strategic bombers. A number of other countries have similar ones too.
(Score: 2) by JoeMerchant on Tuesday June 16 2020, @02:08AM (13 children)
Yes, but plutonium piles operating in cislunar space, virtually untouchable, and available to crash and boom anywhere on Earth from a difficult to detect or intercept approach vector.
🌻🌻 [google.com]
(Score: 4, Interesting) by Kitsune008 on Tuesday June 16 2020, @03:23AM (12 children)
Forget plutonium piles, wait until they resurrect Project Orion, and implement it.
Hundreds of nukes on board, able to be jettisoned to intercept any Earth target at will, and able to maneuver at will.(at least within the confines of known physics, try Kerbal Space Program...orbital mechanics rule)
To paraphrase a half forgotten quote: 'He who controls the orbitals, controls that planet', or something like that.
Bonus: setting off nukes under your ass will release EMP bursts, which may interfere with any targeting or precise tracking.(precise in the context of being able to hit you with something vs having to rely on SWAGs[Scientific Wild Assed Guesses] to maybe hit you)
(Score: 2) by JoeMerchant on Tuesday June 16 2020, @11:34AM (11 children)
Plutonium is a fissile bomb, you just need critical mass and a detonator to assemble it.
Don't tell me that they'll let international inspections confirm the absence of warhead configurations on the craft - things like these have already been released from the X37B.
🌻🌻 [google.com]
(Score: 3, Interesting) by Immerman on Tuesday June 16 2020, @04:09PM (5 children)
Plutonium is NOT a fissile bomb. You can *make* a bomb out of it, but it's a very different process than making a thermal reactor out of it (a reactor may melt down, but it's unlikely to explode)
A nuclear thermal rocket could make a nasty radioactive mess if it crashed (after operating for a long time - the plutonium itself isn't especially radioactive, it's the fission products that are really nasty), but if you want a greater-than-kinetic-impact "boom" then you need to *also* have a warhead on board. And if you have a warhead on board, it doesn't really matter if your rocket is nuclear or not.
(Score: 2) by JoeMerchant on Tuesday June 16 2020, @04:51PM (4 children)
Point being: if they're already launching a plutonium thermal reactor, who's to know if there's also another 11kg of Pu239 onboard (in warhead configuration) for "contingent mission purposes"?
🌻🌻 [google.com]
(Score: 2) by Immerman on Tuesday June 16 2020, @04:59PM (3 children)
Why would you think having a plutonium-fueled rocket would make that any more likely than with a chemically fueled rocket? There could be warheads launched as part of every Starlink launch, do you think anyone inspects them to make sure there's not? You think the US military lets anyone else inspect the payload for any of those "national security" launches?
If anything, *admitting* that you have a nuclear payload on board is going to increase scrutiny, so you'd specifically avoid doing so if you wanted to sneak nuclear weapons into orbit.
(Score: 3, Insightful) by JoeMerchant on Tuesday June 16 2020, @10:52PM (2 children)
I'm not sure what monitoring potential is like in LEO/NEO... if you drive down the road with a medical imaging isotope in you, there's a fair chance that you'll trip domestic terror sensors and have a nice chat with some gentlemen in dark suits. If a satellite or rocket that was supposed to be purely chemical started lighting up somebody's Geiger counter - that would be telling.
But, if the thing is supposed to be loaded with Plutonium anyway, even in the event of a failed launch and self-destruct, simply finding scattered Plutonium isn't going to give away the game - and with no ability to verify, you put "the other side" in the position of assuming the worst.
🌻🌻 [google.com]
(Score: 2) by Immerman on Wednesday June 17 2020, @04:28PM (1 child)
Considering that we're talking about military hardware,exactly who's not-in-the-loop geiger counter do you imagine would be allowed anywhere remotely close enough to detect anything?
And once you're in space, everything is so radioactive that it'd be pretty much impossible to detect anything anyway - especially within a few seconds from many miles away, which is about as close as you're going to get without broadcasting that you're intentionally snooping on foreign military hardware.
Treaties be damned, we almost certainly already have nukes in space, as do the Russians, and quite possibly the Chinese as well. Not to mention all the radiothermal generators for which Plutonium is one of the more attractive fuels (admittedly Pu238 rather than the fissile 239 or 240).
Basically, there's no need for a military to go out of its way to "hide" orbital nukes - as long as they don't tell anyone about them, they're invisible.
(Score: 3, Insightful) by JoeMerchant on Wednesday June 17 2020, @07:01PM
As NASA has demonstrated with the Space Shuttle, you never know what farmer's field pieces will be raining down on.
🌻🌻 [google.com]
(Score: 2) by turgid on Thursday June 18 2020, @10:41AM (4 children)
What has already been released from the X37B?
I refuse to engage in a battle of wits with an unarmed opponent [wikipedia.org].
(Score: 1, Funny) by Anonymous Coward on Thursday June 18 2020, @10:55AM
That's classified. In other news, black helicopters have been dispatched to JoeMerchant's location.
(Score: 2) by JoeMerchant on Thursday June 18 2020, @11:35AM (2 children)
Things - things that go places, carrying classified cargoes. Probably not including 11kg of Pu239 (or anything else that would set off a geiger counter), yet, we would hope.
🌻🌻 [google.com]
(Score: 2) by turgid on Thursday June 18 2020, @01:10PM (1 child)
Oh, I see. It's definitely not used to, for example, keep something very nasty in orbit which can be de-orbited anywhere at the drop of a hat and used to cause mass destruction. That would be quite evil, immoral and in contravention of international law.
I refuse to engage in a battle of wits with an unarmed opponent [wikipedia.org].
(Score: 3, Informative) by JoeMerchant on Thursday June 18 2020, @04:16PM
Oh, of course not - it's just a research platform ;-(
🌻🌻 [google.com]
(Score: 2, Informative) by Anonymous Coward on Tuesday June 16 2020, @12:15PM (1 child)
It would be more likely to run on uranium.
NASA built and ground tested these rockets in the 70s. They worked and were ready to fly. They were canceled because Nixon hated the space program and didn't want to go to Mars, and if NASA had an engine that made going to Mars practical, then Congress might decide to do it.
(Score: 2) by turgid on Thursday June 18 2020, @01:16PM
It would be lighter and more compact if it ran on plutonium, though. Good luck trying to cool it directly with hydrogen, though. Could you have a liquid sodium primary coolant loop? That might make it too heavy and complicated.
I refuse to engage in a battle of wits with an unarmed opponent [wikipedia.org].
(Score: 1) by kanisae on Tuesday June 16 2020, @12:21PM (5 children)
Some impressive misunderstanding of what an NTR does, as it only generates heat and transfers that heat to a working fluid. It can be made with a few different fuels, enriched uranium or a tiny bit of enriched uranium and thorium. Until the reactor is started, the fuels are minimally radioactive, and can be split into multiple launches to minimize risks.
Once the craft is in orbit and fueled, the only exhaust would be the hydrogen heated from the reactor. When you are ready to dispose of the reactor you could park it in a graveyard orbit that would not decay for millions of years, reprocess the fuel, or use the whole reactor as a heat source for another project.
(Score: 3, Informative) by Immerman on Tuesday June 16 2020, @04:20PM (4 children)
Well, it's not like you're spitting fission product out the back end of the rocket like an Orion would, but as I recall, many/most NTR designs use the propellant itself as the working fluid to maximize efficiency, so they are spraying heavily irradiated propellant out the back. If that's pure hydrogen then you'll have have some deutrium and maybe even a little tritium in the exhaust. Probably not a big deal unless it's extremely tritium rich, which seems unlikely. If you're using something more massive though, then you're likely to generate all sorts of ugly radioactive isotopes.
(Score: 0) by Anonymous Coward on Tuesday June 16 2020, @10:45PM (1 child)
It uses hydrogen.
As you surmised, the products are deuterium and tritium. Deuterium is everywhere - I drank a few trillion deuterium atoms this morning - and while tritium is not as common, it occurs naturally and is quite safe.
(Score: 3, Insightful) by Immerman on Wednesday June 17 2020, @04:16PM
If you're counting individual atoms, and are still using numbers with names, even big ones like trillions, then yeah, it's probably not a problem unless you're dealing with something *extremely* nasty. Trillions of atoms is nothing - there's billions of trillions of atoms in a single grain of sand.
Concentrated deutrium though *is* dangerous - a few tastes probably won't hurt you, but drink a glass of heavy water and you're risking severe health problems. And tritium is dramatically more dangerous.
(Score: 0) by Anonymous Coward on Wednesday June 17 2020, @03:22PM (1 child)
The issue is more that constantly jettisoning your primary fluid makes it more difficult to monitor for a fuel containment loss, so you could also be jettisoning fuel fission products as well, which is the really nasty stuff.
(Score: 2) by Immerman on Wednesday June 17 2020, @04:07PM
Unless I'm much mistaken, the fission products remain within the fuel rods, which are quite solid under normal operating conditions. They're not escaping unless the reactor has a meltdown, for which would get *lots* of warning as the temperature climbed.
Really though, radioactive exhaust of all kinds is unlikely to be an issue since for the forseable future these are not designed to be used on Earth. Rockets sometimes fail, and a failed nuclear rocket would be a radioactive dirty bomb. You really don't want that flying overhead.
And in space, it doesn't really matter much how radioactive the exhaust might be - the high exhaust velocity will disperse it far beyond Earth orbit, where the solar wind will have plenty of time to push it further outward before it has a chance to hit Earth on some far-future mutual orbit. You might want to be careful where exactly you aim the thing so you're not irradiating space stations and such, but really, space is so incredibly radioactive already that you'd almost need malicious intent to make things noticeably worse.