For the First Time Since '65, the U.S. Military Will Blast a Nuclear Reactor Into Space

[jemhouston]

This is more like the 21st century I wanted.


https://www.popularmechanics.com/space/ ... nto-space/

SpaceRockets

For the First Time Since '65, the U.S. Military Will Blast a Nuclear Reactor Into Space

The future of space travel looks a lot like fission power.
H

The role of nuclear power may be up for debate on Earth, but in space, fission tech makes a lot of sense.

The U.S. military—after already awarding Lockheed Martin with a contract related to the DRACO program—is forking over another $33.7 million to the aerospace company to make a nuclear-powered spacecraft.

The spacecraft will use nuclear fission to power Stirling engines, creating electricity for propulsion, onboard systems, and payloads.

When it comes to space travel, fission power makes a lot of sense. Nuclear thermal propulsion (NTP) engines are more efficient, can shorten travel times, and can carry bigger payloads. And Lockheed Martin is already hard at work designing an NTP engine for cislunar operations for DARPA’s DRACO program.

But fission can do much more than simple propulsion, and that’s why the U.S. military is forking over $33.7 million for Lockheed Martin—along with Space Nuclear Power Corp (SpaceNukes) and BWX Technologies, Inc. (BWXT)—to start designing a nuclear spacecraft as part of the Joint Emergent Technology Supplying On-Orbit Nuclear (JETSON) project.
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This technology demonstrator will use nuclear fission to power Stirling engines that produce between 6 kWe and 20 kWe of electricity—Lockheed Martin claims that this provides four times the power of conventional solar arrays without the need for constant sunlight. This technique comes directly from lessons learned with NASA’s Kilopower Reactor Using Stirling Technology (KRUSTY) experiment, which investigated how to provide electricity via nuclear power for future outposts on the Moon and, eventually, Mars.


“Nuclear fission development for space applications is key to introducing technologies that could dramatically change how we move and explore in the vastness of space,” Barry Miles, JETSON program manager and principal investigator at Lockheed Martin, said in a press statement.

The fission engine is inert at launch and won’t turn on until the JETSON spacecraft is in a safe, non-decaying Earth orbit. Once the fission reactor creates this energy, the electricity will power Hall-effect thrusters (a kind of ion thruster that is electrified to create acceleration) that are already used on the company’s LM2100 satellites. While fission will provide the electricity necessary for acceleration, it will also provide power for onboard systems and payloads—a one-stop shop for all of the spacecraft’s energy needs.
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This will be the first time that the U.S. military has launched a nuclear reactor into space since 1965, when the U.S. launched the SNAP-10A experimental nuclear-powered satellite (which was also the first ion thruster ever in space). Lockheed Martin says that the spacecraft will “enhance maneuver and power capabilities shaping future space force operations,” and is currently in the preliminary design review stage.

Apart from Lockheed Martin, the Houston-based Intuitive Machines received $9.4 million to develop a spacecraft using a compact radioisotope power system, and Westinghouse Government Services in South Carolina received funds to investigate high-power fission systems for future spacecraft.

The role of fission on Earth is a complicated subject, but when it comes to space, the technology is seeming more and more like a no-brainer.

Darren lives in Portland, has a cat, and writes/edits about sci-fi and how our world works. You can find his previous stuff at Gizmodo and Paste if you look hard enough.
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a close up of the moon

[Nik_SpeakerToCats]

Hmm. I wonder what 'radiator' system they'll use as the 'cold side' of the Stirling engine(s)...

[Belushi TD]

What's the difference between this reactor and the reactors that powered the Voyager spacecraft? Don't those count as nuclear reactors as well?

Belushi TD

[jemhouston]

The Voyagers were powered by radioisotope thermoelectric generator, which uses radioactive decay for power. https://science.nasa.gov/mission/cassin ... generator/

This sounds more like a regular reactor which uses fission.

[David Newton]

RTG power sources have been used much more recently than Voyager. Cassini had one as does New Horizons.

[Belushi TD]

The Voyagers were powered by radioisotope thermoelectric generator, which uses radioactive decay for power. https://science.nasa.gov/mission/cassin ... generator/

This sounds more like a regular reactor which uses fission.

Yeah, I get that. Isn't it still a nuclear reactor? I suppose I'm being a bit of a pedant, but anytime someone says "HASN'T BEEN DONE SINCE....." I always want to look at it and say "yeah, but how about.....".

Belushi TD

[jemhouston]

Could be schematics or trying to avoid protesters.

[David Newton]

The Voyagers were powered by radioisotope thermoelectric generator, which uses radioactive decay for power. https://science.nasa.gov/mission/cassin ... generator/

This sounds more like a regular reactor which uses fission.

Yeah, I get that. Isn't it still a nuclear reactor? I suppose I'm being a bit of a pedant, but anytime someone says "HASN'T BEEN DONE SINCE....." I always want to look at it and say "yeah, but how about.....".

Belushi TD

Isn't it still a nuclear reactor? Absolutely not. A nuclear reactor implies generation of power through fission or (in the future perhaps) fusion of nuclei. An RTG on the other hand relies on the heat generated by radioactive decay to generate power.

What is correct to say is that a fission reactor and an RTG both involve sticking radioactive material on top of a rocket and sending it into orbit or beyond Earth orbit.

[kdahm]

Isn't it still a nuclear reactor? Absolutely not. A nuclear reactor implies generation of power through fission or (in the future perhaps) fusion of nuclei. An RTG on the other hand relies on the heat generated by radioactive decay to generate power.

What is correct to say is that a fission reactor and an RTG both involve sticking radioactive material on top of a rocket and sending it into orbit or beyond Earth orbit.

Technically speaking, your first paragraph says that they're identical. A RTG relies of the heat generated by radioactive decay (fission) to generate power. RTGs essentially use a nest of thermocouples to take the low energy decay of a lump of radioactives directly from heat to electricity. A reactor implies that the fission is fairly high energy, that there is a working fluid involved, that there's a mechanical interface between the working fluid and the electricity, and that there's frequently a phase change on the working fluid.

The other difference is that a reactor implies that the high energy is created by a chain reaction of decay, where the decay of one atom emits particles that cause the decay of other atoms, although a a controlled rate. The RTG does not want a chain reaction, but just the natural random decay at the normal half-life.

Sure it's semantics, but chopping the verbiage fine is what we do around here.

[David Newton]

Nope. Radioactive decay is absolutely not fission in that sense.

Radioactive decay is a purely statistical process that cannot be influenced by outside means

Nuclear fission is an actively-influenced process caused by firing things at nuclei.

[kdahm]

Nope. Radioactive decay is absolutely not fission in that sense.

Radioactive decay is a purely statistical process that cannot be influenced by outside means

Nuclear fission is an actively-influenced process caused by firing things at nuclei.

As I said, semantics and definitions.

Fission is the process where a nucleus emits one or more radioactive particles and becomes a different isotope, element. or multiple elements. See OED: "In Nuclear Physics: to split or break up into fission products; to cause (a nucleus) to undergo fission." Websters is similar: "the splitting of an atomic nucleus resulting in the release of large amounts of energy." Wikipedia, for what little it's worth, says, "the splitting of an atomic nucleus resulting in the release of large amounts of energy." and "Apart from fission induced by a neutron, harnessed and exploited by humans, a natural form of spontaneous radioactive decay (not requiring a neutron) is also referred to as fission, and occurs especially in very high-mass-number isotopes."

For U235, the natural decay chain is U235 -> Th231 + alpha particle -> Pa231 + Beta -> Ac227 + alpha .....
When struck by a neutron, the chain starts off with U235 -> Ba144 + Kr89 + 3 neutrons .....

We can discuss whether thermal or slow neutrons count the same as fast neutrons for the purpose of defining fission. I can also see why defining fission to exclude natural decay can be attractive as a way of categorizing things. But for the U235 above, about 1E-9 times during natural decay, the nucleus splits as for the neutron bombardment chain above instead of the alpha particle chain. As a greater mass of U235 is accumulated, there is a shift to the fast neutron chain and a subcritical reactor is formed.

Technically speaking, fission reactors are also radioactive decay, just artificial radioactive decay that has been accelerated by man.

tl.dr: It's a matter of language, not physics.