Space Nuclear Power

[Technical Ben]

On 5/6/2018 at 7:35 PM, Nuke said:

the iss can generate 120kw from its solar array so thats not much of a boost unless you can make the reactor lighter than that solar array and support hardware. at least not in the inner solar system. outer solar system is a whole other can of worms. if it lets us build a multipurpose long haul nuclear-electric survey ship that can visit multiple locations then its a huge improvement. 

Is it worth it for "emergency" power. A battery is great... but if your solars get blown up (not much can do that, but whatever), a constant 100w, while not 120kw, is better than nothing. Could power lighting/coms etc.

[sh1pman]

24 minutes ago, tater said:

I edited this to fix an errant "k" that appeared. 6 to 7 W per kg.

Meaning that 20t reactor can match the power of the entire ISS solar array set. Not bad, a single FH with full booster reuse can lift it up. I'd imagine these reactors are dense enough to fit in the fairing.

[tater]

5 hours ago, sh1pman said:

Meaning that 20t reactor can match the power of the entire ISS solar array set. Not bad, a single FH with full booster reuse can lift it up. I'd imagine these reactors are dense enough to fit in the fairing.

They've only quoted 2 numbers, the 1kW reactor, and the 10kW one.

So 1kW is ~500kg, and 10kW is about 1,500kg. To scale up under their system, you'd use multiple reactors.

[sh1pman]

1 minute ago, tater said:

They've only quoted 2 numbers, the 1kW reactor, and the 10kW one.

So 1kW is ~500kg, and 10kW is about 1,500kg. To scale up under their system, you'd use multiple reactors.

Yea, I was thinking about 12 10kW reactors.

[winged]

22 hours ago, sh1pman said:

Meaning that 20t reactor can match the power of the entire ISS solar array set. Not bad, a single FH with full booster reuse can lift it up. I'd imagine these reactors are dense enough to fit in the fairing.

I think much less than 20t since larger reactor would have better power to weight ratio.

[StrandedonEarth]

11 hours ago, winged said:

I think much less than 20t since larger reactor would have better power to weight ratio.

Not necessarily as a larger reactor would have a more complex cooling system. It would be much cheaper to use multiple smaller systems that have already been developed than to design one with ten times the output. It would also be more redundant to have multiple smaller units instead of losing all your power if a single large reactor has to be shut down

[Bill Phil]

17 minutes ago, StrandedonEarth said:

Not necessarily as a larger reactor would have a more complex cooling system. It would be much cheaper to use multiple smaller systems that have already been developed than to design one with ten times the output. It would also be more redundant to have multiple smaller units instead of losing all your power if a single large reactor has to be shut down

A larger cooling system, but not necessarily a more complex one.

I would argue that having ten small reactors would require a more complex cooling system than a single large reactor.

Redundancy can be accomplished with a highly redundant design for the larger reactor or by using 2 not quite as large reactors.

[StrandedonEarth]

19 minutes ago, Bill Phil said:

I would argue that having ten small reactors would require a more complex cooling system than a single large reactor.

Redundancy can be accomplished with a highly redundant design for the larger reactor or by using 2 not quite as large reactors.

Cooling all depends on how the system is set up. I don't know what the plan is for cooling the 10kW Kilopower units. If they are spread around the station, they can all be independent, instead of being plumbed into a single cooling system.

As for redundancy, losing one of ten reactors is better than losing half of your power. But again, it all depends on how the base/station/installation is designed to function. So many ways to skin that cat.

[Scotius]

ISS + (200 kW) nuclear reactor + (200 kW) VASIMR engine module = prototype interplanetary spaceship! I so hope we will see such combination before ISS gets scrapped.

[Wjolcz]

Not sure if the ISS is good enough to build something like Nautilus-X out of it. I'm guessing that's what LOP-G is intended for (unless Musk gets to Mars first).

[Scotius]

Of course it's not Currently, ISS doesn't even produce enough charge to power up continuously VASIMR test article that's in the works at Ad Astra company. Add to that huge mass of the station, small thrust of the engine and you have combination barely enough to aid in stationkeeping. But... it still would be enough to save millions of dollars in station's budget

[wumpus]

10 hours ago, Scotius said:

Of course it's not Currently, ISS doesn't even produce enough charge to power up continuously VASIMR test article that's in the works at Ad Astra company. Add to that huge mass of the station, small thrust of the engine and you have combination barely enough to aid in stationkeeping. But... it still would be enough to save millions of dollars in station's budget

But does it make more sense to send up reactor than solar panels?  Granted, the ISS has this big old planet occulting the Sun every 45 minutes or so.  My understanding is that reactors are for Mars and beyond (especially beyond).  Stuffing a multiple falcon heavies with solar panels sounds like a trivial task (both politically and packaging wise) than sending up a reactor.

[kerbiloid]

What would they do with one big or ten small reactors when they get depleted?

[sh1pman]

3 hours ago, kerbiloid said:

What would they do with one big or ten small reactors when they get depleted?

Refuel them with enriched uranium?

[magnemoe]

42 minutes ago, sh1pman said:

Refuel them with enriched uranium?

Nuclear reactors tun for an very long time. 
Note that nuclear submarines run at cruising speed most of the time and reactor run for years, an nerva will just burn for hours on an trip to Mars. 

[kerbiloid]

4 hours ago, sh1pman said:

Refuel them with enriched uranium?

Manually?

P.S.
Either there will appear a new type of Earth quasi-satellite asteroids (and later - meteorites) - spent uranium.
Or they should return the reactors to neutralize them. And how would they do this in space, in a tin can, with a mechanical arm in the best case?
High orbit like now is not an option, unless we want to create a third radiation belt.

So, I believe until the people get high-end gas-core fission reactors with ISP ~tens km/s (which can be self-delivered to a big and safe orbital scrapyard powered with same reactor), all these solid-cores will remain children's toys. In the best case -  a powerplant for Voyagers (let ET pick up our... gifts.). 
They even make not much sense for a Martian ship, because their ISP is low, so huge hydrogen tanks are required. And too weak to cool these huge tanks for 3 years. And have even less ISP if replace hydrogen with anything else.

Also only with high-end gas-core it will be possible to build something meaningful at other celestial bodies, and shuttle there in a reasonable time.

Edited May 21, 2018 by kerbiloid

[hms_warrior]

Uhm...are you by chance mixing up nuclear reactors and nuclear termal rockets?

[kerbiloid]

1 hour ago, hms_warrior said:

Uhm...are you by chance mixing up nuclear reactors and nuclear termal rockets?

I mix any uranium-containing device, looking at them from further utilization perspective.

[Starman4308]

10 hours ago, kerbiloid said:

Manually?

P.S.
Either there will appear a new type of Earth quasi-satellite asteroids (and later - meteorites) - spent uranium.
Or they should return the reactors to neutralize them. And how would they do this in space, in a tin can, with a mechanical arm in the best case?
High orbit like now is not an option, unless we want to create a third radiation belt.

So, I believe until the people get high-end gas-core fission reactors with ISP ~tens km/s (which can be self-delivered to a big and safe orbital scrapyard powered with same reactor), all these solid-cores will remain children's toys. In the best case -  a powerplant for Voyagers (let ET pick up our... gifts.). 
They even make not much sense for a Martian ship, because their ISP is low, so huge hydrogen tanks are required. And too weak to cool these huge tanks for 3 years. And have even less ISP if replace hydrogen with anything else.

Also only with high-end gas-core it will be possible to build something meaningful at other celestial bodies, and shuttle there in a reasonable time.

Graveyard orbits are the best option. You don't want to risk spent fuel reentering Earth's atmosphere. By the time an MEO/HEO orbit decays, the fuel will be pretty much safe, with all the short and mid-duration fission products having decayed.

And no, it will not create a new radiation belt. A few puny reactors will not noticeably irradiate the enormous volume of mid to upper Earth orbit.

Finally, again, this is about a reactor for power generation, not an NTR. You'd need to completely redesign this reactor for propulsion, since I'm pretty sure it's a Stirling generator design, not a liquid loop.

[kerbiloid]

28 minutes ago, Starman4308 said:

Graveyard orbits are the best option.

Unless there would be hundreds of radiological bombs over head, waiting to be hit, intentionally or not, sooner or later.
Satellite/stage debris, lost sats, meteorites - they are waiting.

Rocket technologies - become more and more available.
How long is it till the first antisat missile or a killing sat, targeted at some reactor in orbit just to troll somebody's neighbors?

Private space flights - mean not just space tourists, but also space hijackers. Catch a nuke and throw it down.

Any other kind of disaster. A Kessler syndrome in graveyard orbits would be much more spectacular than Gravity.

28 minutes ago, Starman4308 said:

Finally, again, this is about a reactor for power generation, not an NTR. You'd need to completely redesign this reactor for propulsion, since I'm pretty sure it's a Stirling generator design, not a liquid loop.

Absolutely no difference from this point. Any pack of depleted fuel in orbit is a potential bomb.
Hiding them in graveyard orbits is just like brooming rubbish under cover, or drowning barrels of yperite in Baltic Sea.
Any piece of radioactive junk put in orbit should be collected and neutralized.

Gas/liquid/solid cores here make difference only in sense of possibility.
While space technologies are just at nowadays solid core mumbo-jumbo, the collecting and burning them is impossible. Radioactive trash will be filling the sky.
When efficient gas core will appear, it will be possible to deliver every reactor to an orbital crematorium and burn the depleted core inside its radiating oven, gaining a lot of energy instead.

Edited May 21, 2018 by kerbiloid

[Bill Phil]

A reactor is not a bomb. Maybe a potential radiological incident (although we dump far more of the stuff into the atmosphere with coal plants) but definitely not a bomb. Uranium is generally unfit for nuclear weapons and even if they got nuke grade purity that implies a facility that did it. Spent reactors have a lot of junk in the fuel, so they'd need to enrich the uranium. But if they retrieved the spent uranium from the reactors just about everybody would see them do it. And then it's not too hard to deal with. They'd need a centrifuge in orbit, otherwise dealing with them is even easier.

[wumpus]

1 hour ago, Bill Phil said:

A reactor is not a bomb. Maybe a potential radiological incident (although we dump far more of the stuff into the atmosphere with coal plants) but definitely not a bomb. Uranium is generally unfit for nuclear weapons and even if they got nuke grade purity that implies a facility that did it. Spent reactors have a lot of junk in the fuel, so they'd need to enrich the uranium. But if they retrieved the spent uranium from the reactors just about everybody would see them do it. And then it's not too hard to deal with. They'd need a centrifuge in orbit, otherwise dealing with them is even easier.

If you have a reactor, I'm pretty sure you would find it more useful to dredge Iraq war battlefields for depleted uranium.  If you don't have a reactor, spent fuel isn't going to help you much (and you'd need the centrifuge).  That's not to say that I'd be all that happy with potential terrorist playing with spent fuel: see Randal Monroes' final comment about "swimming in a spent fuel pool here: https://what-if.xkcd.com/29/

You could always use the same to build a "dirty bomb", something otherwise mostly harmless that has been turned into a media/military-industrial-complex boogeyman (at least in the USA) such that setting one off will certainly cause significant death due to the stampede to escape it (ok, not so harmless.  But you are far better off sheltering in place near the explosion than being in the stampede).

It might make a good sci-fi story about Earth refugees that grab a few of these before leaving for elsewhere (or possibly revolting space colonies sneaking in and grabbing the nukes).  It may take awhile to get things going, but then they should be ok.  You get just how far in the future it has to be for it to be a problem.

 

[tater]

There’s so much ambient radiation in space that spent reactors are not even noise. It’s not an issue worth being worried about.

Edited May 22, 2018 by tater

[wumpus]

On 5/21/2018 at 12:49 PM, tater said:

There’s so much ambient radiation in space that spent reactors are not even noise. It’s not an issue worth being worries about.

Radiation doesn't mean it has the right properties to build a bomb/fuel source.  I also doubt it is the right type of neutron source to enrich such stuff it you had it in space.  To be honest, I'd classify spent reactors on *Earth* to be so far in the noise as to not bother about* (I'm fairly sure that the US has emitted more radiation than Japan has since right before Fukishima by using coal power then they ever let loose through direct atomic failure).  Who has access to them might be key, not so much the danger of the reactor to anybody directly.

*Leave the fuel rods in water for a few decades, then glassify and stick in completed [abandoned with known safety standards] mines.  End result may well be safer than solar panels, wildly safer than solar, let alone fossil fuel.  WARNING: the economics of nuclear power pretty much makes this pointless, even if the political factors can be overcome.  The lead time will simply kill your program every time.

[tater]

There was some complaint (from idiots around here) about the Lab pouring some water contaminated with radioisotopes onto the ground... had they mixed the contaminated water with bags of cement---the dry cement would have been more radioactive than the water. People are morons.