…has passed its initial tests. This is one of the most useful things I’ve seen to come out of NASA in a while. Just think what we could be doing if we were doing more of this kind of thing, instead of building a giant rocket and capsule.
12 thoughts on “A Space Nuclear Reactor”
Comments are closed.
The press release and NASA’s own fact sheet (PDF)
https://www.nasa.gov/sites/default/files/atoms/files/ns_kilopower_fs_180111.pdf
don’t mention the total mass of the device. This one produced 4 kW, and the goal is 10 kW. Scaling up the power by a factor of 2.5 probably means scaling up the volume of the uranium rod by a factor of around 25% to 40%. Based on the images and the description of the fuel as a “six-inch chunk of uranium-235” that’s about a two tonne reactor. The working fluid for the Stirling engine will be a significant fraction of the mass of the device.
6-inch chunk of U-235 — so this thing requires HEU?
Stirling engine — so this device is constrained by the size and bulk of its radiator?
What is the power conversion “cycle” used to get electric or other useful energy from the reactor operation?
That may still be TBD. They never resolved that trade for JIMO before it was canceled.
In this 2016 KiloPower overview, they say the 10 KW version would mass 1800 kg.
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20160012354.pdf
That’s better than 5 W/kg, but recall that “Mars in 39 days” via VASIMR requires a magical 1000 W/kg power source.
I’m pretty sure this reactor is aimed at powering fixed bases in places without 24-hour sunlight. As you point out, the power-to-weight is far too low for propulsion.
A kilowatt per kilogram power source isn’t magical – just roughly an order of magnitude better than current SOTA. Me, I’d very much like to see more resources going into narrowing that gap.
That six-inch chunk of U235 is about 35 kg, assuming a sphere. That is, FWIW, several fission bombs’ worth with modern device design (the exact number apparently involving classified data.)
So, alas, we aren’t going to be able to routinely install one of these in our basement to go off-grid.
Useful for high-priority exploration applications where solar isn’t a practical option, possibly. Depends on costs.
That’s the thing with nuclear-electric. You need some sort of heat dissipation and irradiating it out uses so much space and weight that it makes me wonder if you wouldn’t be better off with solar panels in the first place.
It makes a lot more sense on nuclear-thermal, since you can just use the heat as useful propulsive power and eject it out with the reaction mass.
“You need some sort of heat dissipation and irradiating it out uses so much space and weight that it makes me wonder if you wouldn’t be better off with solar panels in the first place.”
The article states that it the device’s top temperature is 800ºC which is1073ºK. It also states that its conversion efficiency is 35%. Given the Carnot Equation, we can then calculate the low temperature at which the waste heat would be radiated away as being 697ºK or 424ºC. That is not too bad a temperature for radiating. If the radiators are still too massive for the launch budget, go to dynamic radiators with metal dust moved through vacuum by magnetic or electrostatic containment, when *in* a vacuum. On Mars, the atmospheric cooling tower may need to be tall, but that is all.
But wait, there’s more! I’m sure that either a Lunar or Mars base could find some uses for the “waste” heat, like melting ice and heating habitats/greenhouses. I’d probably want a secondary loop with a heat exchanger, though.
Faster (and bigger) please.
If anyone is interested in some slides I took photos of a while back, from a talk at the National Atomic Testing Museum on this topic: https://photos.app.goo.gl/g6GFJV46XK5aAWN32
There were some remarkable points he made, such as: The system scales back when you draw less power, no issues with ash particles due to the neutron dynamics, the life limiting parts are the Sterling engines at 10 years, sodium heat pipes, no new facilities to make the cores, cores can sit on a shelf until needed.