Nuclear-Powered Spacecraft

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General Atomics Completes DRACO Nuclear Thermal Propulsion S

General Atomics Electromagnetic Systems (GA-EMS) announced today that it has completed major milestones for the Track A, Phase 1 Demonstration Rocket for Agile
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General Atomics Completes DRACO Nuclear Thermal Propulsion System Design and Test Milestone​

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General Atomics Electromagnetic Systems (GA-EMS) announced today that it has completed major milestones for the Track A, Phase 1 Demonstration Rocket for Agile Cislunar Operations (DRACO) program. Under contract from the Defense Advanced Research Projects Agency (DARPA), GA-EMS delivered a baseline design of a DRACO Nuclear Thermal Propulsion (NTP) reactor and engine and successfully tested key components of the nuclear reactor, including the vitally important high-temperature fuel elements in prototypic conditions at the NASA Nuclear Thermal Element Environmental Simulator (NTREES). The NTP system is intended to allow a nuclear thermal rocket to operate in cislunar space, the region between the Earth and the Moon.

“We have leveraged our expertise in nuclear and space system technologies to design an NTP system and test the vital components of that system to confirm they will withstand the relevant design conditions,” stated Scott Forney, president of GA-EMS. “Unlike electric and chemical propulsion technologies in use today, NTP propulsive capabilities can achieve two to three times the propellant mass efficiency, which is critically important for cislunar missions.”

“The cislunar space domain is essential to our national defense, modern commerce, and scientific discovery. As opportunities in cislunar space continue to expand, more innovative propulsion technologies to access space are increasingly necessary,” said Dr. Christina Back, vice president of Nuclear Technologies and Materials at GA-EMS.
 
This is actually quite cool because the gas is heated by the reactor core, so the specific impulse is massive as well as decently larger thrust. The downside, having spoken to a few experts, is that the gas has to go through the rector core to get the rate of heat transfer required, so it's only suitable for a discardable second stage. It also provided two options for propulsion:

1. Send hydrogen on its own through core for very high impulse and reasonable thrust (note you could use an inert gas, since there is no need to combust it for heat).

2. Send hydrogen and oxygen through reactor and combust. This still provides higher specific impulse than LH2-LOx on it's own, and 'The Expanse' levels of thrust (well almost ;) ).

An older study:


NTR - Nuclear Thermal Rocket using LH2 propellant
LA-NTR - LOx Augmented NTR (LOx serves as an afterburner)

Specific Impulses

NTR - 1000s
LA-NTR - 600s

For comparison (highest SI for chemical propellant rocket):

Aerojet Rocketdyne RL-10B-2cryogenicDelta III, Delta IV, SLS upper stage465.5s


Chemical propulsion tops out at around 450-460s for LH2/LOX. Exotic Lithium-Hydrogen-Fluorine Tripropellant systems have been demonstrated up to 542s, but those are highly impractical.


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infinite.mit.edu

Carlo Rubbia, "New Approach to Nuclear Space Propulsion” - MIT Media Lab Colloquium Series | Infinite MIT

Nobel Laureate Carlo Rubbia discusses new research on nuclear space propulsion, with particular reference to future missions to Mars.
infinite.mit.edu infinite.mit.edu

So now you can make devices which are critical with grams of material, not kilograms. Remember, in the Nerva, you needed one ton of highly fissile bomb-grade uranium. Here, with 20 grams of americium, you're critical. In this continued medium....
So it is possible, with this technology, to make a critical reactor which will operate with a very small amount of material. Remember, 1 milligram a square centimeter is 10 grams per square meter of surface. We are talking about probably 100 square meters, for this mission, so we're talking about between 5 and 10 kilograms [INAUDIBLE] of americium to burn. Which is not very much.

In fact, americium has the same properties as uranium 230-- plutonium 238, which is used now on Cassini mission and was on Voyager. And usually you had more than these kilograms on it. So it's deja vu, as one says in French.

Now, of course, americium 242m is an ideal device. This is a cross-section.

Notice the cross-section drops, when a temperature goes up. This is the temperature of your Hohlraum, 1,000 degrees 2,000 degrees. So you're running here in this region that correspond to those energies. Capture is very high, fission very high, capture very small. Big ratio between the two.
 
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