DRACO: NASA and DARPA nuclear propulsion collaboration

[InterestedEngineer]

This study takes a deep dive into the geopolitical competition for space nuclear systems for both national security and exploration, and recommends three options for in-space demonstrations before the end of the decade.

Publication Link

https://twitter.com/LMSpace/status/1945926512777244687

the insane amount of dead dry mass in that pictorial presentation means someone doesn't understand the nuances of the rocket equation very well.

[Twark_Main]

the insane amount of dead dry mass in that pictorial presentation

It's a shadow shield (you can tell because the triangular radiators are designed so they don't "peek out" and scatter radiation), and the truss increases distance between the crew and the reactor. The inverse square law is lighter than making the shield thicker.

 https://www.projectrho.com/public_html/rocket/radiation.php

[catdlr]

Eager Space video

Nuclear Electric Propulsion - Practical Idea or Crazy Nuclear Rocket Engine?



Sources for the presentation are included below:

Jul 20, 2025
In Nuclear Electric Propulsion, electricity is generated using a nuclear reactor and used power ion or other types of electric thrusters.

Is it a practical idea, or is it another crazy nuclear rocket engine idea?

Thermal Management in Space – Abraham Hertzberg
https://www.nss.org/settlement/nasa/spaceresvol2/thermalmanagement.html

Defense systems information analysis center
https://dsiac.dtic.mil/articles/space-travel-aided-by-plasma-thrusters-past-present-and-future/

Electric propulsion needs by OHB
https://www.researchgate.net/publication/330082426_OHB-System's_View_on_Electric_Propulsion_Needs

VISIMR VX-200 Performance and new-term SEP capability for unmanned mars flight
https://web.archive.org/web/20110311141639/http://spirit.as.utexas.edu/%7Efiso/telecon/Glover_1-19-11/Glover_1-19-11.pdf

Megawatt class nuclear space power systems, multiple volumes:
https://ntrs.nasa.gov/search?q=megawa...

NASA Nuclear electric propulsion for 2033 mars roundtrip
https://www.researchgate.net/publication/237827299_Use_of_High-Power_Brayton_Nuclear_Electric_Propulsion_NEP_for_a_2033_Mars_Round-Trip_Mission

NASA Compass NEP – Chemical Hybrid
https://ntrs.nasa.gov/api/citations/20210017131/downloads/TM-20210017131_errata.pdf

[JulesVerneATV]

Could astronauts travel to Mars on nuclear-powered rockets? These scientists want to make it happen
https://www.space.com/space-exploration/could-astronauts-travel-to-mars-on-nuclear-powered-rockets-these-scientists-want-to-make-it-happen

The use of nuclear power in space has been mixed. Many long-term spacecraft, such as the Mars rovers Curiosity and Perseverance, use radioisotope thermoelectric generators (RTGs) to provide power. Recently NASA has spoken, controversially, about placing a nuclear reactor on the moon. With regards to rockets, scientists in the 1950s explored a much more explosive possibility: driving a spacecraft forward by detonating a sequence of nuclear explosions behind it and riding the propulsive blast waves. Most notable was Project Orion, which was a concept study led by physicists Freeman Dyson and Ted Taylor and funded by the U.S. Air Force, DARPA and NASA. Then, in the 1970s, researchers associated with the British Interplanetary Society produced a comprehensive design study called Project Daedalus, which envisioned a nuclear fusion-powered engine that could reach 12% of the speed of light and reach the nearest stars in half a century.

Evidently, as we're still mostly stuck on Earth, nothing ever came from these nuclear-powered design studies. Although it's not on the same scale as those overly ambitious projects, hopefully CNTR could be the breakthrough that spaceflight needs to become more routine and to reach new frontiers.

A paper describing CNTR was published in the September 2025 edition of the journal Acta Astronautica.

[Jim]

the insane amount of dead dry mass in that pictorial presentation means someone doesn't understand the nuances of the rocket equation very well.

Likewise, somebody doesn't understand radiation shielding.

[Tywin]

Could revive this program with Jared?

[VSECOTSPE]

Probably not.  Isaacman wants nuclear electric propulsion.  DRACO was nuke thermal.

An expert report by the National Research Council a few years ago argued that NASA needs to pursue both for a while and make a downselect later on based on a common set of metrics.  That would be the smart thing to do.

The other smart thing to do would be to set a formal ramp to get off Orion/SLS as soon as possible.  Reactors are a big waste of money as long as NASA is forced to use an HLV that doesn’t launch often enough to support the kind of transit stages these technologies demand and only puts a crew into space once every couple years.

But by and large, NASA and it stakeholders don’t do smart things in human space flight.

FWIW…

[Vultur]

I honestly don't think there is any *NASA* application for nuclear thermal. (Military applications are beyond my knowledge base, but it's at least conceivable that refueling would be something they'd want to avoid.) For anything else, though, in-orbit refueling with chemical propellant would be way cheaper... And its development is already funded, for both SpaceX and Blue Origin (and LOXSAT too I believe). Once you consider that nuclear reactors aren't going to be aerobraking at Earth, thus your total round trip delta-V is much higher; and that far larger LH2 tanks + more aggressive cryo coolers+ heavy nuclear reactor + heavy shadow shield make your mass ratio way worse ... The benefit of the Isp advantage of NTR is basically eaten up already.

Even nuclear electric is pretty questionable for any remotely near term application. Space nuclear reactors have terrible power to weight, solar electric is way better until you get to the outer solar system. Nuclear electric is beyond the budget of science missions and we're nowhere close to sending humans to the outer solar system.

IMO the argument for NASA doing nuclear propulsion is largely that there needs to be an use found for hardware-focused NASA centers/workforce. Which is a very real political issue, but shouldn't be confused with genuine technical benefits.

[InterestedEngineer]

Space nuclear reactors have terrible power to weight, solar electric is way better until you get to the outer solar system. Nuclear electric is beyond the budget of science missions and we're nowhere close to sending humans to the outer solar system.

IMO the argument for NASA doing nuclear propulsion is largely that there needs to be an use found for hardware-focused NASA centers/workforce. Which is a very real political issue, but shouldn't be confused with genuine technical benefits.

Fixing the power/weight ratio of space nuclear is where I'd focus all that workforce.  For nuclear reactors on the moon, mars, and beyond the asteroid belt.

Pretty long term stuff though.  And the workforce is specialized in one-off very expensive projects, not "make 10,000 of these". It's a completely different mentality.

For spaceflight in the outer solar system I'd concentrate the work force on sailing the solar wind, because that far exceeds anything NTR, NEP, SEP, or chemical fuels can do.   That also goes along with existing capabilities of the current workforce, because "make one thing very expensively (like the JWT) and make it go 100km/sec" matches the current workforce.

[JulesVerneATV]

Here we go again with a similar news cycle?

headlines like

NASA’s new nuclear engine could transform deep space

https://morningoverview.com/nasas-nuclear-rocket-push-could-change-space-travel/

[clongton]

Probably not.  Isaacman wants nuclear electric propulsion.  DRACO was nuke thermal.

An expert report by the National Research Council a few years ago argued that NASA needs to pursue both for a while and make a downselect later on based on a common set of metrics.  That would be the smart thing to do.

The other smart thing to do would be to set a formal ramp to get off Orion/SLS as soon as possible. 

Completely agree. But why choose between the 2? I've always felt that a hybrid system would serve the effort pretty well. A standard engine that could be used to power many different spacecraft; NTP for maneuvering and breaking into and out of orbit, then switch to NEP for cruise mode. Nuclear would provide electrical power constantly. I have no specific data to support this, it's simply a gut belief I harbor. Until such time as we can safely build and operate the nuclear lightbulb, we will likely be confined to chemical propulsion to get into LEO, and that's ok. But for in-space transportation, nuclear, of some flavor, is the future, not chemical. Without it we won't be doing anything really major for a very long time. Interplanetary missions of any size require too much propellant mass, CONSTANTLY being replenished, to use chemical propulsion exclusively. Nuclear is the only efficient off-ramp from chemical. And it will take a long time of continual development to get to operational status, so the sooner we begin the effort, the better off we will be.

[Vultur]

Probably not.  Isaacman wants nuclear electric propulsion.  DRACO was nuke thermal.

An expert report by the National Research Council a few years ago argued that NASA needs to pursue both for a while and make a downselect later on based on a common set of metrics.  That would be the smart thing to do.

The other smart thing to do would be to set a formal ramp to get off Orion/SLS as soon as possible. 

Completely agree. But why choose between the 2? I've always felt that a hybrid system would serve the effort pretty well. A standard engine that could be used to power many different spacecraft; NTP for maneuvering and breaking into and out of orbit, then switch to NEP for cruise mode. Nuclear would provide electrical power constantly. I have no specific data to support this, it's simply a gut belief I harbor.

I am no expert on this, but from what I've read, there's just no application where nuclear thermal really wins out.

Even nuclear electric is pretty marginal in the inner solar system; solar electric is better power to mass. Isaacman probably isn't totally working on what makes the most technical sense; there's a constraint to give the hardware-oriented NASA centers something to do.

Interplanetary missions of any size require too much propellant mass, CONSTANTLY being replenished, to use chemical propulsion exclusively.

I don't think so. Or rather, what's "too much"? Once you make propellant in orbit cheap and solve orbital refueling (which at least three projects are currently working on - Starship, Blue Moon, and LOXSAT) lots of propellant mass is no longer a problem.

The ability to use Earth's atmosphere to aerobrake a chemical vehicle also saves a lot of delta-V for Earth returns.

[InterestedEngineer]

Completely agree. But why choose between the 2? I've always felt that a hybrid system would serve the effort pretty well. A standard engine that could be used to power many different spacecraft; NTP for maneuvering and breaking into and out of orbit, then switch to NEP for cruise mode. Nuclear would provide electrical power constantly. I have no specific data to support this, it's simply a gut belief I harbor. Until such time as we can safely build and operate the nuclear lightbulb, we will likely be confined to chemical propulsion to get into LEO, and that's ok. But for in-space transportation, nuclear, of some flavor, is the future, not chemical. Without it we won't be doing anything really major for a very long time. Interplanetary missions of any size require too much propellant mass, CONSTANTLY being replenished, to use chemical propulsion exclusively. Nuclear is the only efficient off-ramp from chemical. And it will take a long time of continual development to get to operational status, so the sooner we begin the effort, the better off we will be.

Show me the designs for a combined NTP/NEP system, I've not seem them yet.   The combined weight for separate would be hideous

Until such time as we can safely build and operate the nuclear lightbulb, we will likely be confined to chemical propulsion to get into LEO, and that's ok. But for in-space transportation, nuclear, of some flavor, is the future, not chemical. Without it we won't be doing anything really major for a very long time. Interplanetary missions of any size require too much propellant mass, CONSTANTLY being replenished, to use chemical propulsion exclusively. Nuclear is the only efficient off-ramp from chemical. And it will take a long time of continual development to get to operational status, so the sooner we begin the effort, the better off we will be.

Until we have a nuclear lightbulb, chemical wins, every time. 

The complaint about interplanetary missions with too much propellant is simply not true, especially when you consider aerobraking giving you a free 5-10km/sec deltaV with about 15t of static mass to do so.  That's less than the mass of a nuclear engine *alone*, not including it's very heavy LH2 tanks and the LH2 itself.

Also consider that chemical fuel at EM-L1 point gives you enough deltaV on a standard starship to escape the solar system, it's simply not true that chemical is "too much mass" or "we won't be doing anything major".

Replenishment is a well solved problem - the coal stations solved it for the British Empire in the 19th century, and the US Airforce and Navy solved it for jetA, bunker fuel, etc in the 20th century.   I include both remote statiions and under-way replenishment in this.  An extremely well known problem, just adapted to space travel.

For Old Space, chemical is "too much mass".  For new space, where we stop throwing hardware away, it's not too much mass.   It's so cheap that mining fuel on remote stations like the Moon is a minor optimization.

Now a lightbulb with an Isp of 2500 or more, that is probably better than chemical for all interplanetary scenarios.  Good luck with that, it's a temperature of about 24,000K. for NTP (temperature is the square of the exhaust velocity).

And as far as NEP, you won't get enough thrust to cut mission times at all, and you also throw away Oberth and aerobraking.  It might make sense for far outer planet missions simply because the electric power will be needed beyond Jupiter for everything.

[Vultur]

Completely agree. But why choose between the 2? I've always felt that a hybrid system would serve the effort pretty well. A standard engine that could be used to power many different spacecraft; NTP for maneuvering and breaking into and out of orbit, then switch to NEP for cruise mode. Nuclear would provide electrical power constantly. I have no specific data to support this, it's simply a gut belief I harbor. Until such time as we can safely build and operate the nuclear lightbulb, we will likely be confined to chemical propulsion to get into LEO, and that's ok. But for in-space transportation, nuclear, of some flavor, is the future, not chemical. Without it we won't be doing anything really major for a very long time. Interplanetary missions of any size require too much propellant mass, CONSTANTLY being replenished, to use chemical propulsion exclusively. Nuclear is the only efficient off-ramp from chemical. And it will take a long time of continual development to get to operational status, so the sooner we begin the effort, the better off we will be.

Show me the designs for a combined NTP/NEP system, I've not seem them yet.   The combined weight for separate would be hideous

Until such time as we can safely build and operate the nuclear lightbulb, we will likely be confined to chemical propulsion to get into LEO, and that's ok. But for in-space transportation, nuclear, of some flavor, is the future, not chemical. Without it we won't be doing anything really major for a very long time. Interplanetary missions of any size require too much propellant mass, CONSTANTLY being replenished, to use chemical propulsion exclusively. Nuclear is the only efficient off-ramp from chemical. And it will take a long time of continual development to get to operational status, so the sooner we begin the effort, the better off we will be.

Until we have a nuclear lightbulb, chemical wins, every time. 

The complaint about interplanetary missions with too much propellant is simply not true, especially when you consider aerobraking giving you a free 5-10km/sec deltaV with about 15t of static mass to do so.  That's less than the mass of a nuclear engine *alone*, not including it's very heavy LH2 tanks and the LH2 itself.

Also consider that chemical fuel at EM-L1 point gives you enough deltaV on a standard starship to escape the solar system, it's simply not true that chemical is "too much mass" or "we won't be doing anything major".

Replenishment is a well solved problem - the coal stations solved it for the British Empire in the 19th century, and the US Airforce and Navy solved it for jetA, bunker fuel, etc in the 20th century.   I include both remote statiions and under-way replenishment in this.  An extremely well known problem, just adapted to space travel.

For Old Space, chemical is "too much mass".  For new space, where we stop throwing hardware away, it's not too much mass.   It's so cheap that mining fuel on remote stations like the Moon is a minor optimization.

Now a lightbulb with an Isp of 2500 or more, that is probably better than chemical for all interplanetary scenarios.  Good luck with that, it's a temperature of about 24,000K. for NTP (temperature is the square of the exhaust velocity).

And as far as NEP, you won't get enough thrust to cut mission times at all, and you also throw away Oberth and aerobraking.  It might make sense for far outer planet missions simply because the electric power will be needed beyond Jupiter for everything.

Yeah, NEP makes sense for Jupiter and beyond but not really for inner solar system. If you want electric propulsion solar panels have much better watts/kg even at Mars orbit, probably even asteroid belt.

Solid core NTR is essentially pointless though (which is sad, since NERVA was really cool). Given that hardware oriented NASA centers need something to work on, it's better to focus on nuclear electric which at least has *some* potential use. Also, a good space rated nuclear reactor with good power/mass would be very useful for lunar night. NEP is basically a power reactor, since it needs to generate electricity; NTR is different.


You might be able to use an open cycle gas core rather than a nuclear lightbulb; probably a lot easier to hit 2500+ Isp that way since you don't have to entirely contain the ridiculously high temperature reacting materials inside a solid vessel. Same for a nuclear-salt-water rocket a la Zubrin. But those would have really expensive fuel, and aren't possible at all until there is enough space industry and infrastructure to do all the building & testing far away from Earth.

[Tywin]

Space Nuclear is back in the menu!!