DRACO: NASA and DARPA nuclear propulsion collaboration

[BrightLight]

Milestone-based contract up to $499M split 50/50 between NASA and DARPA (at 21:42 in the media briefing from post 79 upthread).
https://news.lockheedmartin.com/2023-07-26-Lockheed-Martin-Selected-to-Develop-Nuclear-Powered-Spacecraft

[yg1968]

The US government is taking a serious step toward space-based nuclear propulsion:
https://arstechnica.com/space/2023/07/nasa-seeks-to-launch-a-nuclear-powered-rocket-engine-in-four-years/

[RON_P]

Any more info on the reactor itself ? like T/W ratio , ISP , The core temperature they aim and the type of fuel would it be CERMET , CERCER or even advanced carbides ?

[Asteroza]

Any more info on the reactor itself ? like T/W ratio , ISP , The core temperature they aim and the type of fuel would it be CERMET , CERCER or even advanced carbides ?

I believe BWXT were going for a CERMET HALEU fuel?

[Coastal Ron]

If this gets proved out, I was thinking that a hydrogen-fueled nuclear tug could be built that would lessen the number of propellant trips it would take for a Starship-to-Mars mission. Assuming SpaceX would buy or build such a service, and the tug in LEO could mate to an outgoing Starship and be a more efficient way to push a Starship to Mars.

Then the tug would turn around and return back to LEO to refuel and wait for its next client.

This may require SpaceX to add LH2 fueling to a Starship Tanker version, but I'd have to think that would be doable at some point.

Fingers crossed that this test goes well, since it could really help with interplanetary travel.

[InterestedEngineer]

If this gets proved out, I was thinking that a hydrogen-fueled nuclear tug could be built that would lessen the number of propellant trips it would take for a Starship-to-Mars mission. Assuming SpaceX would buy or build such a service, and the tug in LEO could mate to an outgoing Starship and be a more efficient way to push a Starship to Mars.

Then the tug would turn around and return back to LEO to refuel and wait for its next client.

This may require SpaceX to add LH2 fueling to a Starship Tanker version, but I'd have to think that would be doable at some point.

Fingers crossed that this test goes well, since it could really help with interplanetary travel.

Starship aerobrakes at Mars.

How does the nuclear tug brake ~4 km/sec of deltaV at Mars?

[FutureSpaceTourist]

https://twitter.com/lmspace/status/1684198476723154951

The future of spaceflight is clear. Actually, it's nuclear.

@DARPA has awarded us a contract to develop a nuclear thermal propulsion (NTP)-powered spacecraft under the Demonstration Rocket for Agile Cislunar Operations (DRACO) project, the first demo of an NTP system in space.

The fission-based reactor will use a special high-assay low-enriched uranium (HALEU) and we are partnering with @BWXT to develop the nuclear reactor and produce the HALEU fuel.

https://twitter.com/lmspace/status/1684203209907118080

Chemical propulsion has long been the standard for spaceflight, but for humans to reach Mars, we'll need much more efficient propulsion. Nuclear thermal propulsion (NTP) offers thrust as high as conventional chemical propulsion with higher efficiency. https://www.lockheedmartin.com/en-us/news/features/2022/how-nuclear-technology-will-get-us-to-mars-faster-than-ever.html

[FutureSpaceTourist]

https://twitter.com/robotbeat/status/1684402853085839361

"Officials did not disclose the thrust the DRACO engine will produce, although Calomino said it will have a specific impulse, a measure of efficiency, of about 700 seconds."

https://spacenews.com/nasa-and-darpa-select-lockheed-martin-to-develop-draco-nuclear-propulsion-demo/

[Vahe231991]

The intent for the the DRACO nuclear rocket powerplant to be tested in low Earth orbit brings attention again to the fact that the Partial Test Ban Treaty signed in 1963 prohibits all nuclear detonations except those conducted underground, especially when considering that this treaty doomed Project Orion.

[InterestedEngineer]

https://twitter.com/robotbeat/status/1684402853085839361

"Officials did not disclose the thrust the DRACO engine will produce, although Calomino said it will have a specific impulse, a measure of efficiency, of about 700 seconds."

https://spacenews.com/nasa-and-darpa-select-lockheed-martin-to-develop-draco-nuclear-propulsion-demo/

It's 5710 km/sec from Earth LEO to Mars LEO per the solar system subway map.

For 700s, that's a mass ratio of 2.3 per the rocket equation.

For 100t of payload and 125t of dry mass that requires 300t of H₂ to orbit.  This isn't counting transit losses, which for H₂ will be quite substantial, H₂ really doesn't like to stick around in tanks very long.

Now consider a Starship that aerobrakes.  The deltaV requirement drops to 4270m/sec.

For the 375s of Starship, that's a mass ratio of 3.2.   For the same dry mass that's 500t of O₂ and CH₄ to orbit.

So that's 200t of mass to LEO saved.   Even at a pessimistic $100/kg that's $20M per Mars flight of additional mass to LEO for Starship.

Now let's count the cost of the actual fuel.  H₂ costs $5/kg and CH₄/LOX at their Raptor mix ratios cost $200 per ton.  H₂ costs $5,000 per ton.

That's $1.5M of H2 and $0.1M of CH₄/LOX

So the savings per flight to Mars via NTR is $19M, and that's best case for the DRACO NTR, and assumes no H₂ losses over ~120 days of transit.

Assuming a $10B development cost and launch of a few prototypes (ha!), it would take 500 flights to Mars to pay back the costs of the DRACO/NTR development, assuming OPEX is identical.  (it's not, the NTR has to be refueled or thrown away, Starships are massed produced and NTRs are not, etc.).

for Mars, it's simply not worth NTR when chemical refueling gets you there.

If you think $10B is too high, then look at other Lockheed cost plus contracts.   Also consider that H₂ fuel transfer and storage issues will be 10 times harder than CH₄/LOX.  Then consider the dual crew headquarters development costs (both Starship and tug need proper crew quarters)

[InterestedEngineer]

https://twitter.com/robotbeat/status/1684402853085839361

"Officials did not disclose the thrust the DRACO engine will produce, although Calomino said it will have a specific impulse, a measure of efficiency, of about 700 seconds."

https://spacenews.com/nasa-and-darpa-select-lockheed-martin-to-develop-draco-nuclear-propulsion-demo/

It's 5710 m/sec from Earth LEO to Mars LEO per the solar system subway map.

For 700s, that's a mass ratio of 2.3 per the rocket equation.

For 100t of payload and 125t of dry mass that requires 300t of H₂ to orbit.  This isn't counting transit losses, which for H₂ will be quite substantial, H₂ really doesn't like to stick around in tanks very long.

Now consider a Starship that aerobrakes.  The deltaV requirement drops to 4270m/sec.

For the 375s of Starship, that's a mass ratio of 3.2.   For the same dry mass that's 500t of O₂ and CH₄ to orbit.

So that's 200t of mass to LEO saved.   Even at a pessimistic $100/kg that's $20M per Mars flight of additional mass to LEO for Starship.

Now let's count the cost of the actual fuel.  H₂ costs $5/kg and CH₄/LOX at their Raptor mix ratios cost $200 per ton.  H₂ costs $5,000 per ton.

That's $1.5M of H2 and $0.1M of CH₄/LOX

So the savings per flight to Mars via NTR is $19M, and that's best case for the DRACO NTR, and assumes no H₂ losses over ~120 days of transit.

Assuming a $10B development cost and launch of a few prototypes (ha!), it would take 500 flights to Mars to pay back the costs of the DRACO/NTR development, assuming OPEX is identical.  (it's not, the NTR has to be refueled or thrown away, Starships are massed produced and NTRs are not, etc.).

for Mars, it's simply not worth NTR when chemical refueling gets you there.

If you think $10B is too high, then look at other Lockheed cost plus contracts.   Also consider that H₂ fuel transfer and storage issues will be 10 times harder than CH₄/LOX.  Then consider the dual crew headquarters development costs (both Starship and tug need proper crew quarters)

Now consider faster transit scenarios.   Let's add 2000m/sec to the deltaV and get there 30 days sooner.

For NTR, that's a deltaV of 9710m/sec (2000 going, 2000 braking) or a mass ratio of 4:1.   So that's 700t of H₂ to LEO.   Now we are going to be getting into tank problems with H₂ since the tank always masses about 10% of the fuel, so the real dry mass is going to increase by 40t.  Iterating again it's really 800t of H₂  to LEO.

Starship aerobrakes, so the deltaV is 6270m/sec, or a mass ratio of 5.5.  That's 1000t of fuel to LEO.  No dry mass changes because the tanks hold 1200t of fuel in the current design (1500t in future designs).

You'll note as transit times decrease, the mass difference to LEO doesn't change in absolute numbers (but does decrease in percentage terms).  This is due to both the lack of aerobraking for NTR and the expensive tank mass for long term storage of H₂ .

NTR DRACO simply doesn't pencil out for a Mars tug.

[Coastal Ron]

If this gets proved out, I was thinking that a hydrogen-fueled nuclear tug could be built that would lessen the number of propellant trips it would take for a Starship-to-Mars mission. Assuming SpaceX would buy or build such a service, and the tug in LEO could mate to an outgoing Starship and be a more efficient way to push a Starship to Mars.

Then the tug would turn around and return back to LEO to refuel and wait for its next client.

This may require SpaceX to add LH2 fueling to a Starship Tanker version, but I'd have to think that would be doable at some point.

Fingers crossed that this test goes well, since it could really help with interplanetary travel.

Starship aerobrakes at Mars.

How does the nuclear tug brake ~4 km/sec of deltaV at Mars?

The Starship is already designed for landing on Mars, and I'm not talking about that. What I'm talking about is using a hydrogen-fueled nuclear tug to push a Starship out of Earth orbit and on towards Mars, but the tug stays in Earth-local space and returns to LEO for the next Starship.

This would could:

A. Reduce the amount of Starship refueling trips SpaceX would have to make for each Starship that is bound for Mars.

B. Allow Starships to leave for Mars with far more propellant, which maybe means they can land with more propellant on Mars.

[InterestedEngineer]

If this gets proved out, I was thinking that a hydrogen-fueled nuclear tug could be built that would lessen the number of propellant trips it would take for a Starship-to-Mars mission. Assuming SpaceX would buy or build such a service, and the tug in LEO could mate to an outgoing Starship and be a more efficient way to push a Starship to Mars.

Then the tug would turn around and return back to LEO to refuel and wait for its next client.

This may require SpaceX to add LH2 fueling to a Starship Tanker version, but I'd have to think that would be doable at some point.

Fingers crossed that this test goes well, since it could really help with interplanetary travel.

Starship aerobrakes at Mars.

How does the nuclear tug brake ~4 km/sec of deltaV at Mars?

The Starship is already designed for landing on Mars, and I'm not talking about that. What I'm talking about is using a hydrogen-fueled nuclear tug to push a Starship out of Earth orbit and on towards Mars, but the tug stays in Earth-local space and returns to LEO for the next Starship.

This would could:

A. Reduce the amount of Starship refueling trips SpaceX would have to make for each Starship that is bound for Mars.

B. Allow Starships to leave for Mars with far more propellant, which maybe means they can land with more propellant on Mars.

Your proposal.  You do the math.

[Coastal Ron]

The Starship is already designed for landing on Mars, and I'm not talking about that. What I'm talking about is using a hydrogen-fueled nuclear tug to push a Starship out of Earth orbit and on towards Mars, but the tug stays in Earth-local space and returns to LEO for the next Starship.

This would could:

A. Reduce the amount of Starship refueling trips SpaceX would have to make for each Starship that is bound for Mars.

B. Allow Starships to leave for Mars with far more propellant, which maybe means they can land with more propellant on Mars.

Your proposal.  You do the math.

I'm not a rocket scientist, but what I'm proposing is combining two transportation systems and letting them do less than what they are being designed to do.

Both are being designed to go from Earth to Mars, so using the nuclear tug to only put mass out of Earth orbit and then return should not be outside the capabilities of such a tug. And for the Starship, getting an assist out of Earth orbit would SAVE propellent, either by not being loaded in the first place, or being able to land more propellant on Mars.

In essence, the nuclear tug would be like a Falcon 9 booster, except that it is starting in LEO, and returning to LEO.

And I have no idea about the math, so if someone wants to look into it and make a determination one way or the other, great. It just seems like a good marriage of the two... 

[InterestedEngineer]

The Starship is already designed for landing on Mars, and I'm not talking about that. What I'm talking about is using a hydrogen-fueled nuclear tug to push a Starship out of Earth orbit and on towards Mars, but the tug stays in Earth-local space and returns to LEO for the next Starship.

This would could:

A. Reduce the amount of Starship refueling trips SpaceX would have to make for each Starship that is bound for Mars.

B. Allow Starships to leave for Mars with far more propellant, which maybe means they can land with more propellant on Mars.

Your proposal.  You do the math.

I'm not a rocket scientist, but what I'm proposing is combining two transportation systems and letting them do less than what they are being designed to do.

Both are being designed to go from Earth to Mars, so using the nuclear tug to only put mass out of Earth orbit and then return should not be outside the capabilities of such a tug. And for the Starship, getting an assist out of Earth orbit would SAVE propellent, either by not being loaded in the first place, or being able to land more propellant on Mars.

In essence, the nuclear tug would be like a Falcon 9 booster, except that it is starting in LEO, and returning to LEO.

And I have no idea about the math, so if someone wants to look into it and make a determination one way or the other, great. It just seems like a good marriage of the two... 

without math, what you are proposing makes no sense.

Why would you add 4.2km/sec to a stage, and then have to boost it back the same amount?   There are no gravity losses to overcome.  the mass saved to LEO is practically nothing.  You introduce the problem of long term storage of H₂.

All cost, no benefit.  I've done the math, but I'm not going to show it.  Nobody else bothers.  You can guess at the math from above.

As far as not understanding rocketry, it's just basic algebra.   Rocket equation, solve for mass ratio.

Or go play KSP for a while and get an intuitive feel.

[redneck]

Along these lines I found it interesting to consider HEO to Mars injection of the ship with the tug returning to HEO.  But not a Starship sent to Mars, but rather a fairly dumb cargo container with just enough aero brake capabilities and maneuver thrusters to deliver. Retain the Starships in cislunar space for continuous service.

Accumulate cargo in HEO until Mars window opens. Tug (of whatever tech) drops a container to low perigee for an Oberth burn to Mars injection. Tug then does a retro burn to slow it for rendezvous with the HEO cargo park. Rinse and repeat. Goal being to send as much cargo per dollar possible. The Manned flights obviously different.

[darkenfast]

The intent for the the DRACO nuclear rocket powerplant to be tested in low Earth orbit brings attention again to the fact that the Partial Test Ban Treaty signed in 1963 prohibits all nuclear detonations except those conducted underground, especially when considering that this treaty doomed Project Orion.

What the heck does a ban on nuclear detonations have to do with this? It's not a nuclear bomb. It's a nuclear reactor, powering a rocket motor.

[sevenperforce]

Perhaps this is a FTL design, since the promotional material says "Humans...will travel at speeds faster than ever possible." /s

Can't assume anything from promo mockups, but the presence of multiple auxiliary gold foil tanks does make me want to speculate about a dual-mode hydrolox NTR.

[Coastal Ron]

I'm not a rocket scientist, but what I'm proposing is combining two transportation systems and letting them do less than what they are being designed to do.

Both are being designed to go from Earth to Mars, so using the nuclear tug to only put mass out of Earth orbit and then return should not be outside the capabilities of such a tug. And for the Starship, getting an assist out of Earth orbit would SAVE propellent, either by not being loaded in the first place, or being able to land more propellant on Mars.

In essence, the nuclear tug would be like a Falcon 9 booster, except that it is starting in LEO, and returning to LEO.

And I have no idea about the math, so if someone wants to look into it and make a determination one way or the other, great. It just seems like a good marriage of the two... 

...
Why would you add 4.2km/sec to a stage, and then have to boost it back the same amount?   There are no gravity losses to overcome.  the mass saved to LEO is practically nothing.  You introduce the problem of long term storage of H₂.

The Lockheed Martin video above states that the propulsion will be used for cislunar transportation, and for payloads going to Mars, so this is similar to what I'm talking about. And the video is a little fuzzy about whether the nuclear powered vehicle goes to Mars, but regardless what I'm talking about is more like the cislunar version.

As to long term storage of H₂, ANY use of this technology has that challenge, and is part of the demo. What I'm proposing is in line with what they are already planning for future use.

[InterestedEngineer]

If this gets proved out, I was thinking that a hydrogen-fueled nuclear tug could be built that would lessen the number of propellant trips it would take for a Starship-to-Mars mission. Assuming SpaceX would buy or build such a service, and the tug in LEO could mate to an outgoing Starship and be a more efficient way to push a Starship to Mars.

Then the tug would turn around and return back to LEO to refuel and wait for its next client.

This may require SpaceX to add LH2 fueling to a Starship Tanker version, but I'd have to think that would be doable at some point.

Fingers crossed that this test goes well, since it could really help with interplanetary travel.

Starship aerobrakes at Mars.

How does the nuclear tug brake ~4 km/sec of deltaV at Mars?

The Starship is already designed for landing on Mars, and I'm not talking about that. What I'm talking about is using a hydrogen-fueled nuclear tug to push a Starship out of Earth orbit and on towards Mars, but the tug stays in Earth-local space and returns to LEO for the next Starship.

This would could:

A. Reduce the amount of Starship refueling trips SpaceX would have to make for each Starship that is bound for Mars.

B. Allow Starships to leave for Mars with far more propellant, which maybe means they can land with more propellant on Mars.

assuming 100t of dry mass on the LEO->Mars injection tug, 225t of end mass, that's a dry mass for the tug of 325t.

It requires 4280m/sec of deltaV to inject from LEO to Mars transit.

But the tug needs to turn around and come back (unless you were planning to loop around Mars but you are not from your description).   So it's another 4280m/sec to come back.

Ugh, I hate two-stage calculations without a spreadsheet.

4280m/sec is a mass ratio of 1.9 for DRACO NTR.

Fast forward to tug return we have 100t of dry mass and 1.9 mass ratio for a mass of 190t, of which 90t is fuel.

Then we have 225t of mass for Starship, so a total of 415t of mass at the end of the tug outbound boost.  that's 790t of mass or 374t of fuel.

So the total H₂ to orbit is 374+90  = 464t of H2 to LEO.

Contrast this to 4280 m/sec for Starship to get to Mars Injection velocity from LEO.  A mass ratio of 3.2 or 500t of fuel to LEO.

There's almost literally no savings in mass to LEO especially considering LH₂ requires double insulated tanks and LCH₄ dose not

A tug to get Starships from LEO to Mars Injection doesn't pencil out.

I note that looping the NTR around Mars involves a lot less deltaV and gives times for hot radio nuclides to decay.  But you'll need a lot more of them and Lockheed isn't known for their mass production capabilities.  Building the machine that builds the machine is 10x harder.

TL;DR - you are confusing distance with deltaV.  Distance doesn't matter much in orbits. DeltaV does.

Seriously, go download KSP and play it for a week, you'll get an intuitive feel for it.