The military wants nuclear propulsion to the Moon???

[Exoscientist]

29 minutes ago, DDE said:

No, it doesn't. "Move around cislunar space"

 Actually, cislunar space includes all the space with the vicinity of the Earth and Moon.

  Robert Clark

[sevenperforce]

1 hour ago, Exoscientist said:

This article suggests nuclear thermal propulsion could get to the Moon in hours:
ERIC BERGER - 6/15/2020, 8:18 AM
“With the DRACO program, the US Defense Department could potentially move large satellites quickly around cislunar space. For example, moving a 4-ton satellite from point A to point B might take about six months with solar electric propulsion, whereas it could be done in a few hours with nuclear thermal propulsion.”

What are the possibilities here?

(A) Eric Berger, who we know is quite intelligent, has had a complete mental breakdown and thinks something is possible when it absolutely isn't

(B) The Defense Department has a new, secret version of nuclear thermal propulsion with performance rivaling that of Project Orion

(C) "around cislunar space" simply means "around cislunar space" and does not mean "from LEO to cislunar space"

48 minutes ago, Exoscientist said:

 Actually, cislunar space includes all the space with the vicinity of the Earth and Moon.

It absolutely does not.

[farmerben]

Do they plan on doing the trip many times?  

A single stage of chemical rocket can go from LEO to the moon easily.  NTR does not have more thrust, just more dV.  So a single tank of fuel with an NTR might do the transfer a dozen times.  Solar electric propulsion is totally different.

[tater]

Electric propulsion is astoundingly low thrust, hence months to meaningfully change an orbit. Months of firing the engines.

My take might be that they mean the time the engines run.

A small NTR for testing would still be low TWR for some payloads (the 4t one suggesting in the article), but the high I_sp is valuable. So you run the engine for some hours.

[DDE]

I think I've found the NTR application. Here, top-right.

https://www.c4isrnet.com/battlefield-tech/space/2019/08/27/the-pentagon-wants-to-solve-a-deep-space-problem-with-three-vehicles/

Cislunar scout cruisers. And there's that word again, "maneuver".

On 11/1/2022 at 7:47 PM, DDE said:

Given the last time I've heard of NTRs in the context of US national security, I'm disinclined to take the article above at face value. The article below proposes use of NTRs for (ostensibly purely defensive) Earth-orbit warfare.

https://www.defensenews.com/opinion/commentary/2021/07/08/maneuver-warfare-in-space-the-strategic-imperative-for-nuclear-thermal-propulsion/

My initial reading of this was that someone overdosed on the word "maneuver", read how spacecraft are sitting ducks due to lack of a middle-ground in thrust and ISP, found out that NTRs occupy said middile ground, and ignored their poor responsiveness that makes them unusable as an emergency dodge engine.

However, now that there's a funded program, this seems a lot less silly. The possibility of someone still chasing the word "maneuver" without an articulated end goal should not be discount, but to assume your en... adversaries are stoooooopid is a conclusion preferably avoided.

NTRs are the most readily available option for a military spacecraft designed for intense and frequent orbit changes and dodging. That's likely the totality of the motivation, and it's a somewhat alarming one. Much has been done to differentiate the development of weapons that only briefly enter space, including planet-based anti-space weapons, and the placement of attack capabilities in space proper. It's a major red line.

 

[JoeSchmuckatelli]

2 hours ago, DDE said:

Much has been done to differentiate the development of weapons that only briefly enter space, including planet-based anti-space weapons, and the placement of attack capabilities in space proper. It's a major red line.

I'm not a huge fan of us putting loitering weapons in space... But I've also read several times that the efficacy of doing something like that isn't great.  (c.f. "Rods from God" project).  I.e. an unlikely 'first strike' weapon platform.

What's more likely behind this is 'persistence' in an anti-satellite warfare scenario.  RU, CN and US all have the ability to spy on and damage each other's satellites - and to one degree or another rely upon their satellite networks for ground combat operations.  So in any peer conflict involving these three (and yes it could go any direction, despite RU/CN's current declarations of love and support) - I suspect one of the first targets is each other's satellite networks. 

So this step - far from being a likely 'lets weaponize space and have a first strike capability' is more probably a 'lets build something that is persistent and able to avoid anti-satellite / recon satellites and retain the advantage of high-ground information warfare capability'.

[kerbiloid]

3 hours ago, DDE said:

Cislunar scout cruisers.

They finally have watched Konanykhin and realized in what where they are...

[steve9728]

Let's hope that plan about nuke the moon only stay in the movies

But the movie I watched months ago about when the plan to install engines on the moon to exile it was failed, and the idea of making up for the failed plan by placing thousands nuclear warhead somewhere on the moon to detonate it by chain reaction in phased array was really cool

[tater]

Cool. We need NTP.

[sevenperforce]

2 hours ago, tater said:

Cool. We need NTP.

Surprising exactly…nobody.

But I agree, we absolutely need it. 

[tater]

46 minutes ago, sevenperforce said:

Surprising exactly…nobody.

But I agree, we absolutely need it. 

The NTP people have been ready to fly something—with just some $$$ required to build a flight article—for years. Having this as a mature technology would be transformative I think.

[tater]

 

[sevenperforce]

14 hours ago, tater said:

 

Wow, they're building an FTL engine!?!?

Spoiler

Quote

"Humans...will travel at speeds faster than ever possible."

In all seriousness, this is great.

Of course this is a pure marketing mockup and we shouldn't assume any engineering details from it. I wonder what kind of engine cycle they will go for. The NTR that was intended to serve as a Earth-Lunar ferry as part of the original STS architecture would have been a dual-mode version of NERVA, balancing LOX injection for high thrust at the start of the burn against the pure-LH₂ low-thrust end burn for high efficiency. Nuclear engines have specific impulse to spare and so the usual challenge is trying to get high enough thrust to avoid Oberth losses.

NERVA was a thrust chamber tap-off (or "hot bleed" since you can't say combustion tap-off) design, which is probably why the flight-configured engines in the above mockup and in the BWXT image below are depicted with the turbine exhaust injection manifold wrapped halfway around the nozzle like an F-1 or MVac:

It's unclear why there are two separate flows from the tank and apparently two (or four?) separate turbopump assemblies as well. Maybe it's supposed to have two modes, one with a higher tap-off ratio and one without? Or are the turbopumps running in series?

For ground testing the nozzle extension was not used and so the turbine exhaust had a separate nozzle:

You can see that the tap-off comes from the very bottom of the reactor chamber right before entering the throat.

An alternative approach for a flight-configured engine would have had dual turbine exhaust nozzles, presumably for roll control (or even all control authority if the main engine was fixed:

With the thrust levels that you need from a NTR, a closed expander cycle really isn't possible. Granted, you make better use of the Carnot cycle power because you don't have to pump a bunch of heavy oxygen like closed expander hydrolox, but all that heavy oxygen is what's giving you most of your thrust, so you're right back where you started. Plus, the high mass of the nuclear reactor means that you're really not as concerned about squeezing out extra Isp as you are about getting more thrust.

The LockMart promotional materials in that video depict four gold foil tanks surrounding the reactor. Even though we obviously shouldn't assume anything gratuitously from the pure promotional stuff, it makes me wonder if they're considering a dual-mode design like the STS ferry, or even something more creative like using a hydrolox gas-generator as an independent pump cycle for the main pumps. There are definitely some unique considerations for a nuclear engine, beyond just the obvious (like safety issues). In a conventional liquid bipropellant combustion engine, you have a limited amount of total thermal energy you can extract from a given mass of propellant, but maximizing the heat energy increases the average molecular weight in the exhaust, lowering the total specific impulse. As a result, a bipropellant combustion engine has to balance maximal thermal output against an optimally efficient propellant mix (which is why engines don't typically run stoichiometric). With a nuke, on the other hand, the total amount of thermal energy available is not a function of the amount of propellant you have: instead, total available energy is a function of reactor mass and propellant dwell time. So the baseline assumptions don't always work out quite the same way.