Upper Stages for Deep Space?

[redliox]

When the time comes to consider elements for lunar or martian missions, the most obvious first step is to turn to what's available.  While building a lander or a crewed vehicle in general will be a pain, adapting an upper stage to serve as an injection stage for orbit insertion or departing for Earth seems more straightforward; granted, of course, there have to be some modifications if the thing's going to sit idle for months/years.

Basically I'm curious what's on the market right now that's easy to adapt.  I exclude cryogenics like the Centaur since those modifications would be more extensive as compared to something hydrazine-based; eventually I would assume we'd see long-lasting insulation for hydrolox and methalox but that may be a while yet.  What's available that's either solid or hypergolic?

[edkyle99]

When the time comes to consider elements for lunar or martian missions, the most obvious first step is to turn to what's available.  While building a lander or a crewed vehicle in general will be a pain, adapting an upper stage to serve as an injection stage for orbit insertion or departing for Earth seems more straightforward; granted, of course, there have to be some modifications if the thing's going to sit idle for months/years.

Basically I'm curious what's on the market right now that's easy to adapt.  I exclude cryogenics like the Centaur since those modifications would be more extensive as compared to something hydrazine-based; eventually I would assume we'd see long-lasting insulation for hydrolox and methalox but that may be a while yet.  What's available that's either solid or hypergolic?

Not too many years ago, the U.S. had a good starting point - Aerojet's LR91/AJ11 Titan second stage engine, but that was retired with Titan 4.  Now the U.S. has no comparable pump-fed hypergolic engine.  AJ10 is pressure-fed and its thrust too low.

 - Ed Kyle

[redliox]

Not too many years ago, the U.S. had a good starting point - Aerojet's LR91/AJ11 Titan second stage engine, but that was retired with Titan 4.  Now the U.S. has no comparable pump-fed hypergolic engine.  AJ10 is pressure-fed and its thrust too low.

Hmm any reason you cite the Titan's second stage?

What of more modern 3rd stages? (granted they are smaller of course)

[MATTBLAK]

What about a reusable in-space propulsion stage with 4x AJ10 derivatives? Or if they were returned to Apollo SM standard they'd have about 20,000lbs thrust. Or the Shuttle types which made about 6,000lbs thrust - hence my saying that a quartet of them could be used.

[Katana]

Propulsion is only a small fraction for a deep space mission. Especially conventional propulsion.

[edkyle99]

Not too many years ago, the U.S. had a good starting point - Aerojet's LR91/AJ11 Titan second stage engine, but that was retired with Titan 4.  Now the U.S. has no comparable pump-fed hypergolic engine.  AJ10 is pressure-fed and its thrust too low.

Hmm any reason you cite the Titan's second stage?

What of more modern 3rd stages? (granted they are smaller of course)

The reason I suggested the Titan 4 second stage engine is, first, that it had enough thrust for the suggested mission (106 Klbf) and, second, that it was the highest performing U.S. pump-fed hypergolic propellant engine of that thrust class (nearly 318 sec ISP).

The use of pump fed propulsion allows for much higher propellant mass fractions.  The Titan 4 second stage PMF was 0.923.  The Delta 2 second stage, which uses the pressure fed AJ-10 engine, has a 0.863 PMF.  Both have roughly the same ISP, but the Titan 4 second stage produced 10 times more thrust.

A newly developed pump-fed hyper engine should be capable of 340 sec ISP.  Rocketdyne worked on such engines (N2O4/MMH) in the past, but never fully developed them.

 - Ed Kyle

[edkyle99]

Here's how big, or small, these MMH/N204 deep space stages would have to be, compared with EUS, for trans-mars delta-v.  This assumes 340 sec ISP and 0.94 PMF.  I'm also assuming Titan's 120 inch diameter tanks.

This always looked "do-able" to me.  The stage could be loaded with propellant in steps, using some type of standardized propellant hauler that could be launch-vehicle independent.  Some type of "space dock" would be needed that would provide on-orbit control along with a source of electrical power for propellant heaters and avionics.

 - Ed Kyle

[edkyle99]

The following paper discusses what would likely be a good candidate engine for this work.  Aestus II/RS-72 was jointly developed and tested by EADS  Astrium  and  Pratt  and  Whitney Rocketdyne.  Granted, that was around 2000, but this 2014 paper proposes that its development be completed.
http://elib.dlr.de/89043/1/SP2014_2968378_HTS.pdf

Several of these 12.5 Klbf engines would need to be clustered to power a deep space stage.

 - Ed Kyle

[ArbitraryConstant]

The following paper discusses what would likely be a good candidate engine for this work.  Aestus II/RS-72 was jointly developed and tested by EADS  Astrium  and  Pratt  and  Whitney Rocketdyne.  Granted, that was around 2000, but this 2014 paper proposes that its development be completed.
http://elib.dlr.de/89043/1/SP2014_2968378_HTS.pdf

Several of these 12.5 Klbf engines would need to be clustered to power a deep space stage.

I think electric pumped similar to Rutherford might be an alternative in this thrust level.

In general I would expect electric pumped to somewhat underperform gas generator, but it would outperform pressure fed (should also outperform solid kick), and the simpler cycle and modest thrust makes development and manufacturing of the engine significantly cheaper, which is an asset for what would likely be quite a modest total number of units.

For Earth departure it might well be possible to simply use Rutherford as is with LOX, if storable propellant were required there would need to be a new engine but even then development should be quicker and cheaper for an electric pumped engine rather than gas generator.

Being able to 3D print most of the engine in one part from available alloys avoids reliance on a dedicated industrial base, which has often been an issue for infrequently used engines. Dunno about alloy compatibility with hypergols but it can't be that bad given SuperDraco is also 3D printed.

[Katana]

LR91 have been converted from cryo to hypergolic as well as LR87. Converting Merlin or other kerolox gas generator engine is also OK.

 Aluminium, stainless steel, Inconel 718 and Teflon seals are all compatible to both LOX and hypergolics.

[redliox]

LR91 have been converted from cryo to hypergolic as well as LR87. Converting Merlin or other kerolox gas generator engine is also OK.

 Aluminium, stainless steel, Inconel 718 and Teflon seals are all compatible to both LOX and hypergolics.

That's great to hear systems can tolerate a variety of needs.  I wouldn't be against using kerolox or methalox for instance, so long as insulation can be improved.  Kerolox isn't one I heard of considered before; how would its performance in space compare against hypergolics?

[envy887]

LR91 have been converted from cryo to hypergolic as well as LR87. Converting Merlin or other kerolox gas generator engine is also OK.

 Aluminium, stainless steel, Inconel 718 and Teflon seals are all compatible to both LOX and hypergolics.

That's great to hear systems can tolerate a variety of needs.  I wouldn't be against using kerolox or methalox for instance, so long as insulation can be improved.  Kerolox isn't one I heard of considered before; how would its performance in space compare against hypergolics?

Kerolox gets 5-10% better specific impulse than NTO/MMH, but bulk density is 15-20% lower and it requires extra mass for thermal control.

[baldusi]

Blok-D uses kerolox and was designed to be used on moon missions. I understand that methalox is quite storable in space, specially outside of LEO. An electric pumped engine with and ACES-like electric generator fed by gaseous ch4/o2, would make an amazing deep space stage.

[ArbitraryConstant]

Blok-D uses kerolox and was designed to be used on moon missions. I understand that methalox is quite storable in space, specially outside of LEO. An electric pumped engine with and ACES-like electric generator fed by gaseous ch4/o2, would make an amazing deep space stage.

I was wondering what the best fuel might be if you were willing to use cryo propellants. Isn't pumping energy proportional to volume? A denser hydrocarbon might work better if it saves battery mass.

Another thought I had for a small/inexpensive 3D printed engine was methalox expander bleed. The turbines enjoy fairly benign conditions and the difficulty of tuning the thermodynamics of a closed expander cycle can be avoided.

[baldusi]

Blok-D uses kerolox and was designed to be used on moon missions. I understand that methalox is quite storable in space, specially outside of LEO. An electric pumped engine with and ACES-like electric generator fed by gaseous ch4/o2, would make an amazing deep space stage.

I was wondering what the best fuel might be if you were willing to use cryo propellants. Isn't pumping energy proportional to volume? A denser hydrocarbon might work better if it saves battery mass.

Another thought I had for a small/inexpensive 3D printed engine was methalox expander bleed. The turbines enjoy fairly benign conditions and the difficulty of tuning the thermodynamics of a closed expander cycle can be avoided.

In deep space, where you can rely on a small thermal "umbrella" to keep the stage on the shadow, you can keep LOX and CH4 in liquid state indefinitely. You can't do that with LH2. And using propane offer no advantage since you have to keep LOX liquid anyways. So long term cryo is methalox. Not surprisingly what SpaceX and Blue Origin are basing their projects on.

[ArbitraryConstant]

Aluminium, stainless steel, Inconel 718 and Teflon seals are all compatible to both LOX and hypergolics.

Would a composite tank work with hypergols?

[ArbitraryConstant]

In deep space, where you can rely on a small thermal "umbrella" to keep the stage on the shadow, you can keep LOX and CH4 in liquid state indefinitely. You can't do that with LH2. And using propane offer no advantage since you have to keep LOX liquid anyways. So long term cryo is methalox. Not surprisingly what SpaceX and Blue Origin are basing their projects on.

Here's something interesting: https://www.reddit.com/r/space/comments/4taxfz/rocket_lab_usa_is_building_a_loxrp1_rocket_so_why/

The linked high resolution image is gone from the rocketlab website but it sounds like it might already have been adapted to CH4. I don't think a stage that small wants to deal with the complexity of an ICE generator from boiloff, but with some modest mods it might well do a good job as a poor man's Centaur or even lunar lander stage. You'd contract with Rocket Lab, it would ride as a payload in a fairing on another launcher. Probably small enough to easily use Proton/Falcon 9/Atlas 401/etc.

[Katana]

Aluminium, stainless steel, Inconel 718 and Teflon seals are all compatible to both LOX and hypergolics.

Would a composite tank work with hypergols?

No.
However hypergols are more dense than kerolox and require no heat insulation, consume less pressurization gas. The result is high mass ratio with conventional aluminium or stainless steel tanks.

[ArbitraryConstant]

Something I didn't know but found out via this post by jongoff http://forum.nasaspaceflight.com/index.php?topic=37676.msg1662345#msg1662345

... is that there's two companies (masten and ursa major) working on advanced cycle methalox engines, dual expander and staged combustion respectively, with thrust appropriate for a deep space upper stage.

It seems quite likely that something along these lines would be the best you could do this side of RL-10. There'd even be advantages because methane is much easier to keep liquid for long durations than hydrogen.

[A_M_Swallow]

Something I didn't know but found out via this post by jongoff http://forum.nasaspaceflight.com/index.php?topic=37676.msg1662345#msg1662345

... is that there's two companies (masten and ursa major) working on advanced cycle methalox engines, dual expander and staged combustion respectively, with thrust appropriate for a deep space upper stage.

It seems quite likely that something along these lines would be the best you could do this side of RL-10. There'd even be advantages because methane is much easier to keep liquid for long durations than hydrogen.

RL-10 has a thrust of 110 kN or 24.7k lbf.
The Broadsword engine from Master Space Systems burns methane and produces 25k lbf.
https://en.wikipedia.org/wiki/Masten_Space_Systems

http://www.twcnews.com/ca/antelope-valley/news/2017/04/7/masten-space-systems-wins-nasa-contract.html

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