Random Thoughts: ACES/EUS Public Private Partnership Idea

A few years ago, I did a “Random Thoughts” blog post about synergies between the proposed ACES stage and the proposed SLS upper stage1. Now, I’m still not the world’s biggest SLS fan, and I’m still not a fan of sole-sourcing EUS to Boeing, but I was realizing today that the potential for synergies may be even higher now, and I wanted to throw out an idea for a potential public-private partnership that would benefit both NASA and ULA, and save the taxpayer some money now and in the future.

Current EUS Concept (Credit NASASpaceflight.com)

Current EUS Concept (Credit NASASpaceflight.com)

Here were my thoughts/observations that led to my latest concept (in no particular order):

  1. The most complex part of an upper stage is typically the bottom of the stage where the propulsion systems are located. The tanks themselves are relatively simple comparatively. Tank stretches have always been considered much, much easier and lower risk than changing the diameter of a stage, because now you usually have to redesign all the structures and plumbing on the back end.
  2. Both EUS and ACES are looking at using four RL-10 class engines on their stage. The EUS wants to use a different RL-10 variant with a longer extendable nozzle, but not a wildly different engine2.
  3. The EUS LOX tank diameter has in the past usually been 5.4m diameter, while the ACES stage is now baselined at 5.4m diameter3.
  4. There’s already some interest on the EUS side in leveraging some of the IVF systems as a way of providing auxiliary power.
  5. On the EUS, the LOX tank is likely suspended, with the interstage reacting loads into the bottom of the LH2 tank. This means the LOX tank doesn’t have to take compressive loads on the pad unpressurized.

So here’s my crazy thought: What if NASA had Boeing and ULA develop the EUS as a public-private partnership, with the LOX tank and propulsion section for EUS and ACES sharing a high-commonality design?

  • Have EUS go with the 5.4m diameter resistance-welded CRES tankage from ACES, with a ~4% longer barrel section to compensate for the 10cm (~4in) smaller diameter.
  • Have ACES design its propulsion thrust structure to accommodate both versions of the 4x RL-10 class engines.
  • Have EUS keep the current design for the aluminum 8.4m diameter tank and intertank structure, but have ACES stay with the common bulkhead design and 5.4m diameter CRES LH2 tank.
  • Have the EUS LOX tank sidewalls and top-dome slighly modified compared to ACES to react the loads to/from the intertank structure, and to eliminate the unneeded common-bulkhead, but keep the bottom dome and engine/equipment rack designs the same between the two.
  • If EUS needs more IVF modules, either have ACES leave space and minimal scarring of its structure to allow mounting two more modules 4, or have the EUS LH2 tank designed with IVF mounts (either at the bottom or top, depending on what gives the most bang for the buck).
  • Have Boeing focus on overall stage integration, the LH2 tank, the intertank structure, and the interstage structure, and any EUS-specific long-duration hardware (sunshields, cryo-coolers, radiators, solar panels, deep-space comms, etc).
  • Have ULA focus on the LOX tank and propulsion system, and have them produced on the same line that would make ACES.

There are some risks–this would work best if Boeing was willing and able to keep interfaces between the two halves simple, and wherever possible let ULA drive the LOX tank and propulsion element design without too much micromanaging. SLS, having much higher launch capacity can probably can afford to have EUS be a tiny bit less optimized if it allows for high-commonality and minimum impact to ACES, as opposed to forcing EUS to be hyperoptimized for SLS at the expense of being suboptimal for ULA.

The benefits I could see to NASA is that this would:

  1. If done right, potentially save significant development costs by leveraging both outside investment by ULA, and by having at a more commercially-driven design for at least part of the EUS. This might also accelerate when EUS was available.
  2. If done right, EUS would now share at least some of its fixed and marginal costs with the ACES assembly line, and would benefit from higher production rates on many of the subsystems.
  3. The core subsystems on EUS would see far more flights this way than they would on SLS alone, and the manufacturing team would stay fresh even if the SLS flight rate is modest.
  4. The EUS stage would probably end up with at least slightly better dry mass numbers, and would likely have longer duration built-in.
  5. EUS would be able to leverage at least some of the ongoing enhancements ULA is trying to develop for ACES (refueling/distributed launch, longer duration missions, etc).

ULA would obviously benefit for a few reasons too:

  1. Most of the complexity of ACES is in the LOX tank and propulsion section. The only other complex ACES part that wouldn’t be needed for EUS is the common bulkhead. The LH2 tank is pretty simple. So, if done right, this could help accelerate the development of most of ACES.
  2. If done right, this would both lower the cost of fielding ACES (since NASA would be footing part of the cost of the common elements), and would likely accelerate when they could have ACES flying by 1-2 years or more.
  3. They would effectively have an additional customer stream for ACES hardware.
  4. This would probably better align the interests of at least one of their parent companies with their interests.

If done right, taxpayers would benefit from decreased development and fixed operating costs compared to the current approach.

Now, I have no idea if Boeing or ULA would even consider this. You’ll notice I used the phrase “if done right” a ton of times, and things being done right are rarely a given when talking about government contracting. But it seems like an intriguing approach in a world where SLS is unlikely to get canceled anytime soon.


[Disclaimer: As the founder of a company that has done some work with ULA on their IVF system, I could potentially stand to financially benefit if NASA took this approach. I can’t claim to be an unbiased, unselfish player in this case. But I still feel it’s worth throwing the idea out there, as I think if done right it would make EUS a better stage, save NASA money, get EUS and ACES flying sooner, and generally make both systems better. I still am skeptical that SLS is worth saving per se, but assuming it isn’t going to go away, this seems like a way to get at least some benefit to the commercial space industry out of it.]

The following two tabs change content below.
Jonathan Goff

Jonathan Goff

President/CEO at Altius Space Machines
Jonathan Goff is a space technologist, inventor, and serial space entrepreneur who created the Selenian Boondocks blog. Jon was a co-founder of Masten Space Systems, and the founder and CEO of Altius Space Machines, a space robotics startup that he sold to Voyager Space in 2019. Jonathan is currently the Product Strategy Lead for the space station startup Gravitics. His family includes his wife, Tiffany, and five boys: Jarom (deceased), Jonathan, James, Peter, and Andrew. Jon has a BS in Manufacturing Engineering (1999) and an MS in Mechanical Engineering (2007) from Brigham Young University, and served an LDS proselytizing mission in Olongapo, Philippines from 2000-2002.
  1. then called the DUUS or Dual-Use Upper Stage, now EUS or Exploration Upper Stage
  2. Though to be fair, ACES is still theoretically trading the BE-3U and XCOR 25klbf LOX/LH2 engine, and EUS may still be trading the J-2X
  3. If I’m remembering correctly
  4. at the 12 o’clock and 6 o’clock positions if the current ACES IVF mounts are at 3 and 9 o’clock
Jonathan Goff

About Jonathan Goff

Jonathan Goff is a space technologist, inventor, and serial space entrepreneur who created the Selenian Boondocks blog. Jon was a co-founder of Masten Space Systems, and the founder and CEO of Altius Space Machines, a space robotics startup that he sold to Voyager Space in 2019. Jonathan is currently the Product Strategy Lead for the space station startup Gravitics. His family includes his wife, Tiffany, and five boys: Jarom (deceased), Jonathan, James, Peter, and Andrew. Jon has a BS in Manufacturing Engineering (1999) and an MS in Mechanical Engineering (2007) from Brigham Young University, and served an LDS proselytizing mission in Olongapo, Philippines from 2000-2002.
This entry was posted in Launch Vehicles, NASA, Random Thoughts, ULA. Bookmark the permalink.

10 Responses to Random Thoughts: ACES/EUS Public Private Partnership Idea

  1. Andrew Swallow says:

    Is there a reasonable chance that the 25k lbf thrust methane engines being developed will be ready to fly in the time scale of this project?

  2. Andrew,

    That’s irrelevant. Both EUS and ACES are planned as LOX/LH2 upper stages, and I see almost zero chance that they’d ever got LOX/Methane.


  3. Andrew Swallow says:

    Hydrogen is good for Earth launch vehicles but boil-off makes it poor for lunar/Mars ascent stages and the return trip.

  4. Andrew,

    If you’re running your lunar missions without local ISRU, you’re doing them wrong. And if you have ISRU you probably have three things that mitigate boiloff problems with LOX/LH2 for lunar missions: 1- You probably have storage tanks with much better insulation that you store the LOX/LH2 in during the surface stay–not the flight tanks. 2- You also have a source of LOX/LH2 that could replenish boiloff, but 3- If you have the ability to make LOX/LH2 locally, that implies cryocoolers to cool the O2 and H2 down to liquid temperatures, which means you should be able to suppress boiloff completely. When you’re in a partial-gravity environment, all of the problems of zero-g propellant management go away, so cryocoolers are much more doable solution. Honestly, landing a crycooler setup on your first cargo landing probably makes sense, which means your first manned landing can use the cryocooler to keep its prop cold as long as needed. Cryocoolers are only iffy for use on upper stages because you’re in zero-g, you’re power limited, and you’re usually trying to keep the mass down. Those concerns don’t apply for a surface site.

    For Mars I’m more split. I haven’t run the numbers, but I think that LOX/CH4 might make sense for a Mars Ascent vehicle, since you have a large local source of CO2 to work with.

    But we’re talking EUS and ACES, which aren’t Mars Ascent vehicles, they’re Earth Departure Vehicles, and for ACES it might also be a lunar ascent vehicle (Xeus style).


  5. Andrew Swallow says:

    We will have the ability to land cargo on the Moon several years before we can land people. The ISRU propellant equipment could be waiting for them.

  6. Andrew,

    I’m not sure I agree that we’ll have the ability to land people on the Moon several years before we can land people, but if we can land people, we can pre-land ISRU hardware. So at least for the Moon, I don’t get the benefit of Methane at all.


  7. Andrew Swallow says:

    To land (and take off) people a large lander with life support is needed. Cargo can be sent one way and does not need life support. Small prototype cargo landers have been flying in the desert and KSC for several years.

  8. Andrew,

    The landers they did at KSC and that we did “out in the desert,” while they demonstrated basic vertical takeoff and landing capabilities, were far from something you could actually use for lunar landings. Any lander big enough to land useful cargo would also be big enough to land a crew module of sorts, though I guess depending on how things are done, they might be available before the crew versions were ready.

    But I do agree with the general point that even if you don’t believe you can have robots do a lot of the setup (I’m skeptical) in advance, that you could at least pre-land a bunch of cargo before the first people land. And putting ISRU in that cargo would help.

    However….this has almost nothing to do with ACES or EUS, so let’s try steer back to the original topic.


  9. I’d like to see NASA– accelerating– the ULA’s IVF technology by incorporating it into a new LOX/LH2 single staged reusable extraterrestrial landing vehicle (ETLV) for the Moon, the moons of Mars, and for the surface of Mars (coupled with an ADEPT or HIAD deceleration shield).

    A reusable crew landing vehicle would, of course, require propellant depots. A EUS modified with IVF technology could be utilized as a mobile LOX/LH2 propellant depot capable of storing up to 125 tonnes of propellant for lunar missions.

    If you add a water storage tank capable of storing up to 200 tonnes of water, an electrolysis plant, and cryocoolers to the depot then it could manufacture and liquefy its own propellant. Power for the production of LOX/LH2 from water could be provided from a nearby one to two MWe solar array that it can dock with when it needs to manufacture propellant.

    If deployed by an SLS launch at EML1, water could initially be supplied to the depot by commercial launch vehicles: Falcon Heavy, Vulcan Heavy, etc. Monthly commercial launches could, therefore, transport more than 150 tonnes of water to the EML1 propellant producing depot every year.

    However, once water is being manufactured on the lunar surface at the lunar poles, water could be more cheaply exported from the Moon to EML1.

    In fact, a reusable IVF modified EUS equipped with– landing legs– could transport more than 125 tonnes of water from the lunar surface to EML1 per launch.


  10. CA says:

    At the NAC TI&E Committee meeting in July it was reported that the evaluation of IVF usage on SLS as part of the eCryo project was completed and a final report has been submitted. With any luck we will hear one way or the other if at least that portion of ACES will be incorporated into EUS.

Leave a Reply

Your email address will not be published. Required fields are marked *