Thread by @ULaunchA360

The Advanced Cryogenic Evolved Stage (ACES)

A thread on the upper-stage that could have changed the game (1/15)

(All image credit goes to ULA unless stated otherwise)

Building on the heritage of the Centaur upper stage, ACES was built with many goals in mind:

- Many Engine Burns
- Longer Duration Burns
- Increased Mission Flexibility
- Service Module Type Flexibility

ACES would have had 5.4-meter ultra-lightweight stainless steel balloon tanks, that could contain up to 3x more propellents and would have had 1-4 RL10CX engines.

Versions of the RL10 engine fly on rockets like SLS, Atlas V, and Delta IV Heavy. More engines mean more production which leads to lower costs.

📸: 30th Space Wing

Alright, let's get into the good stuff-

One of the most important aspects of ACES was its Integrated Vehicle Fluids (IVF)

There were 2 IVF modules located at the aft section of Centaur. These modules were able to eliminate main batteries, hydrazine, and helium.

The IVF modules were also able to enable in-orbit refueling and reusability, enhanced performance, and improved ridesharing which lead to ACES being immensely simple and low risk.

You can think of it as an Auxiliary Power Unit. ACES was able to give the stage electricity and remove "waste" propellants.

IVF could have also brought along distributed lift as a big game-changer too, drastically reducing launch costs for high-mass complex missions by eliminating the need for heavy-lift launch vehicles.

Vulcan could easily launch ACES along with the payload to Low Earth Orbit and then launch a refueling mission that would refuel the stage and allow it to have much more payload capability for interplanetary missions. We see this concept being used for SpaceX's Starship rocket.

ACES test articles were built over the years and tested at NASA's Marshall Space Flight Center

A proposed application of ACES was in Masten Space Systems' XEUS (eXperimental Enhanced Upper Stage) lander which aimed to get horizontal landings of crew and cargo on the moon in an affordable and adaptable lander that would have allowed easy access to and from the lunar surface

Bigelow Aerospace also saw potential in this using ACES in plans for a lunar orbiting facility. The plan was to utilize distributed lift and after a refueling mission dock to the facility in lunar orbit.

📸: Bigelow Aerospace

In September 2020 Mark Peller, vice president of major development at ULA stated that ULA was no longer actively pursuing the concept and that some of the technology would be moved on to the Centaur V upper-stage.

This picture is of the first fully assembled Centaur V MK1 tank

Tweets from @torybruno suggested that a future version of Centaur V (Centaur V MK3) would be similar to ACES and would contribute to the Cislunar Economy.

I appreciate it if you read this thread, I worked my hardest to try to have my info spot on. ACES was truly an amazing concept with so much potential especially to Cislunar but I guess it was just too good to be true.