# ULA’s Aspirations to Revitalize ACES Capabilities: A Move Toward Agile Space Operations
United Launch Alliance (ULA), a prominent entity in the aerospace sector, is reigniting its ambitions to create sophisticated in-space transport capabilities, echoing the objectives previously set forth by the Advanced Cryogenic Evolved Stage (ACES). ULA’s CEO, Tory Bruno, recently provided insights into the organization’s vision for enhancing the potential of their upper-stage rockets, notably the Centaur V, to facilitate agile space operations. These improvements could transform how spacecraft navigate and function in space, with profound consequences for both commercial and military space endeavors.
## The Aspiration for In-Space Transportation
Bruno has emphasized that ULA’s long-range aim is to establish a comprehensive in-space transportation framework that would enable spacecraft to move seamlessly between various orbits and execute an array of tasks, including in-space servicing, refueling, and mobility. This aspiration aligns with the U.S. Space Force’s ambition for “dynamic space operations,” a notion that would liberate spacecraft from the conventional constraints imposed by fuel limits.
“What we are aiming to achieve is to extend that substantially,” Bruno remarked, alluding to the capabilities ULA seeks to develop. “And what that would enable us to do is have an in-space transportation capability for maintaining mobility and servicing and similar activities.”
Agile space operations would allow spacecraft to shift between orbits without the constant necessity of returning to Earth for refueling or upkeep. This would unlock new avenues for space missions, encompassing satellite servicing, debris clearing, and long-range exploratory missions. Yet, realizing this vision demands overcoming considerable technical challenges, particularly regarding fuel storage and propulsion.
## The Difficulty of Storing Cryogenic Propellants in Space
One of the primary obstacles to achieving agile space operations is the capacity to retain significant quantities of cryogenic propellants in space for prolonged durations. Cryogenic propellants, such as liquid hydrogen and liquid oxygen, are maintained at extremely low temperatures, often hundreds of degrees below zero. In the emptiness of space, preventing these propellants from vaporizing due to exposure to solar heat presents a challenging thermal management issue.
“No one has attempted to store large volumes of super-cold propellants in space for weeks or more,” Bruno pointed out, underscoring the uniqueness and complexity of the issue. “Accomplishing this is a non-trivial thermal problem, necessitating insulation to prevent solar heat from affecting the liquid cryogenic propellant.”
To tackle this challenge, ULA is running experiments with the Centaur V upper stage, which will be assessed in an upcoming flight. While Bruno was cautious about divulging specific details regarding the experiments for proprietary reasons, he did indicate that the tests would assist in validating ULA’s analytical models concerning the upper stage’s performance in space. These experiments will concentrate on controlling the thermal load that risks boiling off the cryogenic propellants.
“Some of these are devices, some of these are maneuvers because maneuvers make a difference, and some relate to performance in a way,” Bruno clarified. “In certain instances, those maneuvers are aiding us with the thermal load that attempts to boil off the propellants.”
## The Revival of ACES-Like Capabilities
ULA’s ongoing initiatives to bolster the Centaur V upper stage closely resemble the objectives of the now-defunct ACES program. ACES was designed to be a highly efficient upper stage capable of operating for extended durations in space, utilizing innovative technologies to decrease reliance on traditional consumables such as hydrazine, helium, and batteries.
A pivotal aspect of ACES was the Integrated Vehicle Fluids (IVF) system, an internal combustion engine designed to recycle gasified waste propellants to pressurize the propellant tanks, generate electrical power, and supply thrusters for attitude regulation. This system would have enabled the upper stage to forgo the need for hydrazine for attitude control, helium for pressurization, and batteries for power, resulting in a more self-sufficient and efficient framework.
Bruno indicated that ULA continues to pursue comparable objectives for the Centaur V upper stage. “Ultimately, ULA aims to eliminate hydrazine attitude control fuel and battery power from the Centaur V upper stage,” he stated. This endeavor would entail creating systems capable of recycling waste propellants and generating power in space, mirroring the IVF system envisioned for ACES.
## The Future: In-Orbit Refueling and Propellant Depots
Alongside augmenting the capabilities of upper stages like Centaur V, ULA’s vision for agile space operations will likely necessitate the development of in-orbit refueling and propellant depots. These technologies would enable spacecraft to refuel in space, thereby extending their operational lifespans and facilitating more intricate missions.
The idea of in-orbit
