"With the recent international push for lunar missions, the U.S. Space Force has emphasized the need for surveillance of the region beyond geosynchronous orbit, i.e., xGEO and cislunar space, or out to approximately 385,000 kilometers," Dr. Bennewitz explains.

'Cislunar' refers to the regions of space beyond the traditional geosynchronous orbits traveled by satellites orbiting the Earth. "To date, in-space surveillance and object tracking have largely been limited to the range of low Earth orbit, from 160-2,000 kilometers above the Earth's surface, through geosynchronous orbit, or approximately 36,000 kilometers," Dr. Bennewitz points out. "However, to deliver long-term technologies that enable regular cislunar access, advanced in-space propulsion systems are required to meet the demands of satellite maneuvers, including orbit transfer, orbit maintenance, attitude control and station keeping to support a long vehicle lifetime."

To address this need, the Air Force Research Laboratory (AFRL) is currently developing satellite technology as part of the Oracle spacecraft program, with a target launch window in 2026. The object of this mission is to support domain awareness for cislunar access by providing technology for object identification and tracking, both more challenging due to cislunar objects moving in relation to GEO satellites and presenting significantly fainter signatures to surveillance capabilities.

Dr. Bennewitz is associated with the UAH Propulsion Research Center and will serve as Principal Investigator for the work at UAH, a part of the University of Alabama System. "This is a multiyear effort with UAH serving as the primary institution and providing the experimental results," he says. "This research program addresses the underlying physics knowledge gaps required for exploring detonation-based combustion in small-scale thrusters for in-space applications using both methane and hydrogen as fuel."

To meet the challenges this new orbital range presents, Dr. Bennewitz's proposal, titled Multimode Detonation for Small Scale In-Space Propulsion, plans to develop a detonation-based propulsion system, a new technology capable of addressing these needs.

"Multimode operation is significant to explore in these compact thrusters for both low-impulse maneuvers, including orbit maintenance and station keeping, as well as more aggressive spacecraft movements requiring high change in object velocity, such as orbit insertion," Dr. Bennewitz says.

In the case of a rotating detonation rocket engine, or RDRE, fuel and oxidizer are injected into an annular channel, which is then ignited to initiate a detonation wave that travels around the channel. RDREs promise significant improvements over conventional deflagration combustion of older-generation rocket engines.

"A detonation engine offers multiple advantages for propulsion, including the potential for higher engine performance, compact heat release and negligible acoustic instabilities due to mode-locking," the researcher notes.

"This can theoretically produce up to a 10% increase in performance, which will enable increased payload capabilities delivered to cislunar space for strategic satellite insertion to support the timely need for space domain awareness. Additionally, remaining knowledge gaps required to enable long-duration operation of in-space detonation-based thrusters will also be addressed in the proposed work."

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