A novel cryogenic storage solution for atmosphere-breathing electric propulsion systems

Recent interest in missions to Very Low Earth Orbit (VLEO) has led to the emergence of Atmosphere Breathing Electric Propulsion (ABEP). In theory this technology could enable missions to VLEO that forego the need to launch with propellant. This innovative concept could allow the full potential of low altitude regimes to be exploited as propellant consumption no longer limits lifetime. The most promising designs use a passive intake system that requires no moving parts to operate. Natural phenomena caused by the flow conditions at orbital velocity are exploited to provide an electric thruster with an adequate supply of gas. However a previously identified shortfall in its capabilities is that no propellant is stored during operation. This leaves the system at the mercy of the unpredictable conditions witnessed in Earth’s atmosphere. This thesis proposes a solution to this problem. If molecules ingested by a passive intake can be cooled to cryogenic temperatures, they can be temporarily captured so long as they are kept cold. This phenomenon has the potential to be exploited as an in-orbit propellant storage system. To investigate this concept, firstly a baseline mathematical model for an ABEP system was constructed using current design methodologies. Secondly, this system was adapted to incorporate the novel storage concept. The resulting model was then compared to the baseline along common performance parameters in order to assess its feasibility. The results showed that during the collection of propellant the requirements on flow conditions for adequate performance became more stringent. Nevertheless a feasible operating region was found and a baseline system chosen. This design point allowed for a propellant collection rate of between 0.43 mg/s and 0.74 mg/s. At this rate of collection, calculations speculated a potential for >1000 m/s of Δv over an 8 year mission could be gained. If realised, the potential mission applications are vast and could not only complement the performance of ABEP systems but open up novel mission concepts such as in-orbit refuelling.