How Atmosphere Breathing Electric Propulsion Impacts Spacecraft Geometric Design and Layout

Earth observation (EO) and communication payloads could be made lighter and cheaper if the mission altitude were to be reduced to below 450km into what we call Very Low Earth Orbit (VLEO). Optical, synthetic aperture radar, LIDAR
and communications payloads are prime candidates for VLEO missions. VLEO allows improvements in radiometric performance, proportional to the inverse square of the distance. Optical resolution scales linearly with reduction in
altitude. This allows improved payload performance and/or a reduction in the mass and cost of the spacecraft. Atmosphere Breathing Electric Propulsion (ABEP) is a novel form of Electric Propulsion where the propellant is
collected from the residual Earth Atmosphere without requiring pre-stored propellant. ABEP has the potential to make significantly longer missions in VLEO feasible as the requirement for stored propellant is removed. The introduction of ABEP significantly impacts the design of the spacecraft. Alongside the desire to minimise the cross-section (for drag reduction), ABEP requires a front-mounted intake to maximise propellant capture. Consequently, integrating ABEP into a VLEO spacecraft requires special attention to the geometric design and layout.
The aerodynamic stability profile of the spacecraft is also of crucial importance. The need for an intake can shift the centre of pressure of the spacecraft forwards, increasing destabilising aerodynamic torques. The design of the intake is a
crucial design parameter, affecting both the aerodynamic stability profile and the possible thrust produced. Two main types of intakes have been designed: one intake with a hexagonal geometry assuming traditional materials and drag
profiles and a specular intake-based on a parabolic geometrical design.
With these considerations, two basic ABEP configurations are often proposed in the literature. The first are long slender body designs with a single intake, corresponding to virtually the entire cross section of the spacecraft body,
and a single thruster laying behind. The intake can either be diffuse or specular. The second are flat body designs incorporating a series of intakes and thrusters to maximise the intake area/cross section ratio when paired with specular
intakes. This paper uses a holistic approach, considering the constraints imposed by ABEP, with the aid of a morphological matrix. From this two concepts are identified: A more conservative design using methods commonly found in past and present VLEO spacecraft, and a more novel design, utilising some of the features introduced in this paper.