  The operation of satellites in very low Earth orbit (VLEO) has been linked to
a variety of benefits to both the spacecraft platform and mission design.
Critically, for Earth observation (EO) missions a reduction in altitude can
enable smaller and less powerful payloads to achieve the same performance as
larger instruments or sensors at higher altitude, with significant benefits to
the spacecraft design. As a result, renewed interest in the exploitation of
these orbits has spurred the development of new technologies that have the
potential to enable sustainable operations in this lower altitude range. In
this paper, system models are developed for (i) novel materials that improve
aerodynamic performance enabling reduced drag or increased lift production and
resistance to atomic oxygen erosion and (ii) atmosphere-breathing electric
propulsion (ABEP) for sustained drag compensation or mitigation in VLEO.
Attitude and orbit control methods that can take advantage of the aerodynamic
forces and torques in VLEO are also discussed. These system models are
integrated into a framework for concept-level satellite design and this
approach is used to explore the system-level trade-offs for future EO
spacecraft enabled by these new technologies. A case-study presented for an
optical very-high resolution spacecraft demonstrates the significant potential
of reducing orbital altitude using these technologies and indicates possible
savings of up to 75% in system mass and over 50% in development and
manufacturing costs in comparison to current state-of-the-art missions. For a
synthetic aperture radar (SAR) satellite, the reduction in mass and cost with
altitude were shown to be smaller, though it was noted that currently available
cost models do not capture recent commercial advancements in this segment...
