  Aerial communication platforms, stratospheric high-altitude platform stations
(HAPS), have the potential to provide/catalyze advanced mobile wireless
communication services with its ubiquitous connectivity and ultra-wide coverage
radius. Recently, HAPS has gained immense popularity - achieved primarily
through self-sufficient energy systems - to render long-endurance
characteristics. The photo-voltaic cells mounted on the aircraft harvest solar
energy during the day, which can be partially used for communication and
station-keeping, whereas, the excess is stored in the rechargeable batteries
for the night time sustenance. We carry out an adroit power budgeting to
ascertain if the available solar power can simultaneously and efficiently
self-sustain the requisite propulsion and communication power expense. We
further propose an energy optimum trajectory for station-keeping flight and
non-orthogonal multiple access (NOMA) for multi-cell users, which are served by
the directional beams from HAPS communication systems. We design optimal power
allocation for downlink (DL) NOMA users along with the ideal position and speed
of flight with the aim to maximize sum data rate during the day and minimize
power expenditure during the night, while ensuring quality of service. Our
findings reveal the significance of joint design of communication and
aerodynamics parameters for optimum energy utilization and resource allocation.
