Extremely Low earth orbit Imaging and Technology Explorer (ELITE) is an experimental micro-satellite on a mission to demonstrate the very low earth orbit (VLEO) flight, high-resolution imaging, and atmospheric data collection. The spacecraft will be launched at an altitude of 550 km, and it will gradually manoeuvre its orbit into VLEO and perform sustained flights are different altitudes for data collection. The camera on-board uses time-dependant integration (TDI) technology to produce high-resolution images. Therefore, the objective is to orbit as low as possible while maintaining the attitude stability required for TDI imaging. Besides the primary imaging mission, the spacecraft also carries: 1) atomic oxygen (AO) fluence detector for characterising the changing AO field in the region of flight, and 2) an ionospheric probe for in-situ plasma density and drift velocities. To support the orbit manoeuvres and drag compensation, the spacecraft is equipped with a propulsion system. There are numerous challenges to overcome to sustain a flight in VLEO which do not occur in LEO. The atmospheric density increases exponentially with altitude, i.e. the drag increases exponentially as the orbit altitude is lowered. The propulsion system has to be sized with adequate margin for sustained operations in VLEO. The increased drag also applies additional stress on to the attitude control system, compromising the stability of the spacecraft.
The power generation and ground contact will also be affected as the spacecraft shall maintain minimum drag and high stability orientation instead performing sun-tracking or ground tracking. Besides the ambient environmental challenges, the spacecraft is also subjected to surges in atmospheric density due to solar storms. The storms can increase the density by 10 or 100 times which can be catastrophic for the spacecraft. This paper discusses the mission design for ELITE mission considering the estimated launch time. Analytic results are shown for altitude profile, drag analysis, and structure optimisation. The objective is to highlight the mission design process considering the limitations and considerations of sub-systems. ELITE mission is fully funded by Singapore government and developed by Nanyang Technological University
