Mission pointing optimisation of twin satellite system for all-sky burst monitoring

The first detection of gravitational wave has revealed a new page of the astronomical research, which is reinforced when the electromagnetic counterpart of gravitational wave was firstly observed in 2017. Multi-messenger observation has become one of the hot spots in current astronomical research. To capture the precious electromagnetic counterparts of gravitational waves, a special all-sky X/γ-ray monitoring twin nano-satellite GECAM(Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor) is designed.

Each satellite is equipped with a multi-sensor payload, the FoV of which is more than 2π. Therefore the twin satellite shoule be nadir pointing and with 180-degree phase difference can monitoring the all-sky. While for X/γ-ray instruments, they generally need to work in low altitude and low inclination orbit to minimise the impact of high-energy particles on pole regions and SAA region. Constrained by the ground station accessibility, the satellite orbit is defined around 600km with 29 degree inclination. The satellite pointing strategy design then should take into account both the all-sky monitoring mission needs and satellite energy acquisition needs, as well as the optimisation of thermal control and STR pointing and reliability. Different from sun-synchronous LEO nadir pointing satellites, the satellite attitude pointing needs to be specially designed.

This paper presents a satellite pointing law designed suitable for such all-sky monitoring low inclination LEO satellites. Advantages of this pointing law are analysed from the perspectives of constraints satisfaction, energy acquisition and cost of implementation. The realization method of the guidance algorithm on-board is also presented.