Satellite-to-satellite attitude control of a long-distance spacecraft formation for the Next Generation Gravity Mission

Abstract

The paper presents the design and some simulated results of the attitude control of a satellite formation under study by the European Space Agency for the Next Generation Gravity Mission. The formation consists of two spacecraft which fly more than 200 km apart at an altitude from the Earth's ground of between 300 and 400 km. The attitude control must keep the optical axes of the two spacecraft aligned with a microradian accuracy (pointing control). This is made possible by specific optical sensors accompanying the inter-satellite laser interferometer, which is the main payload of the mission. These sensors allow each spacecraft to actuate autonomous alignment after a suitable acquisition procedure. Pointing control is constrained by the angular drag-free control, which is imposed by mission science (Earth gravimetry at a low Earth orbit), and must zero the angular acceleration vector below 0.

The four-tank control problem: Comparison of two disturbance rejection control solutions

“…The relation between the closed-loop spectrum Λ and the gains in (46) can be found in [28] and [29].…”

“…A two-sided inequality like (69), though to the authors' knowledge absent in the literature, is the key asset of Embedded Model Control, and may be converted into an optimization criterion [28]. Of course, (69) may result to be unfeasible, but increasing and/or decreasing may allow the upper bound to be enlarged.…”

“…Embedded model (48) is the same as that of a two degree-of-freedom motion, so pole placement as in [28] applies.…”

“…Model endowment with disturbance dynamics is a key tool for decoupling control strategies as shown in [27] and [28]. As a third extension, the disturbance observer feedback is allowed to be a dynamic system when a static feedback cannot guarantee closed-loop stability [28], [29]. In fact, the state observer feedback is conceived as an output to noise (not as an output to state) feedback, which implies that when driving noise is singular, i.e.…”

“…According to the Embedded Model Control (EMC, [25], [26]) methodology, embedded model must include suitable disturbance dynamics (not necessarily first order as in ESO and ADRC), which is driven by arbitrary bounded signals playing the role of driving noise. Model endowment with disturbance dynamics is a key tool for decoupling control strategies as shown in [27] and [28]. As a third extension, the disturbance observer feedback is allowed to be a dynamic system when a static feedback cannot guarantee closed-loop stability [28], [29].…”