Satellite Attitude Control through Solar Radiation: a New Approach KRISHNA KUMAR Summary This paper first examines the influence of interactions of structural flexibility and the solar radiation pressure on satellite librational performance. A new attitude control approach is proposed, wherein rotation of the thermally deformed panels—with bimetallic construction—about their long axes in accordance with a suitable ‘bang-bang’ feedback control scheme aims at achieving the desired variation of the centre of solar pressure, and hence the resulting control torques. Several typical response results presented here establish the proposed concept. Introduction Solar power generation aboard a satellite at adequate levels is essential for the success of space missions. This is invariably accompanied by the use of large panels. The differential solar heating of these appendages leads to structural flexibility and deformation. This in turn has led to several cases of anomalous satellite attitude behaviour [1] including librational instability. For example, the spin stabilized Canadian satellite Alouette launched in 1962, as well as the American Explorer XX launched in 1964, suffered rapid spin decay leading to excessive attitude drifts and consequent loss of useful satellite lifespan. In both these cases, the decay was attributed to a net solar torque on thermally deformed vehicle appendages [2]. This problem of unintended, and possibly destabilizing, solar torques is rather general, and is likely to adversely affect the space missions with spin as well as gravity gradient stabilized vehicles. The problem is likely to be even more serious in the future, with all-round growth in on-board levels of solar power generated and hence panel sizes. There has been considerable interest in the influence of various environmental disturbing torques on the satellite attitude dynamics [3]. Of these, the influence of solar radiation pressure, particularly significant at high altitude orbits, has been studied quite extensively [4-6]. However, the effect of interactions of structural flexibility due to differential solar heating and the solar radiation pressure has received relatively little attention. This paper first examines the influence of these interactions on satellite librational performance. This leads me to propose a new attitude control approach wherein the thermally deformed panels with ‘bimetallic’ construction are made to undergo rotation about their long axes in accordance with a suitable ‘bang-bang’ feedback control scheme. The rotation of the deformed panels thus regulated aims at Krishna Kumar, Professor, Department of Aerospace Engineering, Indian Institute of Technology, Kanpur 208016, India.
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