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SPS Station Keeping Using Solar Radiation Pressure for Propulsion

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SPS Station Keeping Using Solar Radiation Pressure for Propulsion

The architecture of an SPS system requires that the SPS maintain constant visibility to both the Sun and the ground station. This immediately implies a so-called Geosynchronous Equatorial Orbit (GEO), which is also called a Geostationary Orbit; or a near-GEO Geosynchronous Orbit (GSO). These are substantially the same orbits that are used for existing communications satellites.

In GEO, or GSO (near-GEO), maintaining clearance from other satellites is achieved by assigning a longitude “station”. Each satellite is responsible for “station-keeping” at its assigned station. Station-keeping is perturbed by a number of natural solar, lunar, and Earth gravity effects and also by Solar radiation pressure. The main perturbation effects are caused by gravity and Solar radiation pressure. An SPS is disproportionately affected by solar radiation pressure and exhibits a correspondingly more severe perturbation. Existing communications satellites are equipped with propellant based thrusters that are used to achieve station-keeping by countering the accumulative effect of these perturbations. This is an effective strategy, in part because the solar radiation pressure perturbation is comparatively small. Never-the-less, the required propellant is a significant component of the satellite launch mass and therefore its launch cost, and also the limiting factor determining the satellite’s operational lifetime. For an SPS, the effect of solar radiation pressure is more severe. Consequently a propellant based thruster station-keeping strategy requires disproportionately more propellant, with a disproportional effect on launch mass and therefore on launch cost. An alternative station-keeping strategy is suggested, given the disproportionately affect of solar radiation pressure, perhaps solar radiation pressure can be used advantageously. An SPS may be able to achieve station-keeping by “redirecting” solar radiation pressure (RSRP), by reflection or refraction, in a controlled manner. Such a strategy would require no propellant and would provide an indefinite operational lifetime.

This study uses a simulation approach, corroborated by analysis, to determine the effects of various perturbations and station-keeping algorithms. The relevant perturbations incorporated in this simulation are the Solar and Lunar gravity, the solar radiation pressure, thermal re-radiation, the microwave power beam momentum, and partially the non-spherical Earth gravity.

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