|Institution:||Delft University of Technology|
|Keywords:||geostationary satellites; solar sailing|
|Full text PDF:||http://resolver.tudelft.nl/uuid:c4fe5e21-0a51-4121-b1de-1ce061c829b6|
Solar sailing is a propulsion method using sunlight as energy source, meaning it does not make use of propellants as conventional methods do. The principle of solar sailing is simple: a large lightweight sail acts as a mirror reflecting impinging light. According to the wave-particle duality light can be interpreted as a stream of photons travelling at the speed of light. As these photons impinge upon a solar sail, they transfer their momentum on the sail and thus the spacecraft. This energy transferred is the propulsive force in solar sailing. The achievable force is in the order of mN and thus not very large, but in the frictionless environment that space is it can have considerable effects. Since this force works continuously, the energy input can rise to vast levels over time. One of the possible applications for using a solar sail on a space mission is a displaced geostationary orbit. A geostationary satellite remains at a fixed position with respect to Earth's surface due to its orbital characteristics. A natural geostationary orbit can only be achieved at a specific altitude, eccentricity and inclination, meaning all geostationary satellites orbit the Earth in exactly the same orbital plane. This limitation causes the geostationary band to get more crowded every year and this is why the concept of displaced geostationary satellites is interesting. For this concept, a satellite is put in an orbit that is altered in order to lay outside the standard geostationary band while the relevant orbital properties remain constant and its position thus stays fixed above the Earth' surface. In this thesis a spacecraft equipped with a solar sail is used to achieve such a displaced orbit. Even though the thrust levels possible using a solar sail are limited, the fact that it allows for continuous thrust and does not rely on any propellant make it a promising candidate for this concept. This thesis investigates the feasibility of this idea. A differential evolutionary algorithm is used to search for orbital trajectories that fulfil the set requirements. Promising results were found considering increasing vertical displacement of the orbital plane above the equatorial plane. Using a sail performance of 1 mm/s2 and a trajectory of three revolutions, a displaced orbit with an average offset of 3 km with respect to the desired position throughout the trajectory was found. These results were found considering the most favourable conditions valid around the winter solstice. During other periods of the year, the direction of the sunline has changed and the performance of the solutions found decreases to approximately 20 km average offset. With a desired displacement of 25 km, this is clearly unacceptable high. It can therefore be concluded that achieving a displaced geostationary orbit is possible, although only for a limited time. The solutions found only hold for the conditions valid around December 21, the winter solstice. Throughout the year, the conditions change considerably and become less favourable. As a result no valid… Advisors/Committee Members: Noomen, R..