| الوصف: |
In the field of attitude dynamics and control, passive spacecraft attitude control by spin-stabilisation can already be considered a venerable technique, almost as old as spaceflight itself thanks to its simplicity. Even today it is still used in a variety of missions, ranging from stabilisation during an orbit boost, e.g. the deployment of the first two Galileo IOV spacecraft, to deep-space astronomy, e.g. the Planck space telescope. Mission concepts have been proposed for spin-stabilised penetrator-like spacecraft targeting non-atmospheric celestial bodies such as the Moon, in the Japanese Lunar-A and the British MoonLITE mission proposals, or Jupiter’s Galilean moon Europa in the joint NASA-ESA Europa-Jupiter System Mission (EJSM) proposal, which has recently been extensively remodelled to the mainly European Jupiter Icy Moon Explorer (JUICE). However, the same gyroscopic stability that resists unwanted disturbance torques also has an impact on the commanded manoeuvres. Several techniques have been developed to take into account and whenever possible benefit from the gyroscopic phenomena exhibited by a spinning spacecraft. This thesis will give an overview of the PhD project on single-thruster attitude control of a prolate axisymmetric spacecraft, spin-stabilised around its minimum moment of inertia axis. Having only one attitude thruster on a spinning spacecraft could be preferred for spacecraft simplicity (less mass, less power consumption etc.), or it could be imposed in case of e.g. contingency operations. First of all, the current state-of-the-art slew algorithms Halfcone, Multi-cone, Rhumb Line and the newer Astrium algorithm Sector-Arc Slew have been investigated and qualified. Next, two novel slew algorithms have been identified and developed. One of these is the Extended Halfcone, based on previous SSC work. As the name implies, its intention is to extend the usual Half-cone slew algorithm with a mild form of error correction. Another novel algorithm, the Dual-cone slew was designed to overcome the Half-cone limitations regarding attainable slew angles. It is capable of reaching almost any slew angle using two Half-cones; its energy and time consumption performance is comparable to a Multi-cone slew. The conclusion of this section is that there is not a single ‘best’ slew manoeuvre for all situations. The inertia properties of the spacecraft are directly determining whether a Half-cone (or derived) slew is even possible. Rhumb Line and Spin-Synch effectiveness is also influenced by the spacecraft’s inertia properties, but in different ways. When Half-cone derived manoeuvres are possible, a trade-off is generally required between the energy (propellant) required for a manoeuvre and its duration: a low-cost slew tends to take a long time to complete. Further trade-off considerations are e.g. the attainability of target slew angles and the complexity of the required calculations. Next, robustness analyses have been performed to estimate how well these slew algorithms perform in the presence of disturbances. These analyses have been done analytically (except for the Rhumb Line) and using numerical simulations. The results of these analyses indicate that for the prolate spacecraft under consideration, Half-cone derived manoeuvres are especially sensitive to perturbations in spin rate, which means that in practical applications a high-accuracy gyro may need to be considered to measure this spin rate. The effect of moment of inertia or thrust perturbations is almost negligible in comparison. The Rhumb Line does not exhibit the same sensitivity to spin rate perturbations due to its dependence on an external signal. Finally, the feasibility of using an air bearing table to perform hardware simulations of a prolate spinning spacecraft is investigated. Assembly, calibration and verification of this table and its attitude sensors and actuators are discussed and several free-spin and forced-nutation experiments are performed and analysed. A dual-thruster test method is proposed to enable small nutation angles that stay within the hardware constraints. Another practical experiment discussed is a potential flight experiment on the STRaND-1 microsatellite, currently under cooperative development at Surrey Space Centre and Surrey Satellite Technologies Ltd. This thesis contains the most comprehensive analysis of single-thruster slew algorithms for spinning spacecraft up to date. This includes two novel slew algorithms, the Extended Half-cone and the Dual-cone. The analysis also encompasses an extensive robustness analysis of each algorithm. |