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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 sse 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-conesj 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 exploration of Saturn's giant satellite Titan is considered, with particular reference to its surface which is hidden beneath a thick atmosphere. Groundbased observations, in which great progress has been made recently, and the measurements made by the Pioneer and Voyager spacecraft, are reviewed. Concepts for spacecraft to perform in-situ measurements on Titan are reviewed, as is the development of the NASA/ESA Cassini mission, how the mission constrains scientific investigations, and in tum how the mission has been constrained by funding pressures. The capabilities of the Cassini payload for investigating Titan's surface are critically assessed, and the ability of the Surface Science Package (SSP) on the Huygens probe to determine the composition of surface liquids is examined. Some thoughts on payload selection and the value of individual measurements are presented. The development of an impact penetrometer, and the interpretation of penetrometer and accelerometer data to measure surface mechanical properties, is described. It should be noted that Huygens is not a vehicle expressly designed as a lander, so the impact dynamics are complex. Additionally, the examination of the prospects offered by acoustic instrumentation are investigated. Modelling of a number of Titan surface processes is presented, including rainfall, photochemical and meteoric deposition, tidal dissipation in the interior, regolith processes such as volatile heat transport, annealing and aeolian transportation and the effects of tidal and crustal processes on lakes. A key subtopic of the thesis addresses the theme of planetary exploration as a whole, with the interaction between and the limitations of the exploration 'triad' of observations, insitu measurements and theory. Note is made of the remarkably significant role played by individuals and their perceptions.

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The satellite ERS-1 was launched in July 1991 in a period of high solar activity. Sparse laser tracking and the failure of the experimental microwave system (PRARE) compounded the orbital errors which resulted from mismodelling of atmospheric density and hence surface forces. Three attempts are presented here to try and refine the coarse laser orbits of ERS-1, made prior to the availability of the full altimetric dataset. The results of the first attempt indicate that by geometrically modelling the satellite shape some improvement in orbital precision may be made for any satellite; especially one where no area tables already exist. The second and third refinement attempts are based on the introduction of data from some second satellite; in these examples SPOT-2 and TOPEX/Poseidon are employed. With SPOT-2 the method makes use of the orbital similarities to produce along-track corrections for the more fully tracked SPOT-2. Transferring these corrections to ERS-1 produces improvements in the precise orbits thus determined. With TOPEX/Poseidon the greater altitude results in a more precise orbit (gravity field and atmospheric errors are of less importance). Thus, by computing height differences at crossover points of the TOPEX/Poseidon and ERS-1 ground tracks the poorer orbit of ERS-1 may be improved by the addition of derived radial corrections. In the positive light of all three results several potential modification are suggested and some further avenues of investigation indicated.

In the last twenty or so years the results of theory and experiment have produced much information on the characteristics of gas-surface interactions relevant to a satellite in hyperthermal free-molecular flow. This thesis contains reviews of the rarefied gas dynamics applicable to satellites and has attempted to compare existing models of gas-surface interaction with contemporary knowledge of such systems. It is shown that a more natural approach would be to characterise the gas-surface interaction using the normal and tangential momentum accommodation coefficients, igma' and igma respectively, specifically in the form igma = constant , igma' = igma'0 -igma'1sec i where i is the angle subtended between the incident flow and the surface normal and igma,igma'0 and igma'1 are constants. Adopting these relationships, the effects of atmospheric lift on inclination, i, and atmospheric drag on the semi-major axis, a, and eccentricity, e, have been investigated. Applications to ANS-1 (1974-70A) show that the observed perturbation in i can be ascribed primarily to non-zero igma'1 whilst perturbations in a and e produce constraint equations between the three parameters. The numerical results seem to imply that a good theoretical orbit is achieved despite a much lower drag coefficient than anticipated by earlier theories.