Chemical thrusters are widely used in spacecraft for attitude control and orbital manoeuvres. They produce a plume of neutral gas which produces ions via photoionisation and charge exchange. Measurements of local plasma properties will be aff ected by perturbations caused by the coupling between the newborn ions and the plasma. A model of neutral expansion has been used in conjunction with a fully three-dimensional hybrid code to study the evolution and ionisation over time of the neutral cloud produced by the ring of a mono-propellant hydrazine thruster as well as the interactions of the resulting ion cloud with the ambient solar wind. A parameter survey was performed for varying angles of injection and injection rates, particle kinetics were also investigated. Results are presented which show that the plasma in the region near to the spacecraft will be perturbed for an extended period of time with the formation of an interaction region around the spacecraft, a moderate amplitude density bow wave bounding the interaction region and evidence of an instability at the forefront of the interaction region which causes clumps of ions to be ejected from the main ion cloud quasi periodically and the ways in which these features are modifi ed by the degree of solar wind mass loading and the relative orientation of the magnetic fi eld to the angle of injection. This may a ffect Solar Probe Plus for a signifi cant duration as data taking and delicate sensory equipment may be required to cease operation until local fluctuations return to a more moderate level. The scale of the fluctuations seen are dependent upon the duration of the thruster ring and the speci fic geometry and therefore e ffects may vary in-situ.

Governments have funded the development and production of advanced technology in order to establish supply security and/or to achieve economic growth. The policy of government funding includes three alternatives: the two basic options of maintaining a national project or participating in international collaboration involving a number of sovereign states, and the third option of doing both in parallel. The study examines international collaboration in such a way as to assist in the selection of the appropriate policy option. Particular attention is paid to the perspective of small and large, advanced and less advanced European countries. The research problem is addressed by focusing exclusively on those results which distinguish international collaboration from a national project, summarised under the concepts of collaborative sharing and collaborative efficiency. The former identifies the sharing of funding and technology not to be found in a national project. The latter identifies the difference in efficiency between international collaboration and a national project. Efficiency, indicated by cost, quality and time, is examined under the headings of policy-making, executive management, industrial rationalisation and production volume. Furthermore, collaborative sharing and efficiency are examined in the context of parallel national projects. This focus on the differences between the policy options provides the basis for selecting the appropriate one. Previous studies fail to give convincing answers to the research problem: they concentrate on collaborative efficiency while neglecting collaborative sharing, and they disagree over whether international collaboration or a national project is more efficient. This study attempts to overcome these shortcomings by examining a major case study of international collaboration, namely the European Communication Satellite Programme. The following conclusions are established. To achieve supply security, the collaborative option is considered appropriate for the large, advanced European country, and the parallel option for the large, less advanced countries. To achieve economic growth, the national option is appropriate for the advanced European countries. The smaller, less advanced countries are seen to play only a limited role in government funding of advanced technology.

Characterisation of the interaction between the neutral atmosphere in Low Earth Orbit and spacecraft surfaces is required for a broad range of applications to system and mission definition. For the prediction of spacecraft trajectories in this Free Molecular regime, the nature of the interaction must be accurately modelled. Accurate definition of the interaction is also required for the design of the attitude control system for vehicles such as Space Station which will generate large aerodynamic moments. The methods available to determine this interaction indirectly from observation of the motion of a satellite are reviewed. The orbital analysis technique is chosen for this study. Two methods of modelling complex spacecraft configurations are developed. The first, a Monte Carlo Test Particle approach, is able to account for all the phenomena characteristic of Free Molecular Flow. The second, adopting a panel method approach, accounts only for the possible shielding of surfaces from the flow. Discrepancies between the two modelling programs are identified but for the limited flow range relevant to the ANS-1 mission, good agreement is found and the computationally more efficient panel method program adopted. A new set of momentum accommodation coefficients are introduced to characterise the interaction. These are resolved in an aerodynamic frame. The new coefficients are found to be more robust than classical surface-resolved models and to have greater sensitivity to the nature of the interaction. The theory required to represent the relationship between the changes in the spacecraft trajectory and the gas-surface interaction is then developed. The sensitivity of the derived momentum accommodation to the parameters used in the modelling process is then determined. The most sensitive parameters are found to be the accuracy of the orbital elements semi-major axis and inclination, the rotation rate of the atmosphere, the temperature of the spacecraft surface and the complexity of the spacecraft configuration model. This theory is then applied to the orbital data derived for ANS-1 (1970-70A) by ESOC. The results suggest that the nature of the interaction is close to the classical diffuse case but the accuracy of the results are limited by uncertainties in the measured changes in orbital inclination.