Not available / text

Real-time navigation during the final approach phase of an interplanetary mission can significantly increase the accuracy of aerocapture and pin-point landing. The Mars Network is a versatile telecommunications network that is ideally situated to provide spacecraft-to-spacecraft radiometric navigation during Mars final approach and entry, descent, and landing via the Electra UHF transceiver, which is capable of providing autonomous, on-orbit, real-time trajectory determination using two-way Doppler measurements between a Mars approach vehicle and a Mars Network orbiter. A detailed dynamic analysis and link analysis of the final approach problem is presented, which seeks to determine the expected operating conditions of the Electra transceiver. In particular, the maximum Doppler shift and Doppler rate, which determine the transceiver tracking loop requirements, and the total received signal power and signal-to-noise ratio, which determine the range at which the communications link can be closed, are investigated for a range of Mars Network orbital geometries. A model of the Electra signal is developed on the basis of the results of the dynamic analysis and link analysis and is used as input to a high-fidelity simulation of the Electra transceiver. A Monte Carlo analysis is performed to determine the performance of the Electra transceiver for a range of signal and tracking loop parameters. In particular, the performance analysis focuses on the maximum range at which the link can be closed and on the acquisition and tracking performance of the second-order tracking loop. The analysis of the tracking performance is used to characterize and model the error in the Doppler measurement of the Electra transceiver. The error model is incorporated into the design of an extended Kalman filter, in order to improve the fidelity of the navigation filter design. The information content in the Doppler measurement and the observability of the estimated states are investigated for various orbital geometries and the accuracy of the navigation solution is analyzed.

Not available / text

published_or_final_version / Electrical Engineering / Doctoral / Doctor of Philosophy

No description available.

No description available.

The space elevator has been proposed as an alternate method for launching cargo into space. However, the construction of such a structure requires a material much stronger than any currently in existence. Instead, a partial elevator is considered for satellite placement. In the first part of the thesis, the fundamentals of very long tethered systems are studied. From static analysis on a simple two-body system, it is demonstrated that an assumption made in the conventional analysis does not apply to very long tethered systems. For a uniform tether, the axial stress distribution is obtained. Following the Lagrangian approach, the equations of motion governing the planar librations of a multi-body tethered system are derived. From a linearization of these equations, the libration frequencies are found. Then, by solving the nonlinear equations numerically, the responses to various changes in the system parameters are determined. In the second part of the thesis, the use of a partial elevator in satellite placement is studied. In the case of single climber transit, residual librations occur, which alter the shape and size of the orbit of a satellite launched from the climber. An approach using two climbers is investigated in order to decrease the residual libration and thereby reduce orbit placement errors. Also, some energy calculations are done to determine whether the partial elevator offers significant advantages.

Despite its importance, and the length of the annexed bibliography, Telecommunications is a topic which has been reilatively neglected in legal writing. Partially this may be explained by the numerous extra-legal factors which play a part in the regulation of telecommunications and partially it is due to the initial unattractiveness of the subject. This thesis examines the legal infrastructure of space telecommunications. The need for new communications channels and the technology developed to meet this situation are outlined. [...]

No description available.

Even though international cooperation traditionally is a concept encountered in public international law, it has an important role to play in the private satellite communications sector. Satellite communications being activities that intrinsically have a global outreach, mutatis mutandis they require legal rules that would not focus on purely regional or local interests. National and international space law have for the past decade encountered criticism with respect to obvious insufficiencies that in turn affected space activities. The first reaction of learned space lawyers was to call for some redrafting of international space law. A second thought about it had them take into account national legislation in this possible harmonization process, but in any case this was to primarily be of concern for States. / However, the new millennium has brought its share of intellectual renewal and in the field of space law it has been translated in the acknowledgement that the private sector would have an important role to play, on the international scene, for the improvement of space law. It is this new legal thinking that has been characterized as "international cooperation" as applied to the private sector, that is the subject of this study. Hence, what is looked at is the position of the satellite communications sector on the international scene and what expertise it has to share with public fora for the overall improvement of space law and space activities.