orbital path to ensure the free-flying transmitter was in a co-planar orbit with the rectenna. The advantage of the tether approach is that it is feasible regardless of whether the H.10 is gravity-gradient stabilised or tumbling. However, the length of the tether and the rectenna mass will ensure that any residual tumbling motion before deployment of the rectenna will be small. [27] The experiment can still function even if tumbling persists, as is likely for a GTO orbit. However, a stable gravity-gradient position is desirable from a communications point-of-view and plasma interaction measurements. The feasibility of tether systems is widely understood. [28] However, no significant tether experiment has yet been conducted. As a result, uncertainties exist particularly in the area of the dynamic behaviour of tethers. Like the Powersat demonstrator itself, tether demonstrators are required to verify this concept. Proposing a Powersat that depends critically on the use of a tether and an understanding of its behaviour might not be prudent without verification of the tether concept. Fortunately, two experiments are planned for this year and next. The first will be the joint NAS A/ASI Tethered Satellite System (TSS) flight on the Space Shuttle in late 1992. This will involve the deployment of a 520 kg end mass on a 20 km long tether. [29] The second, and perhaps more relevant tether experiment, is the SEDSAT-1 being built by the University of Alabama in Huntsville (UAH) with the assistance of the NASA Marshall Space Flight Center. [30] The first mission is planned to occur in late 1993 and, similar to the ASAP demonstrator, SEDSAT-1 is launched piggyback on the second stage of a Delta 2 rocket (Figure 5.1-7) and is deployed using spring and gravity-gradient forces. The tether system was developed under NASA sponsorship by the Energy Sciences Laboratories and is designated the Small Expendable-Tether Deployment System (SEDS) which is currently marketed by the Tether Applications
RkJQdWJsaXNoZXIy MTU5NjU0Mg==