gradient stabilization (for the SunTower cases). A very high-leverage, but potentially high-risk, conceptual approach to GN&C was employed in the SolarDisc concept: spin-stabilizing the very large solar array. This approach would allow drastic reductions in in-space infrastructure and in initial system costs. However, power transmission across between the rotating array and non-rotating RF phased array remains a significant challenge. This area requires considerably more study and definition. On-Board Power Transmission and Thermal Control. An essential design concept both the SunTower and the SolarDisc systems is that of exploiting high-voltage, high-temperature superconductor power capability to move power from the solar arrays (whether thin film PV or concentrator PV) to the RF phased array for WPT to the ground. This appears to be a critical technology for all SSP concepts. Telecommunications/Data Processing/Autonomy/Command & Control. Achieving a high-degree of operational autonomy is essential to achieving economicaHy-viable SSP. Staffing levels on the ground associated with each SPS must be less than those typically of GEO-based telecommunications satellites (which are themselves considerably lower than that typical of government satellite operations). Powerful computing power must be resident in diverse elements of the SPS system Innovative new data system architectures may be required. With regard the telecommunications, an active system providing positive control of the power down link must be assured - including automated up link beams from rectenna sites to guide and “authorize” the initiation of the down link. Structure & Harness. Whereas the 1979 SPS Reference concept relied exclusively on conventional compression-stabilized structures (assembled from individual trusses in space), the systems examined in the “fresh look” study depend on a combination of tension- and compression- stabilized structures - with an emphasis on the former. Key technology challenges in this regard involve the viability of very long- lived operations using these very light-weight, tension-stabilized structures - both in space in general and in Earth orbit in particular. Space environmental effects, atomic oxygen effects at high altitudes, micrometeorite and space debris impacts must all be treated in greater depth in order to evaluate the ultimate viability of system concepts using these technologies.
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