Deployable Space Systems (United States)

The structural overheads and mechanical challenges that severely limit the prevailing approach to solar sail engineering are overcome for diffractive sails with the simple ribbon architecture: a film strip in an inherently stable tilted orientation, with the payload at its rear end. Missions with spiral solar trajectories or orbit cranking such as Sun polar observer platforms will profoundly benefit from the consequent thrust efficiency and dramatically simplified design. The concept is introduced and some of the key aspects of its feasibility and expected performance are reviewed and assessed.

The Roll-Out Solar Array (ROSA) is an unfurlable solar panel system that was flight tested on the International Space Station mobile servicing system during a seven day mission following a June 3, 2017 launch on the SpX-11 commercial resupply mission. On June 18, the wing unfurled as planned to the full 5.4 meter length under the power of the stored strain energy in the composite slit-tube booms. The two booms and a thin mesh blanket with III-V photovoltaic cells simultaneously unrolled themselves into a stiff, tensioned state in only a few minutes time. This space flight test confirmed the mechanisms and booms performed well after 10 months of storage, launch, and 215 on-orbit thermal cycles. Following deployment, the wing structural dynamics was measured and the mode shapes of fundamental vibration were observed in the heat of orbital daylight and the cold of night. Finally the power conversion efficiency of the III-V solar power modules was measured to be nominal before and after three complete deployment and retraction cycles at the end of the mission. This mission has validated analytical structural models and proven the robustness of this new class of deployable solar array. Due in part to this mission success, a scaled up version of ROSA is being planned for commercial use by multiple vendors including by Space Systems Loral on their 1300 series satellites.

As the applications of Landsat data become more sophisticated, users have identified a need for improved spatial, spectral, and radiometric resolution in future instruments. Several sensor-design concepts have been developed to address these projected needs; however, the Landsat user community is diverse, and a sensor design optimized for research purposes may differ markedly from one intended for operational or commercial use. For example, an imaging spectrometer with a multiplicity of bands is an ideal tool for investigating phenomenology and elucidating spectral signatures; but, field-of-view limitation, data-rate constraints, and optomechanical complexity make this instrument less attractive as a primary sensor for an operational/commercial Landsat system. Conversely, instrument designs based on the multispectral linear array (MLA) concept can provide better spatial coverage with fewer (perhaps, 8-24) spectral bands tailored to meet the needs of operational/commercial data customers. The design approaches and missions are complementary, with planned spectrometer experiments providing guidance for optimal band selection for future operational/commercial MLA instruments.