Title: Precision Deployable Mast for the SWOT KaRIn Instrument
Presenting Author: Greg Agnes
Organization: Jet Propulsion Laboratory

Abstract:
NASA's proposed Surface Water Ocean Topography (SWOT) mission, scheduled to launch in 2020, would provide critical information about Earth's oceans, ocean circulation, fresh water storage, and river discharge. The SWOT mission concept calls for a dual-antenna Ka-band radar interferometer instrument, known as KaRIn, that would map the height of water globally along two 50 km wide swaths. The KaRIn antennas, which would be separated by 10 meters on either side of the SWOT spacecraft, would need to be precisely deployable in order to meet demanding pointing requirements. Consequently, an effort was undertaken to design build and prototype a precision deployable Mast for the KaRIn instrument. Each mast was 4.5-m long with a required dilitation stability of 2.5 microns over 3 minutes. It required a minimum first mode of 7 Hz. Deployment repeatability was less than +/- 7 arcsec in all three rotation directions. Overall mass could not exceed 41.5 Kg including any actuators and thermal blanketing. This set of requiremnts meant the boom had to be three times lighter and two orders of magnitude more precise than the existing state of the art for deployable booms. To meet these challenging requirements, a new boom architecture was developed which:

• Use filament wound, near-zero CTE M55J/Cyanate Estor booms.
• Joined those booms using precision hinge bodies.
• Latched the hinge bodies using a novel cable driven claming mechanism
• Used mating surfaces with Ball-Cone interfaces to establish deployment repeatability. The end result was a system that was lightweight, thermally stable, with a fundamental mode over the required 7 Hz frequency.