DAWN Mission Bus and Waveguide Venting Analysis Review

Abstract: ³ When commanded to switch on, TWTA No. 1 on Viking Lander 2 failed to produce an S-band RF downlink, probably due to RF breakdown of the high-voltage power converter. High-voltage circuits designed to operate within the Martian atmosphere require special design precautions, such as insulation from ground potential, to avoid corona or other forms of high-voltage breakdown. ´ The primary source of offgas products is moisture adsorbed onto the spacecraft bus. Initial concerns focused on the PMC as the primary adsorbed site. This is a typical concern of several PMC systems such as epoxy or polyimide resin based carbon, glass or Kevlar ® fiber composites. However, cyanate ester resins off-gas and adsorb moisture very little. This resin 954-3, originally from Fiberite now is sold by Hexcel ® . These resins are most often chosen for satellite applications due to their dimensional stability and very low offgas characteristics. Equally as important, cyanate ester resins perform well with respect to re-adsorption of moisture. The following paper offers details of this and the family of the Fiberite 954: cyanate ester systems [ref. 9]: