Using Commercial Off-the-Shelf Fuses in Vacuum

Abstract

In the summer of 2015 during thermal vacuum testing of the Geostationary Operational Environmental Satellite-R series (GOES-R) observatory, a heater circuit that was part of the ground support equipment in the vacuum chamber developed an electrical short. The current flow through the short melted and vaporized approximately a meter of 14-gauge polytetrafluoroethylene (PTFE)– insulated twisted pair copper wire. The test event was treated as a mishap, and an independent team investigated the failure. The mishap investigation team found as a contributing root cause that the test setup lacked sufficient circuit protection, and for future testing of the next three GOES-R observatories, they recommended the use of fusing or circuit interruption to protect the heater circuit wires [1]. In response to this recommendation, the GOES-R flight project traded two fusing options. One option was to locate the fuses for the wires inside the vacuum chamber, and the other was to locate the fuses external to the chamber. To support fusing inside the vacuum chamber, developmental testing of commercial off-the-shelf (COTS) fuses was initiated. Based on the heater circuit design, the testing focused on fusing 9 A at 250 V direct current (VDC) in both soft,∼130 Pa (1 torr), and hard, <30 mPa (2 ⋅ 10(exp −4) torr), vacuum conditions. If the selected fuses do not open a shorted circuit, then the test heater wires could vaporize again and cause another contamination event. If the fuses open below the required 9 A, then the spacecraft thermal vacuum testing campaign will be interrupted to open the chamber to replace test heater fuses.