Power & Thermal Subsystem

Separation Switch

The Separation Switch is a safety device designed to reduce the risk of the spacecraft becoming hazardous during the launch and early orbit phase of the mission. Ulysses was launched on the Space Shuttle 'Discovery' STS-41, and there were some aspects of the spacecraft design that were potentially dangerous to astronauts during an emergency, while Ulysses was in the Shuttle cargo bay. These hazards include the spacecraft thrusters firing in the cargo bay, explosive devices (pyrotechnics) activating erroneously, radiation from the spacecraft antennae, and the deployment of the spacecraft booms while still in the cargo bay - all of which could cause damage to the Shuttle in flight or danger to the astronauts.

The Separation Switch electrically isolated all the potentially hazardous electrical equipment from the Main Bus during Launch and Deployment. Four switches sensed the presence of the Payload Assist Module (PAM-S) booster attachment ring below the spacecraft - it was not until Ulysses was safely away from the Shuttle and the PAM-S detached that the Separation Switch closed and attached the following potentially hazardous equipment to the Main Bus:

  • The Pyrotechnic Electronics, allowing explosive devices to be activated.

  • The Wire Boom Drive and Axial Boom Drive, allowing two 35m booms and one 11m boom to be deployed.

  • The Electronic Power Converters (EPCs), allowing amplification and radiation of X-band signals.

  • The AOCS Converters, allowing full function of thrusters, valves and Reaction Control Equipment.

See here for descriptions of the AOCS Converters and the Electronic Power Converters.