CCSDS Spacecraft Uplink Protocol in a Space-Qualified ASIC

This paper describes the capabilities of the Hardware Command Decode (HCD) application specific integrated circuit (ASIC) developed for the Cassini spacecraft. The ASIC is used on the spacecraft in the Command and Data Subsystem computer to receive and decode uplink commands. The ASIC receives a serial, digital data stream of uplink data from the antenna receiver electronics. Implemented in the ASIC is the "receiving end coding layer" specified in the Consultative Committee for Space Data Systems (CCSDS) Telecommand standard. The CCSDS Telecommand standard is a widely used, international standard. The ASIC also supports direct ground control of up to 32 relays and 24 discrete outputs via Virtual Channel 0 commands. These relays and discrete outputs allow ground control of critical functions independent of the flight software. The fact that the ASIC also contains a variety of additional features unrelated to uplink that are often needed in spacecraft data systems makes this ASIC particularly useful. The ASIC produced in Honeywell's RICMOS technology, is radiation hard, single event upset hard, and highly reliable (Class S). The use of space qualified ASICs is an enabling technology for small satellites. ASICs such as the HCD ASIC, which implement part of the CCSDS downlink standard, are expected to have broad applications in small, commercial satellites.