Command Loss Timer Reset

rdf:langString Command Loss Timer Reset

rdf:langString center

rdf:langString Command Transmission & Verification Operations * Voyager 1 command operations consisted of the uplink of a Command Loss Timer Reset and HPOINT LINK with MRO on 12/21 [DOY 355/1350z]. The spacecraft received all commands sent and all commands were verified. * Voyager 2 command operations consisted of the uplink of seven bracketed Command Loss Timer Resets sent on five-minute centers using 0.5 Hz steps on 12/23 [DOY 357/0212z]. The spacecraft received three of the seven commands sent.

rdf:langString The purpose of the [Command Loss] routine is to provide a means for the [Voyager] spacecraft to automatically respond to an on-board failure resulting in the inability to receive ground commands. Whenever a specified number of hours have elapsed without the CCS [Computer Command Subsystem] receiving a valid command, the CCS assumes a spacecraft failure and attempts to correct that failure by systematically switching to redundant hardware elements until a valid command is received.

rdf:langString NASA

rdf:langString Voyager 30 Year Mission explanation

rdf:langString Voyager Mission Operations Status Report #2009-12-25

rdf:langString Command Loss Timer Resets are part of the CCSDS communications system to spacecraft either in Earth orbit or beyond Earth orbit. The Command Loss Timer Reset, if it is not received in a timely manner by the spacecraft, generally forces the spacecraft to engage in safety and self-protection procedures. * Command Loss Timer Reset systems involve both hardware and software, whereas watchdog timers are essentially hardware-only affairs. * Most spacecraft have more than one Command Loss Timer Reset for subsystem level safety reasons, with the Voyager craft using at least 7 of these timers. * Technically the Command Loss Timer Reset is a glorified array of Watchdog timers, each with different settings. Overall spacecraft safety is very important for missions of multi-year duration. This means that the Command Loss Timer Reset subsystem has to be used to avoid multiple computer reboot events. Generally speaking, when a computer reboots it decreases the overall safety of the spacecraft for a very brief time.