Command Loss Timer Reset

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In a deployed spacecraft, the command and data system (CDS) includes a Command-Loss Timer (CLT) which is reset by the CDS every time it receives a command from Earth, thus restarting the timer. [1] If the CLT times out, it is assumed that the spacecraft's receiver or associated components have failed. In response to a timeout, the CDS will take actions to attempt to restore communication, [1] and it may also initiate safing procedures.

Contents

General concepts

Command Loss Timers can be used for computer system rebooting, but only when multiple timers have not been reset — like the classical "Dead man's switch" of industrial transport use.[ clarification needed ]

Embedded systems on spacecraft need to be self-reliant, because it is not possible for a person to manually reboot the embedded systems on remote spacecraft if the software or hardware hangs.

Other uses

The Command Loss Timer Reset is not strictly limited to spacecraft, as any scientific instrument that is in a situation where remote command could be lost could use this safety measure.

This feature is common with devices connected over the Internet, but not all Internet connected devices use it.

See also

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References

  1. 1 2 "Onboard Systems". Basics of Spaceflight. NASA. Retrieved 16 January 2025.