Command-loss timer
In spacecraft, a Command-Loss Timer (CLT) is a software timer within the command and data system (CDS) which is restarted every time the spacecraft receives a command from Earth. If the CLT times out, it is assumed that the spacecraft's receiver has failed to reliably receive messages and, in response, the CDS will attempt to restore communication or perform safing procedures, or both. A Command Loss Timer is effectively a software watchdog timer which, upon timeout, initiates corrective actions that will in some cases swap to redundant communication hardware.
Robotic spacecraft are accessible to human operators only by command telemetry. Consequently, a spacecraft need to be self-reliant, because its embedded systems cannot be physically accessed if a communication fault occurs. Without a CLT, such faults would result in the spacecraft becoming permanently disabled.
01Other uses
Command Loss Timers are not 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.
Sources and credits
This article is adapted from the Wikipedia article “Command-loss timer”, written by its contributors and licensed under CC BY-SA 4.0. Fathomly has changed the layout, removed citation markers, navigation and maintenance notices, and adjusted punctuation. This adapted version is shared under the same license. For references, see the original article.
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