Does the word telemetry have to be capitalized in a sentence?

No, "telemetry" is not capitalized unless it's the first word of a sentence or part of a proper noun.

For example:

* Telemetry is used to monitor the health of spacecraft.

* The Telemetry Department at NASA is responsible for data collection.

However, if you're referring to a specific telemetry system or program with a proper name, you would capitalize it.

For example:

* The SpaceX Telemetry System is cutting-edge.

* NASA's Telemetry Network is used to collect data from multiple missions.