In cFS, it’s short for “Housekeeping”. The term describes a telemetry packet that contains status information about an app. Apps send a HK telemetry packet in response to the cFS Scheduler (SCH) App’s ‘send HK request’ software bus message that is published at a table-defined rate.

Another use of the HK term is with the NASA cFS open source app called HK. The HK app combines portions of multiple telemetry packets into a single new telemetry packet. The app was originally named HK because it combined portions of multiple HK telemetry packets into a new system HK packet. The HK app can combine the contents of any type of source packet so the name HK can be misleading.

Short for “Hardware”. It can mean computer hardware or solar panels or any other hardware on the vehicle.

Short for “Hertz”. A Hertz is a unit of measure for the number of times an action occurs in one second. For instance, 10 Hz means something happens 10 times per second.