HST

Telecommunications Description

HST is capable of utilizing the full capabilities of the TDRSS. Data can be recorded on on-board tape recorders for later transmission or can be transmitted in real time. Data return is usually via a single-access link with TDRS, while engineering telemetry is nearly continuously transmitted via a multi-access return link. Because HST is in a low-earth orbit, the spacecraft spend a portion of every orbit out of sight of either TDRS (a ``zone of exclusion'' or ZOE). Requests for TDRS time (forward/return, single/multiple-access links) are scheduled in advance of the execution of the one-week observing periods for HST. Any conflicts for time (with other flight projects or TDRSS maintenance) are resolved or the request for time dropped prior to execution of the observing timeline.