What is the maximum number of WFPC2 exposures obtainable per orbit?
This is limited by the tape recorder capacity or the sum of the overhead times. Approximately 20 4-chip readouts can be stored on the onboard tape recorders at any one time. However, several orbits may elapse before the tape recorders are downloaded to the ground so it is generally not practical to obtain 20 exposures every orbit for a long sequence without special effort.