There is a little bit that happens on board jamestin, especially in the instruments. Infered detectors build up their signal over time, and rather than send all those bits to the ground, there are some on board calculations that are done so that they send a bit less to the ground than they actually collected. S j w, s t can store at least 65 gigs. Science data down loads occur in two four hour contacts per day, where each can transmit 20 point six gigs of data.