Latency
Figure roughly 1000 miles each way for low-earth orbit, depending on the exact orbit height... speed of light is about 186,000 miles per second, so 2000 miles takes about 11 milliseconds -- that is, it would take that much longer for a one-way data packet from ground station 1 to satellite to ground station 2 as compared to a perfect zero-latency link. If the internal processing in the satellites can keep up without introducing more delay, that's not too bad.