The S-Band system is one of the primary Orbiter downlink bands. The voice channels are digital slope delta modulated and are multiplexed in with the rest of the Orbiter telemetry and is very difficult to copy. Much of the downlink TV is on S-Band also, but is wideband FM and should be easy to copy. The Ku-Band system is used in conjunction with the tracking and data relay satellites and is used much more heavily in Spacelab flights than in others. These transmissions are directed to TDRS satellites in geostationary orbit on a frequency of 15.003 GHz.
All frequencies are in MHz.
You can also telnet spacelink.msfc.nasa.gov and follow the menus to a listing of repeaters in the USA that offer this service. We have a limited pool of operators available during any single mission. The most difficult days and nights to schedule are usually on the weekends. If you do not hear us and have the means to do so, check our current local weather. Given the nature of our equipment, we typically have at least one major failure during a mission.