The Mars Reconnaissance Orbiter Mission launch was carried live on NASA TV. Digital NASA Television, carried by MPEG-2 signal, could be accessed in the continental United States on AMC-6, at 72 degrees west longitude, Transponder 17C, 4040 MHz, vertical polarization. If you lived in Alaska or Hawaii, NASA TV could be seen on AMC-7, at 137 degrees west longitude, Transponder 18C, at 4060 MHz, vertical polarization, audio at 6.8 MHz in analog through NASA's Space Shuttle Return to Flight mission.
You could also put in a request to your cable company to carry NASA TV.
Additional information on NASA TV is available here:
http://www.nasa.gov/multimedia/nasatv/
