The upgrade to NASA TV's Public Channel (channel 101) affects the most people. The channel is carried by many cable and satellite providers, NASA says, and shows coverage of the agency's missions and events as well as documentaries and archival programming.
The Media Channnel (channel 103) is for local, national and world news organizations. It provides material on missions and news conferences, plus audio and video relevant to news coverage.
The two channels will broadcast in different HD formats. While the public channel will transmit in the MPEG-2 broadcast standard for digital television (at 15.877 Mbps), the media channel will be in MPEG-4 (at 15.409 Mbps), which is more friendly to multimedia applications.
With the change, NASA said its current HD channel (channel 105) will be terminated.
Don't own a TV, or don't subscribe to cable or satellite? you can still watch NASA TV live on the Internet over at NASA's website, which uses UStream to deliver the feed. Although the feed is said to be high-def, some source material isn't, since NASA often shows archive footage or video shot by non-HD cameras.