Click the arrow to watch the TDRS-L video on YouTube. Video source: NASA.
United Launch Alliance is scheduled to launch a NASA communications satellite January 23.
The TDRS-L launch window is 9:05 - 9:45 PM EST. It will launch from the Atlas V pad at Cape Canaveral's Launch Complex 41.
TDRS stands for Tracking and Data Relay Satellite. The TDRS project goes back to 1973. The idea was to provide continuous global coverage in low Earth orbit. Before TDRS, human spaceflight vehicles communicated through ground stations, either on land or through ships at sea.
The current project upgrades the existing constellation. TDRS-K launched in January 2013. TDRS-M is scheduled for 2015.