The Tracking and Data Relay Satellite System (TDRSS) was a concept born out of NASA's effort to rely less heavily on international ground stations and create long-duration and highly available communication coverage.

TDRSS is a space-based network made up of both communication satellites and a ground segment.  The TDRS project was established in 1973.  The prime design goal was to provide continuous, around the clock communications services to NASA's most critical low earth-orbiting missions, and improve the amount of data that could be received.  Launches of TDRS satellites began in the 1980s and have continued through the new millennium.  Most of these satellites are still operational today (with a number of them operating beyond their design life), while more Tracking and Data Relay Satellites are being built for replenishment in 2012 and 2013 (TDRS K and L). 

Since its inception, there have been 10 TDRS launched by NASA. The first generation TDRS were built by TRW, now known at Northrop Grumman in Redondo Beach, CA, in the 1980s and early 1990s. Originally, six TDRS were ordered from TRW. However, TDRS 7 was added as a replacement after TDRS 2 was lost aboard the Challenger in 1986. TDRS H, I, and J, known as the second generation TDRS, were built by Hughes in El Segundo, CA, now known as Boeing, in the late 1990s and early 2000s.

The contract for TDRS K/L was awarded to Boeing in December of 2007. The primary difference between the H,I,J series and the K/L series is the shift from on-orbit beamforming of the S-Band Multiple Access Return services to Ground Based beamforming (a return from spacecraft onboard beamforming to the first generation architecture).  TDRS K is scheduled for launch in 2012, and TDRS L is scheduled for launch in 2013.  The contract has options for two additional spacecraft, TDRS M & N.

The TDRS K/L Project provides follow-on spacecraft necessary to maintain and expand the Space Network. This program also includes modifications to the WSC ground segment required to support these spacecraft.

Launch History: