NASA's Goddard Space Flight Center of Greenbelt, Md., chose Satellite Development Center on Feb. 23, 1995, to build three next-generation Tracking and Data Relay Satellites (TDRS) under a $481.6 million contract. The award ended a hard-fought, 8-year competition and restored the company's association with NASA after a 9-year interval.

The trio of Boeing 601 model spacecraft will replace an aging constellation and serve as the primary means of continuous, high-data-rate communication with the Space Shuttle, with the International Space Station, and with dozens of unmanned scientific satellites in low-Earth orbit. The new satellites will augment the system's existing S- and Ku-band frequencies by adding Ka-band capability. To support this increased capacity, the contract included the upgrade of the two TDRS stations at White Sands, N.M.

The first satellite, TDRS-H, was successfully launched on June 30, 2000. The second satellite, TDRS-I, was successfully launched on March 8, 2002. The third satellite, TDRS-J, was successfully launched on December 4, 2002. NASA supplied three launch vehicles for TDRS replenishment. The satellites will be placed in geosynchronous orbit in strategic positions above the Pacific and Atlantic oceans.

The body-stabilized Boeing 601 model on which the new TDRS satellites are based was introduced in 1987 to perform missions demanding flexibility and high power. The series has proved extremely popular and reliable, with more than 84 purchased by customers around the world.

A unique feature that contributed to Boeing's selection is TDRS' innovative springback antenna design. A pair of 15-foot-diameter, flexible mesh antenna reflectors fold up for launch, then spring back into their original cupped circular shape on orbit. These steerable, single-access antennas can simultaneously transmit and receive at S-band and either Ku- or Ka-band, supporting dual independent two-way communication. The selection of Ku- or Ka-band communications is done on the ground. Receive data rates are 300 megabits/second at Ku- and Ka-band, and 6 Mbps at S-band. The spacecraft carries additional capability for Ka-band receive rates of up to 800 Mbps. Transmit data rates are 25 Mbps for Ku- and Ka-band, and 300 kilobits/second for S-band.

Stowed (left); In Orbit (right)

In addition, an S-band phased array antenna can receive signals from five spacecraft at once, while transmitting to one.

On-orbit power derives from two wings covered with silicon solar cells that generate 2,300 watts. A nickel-hydrogen battery supplies payload power during eclipses.

This procurement was the first in which NASA followed a number of commercial practices. One such practice was identifying requirements and letting contractors find solutions to meet them, instead of developing detailed specifications and requiring contractors to follow them. Also, to enhance its financial efficiency and hardware reliability, NASA changed to greater contractor accountability. As a safeguard against TDRS service failure, the contract specifies a payback schedule to reimburse NASA for any failures incurred during the first 8 years of the satellites' 11-year operational lifetimes.

The satellites were built in Boeing's Integration and Test Complex in El Segundo, Calif., and launched from Cape Canaveral, Fla.