An artist's concept of the TDRS-H satellite in space. Photo: Boeing

Boeing Satellite Systems, El Segundo, CA, has completed the verification and checkout process for the Boeing-built Tracking and Data Relay Satellite, TDRS-H, launched June 2000. NASA and BSS are finalizing conditions for acceptance of TDRS-H, and negotiations are expected to conclude in late August.

Upon acceptance of the TDRS-H spacecraft, NASA's existing fleet will expand to seven on-orbit spacecraft. The agency will move the TDRS-H to its operational location at 171 degrees West longitude in September and rename it TDRS-8. The spacecraft then will be ready to serve the scientific community for years to come.

TDRS-H soon will be joined by TDRS-I and -J. TDRS-I is scheduled to launch Oct. 29 aboard an Atlas 2A rocket from Cape Canaveral Air Force Station, FL, at 11:14 p.m. EST, and TDRS-J will launch in October 2002. Once in place, the three next-generation satellites will double the capacity of data transmission and will provide nearly continuous, high- bandwidth communications links between Earth and space for the International Space Station, Space Shuttle and a host of near-Earth orbiting space research missions into the next decade.

NASA's acceptance of TDRS-H has been delayed due to a performance shortfall on the Multiple-Access (MA) phased array antenna aboard the spacecraft. Five of the 18 communications services provided by TDRS-H are performing at less than specified capability due to this problem. The high data rate services that make use of the 15-foot-diameter Single Access antennas are not affected and are performing nominally. NASA and BSS have tentatively agreed to a settlement, the terms of which are being finalized. Negotiations are expected to be concluded in late August.

"We have identified the cause of the problem to be rooted in one specific material used in the assembly of the antenna, and have implemented straightforward corrective measures for TDRS-I and TDRS-J. We are certain that a repeat of this performance shortfall will not occur," said Randy Brinkley, president of Boeing Satellite Systems. "This antenna design is unique to the TDRS satellites, therefore no other Boeing 601 or 601HP satellites are affected," Brinkley added.

"Boeing has been extremely responsive since the problem was first identified," said Robert Spearing, Deputy Associate Administrator for Space Communications at NASA Headquarters. "Launching TDRS-H ahead of actual need, gave us time to identify any shortcomings and address them successfully before there was an impact on our customers."

"We are convinced that Boeing understands the most probable root cause of the underperformance and has taken the necessary actions to prevent any such shortfall from occurring on TDRS-I and -J," said TDRS Project Manager Robert Jenkens Jr. of NASA's Goddard Space Flight Center in Greenbelt, MD. Boeing has modified and tested TDRS-I and -J to ensure optimal performance.

TDRS-H adds Ka-band Single Access (SA) capability to the TDRS fleet, allowing for higher data rates at a more favorable band and making it less susceptible to interference from the increasingly busy radio environment. The SA data rates on TDRS-H are 300 megabits/second (Mbps) at Ku- and Ka-band, and 6 Mbps at S-band. TDRS-H carries the 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 (Kbps) for SA S-band. The S-band Multiple Access (MA) phased array antenna has been designed to receive signals from five spacecraft at once at up to 3 Mbps, and transmit to a single user at up to 300 Kbps.

The TDRS satellites relay large volumes of user satellite data -- including voice, television and scientific -- from manned missions or orbiting scientific spacecraft back to ground control centers. TDRS supports spacecraft with research targets ranging from the birth of stars deep in distant galaxies to the subtleties of environmental phenomena on Earth. Though research approaches and instruments of these spacecraft vary widely, TDRS' two-way communications will serve all low- and medium-orbit customer vehicles generating this ground-breaking information. The TDRS fleet is also unique in its ability to follow the motion of fast moving satellites, providing nearly continuous communication with controllers and researchers on Earth. In addition to the Space Shuttle, other NASA programs using the TDRS fleet include the Hubble Space Telescope, STARlink, the Tropical Rainfall Measuring Mission (TRMM), Landsat (LSAT), the Earth Observing System (EOS), Expendable Launch Vehicle tracking, and the International Space Station.