Spaceflight Now: Atlas launch report

Switchboard in the sky
Hughes-built TDRS satellite to
upgrade NASA fleet

Posted: June 26, 2000

An artist's concept of the TDRS-H satellite in space. Photo: Hughes
The next generation of communications satellites which link astronauts and Earth, as well as orbiting satellites to their ground stations, will be launched from Cape Canaveral on June 29.

The Hughes 601 satellite, named TDRS-H, is the first of three TDRS satellites built by Hughes Space and Communications (HSC) under a $481.6 million contract with NASA. The trio of satellites will replenish and augment the current TDRS fleet which has served the Space Shuttle and other orbiting spacecraft for almost two decades.

The Tracking and Data Relay Satellite-H (TDRS-H) will be launched onboard an Atlas 2A rocket. The 40-minute launch window opens at 8:38 a.m. (EDT) (12:38 GMT).

"The capacity and flexibility with this new generation of Hughes-built TDRS satellites is unprecedented," noted Tig H. Krekel, HSC President and CEO. "TDRS really is akin to a switchboard in the sky. These next generation TDRS satellites will double the capacity of data transmission and provide nearly continuous communications links between Earth and space. As the flow of science data becomes a torrent and astronauts build humanity's bridgehead in space, the next generation TDRS satellites will help fulfill NASA's mission of service to our nation and our planet.

"TDRS spacecraft are the lifeline of mankind in space, safeguarding astronauts by providing direct contact with Earth," Krekel added. "Beyond human space activities, TDRS supports spacecraft with research targets ranging from the birth of stars deep in distant galaxies to subtleties of environmental phenomena on Earth."

Research approaches and instruments are equally varied, yet TDRS' two-way communications serve all the low and medium orbit customer space vehicles generating this important information. 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.

The new satellite will add Ka-band 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. TDRS-H receive data rates are 300 megabits/second (Mbps) at Ku- and Ka-band, and 6 Mbps at S band. This spacecraft 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 S-band. In addition, S-band phased array antenna can receive signals from five spacecraft at once, while transmitting to one.

In the Spacecraft Assembly and Encapsulation Facility, overhead cranes lower the Tracking and Data Relay Satellite (TDRS-H) onto a payload adapter. Photo: NASA/KSC
The new TDRS spacecraft are equipped with innovative folding antennas that meet NASA's requirements for reflectors with a large surface area, yet low weight. The pair of 15-foot-diameter, flexible graphite 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.

When fully deployed, the TDRS-H satellite measures 68 feet, 10 inches in length and 43 feet, five inches in width. At beginning of life, TDRS-H's weight on orbit will be 3,918 pounds. On-orbit power derives from two wings covered with silicon solar cells that generate 2300 watts. A nickel-hydrogen battery supplies payload power during eclipses.

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 soon the International Space Station.

"TDRS also establishes international compatibility with the Japanese and European space relay programs, allowing mutual support in case of emergencies," noted Krekel. "These new TDRS spacecraft will meet space communications needs for the next decade."

The body-stabilized Hughes 601 model on which the new TDRS satellites are based was introduced in 1987 and is the most widely used satellite model in space.

NASA plans to launch TDRS-I and TDRS-J in 2002 and 2003, respectively. The satellites will be placed in geosynchronous orbit in strategic locations above the Pacific and Atlantic oceans. TDRS-H will be located at 150 Degrees West longitude for on-orbit acceptance testing and post-acceptance testing. It will then move to 171 Degrees West longitude for its operational phase.

HSC is the world's leading manufacturer of commercial communications satellites, having built nearly 40 percent of those in operation. It also is a major supplier of spacecraft and equipment to the U.S. government, and a builder of weather satellites for the United States and Japan. HSC is a unit of Hughes Electronics Corporation, the world's leading provider of digital television entertainment, and satellite and wireless systems and services. The earnings of Hughes Electronics, a unit of General Motors Corporation, are used to calculate the earnings per share attributable to the General Motors Class H common stock.

Next launch
Vehicle: Atlas 2A (AC-139)
Payload: NASA's TDRS-H
Launch date: June 30, 2000
Launch window: 1238-1318 GMT (8:38-9:18 a.m. EDT)
Launch site: SLC-36A, Cape Canaveral, Fla.

Pre-launch briefing
Atlas 2A vehicle data - Overview of the rocket that will launch TDRS-H into space.

History of TDRSS - Past launches of TDRS satellites and their current status.

Launch timeline - Chart with times and descriptions of events to occur during the launch.

Launch windows - Available windows for possible future launch dates of AC-139.

Video vault
Animation shows NASA's Tracking and Data Relay Satellite-H working in geostationary orbit above Earth.
  PLAY (285k, 24sec QuickTime file)
Satellite builder Hughes tests the 15-foot diameter graphite shaped springback reflector antennas on TDRS-H.
  PLAY (169k, 12sec QuickTime file)
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