NASA data-relay spacecraft to launch Wednesday
BY JUSTIN RAY
Posted: January 29, 2013
Rolling to the launch pad this morning, an Atlas 5 rocket now stands perched atop Cape Canaveral's Complex 41 to deploy a data-relay satellite to support the International Space Station, iconic Hubble Space Telescope and NASA's varied science satellites.
Weather forecasters predict a 60 percent chance of acceptable conditions during the 40-minute launch window. A passing cold front bringing disturbed weather and gusty winds will be monitored closely.
Mission managers convened the Launch Readiness Review on Monday, assessing the status of work, remaining technical topics and weather outlook before granting approval for the rollout from the assembly building to the pad.
"The TDRS K launch campaign has gone very well to date," said Tim Dunn, the NASA launch director.
The mobile launch platform began rolling right on time at 10 a.m. EST Tuesday and was hard-down on the pad pedestals at 10:52 a.m. EST.
"We are exciting to go Wednesday. We are ready," said Jeff Gramling, NASA's TDRS project manager from the Goddard Space Flight Center.
This will be the first time NASA has launched one of its communications satellites since 2002, and this deployment begins the third-generation of TDRS spacecraft.
Created in 1973 and launching its first satellite in 1983, the system was conceived to provide constant communications with astronauts and science spacecraft circling the planet in low-Earth orbit. The TDRS design uses a constellation of geosynchronous satellites parked 22,300 miles above Earth to provide global coverage.
Looking down from that vantage point, the TDRS network receives signals from vehicles like the space station flying at a mere 250 miles and routes the telemetry, voice, video and science information to a dedicated ground terminal for delivery to Houston.
No matter where the space station is located at any given moment, TDRS has the outpost in sight for the two-way communications.
What's more, the dazzling views of the cosmos captured by the Hubble Space Telescope are relayed through TDRS, as are the measurements obtained by NASA's fleet of Earth-watching environmental satellites and astronomy birds peering into the universe. There's even telemetry-relay from ascending rockets that beam through the network, including the Atlas-Centaur vehicle carrying TDRS K.
"More satellites have been put on orbit, the user load goes up, so the requirements for the bandwidth and data services go up," said Paul Buchanan, TDRS deputy project manager and contracting officer.
"In the early 90s, we didn't have as many satellites," he added. "We forecast the user demand will be 5-10-15 years from now. We design for the future, not just today."
And with the shuttles no longer around to deliver supplies to the space station, international cargo ships like Europe's ATV and Japan's HTV freighters and commercial craft like the SpaceX Dragon and the Orbital Sciences Cygnus route their telemetry through TDRS.
"Even though the shuttle went away, the need to replenish station hasn't," Gramling said. "Comm bandwidth in space is much like comm bandwidth on the ground -- the demand never really goes down, people find more ways to want more data. In terms of the user loading, since we put the system online I don't think we've ever seen the demand go down."
The first generation of TDRS spacecraft, built by TRW as the system's A through G satellites, launched aboard 7 space shuttle missions between 1983 and 1995. One, however, was lost aboard Challenger in 1986.
Four of the six that went into operation remain in service today, well outlasting their 10-year design life.
A second generation, a batch of three made by Boeing and known as TDRS H, I and J, flew aboard Atlas 2A rockets between 2000 and 2002 to improve the capabilities of the system.
Now, Boeing is providing three more to replenish the constellation and keep it viable into the 2020s. TDRS K will be followed by identical sisters L next January and M in December 2015.
"The top-level requirements were fundamentally the same. We goosed up the performance of the services a little bit," Gramling said of the new-generation compared to the HIJ series.
But the decade between production runs meant massive reengineering of the new satellites to work around out-of-stock components from suppliers.
"Even though the requirements were not dramatically different, technology and parts availability had moved on and necessitated many of the units had to be replaced or redesigned. I think we ended up having to redesign all of the communications units on spacecraft just for obsolence reasons. On the bus-side, many of units that we had flown on HIJ series were unavailable and we had to make some design changes there as well," Gramling said.
"Even though looking at a picture of the spacecraft it looks almost the same but the guts are dramatically different."
And the solar arrays that power the third-generation satellites are the same size as their predecessors, but they have few solar cells than the previous generation. The improved efficiency of cell technology meant less were needed for the job.
The Atlas rocket and its Centaur upper stage will deliver TDRS K into a high-perigee geosynchronous transfer orbit. From there, the satellite will spend about 10 days maneuvering itself into a circular orbit 22,300 miles up to match Earth's rotation and appear parked at 150 degrees West longitude near Hawaii.
An extensive test and calibration period will be conducted on the satellite before NASA accepts possession of the craft from Boeing. Controllers then plan to drift it to 171 degrees West as it enters service under the redesignation of TDRS 11, Gramling said.
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