September 23, 2017

Preview: NASA science-enabling relay satellite poised for launch

The TDRS-M spacecraft is encapsulated in the Atlas 5’s nose cone for atmospheric ascent. Credit: NASA-KSC TV

CAPE CANAVERAL — Resembling a cocooned insect with antennas and appendages tucked snuggly to its body for launch, NASA’s latest communications relay hub will be shot into space Friday to blossom in geosynchronous orbit for routing signals to and from the International Space Station, the Hubble Space Telescope and three dozen science observatories.

The $408 million Tracking and Data Relay Satellite-M, or TDRS-M, will be sent aloft aboard a United Launch Alliance Atlas 5 rocket. Liftoff from Complex 41 at Cape Canaveral is scheduled for 8:03 a.m. EDT (1203 GMT).

“The spacecraft continues our ability to provide a data path for communications and tracking services from all of the different users out there in orbit today from human spaceflight component of NASA to robotic missions,” said Dave Littmann, NASA’s TDRS project manager.

“It continues the critical lifeline of communications to the agency for collecting data and serving the agency’s purposes from a communications standpoint.”

The historical odds of TDRS-M launching on the first try are 77 percent, based on the Atlas 5’s previous countdowns over the past 15 years.

Of the 71 launches of Atlas 5 to date:
-38 have gone at opening of window on first attempt
-17 went on first attempt but slipped later into the window
-13 missions had scrubs (6-Technical, 4-Weather, 3-Range)
-3 missions had more than one scrub

Air Force weather forecasters expect some cloudiness, good visibility, light southwesterly winds, a temperature of 80 degrees F and a 70 percent chance of acceptable conditions for liftoff. Meteorologists will be watching for clouds so thick that they could cause rocket-triggered lightning.

There will be a 40-minute launch window available to boost the 7,610-pound craft into a customized high-perigee geosynchronous transfer orbit ranging from 2,883 statute miles at its closest approach to Earth to 22,237 statute miles at apogee. The inclination is targeted for 26.2 degrees.

Trajectory design specialists at United Launch Alliance and NASA’s Launch Services Program worked in tandem to optimize the TDRS-M satellite’s deployment orbit.

The combined first stage and initial burn of the Centaur upper stage will achieve an elliptical parking orbit around Earth. The Centaur will coast in that orbit for about 90 minutes before reigniting to reach the intended geosynchronous transfer orbit to release TDRS-M.

That coast is about 8 minutes longer than the previous TDRS-K and -L launches on Atlas 5. But this mission will take advantage of the RL10C-1 engine that was added to the rocket nearly three years ago.

“We had the flight design guys look at ways to optimize spacecraft insertion. What they found, in TDRS-M’s case, is if we added additional minutes to the coast we could optimize spacecraft propellant usage such that it adds about 2-2.5 years of potential spacecraft life,” said Tim Dunn, the NASA launch director for TDRS-M.

“That was certainly a trade everybody was willing to take — 8 minutes for 2 years of on-orbit time. That was kudos to our flight design guys that worked hard between LSP and ULA alongside the the TDRS project.”

After separating from the launch vehicle, TDRS-M will use its 100-pound-thrust R-4D main engine to perform five burns over the next two weeks to circularize the altitude to 22,300 miles above the equator.

TDRS-M will be the 12th TDRS satellite orbited. Credit: NASA/ILS/ULA

A geosynchronous satellite’s lifespan is often dictated by the amount of fuel it has left over from the orbit raising to perform necessary stationkeeping maneuvers during operations.

By tweaking the Centaur coast and reaching a slightly different spacecraft injection orbit, Dunn said, that will reduce the amount of fuel TDRS-M would need to expend to reach its operational orbit.

“The spacecraft fuel savings could then be applied to on-orbit stationkeeping, translating to an increased spacecraft lifetime of about 2 years. Because propellant consumption requirements for on-orbit stationkeeping are generally modest for geosynchronous spacecraft, relatively small fuel savings can translate into a significant lifetime increase, as is the case here.”

TDRS-M will become the 12th such satellite orbited in NASA’s long series of relay stations for transmitting data from space. From their vantage point 22,300 miles above the planet, they look down to pick up contacts from lower-orbiting craft like the space station and science platforms to beam telemetry, video and imagery to a central ground facility, either in New Mexico or Guam.

TDRS-A in 1983 through TDRS-M this week. Photos by NASA/ILS/ULA

Starting with the launch of TDRS-A in 1983, the TDRS satellites advanced mission operations from the days of international ground stations providing sporadic coverage of man’s early exploits in space to the creation of an orbiting satellite network that provided constant communications.

This will be the final launch in the third generation of NASA’s tracking stations in the sky. The space shuttles launched the first series, built by TRW, from 1983 through 1995, then three Boeing-built satellites were deployed on unmanned Atlas 2A rockets in 2000 and 2002, and the newest two were made by Boeing and launched by Atlas 5 in 2013 and 2014.

“The first generation has far outlived their (useful) lifetime. The second generation launched in 2000-2002 is now at the edge of its lifetime, at least on paper for what it was designed for anyway. The K, L, M series has about the same lifetime,” Littmann said.

Needing to keep the network functioning well into the next decade, NASA officials opted to pick up the available contract option to build one final satellite in the current series — TDRS-M.

“The base contract provided for K and L, and there were two options that were pre-priced on the contract for this buy. The option for M was pre-set,” Littmann said.

“There was a pre-price in the contract, so we knew what it would cost, and the constellation needs were such that there would be usage and a beneficial need by the agency for that capability.”

TDRS-M is an effective clone of the last two — TDRS-K and -L.

“M has the same function, operation and performance as K and L,” said Paul Buchanan, TDRS deputy project manager.

The 11 previous successful TDRS launches.

“We currently have 9 spacecraft on-orbit in the constellation in the GEO orbit. Two of them are in a back-up capacity and 7 of them are heavily used,” Littmann said.

Two others have been retired and boosted above the geosynchronous belt.

Atlantic Ocean Region:
TDRS-C-3 (STS-26) *in reserve
TDRS-F-6 (STS-54)
TDRS-I-9 (Atlas 2A)
TDRS-L-12 (Atlas 5)

Pacific Ocean Region:
TDRS-E-5 (STS-43) *in reserve
TDRS-J-10 (Atlas 2A)
TDRS-K-11 (Atlas 5)

Indian Ocean Region:
TDRS-G-7 (STS-70)
TDRS-H-8 (Atlas 2A)

Retired to Super-Sync:
TDRS-A-1 (STS-6)
TDRS-D-4 (STS-29)

TDRS-M in the cleanroom being readied for launch. Credit: NASA-KSC TV

“We have different regions in order to provide global coverage — Atlantic, Pacific and Indian Ocean regions. The spacecraft are set up such that they can provide continuous coverage,” Littmann said.

“Across those regions, the usage is fairly constant, it’s a tie, it’s not like one region has a much higher usage than the others. They are all pretty heavily used.”

TDRS-M is the 76th and final Boeing 601-model spacecraft to fly, a venerable design that was once the world’s most popular commercial geosynchronous satellite bus. Hughes introduced the 601 in 1987 and in 1992 saw the first of 67 successful launches to date.

This satellite, a high-power version of the 601, is a tri-frequency craft serving S-, Ku-, Ka-band communications with a design life of at least 15 years.

The encapsulated TDRS-M spacecraft is hoisted atop Atlas 5 rocket. Credit: NASA-KSC TV

The key features that distinguishes TDRS from other 601s: two 15-foot-diameter steerable, flexible graphite composite mesh Single Access reflectors used to lock on and track either the space station or a customer satellite to receive video, voice and telemetry data and then downlink the signals to Earth via a 7-foot-diameter Space-to-Ground Link antenna on TDRS.

The TDRS-M satellite, folded up with its mesh antennas furled like taco shells, stands 27 feet tall in launch configuration. Once fully deployed in orbit, the craft will have a wingspan of 69 feet tip-to-tip.

It will be placed at an orbital testing slot of 150 degrees West for a five-month checkout campaign before drifting to its operational orbital slot, anticipated to be above the Atlantic Ocean region, Littmann said.

Animation of TDRS-M orbit raising and deploying antennas and solar arrays in orbit. Credit: NASA/Scientific Visualization Studio

The future beyond TDRS-M is still on the drawing board, but officials expect laser communications will become part of whatever follows the current TDRS system.

“The agency is looking at where it needs to go or wants to go from here. The TDRS architecture — the way the spacecraft appear (outward appearance) from the first generation that was built by TRW and the following six that were built by Hughes/Boeing — is largely not changed,” Littmann said.

“The agency is assessing if there should be a technology refresh to maybe look at moving to the optical domain. There are some activities looking at the maturity of the optical technology and its ability to be a game-changer in the next generation of communications, possibly extending out to the Mars domain or beyond. There’s not many hard plans on the books right now, but it is in the study phase.”

See earlier TDRS-M launch coverage.

Our Atlas archive.

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