Even the girls launch TDRSes, astronaut Mike Mullane wrote, with an aura of undisguised scorn, in his 2006 memoir, Riding Rockets. He was referring to NASA’s constellation of Tracking and Data Relay Satellites, of which seven were launched by the shuttle between April 1983 and July 1995 on missions widely considered as dull and somewhat “vanilla” in nature. Yet without the presence of TDRS—the latest of which is scheduled to fly from Space Launch Complex (SLC)-41 at Cape Canaveral Air Force Station atop United Launch Alliance’s venerable Atlas V booster on 30 January—both human and robotic exploration of the heavens would still be reliant upon ground stations and ship-based tracking technology.
Described by Craig Cooning, vice president and general manager of prime contractor Boeing Space & Intelligence Systems, as a fundamental “step toward improving how high-resolution images, video, voice, and data are transmitted,” TDRS-K will continue a proud tradition of supporting communications traffic between ground stations and the International Space Station, the Hubble Space Telescope, and more than two dozen other spacecraft simultaneously. And, visually, this latest TDRS looks pretty cool, too.
Contracts to build the first pair of third-generation TDRSes—alphabetically designated “K” and “L,” but destined to be numerically renamed “11″ and “12″ after injection into their operational 22,000-mile-high geosynchronous orbits—were awarded by NASA to Boeing in December 2007. The $695 million agreement (expandable to $1.2 billion, if all options are exercised) was “designed to ensure vital operational continuity” of the network through the first half of the next decade. In November 2011, NASA ordered a third satellite, TDRS-M. According to the Goddard Space Flight Center, TDRS-L is now well into its final months of testing and is expected to be declared “Launch Ready” this coming April. Current projections anticipate its launch in January 2014 and that of TDRS-M (whose fabrication began late last year) in December 2015. All three satellites are designed for 15-year operational life spans.
These new TDRSes are based in design upon Boeing’s “601″ spacecraft bus, first introduced over two decades ago but extensively upgraded over the years, with the intention of meeting the requirements of multiple-payload missions. These have included direct TV broadcasting and the small reception antennas utilized by private businesses and mobile communications users. After the contracts to build the second-generation TDRS-H, I, and J were announced in February 1995, Boeing expanded the 601 satellite bus to handle a much larger communications payload, capable of supporting up to 60 transponders and providing up to 10,000 watts of power.
As well as enabling all navigation, power, propulsion, and command capabilities, the bus has twin solar arrays—each measuring 15 feet in diameter—for use whilst in direct sunlight and battery packs for use whilst in the Earth’s shadow. Its “spring-back” antennas are designed with flexible membrane reflectors, which fold up for launch and spring back into their original, “cupped” circular shape after insertion into orbit. The communications hardware consists of microwave equipment, a pair of gimballed antennas, and a phased-array antenna for forward, return, and tracking services. In addition to operating at S-band and Ku-band frequencies, the second- and third-generation TDRSes provide improved overall service and substantially higher bandwidth through the Ka-band.
In March 2009, Boeing selected the Atlas V as its launch vehicle of choice for the third-generation satellites. The 19-story Atlas will fly in its “401″ configuration, featuring a four-meter-wide (13-foot) payload fairing, no strap-on solid-fuelled rocket boosters and a single-engine Centaur upper stage. The vehicle hardware was declared “flight-ready” by United Launch Alliance in December and stacking of booster components began earlier this month. The “core” segment of the Atlas was hoisted into position in the Vertical Integration Facility (VIF) on 3 January, followed by the attachment of the Centaur upper stage—slightly delayed due to weather issues—over the weekend of the 5th/6th.
Launch was originally scheduled for 29 January, but was last week postponed by 24 hours until the 30th, in order to permit technicians to replace an Ordnance Remote Control Assembly (ORCA). This has produced a knock-on effect on the final pre-launch milestones. The standard Launch Readiness Review will now occur on 28 January, followed by the rollout of the Atlas V/TDRS-K stack from the VIF to SLC-41 on the morning of the 29th. Liftoff on the 30th is slated to occur at the start of a 40-minute “window,” which opens at 8:48 pm EST. Two-and-a-half seconds before liftoff, the first stage’s Russian-built RD-180 engine will roar to life, reaching its full 860,000 pounds of thrust at T-zero, and climb-out from SLC-41 will commence at T+1.1 seconds. This engine is fed by liquid oxygen and a rocket-grade form of kerosene, known as “RP-1,” and is scheduled to burn for a little over four minutes.
Shortly after clearing the tower, the Atlas will execute a combined pitch, roll, and yaw program manoeuvre, which will position it onto the proper flight azimuth for the insertion of TDRS-K into orbit. Eighty-three seconds into the flight, with the RD-180 still burning hot and hard, the vehicle will burst through the sound barrier. At around this time, the maximum aerodynamic stresses are felt through the Atlas’ airframe.
Slightly ahead of engine cut-off, the RD-180 will throttle back to limit acceleration loads and, after separation, the turn will come of the Centaur upper stage. The latter will insert TDRS-K into its required transfer orbit. One hour and 46 minutes after launch, the giant satellite will be released from its payload shroud, and shortly thereafter the deployment of its solar arrays and communications appendages will commence.
TDRS-K arrived at the Kennedy Space Center on 18 December, aboard an Air Force C-17 Globemaster III aircraft from the Boeing Space & Intelligence Systems assembly facility in El Segundo, Calif. Reflecting on the fact that more than a decade has elapsed since the last TDRS launch, Project Manager Jeffrey Gramling noted that the new satellite will “provide even greater capabilities to a network that has become key to enabling many of NASA’s scientific discoveries.”
Following its removal from the C-17, the satellite was transferred to Astrotech’s payload processing facility, near the Kennedy Space Center, for final electrical testing. During the early part of January, its attitude-control system was fueled, its batteries were charged, and on the 14th it was installed onto the Atlas V’s payload adaptor. Two days later, TDRS-K was encapsulated within its protective shroud. Installation of the payload atop the rocket inside the VIF, originally scheduled for the 19th, was postponed by 24 hours due to high winds and finally took place on the 20th.
The network of TDRS satellites celebrates the 30th anniversary of its first launch in April 2013, and it remains quite remarkable that success was snatched from the jaws of what might have been an ignominious failure, as tomorrow’s article will recount.
The second part of this article, to appear tomorrow, will trace the long and difficult evolution process of the TDRS system.