United Launch Alliance (ULA) has successfully accomplished the first of what it hopes will be a record-setting 15 missions for 2014, with the spectacular liftoff of an Atlas V vehicle from Cape Canaveral Air Force Station’s Space Launch Complex (SLC)-41 at 9:33 p.m. EST Thursday, 23 January. Although the launch was delayed by about 28 minutes, due to a telemetry issue associated with its primary payload—NASA’s 12th Tracking and Data Relay Satellite (TDRS-L)—it proceeded with exceptional smoothness, the Atlas’ Common Core Booster and Centaur upper stage completing the delivery to geostationary transfer orbit in 106 minutes. TDRS-L will now spend several weeks undergoing orbital checkout, ahead of being declared the next member of a critical network of communications and data-relay assets to support dozens of spacecraft, including the International Space Station and the Hubble Space Telescope.Weather conditions proved exceptional for Thursday night’s liftoff, with only the most minor of technical issues during the countdown, which commenced at 2:05 p.m. EST with the final efforts to close-out the vehicle for flight. The 19-story Atlas V flew in its “401” configuration, boasting a 13-foot (4-meter) payload fairing, no strap-on boosters, and a single-engine Centaur upper stage. Following standard communications, and electrical and control system checks, the Flight Termination System (FTS)—tasked with destroying the vehicle in the event of a major off-nominal event during ascent—was armed and tested. At T-2 hours, as intended, a 30-minute built-in hold began, ahead of the loading of propellants. All stations were polled and returned a unanimous “Go for Launch.”
Shortly thereafter, the process of loading liquid oxygen aboard the Centaur upper stage got underway and had reached flight levels and entered topping-off mode to replenish the effects of cryogenic boil-off by T-1 hour and 4 minutes. The Centaur is powered by a Pratt & Whitney-built RL-10A engine, which remains subject to an extended investigation, following an incident of abnormally low thrust during its otherwise successful effort to loft a GPS payload into orbit in October 2012. Meanwhile, the three-stage operation of fueling the Atlas’s Common Core Booster with liquid oxygen and a highly refined form of rocket-grade kerosene (known as “RP-1”) got underway, proceeding smoothly through its Slow Fill, Fast Fill, and finally Topping modes. The last propellant to be loaded was liquid hydrogen into the Centaur, which had reached its Topping level by T-39 minutes.
With all tanks confirmed at flight levels, the final checkout of the FTS was performed and ascent software, based upon the real-time weather situation on the Florida coast, was updated. All weather conditions were classified as “Green” (“Go”) for launch. However, as the Atlas prepared to emerge from its final built-in hold and begin the automated countdown sequence, an issue arose, apparently centering on a telemetry drop-out in the TDRS-L payload’s radio frequency (RF) link. The issue was well understood and a workaround solution was implemented, whereby the satellite would remain on “hard-line” telemetry through the ascent phase and revert to the RF link afterwards. The countdown clock resumed, tracking a slightly later launch time of 9:33 p.m. EST, just 12 minutes before the scheduled closure of Thursday’s 40-minute “window.”
Four minutes before launch, all stations returned a “Go for Launch” and the terminal countdown got underway. The vehicle transitioned to internal power and, 60 seconds ahead of liftoff, the Launch Control System was enabled and the Atlas’ computers assumed primary control of all critical functions. Two and a half seconds before liftoff, the Russian-built RD-180 engine—fueled by liquid oxygen and RP-1—roared to life, spooling up to its full 860,000 pounds (390,000 kg) of thrust by T-0. Climb-out of the stack from SLC-41 commenced at T+1.1 seconds, turning night into day across the Florida coast.
Shortly after clearing the tower, the vehicle executed a combined pitch, roll, and yaw program maneuver to position it onto the proper 101.4-degree flight azimuth for the injection of TDRS-L into orbit. A little over a minute into the flight, with the RD-180 still burning hot and hard, the rocket burst through the sound barrier, at which point maximum aerodynamic stresses (known as “Max Q”) were experienced through the Atlas’ airframe. In response to this aerodynamic situation, the RD-180 was temporarily throttled back to 95 percent of its rated performance. “Guidance steering is enabled approximately 120 seconds into flight,” noted ULA in its TDRS-L mission brochure. “At 212 seconds, the vehicle throttles up to a constant 5.0 G-level. Approximately 10 seconds prior to Booster Engine Cutoff (BECO), the Atlas V throttles down to a constant 4.6 Gs.” This final throttling-down of the RD-180 occurred at T+4 minutes and 22 seconds and, after separation, the turn came for the Centaur upper stage, which carried the key responsibility for delivering TDRS-L into geostationary transfer orbit.
The RL-10A is capable of restarting in flight and supported two discrete “burns” to inject its payload into orbit. The first burn lasted for a little over 14 minutes and served to place the TDRS-L/Centaur into a “parking orbit,” after which the combo coasted for about 80 minutes, ahead of a second burn, lasting just 63 seconds. Shortly after the completion of this second burn, the Centaur began a “Spacecraft Separation Attitude Alignment” and spun itself up to five revolutions per minute. Finally, 106 minutes after launch, TDRS-L was released into space to begin the complex process of deploying its solar arrays and communications payload. At the time of separation, the satellite was in an orbit with a perigee of 3,008 miles (4,841 km) and an apogee of 22,255 miles (35,817 km), inclined 25.5 degrees. These orbital-insertion figures closely paralleled ULA’s pre-mission predictions.
This launch marks the second member of the current third generation of TDRS satellites, the inaugural contracts for which were signed between NASA and Boeing in December 2007. Under the provisions of that agreement, the aerospace giant built TDRS-K—launched in January 2013—and TDRS-L, at a cost of $695 million, in order to “ensure vital operational continuity” of an orbital network of communications and data-relay assets which presently support dozens of spacecraft, including the International Space Station and the Hubble Space Telescope. The NASA-Boeing agreement is expandable to $1.2 billion if all options are exercised, and this indeed seems to be the case, for the space agency ordered a third satellite, TDRS-M, in November 2011. Current plans anticipate its launch in December 2015. All three satellites are designed to support 15-year operational lives, which enables continuity until the middle or even the end of the 2020s.
The orbital emplacement of these new satellites coincides broadly with the retirement of the TRW-built first generation of TDRS, designated “A” through “G,” which were launched by the shuttle between April 1983 and July 1995. Of this first generation, one (TDRS-B) was lost in the Challenger disaster, whilst two others (TDRS-A and D) have already been shut down. The others are expected to follow in the near future. A second generation of three satellites—TDRS-H, I, and J, all built by Boeing—were launched aboard expendable rockets between June 2000 and December 2002 and remain fully functional, despite having endured a handful of technical troubles.
With last January’s successful launch of TDRS-K, a hiatus of more than a decade since the flight of the last satellite was closed. The new third generation is visually quite distinct from its cousins of the first generation. It is based upon Boeing’s 601 spacecraft bus, first introduced more than two decades ago, but heavily upgraded over the years, and can support multiple payloads and objectives, including direct TV broadcasts and the needs of private businesses and mobile communications users. The size and output of its communications payload has also expanded, and it is capable of housing up to 60 transponders and producing 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 (4.5 meters) 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 orbital insertion. The communications hardware consists of microwave equipment, a pair of gimbaled 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 TDRS provide improved overall service and substantially higher bandwidth through the Ka-band.
In March 2009, Boeing selected ULA’s 19-story Atlas V as its vehicle of choice to deliver the third-generation satellites into orbit. Like its predecessor, TDRS-L will ride an Atlas in the “401” configuration, with a 13-foot (4-meter) payload fairing, no strap-on rocket boosters, and a single-engine Centaur upper stage. The final member of the group, TDRS-M, will also utilize an Atlas V 401 when it is delivered into orbit in December 2015.
ULA has a packed calendar this year, with highlights in July when it returns its Delta II rocket to flight with a replacement for the failed Orbiting Carbon Observatory (OCO-2) and in September when a Delta IV Heavy boosts the long-awaited Exploration Flight Test (EFT)-1 of NASA’s Orion spacecraft on a two-orbit, high-energy shakedown mission. Other payloads include three Global Positioning System (GPS)-IIF satellites, the Soil Moisture Active Passive (SMAP) environmental satellite, DigitalGlobe’s World View-3 Earth-observations satellite, a polar-orbiting Air Force weather satellite, NASA’s Magnetospheric Multiscale (MMS) mission, and the classified NROL-67 and NROL-33 payloads for the National Reconnaissance Office (NRO). According to Spaceflight Now, ULA will also launch its troubled Delta IV vehicle, after several months of technical troubles surrounding the RL-10 upper stage engine, no sooner than 20 February.