After several delays, a United Launch Alliance (ULA) Atlas V rocket thundered aloft on time this afternoon (Tuesday) on a mission to deliver a secretive and controversial U.S. Air Force mini-shuttle into orbit. Liftoff occurred at 1:03 pm EST, right at the opening of a five-hour “launch window,” from Space Launch Complex (SLC)-41 at Cape Canaveral Air Force Station located in Florida.
The mission has been repeatedly postponed, following an incident in which a ULA Delta IV medium rocket experienced abnormally low thrust from its RL-10 upper stage engine, during an otherwise successful effort to insert a Global Positioning System (GPS) satellite into orbit on 4 October. ULA manages both the Delta IV and Atlas V family of launch vehicles, and both rockets utilize slightly different versions of the Pratt & Whitney Rocketdyne-built RL-10.
As a precautionary measure—and one which ULA’s vice president of Mission Operations, Jim Sponnick, described as a “relentless focus” upon “attaining Perfect Product Delivery”—the mission was postponed as investigative work got underway. On Friday 7 December, ULA announced that the Atlas V had finally been cleared for flight and today’s launch adds to the rocket’s near-impeccable record.
Preparations to move the 196-foot-tall Atlas launch vehicle out to the pad began around 11 hours ahead of launch, punctuated by detailed weather and payload status checks. The Mobile Launch Platform rolled out of the giant Vertical Integration Facility (known as the VIF) at T-8 hours and was “hard-down” on the SLC-41 surface within the next hour. This was followed by a flurry of activity to establish pad connections, perform pneumatic and other checks, and verify the performance of the Atlas’ flight control systems. Status checks were conducted late in the count, with the weather predicted at only 30 percent favorable.
Key concerns ranged from local lightning, cumulus cloud, “disturbed weather,” and a thick cloud deck at altitude. However, the fuelling of the Atlas continued and the vehicle was fully loaded by 12:10 pm EST. Shortly thereafter, the weather began to show signs of improvement and was listed as “Green” for at least the first half of the window. The countdown emerged from its final scheduled hold, not long before 1:00 pm, and the Atlas vehicle transferred to its internal power at T-2 minutes.
In readiness for today’s launch, the booster and payload hardware were delivered quite literally from points all over the United States and elsewhere in the world. From ULA’s own headquarters in Denver, Colo., to the launch site in Florida, and from the fabrication of the Centaur upper stage fuel tank in San Diego, to its final assembly in Decatur, Ala., and from the manufacturing of the RD-180 first-stage engine in Khimki, Russia, to the construction of the Atlas V payload fairing in Zurich, Switzerland, this most secretive of launches boasts the distinct flavour of many states and many nations. All of those elements converged on Cape Canaveral Air Force Station to be blasted into orbit.
The Atlas V flew in its “501” configuration, with a 5.4-meter-wide (18-foot) payload fairing, no strap-on solid-fuelled rocket boosters and a single-engine Centaur upper stage. (The troublesome RL-10 provides this single engine and has a total yield of 25,000 pounds of thrust in a vacuum.) Two-and-a-half seconds ahead of liftoff, the first stage’s Russian-built RD-180 engine—with a thrust of 860,000 pounds—ignited, and climb-out from SLC-41 occurred at T+1.1 seconds. Shortly after clearing the tower, the Atlas executed a combined pitch, roll, and yaw program manoeuvre, which positioned it onto the proper flight azimuth for the insertion of its classified payload into orbit. Eighty-three seconds into the flight, with the RD-180 still burning hot and hard, the vehicle burst through the sound barrier. At around this time, the maximum aerodynamic stresses were felt through the Atlas’ airframe.
Three-and-a-half minutes after launch, the huge, two-piece payload fairing encapsulating the Air Force’s Orbital Test Vehicle (OTV-3) mini-shuttle was jettisoned, thereby exposing it to vacuum for the second time in its career.
As described in this recent AmericaSpace article, Tuesday’s launch was the first occasion on which an OTV has ever been used for a second mission. It previously flew for 224 days in April-December 2010, and a sister ship flew the OTV-2 mission for 15 months from March 2011 until mid-June of this year. It is not yet known how long OTV-3 will remain in orbit and its precise mission objectives remain heavily classified.
A minute after jettisoning the payload fairing, the first-stage engine was shut down and the 41-foot-long Centaur upper stage and attached OTV-3 separated. Four minutes and 39 seconds after leaving Cape Canaveral, almost two months of work on the RL-10 engine were put to the ultimate test, as it commenced a 13-minute burn to insert the mini-shuttle into orbit. Although the RL-10 is designed to be restartable in flight, it actually required only a single engine firing to deliver the 11,000-pound OTV-3.
Early indications suggest that the engine performed as expected. Judging from its two previous flights, the mini-shuttle—which looks uncannily similar to NASA’s retired Space Shuttle, albeit a quarter of the size—parted company with the Centaur and began its mission about 19 minutes after launch.
“The ULA team is proud to have played a critical role in successfully launching these three important Orbital Test Vehicle missions for the Air Force,” said Jim Sponnick. “This is a unique spacecraft, since it is the first to launch on an Atlas V, return to Earth, landing at Vandenberg Air Force Base in California, and then fly again on this mission.” Sponnick also paid tribute to the ULA team, which had supported ten successful missions in 2012.
Described as “the United States’ newest and most advanced re-entry spacecraft,” the OTV’s close resemblance to the Shuttle is misleading. In orbit, it deploys an array of gallium arsenide solar cells, which, when combined with power from a set of lithium-ion batteries, have thus far enabled it to remain aloft for more than 30 times longer than the average Shuttle mission. Its payload bay measures 7 feet long and 4 feet wide and can house cargoes weighing between 500-660 pounds. An advanced avionics suite and airframe, together with electromechanical actuators and autonomous guidance controls, has focused the OTV’s mandate onto “risk reduction, experimentation, and operational concept development for reusable vehicle technologies in support of long-term developmental space objectives.”
Its thermal protection materials are impressive…and so are their acronyms: Toughened Uni-piece Fibrous Refractory Oxidation-resistant Ceramic (TUFROC) tiles line the leading edges of the wings, instead of the reinforced carbon-carbon used on the Shuttle, whilst highly-durable Toughened Uni-piece Fibrous Insulation (TUFI) impregnated silica tiles and Advanced Conformal Reusable Insulation (CRI) blankets cover the airframe.
Like the Soviet-era Buran vehicle, the OTV has the capacity to land autonomously on a runway at either Edwards or Vandenberg Air Force Bases in California, after a hypersonic re-entry, although there has been recent speculation that the Kennedy Space Center’s Shuttle Landing Facility might be a future option.