United Launch Alliance (ULA) is celebrating its successful 75th launch tonight, after an electrifying night-time liftoff of an Atlas V booster from Space Launch Complex (SLC)-41 at Cape Canaveral Air Force Station, Fla. Despite concerns about high-level winds and thick clouds at altitude – which prompted the Eastern Range to declare itself “Red” (“No Go”) and enforced a 66-minute delay into the two-hour “launch window” – the venerable Atlas speared into the darkened Florida sky at 4:10 a.m. EDT Wednesday. Aboard the vehicle is the U.S. Air Force’s third Advanced Extremely High Frequency (AEHF-3) satellite, destined to form part of a “constellation” of spacecraft to provide fast and secure communications to link civilian leaders with military commanders and assets, anywhere in the world.
Tonight’s liftoff marked the 75th mission by ULA, which has been in existence since 1 December 2006. Plans to form the company as a merger between Boeing and Lockheed Martin were announced in May 2005 and although the venture was initially challenged by SpaceX – which criticized its anti-trust legality in terms of launch services monopoly – it received staunch support from the Department of Defense and was cleared by the Federal Trade Commission in September 2006. The company staged its first launch less than two weeks after it officially came into being, with the 14 December 2006 flight of a Delta II rocket from Vandenberg Air Force Base, Calif. This mission inserted the USA-193 reconnaissance satellite into orbit. Although the satellite subsequently malfunctioned and was intentionally and controversially destroyed in February 2008 by an SM-3 missile deployed from the U.S.S. Lake Erie, off western Hawaii, the launch itself inaugurated a remarkable string of successes for ULA. In March 2007, the company launched its first Atlas V from Cape Canaveral Air Force Station, placing six research satellites into orbit, and the following November despatched its first Delta IV. The latter flew in its “Heavy” configuration and lofted a Defense Support Program (DSP) early warning satellite.
All told, including today’s launch, ULA has flown 32 Atlas Vs, 26 Delta IIs and 17 Delta IVs. Aboard the Atlas, payloads have included the latest Landsat, NASA’s Juno spacecraft to Jupiter and the Mars Science Laboratory (MSL) with the Curiosity rover. Meanwhile, Delta IVs have delivered a wide range of reconnaissance satellites, weather satellites, military communications satellites and early warning satellites into orbit, with the Delta II having logged the launches of NASA’s Phoenix mission to Mars, the Dawn asteroid explorer and the Kepler extrasolar planet-hunter in its overflowing success record book. None of the 75 missions have produced a launch failure, although an Atlas V experienced a Centaur upper stage glitch in June 2007 and a Delta IV suffered a problematic launch last October. As for the Delta II, it is one of the most reliable U.S. launch vehicles currently in active operational service. Although it has not flown since October 2011, it is slated to loft NASA’s Orbiting Carbon Observatory (OCO)-2 in July 2014.
For only the third time in its operational history, today’s Atlas V flew in its “531″ configuration, boasting a 5.4-meter (17.7-foot) payload fairing, three strap-on rockets and a single-engine Centaur upper stage. With the potential to deliver payloads weighing up to 34,300 pounds into low-Earth orbit and up to 16,480 pounds into geostationary transfer orbit, the vehicle was perfectly suited to launch the 13,600-pound AEHF-3 satellite. Stacking of the Atlas at Cape Canaveral Air Force Station began on 2 August, when the Common Booster Core (CBC) – the central component of the rocket’s first stage – was rotated into position on its Mobile Launch Platform. Over the following days, the three Aerojet-built boosters were fixed to their mounting points on the first stage and on 13 August the Centaur was hoisted atop the stack.
In the meantime, AEHF-3 arrived in Florida on 10 July from prime contractor Lockheed Martin’s facility in Sunnyvale, Calif. Following the loading of maneuvering propellants and final clean room checks, the spacecraft was encapsulated within a two-piece (“bisector”) payload fairing and mounted atop the Atlas. Rollout to SLC-41 occurred on Monday 16 September, with ULA tracking an opening launch attempt during a two-hour “window” which opened at 3:04 a.m. EDT on Wednesday. At the time of rollout, weather forecasts were reportedly about 60 percent favorable for an on-time launch, with primary concerns centering on the presence of cumulus clouds and thick clouds at altitude. By late Tuesday night, according to ULA’s Facebook page, the weather had deteriorated still further to just 40 percent.
Launch preparations on the Atlas V and payload continued and at 1:15 a.m. EDT Wednesday, the process of chilling down the Centaur’s propellant lines to avoid the danger of thermally shocking the hardware was concluded and fueling began. Cryogenic liquid oxygen and hydrogen were loaded into the Centaur upper stage’s tanks to power the RL-10A engine during second-stage flight. AmericaSpace’s Launch Tracker reported at 2:13 a.m. that testing of the Atlas V’s Flight Termination System (FTS) – which would destroy the vehicle in the event of a major accident during ascent – was underway. A few minutes later, fueling was concluded and entered a process of “topping-off” to maintain liquid oxygen and hydrogen levels to replace any propellant which boiled off. Final processing of the Atlas V itself was exceptionally smooth. “A problem with a vent valve on the core booster,” noted the Tracker, “has been determined not to be an issue.”
However, the weather remained very much an issue. Heavy cumulus clouds violated Launch Commit Criteria and left the Eastern Range to declare itself “Red” (“No Go”) on weather. The countdown entered a planned ten-minute built-in hold at 2:51 a.m., with the clock holding at the T-4-minute mark, to provide controllers with a final opportunity to make adjustments to the flight plan, before entering the Terminal Count at T-3 minutes and 30 seconds. With Air Force meteorologists expecting the weather to clear early in the launch window, these adjustments included work to establish a new T-0 liftoff time. Shortly after 3:00 a.m., a weather balloon was despatched to determine the state of upper level winds and by 3:30 a.m. the Range declared itself “Green” (“Go”) on weather.
Chances of getting the Atlas off the ground dimmed again shortly after 3:40 a.m., when an unauthorized vessel strayed into the launch exclusion zone. Since the latter is a region of ocean in which spent hardware from the rocket would splash down, another wait was enforced before a new T-0 time could be declared. At length, with new software uploaded into the Atlas avionics, the new T-0 time was announced as 4:10 a.m. EDT. In the final minutes, all weather criteria was classified as “Green” and at 4:06 a.m. the countdown clock was released from its hold at T-4 minutes. “The launch team has just been polled for a final time and all 27 stations have reported Go for Launch,” noted AmericaSpace’s Launch Tracker. “The Launch Director has given permission to launch!”
By now, all propellant tanks had reached their proper flight pressures and the countdown entered its Terminal phase. The process of topping-off the liquid propellants concluded and the Flight Termination System was armed and enabled.
Ignition of the first stage’s 930,000-pound-thrust RD-180 engine occurred at T-2.7 seconds, after which a computer-controlled check of its healthy start-up sequence was conducted. At T+0.8 seconds, the command to fire the three strap-on, solid-fueled boosters was issued and liftoff from SLC-41 took place at T+1.1 seconds. Rapidly ascending away from the launch complex, the Atlas executed a combined roll, pitch and yaw maneuver to establish itself onto an easterly trajectory and the proper flight azimuth of 90.13 degrees. Forty-six seconds into the flight, the vehicle encountered maximum aerodynamic turbulence – known as “Max Q” – on its airframe. The three boosters burned out at T+92 seconds, although they remained attached to the Atlas for a further 20 seconds to ensure that they did not re-contact the first stage upon separation. Two of the boosters separated at T+115 seconds, with the third following a second or two later.
With the boosters gone, the RD-180 engine continued to burn hot and hard for a further three minutes, during which time the bulbous payload shroud and fairing were jettisoned. Shutdown of the engine occurred at T+257 seconds, after which the Centaur and its attached AEHF-3 payload separated and commenced independent flight. The Centaur fired its 22,300-pound-thrust RL-10A engine at T+279 seconds, burning for a little under ten minutes and cutting off about 14 minutes into the mission. The combo then “coasted” for eight minutes, ahead of a second burn, lasting five minutes. The Centaur then readjusted its attitude and performed a passive roll maneuver for thermal control, preparatory to the separation of AEHF-3. This separation was scheduled to occur about 51 minutes after launch and would see the satellite inserted into a “supersynchronous transfer orbit”, with a high point (or “apogee”) of about 27,000 nautical miles – several thousand miles higher than geostationary orbit – and a low point (or “perigee”) of about 125 miles.
As noted in AmericaSpace’s AEHF-3 preview article, the 13,600-pound satellite has been built by Lockheed Martin and as a constellation will replace the outdated Milstar network in providing fast and secure communications to link civilian leaders with military assets, anywhere in the world. Its first mission, AEHF-1, was launched in August 2010, followed by AEHF-2 in May 2012. After the launch of AEHF-3, three more satellites in the network will fly, in the 2017-2019 timeframe. The satellites operate at extreme high frequencies (44 GHz uplink) and super-high frequencies (20 GHz downlink) and can relay communications directly without passing through ground stations. Their phased array antennas help to eliminate possible sources of radio jamming and each AEHF spacecraft can support data rates as high as 8.192 Mbits/sec. By the time the sixth and final member of the constellation reaches operational service, AEHF will provide full surface coverage between 65 degrees North and 65 degrees South latitude.