United Launch Alliance (ULA) is primed to launch its sixth mission in less than four months on Thursday, 22 May, when it delivers the classified NROL-33 payload into orbit on behalf of the National Reconnaissance Office. Liftoff of the Atlas V booster, which is flying in its “401” configuration, equipped with a 13-foot-diameter (4-meter) payload fairing, no strap-on solid-fueled rockets, and a single-engine Centaur upper stage, is scheduled to occur at 9:05 a.m. EDT from Space Launch Complex (SLC)-41 at Cape Canaveral Air Force Station, Fla. Thursday’s mission will be the 46th flight by an Atlas V, as well as marking the 83rd total launch under the auspices of ULA—which also operates the Delta II and Delta IV boosters—since the company’s formation back in December 2006.
Yesterday (Tuesday), the 196-foot-tall (60-meter) Atlas V left the giant Vertical Integration Facility (VIF), atop its Mobile Launch Platform (MLP), at about 10 a.m. EDT for the 35-minute journey to SLC-41. “On arriving at the launch pad, the MLP was carefully centered in position to begin the process of connecting propellant umbilicals and electrical and data lines later on Tuesday,” explained Spaceflight101. “The trackmobiles will be removed later in the day and teams will begin preparations for countdown operations that are set to start at 2:00 a.m. on Thursday.” The rollout came less than 24 hours after Monday’s Launch Readiness Review, which verified that the vehicle, its payload, and all supporting ground stations were in a full state of preparedness to execute the mission.
The classified nature of NROL-33, including its destination orbit, carries such sensitivity that tomorrow’s launch webcast will end at the moment of the Atlas V payload fairing separation. Confirmation of mission success will only be provided after NROL-33 has departed the final stage of the rocket. However, the 401 configuration of the Atlas V—its most commonly used variant, employed on 21 of the rocket’s 45 past missions, including its maiden voyage, back in August 2002—has the potential to deliver payloads weighing up to 21,600 pounds (9,800 kg) into low-Earth orbit and up to 10,470 pounds (4,750 kg) into geostationary transfer orbit. This has offered some indication of the possible size and dimensions of the NROL-33 satellite.
Much speculation has abounded that NROL-33 may be an upgraded Satellite Data System (SDS) military telecommunications payload, perhaps bound for geostationary transfer orbit at an altitude of about 22,300 miles (35,900 km). The Air Force began to develop the first-generation SDS-A satellites in 1973 to provide America’s intelligence community with a network of orbiting relays, capable of transmitting real-time data and images from low-orbiting reconnaissance satellites which were out of range of ground stations. Another of their responsibilities was to support voice and data communications for covert military activities. This first generation is believed to have been launched between 1976 and 1987, aboard Titan boosters from Vandenberg Air Force Base, Calif. The second-generation SDS-B satellites—three of which are thought to have been deployed on the classified shuttle missions STS-28, STS-38, and STS-53 between August 1989 and December 1992—operated in high-apogee and low-perigee orbits, ranging from as low as 300 miles (480 km) and as high as 23,600 miles (38,000 km), and at steep inclinations which achieved their highest point over the Northern Hemisphere. This enabled them to cover two-thirds of the globe, relay spy satellite data of the entire Soviet land mass, and cover the entire north polar region in support of Air Force communications. More recently, the third-generation SDS-C satellites are believed to have been aboard several Atlas missions from Cape Canaveral Air Force Station since 1998, the most recent being NROL-38, which was lofted aboard an Atlas V 401 in June 2012.
Tracking a launch at 9:05 a.m. EDT Thursday, at the start of a 70-minute “window,” it is expected that formal countdown activities for tomorrow’s mission will begin about seven hours before T-0. Technicians will firstly activate the Atlas V systems and run through a complex series of electrical and communications checks and a T-2 hours a 30-minute built-in hold will commence, ahead of efforts to load propellants aboard the vehicle. At this stage, all stations will be polled for their readiness to support the launch and a unanimous “Go for Launch” will be needed in order to authorize the pumping of liquid oxygen into the Centaur upper stage. Meanwhile, the three-stage operation of fueling the Atlas’ Common Core Booster (CCB) with liquid oxygen and a highly refined form of rocket-grade kerosene (known as “RP-1”) will also get underway, proceeding through Slow Fill, Fast Fill, and Topping modes. The final propellant to be loaded will be liquid hydrogen into the Centaur, which should reach its Topping level by T-40 minutes.
With all tanks confirmed at flight levels, a final checkout of the Flight Termination System (FTS)—tasked with destroying the Atlas V in the event of a major, off-nominal event during the climb to orbit—will be performed and the ascent software, based upon the real-time weather situation in the Cape Canaveral area, will be updated. As of Tuesday evening, Air Force meteorologists were predicting an 80 percent likelihood of acceptable conditions at T-0 for an opening launch attempt on Thursday. “On launch day, high pressure and fair weather persists over Central Florida, with a loose pressure gradient and light winds” the 45th Weather Squadron at Patrick Air Force Base noted Tuesday. “Although slight, the primary concern is for Cumulus Clouds associated with coastal showers with on-shore winds in the low and mid levels of the atmosphere.” Should Thursday’s launch attempt be scrubbed, weather conditions are also anticipated to be about 80 percent favorable on Friday, with the 45th Weather Squadron also pointing to cumulus cloud cover as the principal meteorological concern. “In the event of a 24-hour delay, the next cold front encroaches into Georgia and is expected to remain to the north with high pressure and fair weather over Central Florida,” it was explained. “The primary concerns for a 24-hour delay are Cumulus Clouds coming in off the Atlantic.”
Four minutes before launch, the “Terminal Countdown” will get underway. The Atlas V will transition its systems to internal power, and, 60 seconds ahead of liftoff, the Launch Control System will be enabled and the Atlas’ computers will assume primary command of all critical functions. Two-and-a-half seconds ahead of liftoff, the first stage’s Russian-built RD-180 engine—with a propulsive yield of 860,000 pounds (390,000 kg)—will roar to life and climb-out from SLC-41 will occur at T+1.1 seconds. Shortly after clearing the tower, the Atlas will execute a combined pitch, roll, and yaw program maneuver, which will position it onto the proper flight azimuth for the insertion of the NROL-33 payload 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, maximum aerodynamic stresses (known as “Max Q”) will be felt through the Atlas V’s airframe. In response to this aerodynamic situation, the RD-180 will be temporarily throttled back to 95 percent of rated performance. “Guidance steering is enabled approximately 120 seconds into flight,” noted ULA in its brochure for the TDRS-L mission, also flown aboard an Atlas V 401. “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 should occur at about T+4 minutes and 22 seconds, and, after separation, the turn will come for the Centaur upper stage, which carries key responsibility for delivering NROL-33 into orbit.
Shortly afterward, the Centaur/NROL-33 combo will separate from the Atlas and its Pratt & Whitney Rocketdyne-built RL-10A engine will roar to life. The engine provides 25,000 pounds (11,340 kg) of thrust in a vacuum to complete the climb into orbit. It has the capacity for multiple restarts, although the classified nature of the mission makes it unclear at present how many “burns” will be necessary to deliver NROL-33.
Tomorrow’s mission represents the sixth ULA flight in less than four months. Already in 2014, the company—which was formed as part of a merger between Boeing and Lockheed Martin—has delivered NASA’s latest Tracking and Data Relay Satellite (TDRS-L) into orbit on 24 January, the Global Positioning System (GPS) IIF-5 and 6 satellites in February and on 17 May, and the Defense Meteorological Satellite Program (DMSP)-19 and classified NROL-67 payload in April.
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