It has been more than two years since Vandenberg Air Force Base, Calif., was rocked by the thunderous roar and titanic rattle of the world’s largest rocket currently in active service. Although the Delta IV Heavy has launched several times from Cape Canaveral Air Force Station, Fla., it has flown just once from the California site. On 20 January 2011, it delivered the NROL-49 reconnaissance satellite into orbit for the National Reconnaissance Office. On Wednesday, 28 August, a second Delta IV Heavy is slated to roar aloft from Vandenberg, carrying another classified NRO payload, known only as “NROL-65.” According to the Air Force, liftoff will occur from Vandenberg’s Space Launch Complex (SLC)-6 at 10:52 a.m. PDT (1:52 p.m. EDT). It was reported that Col. Keith Balts, commander of the 30th Space Wing, will be the launch decision authority.
Unsurprisingly, both United Launch Alliance (ULA)—who is responsible for Wednesday’s launch—and the Pentagon are remaining tight-lipped about the precise nature of NROL-65, although suspicion has been voiced that the payload may be a top-secret optical imaging satellite of the KH-11 “Kennan” class. First launched in December 1976, these satellites have passed through an estimated four generations and are thought to have been responsible for producing many detailed images of the landmasses of the former Soviet Union, China, Afghanistan, and Sudan. Two years ago, the NRO offered two obsolescent Optical Telescope Assemblies (OTAs) to NASA, and in June 2012 the space agency accepted the donation. Developed in the late 1990s and early 2000s, it was suggested that both assemblies may represent KH-11 imaging hardware and possess far higher resolutions than the Hubble Space Telescope.Whatever the nature of NROL-65, its allocation to the 229-foot-tall Delta IV Heavy is suggestive of a large and massive payload, possibly bound for a near-polar orbital inclination. The NROL-49 spacecraft—also codenamed “USA-224”—was reportedly inserted into an orbit of 160 x 600 miles, inclined 97.93 degrees to the equator.
Both the first and second stages of the Delta were fabricated by ULA at Boeing’s 1.5-million-square-foot Decatur, Ala., facility, after which they were transferred to Vandenberg Air Force Base aboard the M/C Delta Mariner cargo vessel. Upon arrival at the launch site, the stages underwent final assembly inside the seven-story Horizontal Integration Facility (HIF), and rollout of the Delta IV Heavy to SLC-6 took place in late April 2013, atop a diesel-powered Elevating Platform Transporter. Once the stack was “hard down” on the SLC-6 surface, a Fixed Pad Erector raised it to a vertical orientation within the 260-foot-tall Mobile Service Tower (MST).
Elsewhere, an environmentally-controlled Payload Attach Fitting (PAF) was installed on the Delta build-up stand and readied for the arrival of the NROL-65 payload. As described by ULA in its Payload Planners Guide, the installation of the spacecraft was followed by the closure of the payload fairing and transportation of the entire combination to SLC-6. During the 5 mph transfer process, dynamic loads on NROL-65 were constantly monitored. Upon arrival at the pad, environmental controls were disconnected and the PAF was lifted into the MST and mated to the Delta. Environmental control of the payload was then re-established with highly pure “Class 5000” air.
The Delta IV Heavy consists of three 134-foot-tall Common Booster Cores (CBCs): one serving as the first stage “core” and two as strap-on rockets. Topping off the stack is the 16-foot-wide (5-meter) Delta Cryogenic Second Stage (DCSS) and payload fairing, and the entire vehicle weighs an estimated 1.6 million pounds. Each CBC carries approximately 440,000 pounds of liquid hydrogen and oxygen and each utilizes a single RS-68 cryogenic engine, developed by Pratt & Whitney Rocketdyne. When this engine was introduced in 2002, it became the first large liquid-fueled powerplant to be developed in the United States since the Space Shuttle Main Engine.
Loading of propellants into the CBCs for Wednesday’s launch of NROL-65 will require a complex procedure, terminating a little over two hours ahead of launch. Ignition of all three RS-68s will occur at T-5 seconds, enabling each engine to ramp up to its maximum 705,900 pounds of thrust. After telemetry data confirms that the start-up sequence is satisfactory, the liftoff command will be issued and the Delta IV Heavy will depart the SLC-6 pad at T-0.
Shortly after clearing the tower, the rocket will execute a computer-commanded pitch, yaw, and roll program maneuver. Pitch and yaw controllability is affected by gimballing the engines themselves, whilst roll controllability is accomplished by vectoring the turbine exhaust gases of the RS-68s. This will actively guide the Delta IV Heavy onto its proper heading and flight azimuth to deliver NROL-65 into orbit. Fifty seconds into the ascent, the core CBC will throttle back to about 57 percent of rated performance to save propellant. The vehicle will pass through the region of maximum aerodynamic turbulence—known as “Max Q”—at T+81 seconds and will hit Mach 1.5 shortly afterwards.
At T+235 seconds, the thrust of the two strap-on CBCs will also be reduced to 57 percent and they will shut down and separate about seven seconds later. By running at 57 percent for the early phase of ascent, the core CBC will therefore have enough remaining propellant to support its climb after the strap-on boosters have been jettisoned. At T+246 seconds, its RS-68 will throttle back up to 100 percent performance and will burn for another 80 seconds. It will shut down at T+328 seconds, separating a few seconds thereafter.
The turn will then come for the DCSS second stage and its single, hydrogen/oxygen-fueled RL-10B2 engine, capable of 24,750 pounds of thrust. This is due to ignite at T+347 seconds after launch. The engine features an electrically-driven extendable carbon-carbon nozzle to enhance its specific impulse and has the capacity to conduct multiple “burns” of up to 18 minutes and 45 seconds to inject its payload into orbit. The DCSS also houses the Delta’s avionics, navigation, telemetry, and communications systems and can remain “active” for more than seven hours during extended-duration mission profiles. It can also execute Contamination and Collision Avoidance Maneuvers after the separation of its primary payload. As a launch vehicle, the Delta IV Heavy can place up to 50,000 pounds of payload into low-Earth orbit, 29,000 pounds into geostationary transfer orbit, and almost 14,000 pounds directly into geostationary orbit, more than 22,300 miles above Earth.
Recent reports have quoted Lt. Col. James Bodnar, commander of the 4th Space Launch Squadron, who noted that “no major issues” were threatening the upcoming flight of NROL-65 at the present time. “The launch business is probably one of the most risk-averse businesses out there,” Bodnar explained. “The extra time the reviews take are well worth the cost, because the alternative is unthinkable.”
United Launch Alliance has overseen six Delta IV Heavy launches since the variant’s maiden voyage from Cape Canaveral Air Force Station’s Space Launch Complex (SLC)-37B on 21 December 2004. On its first flight, the rocket suffered a premature shutdown of its CBCs, which placed its DemoSat payload in an incorrect orbit and left the Three-Corner Satellites (3CS)—a trio of student-built “microsats”—at an altitude of only 65 miles, which led to their rapid decay. The cause of the failure was traced to a faulty sensor signal in the rocket’s first stage, caused by “bubbles” forming in the liquid oxygen feedlines. A second Delta IV Heavy flew from the Cape in November 2007, successfully delivering the Defense Support Program (DSP)-23 satellite into geostationary orbit.
Subsequent assignments for the mammoth rocket from the Cape included the NROL-26 reconnaissance satellite in January 2009, the NROL-32 electronic intelligence satellite in November 2010, and, most recently, the NROL-15 mission in June 2012. Together with January 2011’s NROL-49 launch from Vandenberg, this leaves the Delta IV Heavy with a current tally of six flights. Wednesday’s NROL-65 mission will be the seventh, after which another Heavy is slated to carry NASA’s first Orion spacecraft into orbit on the Exploration Flight Test (EFT)-1 from the Cape in September 2014.
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