ULA’s penultimate Delta IV Heavy launches NROL-68 mission

by William Graham

United Launch Alliance’s penultimate Delta IV Heavy rocket took flight on the NROL-68 mission Thursday, lofting a secretive payload for the National Reconnaissance Office. Liftoff, from Space Launch Complex 37B at Cape Canaveral, is expected at 05:18 AM EDT (10:18 UTC). The mission was set to launch on Wednesday before ULA scrubbed the attempt due to an issue with a ground system pneumatic valve.

The mission, designated NRO Launch 68 (NROL-68) was flown on behalf of the National Reconnaissance Office (NRO), the agency responsible for operating the United States’ fleet of reconnaissance and intelligence-gathering satellites. Like most of the agency’s spacecraft, the true nature and purpose of the NROL-68 mission remains classified, however, clues from previous missions and information that has over time leaked into the public domain do paint a picture of what most of the NRO’s satellites are used for.

In the case of NROL-68, the two most significant pointers are the use of a Delta IV Heavy rocket, and the choice of launch site. Recent SpaceX polar corridor missions aside, Cape Canaveral Space Force Station is primarily used for launches targeting low and mid-inclination orbits, with rockets flying in an easterly direction over the Atlantic Ocean. In contrast, Vandenberg Space Force Base in California handles the majority of high-inclination launches. Navigational areas posted for the launch corroborate that this was a low-inclination mission with the hazard areas for the mission indicating that the rocket would fly due east after liftoff.

This suggests that the launch was targeting a geosynchronous or geostationary orbit, while the use of a Delta IV Heavy — one of the most powerful rockets at the NRO’s disposal — indicates that a significant amount of performance was required to complete the mission. This suggests a reasonably heavy payload for the target orbit.

The launch marked the 15th flight of a Delta IV Heavy, and its eleventh mission in support of the NRO. Its ten previous NRO missions have been an even split between high-inclination low-Earth orbit launches from Vandenberg and geostationary launches from Cape Canaveral. All of the geostationary launches are believed to have carried the same type of payload: an electronic signals intelligence (ELINT) satellite which is known as Orion. It is therefore reasonable to assume that the launch carried another Orion satellite.

Another indication that NROL-68’s payload is an Orion satellite is the payload fairing used on this launch; a trisector fairing made of aluminium, derived from the Titan IV’s payload fairing, rather than the more modern composite material bisector fairing that was developed for the Delta IV program. A trisector fairing differs from a more common bisector one in that it separates into three sections instead of two. The Orion satellites, which were launched aboard Titan IV prior to its retirement, seem to require this fairing as all of the previous geostationary NRO missions on Delta IV have used it — as did one early non-NRO mission which was also carrying a legacy Titan payload.

The Orion satellites themselves were introduced to replace a series of four smaller satellites named Rhyolite and later Aquacade, which were launched on Atlas-Agena rockets between 1970 and 1978. Orion itself appears to have gone through at least two generations of satellites, with the first two satellites being deployed from Space Shuttle Discovery with the aid of an inertial upper stage during its STS-51C and STS-33 missions in 1985 and 1989 respectively. After national security missions transitioned back to expendable launch vehicles, two more satellites were launched in 1995 and 1998 using Titan IV rockets with Centaur upper stages.

Leaked documents published by the news website The Intercept in 2017 showed that these first four satellites were designated Mission 7605 to 7608, while later satellites began a new series beginning with 8301. These documents also indicated that the 8300-series satellites included communications intelligence capabilities allowing them to take over this role from a previous series of dedicated satellites which had been known by several codenames including Chalet, Vortex and Mercury.

The NROL-68 mission patch. (Credit: NRO)

The first of these new-generation satellites was launched in September 2003, marking the final Orion mission aboard a Titan IV rocket before missions switched to the Delta IV. Subsequent launches followed in January 2009, November 2010, June 2012, June 2016, and most recently December 2020 with the NROL-44 mission. The Delta IV Heavy’s final flight is scheduled to occur from Cape Canaveral next year with the NROL-70 mission, which will most likely carry another Orion.

The mission patch for the NROL-68 mission prominently features a dragon — a symbol that has appeared on patches for a number of previous NRO signals intelligence missions, and particularly previous Orion launches.

Delta IV is one of two rockets developed under what was then the US Air Force’s Evolved Expendable Launch Vehicle (EELV) program, which began in the 1990s to replace the fleet of rockets then servicing the US military’s launch needs with a pair of standardized designs. Both successful rockets, Boeing’s Delta IV and Lockheed Martin’s Atlas V, first flew in 2002 and were offered in a variety of configurations to meet the differing requirements of various missions. Originally these included small, medium, and heavy versions of the rockets, although neither rocket would ever fly in its “small” configuration, and the Atlas V Heavy configuration would also never make it to the launch pad — leaving the largest and heaviest national security payloads solely to Delta IV Heavy until the advent of SpaceX’s Falcon Heavy.

United Launch Alliance (ULA) was formed in December 2006, merging Boeing and Lockheed Martin’s Delta and Atlas programs under a single operator as part of the settlement of a lawsuit between the two companies. Boeing had previously been found to have illegally acquired documents from Lockheed Martin related to the Atlas V rocket and Lockheed Martin’s EELV bid.

The EELV program has since been renamed National Security Space Launch (NSSL) and is now operated by the US Space Force. NSSL Phase 2 contracts were awarded in August 2020 to SpaceX for its Falcon rockets and ULA for its next-generation Vulcan launch vehicle, to replace Atlas V and Delta IV. Two other proposals were rejected: Northrop Grumman has since abandoned work on its OmegA rocket, while Blue Origin is continuing to develop its New Glenn vehicle outside of the program.

Delta IV Heavy launches with NROL-44 in 2020, its most recent East Cost mission. (Credit: Stephen Marr for NSF/L2)

With Falcon 9 and Falcon Heavy already in service and Vulcan scheduled to make its maiden flight later this year, Atlas V and Delta IV are both winding down operations. The last medium-class Delta IV launch was made in 2019 using the Medium+(4,2) configuration, with remaining launches in this weight class using Atlas V or Falcon 9. Delta IV Heavy has been kept in service due to its unique capabilities and is flying out its manifest of specialist national security missions. The most recent Delta IV Heavy launch took place last September with NROL-91, and marked the rocket’s final mission from Vandenberg Space Force Base on the West Coast.

Delta IV launches from the East Coast take place from Space Launch Complex 37B (SLC-37B) at the Cape Canaveral Space Force Station. This launch pad was originally constructed for the Apollo program in the 1960s, but was completely rebuilt for Delta IV ahead of its maiden flight in 2002. Rockets undergo assembly in the horizontal integration facility close to the launch pad before being erected in position. A mobile service tower (MST) encloses the rocket while it is on the launch pad and supports the installation of the payload — already encapsulated in its fairing — after the rocket has already been raised to its vertical orientation and completed its wet dress rehearsal.

Delta rockets have been given flight numbers, or Delta numbers, dating back to the first flight of the Thor-Delta rocket in May 1960. Although Delta IV is a very different rocket from previous members of the Delta family, it has continued this tradition, and this mission is numbered Delta 388 (D388).

Delta IV Heavy is rolled to the launch pad ahead of the NROL-68 mission. (Credit: United Launch Alliance)

Delta IV Heavy is a two-stage rocket that burns only cryogenic propellant: liquid hydrogen oxidized by liquid oxygen. Its first stage consists of three common booster cores (CBCs) burning in parallel, with a five-meter-diameter Delta cryogenic second stage (DCSS) stacked on top. Each CBC is powered by a single Aerojet Rocketdyne RS-68A engine, while the DCSS has an RL10C-2-1 powerplant.

The final countdown to launch begins with the MST being moved away from the rocket and propellant loading commencing on the CBCs and DCSS. Due to the extremely cold temperatures, propellant will continually boil off as the countdown progresses so the tanks will continue to be topped off until the tanks are pressurized a few minutes before liftoff.

The ignition sequence for Delta IV Heavy begins at about the T-7 second mark in the count when the RS-68A engine on the starboard CBC is lit. The port and center cores will ignite about two seconds later, with the staggered startup serving to burn off hydrogen around the base of the rocket, reducing the fireball that has been seen in this area during previous launches. It is not uncommon to see a Delta IV Heavy lift off with insulation at the aft end of the rocket on fire, however, this does not pose a significant risk to the mission and will quickly burn out as the vehicle ascends.

Liftoff itself is expected at T0, with the rocket beginning a pitch-and-yaw maneuver after clearing the tower, about 9.4 seconds into the mission, to put it on an easterly track toward geostationary orbit. Shortly afterwards the core CBC’s engine will be throttled down to its partial thrust mode. Delta 388 will reach Mach 1, the speed of sound, about 78.5 seconds after liftoff. Two seconds later it will pass through Max-Q, or maximum dynamic pressure, the point in the flight at which it is exposed to the greatest stress by aerodynamic forces.

About three minutes and 56.3 seconds after liftoff, the two outboard CBCs will shut down. The boosters will separate 1.8 seconds after cutoff, with the center core throttling back up to its high power level as first stage flight continues. Burnout of the center CBC, designated booster engine cutoff (BECO), is expected at the five-minute, 36-second mark in the mission. Six and a half seconds after BECO, the first and second stages will separate, with the DCSS taking over for the remainder of this mission.

The DCSS will ignite its RL10C-2-1 engine seven seconds after staging, having first deployed its extendable nozzle. NROL-68 is the second launch to feature the RL10C-2-1, which was introduced on last year’s NROL-91 mission to replace the RL10B-2 used on previous Delta IV missions. The RL10C increases standardization across the RL10 family of engines, with the RL10C-1 having replaced the RL10A-4-2 on Atlas V launches with single-engine upper stages.

Payload fairing separation is scheduled for six minutes, 37.5 seconds mission elapsed time. On NRO launches, fairing separation is the point in the flight at which official coverage and updates on the launch conclude, and the mission enters a media blackout. Since Orion satellites need to be inserted directly into geostationary orbit, the mission will continue for several hours during which time the DCSS will perform three burns.

Based on timings from the first Delta IV Heavy launch, which carried a demonstration satellite and aimed to simulate a national security launch to geostationary orbit, the first burn can be expected to last about seven minutes to set up an initial parking orbit. After a short coast, the DCSS will restart its engine for about eight minutes to reach geostationary transfer orbit. After an extended coast of around five hours — allowing it to reach the apogee, or the highest point, of its orbit — the DCSS will fire its engine for a third and final time. This burn, of around three and a quarter minutes, will circularise the orbit at geostationary altitude and reduce its inclination to zero degrees.

Delta 388’s second stage during integration operations. (Credit: United Launch Alliance)

Since the Delta IV has evolved since its maiden flight, it is likely that the timings of these burns may be slightly different during this mission, however, details are unlikely to be made public. Spacecraft separation can occur a few minutes after the end of the final burn, with DCSS then performing a collision avoidance maneuver to take itself out of geostationary orbit, reducing the risk of it colliding with other satellites.

Following this mission, ULA has only one Delta IV launch remaining: NROL-70 is currently scheduled to lift off from the same launch pad at Cape Canaveral next February. Before then, ULA plans to launch the debut flight of its Vulcan rocket with the commercial Peregrine lunar lander aboard. The company also has several Atlas V missions planned later this year, including the first crewed mission for Boeing’s Starliner spacecraft.

(Lead image: Delta IV Heavy D388 at SLC-37B ahead of the NROL-68 mission. Credit: United Launch Alliance)

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