ULA ready to try again for NROL-44 launch on Delta IV Heavy

United Launch Alliance (ULA) is once again preparing to launch the NROL-44 mission for the National Reconnaissance Office.  After the first attempt ended with a scrub and the second resulted in a pad abort at T-3 seconds in August, ULA stood down for about a month to fix the issue before a swing arm retract issue moved the mission to 29 September at 00:02 EDT (04:02 UTC).

The mission, designated NRO Launch 44 (NROL-44), will mark the first Delta IV mission since the Medium+ variant of the rocket retired in August 2019 and the first Delta IV Heavy since January 2019. Although ULA is phasing out the Delta IV in favor of its Vulcan rocket, the Heavy configuration has five contracted missions through 2024.

(Lead image via Julia Bergeron for NSF)

The previous attempts

The mission reached its first launch attempt on 27 August 2020, which ended without fueling of the vehicle after a heater and pneumatic issue forced controllers to scrub the launch attempt.  The second attempt was originally set for 28 August before being pushed to 29 August when engineers needed more time to solve the pneumatics issue.

The second attempt saw the Delta IV Heavy fueled before a temperature issue on the rocket forced controllers to push into its launch window that day.   The issue was eventually resolved and teams cleared the mission for launch.  The engine start sequence began at T-7 seconds with ignition of the starboard booster’s RS-68A engine, followed two seconds later by ignition of the core and port boosters’ RS-68A engines.

At T-3 seconds, a Terminal Countdown Sequencer Rack initiated an automatic abort, shutting down the three RS-68A engines and triggering a series of safing sequences to place the Delta IV Heavy into a safe and stable configuration for post-hot fire abort safing and detanking.

The cause of the abort was first traced to a “high volumetric flow rate pressure regulator [that] did not open,” said Tory Bruno, CEO of ULA.  Further investigation revealed the regulator failure occurred when a diaphragm tore.  There are three regulators total, and all three, according to Tory, were replaced during the stand down period.

The Payload

NROL-44 payload is owned by the National Reconnaissance Office (NRO), the US Government agency responsible for operating America’s fleet of spy satellites. Although details of NRO spacecraft are officially classified, many pieces of information about previous missions have slipped into the public domain. From these, coupled with what has been revealed about NROL-44, a fairly clear picture of the satellite’s likely identity and role can be extrapolated.

The NRO operates satellites that fill a variety of roles – including optical and radar imaging of Earth’s surface, detection and tracking of ships on the high seas and interception of radio signals and communications. The two types of satellites which require the largest rockets are a series of optical imaging satellites – known as Crystal – and a series of large signals intelligence (ELINT) satellites known as Orion. Crystal satellites typically operate in near-polar sun-synchronous orbits, while Orions operate in an equatorial geostationary orbit.

Despite the top-secret nature of the mission, Notices to Airmen (NOTAMs) and Mariners (NOTMARs) must be published before every rocket launch. These include an immediate hazard area around Cape Canaveral, as well as areas downrange where debris may fall as the rocket sheds its lower stages and payload fairing on the way uphill. These hazard areas show Delta IV Heavy will be heading in an easterly direction out over the Atlantic Ocean – and is therefore almost certainly heading to a geostationary orbit.

With this established, there is little doubt that the NROL-44 payload is either a continuation of or successor to the Orion satellites.

The first two Orion satellites, launched in January 1985 and November 1989, were both deployed from the payload bay of Space Shuttle Discovery using an Inertial Upper Stage (IUS) to reach geostationary orbit. Designed as Foreign Instrument Signals Intelligence (FISINT) satellites optimized for intercepting telemetry and command signals, they replaced the previous-generation Aquacade satellites.

Two larger, second-generation Orion satellites were deployed in May 1995 and May 1998 via Titan IV rockets. Another Titan launch occurred in September 2003 carrying a further-upgraded third-generation satellite.

As Orion has evolved, it is believed to have taken on the roles of other NRO signals intelligence programs – most notably that of the Mercury communications intelligence (COMINT) system. This function, intercepting audio and textual communications between people, has been reported to have now become the satellites’ primary mission. Later-series satellites are sometimes unofficially known as “Advanced Orion”.

The four principal satellites currently in service were launched by Delta IV Heavy rockets between 2009 and 2016. Designated USA-202, 223, 237 and 268 – and launched as NROL-26, 32, 15 and 37, respectively – these spacecraft are likely assisted by several of their older siblings which may remain in service.

NROL-44 is likely a replacement for the eleven-and-a-half-year-old USA-202, with the displaced satellite taking on a reserve role in the constellation – either providing auxiliary data collection or serving as an on-orbit spare. This will likely be the start of a new wave of Orion launches, with the NROL-68 and NROL-70 missions slated to fly from the Cape aboard Delta IV Heavy missions in 2022 and 2024 as probable candidates for the next flights.

A Delta IV Heavy nears side core shutdown and separation. (Credit: Mack Crawford for NSF/L2)

It is not clear whether these spacecraft are additional third-generation Orion satellites, or part of a new generation.

NROL-44 is a temporary designation, referring primarily to this mission. Once in orbit, the satellite will receive a new name – which is expected to be USA-309. This series of generic “USA” designations began in 1984 and encompass a wide range of American military satellites, ranging from highly-classified missions to less sensitive payloads such as GPS satellites.

Since 2006, the numbers have been assigned sequentially to satellites in order of their launch. The most recent satellites to receive USA designations were the four satellites – USA-305 to 308 – launched on the NROL-129 mission in July 2020.

The launch will be carried out by United Launch Alliance, a company formed in 2006 to provide launch services to the U.S. government, which took over the Atlas V program from Lockheed Martin and Boeing’s Delta II and Delta IV rockets.

Atlas V and Delta IV were both developed under the Evolved Expendable Launch Vehicle (EELV) program initiated in the 1990s – which is today known as National Security Space Launch (NSSL). While Boeing and Lockheed Martin were both awarded contracts, allegations of corporate espionage on the part of the former quickly came to light, and the agreement to pool their resources in ULA was part of the final settlement in subsequent litigation.

While ULA initially continued to operate Atlas V and Delta IV alongside each other in order to ensure access to space should one vehicle ever be grounded, the advent of the company’s next-generation Vulcan rocket and increased competition from rival SpaceX have seen a rationalization of this product line, with Delta IV and Altas V to be phased out in favor of Vulcan.

In August 2020, the U.S. Space Force announced that Vulcan was chosen to receive contracts under NSSL Phase 2, the replacement for the current NSSL program, which begins in 2022. Vulcan was awarded 60% of the contracts while SpaceX will carry out the remaining 40% of the launches with their Falcon 9 and Falcon Heavy rockets.

Vulcan is currently expected to make its first flight in 2021, carrying out the first of two certification missions before being cleared to carry out critical launches for the Space Force.

ULA included the Atlas V as a backup vehicle for those NSSL Phase 2 missions should Vulcan encounter an issue and not receive certification in time for them.

Like the Atlas V, the Delta IV was designed as a modular rocket, capable of flying in different configurations depending on mission requirements. This Delta IV design centered around the Common Booster Core (CBC), which serves as the first stage of the rocket. Powered by a single RS-68A engine – originally an RS-68 – it is fuelled by liquid hydrogen and liquid oxygen.

The rocket’s smallest configuration, the Delta IV Medium, consisted of a single CBC, with a four-meter diameter Delta Cryogenic Second Stage (DCSS) atop it. The DCSS, powered by an RL10B-2 engine, burns the same cryogenic propellants as the CBC.

Several intermediate “Medium+” configurations added two or four solid rocket boosters to the first stage and optionally replaced the upper stage with a five-meter DCSS – and a corresponding enlarged payload fairing. It was a Medium+ configuration that made the Delta IV’s first launch in November 2002, carrying the Eutelsat W5 (later Eutelsat 33B) communications satellite into orbit.

The Delta IV Medium made three launches between 2003 and 2006, but was subsequently discontinued. Delta IV Medium+ launches continued until August 2019.

The first Delta IV Heavy flew on 21 December 2004, carrying out a demonstration mission for the U.S. Air Force. This configuration uses three Common Booster Cores burning together at liftoff, with the two cores strapped to the sides of the rocket separating ahead of the center core. A five-meter DCSS upper stage completes the stack and is capable of making multiple burns to inject its payload directly into geostationary orbit if required.

A Delta IV Heavy lifts slowly from SLC-37B to being the launch sequence of NASA’s Parker Solar Probe, August 2018. (Credit: Nathan Barker for NSF/L2)

During the 2004 demo mission, cavitation (small vapor-filled cavities) in the rocket’s fuel lines as the CBCs began to run out of propellant led to the premature cutoff of their engines. The upper stage was still able to reach orbit, although a significantly lower one than had been planned.

This remains Delta IV’s only launch failure to date. Three years later, the next Delta IV Heavy successfully orbited the DSP-23 missile detection satellite. The Heavy has primarily been used for military launches, although it has also carried out two key missions for NASA – with the EFT-1 test flight of NASA’s Orion spacecraft in 2014 and deployment of the Parker Solar Probe in 2018.

NROL-44 will be the 41st flight of Delta IV and the 12th of the Heavy configuration.  It uses vehicle Delta 385. The launch will take place from Space Launch Complex 37B (SLC-37B) at the Cape Canaveral Air Force Station.

SLC-37B is the East Coast home of the Delta IV, serving alongside the rocket’s West Coast pad – Space Launch Complex 6 (SLC-6) at Vandenberg Air Force Base. SLC-37B was built on the site of the Apollo-era Launch Complex 37B (LC-37B), which was used in the mid-1960s for uncrewed orbital test flights of the Saturn I and IB rockets – culminating in 1968’s Apollo 5 mission which tested the Lunar Module in low Earth orbit.

Complex 37 originally consisted of two pads – 37A and B, sharing a common Mobile Service Tower (MST) – although LC-37A was never used for a launch. Following Apollo 5, the complex was mothballed ahead of an expected role in the Apollo Applications program after the race to the Moon had been won. After this project was scaled back, the complex was demolished and abandoned until the 1990s.

After arriving at Cape Canaveral aboard ULA’s Rocketship – formerly the MV Delta Mariner – Delta IV was taken to the Horizontal Integration Facility at SLC-37 to begin processing for its launch. Here, the three Common Booster Cores and the DCSS were mated before the combined vehicle was transported to the launch pad and raised into place. The NROL-44 payload, encapsulated in its payload fairing, was mated to the rocket vertically using the pad’s MST.

The Delta IV Heavy for NROL-44 is rolled out to SLC-37B in November 2019. (Credit: ULA)

Five seconds before the scheduled launch, Delta’s three RS-68A engines will begin to ignite. At this point, a fireball will form around the base of the rocket. This is caused by the engines igniting residual hydrogen that has boiled off from the rocket. The process is well understood and harmless but has charred or set fire to the insulation on several previous flights.

Once the three engines have built up to full thrust, Delta IV Heavy will lift off to begin its mission. Liftoff will occur at the T-0 mark in the countdown when the thrust the rocket’s engines are generating exceeds the weight of the vehicle. For the first 9.4 seconds of flight, Delta will climb straight up, before initiating a pitch and yaw maneuver to place it on an easterly trajectory for the climb into orbit.

Shortly after this, the center core will throttle down into partial-thrust mode, limiting loads on the vehicle early in the mission and conserving fuel so it can continue to burn after the side boosters separate.

One minute and 18.4 seconds into the mission, Delta will reach Mach 1, the speed of sound. A second and a half later it will pass through the area of maximum dynamic pressure – Max-Q – where it experiences peak mechanical stress from aerodynamic forces.

Three minutes and 56 minutes after liftoff, the two side boosters engines shut down, with the spent CBCs separating from the vehicle two seconds later. Around this time, the center core will throttle back up to full thrust as it continues the boost phase of the mission. Its role in the flight will end with Booster Engine Cutoff, or BECO, at five minutes, 42.8 seconds mission elapsed time.

About six and a half seconds after BECO, the first and second stages will separate, with the final CBC falling away from the rocket. The second stage RL10B-2 engine will extend its deployable nozzle and initiate its pre-start sequence – with ignition coming 13 seconds after stage separation.

About 42 seconds after the second stage ignites, Delta’s payload fairing will separate. The fairing is the nose cone of the rocket which protects the payload during ascent through Earth’s atmosphere and gives the rocket a consistent aerodynamic profile. Once the rocket reaches space, the fairing is no longer needed and can be discarded to reduce mass.

There are two different payload fairings that can be used on the Delta IV Heavy – a composite fairing which was designed for the Delta, and a metallic fairing made of aluminum which was inherited from the Titan IV. The launch will use the latter, which measures 19.8 meters (65 feet) in length. This is a trisector fairing, meaning that when it falls away from the rocket it separates into three segments, not two as with most contemporary fairings. The metallic fairing was first used on Delta IV for the DSP-23 launch in 2007, and has subsequently been used for all of the NRO’s geostationary launches on the Heavy.

Northrop Grumman builds the payload fairings for the Delta IV as well as all composite structures and the RS-68A engine nozzles on the Delta IV.  In short, all the white parts visible on the rocket are built by Northrop Grumman.

With fairing separation, the mission will enter a media blackout – as is typical for NRO missions. The only likely official updates after this point will be a confirmation of mission success once the NROL-44 payload has separated from Delta IV Heavy. Given that the launch is targeting a geostationary orbit, this will not occur until six or seven hours after liftoff.

In this time, the DCSS upper stage can be expected to perform three burns. The first, which began after separation from the first stage, will continue for about seven minutes. This will establish the upper stage and its payload in their initial parking orbit. Based on the published flight profile of Delta IV Heavy’s initial demo mission – which was rumored to be simulating deployment of an Orion satellite – after coasting for a little under eight minutes, the rocket will fire its RL10 engine again for another eight-minute burn.

Now in geostationary transfer orbit, DCSS will coast for about five hours before commencing its final burn. This will last for about 3 minutes and 15 seconds, increasing the orbit’s perigee and decreasing its inclination to deploy its cargo directly into a circular geostationary orbit. Following spacecraft separation, the DCSS will perform a collision avoidance maneuver to take itself out of the geostationary belt and minimize the risks of a future collision with a satellite.

(Lead image: Brady Kenniston, NSF/L2)

The post ULA ready to try again for NROL-44 launch on Delta IV Heavy appeared first on NASASpaceFlight.com.



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