Atlas V prepares to fly its last ever national security mission

on

United Launch Alliance, formed in 2006 to merge the Boeing and Lockheed Martin launch vehicle programs, has flown 99 national security missions over the last 18 years using the Delta II, Delta IV, and Atlas V rocket families. USSF-51 will be ULA’s 100th national security launch, and the last ever flown by an Atlas-family rocket.

An Atlas V 551, AV-101, has been rolled out to Space Launch Complex-41 at the Cape Canaveral Space Force Station to fly a classified national security payload for the US Space Force. The USSF-51 mission is scheduled to launch on Tuesday, July 30, at 6:45 AM EDT (10:45 UTC), at the beginning of a five-hour launch window. This window closes at 11:45 AM EDT (15:45 UTC).

The Atlas V will be flying eastward on a trajectory used to fly payloads to a geosynchronous equatorial orbit 35,786 kilometers above Earth. Past Atlas V national security launches from Florida have flown satellites used for secure communications by the United States Armed Forces along with missile warning and signals intelligence spacecraft.

The Atlas V 551 for USSF-51 prior to being rolled out of the Vertical Integration Facility (VIF) to Pad 41. (Credit: Julia Bergeron for NSF/L2)

The Atlas V 551 is the most powerful variant of the Atlas V family, which made its launch debut in 2002. This variant, debuting in 2006, uses a five-meter payload fairing, has five solid rocket boosters, and a single-engine Centaur upper stage. The core stage uses one Russian-made RD-180 engine that uses liquid oxygen and RP-1 kerosene as propellants along with two combustion chambers and two nozzles.

After the RD-180, derived from the RD-170 engine used on the Soviet Energia rocket, ignites just over two seconds before launch, the engine will run briefly before liftoff. At T0, the nearly 60-meter tall USSF-51 vehicle will launch on the power of that engine and five Northrop Grumman GEM-63 solid rocket boosters built in Promontory, Utah. Together, the RD-180 and five GEM-63s will generate 12 meganewtons (around 2,700,000 pounds) of thrust.

The rocket, massing 587,000 kilograms at launch, will fly through the lower atmosphere on an eastward trajectory before reaching the speed of sound at 35 seconds past liftoff. USSF-51 will reach maximum dynamic pressure, or Max Q, at 47 seconds past liftoff, where the aerodynamic forces on the vehicle are greatest.

The USSF-51 launch will be visible in Florida and the Caribbean. Sunrise at Cape Canaveral will be at 6:43 AM EDT on July 30, two minutes before the USSF-51 launch window starts. (Credit: ULA)

As the rocket flies into the thinner upper atmosphere the forces on the Atlas V diminish, and the five solid rocket boosters are jettisoned at the one-minute 44-second mark. The payload fairing is jettisoned at three minutes and 13 seconds, exposing the USSF-51 payload and the Centaur upper stage to space since they no longer need to be protected from the atmosphere.

After the core stage shutdown, known as booster engine cut off (BECO), and stage separation, the single-engine Centaur, powered by a single Aerojet Rocketdyne RL-10 engine, will continue the rest of the trip to an initial parking orbit.

`This stage, using liquid oxygen and liquid hydrogen, will power the USSF-51 payload to its final orbit, though details of this sequence are classified. The specific timing of BECO has not been published for this flight, and ULA video coverage typically ends after payload fairing separation on its classified flights.

The initial launch weather forecast for this flight is 80 percent favorable for Tuesday as per a ULA posting on X. Closer to the launch, an official forecast will be issued by the US Space Force’s 45th Space Weather Squadron based at Patrick Space Force Base next to CCSFS.

After the USSF-51 flight, the Atlas V has 15 more flights scheduled before it is retired later this decade in favor of its successor, the Vulcan. This is the 58th and last national security flight for the Atlas V, and ULA is working on getting the Vulcan certified for national security payloads with its second flight coming as early as September.

Most of the remaining Atlas V flights are to be divided up between Project Kuiper broadband satellites using the Atlas V 551, and Starliner flights using the Atlas V N22. One flight, also using the 551, is earmarked for the ViaSat-3 EMEA communications satellite at the time of writing.

The USSF-51 mission patch and USSF logo on the 5-meter wide short payload fairing during processing. (Credit: ULA)

The USSF-51 mission patch was released with the motto “Alis Grave Nil” which in Latin means “nothing is too heavy for those who have wings.” The patch also contains a winged horse and a bright red star. Many patches for Space Force missions have symbolism related in some way to the mission.

Out of the 58 national security launches that will have been conducted for the Atlas V family, 53 of these have been conducted as part of the National Security Space Launch (NSSL) procurement since 2007. USSF-51 mission director Dr. Walt Lauderdale stated “this NSSL partnership is a prime example demonstrating our resiliency and capacity to support national security objectives in a time of evolving Great Power competition.”

ULA is one of three companies, including Blue Origin and SpaceX, that have qualified to compete for launches under the upcoming NSSL Phase 3 Lane 1 procurement, with at least 30 missions being flown to low-Earth orbit for the USSF and the National Reconnaissance Office. The company is also flying additional missions starting in 2025 under the NSSL Phase 2 procurement which was awarded in 2020 to ULA and SpaceX.

The USSF-51 core stage is being loaded into the VIF during processing. The core and Centaur upper stages are transported from the ULA Decatur, Alabama factory to the launch site. (Credit: ULA)

The NSSL Phase 3 Lane 2 procurement, involving more challenging missions to different orbits, is to be announced at a later date. The Vulcan is designed to fly the full range of missions that had been done by the Atlas V and Delta IV families, including missions that only the Delta IV Heavy could previously fly, while SpaceX’s Falcon Heavy and Blue Origin’s New Glenn can also fly heavier payloads than any Atlas V could.

The Atlas V’s reliance on Russian-made RD-180 engines became problematic after the Russian invasion and annexation of Ukraine’s Crimea peninsula in 2014. ULA contracted with Blue Origin to build the BE-4 engine, using liquid natural gas and liquid oxygen as propellants, as a US-built replacement for the RD-180, and it is this engine that now powers the Vulcan rocket.

The Atlas V is a very distant descendant of the SM-65 Atlas ICBM developed for the USAF. This Atlas stands in front of the Strategic Air Command Museum in Nebraska. (Credit: Justin Davenport for NSF)

While the Atlas V flies out its remaining manifest, the Atlas family’s legacy extends to the earliest days of the Space Age. Atlas family rockets have flown 682 reported times since 1957, with Convair building the first SM-65 Atlas intercontinental ballistic missiles in a plant in San Diego, California in that timeframe. USSF-51’s flight closes out a long history of rockets with the Atlas name flying or standing alert for national security purposes.

(Lead image: The Atlas V 551 stands on Pad 41 for the USSF-51 launch. Credit: Julia Bergeron for NSF/L2)

The post Atlas V prepares to fly its last ever national security mission appeared first on NASASpaceFlight.com.



Comments

Post a Comment