Atlas V set for final missions ahead of retirement

on

United Launch Alliance (ULA) will soon close out production of its Atlas V rocket, completing a stock of 15 boosters set to fly on contracted missions. With ULA’s future focus on the Vulcan rocket, Atlas V will aim to end on a high, adding to over one hundred successful launches. 

The last Atlas V Common Core Booster will shortly be completed in Decatur, Alabama, at the United Launch Alliance (ULA) manufacturing plant. The final booster will be tested and then held in readiness for its eventual mission. ULA will then have fifteen complete Atlas V boosters in stock—all of which are already sold and assigned to a mission. The remaining missions are mostly allocated to Amazon for Project Kuiper and Boeing’s Starliner.

Atlas V first flew on Aug. 21, 2002. Many of its subsequent missions have been for the United States Air Force (USAF).  The USAF has used many Atlas Vs to launch both classified and unclassified payloads, taking full advantage of the rocket’s ability to do its job.

Background

The requirement for Atlas V was created under the 1994 Evolved Expendable Launch Vehicle (EELV) launch system program. The program was anticipated to develop affordable and dependable vehicles for the United States military, who in turn, were developing ever larger and more complex satellites. The EELV was expected to produce vehicles that used common fairings, solid rocket boosters, liquid fuels, and upper stages. The $3 billion program eventually produced the Boeing Delta IV and the Lockheed Martin Atlas V. Each vehicle has a range of configurations that use a distinct set of common parts.

In 2006, events beyond the scope of this article led to the creation of a joint venture between Boeing and Lockheed Martin, which became the United Launch Alliance. Each company retained a 50 percent share in the new venture, which would own and operate the two launch vehicles.

While Lockheed Martin had been producing Atlas boosters in Littleton, Colorado, ULA moved production of Atlas V to the 1999-2000 built Boeing Delta rocket production facility in Decatur. The 1.6 million-square-foot factory employs around 1,000 people. Ten to twelve Atlas V boosters were built at the plant each year, alongside the Delta family of rockets.

Construction

Earlier versions of Atlas boosters had made use of balloon tanks, which require pressurizing to retain their structural strength. Atlas V’s first stage is constructed in the now conventional manner, utilizing plates of computer-milled aluminum with an iso grid pattern to produce lightweight yet strong panels. The panels are then pressed into curves by specialist workers operating a large hydraulic press.

Machine milling

A computer milling machine creates iso grid patterns on a sheet of aluminum. (Credit: ULA)

The parts are friction stir-welded into stages that possess sufficient structural integrity to stand upright and unpressurized. The stages measure 3.7 meters in diameter and 32.5 meters in length. The boosters are powered by a single RD-180 engine with two nozzles, propelled by liquid oxygen and kerosene. The engine burns for around four minutes and produces 4 MN of thrust.

The RD-180 engine was developed in Russia by Energomash from the RD-170 engine used on the Zenit boosters of the Energia rocket. The engines were sold to Lockheed Martin and later ULA. These deals ensured that ULA received its engines in batches. Consequently, ULA had sufficient stock of RD-180s to fulfill its needs when sales were halted as a result of the political unrest in Ukraine.

The Atlas V booster uses the Centaur III or Common Centaur upper stage, powered by Pratt & Whitney’s RL10 engine which burns liquid hydrogen and liquid oxygen. The Centaur has been in use since 1962 and continues today with Centaur V, which flies atop Vulcan.

Variants

As specified in the EELV requirements, the Atlas V variants include many common parts. The design allows for up to five strap-on solid rocket boosters to be added, each increasing the available thrust by 1.27 MN for 94 seconds.

Both Aerojet AJ-60A and Northrop Grumman GEM 63 solid rocket boosters have been used, with the GEM 63 replacing the AJ-60A since November 2020.

The fairings used are variable in size. Initially, the fairings were available in 4.2 meters diameter and lengths of 9, 10, and 11 m. However, a 5.4 m diameter fairing was developed by RUAG Space of Switzerland. This fairing envelops the Centaur upper stage as well as the payload. Versions of this larger fairing are available in 20.7, 23.4, and 26.5 m length variants.

Schematic of the Atlas V 500 series. (Credit: ULA)

Each flight is allotted a three-digit configuration code: The first digit is either 4 or 5 to indicate the fairing diameter, or N if a crew capsule is being used and no fairings are required. The second digit provides the number of solid rocket motors being used, and the third digit signifies the number of engines fitted on the Centaur upper stage — either 1 or 2.

Tory Bruno let it be known that ULA has unofficial nicknames for some of the variants. Bruno later confirmed on X that the names included:

551  Bruiser; 541  Beast; 531  Thunderer; 421  Sprinter; 411  Slider; 401  Slick Atlas

Missions

Atlas V flew its missions from dedicated pads on both US coasts. The West Coast base is at Space Launch Complex (SLC) 3 East, in Vandenberg Space Force Base, California. SLC-41 at Cape Canaveral Space Force Station, Florida remains in use today on the East Coast, now shared with Vulcan, the successor to Atlas V.

With 101 missions all flown successfully, Atlas V has made a huge contribution to American spaceflight. Capable and dependable, the vehicle has delivered a spectrum of mission profiles from low-Earth orbit to interplanetary for over twenty years.

Notable Atlas V payloads have included Mars Reconnaissance Orbiter, New Horizons, Mars 2020, and Lunar Reconnaissance Orbiter. The launch roster contains familiar names such as Landsat, NROL, GOES, TDRS, and Cygnus. Scientific payload highlights have been LUCY, OSIRIS-REx, and Juno.

The final Atlas V to launch from the West Coast was the JPSS-2 weather satellite JPSS-2 weather satellite.  Launched on Nov. 10, 2022, this flight was also the last to utilize the 4-meter fairing.

The final classified mission to fly was USSF-51. The lift-off occurred on July 30, 2024, from SLC-41.

Crewed Missions

Starliner launches on Atlas V. (Credit: Mike Deep for NSF)

The campaign to certify Atlas V for crewed flights took a long and tortured path. As early as 2005, NASA had considered Atlas as a Space Shuttle replacement in the Exploration Systems Architecture Study (ESAS). Based on the heavy Orion spacecraft, NASA thought the vehicle unsuitable for crewed missions at this time, but meanwhile, Atlas V continued to launch uncrewed payloads with unfailing reliability.

In 2011, ULA signed an unfunded Space Act Agreement with NASA to work toward crew certification. The Agreement examined the use of vehicles such as the Dream Chaser, Boeing CST-100 Starliner, and Blue Origin’s spacecraft being flown aboard Atlas V.

This process continued to certification to launch Starliner. NASA and ULA took until 2018 to pass the Design Certification Review (DCR). The subsequent launch of the uncrewed Orbital Flight Test 1 for Boeing’s CST-100 Starliner spacecraft occurred in December 2019.

Four more years would pass before the first crewed launch, Starliner’s Crewed Flight Test. This mission eventually lifted off on June 5, 2024, 22 years after Atlas V’s first flight.

The certification and successful flights have come late in Atlas V’s history, and only a few further crewed flight opportunities remain, with a maximum of six additional Starliner missions available.

Incidents

Atlas V is one of the most reliable vehicles produced. Only two missions have been affected by hardware issues, and only one of these was booster-related.

The first mission to suffer an issue was the 2007 launch of the NROL-30 classified payload mission. The payload of a pair of spacecraft was deployed into a lower-than-intended orbit when the Centaur upper stage shut down ahead of schedule.

Cygnus-6 became the sole (to date) mission to suffer any kind of issue with the booster. Its RD-180 engine shut down six seconds early as it lifted the Cygnus spacecraft toward a rendezvous with the International Space Station. “The ULA engineering team has reviewed the data and has determined an anomaly with the RD-180 Mixture Ratio Control Valve (MRCV) assembly caused a reduction in fuel flow during the boost phase of the flight,” noted the company, pointing to the assumed issue with the fuel ratio causing the early shutdown.

The Centaur upper stage was able to extend its burn and delivered Cygnus to the desired orbit. However, with less residual fuel available, the stage was deorbited to a contingency debris zone south of New Zealand.

The Future

At the time of writing, there are only 15 Atlas V missions outstanding. One is for ViaSat, eight for Amazon’s Project Kuiper, and the remaining six for Boeing’s Starliner missions to the ISS. Many of these boosters have already been delivered to Cape Canaveral and are in storage, ready for use. The timetable could see Atlas V still flying as late as 2030.

Recently, further delays were announced to Starliner’s schedule. Following the issues experienced on the CFT-1 mission, Boeing requires more time before flying the spacecraft again. It is conceivable that the ISS could be decommissioned before Boeing has had time to fly all of its expected missions to the Station. This situation could find ULA with several spare Atlas Vs.

(Lead image: Atlas V 531 (AV-090) launches the NROL-101 mission. Credit: United Launch Alliance)

The post Atlas V set for final missions ahead of retirement appeared first on NASASpaceFlight.com.



Comments

Post a Comment