An Atlas 5 551 rocket stands tall at Space Launch Complex 41 (SLC-41) in anticipation of the USSF-51 mission launch. Image: Michael Cain/Spaceflight Now

United Launch Alliance’s Atlas 5 rocket is preparing for its swan song when it comes to launching critical missions connected to U.S. national security. The launch provider is prepping to send up a classified payload as part of the United States Space Force-51 (USSF-51) mission, marking the 100th such operation for ULA.

Liftoff from Space Launch Complex 41 (SLC-41) at Cape Canaveral Space Force Station (CCSFS) is targeting Tuesday, July 30, during a three-hour window that opens at 6:45 a.m. EDT (1045 UTC). Spaceflight Now will have live coverage beginning nearly two hours ahead of liftoff.

Out of the 99 national security flights so far, ULA used an Atlas 5 rocket for 57 of them. That partnership between the rocket and the Department of Defense goes back to first such mission, Space Test Program 1 (STP-1), which launched in March 2007.

These national security missions were originally contracted under the Evolved Expendable Launch Vehicle (EELV) program. The program name changed to National Security Space Launch (NSSL) in March 2019 about nine months before the establishment of the U.S. Space Force.

“The next five missions, starting with that one, were National Security Space Launch missions and represented a forging of a tremendous partnership with United Launch Alliance that has continued up till this day,” said Dr. Walt Lauderdale, the USSF-51 mission director.

“We’ve put a lot of national capability on orbit to support our warfighter and our intelligence communities, capabilities we can’t go beyond in some areas to talk about, but things that help our folks on the sea, in the air and on the ground all across the globe every single day.”

ULA spent a good part of the day on Saturday rolling the Atlas 5 rocket out of its Vertical Integration Facility making its final one-third-of-a-mile (550 meter) journey to the launch pad at SLC-41. It came after ULA Launch Director Steve Huff led and completed the launch readiness review on Friday.

“This is the final Space Force Atlas 5 launch and it’s one of the most critical payloads that we’ve put up to date, I would say,” said Gary Wentz, ULA’s vice president of Government and Commercial Programs. “We can’t talk a lot about that, but it’s definitely critical to the defense of our nation as well as our allies.”

A closeup shot of the payload fairings of the Atlas 5 551 rocket that will launch the USSF-51 mission. This will be the final national security mission launched on an Atlas 5 rocket. Image: Michael Cain/Spaceflight Now

The USSF-51 mission was tasked to ULA as part of the NSSL Phase 2 Order Year 1 assignment. ULA and SpaceX were awarded $3.4 billion and $3.3 billion Indefinite Delivery Requirements (IDR) contracts in May 2019 to launch an estimated 34 mission, split 60/40.

Earlier this month, a contract modification was announced to “increase the estimated total contact dollar value due to the increase in estimated mission quantities that will be ordered under the Phase 2 contract.”

“Per DFARS 205.303, a public announcement must be made after the initial estimated face value is reached.  The government put a good faith manifest estimate in the Phase 2 Request for Proposal, released May 2019, to allow potential bidders to adequately develop their proposals,” a spokesperson for the U.S. Space Systems Command told Spaceflight Now in a July 19 statement. “We estimated 34 missions would be ordered during Phase 2 and the 34 missions (split 60/40) were used to develop the $3.4 billion and $3.3 billion ULA and SpaceX contract values, respectively.”

“As FY24 is the final order year of Phase 2 this modification was updating the contracts to the actual number of missions ordered FY20-FY24 to 49 and thus the need to increase the contract values to $4.5 billion and $4.0 billion, respectively.”

The 49th mission, NROL-95, is anticipated to be awarded by the end of July, according to the SSC.

Originally, USSF-51 was scheduled to launch on a Vulcan rocket, but because of development delays, in June 2021 the U.S. Space and Missile Systems Center (changed to the SSC in 2021) approved switching the launch vehicle from Vulcan to Atlas.

‘The Bruiser’ era

While neither ULA nor the U.S. Space Force offered specifics about the mission, it is calling upon what ULA calls “the highest performance configuration of the (Atlas) rocket with a full compliment of five solid rocket boosters.” ULA termed this as an Atlas 5 551 configuration or as ULA President and CEO Tory Bruno nicknamed it, “The Bruiser.”

This version of an Atlas 5 rocket will be seen several more times before the rocket is ultimately retired. Wentz told Spaceflight Now on Saturday that all of its remaining commercial launches will fly the 551 configuration, which include eight missions for Amazon’s Project Kuiper and one for Viasat.

“Every time you fly, you learn a lot and we’re flying five GEM (Graphite-Expoxy Motor) 63s on this mission,” Wentz said. “So, we’ll learn from that, we’ll continue to get data and going forward, we’ll apply that to the subsequent Atlas missions.”

Prior to the USSF-51 launch, ULA launched 13 previous missions using the 551 configuration. ULA first flew an Atlas 5 551 rocket on Jan. 19, 2006, when it launched NASA’s New Horizons mission to Pluto. This was the seventh launch of an Atlas 5 rocket overall.

“The Bruiser” version of Atlas 5 also launched the following missions:

Aug. 5, 2011 – Juno Feb. 24, 2012 – MUOS-1 July 19, 2013 – MUOS-2 Jan. 20, 2014 – MUOS-3 Sept. 2, 2015 – MUOS-4 June 24, 2016 – MUOS-5 April 14, 2018 – AFSPC-11 Oct. 17, 2018 – AEHF-4 Aug. 8, 2019 – AEHF-5 March 26, 2020 – AEHF-6 Dec. 7, 2021 – STP-3 Sept. 10, 2023 – NROL-107

“The team goes through, they model, they predict the performance. They’ll then look at all the flight characteristics, what the mission needs and what margins that we have. Then when we come down here, the team goes through excruciating detail, stacking the booster, mating the solids, the upper stage, integrating the payload,” Wentz said. “They just continually focus on safety of not only the hardware, but our personnel throughout the process to meet 100 percent mission success.”

Vulcans on the horizon

Once the USSF-51 mission is in the rearview mirror for ULA, it will shift its focus to the second certification flight of Vulcan, known as Cert-2. It’s first launch, Cert-1, proved successful in January when it launched the Astrobotic Peregrine lunar lander.

ULA is aiming for the second launch to take place in September with an inert payload onboard that will include some Vulcan technology demonstrations.

“We’re in the final phases of our certification. ULA is completing their final qualification tests, which are going well, and we’re postured to be complete and waiting on data from this next certification flight and then ready for our first national security bulk admission in the October timeframe,” said Col. Jim Horne, Senior Materiel Leader of the Launch Execution Delta.

“Things are progressing well. We’ve had a lot of good reviews, we’ve over come some major obstacles and we’re excited to get going this year.”

In recent weeks, Bruno shared several images of the progress of the Vulcan vehicle, stating in a post on X, formerly Twitter, that there are currently “23 Vulcans in production!!!”

Another #VulcanRocket departs Alabama and heads to Florida, making room in our crowded rocket factory. 23 Vulcans in production!!! pic.twitter.com/CIfBl8yKMS

— Tory Bruno (@torybruno) July 26, 2024

That exclamation punctuated the third Vulcan booster to leave ULA’s factory in Decatur, Alabama, to begin the voyage to Florida. It will support the USSF-87 mission, which will launch towards the end of 2024.

The first operational mission of Vulcan will be the USSF-106 mission, which Horne referenced. Before that happens, Horne said he and others are eager to watch the performance of the Cert-2 mission.

Originally, Cert-2 was going to launch Sierra Space’s Dream Chaser spaceplane, but because it was falling behind schedule in its final, prelaunch work, ULA and Sierra Space decided to punt that mission to another launch in order to progress through the certification process.

“At this point, the data (from Cert-1) correlated pretty closely with our model. So this is just another verification that we have the right analysis tools in place for future flights and make sure we’ve captured the environment for the spacecraft as well as the rocket,” Horne said.

“This will be a really good verification for us of what we saw in Cert-1. The configuration differences were well inside our certification plan. Based on that, it was just some adjustments they had to make for this mission. But we’re excited to get the data.”

A Vulcan booster sits inside United Launch Alliance’s Horizontal Integration Facility at Cape Canaveral Space Force Station. It will support the second certification flight of the rocket prior to launching national security payloads. Image: Will Robinson-Smith/Spaceflight Now