United Launch Alliance (ULA), the prime contractor for the Space Launch System’s (SLS’s) Interim Cryogenic Propulsion Stage (ICPS), has declared the stage’s overall performance on the Artemis I mission as “perfect.”
The ICPS is the in-space upper stage of the SLS stack. On Artemis I, it was responsible for raising the initial orbital perigee and then performing the all-important translunar injection (TLI) burn to send Orion and the European Service Module duo on their way to the Moon.
“There was nothing unique or out of the ordinary for this vehicle,” said Gary Wentz, Vice President of Government and Commercial Programs at ULA, in an interview with NASASpaceflight.
“The vehicle was very similar to what we fly for Delta IV, and all the modifications that we made to adapt and enable the Artemis mission really didn’t have an effect on performance. And so it delivered the Orion capsule right where we were supposed to.”
The performance accuracy of ULA rockets and stages is something the company’s CEO Tory Bruno routinely discusses on missions where that is possible. Artemis I was no exception, with Bruno tweeting a graphic (below) showing a cluster of dots very near the center — a bullseye, so to speak.
— Tory Bruno (@torybruno) November 29, 2022
Discussing the insertion accuracy of the ICPS’s translunar injection burn, NASA officials had previously been quoted as saying it was “dead on.”
Wentz elaborated with a reference that could be used to help understand the accuracy. In this scenario, an archer is given the requirement to hit the center of a 46 cm (18-inch) target located 18 meters (60 feet) away.
If the archer had the same accuracy as the ICPS did for its TLI burn, the archer would hit the center of the target within 21 mm (0.8 in).
In other words, a bullseye when it comes to space travel.
This accuracy, too, came after two notable firsts for ULA and the ICPS, which is itself derived from the Delta Cryogenic Second Stage used on the Delta IV rocket line. These two firsts included a prolonged time from leaving the launch pad to the stage firing for the first time, and the longest-ever RL engine burn to date.
To the first point, Wentz noted that the coast “was on the order of 3,000 seconds … before we did our first burn. And that is not characteristic of how we fly the Delta IV. But the vehicle performed great.”
Following the perigee raise maneuver to ensure the remaining launch stack would not follow the Core Stage on its destructive plunge back into the atmosphere, the ICPS performed the mission-critical translunar injection burn.
This was a nearly 18-minute firing of the RL10B-2 engine from Aerojet Rocketdyne. “It was also the longest burn in RL10 history,” said Wentz. “So that was a pretty significant accomplishment for the team. And it performed just perfect. We had no issues.”
ICPS status for Artemis II and III
Looking ahead to the next two Artemis missions, which will also use the ICPS, Wentz looked back on the first ICPS’s processing flow and lessons learned from those operations.
“This being the first processing of an ICPS, working with the SLS team, there’s a lot of things that we learned in that process. This vehicle was delivered a pretty long time ago. So it sat in storage for a while, and we ended up doing a couple of rounds of testing with it.”
“So I would say, the main thing that we learned is we’re going to work with the government team and make sure that the testing is in line with their expectations.”
(Photo caption: The ICPS, just above the orange foam and with the US flag painted on it, sits ready to take Orion and the European Service Module to the Moon. Credit: Jack Beyer/NASASpaceflight)
Wentz also touched on the first-time nature of stacking and ground systems interface with the ICPS and overall SLS stack, saying “interfacing with a new [Mobile Launcher], the NASA team hasn’t launched anything off those pads or that facility in over a decade, and it was new hardware. And so after this flight, we’ll go back through and look at the detailed procedures of any tweaks that we need to make.”
However, Wentz stressed that from the ICPS perspective, the minor tweaks that were needed going through the first flow were largely within the family of expectations teams had going into the operations.
“There was nothing significant, nothing detrimental, or [anything] that created an issue with our planned procedures. It was a fairly benign flow, and going forward, it’s mainly just process improvements and working together with a new teammate.”
Those process flow improvements will be on display in 2023 as ULA takes the ICPS for Artemis II through its dock checkouts at the Cape Canaveral Space Force Station. The stage itself was delivered to the Cape more than a year ago in August 2021.
Dock checkouts will occur at the Delta Operations Center and will fully checkout the stage to make sure its various systems are working both independently and cooperatively and are ready for stacking and flight.
Once those checkouts are complete, ULA plans to formally deliver, or hand over the stage, to NASA in mid-2023 per current timelines.
Meanwhile, the ICPS for Artemis III is nearly complete at ULA’s Decatur, AL, production facility. Current schedules call for its shipment to the Cape in late 2023, with dock checkouts in early 2024 before a handoff to NASA later that year.
“The hardware is in good shape, and we’re ready to support NASA and our Boeing teammate as soon as they’re ready to launch Artemis II and III,” said Wentz.
The ICPS is part of the overall Block 1 configuration of the SLS rocket and will be retired with the Artemis III mission in favor of a more powerful variant of the rocket called Block 1B.
Block 1B will replace the ICPS with the larger, more powerful Exploration Upper Stage (EUS) that will permit co-manifested payloads with Orion crew launches.
While its use will be short, with only three flights, the ICPS did provide ULA teams with valuable insight into production and manufacturing processes ahead of Vulcan build operations. This stemmed mainly from the modification work needed to turn the DCSS into an ICPS by adding and stretching existing tanks.
“It did give us some experience in modifying the existing tanks, existing engineering,” said Wentz. “And that’s helped the team from an engineering and a production perspective that can be leveraged on Vulcan since Vulcan is using bigger tanks, both in diameter as well as length.”
“So that allowed us to refine the processes of making those changes.”
Finally, Wentz related the ICPS’s first flight as a first of its own for ULA… the first of three major firsts in ICPS’s first flight, the first crew flight on Atlas V, and Vulcan’s first flight. All three of those major milestones now stand to happen relatively close to one other per current schedules.
“With our first flight of crew on an Atlas, we just successfully flew SLS being a first flight vehicle, and we’re headed towards a Vulcan first flight,” related Wentz, “and the teams’ posture is to be able to learn from all those and apply it to the next challenge in front of us.”
“In the over 30 years I’ve been doing this, these kinds of events don’t come around often where you’re doing first flights. And in the next decade, it’s gonna be a lot different than it was for the past 30 years. And so the workforce has a lot of opportunities to learn and build on these experiences. It’s gonna be exciting.”
(Lead image: Artist’s impression of the ICPS firing to take Orion to the Moon. Credit: Mack Crawford/NSF)