United Launch Alliance (ULA) delivered the last-ever Space Launch System (SLS) Interim Cryogenic Propulsion Stage (ICPS) from its Decatur, Alabama, factory to Cape Canaveral Space Force Station (CCSFS) in early August for eventual use on the Artemis III lunar landing mission. ICPS-3 was also the last Delta hardware to depart Decatur and will support NASA’s third and final launch of the SLS Block 1 rocket before it is upgraded to the Block 1B configuration beginning on Artemis IV.
The SLS in-space stage will remain mostly in storage at ULA’s CCSFS facilities until NASA is ready to fly Artemis III; the mission is aspirationally targeted for the end of 2025 but is not expected until 2026 at the earliest and could possibly fly later than that. In the meantime, ULA and SLS teams will make final preparations for ICPS-2 to be stacked for the Artemis II circumlunar test flight next year; that stage is fully outfitted and ready to be formally turned over from ULA when NASA Exploration Ground Systems (EGS) needs it.
ICPS-3 delivered to CCSFS from Decatur plant
ULA’s seagoing cargo ship, R/S RocketShip, arrived at Cape Canaveral in early August, where the ICPS stage was offloaded still inside its shipping container and taken to the company’s Horizontal Integration Facility (HIF). “That’s the big building that is right down the street from their Delta pad, they process mostly Delta hardware in there,” Chris Calfee, NASA SLS deputy manager for the Spacecraft/Payload Integration and Evolution (SPIE) office, said in a recent interview with NSF.
“So, we’ll stage the ICPS there, it will stay in the horizontal position. It will allow us to actually barbeque roll it and do inspections and those sorts of things if we need to, but it’ll stay there until we’re ready to take it down the street to ULA’s Delta Ops Center, we call that the DOC.”
With the second ICPS stage currently in storage at the DOC, ICPS-3 will remain in the HIF until next year. “Every ICPS has been staged there, ICPS-1 was staged there, [and ICPS-]2 was staged there before it went to the DOC,” Calfee noted. “Let’s say ULA has a data observation on a Delta flight or even an Atlas flight that would have cross-fleet components and they say, ‘Hey we want to get a heads up on this component,’ we’ve actually pulled the component off of the stage in the HIF.”
“We don’t plan to do anything, but it kind of depends on if something comes up with a cross-fleet issue or some other issue where we want to do an inspection. You can’t do testing, but you can put scaffolding up and remove a component if you need to.”
The Interim Cryogenic Propulsion Stage is used as an in-space stage in the SLS Block 1 vehicle design to transport payloads out of low Earth orbits. The ICPS is a close cousin to the Delta Cryogenic Second Stage (DCSS) used on the soon-to-be-retired Delta IV vehicle, with the major differences being a slightly longer liquid hydrogen tank, an extra hydrazine bottle for the stage’s attitude control system, and Orion-specific interfaces, since NASA’s crewed spacecraft is the sole primary payload that ICPS and SLS Block 1 will fly.
ICPS-3 is also likely to be the last Delta IV stage to fly, and Calfee said it will stay stored in the HIF until after the last planned Delta IV flight hardware is tested and checked out in the DOC next year. “Right now, the ICPS-3 [is scheduled] to go into the DOC in spring of 2024,” he said.
“There’s a test cell in there where we’ll do final testing and checkout, run approximately 20 different tests on the stage before we do final acceptance and go into storage. ULA has one final Delta DCSS stage that will go into that cell before us, it flies on a mission called NROL-70, which flies middle of next year I believe, it’s the last Delta IV Heavy flight.”
“So ICPS-3 will go into the test cell after that [NROL-70] stage moves out,” Calfee added. NASA continues to target December 2025 for the Artemis III launch, and Calfee said that the EGS need date would be the spring of 2025. Once EGS receives the stage from ULA, it will be moved to the Multi-Payload Processing Facility (MPPF) in the nearby industrial area of Kennedy Space Center (KSC) where the attitude control system hydrazine bottles will be loaded for flight before the stage is then transported to the Vehicle Assembly Building (VAB) to be stacked with SLS.
ICPS-2 stage outfitted and checked out for flight
ICPS-3 will follow the same path for Artemis III that ICPS-2 is taking for Artemis II. The stage that will help send the first astronauts to the Moon in over 50 years is now prepared for the Artemis II launch campaign when it begins next year.
ICPS-2 was originally delivered to Cape Canaveral two years ago in the summer of 2021; this spring, ULA moved it from the HIF to the DOC to get it ready for Artemis II. “It’s actually complete in the DOC,” Calfee noted.
“It had been in there since we rolled it down the street from the HIF into the DOC. All that testing is complete, it just wrapped up a couple of weeks ago and the stage was moved from that test cell, down the transfer aisle, into its storage cell.”
(Photo Caption: ULA moved ICPS-2 to the Delta Operations Center in April to complete final outfitting, test, and checkout of the stage before putting it in storage while waiting for Artemis II vehicle stacking next year.)
After the stage was moved into the test and checkout cell in the DOC, the nozzle extension for the RL10 engine and flight computers for the stage were installed; then, the stage went through a series of tests.
“We do avionics testing, we have a version of the flight software that we exercise the system with,” Calfee said. “The main testing that we do there, the most critical test, is we actually extend the RL10 nozzle. The RL10 on the ICPS is an extendable nozzle, it’s stowed in-flight and it extends right before it fires.”
“We actually do several tests of that nozzle extension, where we extend it all the way down. It’s a mechanical test in the DOC and then we slew the engine, back and forth, pitch and yaw, all those angles to ensure that it’s functioning properly.”
“It’s called the NEDS (nozzle extension and deployment system), [it’s] added to the stage in the DOC test cell,” he added. The ICPS flight computer takes over control of the flight after separation from the SLS Core Stage and the avionics are crew-rated for Artemis II.
“There’s a few select avionics components,” Calfee explained. “The INCA (Inertial Navigation Control Assembly), which is our flight computer; [the stage] is shipped from Decatur without that, so we put a test INCA in the DOC for testing.”
“For Artemis II we have what is called the emergency detection system. The emergency detection system will be used to predict a catastrophic scenario the ICPS would be experiencing on ascent or during in-space operations, which would essentially send a signal to the crew to say ‘Hey, we’re having a bad day, get off.'”
“That’s one of the key differences between [Artemis I and Artemis II], and that component is not on there when we ship it from Decatur either, so those are your three primary components that are [installed], the two avionics boxes, the INCA and the emergency detection system, and the nozzle extension.”
(Photo Caption: One of the centerline targets is seen following installation on ICPS-2 in May. The target was installed on the stage in a test and checkout cell at ULA’s Delta Operations Center, shown in the inset, upper right.)
One of the crew-rating modifications evaluated for ICPS was adding some shielding to reduce the risk of micrometeoroid and orbital debris (MMOD) impacts; however, Calfee noted that idea turned out to be more trouble than it was worth. “We looked at concepts for beefing up some of the components in particular areas that were the most suspect to strikes with shielding and those sorts of things and determined that it just wasn’t feasible, that there would likely be unintended consequences, and actually add risk instead of reducing the risk of a catastrophic micrometeoroid strike,” he said.
“So that risk will actually be the same for Artemis II and III. Now the trajectory is very different that we fly for Artemis II and III, so we will fly a trajectory to minimize the risk of a strike.” For example, all three SLS Block 1 missions using the ICPS plan to fly only one revolution of Earth — the first one — within the range of orbital altitudes that carry the highest calculated risks of MMOD strikes.
Also installed on ICPS-2 at the Delta Operations Center was a rendezvous target that will be used by the Artemis II flight crew as a part of an Orion proximity operations and handling qualities demonstration on the first day of the mission. The centerline target is one of two that will be used by the crew in approaches to the stage and its still-mated launch adapters.
When Orion separates from ICPS, it leaves the Spacecraft Adapter cone and Orion Stage Adapter with the stage. Another centerline target will be installed on the diaphragm of the OSA that plans call for the crew to use for its first close approach. Later in the proximity operations demonstration, the ICPS will maneuver so that the second target that is attached to the side of the stage structure faces Orion for another close approach manually flown by the crew.
Calfee noted that the storage cell in the DOC is something that NASA funded to convert for SLS. “The Delta Operations Center has four test cells in it, only one is active,” he said. “We actually funded a storage cell; it was a cell that ULA had mothballed.”
“When we decided we wanted to fly two additional ICPS-es a few years back, we predicted that we would need some storage capability, so we converted one of those test cells into a storage cell. That’s where ICPS-2 is now, is in that storage cell.”
Eventually, ICPS-3 will also end up in that storage cell when it is finished and waiting to get the call from EGS that it is time for Artemis III stacking.
For now, ICPS-2 is waiting to get that call for Artemis II first. “Our target launch date for Artemis II is late calendar year 2024, we do have a partnering agreement with EGS on transfer of ICPS-2 and it’s in the spring timeframe of 2024,” Calfee said.
When the time comes, ICPS-2 will be moved using the canister that the first ICPS sat in for so much time. “That canister is called the VTF, the vertical transport fixture,” Calfee noted.
“That’s unique GSE just for Artemis and the ICPS. We use that to transport it from the DOC over to EGS; the first stop for the ICPS is at the MPPF, we load our hydrazine bottles there for [the attitude control] system and then we use the VTF to transport it into the VAB.”
LVSA, OSA status for Artemis II and III
The SPIE element within the SLS program is responsible in part for managing all the pieces of the Integrated Spacecraft and Payload Element (ISPE) of the launch vehicle. For the initial Block 1 vehicle configuration, that includes not only the ICPS, but the two adapters that connect the SLS stages and Orion.
The Launch Vehicle Stage Adapter (LVSA) connects the Core Stage and ICPS; it encloses most of the stage, including the RL10 engine. SLS is also responsible for the Orion Stage Adapter (OSA) that connects Orion to ICPS.
Work to complete production of the Block 1 adapters for Artemis II and III is currently in progress at the Marshall Space Flight Center (MSFC) in Huntsville, Alabama. “They have switched buildings in the last month, so there’s been some pictures of some transfers,” Calfee noted.
“LVSA-2 is completely finished, it is in storage here at Marshall Space Flight Center in Building 4708. It is ready to ship whenever EGS needs it. We do have an agreed-to tentative date that it will ride the Pegasus barge down to the Cape from Marshall. It’s early spring or late winter so I want to say a February/March timeframe, that is our planned barge date.”
The LVSA for Artemis III has now taken the spot that LVSA-2 vacated. “LVSA-3 moved from where they were doing the TPS (thermal protection system) application,” Calfee said. “[It] moved just a couple of weeks ago into Building 4649, which is where LVSA-2 moved out of.”
“What we’ll do there is final integration of specifically the frangible joint and the pneumatic actuation system, which is the separation hardware that provides the separation of ICPS from LVSA,” he added. “That is actually ULA-provided hardware, so ULA provides the hardware to the government, we provide the hardware to [LVSA prime contractor] Teledyne Brown, and Teledyne Brown makes that integration of the [separation] system to the top of the LVSA. That is ongoing as we speak.”
The OSA for Artemis II is also nearing completion and readiness for delivery to Florida. “We’re in final assembly there,” Calfee said. “We got direction – I guess it was a couple of years ago – to accommodate secondary payloads on Artemis II. If you remember for Artemis II, the original baseline was it was not going to need secondary payloads.”
“That was reversed a while back and those secondary payloads are mounted inside of the OSA. So, we are doing the final integration of that bracketry [and] an avionics unit that controls the deployment of those secondary payloads.”
“That’s ongoing right now, but we’re forecasting that to be complete in October of this year and then OSA-2 will go into storage,” he added. Eventually, the OSA will be shipped to Kennedy Space Center on NASA’s Super Guppy cargo aircraft. “It would be about the same timeframe as the [LVSA], which would be spring of 2024,” Calfee said.
Speaking about the OSA for Artemis III, Calfee noted: “OSA-3 is actually sitting in the same room as OSA-2, of course it lags behind as far as production goes there.”
“It has a diaphragm which protects the volume from environments above it and from Orion,” he noted. “That diaphragm is delivered from a company called Janicki [Industries] in Washington state, that’s the next step for OSA-3.”
SPIE supporting development, training for Orion and Flight Operations Directorate
In addition to the production of the flight stage and connector hardware for Artemis II and III, Calfee noted that the element also provides data products and analysis to support the Orion program and the Flight Operations Directorate (FOD) at the Johnson Space Center in Houston, Texas.
“One of the things that is unique to SPIE and specifically to ICPS is this support to Orion and FOD,” he said. “Orion for their flight software development and FOD for training the crew.”
(Photo Caption: The pieces of the SLS launch vehicle that are managed within the program by the Spacecraft/Payload Integration and Evolution (SPIE) office, the two adapters that connect Orion and the SLS stages, and the Block 1 in-space stage, the ICPS.)
“We support [FOD] with various scenarios of in-space anomalies so they can train the crew and their console folks down at the MCC (Mission Control Center) for those potential scenarios. None of the other SLS elements participate like that with Orion and FOD.”
“To me that’s exciting,” he added. “We talk about this all the time; it’s been a challenge for us.”
“It’s been a challenge to provide the number of products that FOD and Orion need from us, but to be able to work with those programs, to me, is an amazing opportunity, so that is something that is even more important now with crew on Artemis II and Artemis III. We provided a little bit of those kinds of products for Artemis I but not near the number that we are providing now.”
They will also be supporting the upcoming flight analysis cycle for Artemis II, where the launch periods that we became familiar with for Artemis I in 2022 are calculated. “We go through a trajectory assessment process with ULA and with the SLS Level II vehicle management team,” Calfee explained.
“The first phase of that process is called the TFA, trajectory feasibility assessment, that’s essentially ‘Hey look, this trajectory will work, we know this trajectory will work.’ And then it evolves into PMA, preliminary mission assessment, where you dig down into those trajectories to make sure they will work, any nuances, and then the period where you do those launch period assessments is called the FMA, the final mission assessment.
“We’ve completed the second phase, we’ve just completed PMA,” he added. “Our flight software is nearing qualification and completion, to where we’ll declare our flight software as qualified, and then we will enter that [FMA] phase.”
“That’s scheduled for fall of this year, the start [of] the final phase.”
(Lead image: ICPS-3 is moved into storage at ULA’s horizontal integration facility (HIF) in August. Credit: United Launch Alliance.)