NASA’s Exploration Ground Systems (EGS) and prime launch processing contractor Jacobs hoisted the in-space stage for the Artemis 1 Space Launch System (SLS) vehicle into High Bay 3 of the Vehicle Assembly Building (VAB) at Kennedy Space Center (KSC) and placed it on top of the stack, that is resting on Mobile Launcher-1, on July 6. Stacking of the Interim Cryogenic Propulsion Stage (ICPS), which will send an Orion spacecraft to the Moon on Artemis 1, comes a week after the interstage Launch Vehicle Stage Adapter (LVSA) was securely mated to the SLS Core Stage below.
The stacking work for Artemis 1 is the first-time an SLS flight vehicle is being put together, and the deliberate process is consuming some of the “assessed risk” time in the schedule. EGS expected the work would take longer than baseline forecasts as the Artemis 1 integrated operations team in the VAB works towards possible launch readiness in late 2021, or more likely in 2022.
ICPS stacking connects Artemis 1 SLS stages
The ICPS for Artemis 1 was lifted up out of its storage container in the VAB Transfer aisle on July 5 by one of the 325-ton cranes in the building. After final inspections and closeout imagery was taken while the in-space stage for SLS was hanging over the floor, it was lifted up into the High Bay 3 integration cell on the night of July 5 into the morning of July 6 and lowered down onto the upper flange of the LVSA where the two elements were soft-mated.
Hard-mate occurred during the follow-on shifts on the evening of July 6 overnight into July 7, completing structural attachment of the ICPS and the LVSA.
Built by United Launch Alliance (ULA) for Boeing, the first flight ICPS was delivered to KSC in 2017 and had been in storage in the Space Station Processing Facility (SSPF) for most of the intervening time. The stage is a derivative of the Delta Cryogenic Second Stage (DCSS) used in the Delta IV launch vehicle, and the unit was moved back to the Delta Operations Center at nearby Cape Canaveral for some periodic maintenance in 2020.
Following a short return to the SSPF, the stage was temporarily stored in the Multi-Payload Processing Facility (MPPF) early in 2021 before its attitude control system (ACS) tanks were filled with hydrazine at the beginning of June. The stage was moved to the VAB Transfer Aisle in its storage container on June 19 in anticipation of a lift a few days later; however, issues slowed down hard-mating of the LVSA with the SLS Core Stage, and some additional pre-stacking work was required on the ICPS pushing back the lift until the end of the July 4th holiday weekend.
Credit: NASA/Kim Shiflett.
(Photo Caption: The Artemis 1 ICPS is lifted into the figurative rafters of the VAB late at night on July 5 under a lifting beam carried by one of the 325-ton cranes. In the background, several workers are gathered on Platform C in High Bay 3 around the upper flange of the LVSA to begin structural mating activities with the SLS in-space stage.)
The ICPS is a stretched variant of the Delta second stage; in SLS, it is used as an in-space stage versus its second stage role for Delta IV. In contrast to its dual-use on Delta IV as both an upper stage during ascent to complete insertion into low Earth orbit (LEO) and an in-space stage for transfers out of LEO, ICPS is already on a nearly-complete suborbital trajectory when it separates from the Core Stage.
The LVSA and the ICPS are major pieces of the SLS Block 1 Integrated Spacecraft and Payload Element (ISPE), which also includes an SLS-built Orion Stage Adapter (OSA) that connects Orion to ICPS. The SLS Boosters and Core Stage are the base blocks of the launch vehicle and in the Block 1 configuration they take Orion and the ISPE into orbit.
Following Core Stage main engine cut off, the LVSA stays with the Core and the ICPS separates from the top of the adapter. The top of the LVSA includes a separation system and a frangible joint assembly that will instantaneously separate the ICPS from the adapter without generating any debris from the explosive detonation.
On Artemis 1, ICPS will coast with Orion for over 40 minutes after Core Stage separation, up to a 1,805 kilometer apogee before the first start of its single Aerojet Rocketdyne RL10 engine. Following that short perigee raising burn, akin to the Space Shuttle’s OMS-2 maneuver and Starliner’s Orbit Insertion Burn which raise vehicle perigee to orbital height after an initial suborbital drop-off for lower stage disposal, ICPS will make the translunar injection (TLI) burn to place Orion and itself on a trajectory to the Moon.
Finishing the first vehicle stack
Although the Artemis 1 SLS propulsion systems are now stacked on the Mobile Launcher, the integrated operations team is still laying the groundwork for the first tests in the Integrated Test and Checkout (ITCO) campaign. Two more test articles remain to be placed on top of the ICPS in support of the first round of testing: the structural test article (STA) for the Orion Stage Adapter (OSA) and a metal cylinder called the Mass Simulator for Orion (MSO).
The two pieces will be used to support powering up the integrated SLS vehicle for the first time and three major ITCO tests. The OSA STA is standing in for the OSA flight article during the first ITCO tests to provide more schedule flexibility for installing the set of 13 cubesats that will fly inside the OSA flight article during Artemis 1. The MSO is low-fidelity test hardware that has roughly the same mass and center of gravity as the Orion launch stack.
Credit: NASA/Cory S. Huston & Chris Swanson.
(Photo Caption: The two pieces of test hardware that will complete the first Artemis 1 vehicle stack are seen in High Bay 4 on June 21. The white cylinder on the far left is the Mass Simulator for Orion (MSO); the structural test article (STA) of the Orion Stage Adapter (OSA) is sealed in the white plastic wrap. The OSA STA will be lifted next, currently planned for the week of July 12, following )
Lifting and mating of the OSA STA to top of the ICPS is currently forecast for early in the week of July 12. While those two test articles are being lifted to top out the first stacked vehicle configuration, activity continues inside, outside, and around the integrated SLS.
The stacking schedule is running longer than the “work to” baseline, which EGS had anticipated. Several months of “assessed risk” were projected as possible, spread out over a six-month work plan. Some schedule slippage was a “known unknown,” but there are multiple work paths currently in progress, and delays in one area do not necessarily directly impact work in other areas.
With the parallel work and some rearrangement of task blocks, it’s unclear how the delays in stacking will translate into delays to the Artemis 1 launch readiness. Below the stacking work, other teams have been establishing work access inside the dry volumes of the Core Stage. After the Core Stage was mated to the Boosters in mid-June, access doors to the forward skirt, intertank, and engine section were opened for the first time since the stage’s arrival at KSC in late-April following its 16-month long Green Run design verification test campaign at the Stennis Space Center.
Once the team had internal access to the Core Stage, receiving inspections and documentation started, along with reinstallation of internal work platforms. Over the next several weeks, systems inside Core Stage will be reconfigured from supporting Green Run testing and post-test transportation to supporting pre-launch testing.
Internal Green Run ground test instrumentation will be removed, crossover cabling between the Core and Boosters will be connected, periodic maintenance will be performed, and new test instrumentation for the upcoming Integrated Modal Test will be installed.
Core Stage prime contractor Boeing will also be making repairs to the Main Propulsion System prevalve clutch mechanisms inside the engine section and finishing up installation of thermal protection system (TPS) cork on the base heatshield. During Green Run checkouts the clutch mechanism for two of the prevalves failed and had to be repaired at Stennis; it was decided to go ahead and make the repairs to all eight of the prevalves in the VAB before launch.
Credit: Philip Sloss for NSF/L2
(Photo Caption: The heavily-charred base heatshield of Core Stage-1 inside the Pegasus barge at KSC on April 28.)
The prevalves functioned correctly during the two Hot-Fire tests conducted, which is where the base heatshield cork was heavily scorched during the eight-minute long second firing in mid-March. The charring was expected from the ground test firing and the blackened sections were removed in May while the stage was horizontal in the VAB.
One example of a work task that is being repositioned on the schedule is application of spray-on foam insulation (SOFI) to the bolted flange between the Core Stage and the LVSA. The foam sprays were planned to start right after the LVSA and Core Stage were mated, but the timing of that work is now being reviewed for an opening or openings later in the testing and checkout schedule in the VAB to minimize interference with other tasks.
In addition to the work inside the Core Stage, umbilicals from the Mobile Launcher will be connected to the Core and ICPS, and additional modal test instrumentation will be installed on the outside of the integrated SLS vehicle.
Next steps leading to first SLS power up, first ITCO tests
Stacking of the SLS vehicle, internal reconfigurations, and connecting the Mobile Launcher umbilicals all lead up to the beginning of ITCO. The kickoff of ITCO pre-launch checkouts will begin with the first SLS vehicle power-up, which will be a major milestone in the Artemis 1 launch campaign. Currently the first power-up is forecast for some time in August.
SLS power-up will start the first ITCO test, called the Interface Verification Test (IVT). The connections between all of the SLS flight hardware and the Mobile Launcher will be checked out in this test.
The next test, the Umbilical Release and Retract Test, will verify the Mobile Launcher’s launch release system, which must safely detach the ground umbilical connections from the vehicle beginning at T0 and quickly swing the umbilical arms away.
Credit: NASA/Glenn Benson & Ben Smegelsky.
(Photo Caption: The Artemis 1 ICPS begins its lift from the VAB Transfer Aisle up onto the SLS stack. The ICPS is derived from the Delta IV second stage, with a stretched liquid hydrogen (LH2) tank (with the American flag), and an additional hydrazine tank to provide additional fuel for the stage’s attitude control system. The stage retains the extra long, deployable nozzle extension for its Aerojet Rocketdyne RL10 engine; as seen here, the nozzle extension completely enshrouds the rest of the engine.)
The third test is the Integrated Modal Test, which is also a major sync point in the overall Artemis 1 pre-launch campaign. The test will be performed with the SLS vehicle and Orion mass simulator disconnected from the Mobile Launcher umbilical and support arm connections, and all the internal work platforms and access kits will be broken down and removed beforehand — which will temporarily suspend internal work.
Following the Integrated Modal Test, internal access to the Core Stage engine section, intertank, and forward skirt will be re-established, all the Mobile Launcher umbilical arms will be reconnected, and the OSA test article and Orion simulator will be destacked. Following removal of the test articles, integrated operations in the VAB will be ready for stacking of the Artemis 1 Orion spacecraft and several secondary cubesats.
Orion is still in the MPPF in the KSC Industrial Area; its move to the nearby Launch Abort System Facility (LASF) is currently scheduled for Friday, July 9. While the beginning of the SLS pre-launch testing and checkouts gets underway in the VAB, the Launch Abort System hardware for Artemis 1 will be integrated with Orion across two months of work.
The Artemis 1 LAS is similar to the Exploration Flight Test-1 unit, with only a live jettison motor and abort functionality disabled. The LAS tower will be stacked on top of the Orion Crew Module and integrated with the spacecraft, followed by installation of the four-panel, ogive-shaped launch fairing for the Crew Module.
After functional checkouts between the LAS and the spacecraft, leak checks, and closeouts, the Orion launch stack will be ready to move to the VAB to join SLS. That move is currently scheduled for no earlier than some time in September.
Lead image credit: NASA/Glenn Benson & Ben Smegelsky.