NASA Artemis Manifest Hindered by Lack of SLS Rockets

NASA is facing concerns about the low flight rate planned for its crewed Orion spacecraft and Space Launch System (SLS) rocket. The space agency does not have enough vehicles to fly more frequently in the coming decade. The hardware to launch only two more SLS vehicles is available until the completion of the Exploration Upper Stage (EUS) upgrade, which is expected to be ready by late 2028 at the earliest.

After the planned Artemis II lunar flyby test flight late next year, the Artemis III Orion and crew could be the only ones flying to the Moon in the following four years. However, NASA still has the option to buy more Interim Cryogenic Propulsion Stages (ICPS) built by United Launch Alliance (ULA) and continue flying the current Block 1 version of SLS. ULA has noted that the ICPS production line will remain open until next year when the Delta IV, from which ICPS is derived, retires. However, NASA has affirmed its choice not to buy any more ICPS units.

The gap between Artemis III and Artemis IV in the Artemis mission schedule has increased in the last year. Artemis III will be the final launch of the initial Block 1 version of SLS, which uses ICPS as an in-space second stage. Artemis IV will be the debut launch of the SLS Block 1B version, which replaces ICPS with the Exploration Upper Stage. However, the EUS upgrade is still in development and will require a new mobile launcher.

The delay in completing the Mobile Launcher-2 (ML-2) project, as detailed in the NASA OIG report in June 2022, could push back the planning date for Artemis IV to as late as August 2027. The development of the EUS upgrade has also experienced delays in recent years. According to NASA’s budget request released in February, the planning date for Artemis IV has moved to September 2028.

NASA and the prime contractors for the Orion and SLS vehicles are increasing production, but there is not enough hardware to assemble a full SLS between Artemis III and IV. This limitation means that Artemis is limited to the final two SLS Block 1 launches of Orion crewed spacecraft for the next five years, until all the Block 1B and Mobile Launcher hardware for Artemis IV is developed, constructed, assembled, and tested.

NASA’s Advisory Council and the National Academies have raised concerns about the long gaps between Artemis missions, which could lead to a loss of skills and experience among the ground and launch workforce. NASA acknowledges the risks but does not have the resources to fly annually until the end of the decade. The target for reaching an annual flight rate is Artemis V, which has been pushed back to September 2029.

An alternative solution would be to continue flying SLS Block 1 and add additional missions to fill in the gaps in the Artemis manifest by using ICPS until EUS, Block 1B, and ML-2 are completed. However, NASA has shown little interest in this option. The agency has chosen to support the move from SLS Block 1 to Block 1B on Artemis IV. There is no indication of interest in more Block 1 flights after Artemis III.

The production line for ICPS remains open until the final Delta IV launch in early 2024. ULA has completed production of all its hardware commitments for the final Delta IV Heavy launch and the final two planned ICPS units. ULA plans to maintain the Delta/ICPS production line until the final Delta flight is completed. NASA and/or Congress have a few more months to think building more ICPS units before the production tooling needs to be mothballed.

In conclusion, NASA is facing limitations in its Artemis manifest due to the low flight rate planned for its crewed Orion spacecraft and SLS rocket. The agency does not have enough vehicles to increase the flight rate until the completion of the EUS upgrade. The gaps between Artemis missions have raised concerns about a loss of skills and experience among the workforce. NASA has the option to continue flying SLS Block 1 and add additional missions using ICPS, but it has chosen to support the move to Block 1B on Artemis IV. The ICPS production line will remain open until the final Delta IV launch in early 2024.