SpaceX's Starship lunar lander for NASA's Artemis program may be too large to easily dock with the space agency's planned lunar space station, according to a new report released by the U.S. Government Accountability Office (GAO).

SpaceX’s final Starship stage during IFT3: SpaceX

The U.S. Government Accountability Office conducted a study of the space station's mass limitations and concluded that the total mass of the station's two major components, the Habitation and Logistics Outpost (HALO) and the Power and Propulsion Element (PPE), exceeded their goals. The study also found that if large aircraft such as SpaceX's StarshipDock are carried on PPE, the PPE may not be able to properly control the aircraft because although PPE meets the performance requirements set by NASA, these requirements do not take large aircraft into account.

NASA currently has to launch a lunar space station called Gateway by 2027, or before the Artemis IV mission takes flight. The Artemis IV program is the second manned lunar landing flight of the Artemis program. The mission is currently scheduled to take off in September 2028. Gateway must enter lunar orbit a year before Artemis IV launches so NASA can assess the station and ensure all systems are in working order before crews can board the space station.

According to the U.S. Government Accountability Office, NASA's current baseline capability to launch "Gateway" is December 2027, three months later than planned. NASA plans to update Gateway's current costs and confidence levels in September this year to determine whether launching Artemis IV in September 2028 can achieve all of the mission's goals. The last such analysis was conducted in May last year, and since then the space agency has had to risk manage the station's habitability systems and communications networks.

The picture on the left shows SpaceX's Starship docking with Gateway. The picture on the right shows astronauts on the moon with the Starship in the background. Image: U.S. Government Accountability Office renderings

The U.S. Government Accountability Office identified quality as another key constraint on the Gateway program. This includes both the mass of the space station and the mass of some aircraft that may dock with the space station. The report noted that the total mass of the space station's logistics and propulsion components exceeded NASA's mass requirements. The report also adds that the mass of some vehicles may prevent the propulsion unit from guiding the space station according to mission conditions, which may ultimately affect the space station's mission.

The higher mass means NASA will have to have some of the "Gateway" components travel independently to ensure the space station can get into the right orbit. Another option is to reduce mass by removing components. Both approaches come with trade-offs, as flying components individually is expensive and reducing them would impact the station's performance.

While Gateway may have exceeded mass requirements, its PPE is still not strong enough to manage the heavier spacecraft while docking with the space station. This affects the space station's ability to maintain orbit and communicate with Earth in the right direction. According to the U.S. Government Accountability Office, citing NASA managers, although the PPE met the design stage requirements, these requirements were not sufficient for vehicles such as SpaceX's "Starship" that have a mass that is 18 times greater than the PPE design capabilities.

The U.S. Government Accountability Office revealed that NASA plans to let visiting aircraft share some of the PPE duties of "Starship" to control the space station. The agency is also considering software upgrades to efficiently manage the space station's thrusters. If neither approach is successful, NASA may change the design of the PPE and impose additional cost and schedule constraints on the Gateway program.