NASA's hopes of returning astronauts to the lunar surface by 2024 is all but impossible, according to the agency's Office of Inspector General (OIG).
One of the major issues is the development of the new spacesuits, the Exploration Extravehicular Mobility Unit (xEMU), the OIG's audit found.
The agency set the 2024 goal as part of the launch of its Artemis programme, the first step in its plan to land astronauts on Mars.
"We need to act fast to make this vision a reality, and a crewed lunar landing by 2024 is the key to a successful Moon to Mars exploration approach," the agency said at the time.
But that timeline is now incredibly unlikely due to the timescale required to have xEMUs ready on time - and despite having spent US$420 million on suit development in the last 13 years.
"NASA's current schedule is to produce the first two flight-ready xEMUs by November 2024, but the agency faces significant challenges in meeting this goal," the report states.
"However, a flight-ready suit remains years away from completion. NASA officials expect to spend over US$1 billion on design, testing, qualification, and development efforts before two flight-ready suits are available for use."
Twenty seven companies are supplying components for the spacesuits.
Multiple challenges including budget reductions, the impact of COVID-19 and technical problems have also resulted in around 20 months of delay to the schedule.
With more delays anticipated due to the pandemic and technical issues identified during testing, "a lunar landing in late 2024 is not feasible", the report concludes.
That hasn't stopped billionaire Elon Musk offering to help, saying his company SpaceX "could do it if need be".
However a follow-up question asking if SpaceX was actively developing spacesuits went unanswered by the Tesla founder.
Musk has previously signalled his intention to create a human colony on Mars, with SpaceX attempting to land humans on the Red Planet by 2026.
The audit also found other issues that could preclude the agency from a 2024 Moon landing, including delays in the Space Launch System rocket and Orion capsule.
The delay in the US$2.9 billion lander contract, confirmed recently after Jeff Bezos's Blue Origin protested the decision to award it to Space X, has also played a part, the report states.
NASA this week opened applications for four crew members for a year-long mission to live on Mars - but without leaving Earth's surface.
The selected individuals will live in a 3D-printed environment and simulate what life will be like on the Red Planet.