The Nasa administrator, Bill Nelson, announced has announced new delays in the US space agency’s Artemis programme to return astronauts to the moon for the first time since 1972, pushing back the next two planned missions amid potential policy changes under president-elect Donald Trump’s administration.

Nelson told a news conference on Thursday at Nasa headquarters that the next Artemis mission, sending astronauts around the moon and back, has been delayed until April 2026, with the subsequent astronaut landing mission using SpaceX’s Starship planned for the following year.

“Assuming the SpaceX lander is ready, we plan to launch Artemis III in mid-2027,” Nelson said. “That will be well ahead of the Chinese government’s announced intention to land on the lunar surface by 2030,” Nelson added, illustrating the competition between the world’s top two space powers as they race to the moon.

The newly announced delays came after Nasa concluded an examination of the Orion crew capsule, made by Lockheed Martin, and its heat shield, which had cracked and partially eroded during reentry into Earth’s atmosphere on its debut 2022 uncrewed test mission, Artemis I.

The Artemis programme was established by Nasa during Trump’s first administration and represents a flagship American effort to return astronauts to the moon for the first time since the US space agency’s Apollo 17 mission. It is estimated that the Artemis programme will cost $93bn (£72.8bn) in 2025.

Unlike the Apollo missions, the Artemis programme also calls for building lunar bases that will help pave the way for the more ambitious future goal of sending astronauts to Mars. The Artemis programme has made noteworthy progress, including Orion’s 2022 uncrewed launch atop Nasa’s giant Space Launch System (SLS), but also has experienced various delays and rising costs.

The SLS’s roughly $2bn for each launch price tag and its heavy cost overruns in development have made advisers to Trump eager to upend the Artemis programme and focus more heavily on Mars using SpaceX’s Starship. Trump takes office on 20 January.

Nasa’s Artemis I mission was a 25-day voyage around the moon that ended when the Orion capsule, carrying a simulated crew of three mannequins, made a splash down in the Pacific. During its blazing atmospheric re-entry, heat became trapped inside the Orion heat shield’s outer layer, causing cracks and raising concerns after the mission about the capsule’s future models.

Nelson said he and other senior Nasa officials unanimously decided at a meeting this week to keep the heat shield design as is for Artemis II, but change the capsule’s return trajectory to prevent the cracking issues.

Orion capsules on missions beyond Artemis II will have an upgraded heat shield. Replacing the Artemis II heat shield would have caused a much longer delay of at least a year, according to Pam Melroy, Nasa’s deputy administrator.

The Artemis II mission, a flight carrying astronauts around the moon in Orion but without a landing, has experienced previous delays as well, including one announced by Nelson in January pushing back its timetable to September 2025.

The Artemis III lunar landing mission involves Orion transferring the astronauts in space on to Starship, which will land them on the surface.

The US and China, an ascending power in space, are both courting partner countries and leaning on private companies for their moon programmes.

The Artemis programme has been Nasa’s top priority under Nelson. Trump’s first Nasa chief, the former US congressman Jim Bridenstine, launched the Artemis programme and persuaded Congress to increase the agency’s budget to fund it.

Trump on Wednesday picked the billionaire businessman Jared Isaacman, an associate of the SpaceX founder, Elon Musk, to succeed Nelson as Nasa chief. Nelson said he spoke briefly to Isaacman to congratulate him and that he expects the incoming Trump administration to carry Artemis forward under the current plan.