The bill’s most recent version allocates $19.5 billion for the agency in the upcoming fiscal year. It calls for NASA to develop a clear plan for human space exploration beyond Earth orbit, including to the moon, the surface of Mars and its own moons, and beyond.

The agency’s goal should be “the peaceful settlement of a location in space or on another celestial body and a thriving space economy in the 21st century, and to achieve human exploration of Mars”, the bill says.

But Congress is less enthusiastic about the proposed Asteroid Redirect Mission, which would move a multi-tonne chunk of an asteroid to a stable orbit around the moon so it can be visited by astronauts in the 2020s. The mission is partly meant as practice for the technology and skills needed to send humans to Mars in the 2030s. But it is competing for limited funds against the expensive Space Launch System, which is a new heavy-launch rocket, and the Orion crewed spacecraft, the bill says.

“The technological and scientific goals of the Asteroid Robotic Redirect Mission may not be commensurate with the cost,” the bill reads. “Alternative missions may provide a more cost effective and scientifically beneficial means to demonstrate the technologies needed for a human mission to Mars.”

The bill requires NASA to evaluate other mission concepts that can be compared with the asteroid mission.

Health monitors

The measure separately funds the space agency’s commercial crew development programme, aimed at hiring private space contractors to ferry US astronauts to the International Space Station instead of relying on Russian transport. It also calls for a post-ISS transition plan that would move NASA’s activities to commercial spacecraft by the mid-2020s.

On Earth, the bill creates a new health monitoring programme named for astronaut Scott Kelly, who spent a year in space so scientists could study its effects on his fitness.

A Senate space committee will take up the measure this week, but it may be several weeks before its sponsor, Senator Ted Cruz, Republican of Texas, can get the plan through Congress.