President Bush is set to endorse using nuclear power to explore Mars and open up the outer Solar System.

He is expected to back the US space agency’s recent nuclear propulsion initiative, Project Prometheus, either in his State of the Union speech, due on 28 January, or later this year when he submits his 2004 budget to Congress.

It is believed he will give the initiative $1bn over five years, arguing that nuclear propulsion represents an essential technology for the manned and unmanned exploration of space.

Supporters say nuclear power could change the nature of space exploration, but add that it will take many years and significant resources to develop.