The European Space Agency has postponed its selection of a large space mission to launch in the 2020-2021 timeframe, following advice from NASA that the US is unlikely to be able to contribute its share of funding to the winning selection. The selection of the so-called L-class mission had been expected to take place this June, but is now set for February 2012. “The decision was made very reluctantly,” says David Southwood, Director of Science and Robotic Exploration at ESA Headquarters in Paris, France,“NASA could not meet our timetable to launch.”

The three competing missions affected by the decision (pictured from top right to bottom right) are the Laser Interferometer Space Antenna (LISA), which would detect gravitational waves from space, the Europa-Jupiter System Mission, a mission to the moons of Jupiter (called ESJM-Laplace), and the International X-ray Observatory (IXO), an X-ray space telescope. In a 14 March email, Fabio Favata, ESA coordinator for astronomy and fundamental physics missions asks member of ESA’s Science Program Committee, which will choose between the three proposed missions, to work out whether they could fly on a Europe-only budget , with minimal cooperation from NASA. Under such a scheme, says Southwood, the 700 million Euros that ESA has budgeted for the L-Class mission must now be considered as the mission’s total cost rather than 40-50% of a joint NASA–ESA effort. “It’s a big change and maybe the challenge can’t be met,” Southwood acknowledges.

NASA’s reluctance to commit to ESA’s timetable was a consequence of the tight fiscal situation in the US federal government, and two recent US advisory reports that ranked the L-class missions below others as the top US funding priorities. In August 2010, the Astro2010 decadal survey ranked IXO and LISA below the Wide Field Infrared Survey Telescope (WFIRST) a planned infrared space telescope that would take measurements to get a handle on the nature of the dark energy pervading the universe. On March 7, NASA’s planetary sciences decadal survey ranked the mission to Jupiter below a possible sample return mission from Mars. In the ten days since the planetary sciences decadal survey Southwood and his counterparts at NASA have been analyzing the situation and concluded that NASA would now be unlikely to to be a major partner in any of the missions – whichever one was selected – on the timescale that ESA needed for the mission to make the launch date. Rather than give up on the idea of a larger space mission, ESA has decided to go it alone, and has now asked the mission scientists to rewrite their proposals accordingly, necessitating the delay, Southwood says.

The next step will be for the teams behind LISA, IXO and ESJM-Laplace to rescope their missions for the rejigged competition. Astrophysicist Jack Hughes at Rutgers University in New Brunswick, New Jersey, a member of the science definition team for IXO, says he’s cautiously optimistic. It’s already been clear from NASA’s difficulties with the cost overrun of the James Webb Space Telescope (now estimated at $6.5 billion) that the agency would probably not be able to invest in a next generation space mission until JWST has launched, so it’s good to see that ESA’s prepared to move forward without it, he says. “ESA’s being practical and saying what can we do to advance the science goals we’re interested in and I think that’s a rational and logical approach,” he says.

In a related story, the blog SpacePolicyOnline.Com notes that NASA must now depend on a renewed partnership with ESA to fly the MAX-C sample return mission to Mars — the highest rated project in the planetary decadal survery — because it cannot afford the $2.5 billion needed to underwrite the mission’s intial stage. The revelation was made yesterday by Jim Green, director of NASA’s Planetary Science Division during a meeting of the Planetary Science Subcommittee of the NASA Advisory Council. NASA and ESA officials are scheduled to meet at the end of this month to discuss the agencies’ planetary partnerships and implications for future joint missions.

Update March 18: this blog was updated to reflect that the date of the ESA email was March 14, not 15 as originally reported.