Astronomers' elation at the prospect of a rescue for the Hubble Space Telescope is turning to dismay as the price of saving the venerable observatory becomes clear.

Last week, NASA turned in a revised budget plan to Congress that includes cuts and delays to several programmes, including the roving Mars Science Laboratory and searches for planets like Earth. The proposed cuts would also lead to belt-tightening in the Hubble project itself, where grants for guest observers would be reduced by an average of 13%.

Two planet-hunting projects — the Space Interferometry Mission (SIM) and the Terrestrial Planet Finder (TPF) — have been deferred until as yet unspecified dates. SIM would orbit the Sun, measuring stars' positions and trying to detect planets similar to Earth. The TPF, which consists of two space-based observatories, would follow up SIM's findings between 2014 and 2020 with detailed spectral analyses.

Both projects have been scaled back before. SIM is currently undergoing another redesign in an attempt to keep its cost below $1.2 billion. One possibility, says Charles Beichman of the Jet Propulsion Laboratory in Pasadena, California, who is on the SIM and TPF teams, is to advance its launch to 2010, because shorter development times often reduce costs. But that now looks unlikely. The TPF was among the top recommendations of a National Research Council panel that set priorities in 2000 for the next decade of astronomy. But it is fraught with technical challenges — the panel called it “the most ambitious science mission ever attempted by NASA”. Deferring SIM and the TPF would be a blow to NASA's planetary search programme, which is already struggling with near-term projects. A plan to supplement the 10-metre ground-based optical Keck Telescopes, on Mauna Kea in Hawaii, with small ‘outrigger’ telescopes to detect Uranus-sized planets has been bogged down for years by battles with local cultural-rights groups (see Nature 417, 5; 200210.1038/417005a). And recent budget cuts have delayed the launch of the Kepler mission to look for very distant planets by eight months to June 2008. Ground-based telescopes have found 155 planets around other stars and the European Space Agency lists the search for such ‘extrasolar’ planets among its priorities for the next decade. This leaves Beichman and others worried that NASA is neglecting a promising field. The Terrestrial Planet Finder will hunt for other Earths, if NASA ever finds the cash to get it off the ground. Credit: NASA Some are also anxious that the cost of a shuttle rescue mission to Hubble is squeezing — or giving NASA an excuse to squeeze — other projects. Most astronomers would support saving Hubble if money were no object. But an increasing number agree with Nobel laureate and astrophysicist Joseph Taylor of Princeton University, New Jersey, who told a congressional committee: “I do not favour such a plan if it would require major delays or reordering of NASA's present science priorities.” David Black, chairman of the American Astronomical Society's public-policy committee, says the balance of opinion has shifted towards the idea that Hubble isn't worth the sacrifice of future missions. Yet he says the telescope is only one of NASA's financial headaches. Equally to blame are congressional ‘earmarks’ for pet projects, and cost overruns in many of its science programmes. The latest example of that is the James Webb Space Telescope, due to launch in 2011. In early May, project managers learned of a$1-billion overrun that has raised its price to a whopping \$3.5 billion. No obvious solution is in sight, says project scientist John Mather of the Goddard Space Flight Center, based just outside Washington DC. Shrinking the telescope is not acceptable to astronomers. “What comes next we don't know,” says Mather.

The new NASA administrator Michael Griffin presented the revised budget to a Senate appropriations panel last week. “NASA cannot afford everything that is on its plate,” he says.

Griffin's solution is to cut projects in the early stages of development. He also made it clear that: “In order to service the Hubble Space Telescope and provide for a safe deorbit, NASA will need to defer work on more advanced space telescopes.”

He did have some good news — a NASA team thinks it can cut the number of missions required to complete the International Space Station from 28 to 18, and it is still trimming. At half a billion dollars per shuttle flight, such savings are very welcome.