Managers of Europe’s biggest-ever space science mission, the two-satellite Herschel-Planck astronomy project, are struggling to correct small leaks in the Herschel cryostat tank and telescope-related issues in time to prevent the program from slipping further behind schedule.

The two satellites are moving in parallel toward assembly and testing on the assumption that the cryostat leaks and unrelated telescope issues can be overcome in time to permit a launch of the Herschel and Planck satellites together on a single Ariane 5 rocket in early 2008.

Keeping that launch date would mean Herschel and Planck are a year late in entering operations. Earlier difficulties with delivery of the payload instruments — combined with what European space science managers say was a serious underestimation of the costs and technical challenges — pushed the Herschel-Planck budget 20 percent beyond its initial budget.

As of late 2005, the best-guess estimate for the final tally on the Herschel-Planck budget was 1.6 billion euros, or $1.92 billion at current exchange rates.

Jacques Louet, head of science projects at the European Space Agency (ESA), said the latest difficulties have had no appreciable impact on that revised budget. But he said the program now is stretched to the limit and that any further delays in key hardware deliveries, particularly the cryostat, will threaten the schedule.

“It is clear that if we conduct acceptance testing of the cryostat in October and encounter no problems, we will be confident about a February 2008 launch,” Louet said here April 11. “If we cannot perform these tests in October, then there is no way we can launch then.”

Because of its size and complexity, Herschel-Planck remains the principal wild card in ESA’s future science program. If schedule delays can be kept to a minimum from here on, the Herschel-Planck budget demands will not threaten other ESA missions.

ESA’s Science Program Committee recently approved continuation of the BepiColombo mission to Mercury in 2013 partly on the assumption that Herschel-Planck’s main issues were settled.

Requests for bids from industry for BepiColombo were issued in February, with final bids due in mid-May. A decision on a prime contractor is expected in July, with a contract to be signed before the end of the year. BepiColombo, to be launched in 2013, is expected to cost around 650 million euros including launch and operations, of which around 350 million euros is reserved for the satellite’s construction.

ESA is also about to sign a contract with EADS Astrium for construction of the Gaia star-mapping satellite, to be launched in late 2011. The Astrium contract of some 317 million euros is part of an overall Gaia budget of about 550 million euros, according to ESA estimates.

EADS Astrium’s French division and other French establishments will be performing much of the work on Gaia, a fact that because of ESA’s geographic-return policy will automatically consign France to a very small role in BepiColombo.

ESA is obliged to ensure that each government’s domestic industry receives contracts that closely match the government’s level of investment in ESA. For science programs, government contributions are mandatory and based on gross domestic product.

ESA does not award big science contracts every year, so France’s excess return on Gaia will necessarily be followed by a correspondingly low return for BepiColombo. The BepiColombo contract is likely to be a competition between Alcatel Alenia Space’s Italian site in Turin and EADS Astrium’s branch in Friedrichshafen, Germany.

Europe’s Science Program Committee is expected to begin a new round of mission solicitations this year for satellites to be launched starting in 2015 despite warnings from some ESA officials that doing so would threaten the budget security of the entire ESA science program.

Louet did not deny the risks but said that ESA’s science program has safeguards, including delaying missions whose construction has not begun, that allow managers to minimize budget pressures if needed. He did acknowledge, however, that any serious delay in Herschel-Planck will mean that all bets are off.