Gravity Probe B (GPB), a half billion-dollar space mission designed to prove Einstein right or wrong, is struggling with technical difficulties, rising costs and a receding launch date. NASA managers say they will give the program until summer to shape up before considering whether or not to cancel the effort led by California's Stanford University.

The mission idea dates to the late 1950s, and is elegantly simple in concept. A spacecraft hovering 400 miles (645 kilometers) above Earth will use sensitive gyroscopes to detect any movement which would signal that the mass of the planet warps Einsteinian space-time -- that is, the four dimensions which represent the universe in relativity theory. If there is such a movement, it could provide proof that Einstein's theory is correct. But more than 40 years later, that concept has proved complicated, costly and challenging to translate into hardware.

A recent independent report done for NASA's Office of Space Science has reached the conclusion that GPB is not likely to meet its September 2001 launch date. It estimates that the program will need about $70 million more to work out technical glitches and warns that some management changes are needed to ensure it gets back on track. "This growth against a prior total program cost commitment of $540 million represents an increase of 13 percent," the report said. It was prepared by a panel chaired by retired aerospace engineer Parker Stafford at the request of Ed Weiler, NASA's space science associate administrator.

The technical problems revolve around the gyroscopes and their housing in an insulated canister which is super-cooled. Last fall, a series of tests showed problems with the gyros and revealed that heat was building up in one section of that canister. The science package containing the gyros had to be removed from the canister -- a costly and time-consuming process. Managers at Stanford University say they now have the problems under control. "We're on the road to recovery," says Francis Everitt, GPB's principal investigator.

Unlike most NASA projects, Stanford has had primary oversight of the effort, rather than the space agency itself.

The Stafford report does conclude that the project "is in good shape from a technical standpoint," but it also warns that the root cause of the higher temperatures remains disturbingly unclear. In addition, panel members say that GPB needs "an on-site NASA project manager and chief engineer" and an experienced integration and test manager. Several critical tests are planned to start this summer when the science package containing the gyroscopes is re-inserted into the insulated canister. That hardware then must be integrated into the larger spacecraft.

How quickly this can be done is unclear. Everitt maintains that he still has a good shot at meeting the September 2001 launch date, but the Stafford panel thinks there is a higher likelihood of additional delay. NASA officials familiar with the project's status predict that it will be April 2002 before the spacecraft gets off the ground on a Delta rocket. And every day adds costs.

Everitt thinks the cost overruns will be less than the Stafford panel projects. He estimates that a September launch would only involve $40 million in additional costs, while an April date would boost that to $60 million or more.

NASA officials are keeping a wary eye on GPB, given its long history of delays (launch was once slated for 1999), its technical obstacles and the creeping cost. To find the $70 million which is probably necessary to keep the program on track, Weiler says he has three options: to slip launch of the Europa Orbiter 26 months, and eliminate plans for new missions; to delay a new set of missions in the series of mid-sized spacecraft called Midex or to ask NASA managers to consider canceling the project.

The upcoming tests will be critical for the program's fate. At a recent meeting of NASA's space science advisory panel, Weiler said he supports "giving Stanford a chance" to fix the technical problems in the coming months. "We've sunk $450 million into this program in the past 35 to 40 years," he added. "There's a certain driving force" keeping it afloat. "If they make the milestones, we'll find the money."

Others are not so charitable. GPB has long aroused the ire of other researchers, in part because of its cost and in part because it is a physics project funded by an agency that primarily focuses on planetary exploration or astrophysics and astronomy. Previous administrations repeatedly tried to cancel the probe, but it has strong supporters in Congress, who just as often put funding back in to continue the effort.

Several members of the NASA advisory panel grumbled at news of the delays and added costs -- and at Weiler's decision not to make a decision, which some say sends a poor signal to contractors. "There is an issue of credibility here," warned David Black, a planetary scientist at the Lunar and Planetary Institute in Houston. "Continued waffling is hurting your credibility."

He added that "it's almost reaching the level of laughability (sic)." But despite the giggle factor, NASA and Stanford officials say GPB still stands a good chance of testing Einstein's famous theory.