Probe eyes key concept of physics
It took more than 44 years to build, was canceled seven times, and is considered by some scientists to be the most technically difficult mission NASA has ever undertaken.
Yesterday, the space agency announced that Gravity Probe B is finally ready for launch on April 17. Its goal is to help prove one of the most confounding concepts in physics: the strange twist in space-time predicted by Einstein's theory of general relativity.
Despite the modest name, Gravity Probe B carries a payload of superlatives. It has taken longer to finish than any other project at NASA. It is armed with some of the most precise instruments ever built. And in a space agency known for its delays and cost overruns, the $700 million project remains singular in its ballooning schedule and budget, some observers say.
"Gravity Probe B has been 5 years away from launch for the 25 years I've been involved in space programs," said Keith Cowing, editor of Nasawatch.com, a group that monitors NASA.
Since the project was conceived by three scientists after a naked midday swim at Stanford University's pool, more than 1,000 people have worked on the satellite. Two of its founders are dead. More than 90 people have earned their doctorates working on the project. Gravity Probe B has been on the chopping block so many times that its bespectacled lead scientist has become a fixture on Capitol Hill for his successful lobbying to keep it funded.
Inside the satellite are four gyroscopes whose movement could confirm the theoretical underpinnings of modern physics -- or turn them on their head.
"The expectation is we are going to see [the movement]," said Robert Reasenberg, associate director of the Harvard-Smithsonian Center for Astrophysics, in Cambridge, which is helping calculate key astronomical measurements for the project. "If we don't see it, it is an astounding result. It will turn physics upside down."
In 1916, Einstein shocked the world of physics by introducing a new description of gravity, one that is caused by massive objects curving the fabric of space and time. Large objects like the earth can "warp" space-time, the way a basketball placed on a taut rubber sheet warps the sheet and causes other nearby objects to roll toward it. At the same time, if the basketball is turning, its motion will twist the sheet slightly -- a phenomenon known as "frame dragging."
Ever since it was proposed, scientists have wanted to test Einstein's general relativity theory using the earth itself. But the earth's "warping" effect on space and time is tiny -- more of a marble than a bowling ball -- and no precise measuring tools were available.
Now, the scientific supporters of Gravity Probe B say the extraordinary predictions made by general relativity can finally be tested. Thanks to dramatic, and expensive, advances by the project team, the probe will be able to measure once-undetectable changes in the gyroscope's spin related to a distant star.
The project has been hailed as a marvel for its work with cryogenics and engineering. The gyroscopes' four spherical rotors, each the size of a ping-pong ball, are considered the roundest manmade objects in the world. Scientists can also detect a change of angle equal to the width of a human hair as seen from 10 miles away. To ensure the experiment's success, scientists had to create almost unheard-of conditions inside the satellite, where the instruments will be kept chilled at minus 455 degrees Fahrenheit with liquid helium.
The probe can even boast its own spinoff technologies. Graduate students who worked on the project helped develop better GPS systems that are now used in aircraft landings. They also created a type of superglue that can stand up to the pressures of space.
Still, the project is not without its critics, who complain that its rising costs have sucked money from more worthy missions. Others say that the project has lost much of its value since it was first planned, because other experiments have been conducted that appear to prove Einstein's theory.
"When it was first conceived it would have taught us something new about gravity theory . . . but not now," said Kenneth Nordtvedt, a gravity specialist and retired physics professor at Montana State University.
The project's scientists, however, say the probe will provide the most accurate test yet -- and will be the first experiment to test the frame dragging effect.
They note that every time the project has been on the budgetary chopping block, it has been upheld by a review panel of researchers or by Congress.
"The thing that drives Gravity Probe B is the measurement accuracy," said Rex Geveden, program manager.
Now, as the launch date approaches at California's Vandenberg Air Force Base, invitations have been sent out to the scientists, engineers, and students that have in some way helped create it.
Few are as excited as Robert H. Cannon Jr., the lone surviving scientist who started the project and went on to be the Air Force's chief scientist and a US assistant secretary of transportation. When he first imagined the project with the physicists Leonard Schiff and William Fairbanks, the latter physicist said it might take 10 years to test. Cannon thought it would be more like 20 years.
That was 1959.
"It's been a long wait," Cannon said this week. "Bill Fairbanks was off by four and I was off by two. But I'll be there [at the launch]. My whole family will be there."
Beth Daley can be reached at bdaley@globe.com.
