Long-awaited Gravity Probe B finally near launch into space

Project took 44 years to build

goal is to help prove twist in space-time


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 ready for launch 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 the National Aeronautics and Space Administration. 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 five 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 at Stanford University, more than 1,000 people have worked on the satellite. Two founders are dead. More than 90 people earned doctorates working on the project. Gravity Probe B has been on the chopping block so many times that its 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, 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 huge objects curving the fabric of space and time. Large objects like 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."

New advances

Since it was proposed, scientists have wanted to test Einstein's general relativity theory using the earth. 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, scientific supporters of Gravity Probe B say the extraordinary predictions made by general relativity can be tested. Thanks to substantial 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 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 boast spinoff technologies. Graduate students who worked on the project helped develop better GPS systems now used in aircraft landings. They also created a type of super glue that can stand up to 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.

Test of frame dragging

The project's scientists 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.

As the launch date approaches at California's Vandenberg Air Force Base, invitations have been sent to the scientists, engineers, and students who 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 U.S. assistant secretary of transportation. When he first imagined the project with the physicists Leonard Schiff and William Fairbank, Fairbank 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."

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