The longest experiment in space physics began with three men in a university swimming pool arguing about Einstein. It ended Wednesday, after 52 years and $750 million, with scientists affirming his theory of relativity after studying the most perfect spheres ever made as they orbit around the Earth.

Called Gravity Probe B, the exotic experiment measured how the revolving mass of Earth imperceptibly twists the fabric of space in a test of Einstein's general theory of relativity. By one finding, the distortion amounts to 1.1 inches off true across the 24,900-mile circumference of Earth.

During decades of trial and error, the Stanford University scientists overcame engineering glitches, launch delays, budget fights, solar flares, faulty data and seven federal investigations. NASA threatened to cancel the project so many times that researchers could complete their work only through a $500,000 contribution from the founder of Capital One Financial Corp. , Richard Fairbank—a son of one of the physicists who conceived the experiment by the pool—and help from the Saudi royal family.

Their achievement may stand largely as a milestone in scientific persistence. In the intervening years, Italian, German and U.S. research groups had already confirmed Einstein's ideas. "There ain't much room for surprise," said Nobel Prize-winning physicist Sheldon Glashow at Boston University, who wasn't involved in the projects.

Albert Einstein published his theory of general relativity in 1916, offering a description of gravity, space and time that transformed how scientists understand the physical laws governing the known universe. It better accounted for oddities of nature, such as anomalies in the orbit of Mercury, that classical physics, as formulated by Newton, could not explain.