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Gravity Probe B

Testing Einstein's Universe

Spin-off Technology from Gravity Probe B

What does Gravity Probe B have to do with the military's Global Positioning System and an automated tractor? GP-B uses the GPS system to give a very accurate position and time stamp to all its opertions. We are a civilian project, and normal civilian GPS receivers have a precision of about 100 yards. Measuring minute changes in spacetime requires a better positioning accuracy than that, so we began looking at alternatives. A system called differential GPS can provide meter-level accuracy. Graduate students here have improved the system to provide centimeter-level precision which has been applied to develop automated tractors and automated aircraft landing. That's a big deal. For more information, read the Stanford Report article: ‘Tractor drivers soon may say, "Look, Ma! No hands!"’ and see what the Stanford School of Engineering Annual Report has to say about GP-B graduate Clark Cohen.

How do you bond the quartz optical and mechanical components of a science instrument so as not to interfere with its workings? You'd need a bonding technology that was transparent to visible and near-infrared light, which worked in the vacuum of space, which didn't create any magnetic disturbance and was capable of handling rapid temperature changes and extreme cold (going from room temperature to below -271 degrees Celcius without even a hairline crack!). So much for Elmer's glue... Scientist Jason Gwo invented a new material called OptoBondTM to do the job. Industry applications include bonding improvements in optoelectronics, precision optics, laser optics, laser crystal augmentations, general optomechanical applications and creation of optical systems. For more information on OptoBondTM, contact Kirstin Leute of the Stanford Office of Technology Licensing at or read the Brainstorm article

Our engineers created a revolutionary detector mount system to provide thermal insulation between detector electronics operating at 80 degrees kelvin and a quartz telescope operating at 2.5 degrees kelvin. Did we mention that the two dual photo-diode detectors also have to withstand 5.0 g forces and use less than one milliwatt of power per detector? The signals from these detectors must be clean enough to provide the star-tracking telescope of GP-B with an accuracy approaching 100 millionths of an arc-second per year. What's the practical application? Faster and more efficient digital cameras, among others. Hey - with technology allowing 5 g's of shock tolerance, you might be able to drop that camcorder a few times. Check out the article from Laser Focus World

"The most important motive for study at school, at the university, and in life is the pleasure of working and thereby obtaining results which will serve the community. The most important task for our educators is to awaken and encourage these psychological forces in a young man {or woman}. Such a basis alone can lead to the joy of possessing one of the most precious assets in the world - knowledge or artistic skill."
--Albert Einstein

Gravity Probe B has been a proud participant in higher education for forty years. To date we have awarded 73 Doctorates, 15 Master’s Degrees and 5 Engineer’s Degrees at Stanford University, and have aided in the completion of 13 Doctorates at other universities.

Would you like to know more about just how the U.S. space program has contributed to daily life? View the Spinoffs web page at NASA. You can also visit the Space Technology Hall of Fame honoring America's space technologies. Or, take a tour of how space research has impacted our society at the Space Research and Technology Transfer web site.