April 15, 2004
Gravity Probe B to Fly
Gravity Probe B, the physics experiment at Stanford that was indirectly the proximate cause for my Ph.D., is finally set to launch on Monday. Note that this experiment was conceived 40 years ago, and it simply took this long to have the technology to catch up to the idea. According to this article, over 100 Ph.D.'s have been spun out of this effort (of which I am one), though I think the actual number is much higher.
By all accounts the experiment now at Vandenberg is a technical tour de force. At its heart, isolated as much as possible from the universe, are the gyroscopes: four quartz spheres slightly larger than golf balls. They are said to be the most perfectly spherical objects ever made by humans — out of round by only 40 layers of atoms. If the Earth were this perfect, the tallest mountain would rise just six and a half feet.
In space, they will be suspended by electrical fields and spin at 10,000 revolutions per minute inside a quartz telescope trained assiduously at the star IM Pegasi.
To make sure that no outside influence imparts a stray wobble to the spinning balls, the telescope floats freely inside an external spacecraft equipped with jets to sense and counter any drag from stray wisps of atmosphere. It is also surrounded by a superconducting lead bag that shields it from magnetic fields. And the whole assembly is cooled by liquid helium to less than 2 degrees above absolute zero, or about minus 456 degrees Fahrenheit.
But that's only the beginning. After having isolated the gyroscopes from the rest of the universe and aligned them with IM Pegasi, the scientists have to monitor which way they are spinning.
To this end, the quartz balls are coated with niobium, which loses all resistance to electrical current at these temperatures. As a result, when the balls rotate, some of the electrons in the niobium slip behind their atoms. Their relative motion creates a small current that generates a tiny magnetic field, located by detectors known as squids — superconducting quantum interference devices — built into the gyroscope.
To all the people who worked on GP-B over the years, good luck on Monday! For everyone else, you can see a webcast of the launch here and here.
Posted by elkaim at April 15, 2004 12:20 PM