# Gravity Probe B's Lithographs

The Gravity Probe B Lithographs were created to provide a clear explanation of several concepts and technologies that are part of the relativity project.

• The Gravity Probe B Mission
In 1959/1960, independently, Stanford University physicist Leonard Schiff and Defense Department physicist George Pugh suggested that the presence of local spacetime could be "seen" by using orbiting gyroscopes.
• Newton's Gravity or Curved Spacetime?
In the early 20th century, Einstein discovered a contradiction between Newton's theory of gravity and Einstein's theory of special relativity (1905).
• 'Frame-Dragging' in Local Spacetime
In 1918, just two years after Einstein presented his theory of general relativity to the world, two other physicists, Josef Lense and Hans Thirring, predicted that large rotating masses, such as planets and stars, would tend to drag local spacetime around with them.
• The Gravity Probe B Satellite
The Gravity Probe B satellite is an amazing piece of equipment, finally completed in 2003 after four decades of development and construction. From its largest to smallest parts, it is fi lled with cuttingedge technology and materials, many of which were invented specifi cally for the Gravity Probe B mission.
• The World's Roundest Gyroscopes
In order for Gravity Probe B to measure any 'twist' or curvature of local spacetime, it must use a gyroscope that is nearly perfect—one that will not wobble or drift more than one-hundred-billionth of a degree in an hour while it is spinning.
• Using Superconductivity to "See" a Spin Axis
Given GP-B's need for ultra-smooth and ultra-stable spinning gyroscopes, how could GP-B measure, to 0.1 milliarcseconds, the orientation of the spin axis of this perfect unmarked sphere—and do so without disturbing its perfectly balanced rotation?
• Focusing On the Guide Star
In order to provide a reference point for measuring tiny deflections in the tilt axes ofthe GP-B gyroscopes, the on-board telescope must be focused on a very stable, distant star. Furthermore, the telescope must remain exactly centered on that star throughout the mission.
• Measuring a Miniscule Angle
The success of Gravity Probe B entirely depends upon its ability to measure two incredibly small angles.
• The 650-Gallon Dewar
One of the greatest technical challenges for Gravity Probe B is to keep the liquid helium surrounding the science instrument in a superfluid state, at a temperature near absolute zero, for a year or more.