Hi Sam,

There is no friction in space, but there is gravity and other forms of energy. I think the mission of GP-B is to probe the effect earth's rotation has upon such energy or gravity. Gravity can effect the movement of energy as it travels through space. For example, light has been observed to bend as it passes by a mass, like our sun, so the gravity of the sun bends light as it travel through space, just like gravity can bend a mass traveling through space, or even cause one mass to orbit around another mass.

Even though there is no friction in space, space is not exactly empty, as there is energy throughout it, like gravity wave and electromagnetic field energy. Without electromagnet field energy, light would not exist. Light propagates using electromagnetic field energy, kind of like electricity needs a wire in order for conduction to take place which allow electricity to be focused, captured and used at in different locations, so light, and other source of energy, need electromagnet field to propagate.

It's interesting that GP-B's orbit is a polar orbit 400 miles above the earth. Since the orbit of GP-B is directly lined up with the earths axis, it passes directly over earths north and south poles in a direction lined up with earth magnetism. Also, the probe is positions within this orbit, so it is alway in the same position relative to the guide star, so like a gun aimed at the guide star, the GP-B's position remains constant relative to the guide star. This is important because the gyro are also in an alinement that should remain constant, unless acted upon by some other force.

This should allow GP-B to detect any variance in the electromagnetic field caused by earth rotation, as it travels through space.

This is only my limited understanding of the test, so I'm not even entirely sure what is begin dragged around with the earth as it rotates on its axis, but I assume it is the electromagnetic field, ether, aether, or gravitation waves are some such.

Regards,

LelandJ