Gravity Probe B: Gyroscope Orientation and Precession

In summary, the conversation discusses the orientation of the gyroscope spin axes in relation to the Gravity Probe B satellite and its orbit. It is noted that the orientation should be parallel to the axis of the orbit, rather than perpendicular or in the direction of movement of the satellite, in order to minimize precession. The conversation also mentions the effects of geodetic precession and frame-dragging due to Earth's rotation, and the importance of using nearly perfect spherical gyroscopes to prevent precession caused by tidal forces.
  • #1
Paulanddiw
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I was looking at some web sites about the Gravity Probe B. Some show the spin axes of the gyroscopes oriented perpendicular to the Earth or else in the direction of movement of the satelite. Wouldn't these orientations cause lots of precession? I'd expect the gyroscopes' axes of rotation to be orientated paralled to the axis of the orbit.
 
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  • #2
Paulanddiw said:
... I'd expect the gyroscopes' axes of rotation to be orientated paralled to the axis of the orbit.

The satellites are in free fall; there is no classical precession expected.

The gyroscope spin vectors (axis) are pointed approximately in the plane of the satellite's polar orbit, in the direction of the guide star. Oriented as such the measurement of the two predicted relativistic precessions are at right angles to each other, one along the plane of the orbit and one orthogonal to it in the direction of Earth's spin.
 
  • #3
As I recall, there is a geodetic precession in the plane of the orbit (which is a polar orbit) which is fairly large, and a smaller component of the precession, due to the Earth's rotation, which is smaller. Because the orbit is polar, the geodetic precession effect in the orbital plane is in a different direction than the frame-dragging effect due to the Earth's rotation.

Preventing precession due to classical tidal forces is the reason that the gravity probe B gyroscopes had to be such nearly perfect spheres. Tidal forces can cause torque on an oblate rotating body, but not a spherical one.
 

1. What is Gravity Probe B and what is its purpose?

Gravity Probe B is a satellite built by NASA to test Einstein's theory of general relativity. Its purpose is to measure the effects of the Earth's gravity on four gyroscopes in order to confirm the theory's predictions.

2. How does the gyroscope orientation and precession work in Gravity Probe B?

The four gyroscopes in Gravity Probe B are made of quartz spheres and are kept in a superconducting housing. As the satellite orbits the Earth, the gyroscopes maintain their orientation, but due to the Earth's gravitational pull, they experience a slight precession or wobbling motion. This precession is measured by sensitive sensors on the satellite and is used to confirm Einstein's theory.

3. How long did it take for Gravity Probe B to confirm Einstein's theory?

Gravity Probe B was launched in 2004 and collected data for over a year before it was able to confirm Einstein's theory in 2011. The data took several years to analyze and interpret before the confirmation was announced.

4. What were the challenges in conducting the Gravity Probe B experiment?

One of the main challenges was designing and building a satellite that could maintain precise orientation in orbit for an extended period of time. Another challenge was developing sensitive sensors that could accurately measure the tiny precession of the gyroscopes caused by the Earth's gravity.

5. How does the confirmation of Einstein's theory impact our understanding of gravity?

The confirmation of Einstein's theory by Gravity Probe B provides further evidence for the general theory of relativity and solidifies our understanding of gravity as a curvature of space and time. It also opens up new possibilities for further research and exploration into the nature of our universe.

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