Gravity Probe B

PhiAlpha
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Topic 193374

There is a recent update on the Gravity Probe B site which I enjoyed reading. I think you may find it interesting as well.

"Everything should be made as simple as possible, but not simpler." A. Einstein

Mike Hewson
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Gravity Probe B

Quote:
There is a recent update on the Gravity Probe B site which I enjoyed reading. I think you may find it interesting as well.

Well spotted! The Gravity Probe B experiment is a tour de force of modern technology and systems integration. It is a really simple idea as experimental design goes. Envisioned about fifty years ago, it had to await technological development. A bit like LIGO really. The link makes absolutely fascinating reading. Highlights are :

- finds the 'missing inch' in orbital circumference because of the presence of the mass of the Earth. That is, the warping of spacetime causes the ratio of circumference to diameter to differ from PI by a teensy bit. This accumulates over many orbits to tilt the onboard gyros with respect to a distant reference star.

- finds the spiral pull on the local reference frame due to the Earth's rotation, known as frame dragging.

- spectacular *polar* orbital insertion to within tens of metres. This is a really hard task! Wow!

- amazing accuracy of spacecraft pointing. The guide star is acquired once per orbit, taking about a minute to achieve, the accuracy required is astonishing using a split prism system to compare and balance light flux between quadrants of the guide star image!

- an accurate emphemeris of the guide star's proper motion with respect to really distant quasars, produced by a prolonged very long baseline radio astronomy study. This is gives a cosmic reference frame to compare or *relate* your local spacetime with the remote one.

- the gyros are amazingly perfect spheres. If expanded to Earth size, the maximum deviation from pure sphere would be no more than 8 feet!

- minute current detection using quantum level increments to sense gyro orientation. Oh, and by the way it's superconducting....

- a brilliant system of shrouds and chambers to isolate electromagnetic influences.

- a microthruster system to literally make the spacecraft follow the free fall path of a selected gyro, the 'drag free' test mass. The thrusters use Helium gas evaporating from the cryogenics!

- nearly all the instruments, including the Cassegrain 'scope, are 'carved' from or embedded in an exceedingly pure quartz crystal support ( very low changes in dimensions with temperature ).

- pretty impressive 'human management' approach too.

I could go on with superlatives ..... I think this project will be a benchmark for 'How To .... ' in space science for a long time!

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

Rod
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RE: There is a recent

Quote:
There is a recent update on the Gravity Probe B site which I enjoyed reading. I think you may find it interesting as well.

Good Project... It looks like they to the time to get the engineering right

There are some who can live without wild things and some who cannot. - Aldo Leopold

PhiAlpha
PhiAlpha
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The Gravity Probe B website

The Gravity Probe B website has been reorganized and there is an update in the news section.

"Everything should be made as simple as possible, but not simpler." A. Einstein

tullio
tullio
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When I was studying physics

When I was studying physics in the fifties and sixties at Trieste, frequenting also the International Center for Theoretical Physics led by Abdus Salam, whenever I spoke of General Relativity people would simply laugh at me telling "that is old stuff, you should study S-Matrix theory". So I had to accept a position in a publishing house, gave some space in a Yearbook to the first attempts by prof. Joseph Weber to detect GWs and was reprimanded by an eminent Italian elementary particle physicist (but not by prof. Amaldi). Now GR has spawned some of the finest experiments ever done by physicists. Bravo Albert!
Tullio

PhiAlpha
PhiAlpha
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Some bad news on the project

Some bad news on the project site I was surprised to read. I wish the project good luck in the search for funding.

"Everything should be made as simple as possible, but not simpler." A. Einstein

tullio
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RE: Some bad news on the

Message 76293 in response to message 76292

Quote:
Some bad news on the project site I was surprised to read. I wish the project good luck in the search for funding.


This is another consequence of the foolish "Moon, Mars and beyond" program launched by President Bush. All NASA resources are committed to the Orion launcher program, The Shuttles will retire in 2010 and the ISS which is being built a at great expense also of Europe and Japan will depend on the aging Soyuz spacecrafts, or on a still unplanned European manned spacecraft based on the Ariane 5 heavy launcher.
Tullio

tullio
tullio
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RE: RE: Some bad news on

Message 76294 in response to message 76293

Quote:
Quote:
Some bad news on the project site I was surprised to read. I wish the project good luck in the search for funding.

This is another consequence of the foolish "Moon, Mars and beyond" program launched by President Bush. All NASA resources are committed to the Orion launcher program, The Shuttles will retire in 2010 and the ISS which is being built a at great expense also of Europe and Japan will depend on the aging Soyuz spacecrafts, or on a still unplanned European manned spacecraft based on the Ariane 5 heavy launcher.
Tullio


Astronaut John Glenn has said that going to the Moon is not the way to go to Mars, but a waste of energy. I agree.
Tullio

Rod
Rod
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Look like Gravity Probe B got

Look like Gravity Probe B got some more funding..

Bailout

There are some who can live without wild things and some who cannot. - Aldo Leopold

tullio
tullio
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RE: Look like Gravity Probe

Message 76296 in response to message 76295

Quote:

Look like Gravity Probe B got some more funding..

Bailout


I am glad, of course. But something does not convince me. They have 2 TB of data and 20 SUN WS. This means that each WS must crunch 100 GB of data, an almost impossible task. What about giving them 200 or 2000 WS via a project like Einstein@home?
Tullio

Mike Hewson
Mike Hewson
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Interesting to note is the

Interesting to note is the comment:

Quote:
..... GP-B had weakly confirmed one of the effects, frame dragging, to only the 25 to 33 percent range ....

Considering it is within an order of magnitude at all, and for such a subtle effect - as one gets out here in a low gravity field environment of ~ 10 m/s^2 - then I'm quite impressed.

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

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