LARES

tullio
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Topic 196184

The LARES (Laser Relativity Satellite) has been launched by the Vega Launcher at Kourou, French Guyane. Vega has been been built by a consortium of European firms, 65% Italian. LARES is designed to measure the Lense-Thirring effect, that is the frame dragging of a rotating body, like it was done by the Gravity Probe B of Stanford University.LARES was designed by the La Sapienza University of Rome and Universita' del Salento. LARES is a tungsten sphere with laser retroreflectors. Go, LARES!
Tullio

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LARES

Quote:
... LARES is a tungsten sphere with laser retroreflectors. Go, LARES!
Tullio

OK... So why tungsten rather than some lighter alloy?

Keep searchin',
Martin

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Mike Hewson
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RE: OK... So why tungsten

Quote:
OK... So why tungsten rather than some lighter alloy?


My guess is because it's a metal with one of the least size changes with temperature changes - 'coefficient of thermal expansion'. I think there are some alloys that do a bit better. Spacecraft have to suffer either large temperatures changes over time and/or across themselves from sunlit side to dark side. For this type of experiment then clearly any alteration in the dimensions of the 'ruler' is quite significant.

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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RE: RE: OK... So why

Quote:
Quote:
OK... So why tungsten rather than some lighter alloy?

My guess is because it's a metal with one of the least size changes with temperature changes - 'coefficient of thermal expansion'. I think there are some alloys that do a bit better. Spacecraft have to suffer either large temperatures changes over time and/or across themselves from sunlit side to dark side. For this type of experiment then clearly any alteration in the dimensions of the 'ruler' is quite significant.


Thanks, good points. Especially for suffering about -160 deg C to +120 deg C each orbit.

Keep searchin',
Martin

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Bikeman (Heinz-Bernd Eggenstein)
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Hi It seems that tungsten

Hi

It seems that tungsten was also chosen because it is very dense: the test mass that the sat represents should have only minimal drag to not disturb the measurements (it's in a relatively (no pun intended) low orbit where size ( well, area) still matters wrt drag .

https://c3.nasa.gov/nex/projects/435/

HB

Mike Hewson
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RE: Hi It seems that

Quote:

Hi

It seems that tungsten was also chosen because it is very dense: the test mass that the sat represents should have only minimal drag to not disturb the measurements (it's in a relatively (no pun intended) low orbit where size ( well, area) still matters wrt drag .

https://c3.nasa.gov/nex/projects/435/


Yeah, there's an interesting 'tension' in the experiment where you want to be deeper in the gravity well to enhance the GR effects of interest BUT that means you get more buffeting from the atmosphere there. The interior of the experiment needs to be in 'free fall' - so not subject to non-gravitational influences - and thus the world-line is a true geodesic available for comparison with something else. So you have an outer shell on the craft to push aside the impacting gas molecules etc, and with suitable control the craft flies 'around' the test components inside.

Cheers, Mike.

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

tullio
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According to Giovanni Bignami

According to Giovanni Bignami of the Italian National Astrophysics Institution (INAF) Lares has demonstrated frame dragging with a 5% precisioni in four years of observations.
Tullio

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Thanks for the update! Any

Thanks for the update!

Any news/science articles that explain the results so far?

Thanks,
Martin

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tullio
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A full page article on La

A full page article on La Repubblica yesterday says that the result has been published on a scientific Journal. I suspect it could be Nature Physics and am waiting for it.
Tullio

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