Pie in the Sky

Mike Hewson
Mike Hewson
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Topic 190407

Putting aside for this question any practical issues of cost, engineeering problems etc ( we'll employ the Magic Land of Narnia Funding & Construction Agency ), are there any advantages to interferometers arrays that are non-planar. For instance, dropping a shaft down ( or a tower up ) orthogonal to the current arms at any of the LIGO's, or having the LISA a tetrahedron rather than a triangle?

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

Solomon
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Pie in the Sky

Quote:
Putting aside for this question any practical issues of cost, engineeering problems etc ( we'll employ the Magic Land of Narnia Funding & Construction Agency ), are there any advantages to interferometers arrays that are non-planar. For instance, dropping a shaft down ( or a tower up ) orthogonal to the current arms at any of the LIGO's, or having the LISA a tetrahedron rather than a triangle?

I would say yes. It would significantly improve the ability to identify the direction a signal originated from. Although, I doubt it would be able to come close to the resolution of optical, or even radio telescopes.

Of course, it's not really a practical thing to do, particularly for LISA. The nature of orbital dynamics is such that a coplanar alignment can remain stable, while any other cannot.

MarkF
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Mike The effects of a

Mike
The effects of a passing gravity wave on planar interferometer are strongest when the GW is propagating perpendicular to the plan and drop to half when the GW is propagating in the plan. A tetrahedron arrangement would more omnidirectional.

But hay if we can hire the “Magic Land of Narnia Funding & Construction Agency� I say go for an icosahedron.

MarkF
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For starters you replace the

For starters you replace the 30 edges with carbon nano-tube ropes. Then attach solar powered ion-engines at the 12 vertexes to keep everything properly tensioned and power the rest of the installation. Then you put all heavy stuff in the center, communications gears, guidance computers and lasers. This way the mass of vertexes could be minimal only the mirrors and fine adjustment actuators. Twelve more ropes to keep the central package in its proper place.

Wa-la there you have 60 independent interferometers monitoring almost every direction equally. That should keep us busy for a while.
Oh by the way I want a pony.

Ben Owen
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Mike Hewson

Mike Hewson wrote:

Quote:
Are there any advantages to interferometers arrays that are non-planar?

There is one, but it's not worth it.

An interferometer laid out horizontally is most sensitive to waves coming from directly overhead or underfoot. It's less sensitive as you change the angle, and technically can't see at all any waves emitted from sources in the same plane. So if you overcome the many daunting and expensive hurdles to drop a shaft down from the LIGO corner station, you could get more sensitivity in some directions.

But you get pretty good sensitivity all over the sky anyway.

When you look for pulsars you analyze very long stretches of data. Since LIGO is stuck to the surface of the Earth, its plane changes throughout the day as the Earth rotates. So any pulsar that happened, by an incredible coincidence, to be right near a blind spot at a given time would soon move out of it for the rest of the day.

LISA is in a similar situation. Everything it's going to look for lasts a long time, and the triangle that the spacecraft sit on is rotating around in a complicated three-dimensional way. So you get coverage of the whole sky.

But what about a very short-lived source that goes off in the instantaneous blind spot of LIGO? Due to the curvature of the Earth, it won't be in the blind spot of the other LIGO site because they can't share the same plane. Or VIRGO, or the other interferometers.

The result is that it's much easier and cheaper to leave each individual detector in a plane and have some scientists working on how to untangle all the motion and multiple-detector issues in the signal processing. Data analysis and associated math tricks are always cheaper than more construction.

Hope this helps,
Ben

Mike Hewson
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RE: There is one, but

Message 21925 in response to message 21924

Quote:
There is one, but ....... math tricks are always cheaper than more construction.
Hope this helps,
Ben


Yes, thanks - several sites on different planes, rotating earth, long looks, scientists, signal analyses - collaboration. I saw some estimates of detection rates for various phenomena here, that indicate by using 'mature interferometers' pretty much a busy time will be had by all. Exciting!
Cheers, Mike

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

Mike Hewson
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I've stuffed up the BBCode

Message 21926 in response to message 21925

I've stuffed up the BBCode for that reference. Try this link:

http://www.ligo.caltech.edu/docs/P/P000024-00.pdf

Cheers, Mike

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

Ben Owen
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Mike, There is an updated

Message 21927 in response to message 21926

Mike,

There is an updated review of sources and event rate estimates here.

Actually, it's almost four years old and things have been moving so fast that even that needs to be updated.

In principle, that review is a technical article. But large parts of it are pretty non-technical, so it should give you a good idea of what's going on.

Ben

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