Gravitational Waves

Bikeman (Heinz-Bernd Eggenstein)
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RE: Europe has built a

Message 79478 in response to message 79477

Quote:

Europe has built a heavy launcher, the Ariane V. If ESA wants to maintain its role in space science it should consider building and testing a crew module, perhaps a modernized Soyuz craft with Russia's help. An automated cargo craft is already on the launching pad, the Automated Transfer Vehicle.
Tullio

Indeed, and that is exactly what ESA is currently investigating (known as the CSTS ). But it won't be operational before 2014 either, if it's ever built at all.

CU
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rbpeake
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RE: RE: Europe has built

Message 79479 in response to message 79478

Quote:
Quote:

Europe has built a heavy launcher, the Ariane V. If ESA wants to maintain its role in space science it should consider building and testing a crew module, perhaps a modernized Soyuz craft with Russia's help. An automated cargo craft is already on the launching pad, the Automated Transfer Vehicle.
Tullio

Indeed, and that is exactly what ESA is currently investigating (known as the CSTS ). But it won't be operational before 2014 either, if it's ever built at all.

CU
Bikeman


Speaking in general as a space enthusiast, it sure would be nice if Europe had an independent capability to put people into orbit! :)

tullio
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Adelante! Adelante las naves!

Adelante! Adelante las naves! (Cristoforo Colombo)
Tullio

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The Automated Transfer

The Automated Transfer Vehicle has been launched from the Kourou base atop an Ariane 5 rocket and is on its way to the International Space Station.
Tullio

Chipper Q
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RE: Hence, the tools being

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Hence, the tools being used to detect such a small warp in space-time metric are interferometers (like those providing the data that we're all crunching in Einstein@Home), and resonant bar detectors (where the small warp would cause a corresponding change in the resonance of the solid bar)...


I just learned that spacecraft Doppler tracking has also been used in an attempt to detect low-frequency gravitational waves. It's very similar to using the interferometers, where the spacecraft and the Earth are acting as the free test masses (like the mirrors in the LIGOs) but instead of measuring a change in distance between the test masses caused by a gravitational wave, the Doppler tracking measures a change in the relative velocity between the spacecraft and Earth. Here's an article I just ran across (from November 2001) that tells about the effort that went into the Cassini-Hugygens mission to improve the sensitivity an order of magnitude beyond previous spacecraft missions:NASA Spacecraft to Hunt for Elusive Gravity Ripples

Doppler tracking is still not as sensitive as the LIGOs, but the much greater distance between the test masses (hundreds of millions of miles compared to 4 kilometer arms in the interferometers) means that it's sensitive to gravitational waves having much longer wavelengths than those that could be detected by the interferometers, so the efforts complement each other.

For anyone interested in the nitty-gritty physics of using Doppler tracking for trying to detect gravitational waves, I found this: Low-frequency Gravitational Wave Searches Using Spacecraft Doppler Tracking. Section 8, an update, is about the LISA (Laser Interferometer Space Antenna); I thought it was ingenious obtaining “extra� gravitational wave data from spacecraft that have other primary missions, but it's easy to see why it's far better to have a full-time mission using sciencecraft dedicated specifically to the effort.

John McCallum
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Gravity 'ripples' hunt

Gravity 'ripples' hunt upgraded from the BBC science news site

I think there's a world market for maybe five computers - Thomas Watson, IBM

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RE: Gravity 'ripples' hunt

Message 79484 in response to message 79483

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Gravity 'ripples' hunt upgraded from the BBC science news site

I had not read much about advanced LIGO, so that was a very informative read.

Thanks for posting it! :)

Rod
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I have a question for this

I have a question for this linear thinker who has a hard time getting his head around general relativity:-).

There is a relationship between mass and gravitation. If a gravity wave passes through the solar system, Would the mass of solar system vary thus dampening the wave?

I am just curious what is the typical wavelength of a gravitational wave that we are looking for

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

Mike Hewson
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RE: I have a question for

Message 79486 in response to message 79485

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I have a question for this linear thinker who has a hard time getting his head around general relativity:-).


Join the club! Incidentally linear is a key word here, so do read on ...... :-)

Quote:
There is a relationship between mass and gravitation.


Yup, it's a fascinating connection. Mass ( or energy ) bends space, and mass moves according to that.

Quote:
If a gravity wave passes through the solar system, Would the mass of solar system vary thus dampening the wave?


Ah, now that's a real head banger! :-)

The 'pure' answer is yes : in that the wave itself has energy ( = mass ), it causes altered movement by it's passage, that altered movement could create waves, which themselves have energy ( = mass ), would could interact with the original incoming wave, which .......... etc Arggh!!!

The 'self' energy of the field is what makes solving Einstein's tensor equation ( 16 factors with 10 of them independent ) such a bitch. Photons ( at ordinary energies ) will not interfere with each other's passage, hence a light beam can be shone across another light beam and neither will be upset. If several photons arrive at a point they add, a linear superposition with phase adjustments. [ At higher energies coupling with other fields can occur and, say, an electron/positron pair might result ..... ]

Thus solving these gravity equations is non-linear. There's a few groups ( numerical relativists ) who use computers to approximate black hole mergers for instance. For LIGO, out here in detection land a long way away from the sources, approximations are made that:

- space is otherwise basically flat ( Minkowski metric )
- perturbations are small & linear
- distinct disturbances add like electromagnetic waves do

even though strictly speaking that's not true. But hey, the higher order terms should be small right?

Quote:
I am just curious what is the typical wavelength of a gravitational wave that we are looking for


The wavelengths that LIGO is sensitive to .... :-)
Seriously, the 'sweet spot' for the IFO's is ~200Hz but it's broadband also - hence our task units are working upwards through the frequencies. As the waves go at the speed of light ( 3 x 10^8 m/sec ) then 200Hz corresponds to a wavelength of = 3 x 10^8 / 200 ~ 1.5 x 10^6 m ~ 1.5 x 10^3 km. It's worth noting that the interferometers are of the order of 4km long and hence they 'sample' only a small part of the wavefront with a single circuit of the arms. You could liken this to a small boat being raised and lowered by the passage of a very long ocean 'swell'.

Oh, and just to be annoying, the 'waves' we are discussing are transverse to the direction of propagation. This means that if one were to go through my chest, going 'square-on' travelling from my front to my back, then it is my width from shoulder tip to shoulder tip and my length from head to toe that will alternately stretch and contract. My shoulders separate while I get shorter and they scrunch closer when I get taller. But my dimensions from breastbone to backbone are unaltered!

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: RE: I have a

Message 79487 in response to message 79486

Quote:

Quote:
I have a question for this linear thinker who has a hard time getting his head around general relativity:-).

Join the club! Incidentally linear is a key word here, so do read on ...... :-)

Cheers, Mike.

Thanks Mike for the answer.. I believe those approximations should be valid considering the magnitude of the gravitational wave and our current understanding of the universe..

But remember the goal is... the detection of gravitational waves in my lifetime :-). Now do I have an ego or what :-)

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

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