LISA

tullio
tullio
Joined: 22 Jan 05
Posts: 1,994
Credit: 32,107,623
RAC: 8,114

At least the ISS project is

At least the ISS project is going on. A Japanese cargo ship has just lifted off, to be followed soon by a Russian and then a European.ship. But the press does not care for these launches, they are not interesting enough.
Tullio

Rod
Rod
Joined: 3 Jan 06
Posts: 4,396
Credit: 811,266
RAC: 0

RE: [Of all the major space

Quote:

[Of all the major space primes, they are probably the worst when it comes to bidding aggressively to win and then making it back (and then some) on the cost overruns. And the cost overruns are always "someone else's" fault (subcontractor, government, etc.). We had a subcontract from them where they deliberately lied to the customer saying we were the reason they were late in order to cover up one of their screwups. Drives those of us who like to bid ethically nuts.

It is the strategy of most prime defence contractors that cut their teeth on Pentagon Contracts. Get them to spend enough resources, develop enough product, put business in states of senators on appropriations committee. They will chase their loss.(sometimes it works out) Take the F** which (Approx) takes a man week of maintenance for every hour of flight time. They have been trying to drive a stake through its heart for while. But LM builds a part of it in every freakin state.

Edit: Where does the fault lie. With an Opportunistic Business or with a crappy congress:-)

A endearing term used by the pentagon for contractors is Beltway Bandits..:-) with reference to the Washington Beltway where every contractor has at least a suite.

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

svincent
svincent
Joined: 24 Oct 05
Posts: 5
Credit: 167,049
RAC: 0

I have a couple of questions

I have a couple of questions on this:

My physics is rusty but I don't quite see how LISA will be able to detect a gravity wave that comes from a source lying in a direction perpendicular to the plane defined by the three spacecraft. In principle, aren't four spacecraft at the corners of a tetrahedron necessary?

Secondly, is it a prerequisite that LISA Pathfinder flies and validates the necessary technologies before going full steam ahead with LISA itself? It seems LISA Pathfinder is running into problems with the mechanism that holds the test masses during launch and releases them when in space (see link in Tullio's post on 20th Jan above) and won't fly until 2013 at the earliest. Meanwhile ESA was supposed to decide this year between LISA, a new X-Ray telescope, and a Ganymede Orbiter, and even though that selection process has been thrown into disarray by NASA's budgetary problems, a decision is planned to be made by 2012. The fact that there's no chance of flying LISA Pathfinder before then seems to suggest that the odds are stacked against LISA in that selection.

tullio
tullio
Joined: 22 Jan 05
Posts: 1,994
Credit: 32,107,623
RAC: 8,114

Latest article on LISA in

Latest article on LISA in "Nature" magazine:
ESA
Tullio

Mike Hewson
Mike Hewson
Moderator
Joined: 1 Dec 05
Posts: 6,049
Credit: 108,411,197
RAC: 70,987

RE: My physics is rusty but

Quote:
My physics is rusty but I don't quite see how LISA will be able to detect a gravity wave that comes from a source lying in a direction perpendicular to the plane defined by the three spacecraft. In principle, aren't four spacecraft at the corners of a tetrahedron necessary?


Fair point, it will be unable to disambiguate signals along a line perpendicular to the common plane that passes through the midpoint of the triangle. A fourth craft would remove that issue.

Cheers, Mike.

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

tullio
tullio
Joined: 22 Jan 05
Posts: 1,994
Credit: 32,107,623
RAC: 8,114

Latest on LISA from

Latest on LISA from ESA:
LISA
Tullio

Bikeman (Heinz-Bernd Eggenstein)
Bikeman (Heinz-...
Moderator
Joined: 28 Aug 06
Posts: 3,515
Credit: 436,596,914
RAC: 111,203

Hi! As far as direction of

Hi!

As far as direction of a source is concerned, LISA seems to rely on the same mechanisms that we here at E@H use: modulation of a persistent signal by Doppler drift caused by the detector's motion thru space (in LISA's case, it's orbit).

See http://lisa.nasa.gov/faq/index.html#FAQ6

CU
HB

svincent
svincent
Joined: 24 Oct 05
Posts: 5
Credit: 167,049
RAC: 0

Thanks for the comments and

Thanks for the comments and links. Unfortunately in the last couple of days it seems NASA has formally abandoned any participation in this project, making it even less likely it'll proceed any time soon. See

Dynamics of Cats
and
Cosmic Variance

Bikeman (Heinz-Bernd Eggenstein)
Bikeman (Heinz-...
Moderator
Joined: 28 Aug 06
Posts: 3,515
Credit: 436,596,914
RAC: 111,203

This is bad news :-( It's

This is bad news :-(

It's now official on the NASA web site for LISA. I feel really sorry for all the scientists and engineers who have already invested a considerable part of their careers into this project and are now facing an uncertain future.

Will ESA be able to keep this project running on their own? We will see.

So will LISA Pathfinder, planned to launch in 2013, continue or be stopped right away ?

CU
HB

Matt Giwer
Matt Giwer
Joined: 12 Dec 05
Posts: 144
Credit: 6,891,649
RAC: 0

RE: RE: My physics is

Quote:
Quote:
My physics is rusty but I don't quite see how LISA will be able to detect a gravity wave that comes from a source lying in a direction perpendicular to the plane defined by the three spacecraft. In principle, aren't four spacecraft at the corners of a tetrahedron necessary?

Fair point, it will be unable to disambiguate signals along a line perpendicular to the common plane that passes through the midpoint of the triangle. A fourth craft would remove that issue.

Cheers, Mike.

Yes but there are no stable "fourth" places if I understand it right. Three go into exactly the same orbit and they "dance" but corrected by the measured separation. A perpendicular fourth is in a different orbit which needs constant correction (propulsion fuel which has a limited life) to stay close enough to be part of the project.

On the other hand any wave that is repetitive such as binaries will be theoretically detectable as the triad moves in its orbit. So really the only one theoretically undetectable are those at the absolute north and south of the triad's orbit.

Of course baby steps first. After the detecting the first gravity wave we can worry about the details. After the champagne we can worry about finding the second one.

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.