LISA satellite and lasers
Posted on 04/19/2005 5:20:02 PM PDT by PatrickHenry
A hundred years ago, Albert Einstein published his theory of relativity. On this occasion, Euronews' Space magazine plunges into the subject of gravitational waves and features the joint ESA-NASA "LISA" mission which hopes to detect them in space.
The existence of gravitational waves stems from Einstein's postulates. When very massive bodies are disturbed, they radiate waves or ripples that travel through space. When these waves hit an object, this will make minute movements as a consequence of the deformation of the space-time texture in which it is at rest.
The Laser Interferometer Space Antenna (LISA) mission, whose launch is envisaged for 2013, will use laser interferometers - very sensitive tools to measure tiny variations in the distance between objects – and proof masses on board three spacecraft flying in formation.
The system is designed to detect low-frequency gravitational waves which originate from, for instance, black holes swallowing massive neutron stars or binary star systems revolving around each other. They were also produced at the very origins of time, when the Big Bang occurred.
"As far as we know, the Universe began 13.7 billion years ago," explains Karsten Danzmann, Principal Investigator for the LISA mission at the Max-Planck-Institut fur Gravitationsphysik in Hanover in Germany.
"We have the dream of listening to that Big Bang itself by detecting and studying gravitational waves. It will give us a chance of listening to the dark, invisible side of the Universe."
Gravitational waves are so weak they are extremely difficult to hear. Because of our planet's own gravity, laser interferometers on Earth can only detect high frequencies, stemming from sources which are relatively close.
"If you want to listen to the high pitch notes of a concert you can do so with small ears, but if you want to listen to the real low pitches, you need big ears, and the only place where you can have big ears is in space," says Danzmann.
The LISA mission is one of the most ambitious ever undertaken: positioning and flying three spacecraft in a triangular formation, 5 million kilometres apart. The constellation will orbit the Sun, following the Earth at a distance of 50 million kilometres so as not to be perturbed by its gravity.
Infrared lasers will be beamed between the spacecraft, arriving on small 2-kilogram proof masses, 4-centimetre cubes made of gold and platinum.
At the University of Trent in Italy, Euronews was able to see the first of these proof masses destined for the LISA Pathfinder precursor mission. Due to be launched in 2008, its single satellite will test the general concepts and technologies of the LISA mission.
"We will be flying totally new technologies in space," says Professor Stefano Vitale, the Principal Investigator for the LISA Pathfinder mission. "The structure of the satellites will protect the proof masses. They will float much like astronauts hover in the void of space. But their precise position will be constantly monitored to detect when they are influenced by a passing gravity wave."
Precise is a euphemism when one details the accuracy of such measurements: LISA will need to detect infinitely minute movements of the proof masses, of the order of a tenth of an atom, that is a billionth of a millimetre! It will also identify the polarisation of waves, and thus the direction they come from.
The detection of these gravitational waves will complete the missing links in Einstein's theory of relativity and throw wide-open a new avenue of exploration in fundamental physics and astronomy.
"Einstein had foreseen the eventual detection of gravitational waves," concludes Stefano Vitale. "But a hundred years ago, no suitable instruments were available and Einstein's work was entirely theoretical. Now we have the technologies, we are picking up the challenge, and he would no doubt be greatly pleased to see that we are pursuing his work."
[A bit more text and pics are at the original article.]
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Detecting gravitational waves would be nice. It would be a way to confirm the speed with which gravity propogates, which is still an open question.
They will have to know where Michael Moore is at all times and subtract this contribution to the disturbance.
This is nothing, compared to the wonders of creation science.
Theyre still trying to figure out this crazy radioisotope dating stuff.
Can't blame them. Radiometric dating lost all credibility when it failed to validate the Shroud of Turin.
Kinda like when TedK does a cannonball.
The problem michael moore presents to modern science is a subset of the uncertaintly principle. The more precisely we know his position, the less precisely we know his honesty.
Three craft - I guess they must plan on flying it co-planar with the bulk of the galaxy for best sensitivity.
Now that you mention it, I'd fly them in a plane perpendicular to the plane of the galaxy. That way, the arrival of a wave would be detected at slightly different times by the masses. I suppose the rig is sensitive enough to detect the minute delay in a wave's arrival time at the most distant of the three.
YEC INTREP
No - if you fly it perpendicular (face on to the source) they'd all register it at the same time (being all at the same distance they'd all move simultaneously). If something approaches edge-on, THEN you have the best chance of detecting it because one is closest, one is farthest, and one is proportionally-spaced in-between..
We agree. I had intended to say edge-on when I said perpendicular to the plane of the galaxy. I had in mind two planes, perpendicular to each other, rather than parallel. I guess I didn't get my meaning across.
It depends. Are gravity waves longitudinal or transversal? In other words, are they like sound waves where the oscillation parallels the direction of propagation, or are they like light waves where the electric field oscillates perpendicular to the direction of propagation?
yeah, okay - I should have thought of that too - if the source is along the X axis then you'd want to be aligned either X-Y or X-Z. Y-Z would put them all at the same distance.
I haven't a clue. But either way, the waves have to arrive at the masses from their source, so the masses should be spaced so there's an interval from the time the waves hit the first mass and the time they hit the last. Assuming the apparatus can sense this.
I wonder if the new theories of gravity developed from string theory (compactification and 10-dimensions) produces far lower gravity wave energies than anticipated?
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