ASI To Develop Isolation Systems for Gravitational-Wave Measurements

TECH SPACE

LIGO in the fab

Pasadena - Nov 24, 2003
Alliance Spacesystems Inc. (ASI)announced Thursday that it has entered into a contract with the California Institute of Technology (Caltech) for the development of next-generation seismic isolation systems. The contract award is for Phase II of the Advanced LIGO effort, consisting of the design of two system types and the fabrication of prototype units.

These systems will be key to the performance of the Laser Interferometer Gravitational-Wave Observatory (LIGO), a terrestrial facility intended to detect and measure cosmic gravitational waves. These gravitational waves are ripples in the fabric of space and time produced by violent events in the distant universe such as the collisions of stars and the vibrations of black holes. Einstein predicted the existence of such waves but they have never been detected directly.

LIGO uses laser interferometers housed in two of the largest ultrahigh vacuum systems in the world, each consisting of 4-foot diameter vacuum beam tubes in the shape of an L with 4- kilometer arms. At the vertex of the L and at the end of each arm are test masses polished to a mirror finish and suspended with wires. Extremely stable laser beams traversing the beam tubes measure the effect of the gravitational waves on the location of the test masses.

When the waves pass through the detector, they will increase the distance between the test masses in one arm while decreasing the distance in the other. Since the changes in distance are minute (10-16 cm or one-hundred-millionth the diameter of the hydrogen atom over the 4-km length) the test masses must be isolated from all other disturbances � hence the requirement for the seismic isolation system.

Two widely separated installations have been built, one in Louisiana and the other in Washington, to negate the potential effects of regional phenomena such as micro-earthquakes or acoustic noise.

The seismic isolation system consists of two similar configurations, one for installation into the Beam Splitter Chamber and the other into the Horizontal Access Module. Both devices are required to perform in vacuum and be extremely clean due to the sensitivity of the optics.

Approximately 77" (2.0 m) in diameter and 32" (0.8 m) tall with two suspended stages, the devices combine a mechanically stiff suspension with active control to achieve the desired six-degree of freedom isolation. Subassemblies include seismometers, blade springs and flexures, sensor-actuator pairs, adjustable masses, and a multiple interface optics table.

LIGO is sponsored by the National Science Foundation and is being designed and constructed by a team of Caltech, Massachusetts Institute of Technology (MIT), and industrial contractors.

COSMOLOGY

Gravity Probe B To Test Einstein's Theory of Relativity

Washington - Oct 23, 2003
NASA's spacecraft, Gravity Probe B is scheduled to launch from Vandenberg AFB aboard a Boeing Delta II rocket December 6, 2003. The GP-B mission is expected to be approximately 16 months long and its objective is to test Einstein's unverified theory of relativity that states space and time are very slightly distorted by the presence of massive objects.

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