By John McHale
PASADENA, Calif. - Experts from three aerospace contractors are starting preliminary design of a solar-powered optical-sensing spacecraft that astronomers expect to draw the most detailed and accurate maps of the galaxy ever produced.
The star-mapping spacecraft project is called the Space Interferometry Mission (SIM), which will have a high-precision optical instrument called an interferometer to measure small changes in star positions 500 times more accurately than the best available mapping system today.
Officials at the NASA Jet Propulsion Laboratory (JPL) in Pasadena, Calif., are selecting a SIM team of the TRW Space & Electronics Group in Redondo Beach, Calif., Eastman Kodak of Rochester, N.Y., and Hughes Danbury Optical Systems of Danbury, Conn., to complete a four-month preliminary architecture study.
SIM is one of several high-resolution space astronomy missions planned for deployment early in the 21st century as part of NASA`s Origins program.
This will be the first space mission with an optical interferometer as its primary instrument. An astrophysics mission, SIM will precisely determine the angular positions of stars in the Milky Way galaxy and generate high-resolution images. It will achieve an accuracy, over the entire sky, of four microarcseconds - more than 250 times better than the best available star catalogs.
The mission will not produce reliable results until three years after sending the first image, says Mike Shao, director of JPL`s Interferometry Center.
SIM will generate images with an angular resolution of 10 milliarcseconds using aperture synthesis - performance which exceeds any ground-based optical telescopes, and exceeds the resolution of the Hubble Space Telescope by about a factor of four.
SIM`s active optics technology uses a combination of steerable mirrors and delay lines, which compensate for structural disturbances by varying internal optical paths and tilts. One of the technical challenges is to provide a kind of "shock absorber" for the craft`s moving parts, Shao says.
To solve this problem, SIM uses vibration isolation and suppression, which provides structural quieting at frequencies above the bandwidths of the active optical control loops. This reduces the control burden on the active optical system.
Artist`s rendering of future SIM spacecraft