WAILUKU, Maui — The profile of the Haleakala summit is changing slightly as construction continues on a telescope facility that will be used to spot asteroids that could collide with Earth.

The building that will house the Pan-STARRS prototype telescope is being erected at the site of the old Lunar Ranging Experiment Observatory, a NASA-financed satellite-tracking facility that was decommissioned in 2004. Work on the new observatory began in July.

The building that will hold the telescope was manufactured by Electro Optic Systems of Australia and is being assembled on site by Taisei Construction Corp. of Maui. It is being erected next to a dome that houses the Japanese Magnum Telescope.

The prototype telescope is being built in Tucson, Ariz., by EOS Technologies Inc. It will be one-quarter of the size of the full version of the Pan-STARRS, which will be either atop Haleakala or on Mauna Kea on the Big Island.

The smaller version, scheduled to be operating early next year, will allow scientists to test the technology and work out any bugs in the telescope design, cameras and software. The compact scale of the Pan-STARRS array means construction can be done relatively quickly, and officials hope the full version will see "first light" in 2007.

The Air Force is funding the $20 million Pan-STARRS, which is short for Panoramic Survey Telescope and Rapid Response System.

The powerful array of small telescopes will employ electronic detector technology, featuring cutting-edge optical sensors with billions of pixels, or picture elements.

The University of Hawai'i Institute for Astronomy is collaborating with Lincoln Laboratories at the Massachusetts Institute of Technology to develop the advanced detectors.

"The telescopes will have a very large field of view, allowing them to image an area about 30 to 40 times that of the full moon in a single exposure," according to the Institute for Astronomy.

Pan-STARRS will survey the sky every four days, providing photos that researchers will be able to use to spot potentially dangerous asteroids and other objects.

The Maui High Performance Computer Center in Kihei will help process the data, and information generated by Pan-STARRS will be available over the Internet to educators and researchers.

Reach Christie Wilson at cwilson@honoluluadvertiser.com.