March 09, 2007

Update on Pan Starrs- Asteroid detector

Four 71-inch mirrors gathering light for Pan-STARRS would each be hooked up to what would be the four largest digital cameras ever built. The system would be able to survey the entire sky once a week, and would be able to detect asteroids as small as 1,000 feet across. They face opposition from environmentalists who want to protect Mauna Kea.

When completed in 10 or 15 years, the Pan-STARRS survey should provide decades of warning about an impending collision with an asteroid or comet, the scientists said.

The single-mirror prototype for Pan-STARRS on Haleakala, is now complete. The full 60-chip camera will be installed at the end of 2007.


the gigapixel cameras (seen above) that are used are key to the systems performance

The focal plane of each camera contains a 64 x 64 array of CCD devices, each containing approximately 600 x 600 pixels, for a total of about 1.4 gigapixels. The individual CCD cells are grouped in 8 x 8 arrays on a single silicon chip called an orthogonal transfer array (OTA) , which measures about 5 cm square. There are a total of 64 OTAs in the focal plane of each telescope.

Why so many CCDs?

- Small CCDs can be read out more quickly than large ones.
- A manufacturing defect usually cripples a single CCD. By dividing the focal plane into a large number of CCD devices we limit the damage caused by a chip faults. The ability to make good use of slightly imperfect chips results in a very large saving of both cost and manufacturing time. One of the reasons we use four cameras is to mitigate the effect of chip defects.
- Bright stars can saturate CCDs very quickly. CCDs which include a bright star image can be set to read out very fast, with no ill-effects on the neighboring CCDs.
- The CCDs all use orthogonal transfer technology (see next section) that reduces blurring by the earth's atmosphere.

Orthogonal Transfer Charge Coupled Device (OTCCD) will be used to allow for image motion compensation in the focal plane itself. During an exposure, selected bright stars have their positions rapidly monitored in order to calculate the immediate effects of atmospheric phase fluctuations. In a traditional "tip-tilt" adaptive optics system, these position errors are fed back to a small mirror whose angle is rapidly adjusted to compensate for the atmospheric disturbance. An OTCCD achieves the same goal by electronically shifting the image within the CCD itself rather than by moving a mirror.

Performance

There are currently about 100,000 known moving objects in our solar system that are tracked by professional astronomers. With Pan-STARRS, estimate being able to catalog up to 10 million main-belt asteroids and tens of thousands of NEOs and TNOs.

the Pan-STARRS survey will reach about 5 magnitudes (a factor of 100) fainter objects than observed by current NEO surveys.

Pan-STARRS can detect a body like Pluto out to 300 AU, Earth out to 600 AU, Neptune out to 1200 AU and Jupiter (or heavier) out to 2000 AU. PS will help resolve the question of whether there is a planet X anywhere near the existing solar system.
This pdf describes the capability of the system for finding planets in the outer solar system and competing capabilities of other telescopes. The US National Large Synoptic Survey Telescope (DMT/LSST) will be more powerful but is not expected to be done until 5 years after Pan-STARRS.

Pan-STARRS will produce the deepest and most complete survey of the Solar System so far. We expect about 100,000 Jupiter Trojans asteroids, 1,000 Centaur asteroids, and several hundred comets.

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