NEAT system tracks Earth-threatening asteroids

Like a plot from a science-fiction movie, NASA and the Air Force have collaborated to develop an automated computer system that scans the skies for asteroids and comets that might be on a collision course with the Earth.

The Near Earth Asteroid Tracking (NEAT) system takes the place of spotty, manual NASA searches and automated Air Force systems that concentrated on searching for man-made objects in the Earth's orbit.

Looking for Trouble

Located at the Air Force's observatory atop the Haleakala volcano on the Hawaiian island of Maui, NEAT's job is to emulate a human astronomer with a serious coffee and Jolt Cola habit. A team of astronomers working with film-based cameras might find between 20 and 50 asteroids in a month. Since the system started searching for asteroids in December 1995, it has spotted more than 2,400 objects, fewer than half of which were previously known. During March alone, better weather conditions allowed NEAT to find 1,000 objects. Two of them are classified as "potentially hazardous asteroids capable of coming exceedingly close to the Earth," according to the Air Force. The immediate goal of the search for objects is to gauge the likelihood of a collision in the near future. If an object threatened the Earth now, what could the Air Force do about it? "In the short term, not much," an Air Force spokesman said.

That is why NASA is searching for asteroids and comets that are in our astronomical neighborhood—so we can decide how urgently we need to develop the ability to do something about it. "The consensus is that we need to learn more about the threat," said John Darrah, chief scientist of the Air Force Space Command.

The stakes are potentially high. The Air Force points out that an asteroid only 250 feet in diameter flattened 800 square miles of Siberian forest in 1908. A collision with a six-mile-diameter asteroid is widely blamed for the extinction of the dinosaurs. Last year the comet Shoemaker-Levy plowed into Jupiter. "[The Air Force] took notice of that collision," said Steven Pravdo, task manager for NEAT. The larger of the two potentially hazardous asteroids NEAT has spotted is 1.8 miles in diameter.

NASA uses a dual-processor Sun Microsystems Inc. SPARCstation 20 workstation equipped with custom interface hardware to point the Air Force telescope, take pictures with a special digital camera and analyze the images in search of moving objects. The single-workstation approach was chosen because it was easier to manage the critical timing of real-time events and to move huge amounts of image data within one computer, said Steve Groom, who was the operations engineer at the Jet Propulsion Laboratory (JPL), Pasadena, Calif. The computer uses the telescope to scan the sky, records what it sees with the camera and then analyzes the results. In the morning, the computer calls JPL using its 28.8 kilobit/sec modem and sends over the details on objects it spotted. This transfer only takes about half an hour because the SPARCstation sends only distilled results, not the whole night's observations. Right now, that would be about 10G of image data, and the system will grow to study as much as 40G of information a night.

It takes the camera about 20 seconds to capture an image, and it takes the computer about 100 seconds more to store that image, so NEAT takes pictures about every two minutes. Every half hour it goes back and takes follow-up images of the same sky locations for comparison. After three shots are taken and compared of each part of the sky, NEAT moves on to new territory.

If the photo image analysis time becomes a limitation, NASA can upgrade its SPARCstation 20 from its dual 75 MHz SuperSPARC processor configuration to dual 200 MHz UltraSPARC chips if needed. The machine is already loaded with 256M of RAM, but it will accept as much as 512M.

NEAT only scans the sky 12 nights a month, centered on the new moon, because the moonlight obscures dim objects the rest of the time. During the day, JPL scientists study the previous night's work. They will tell the computer to go back and study any interesting areas again and may even put out word to other observatories to look for unusual items NEAT has spotted.

A challenge was the requirement that the NEAT system do all of this work without human intervention. NASA has no staff at the observatory, and the Air Force agreed to do little more than turn the computer on. "The system had to run by itself all night long," Groom said.

The NEAT system's work could have been done earlier by other systems, but it would have been much more expensive.

"Part of the challenge was not so much a technical challenge in absolute terms; it was in making a lot with a little," Groom said.