April 10, 2003

Barndoor Tracker
Credit: Don Pettit, ISS Expedition 6 Science Officer, NASA

Explanation: The lights of Earth-cities at night are a beautiful sight from the International Space Station (ISS) so, naturally, astrophotographer and ISS science officer Don Pettit wanted to take pictures of them. But there was a problem: The station, traveling 17,500 mph, races around Earth in only 90 minutes. Lights on Earth's surface move through the window too quickly for long exposures.

"I needed something to help me track the city lights, to cancel the orbital motion of the station," recalls Pettit. "So I assembled a 'barn door tracker.' It's based on the fine gimbal movements in the IMAX camera mount for the Destiny Lab window. I figured out a way to mount a threaded screw and nut (scavenged from a Russian Progress rocket) and drive it with a Makita drill driver." The drill turns the screw, which moves the camera and its spotting scope. "All of these modifications clamp on to the IMAX mount and do not change its original function in any way," notes Pettit.

"I manually compensate for the station's motion by looking through the spotting scope and running the drill at the same time. It takes a bit of practice, but you do learn to track." Using this ingenious device, pictured above, Pettit has photographed many cities around the world including Los Angeles, London and Buenos Aires.