“Shooting” the Space Station
June 28, 2007 — When it comes to optical precision, few telescopes can match the Clay Center Observatory’s big gun — a customized scope with a primary mirror 25 inches (0.64-m) across. More than a year in the making, the telescope’s reflective surfaces were painstakingly shaped to an accuracy of just 20 nanometers (less than one-millionth of an inch) or, in the parlance of opticians, to 1/40 the wavelength of the light they focus.
The combination of superb optics and a generally steady atmosphere above the observatory’s location in suburban Boston enables the 25-inch telescope to produce sharper images than telescopes several times its size. A prime example of this photographic prowess is this remarkable image, taken yesterday, of the International Space Station and (lower left of center) the docked Space Shuttle orbiter Atlantis.
At the time (10:14 p.m., 2 hours after sunset), the paired spacecraft were about 220 miles (355 km) up. Astronomers Ron Dantowitz and Marek Kozubal used customized tracking software they’d developed and a digital video camera to record the fast-moving targets as they glided overhead. In the sharp picture, you can easily make out windows in the space station’s hull and the ribbing in its solar-cell arrays. (The large set of solar-cell arrays at lower right was delivered during this shuttle visit.) Atlantis is oriented with its aft end toward Earth; its three main engines appear just below the craft’s vertical tail, which is glinting in the sunlight. With the Sun shining from below, the body of the orbiter casts a long shadow across the ISS itself.
“It’s like having a camera with an enormous 12,200-mm telephoto lens,” Dantowitz explains. The Clay Center Observatory’s telescope collects roughly 8,000 times more light than your eye can, even when fully adapted to darkness.
Rather than just clicking off one image at a time, the telescope’s video recorder captured thousands of frames during the ISS’s pass. Then a computer sifted through all the images to find the sharpest ones (which requires atmospheric stability at that exact moment) and “stacked” (added) them together electronically. The result is much crisper and more detailed than a single frame alone would be.
It also caught the attention of officials at NASA’s Goddard Space Flight Center, who proclaimed it today’s “Astronomy Picture of the Day.”