Determined to do something about it, however, we designed a tracking system from spare parts on the space station. These allowed for manual but precise tracking of cities at night, and canceled out the effects of orbital motion while holding all other axes steady during the exposure. We found the movie camera mount that had been used to film parts of the Imax feature "Space Station." It had been dismantled and stored in a closet, so we figured nobody would mind if we used it. That mount became the framework for our tracking system. We attached it to the US LAB window, and aligned one axis of a gimbal with the direction of orbital motion. By steadily panning the mount, we could cancel that motion. To precisely move the axis, we attached a long threaded bolt driven by a variable speed drill driver, which pushed on the platform and gave us a smooth motion. With a gradual squeeze of the trigger, our variable speed drill driver rotated the bolt in a smooth and precise way.
We mounted two cameras on the platform. One had a telephoto lens that simply acted as a spotting telescope. We looked through this lens and squeezed the drill driver trigger until the image of cities stood stationary, which told us our orbital motion had been precisely cancelled. With the second camera, we took the picture with a cable release.
Amateur astronomers will recognize that what we cobbled out of spare parts on the space station is no more than what they have been doing for decades with a simple tracking system dubbed a "barn door." This consists of two boards, a piano hinge, and a manually rotated bolt. This simple platform lets you counter Earth’s rotation while taking images of space. Our "barn door" allowed the reverse: from space we countered our orbital motion while taking images of Earth.
This tracking system allowed for much greater precision. The resulting images proved spectacular. While still short of what the eye sees, they are a significant improvement. The system gave us a resolution of ground objects in the 200-foot range.
Once we had refined the technique of operating our barn door tracker, we systematically took images all over Earth. Not only did we record the bright and striking urban areas, but remote, dark regions as well. As long as sufficient light allowed us to focus and track, we took photos. During Expedition 6, we recorded over 2,500 images. Counting subsequent missions, there is now a database of over 5,000 images that are in the process of being assembled at NASA’s Ames Research Center into a nighttime “Google Earth” model. Collectively, this data set will have scientific value as a snapshot of humanity's nocturnal footprint, including a record of light pollution.
The International Space Station is an orbital laboratory. As with most labs, it was designed with specific research purposes in mind. And, as so often happens in earthly laboratories, the real value of discoveries falls outside the realm of the preconceived intent.
NASA astronaut Don Pettit is scheduled to fly aboard space shuttle Endeavor in early November on mission STS-126, a resupply visit to the space station. See his article in the October/November 2008 issue of Air & Space about his harrowing return to Earth in a Soyuz vehicle.