Tracking "Space Junk"

Tracking Earth-orbiting satellites visually can be a great outdoor "homework" assignment. Literally thousands of objects orbiting our planet are listed in the latest Satellite Situation Report compiled by NORAD (North American Air Defense), and distributed by the Goddard Space Flight Center. Any satellite larger than a softball is tracked by NORAD, and the data is disseminated by NASA. Many of these are debris from payloads and rocket bodies, called "space junk." On any clear evening, you have an excellent chance of seeing a satellite about 1 to 1 1/2 hour after sunset. Most will be observed in north-south or south-north orbit. In the space of an hour or more, you could see a dozen satellites. Brightness of the objects will vary depending on orbital altitude, size, and spin rate. Although you are in the sun's shadow, the satellite is still in sunlight, and the reflected sunlight illuminates it for us watchers on Earth.

How does one know when and where to look for specific satellites, such as the Soviet Mir Space Station, and, on occasion, even the US Space shuttle? Amateurs have been tracking satellites for more than two decades. Before the microcomputer became a household item, Hams plotted orbits on maps to determine when the satellites could be seen overhead. This method is still in use and is a good primer for those interested in tracking orbiting satellites. Later, we will focus on how to construct and use this simple tracking device.

In 1969, interested Hams formed the Radio Amateur Satellite Corporation (AMSAT) to continue to enhance amateur satellite communication. Through the years, AMSAT has been a leader in research and development for amateur satellite technology. With the advent of microcomputers, tracking programs were written to automatically track specific satellites of interest, thus leaving the operator with more time to communicate. Software is available for almost every popular home and business computer through the AMSAT software exchange.

How does the computer operator know which satellite is which? The user must input information for each satellite. These numerical data sets are called Keplerian Elements, named after Johannes Kepler. These elements, unique to each satellite, are orbital parameters which define individual orbits. They are available from a variety of sources, including SpaceLink or via a number of electronic bulletin boards. Many of the newer tracking programs, including Instatrack and Quicktrak for the PC, provide users with a very quick means of updating elements. Complete files can be downloaded in a matter of minutes, and the computer software updates elements for as many as 200 satellites in seconds. Compare this with the arduous task of updating each satellite via computer keyboard, which takes several minutes per satellite. Either way, information is available for all satellites of interest to educators, including weather satellites, amateur satellites, and objects of high visibility such as the Mir space station. It is important to secure the latest Keplerian element sets available when tracking the Russian Mir Space Station or the Space Shuttle.