Revelations in the hidden sky

WINTRAK PRO. By Paul Traufler. (+1 256 837 0084 www.hsv.tis.net/wintrak). US$69.95. Windows 95/98/NT CD. Windows 3.11 and DOS versions also available.

In the early days after the launch of Sputnik, one group of British educationists stole a march on the world science community by devising kitchen-sink methods of tracking satellites that involved no more than telescopes, binoculars and ham-radio equipment. Led by former Kettering schoolmaster Geoffrey Perry, generations of physics students had a thorough practical introduction to this increasingly important branch of applied physics. More than once, groups like Perry's made significant discoveries about function that were concealed by satellites' owners. They even found satellites that were previously lost in space.

Thirty years later, tracking satellites by visual means rather than through powerful radars still requires persistence and ingenuity as well as a thorough understanding of orbital mechanics and planetary motion. But the scope and power of what can be done has been enhanced enormously by new computer tools and the Internet. In the past few years, information libraries and software tools have automated the drudgery of getting basic data and turning it into a picture of the skies. The most delightful of these new software tools is Wintrak. It is a remarkably easy-to-use program for tracking satellites in real time. Anything and everything in space can be selected from a catalogue of space objects as large as the user wishes. Their current and future ground tracks and visibility (or "footprint") can be portrayed in a rich variety of formats, including a 3D globe and alternative Mercator formats. They can also be viewed as moving objects against the background of the stars.

Each of these images updates continuously in real time. Assuming that the computer clock is accurately set and that up-to-date orbital data has been loaded, users can select an object or objects of interest and wait for a verbal and on-screen announcement: "satellite rise".

Around dusk or dawn, the larger sky objects can easily be seen with the naked eye. The space station Mir has the largest visual magnitude, followed closely by (of all things) a group of secret American satellites called Lacrosse, that image the earth's surface at all times and in all weathers using high-definition radar.

The value of this software is it that it brings the physics of near space to life with a few clicks. After many years of writing about the relevance of ground tracks, orbital inclination, ellipticity and kindred parameters of importance to the mission of the thousands of satellites now in orbit, I found Wintrak a striking and useful tool for enhancing understanding as well as looking at practical data. The progress across the skies of orbiting earth objects is a live demonstration of dynamics. Wintrak's help function offers pull down tutorials on the rich nature of the space environment, as well as on Kepler's laws of planetary motion and Newtonian physics.

The key input to any space-watching software system is an up-to-date catalogue of "two line elements" (TLEs). Besides defining data such as country and year of launch, the TLEs include numerical orbital data from which the current position and future track of each satellite can be predicted. Mainly because of the effects of atmospheric drag and gravitational perturbation on low and medium earth orbits, TLEs need to be frequently updated. Wintrak provides for up-to-date TLEs to be downloaded automatically from a variety of web sites.

The practical applications of software tools like Wintrak have already been many and diverse. The makers of the latest Bond film, Goldeneye, used Wintrak to drive fictional film displays. The planners of the recent Indian nuclear test used something like it to ensure that their preparations for their 1998 test only took place when American reconnaissance satellites were not watching. As new satellite constellations such as GPS (the global positioning system) and new global communications networks come into use tools such as this which explain and visualise what is happening in near space will be increasingly useful to have around.