Arthur C. Clarke died on Tuesday at his home in Sri Lanka at age 90. A Google search Tuesday evening turned up numerous articles about Clarke and his concept of the using stationary satellites for radio communications.
Most of these articles state that Clarke conceived the idea of the geosynchronous orbit, and claim that this orbit is widely used today for communications satellites.
In fact, Clarke's concept was the geostationary orbit, although he called it simply a "stationary" orbit. The terms "geosynchronous" and "geostationary" are not synonymous.
A geosynchronous orbit meets only one criterion: it is synchronous with the earth's rotation (i.e., it has an orbit period of one sidereal day, or 23 hours 57 minutes 4 seconds). However, the term "geosynchronous" says nothing about the shape (eccentricity) of the orbit, or the angle of the orbital plane with respect to the earth's equatorial plane.
Indeed, there's an infinite number of possible geosynchronous orbits. One significant geosynchronous (but not geostationary) orbit is called a "tundra" orbit; it lies at an angle of 63.4 degrees with respect to the earth's orbital plane. Sirius Satellite Radio operates three satellites in tundra orbits.
Most other communications satellites (including XM Satellite Radio) lie in geostationary orbits. To be geostationary, the orbit must meet three criteria:
- It must be geosynchronous (period = one sidereal day).
- It must be circular (eccentricity = 0).
- It must lie in the earth's equatorial plane (latitude = 0 degrees).
Most popular-press writers don't understand this difference, and use "geosynchronous" when they mean "geostationary". Even WIRED magazine, of all publications, doesn't understand the difference.
To its credit, Wikipedia got it right.
Clarke was a visionary and prophet, not appreciated in his time.
His idea on Geostationary satellites was never patented, but since he conceived it in the late '40's, it didn't matter: the patent would have expired before Telstar.
Bill Horne Temporary Moderator
(Please put [Telecom] at the end of the subject line of your post, or I may never see it. Thanks!)