Historically, there's been no shortage of ideas for relaying radio signals - and the same holds true today. Though balloons remain an option (see "Space Case," Wired 4.09, page 112), here's a summary of the more credible telecom-satellite options organized by their distance from Earth:
Geostationary Earth orbit
GEO satellites maintain a constant relative position 22,300 miles up. The extreme distance makes them unsuitable for high-bandwidth Net interaction. However, INMARSAT is developing technology to improve GEO transmissions.
Medium Earth orbit
MEO satellites tend to circulate at 6,000 miles. At that altitude they must orbit faster to resist gravity. Consequently, they are in motion relative to the Earth's rotation, and 9 to 12 satellites are needed to ensure global coverage. Among the many MEO proposals are ORBLINK from Orbital Sciences PENTRIAD using 13 satellites ROSTELESAT a Russian scheme combining MEO and LEO satellites.
Low Earth orbit
LEO satellites cruise between 300 and 1,000 miles high. At this height, 70 or more satellites may be needed. There are five LEO initiatives of note: IRIDIUM funded largely by Motorola, is the first functioning LEO-satellite telephone service, but it does not offer broadband data. GLOBALSTAR an international consortium owned 42 percent by Loral Space and Communications, hopes to offer free roaming voice and messaging service by 2000, but it will restrict data to 9600 bps or less. TELEDESIC a privately held company funded primarily by Craig McCaw, Bill Gates, Motorola, Boeing, and Saudi prince Alwaleed Bin Talal, promises broadband - high-speed data links with one type of terminal offering 2-Mbps uplink and 64-Mbps downlink. Roaming, however, will not be possible. ELLIPSO financed by Boeing and Lockheed, also promises broadband service by 2001. SKYBRIDGE funded by Hughes, plans an 80-satellite service available by 2001, predicting data rates of 2-Mbps uplink, 20-Mbps downlink.
Want to know more? Check Lloyd Wood's homepage at www.ee.surrey.ac.uk/Personal/L.Wood/constellations. Sky Report offers a free monthly news update at www.skyreport.com.
