Satgen267 The Global Phone Saga Part 2 by GM4IHJ 7th May 94 BID of this msg is SGEN267 Please use this BID if you retransmit this msg In satgen 218 some interesting developements which tied together Low Earth Orbit satellites and, mobile phones, were explored. Since then the story has begun to gather pace and has added a further rather "odd" system. Two of the proposals in satgen 218 have made considerable progress :- 1. The Loral ( ex Ford Aerospace ) Globestar bent pipe system will use 48 sats. You connect to one in range. It then connects you to a ground terminal and thence via ordinary cable/geosat links, to the area where your recipient is located. The distant ground terminal then uplinks to a sat which is in range of your recipient. This idea uses simple hardware and software on the ground and in space but it suffers from using the very disparate world wide cable/geosat links for its main connections, inviting similar problems to those already bedeviling some international calls. 2. Iridium . Motorola's 66 sats in LEO orbit has no ground terminals. Your call is daisy chained from sat to sat to your distant recipient, and sats passing in/out of range keep you auto connected. So hardware and software in space is going to be very complex, and it remains to be seen whether 66 sats = maybe 2 in range at any time will be sufficient for densely populated area like Europe or, the US East coast conurbations. Now you must add to the above the recently announced Teledesics (McCraw Cellular Communications system) which proposes to use 840 LEO sats at 435 miles altitude using 28 GHz communications. Please note however that the proponents of this system say it WILL NOT BE FOR MOBILE PHONES. It is intended to connect remote communities via ground stations in each community. So far Motorola have got at least one third of the cash required for Iridium, and they have FCC approval for a 2 or 3 sat trial over the next two years. Loral Globestar have not as yet given test details but both Globestar and Iridium would be expected to be operational at the turn of the century ie 6 or 7 years time. By contrast the Teledesics proposal ( backed privately by Bill Gates of Microsoft ), is getting a lot of adverse comment. In particular it is doubted whether a system purely for remote locations can ever be viable, and , there are lots of question marks about the proposed use of 28 GHz for up and downlinks. Even though 840 sats should provide constant access to a sat at a high elevation angle , absorption of the signal by atmospheric oxygen and water vapour may well be a problem. Whilst a problem facing all three systems , is can the necessary finance for all three systems, be obtained at the same time, noting that the outlay will be at least 2,000,000,000 US Dollars. Less publicised but very important to Radio Astronomers. the proposed Globestar , Iridium links , Uplink 1610 to 1626.5 and Downlink 2483.5 to 2500 MHz may cause problems. The second harmonic of the downlink is right on a radio astronomy continuum frequency. So it is no surprise that US authorities are suggesting banning mobile phones within 100 miles of important radio astronomy sites in Puerto Rico and Western USA. Radio astronomers have complained for some time that US Nuclear Warning sats and the Russian Glonass Navsats interfere with their work. The Russians have agreed to shift their Navsat frequencies but as yet there is no respite from the Nuclear Alert sats. So the forthcoming mobile phones are not being welcomed by the radio astronomers. 73 de GM4IHJ @ GB7SAN