Howard.Gayle@cmu-cs-g.arpa (08/04/84)
I don't understand why Geostar users will, at least in principle, pay so much less than Navstar users. (Note that I am talking here about direct costs to the user, like hardware and user fees. I exclude indirect costs like the taxes that pay for the Navstar satellites.) A Geostar transceiver consists of an antenna, a receiver, a processor, a display, and a transmitter. A Navstar receiver consists of the same functional units, but without the transmitter section and its relatively expensive, high peak power components. A Navstar receiver contains a much more complex processor, but this is just silicon, so once mass production starts, i.e., once the custom VLSI design is done, this should be negligible. Geostar will charge a user fee, but DOD has announced that there will be no user fee for Navstar. A Navstar receiver will probably have a simpler antenna, since it will not need to handle transmitter power. A Geostar transceiver will probably need an FCC radio station license. Present military Navstar prototype receivers are, of course, very expensive, but Aviation Week is already talking about pocket size receivers. I expect the Japanese to produce a pocket size Navstar receiver for well under $1000 (1984 dollars). I would like to read technical replies to this post, but please no flames about DOD stupidity, Free Enterprise, etc.
dietz@cornell.UUCP (Paul Dietz) (08/07/84)
A Navstar ground unit must receive signals from four navstar satellites simultaneously, so it must have 4 receivers (actually, two frequencies are transmitted by each satellite, so the unit must receive 8 signals). A Geostar ground unit need only have one receiver. Geostar ground unit must transmit a powerful microwave pulse, but the average power is very low (milliwatts), so microwave semiconductors can be used. There is some contention about the accuracy of the Geostar system. The Navstar system uses two different frequency signals from each satellite in order to compensate for the slowing of microwaves passing through the ionosphere (a frequency dependent effect). Geostar could do this also by having the ground unit transmit two reply pulses at different frequencies, but I don't know if O'Neill has put this feature in. The biggest gain for Geostar is the added functionality. Since signals are transmitted from ground units, they can be used for communication as well as position location.
al@ames.UUCP (Al Globus) (08/07/84)
This isn't technical, but it's not a flame either. Navstar and Geostar are designed for very different missions. Navstar is worldwide, Geostar is North America. Also, much more fundimental, Navstar is designed to fight wars with. It is designed to survive hostile attack by intelligent, powerful enemies. This sort of thing costs a lot of money and has enormous impact on design.
henry@utzoo.UUCP (Henry Spencer) (08/07/84)
> I don't understand why Geostar users will, at least in principle, > pay so much less than Navstar users. (Note that I am talking > here about direct costs to the user, like hardware and user fees. > I exclude indirect costs like the taxes that pay for the Navstar > satellites.) A Geostar transceiver > consists of an antenna, a receiver, a processor, a display, and a > transmitter. A Navstar receiver consists of the same functional units, > but without the transmitter section and its relatively expensive, > high peak power components. A Navstar receiver contains a > much more complex processor, but this is just silicon, so once > mass production starts, i.e., once the custom VLSI design is > done, this should be negligible. Geostar will charge a user fee, > but DOD has announced that there will be no user fee for Navstar. > A Navstar receiver will probably have a simpler antenna, since it > will not need to handle transmitter power. A Geostar transceiver > will probably need an FCC radio station license. > Present military Navstar prototype receivers are, of course, very > expensive, but Aviation Week is already talking about pocket > size receivers. I expect the Japanese to produce a pocket size > Navstar receiver for well under $1000 (1984 dollars). As I said in a previous article, which may not have got to you yet, the answer is simple. A Geostar transceiver is basically just a digital radio. A Navstar receiver needs a complex receiver (it has to decode time signals very accurately, something Geostar does in the centralized part of the system), probably a very accurate clock, and quite a bit of computing power. This is not free, and not cheap, despite the overblown claims of Navstar advocates. The only reason DoD isn't going to charge a user fee for Navstar is that they don't see any way to collect one, since the Navstar signals are broadcast transmissions that anyone can pick up. Geostar is in a position to charge a fee, since getting your position from it needs cooperation from the central computer. A Geostar transceiver shouldn't need an FCC licence any more than a cellular-mobile telephone needs one. Both are radio transceivers, but both get handled in different ways from normal transmitters. Please note that one reason why Geostar is much more accurate than Navstar is that the high-accuracy version of the Navstar signals can be received only if you have the right decryption key, which will be available only to the US military. Civilian Navstar users get only the low-accuracy version. -- Henry Spencer @ U of Toronto Zoology {allegra,ihnp4,linus,decvax}!utzoo!henry