MR

On Sat, 13 Sep 2003 11:16:21 GMT, "Jon Dough" <nobody@home.com> wrote:

>I'm constantly amazed that my GPS receiver can receive signals directly from
>satellites overhead, and translate that information into a display loaded
>with location, speed, direction, and time data..... Most of the time we
>accept technology as a given, but sometimes I'd like to know a little more
>about it. For example:
>
>1. How large (size and weight) are the satellites? I'm guessing that they
>are solar powered, so there are probably large panels deployed once they
>reach orbit, but what are the general dimensions? Larger than a
>refrigerator? A car?
>
>2. I've seen references to onboard clocks being "switched" from Cesium to
>Rubidium... How many clocks do they have, what happens that makes switching
>necessary, and is one type of clock significantly more accurate than the
>other?
>
>3. My understanding is that the satellites require constant monitoring and
>ground-based support to maintain the accuracy of the GPS system...
>Hypothetically, if support from ground stations were to cease, how long
>would the GPS system continue to provide useful navagational information?
>Are we talking hours, days, weeks, what?
>
>4. Who pays for the system? What assurance do we have that it will not be
>suddenly cut off without warning? I understand there is provision for
>decreasing the accuracy, but what is the worst case I can expect to see?
>
>5. When there is a reference that a given satellite is nearing the end of
>its life, I'm guessing that means it's running out of propellant to adjust
>it's orbit when necessary. Is it just "shut down" or do they "de-orbit" it
>and let it burn up on re-entry? What do they cost anyway?
>
>
>m9876c at yahoo dot com

You can find info on your questions here http://www.gpsy.com/gpsinfo/
MR