Jon Dough 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?
Approximately
>
> 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?
See:
http://WWW.SCHRIEVER.AF.MIL/GPS/PAWG/pawg.htm
>
> 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?
Approximately 180 days... enough to complete a global nuclear war.
>
> 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?
American Taxpayers... GPS is a "world utility"... Worst case: you won't
see it at all, as was the case in the Middle East recently.
>
> 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?
Boosted to higher "out of the way" orbit