Sattelite Lifespan

Yes, rocket engines. Since the amount of fuel that can be carried is finite, the end of fuel has pretty much been the end of life for a satellite.

The Research and Development (R&D) division of LynDoor^® Aerospace has been investigating the feasability of a refuel satellite. I am sad to report that these guys have beaten us to it.

^{Another $13,000,000 down the drain... and why is our stock price tumbling, can someone PLEASE answer me that?}

We're also over budget on the solar powered umbrella and the water activated sprinkler system.

I did just get an order for a truck load of generator barges to power those wind mills when there's no wind.

In addition to chemical thrusters, plasma or ion thrusters and reaction wheels may help.

Orbital_stationkeeping

Reaction_wheel

"the most crucial thing affecting one satellites lifespan"

Is the distance from Earth. Satellites in geostationary orbit are so far from atmosphere that they don't require any fuel to remain there (at least for few thousand years), satellites in lower orbits need occasional burning of fuel to keep them from falling into atmosphere. Drag from minute particles in upper atmosphere causes satellites to "drop" down towards Earth. I'm not sure of orbits GPS constellation of satellites however I would assume that they are smaller satellites in geostationary orbit without thrusters on board.

Huh? GPS and GEO sats both require station keeping thrusters.

http://www.colorado.edu/ASEN/asen5090/questions.html

http://en.wikipedia.org/wiki/Orbital_stationkeeping#Station-keeping_in_geostationary_orbit