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To: Ilaine who wrote (7798)	8/27/2001 5:36:35 AM
From: ig	Read Replies (1) \| Respond to of 74559

Larger satellites experience more atmospheric drag. A large satellite -- especially one with great solar panel "wings" -- in low earth orbit where the atmosphere is thicker, without the help of thrusters to restore its steadily decreasing velocity caused by atmospheric drag and subtle pressures of solar radiation, WILL come down sooner rather than later. The larger and lower they are, the sooner they fall. The smaller and higher sats don't need much help. Vanguard I, the size of a grapefruit and weighing all of 3 lbs, has been orbiting since 1958 with no thrusters. It is expected to stay up another several hundred years. ig

To: Ilaine who wrote (7798)	8/27/2001 6:32:34 PM
From: Maurice Winn	Read Replies (1) \| Respond to of 74559

CB, <If Wildstar is correct that "once the object reaches orbital velocity, no fuel is needed to keep the object in orbit", then why do satellites have thrusters, whether powered by hydrazine, plasma, nitrogen, or whatever? And why are satellites' effective life over when their thrusters run out of fuel? > Two different ideas. In the graveyard orbit, where space junk is sometimes dumped, it goes around forever [near enough for human purposes]. No fuel is needed to keep the junk in orbit. That's where Globalstar will go sometime. The fuel and thrusters are needed for station-keeping which is different from staying in orbit. Satellites are like stockmarkets, with exogenous events unpredictably jerking them around. There are little ones, such as solar wind, earth's shadow, specks of dust and big ones, such as crashing into a comet or being pulled by the moon. You are both right, but using the same words to mean different things. When out of fuel, the satellites lose their orientation which is needed for collecting sunlight on their wings [that's meaning the photovoltaics] and pointing the antennae in the right direction. They stop working, apart from going off course. Just as with satellites, we need Uncle Green$pan constantly firing the jets to keep the financial world in orbit, or more accurately, to maintain position, orientation and optimum performance. If it runs out of fuel, it's Zenit time... I have to go right now. More to come. You lucky thing. Mq