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To: Wildstar who wrote (7852)	8/28/2001 8:51:42 AM
From: Ilaine	Read Replies (1) \| Respond to of 74559

>>However, for a satellite in orbit, there is another force acting on the satellite - the force created by traveling in a circular path.<< Not sure what you are trying to say here - do you mean centrifugal force? Which isn't a force but an effect. Theoretically, the mass of the satellite doesn't matter there because the little m (for mass of satellite) in the formula for centripetal force cancels out the little m in the formula for gravitational force. But notice the circular reasoning involved. Since the mass of the earth and the gravitational constant are both constants, a satellite can assume an orbital radius if and only if it possesses the appropriate velocity. If the satellite doesn't maintain the proper velocity, it won't stay in the proper orbit. So, can humans put a satellite in exactly the right orbit at exactly the right speed? I don't think so, but even if we could, the perturbations caused by the earth rotating on its axis (Mq is wrong to say that this doesn't matter - the earth's gravitational field is not uniform), the earth revolving around the sun, the angle of the earth's axis changing (that's what causes seasons), the moon rotating around the earth, and the solar system moving through the universe do affect the orbit of satellites. And despite the fact that Globalstar's satellites are too high up to feel much atmospheric drag, per se, there is magnetic drag, and some drag caused by ions leaving the atmosphere, especially every eleven years at solar maximum, as well as the pressure of solar radiation. I think it would be most accurate to say that the orbits of artificial satellites in lower earth orbit decay very slowly, but they do decay - even though LEO satellites use thrusters and momentum wheels to maintain their velocity, there's no such thing as perpetual motion. T >>You could place a cannonball in one seat and a tennis ball in the other seat and either they both fall out at the top or neither do, depending on the speed. It is impossible for one to fall and the other to stay. Mass is not a factor.<< The mass of the earth in relationship to the two balls is so great that the mass of the balls is negligible. However, the gravitational force of the earth on the balls is proportional to their mass, just as the gravitational force the balls exert on the earth is proportional to their mass. In the real world, when designing a chemical plant, chemical engineers cannot factor in every thing possible, so they design in a "fudge factor." In the real world, satellite engineers don't use fudge factors, they design on-board devices like earth sensors, thrusters, gyroscopes, reaction wheels, momentum wheels, and magnetic torquers. All of which would be unnecessary if the orbit of a satellite around the earth was as simple and stable as you seem to think. Lower earth orbits are less stable than upper orbits. Now, have we beaten this horse enough? Because I really need to do other things.