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Earth's rotation and mass calculation
As the earth rotates, it imparts a "centrifugal force" on objects which
would lessen their weight. And this varies depending on your elevation as well as latitude. (at the pole, there would be no such "force"). And then there is the issue of the earth not being round, so I assume that gravity is not even everywhere on earth. When NASA calculates an object's mass for a space vehicle, must it take the above stuff into consideration, or is that so tiny that it isn't even worth considering even for unmanned probes that must travel a precise path over 10 year period ? (I realise that a true scale simply compares the weight of two objects, but the problem is then shifted on how to manufacture the reference object so its mass is absolutely exact) |
#2
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Earth's rotation and mass calculation
I can't address your exact question, but I have worked building
gravimeters, which can also be described as extremely sensitive vertical accelerometers. While I was there we didn't sell any to NASA, but there is another U.S. government outfit that was mighty interested in mapping the gravity field. They specialized in lobbing ballistic missiles at enemies. The warheads must fly to their targets through a lumpy gravity field with no outside help once they leave the bus. The more that is known about the gravity field the better the corrections and accuracy can be. John Doe wrote in : As the earth rotates, it imparts a "centrifugal force" on objects which would lessen their weight. And this varies depending on your elevation as well as latitude. (at the pole, there would be no such "force"). And then there is the issue of the earth not being round, so I assume that gravity is not even everywhere on earth. When NASA calculates an object's mass for a space vehicle, must it take the above stuff into consideration, or is that so tiny that it isn't even worth considering even for unmanned probes that must travel a precise path over 10 year period ? (I realise that a true scale simply compares the weight of two objects, but the problem is then shifted on how to manufacture the reference object so its mass is absolutely exact) |
#3
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Earth's rotation and mass calculation
In article , John Doe wrote:
As the earth rotates, it imparts a "centrifugal force" on objects which would lessen their weight. And this varies depending on your elevation as well as latitude. (at the pole, there would be no such "force"). For long and involved reasons, the above factor "doesn't matter". Starting with the fact that 'centrifugal force' exists _only_if_ your frame of reference is rotating. Ballistic calculations assume a stationary reference base. Also, you're neglecting several other factors -- including the rotation of the solar system around Betelgues, the rotation of the Milky Way, as a whole, etc. grin And then there is the issue of the earth not being round, so I assume that gravity is not even everywhere on earth. True. not only is the Earth "not perfectly round', but it is "lumpy" -- parts of it are more dense (and hence 'heavier') than other parts. This _does_ have noticiable effect on objects in Earth orbit. When NASA calculates an object's mass for a space vehicle, must it take the above stuff into consideration, or is that so tiny that it isn't even worth considering even for unmanned probes that must travel a precise path over 10 year period ? The varience due to the factors you cite is inisignificant _relative_ to other sources of error. Which is why the 'long time travelling' devices have been equipped with devices for adjusting their trajectory -- to correct for the *inevitable* errors that creep in. (I realise that a true scale simply compares the weight of two objects, but the problem is then shifted on how to manufacture the reference object so its mass is absolutely exact) mass is mass. as long as you collect all the data in the _same_ frame of reference, you'll have consistent values. And, obviously, the further apart the masses are, the more nearly they interact as true 'point' sources. |
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