Subject: RE: [amsat-bb] Re: info on satellite placement
That is the most lucent simple explanation I could have imagined. The missing link was the realization the rocket headed horizontal (or a srequired for a specific orbit). Obviously the further out, the longer it takes to do a revolution. I imagine at some point earths gravity will not be sufficient to hold an object of given mass in a circular
orbit?
Exactly, If you are at a given altitude and you are going to slow, then your satellite will "fall" towards earth.. But as it falls, it speeds up as it approaches its lowest point (on the other side) and that makes it go higher to arrive back where you are on this side... In otherwords, the circular orbit becomes an elipse with a high side and a low side.
Now, If you were at a given altitude and you were going to fast for that altitude, then you would end up going higher on the other side and slower... Again an elipse.... And because it is higher and slower on the other side, it will fall back to where you were in the first place... Again, an elipse.
The only problem with going too slow, or going to fast is whether the elongation of your elipse just happens to run into Earth. That makes for a bad day.. Remember, the satellite is orbiting around the CENTER of the Earth and its Gravity. The satellite has no idea how big the "earth" is... So as long as the low point of an eliptical orbit stays about 4500 miles above the center of the earth, then it wont run into earth... But if the low point gets below that, then it runs into earth or the atomsphere and dies...
Or would it have to slow down below the speed limit in weaker
gravity?
Whatever speed at what ever altitude will always define an eliptical orbit. The only question is, is whether the Earth gets in the way of that elipse...
Neat stuff! Bob, Wb4APR
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Robert Bruninga Sent: Tuesday, 31 October 2006 12:56 AM To: 'Simon'; [email protected] Subject: [amsat-bb] Re: info on satellite placement
I was wondering if any one can suggest where I might find information on "how a satellite" gets placed into orbit. I ... can only find that a rocket gets it there.
Actually, the only thing the rocket does is get it going fast enough. The only way to stay in orbit is to be going 17,500
MPH
You could orbit the earth at tree-top level if it were not for air friction which would cause you to loose your speed and
hence
fall to the ground.
So the only thing the rocket does is 1) Get you going fast enough to stay in orbit, and conicidently, get you a hundred
or
so miles above tha atmosphere so you can keep that speed up
long
enough to do something useful.
Notice how the rocket almost immediately starts turning
towards
the horizon after launch, because it is horizontal speed that
is
what defines an orbit. It does travel upward at first to get
to
less dense air friction as soon as possible, but then begins
to
head horizontal until 17,500 MPH is achieved.
I hope to learn how and when its gets kicked off the rocket, and what happens after that.
Once the rocket gets to 17,500 MPH horizontally at the
altitude
you want, that is when you separate the satellite and let it continue. Usually the rocket uses some left over fule to slow-down and hence, fall back to earth.
If you are not perfectly horizontal and not exactly at the
right
speed, then your orbit will not be circular but will be an elipse. AO-40 was launched into a very eliptical orbit to get out to 40,000 km at apogee for a very large footprint. Eliptical orbits are just fine, as long as they do not
intersect
the earth or the earth's atmosphere.
I said 17,500 MPH as a representative number. It is different for each altitude orbit relative to the center of the earth. Remember that a 500 mile orbit (above the Earth's surface) 1s 4,500 miles above the center of the Earth. But a 200 mile
orbit
is 4,200 miles above the center, so the speed is not that much different.
Hope that helps. Bob, WB4APR
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Robert Bruninga wrote:
Subject: RE: [amsat-bb] Re: info on satellite placement
That is the most lucent simple explanation I could have imagined. The missing link was the realization the rocket headed horizontal (or a srequired for a specific orbit). Obviously the further out, the longer it takes to do a revolution. I imagine at some point earths gravity will not be sufficient to hold an object of given mass in a circular
orbit?
Exactly, If you are at a given altitude and you are going to slow, then your satellite will "fall" towards earth.. But as it falls, it speeds up as it approaches its lowest point (on the other side) and that makes it go higher to arrive back where you are on this side... In otherwords, the circular orbit becomes an elipse with a high side and a low side.
Thanks for posting these responses Bob, your explanations are quite clear.. I wish my high school physics professor had been nearly as clear. Your answer made me think.. if the ellipse crosses the path of the earth (or a path through enough atmospheric resistance that sufficient energy is lost) it will not continue to orbit. Simple enough. What I'm interested in, then, is how do you determine if an object has sufficient energy to escape orbit entirely? I can comprehend that the gravitation between two objects is inversely proportional to the square of the distance between them.. that at least "stuck" back in school.. so as near as I can figure, if you double the distance of the orbiting object from the center of the earth, it would take 4 times less speed to escape. Is that even in the ball park? I'd imagine, from that, that given a measure of gravitational pull on a measurable mass you could derive a speed at which the forces would no longer be equal, and the ellipse would never return back to the original spot.
I'd once set a goal for myself of being able to do at least the rudimentary math involved in how the Apollo missions were able to orbit the Moon, even assuming the two objects were stationary, but since I never learned Calculus to me it's all just squiggles. I appreciate plain language explanations like yours.
Thanks for the elucidation,
Jason - N1XBP
BTW, if anyone else is as curious as I am, I found the ARRL Extra class study guide to have an easy to read and understand section on Kepler's laws.
Robert Bruninga wrote:
Subject: RE: [amsat-bb] Re: info on satellite placement
That is the most lucent simple explanation I could have imagined. The missing link was the realization the rocket headed horizontal (or a srequired for a specific orbit). Obviously the further out, the longer it takes to do a revolution. I imagine at some point earths gravity will not be sufficient to hold an object of given mass in a circular
orbit?
Exactly, If you are at a given altitude and you are going to slow, then your satellite will "fall" towards earth.. But as it falls, it speeds up as it approaches its lowest point (on the other side) and that makes it go higher to arrive back where you are on this side... In otherwords, the circular orbit becomes an elipse with a high side and a low side.
Thanks for posting these responses Bob, your explanations are quite clear.. I wish my high school physics professor had been nearly as clear. Your answer made me think.. if the ellipse crosses the path of the earth (or a path through enough atmospheric resistance that sufficient energy is lost) it will not continue to orbit. Simple enough. What I'm interested in, then, is how do you determine if an object has sufficient energy to escape orbit entirely? I can comprehend that the gravitation between two objects is inversely proportional to the square of the distance between them.. that at least "stuck" back in school.. so as near as I can figure, if you double the distance of the orbiting object from the center of the earth, it would take 4 times less speed to escape. Is that even in the ball park? I'd imagine, from that, that given a measure of gravitational pull on a measurable mass you could derive a speed at which the forces would no longer be equal, and the ellipse would never return back to the original spot.
I'd once set a goal for myself of being able to do at least the rudimentary math involved in how the Apollo missions were able to orbit the Moon, even assuming the two objects were stationary, but since I never learned Calculus to me it's all just squiggles. I appreciate plain language explanations like yours.
Thanks for the elucidation,
Jason - N1XBP
BTW, if anyone else is as curious as I am, I found the ARRL Extra class study guide to have an easy to read and understand section on Kepler's laws.
Thanks for posting these responses Bob, your explanations are quite clear.. I wish my high school physics professor had been nearly as clear. Your answer made me think.. if the ellipse crosses the path of the earth (or a path through enough atmospheric resistance that sufficient energy is lost) it will not continue to orbit. Simple enough. What I'm interested in, then, is how do you determine if an object has sufficient energy to escape orbit entirely? I can comprehend that the gravitation between two objects is inversely proportional to the square of the distance between them.. that at least "stuck" back in school.. so as near as I can figure, if you double the distance of the orbiting object from the center of the earth, it would take 4 times less speed to escape. Is that even in the ball park? I'd imagine, from that, that given a measure of gravitational pull on a measurable mass you could derive a speed at which the forces would no longer be equal, and the ellipse would never return back to the original spot.
I'd once set a goal for myself of being able to do at least the rudimentary math involved in how the Apollo missions were able to orbit the Moon, even assuming the two objects were stationary, but since I never learned Calculus to me it's all just squiggles. I appreciate plain language explanations like yours.
Thanks for the elucidation,
Jason - N1XBP
BTW, if anyone else is as curious as I am, I found the ARRL Extra class study guide to have an easy to read and understand section on Kepler's laws.
Robert Bruninga wrote:
Obviously the further out, the longer it takes to do a revolution. I imagine at some point earths gravity will not be sufficient to hold an object of given mass in a circular orbit?
Exactly, If you are at a given altitude and you are going to slow, then your satellite will "fall" towards earth.. But as it falls, it speeds up as it approaches its lowest point (on the other side) and that makes it go higher to arrive back where you are on this side... In otherwords, the circular orbit becomes an elipse with a high side and a low side.