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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