why must an earth satellite that is to be placed in orbit have a horizontal thrust?

Answer 1

well actually, it doesn't really need horizontal thrust once it's in orbit. it needs horizontal thrust to enter orbit. once it's orbiting, it needs no thrust, only horizontal velocity. which is obtained by the horizontal thrust you did at the beginning. but once the orbital velocity is obtained, you turn off the engine because there is nothing to slow you down. if you were to keep the thrusters on, you would constantly be increasing your speed. which would either cause you to leave earths orbit, or you would have to drop in altitude so there is more gravity to keep you in orbit. the faster you go, the closer you gotta be to the planet. this is why mercury moves the fastest around the sun. the earth orbits the sun at a constant velocity with no thrusters involved. well that is if you discount the elliptical shape of our orbit with is almost a circle anyway.

Answer 2

Orbits always form a closed loop. Basically, that implies that, once you turn off the engines, gravity will take you in an elliptical path that causes you to return eventually to the spot in space where you shut the engines down; AND when you return to that spot, you'll going in the same direction you were heading at engine shutdown.

Now, if you happen to be heading mostly "straight up" at the moment you shut off the engines, you have a problem. Gravity will pull you into an elliptical path all right, but it will be a very long, skinny ellipse that (gulp) happens to intersect with the earth! This is a nice way of saying: you'll crash.

The only way to achieve an ellipse that is "fat" enough to miss the earth's surface all the way around, is to apply some sideways (horizontal) thrust before shutting off the engines.

p.s. Alexander's answer is also correct, if you want to look at it in mathematical terms.

Answer 3

Well, I'm no Rocket Scientist.... Anybody ?!?!?

But it would seem that it would have to be with positioning of the satellite.

Geosynchronous orbiting satellites have to be positioned directly above a certain spot on the Earth so they don't seem to move. That way, you can point your Direct TV dish at it and it will continue to see it even though the Earth is rotating. They are shot off East-West.

Polar satellites are shot off North-South and circle the Earth in that direction as the Earth rotates East-West. These are the spy satellites and mapping satellites that will eventually see the whole Earth.

East-West satellites are shot from Florida (Cape Canaveral) and North-South from California (Vandenberg AFB).

Hope this helps.

Answer 4

when an object is put into orbit above earth, it still falls, so the object must have a horizontal thrust to get it to orbital velocity so that when it falls, it's horizontal velocity coincides with the earth's surface curvature so that it is always the same height above the earth.

Answer 5

Because this thrust, in contrast with earth's gravitational pull, keeps the satellite at a constant distance continually going around, thus, orbit. The earth is moving "forward" in a sense, but the sun is pulling it in towards itself. So, the earth never gets any farther away from the sun and the sun never pulls the earth any closer to itself.

Answer 6

Angular momentum of satellite at launch time is zero. Angular momentum of satellite on orbit is mvR. Gravitation of earth is central force and cannot change angular momentum of satelite.


The only source of angular momentum is horizontal component of thrust.

(Well, not exactly. Usually it's possible to provide some angular momentum using airlift acting on the rocket leaving the atmosphere. The nose of the rocket is intentionally tilted wrt its velocity at certain angle)

Answer 7

In order for the satellite to leave the gravitational pull of the earth, without putting too much strain on the satellite, the satellite is lauched with a horizontal thrust.
May God bless you.

Answer 8

Horizontal acceleration adds to orbital speed. The higher the orbital speed, the higher the satellite orbits, up to the point that it escapes Earth's gravity all together.

Basic mechanics tells you that if you shoot something straight up, it will fall straight back down unless you could atttain escape velocity vertically. That would require an unattainable amount of fuel.