Why are satellites normally sent into orbit by firing them in an easterly direction?

Question

(The direction in which the earth spins)

Answer 1

Gravity doesn't push.

They are fired in the same direction of the spin to reduce the amount of energy the rocket must provide the satellite to put it into orbit. If you wanted to put it in orbit by launching the opposite direction, you'd have to apply the entire amount of energy to get it into orbit PLUS cancel the velocity the satellite has sitting on the ground because of the Earth's rotation.

if V_g is the velocity on the ground and V_o is the velocity needed for a particular orbit then

dV_e = V_o - V_g going East
or
dV_w = -V_o - V_g going West

so |dV_e|<|dV_w| so its cheaper to launch that way. Then if the satellite needs to orbit that direction then they are done in orbit since it requires less energy to do that than by launching it West.

Answer 2

Many people have pointed out that launching eastwards gives you a head start in reaching orbital velocity. Captsnuf also made the very good point that launching east from the east coast makes sense from a safety point of view.

There are occasions, however, when you want to launch to the west and perhaps not surprisingly such launches often take place from Vandenburg on the west coast (that is launches conducted by the USA).

Launching east saves energy for an equatorial orbit but if you want to reach a polar orbit (eg for a weather satellite that wants to look at the whole Earth by having it rotate "underneath" it) then you have to cancel out that initial eastward motion, hence you launch in a westerly direction.

Answer 3

The Earth spins from East to West, and the surface moves about 1000 miles per hour at the Equator. So, the closer to the equator you are, the faster you're moving East - so, by launching a rocket close to the equator, going east, you're giving that rocket almost a 1,000 mile per hour boost in that direction.

If you launched it west, you'd have to counter the easterly-motion you have, then boost it an additional 17,500 MPH to achieve a westerly orbit.... That's a lot more fuel you would need.

Answer 4

An object has to circle the earth at a certain rotational speed to remain in orbit. By launching a rocket east (with the earth's spin), the rocket starts with the earth's rotational speed as a bonus. This means less fuel is required to get the rocket up to orbital speeds. Less fuel means a lot less money.

In short: it's cheaper.

Answer 5

Because the velocity of the Earth spinning gives that same velocity to the rocket, and the motors add more.
If they fired in the opposite direction, the rocket would have to use a lot of energy in overcoming the motion it gets from being on a spinning earth.

Think of paddling a canoe on a river. Paddle downstream and you can go fast. But paddle upstream and a lot of your effort is used just to overcome the force of the river.
Its the same sort of thing for rockets.

Answer 6

Because it saves fuel-and spacecraft have to have so much fuel and thus small payloadsfor their size, even a small savings makes a big difference.

This works because the spacecraft on the ground is already "spinning" in that it is rotating along with the rest of the earth's surface. Thus it doesn't need quite as much speed to achieve orbital veloscity.

Answer 7

relative to a stationary coordinate system centered on the earth objects on the surface of the earth have a tangential velocit of about 1000 mph to the east. the path to orbit is roughly a spiral, going out from the earth. so the 1000mph is free energy. if you go to the west the angle of the spiral would be flatter, meaning a longer burn time to reach orbit, and so more fuel and weight to contend with.

Answer 8

Because of the speed of the earth's surface, it requires less energy when this speed is already built into satellite, and the closer to the earth's equator the easier it is.

Answer 9

all this east direction and numbers and reasons sounds real good and impressive, children, but they are fired easterly to go over the water and not the land (from cape canaveral) incase of a mishap.

Answer 10

Gravity is pushing the rocket in the same direction as the spin. To go against the spin would waste energy. Speed and efficiency is needed to break thru the atmosphere.
Example...While driving, throw a marble forward...it goes fast, easily. Throw a marble backwards, much slower.