# An interesting question

1. Dec 10, 2007

### mysqlpress

Well, geostationary satellites are satellites which moves around in the same manner as the earth. This is true. and the derivations indicates that the centripetal force are provided by gravitational force of the earth on the satellite which causes the circular motion.

However, the Earth rotates from the West to the East. but the force doesn't imply the direction of circular motion(i.e. closewise/anti-closewise or the same manner as the earth/opposite to that). Hence, is it possible to move in the opposite direction as the Earth?

the energy required seems not the same ? I can't see any deviations on the net.

Thanks.

2. Dec 10, 2007

### Staff: Mentor

But that wouldn't be quite geosynchronous, would it?

But you're right: the same orbital speed and distance applies regardless of the direction or orientation of the orbit.

3. Dec 10, 2007

### mysqlpress

Yes, perhaps my question is not well-presented... haha

and why aren't there some satellites with this kind of behaviour?

4. Dec 10, 2007

### Staff: Mentor

There are satellites in inclined geosynchronous orbits. But if you are in a geosynchronous orbit about the equator and move in the same direction as the earth rotates, then you are in a geostationary orbit: You are in a fixed position with respect to the earth's surface. This is a very important feature for communications satellites.

5. Dec 10, 2007

### LURCH

There are few applications in which this type of orbit would be advantageous. The cost of getting to such an orbit would be quite high. Cost/benefit dictates that sattelites be launched to orbit the Earth in the same direction in which it rotates.
Not the same. The energy required to get into orbit in the same direction as planetary rotation is the total energy needed for the orbit minus the energy provided by the rotation. The energy needed for launching into retrograde orbit is the energy required for the orbit plus the energy of planetary rotation. This is also why we always launch from someplace close to the equator. The ground at the equator is moving at almost 1000mph toward the East. To launch to the west, you'd have to get up to 1000mph (groundspeed) just to be standing still, then accelerate to orbital speed from 0.

6. Dec 11, 2007

### mysqlpress

Can you show me some math proof on this ?

7. Dec 11, 2007

### rbj

it's like having a radio transmission tower that is 22,000 miles tall. and no friggin' guy wires.

keep in mind, assuming you are not at either the north or south pole, that just sitting where you are, you are already whirling around the Earth's axis. if you are at the Equator, you're speed is about 1600 km/hr. now if you're lauching a satellite (or Shuttle) does it not make sense to orbit in the same sense of rotation as the "head start" you've already been given?

8. Dec 11, 2007

### LURCH

Keep in mind that orbutal velocity for a low-Earth Orbit is about 27000 km/hr (if I remember correctly). So, if you statr off at 1600, you must accelerate an additional 25400 km/hr (roughly), to achieve orbit. Unless you attempt retrograde orbit, in which case you must accelerate to about 1600 km/hr (relative to the pad from which you launched) just to become stationary relative to the Earth's center of gravity. Then, you would have to acelerate another 27000 km/hr to reach orbital velocity. Altogether, you would have to accelerate to 28600 km/hr relative to the point from which you launched. That's 3200 (or 2*1600) km/hr more than you need to get to orbit in the forward direction. That's a huge difference in expense. It could eb done, but somebody would need a real good reason.