Space orbits

[rov1200]

Do all man made objects blasted off from Earth orbit clockwise or anticlockwise? Have any collided?

[Clanad]

Satellites orbit both directions relative to Earth's rotation as well as over both poles. Geo-synchronous satellites remain over a fixed location relative to the Earth...
No collisions have been reported. The flight path is carefully planned before launch...

[Buenchico]

The concepts of 'clockwise' and 'anticlockwise' cease to have much meaning in three dimensions. Something which is apparently moving 'clockwise' around the earth's equator when viewed from above the north pole will appear to be moving 'anticlockwise' if viewed from above the south pole.

A large number of man-made satellites (e.g those which provide satellite TV services) simply follow the rotation of the earth (i.e. they're 'geostationary' = permanently above the same point on the earth's equator). To ensure that they move at the same rotational speed as the planet's surface, that means that they must be 22,240 miles above the equator. There are thousands of satellites positioned in a circular band at that height but (because of the vast circumference of the band) there's no risk of them bumping into each other.

However, while individual satellites don't pose a risk to each other, the space debris created by launching and positioning them does pose a significant risk . There are millions of items of debris (anywhere between the size of a pinhead and the size of a fridge) out there. They pose a potential hazard to all space launches and they've already been attributed to the failure of existing satellites:
http://news.skymania.com/2006/04/collision-kno cks-out-satellite.html

Chris

[mibn2cweus]

Most satellites are launched in an eastward direction to take advantage of the Earth's rotational velocity in reaching orbital velocities. Two notable exceptions to this policy are when an eastbound launching rocket would have to fly over inhabited territory or when it is important to place a satellite in a constantly sunlit orbit since with respect to the Earth's surface the Sun 'moves' east to west.

[dundurn]

Can you have a constantly sunlit orbit by moving East to West? Sounds to me like you'd be stationary relative to the Earth, i.e. not in Earth orbit at all but in solar orbit. This would presumably have to be at one of the Earth-Sun Lagrange points, otherwise your orbit would be unstable.

[Teddio]

A satellite launched in low Earth orbit from the equator in an easterly direction will require the minimum amount of chemical energy from its rocket motors. The satellite will have an initial speed of 1000mph by virtue of its launch direction.
A satellite launched westwards from the equator would need an extra 2000mph of delta v and a polar orbit (used for spy satellites) would need 1000mph.
The ISS and Hubble Telescope are in inclined to the equator but still orbit in an anticlockwise direction (wrt Earth's north pole)

[mibn2cweus]

regarding dundurn's inquiry

sun-synchronous orbit

dawn/dusk orbit

[mibn2cweus]

. . . actually wikipedia casts some light on Sun-synchronous orbits.

[dundurn]

Sounds complicated! Especially the bit about precession. Still unsure about the need to launch East-West, however, since the orbit is essentially a polar one and the terminator which the satellie is riding is not due North-South due to the Earth's axial tilt. I know a lot of the US spy satellites, some of which are in polar orbits, others with relatively high inclinations, are launched to the SW from Vandenberg in California but that's a matter of security as much as anything else. I reckon the same effect could be achieved with a NE launch from Kennedy. Must read more!! Retired yesterday, so as soon as Christmas is over I should have the time!!

[rov1200]

Thanks for all your informative answers. I suppose the boffins know whats going on out there but you do not hear of any mishaps in the general press.