Equatorial Rocket Launches

I heard once that it's better to launch rockets into orbit closer to the equator. Can you explain why?
- question from name withheld
It is better to launch rockets closer to the equator because the Earth rotates at a greater speed here than that at either pole. This extra speed at the equator means a rocket needs less thrust (and therefore less fuel) to launch into orbit.

You can better understand this speed differential by thinking of the Earth as a basketball being spun on your finger. The rotational speed of the ball at the surface is minimum along its axis (i.e. the "poles") and maximum along the circumference that is farthest from the poles (i.e. the "equator). So the closer to that line that a rocket is launched, the more you can take advantage of the greater speed to get into orbit.

In addition, launching at the equator provides an additional 1,036 mph (1,667 km/h) of speed once the vehicle reaches orbit. This speed bonus means the vehicle needs less fuel, and that freed space can be used to carry more payload.

This line of thinking explains the launch locations selected by the US, Russia, and European Space Agency. ESA has been most blessed since it was able to construct a site very near the equator at Korou, French Guinea thereby maximizing the benefits of increased equatorial launch speeds. Both the US and Russia also built facilities as far south as possible within their national boundaries. NASA's site at Cape Canaveral, Florida, is at 28.5° north latitude which yields a free 915 mph (1,472 km/h) speed bonus. Russia was able to go no further south than the Baikonur Cosmodrome in Kazakhstan, however, which is located at 45.6° north latitude. Launching at this location provides only an additional 730 mph (1,174 km/h).

A final point to make is that this speed bonus also explains why rockets are launched towards the east. Since Earth rotates west to east, launching an orbital satellite in that direction maximizes the effect of the rotational speed bonus. The only rockets for which this is not true are those going into polar orbit which launch towards the west. This explains why all US polar launches are done from Vandenburg Air Force Base in California rather than from Florida.
- answer by Aaron Brown, 9 June 2002

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