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In Florida (28 degrees north) the earth surface travels at 400 m/s eastwards. (earth circumference * cos(28) / day) A spacecraft that would launch from the gro

In Florida (28 degrees north) the earth surface travels at 400 m/s eastwards. (earth circumference * cos(28) / day) A spacecraft that would launch from the ground and start westwards, would, after gaining the first 400 m/s relative to its starting point only be stationary relative to the earth's center. Then after 800 m/s, it would travel at 400 m/s westwards. Say if your orbital velocity is 8.0 km/s. Your total delta vee would be 8.4 km/s. In comparison, an eastward flying rocket would start from 0.4 km/s , and would need rocket propulsion only for the remaining 7.6 km/s. A 10% saving compared to the westward rocket! In reality it's a bit more complex as you don't launch straight east or west anyway, and ISS is at a 50 degree inclination etc...

peeters 12y ago
Exactly, and this is maximized by putting launch sites close to the equator. This is one reason why the European Space Agency launches from South America, by the way: > Kourou lies at latitude 5°3', just over 500 km north of the equator. Its nearness to the equator makes it ideally placed for launches into geostationary transfer orbit as few changes have to be made to a satellite’s trajectory. > Launchers also profit from the ‘slingshot’ effect, that is the energy created by the speed of the Earth’s rotation around the axis of the Poles. This increases the speed of a launcher by 460 m per second. These important factors save fuel and money, and prolong the active life of satellites. http://www.esa.int/Our_Activities/Launchers/Europe_s_Spaceport/Europe_s_Spaceport2 http://www.esa.int/Our_Activities/Launchers/Europe_s_Spacepo...