Ex­tra engine power = faster space travel

Science Illustrated - - SPACE -

A jour­ney from A to B is easy to plan on Earth, as the two lo­ca­tions on the map do not move in re­la­tion to each other. In space, it is not that sim­ple.  In the So­lar Sys­tem, all plan­ets are or­bit­ing the Sun at high speeds. As Earth’s or­bit speed is about 30 km/s, all rock­ets au­to­mat­i­cally be­gin their jour­ney at this speed. If the rocket is go­ing to Mars, which is fur­ther away from the Sun than Earth, the en­gines must in­crease the or­bit speed, al­low­ing the rocket a new el­lip­ti­cal or­bit around the Sun, which crosses Mars’ or­bit. But as Mars or­bits more slowly than Earth, the rocket might travel too fast for the planet’s grav­i­ta­tional field to cap­ture it. It is ex­pen­sive to equip the rocket with fuel for brak­ing, so as­tro­physi­cists of­ten plan So­lar Sys­tem mis­sions via Hohmann trans­fer or­bits, i.e. el­lip­ti­cal or­bits, which reach the point fur­thest away from the Sun where the des­ti­na­tion is, so the rocket is slowed down as much as pos­si­ble by the Sun’s grav­ity, when it ar­rives to the planet.

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