Extra engine power = faster space travel
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.