Sophie Flett, of Milton School, asks :-

Do we need to orbit a planet before landing on its surface?

Marlyn Jakub, a physicist at Otago University, responded.

Not always. However, there are several advantages in establishing an orbit before landing, as an orbit may be useful in solving the difficult problems of landing a vehicle on the surface of a planet.

In the trips to the Moon, which has no atmosphere, a Lunar Lander vehicle separated from the orbiting spaceship. By having a smaller vehicle for the actual Moon landing, less rocket fuel was needed to slow the landing vehicle, and later, less fuel was needed to lift it off and power it back into Moon orbit to rejoin the orbiting vehicle.

When a gaseous layer surrounds the planet, for example Earth, the friction of the gases and the high speeds associated with your spaceship would cause your ship's outside surface to become heated, usually to temperatures which make metals glow at least yellow-hot. These heated outside surfaces must be protected with special materials, such as the tiles on the Space Shuttle, to prevent the space craft and yourself burning up.

When the spaceships returned from the Moon to the Earth, there was no Earth orbit established. The re-entry vehicle used a shallow entry angle path to ensure that the spaceship did not enter the Earth's atmosphere too quickly and burn up. The entry angle also could not be too small, otherwise the spaceship might tumble or skip off the atmosphere, much as a flat stone skips off water.

Most meteorites and other objects entering the Earth's atmosphere do not have the necessary combination of slow speed and shallow angle of entry, so they burn up in the outer atmosphere before they can impact the Earth's surface. At night you may see these 'shooting stars' as they burn up.