The Earth’s atmosphere causes significant drag. Image credit: NASA/Bill Ingals
Asked by Serena Fox
In order to leave the Earth’s atmosphere a spacecraft needs to be travelling very quickly. In the atmosphere a spacecraft experiences drag, which would slow it down enough and eventually bring it back to Earth. Having a spacecraft leave the Earth’s atmosphere means it can stay in orbit for some time without needing constant thrust from an engine – therefore saving fuel.
To maintain an orbit above the Earth’s atmosphere you need to be traveling thousands of kilometres an hour. The International Space Station sits around 400 kilometres (248 miles) above the Earth, to maintain its orbit it must travel at 27,600 kilometres (17,149 miles) per hour. Even at this height there is still a tenuous atmosphere that erodes the Space Station’s orbit so it must periodically re-boost to a higher orbit to prevent crashing.