Ever wondered what happens inside the International Space Station during a reboost? ESA astronaut Tim Peake filmed inside during last week's firing of the Progress thrusters.
Even at 400 km, there are still enough molecules of the atmosphere to create some 'atmospheric drag', which causes the Station to drop by about 2 km a month. Because of this we need to raise the Station's orbit every so often. On 17 February the engines of the Progress M-29M spacecraft that is docked to aft port the Zvezda module were fired for 11 minutes.
The burn primarily focused on raising the Station’s perigee, making the orbit more circular.
Pre-reboost: 398.2 x 407.4 km - inclination 51.64° - Period: 92.62min
Post-reboost: 402.1 x 406.9 km - inclination 51.64° - Period: 92.66min
More about the Principia mission: http://www.esa.int/principia