Can ion engines be used to take off from Earth?
No. Ion engines generate a very gentle thrust. SMART-1 will be accelerated just 0.2 millimetres per second per second, with a push equivalent to the weight of a postcard. This is why solar-electric propulsion cannot be used for taking off from Earth – it only works in the vacuum of space. However, once launched, and compared to conventional chemical rockets, which burn for a few minutes, ion engines work for years, or for as long as the solar panels keep providing electricity. Therefore the ion ‘tortoise’ will eventually overtake the chemical ‘hare’.
