BLOOSTAR

he most demanding part of an orbital launch is not reaching 28,000 kilometres (17,400 miles) per hour in space, but powering through the thick lower atmosphere; this uses a significant part of a rocket’s propellant load and puts stress on the craft. Around 80 per cent of Earth’s atmosphere is in the first 11 kilometres (6.8 miles) of altitude – the height jet airliners fly at – and aerodynamic drag, the force pushing back on the rocket as it flies,