When man is launched into space, a consideration as earthly as the weather often has the last say on whether the crucial liftoff goes ahead as scheduled. China's second manned space mission is no exception. This morning, weather permitting, the Shenzhou VI orbital module and its two astronauts will be launched by a Long March rocket on their five-day mission.
On the eve of what is expected to be another technological and scientific milestone for China, the expected arrival of a strong cold air mass over the Jiuquan space centre in Gansu province was not the only focus of attention.
The nation was kept waiting until the last moment for confirmation of which pair of the six astronauts shortlisted for the mission were to have the honour of being the country's second and third men in space.
As with the launch of the Shenzhou V space mission two years ago - China's first manned space flight - preparations for the launch were shrouded in secrecy.
The fact that all six astronauts, in three mission-ready pairs, were taken to the space centre for the launch is evidence of meticulous preparations aimed at leaving nothing to chance.
It is a reminder, more than four decades after the former Soviet Union and the United States launched the manned-flight club, that space exploration remains a highly risky enterprise.