China’s ambitious Chang’e-7 mission was ready for launch. The spacecraft had been rolled out to the launch pad atop a powerful Long March 5 rocket, with liftoff planned for Monday morning. Yet, just before launch, China postponed the mission by an entire year.
The reason highlights one of the most difficult realities of lunar exploration: being ready to launch is not enough. You also need the Moon, the weather and orbital mechanics to cooperate.
Chang’e-7 is headed for one of the most extreme locations in the Solar System, the Moon’s south pole.
Its primary objective is to investigate permanently shadowed regions where water ice may have survived for billions of years. But reaching and landing near these regions requires an extremely precise trajectory.
The immediate problem was weather around the Wenchang Space Launch Site in southern China. Unfavourable atmospheric conditions can pose risks during the ascent of a heavy-lift Long March 5 rocket.
Strong winds, thunderstorms and other adverse conditions can force a launch scrub even when the rocket and spacecraft are technically ready.
However, the bigger challenge was the launch window.
Unlike missions heading into Earth orbit, Chang’e-7 cannot simply launch on any convenient day after the weather improves. The spacecraft’s journey to the Moon and its eventual landing must be timed to ensure the correct lighting conditions at its intended landing site.
The lunar south pole is particularly challenging because sunlight arrives at extremely low angles. The mission must ensure that its lander has sufficient illumination for solar power while also allowing instruments to investigate nearby permanently shadowed areas believed to contain water ice.
A delay of even a few days can therefore disrupt the carefully planned sequence of Earth departure, lunar arrival and landing conditions. Missing the optimum window may mean waiting for another suitable combination of orbital geometry and illumination.
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