China lands a rover on Mars

CHINA WOKE up on May 15th to see a new slogan on its television screens and spreading through its social media: Ni Hao Huo Xing, “Hello Mars”. A few hours previously the Tianwen-1 mission, which has been circling Mars since February 10th, had changed its orbit and dropped a landing capsule into the planet’s atmosphere. Nine minutes later China became only the second country ever to land a rover successfully on the surface of the planet. It is an impressive achievement.The undertaking had not been widely trailed, presumably because the risk that the landing would fail was deemed quite high, and the idea that it might do so publicly unpalatable to the Chinese National Space Administration and the Communist Party. The reticence is understandable. To land, the spacecraft had to decelerate from an orbital speed of 17,000 kilometres an hour; it did so first through friction, blazing through the upper atmosphere like a meteor, then by means of a parachute, then with rocket engines. For this to work properly the initial angle of entry had to be just so, the parachute deployment perfect, and the mechanisms for letting go of the heatshield and, later, the parachute assembly properly timed.