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China's Mars leap - A long march
Read more on - Polity | Economy | Schemes | S&T | Environment
- The story: On May 14th, 2021, the Tianwen-1, a Chinese mission orbiting Mars since February 10th, made a subtle adjustment to its trajectory—one that put it on course to hit the planet’s surface six hours later. After three hours, it broke itself in two. One part readjusted its path so as to skim past the planet and stay in orbit. The other, a sealed shell with a heatshield on the outside and a precious cargo within, plummeted on towards the surface at 17,000 km an hour.
- The other part: It entered the atmosphere about 125 km above the ground, blazing like a meteor. Once friction with the air had bled off most of its kinetic energy it deployed a parachute.
- Falling - The shell broke open, revealing a landing platform with four legs, a rocket engine and a six-wheeled rover fastened to its top. The engine ignited. When the platform had just 100 metres left to go it paused briefly, hovering as its sensors looked for obstacles that would impede a safe landing. Then it set itself down in a cloud of red dust on Utopia Planitia, one of the great flat plains of Mars’s northern hemisphere.
- Touch down - Entry, descent and landing (EDL) is historically the riskiest part of any mission to the Martian surface. Every engineering system has to work perfectly. It all has to happen entirely on the basis of onboard data processing and programming, unsupervised by any human being. Mars is currently 320 million kilometres from Earth, meaning radio signals between the planets take 18 minutes to travel each way. By the time the engineers at the Beijing Aerospace Control Centre would know for sure, it'd be all done and dusted!
- A triumph: As news of its arrival reached mission control, Chinese media announced the triumph. The announcement stressed not just the landing itself, but the complete success of the mission it capped. By orbiting and landing on a planet China had never previously visited, Tianwen-1 had become the most successful first mission to Mars in human history. America did not land on Mars until five years after first orbiting it.
- From 1970s to 2020s: Both America’s first orbiter and its subsequent Viking landers made their trips in the 1970s. The Soviet Union managed a landing then, too. But the European Space Agency (ESA) has twice failed at the task, in 2003 and 2016, the second of those attempts a partnership with the Russian space agency, Roscosmos. Getting it right first time definitely ranks as an achievement. In January 2019 China became the first country to put a rover on the far side of the Moon. And in April 2021 it launched the first part of a new space station. A second part is due up shortly.
- Zhurong versus Perseverance: China has some way to go, as the capabilities of Perseverance, the one-tonne lander which America’s NASA deposited at a precisely chosen location in Jezero crater on February 18th, 2021, far outstrip those of the Chinese rover, Zhurong, which is a quarter of the size. Perseverance has the benefit of established orbital infrastructure in the form of the Mars Relay Network, five satellites (three American, two European) that can send high-bandwidth data back to Earth. A reason for Zhurong’s failure to send back pictures until May 19th was that the Tianwen-1 orbiter had to refine its orbit yet again in order to pass on messages.
- Finding ice on Mars: When Zhurong does trundle off its platform and on to the plain, attention will focus on data from its ground-penetrating radar, which is designed to be able to detect ice at depths of up to 100 metres. The distribution of ice is of consuming interest to those who study Mars, defining as it does the limits of the planet’s potential habitability both in its less-arid past and, perhaps, its human-settled future.
- The Mars Subsurface Water Ice Mapping project (SWIM), an attempt to synthesise results from many different approaches to the question, suggests that when Viking-2 scraped the surface at its landing site in another part of Utopia Planitia in the 1970s, its robotic arm may have been within centimetres of permafrost.
- But that was at 48°N. Zhurong’s landing site, at 25°N, is within the Martian tropics, where underground ice is much less likely to persist close to the surface. Unlikelihood, though, is not impossibility—and it would make any icy discovery even more exciting.
- Wild rovers: How far Zhurong will be able to go in search of ice is hard to say. It is similar in size and design to Spirit and Opportunity, two rovers America landed in 2004, and like them it has an official life expectancy of 90 sols (a sol is a Martian day, 40 minutes longer than an Earthly one). Spirit ended up lasting six years, Opportunity 14, over which it travelled 45km. If Chinese engineering is of a similar calibre and its operation teams similarly canny, Zhurong may still have quite a journey ahead of it.
- Summary: China is reported to be planning a sample-return mission, too, for launch around the end of the decade. The space race is definitely on!
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