"Farewell to Yutu"
February 12th, 2014
By now, it seems almost certain that China's Yutu Moon rover has died a premature death in the cold lunar night. The rover has been exposed to sunlight for a few days, and there has been no word of it waking up.
Yutu was carried to the Moon aboard China's Chang'e-3 Moon lander, a boxy structure reminiscent of the base of an Apollo lunar lander from the 1960s. Chang'e-3 made history by becoming China's first mission to land on the Moon, and the first object to softly land there in more than three decades.
Yutu's problems began roughly three weeks ago when a solar panel failed to fold inwards over the rover's body, just before night fell at the rover's landing site. The folding panel was designed to protect the rover's interior during the two-week lunar night, by trapping heat from a radioisotope source. Without this protection, the rover's electronics have apparently frozen.
China had originally expected Yutu to function for roughly three months. The failure of Yutu after less than a month of nominal surface operations is a disappointment.
Apart from mourning its loss, the major priority for China's space program will be conducting a post-mortem for Yutu. It is vital to know how it malfunctioned. Fortunately, there seems to be a lot of data that was obtained before night fell.
We know that the solar panel did not close. We can easily deduce how this affected the thermal protection for the rover. Much work will need to be performed to work out exactly why this mechanical failure occurred in the first place.
Moving parts are always tricky for spacecraft. Getting them to work on the Moon is even more difficult. Apart from the vicious cycles of heat and cold, there is the ever present problem of dust. We do not know if the hinges were jammed by dust, or if there was a failure of the motors or mechanisms designed to close the panel for some other reason. Lubricant could have been worn away from some part, causing friction or even a "cold welding" of metal surfaces in a vacuum. China will probably be conducting simulations to determine the most likely cause.
With Yutu's case file certain to close in the near future, it will be time to consider the fate of China's next Moon mission. China has already built a back-up lander, dubbed Chang'e-4, which it planned to launch in a few years. This is a typical strategy of China's lunar exploration program: Two identical spacecraft are built in case one fails.
China's first lunar mission, Chang'e-1, was launched to orbit the Moon in 2007. The mission was a complete success. Thus, China decided that its back-up spacecraft, Chang'e-2, would not precisely repeat its predecessor's mission. It was launched in 2010 with a more powerful rocket that helped the spacecraft to save its fuel reserves. Chang'e-2 was sent on a shorter mission to the Moon and then flown into deep space to fly past the asteroid Toutatis.
This time, China will probably need to use the back-up lander to repeat the tasks that Chang'e-3 failed to complete. There will probably be an overview of the design of some of its most critical components, to strengthen them against failure.
This analyst expects that China will want to land a second rover with this mission, but we can expect that it will be thoroughly overhauled. China will want to ensure that the solar panel will not fail again, and will probably look for other potential problems. The next rover will probably look the same as Yutu but it will be improved.
Exactly when Chang'e-4 will launch is unclear. The problems experienced by this latest mission suggest that China will want to take a fair amount of time for troubleshooting, redesign and testing. Any previous speculation on the approximate launch time is probably no longer reliable.
We will need to wait for China to advertise a new launch timetable. In turn, this could affect the fate of the two lunar landers that are expected to come after Chang'e-4. These missions, dubbed Chang'e-5 and 6, are sample-return missions. It could take longer to launch them, and their design could be revised in the wake of the Yutu investigations.
Whatever China does with its second rover, one change should be suggested. The rover needs a new name. China should remember that saying "Yutu 2" in English sounds stranger than it does in Chinese!