Sean's blog

China’s Lunar Lander – did it Crash?

I first saw the video of the Chang’e 3 lunar landing at LiveLeak and have to say I thought it was beautiful: the smooth motion and clear images reminded me of looking out of the window of an aeroplane as it banks while lining up to land at a destination airport. The video is over 6 minutes long at almost 30fps (frames per second – 29.97fps according to mplayer).

The next video I saw was in an article at the Telegraph under the subtitle “Chinese state television releases video of the Chang’e-3 space probe crash landing on the moon”! This second video later made its appearance at Liveleak (“Deployment of China’s Rover on the Lunar Surface”), again at 29.97 fps (perhaps that’s LiveLeak’s preferred transcoding rate?). The ‘crash landing’ in the Telegraph title is repeated in the article text:

The footage shows the surface of the moon getting closer and closer to the probe before it crashes into the dust.

an odd thing to repeat in an article reporting a successful “soft landing”!

The first video’s 6+ minutes does make the landing look almost serene, but I can’t imagine a lander would have ‘hung around’ much – the Chinese Space Agency surely wouldn’t have launched much more fuel into space than absolutely necessary to reach the Moon’s surface? The faster video seems to start at about the same point as 03:47 in the slower video. Touchdown is at 00:22 in the faster video, 06:07 in the slower video, so 22 seconds (fast) versus 140 seconds (slow).

So was it a gentle glide or a terrifying crash? I can’t find a ‘reference’ version on the WWW, perhaps because it’s published in Chinese. If anybody knows how fast the landing was and which one (if either) of the videos portrays the landing correctly, I’d love to know. I’d also like to hear some audio from the Moon. I see a lot of people saying “there’s no sound in space”, but I bet there’s some terrific vibrations from the lander’s thrusters and some great crunching / whining going on in Yutu / Jade Rabbit (the rover)!

[More] A Channel 4 article says

fall from 15 kilometres above the moon’s surface to 2.9 metres above it at a speed of 1.7 kilometres per second

which makes 20 seconds sound about right – if it was a vertical drop (unlikely?) or ‘speed’ has been used in place of ‘descent’.