# Chang'e 4 lunar rover movement

Recently China has released images of the far side of the Moon taken by Chang'e 4 mission's rover Yutu-2. While pictures are really nice and beautiful, I have stumbled to one rover movement feature which seems interesting to me:

If you look closely, you will see that there are arc-like rover movement paths (painted in red) and also full circles (painted in green color). Now, here comes the question- Why there is such rover curved movement paths with circles instead of just straight-line segments trajectory?

I can only think of a few reasons:

1. Such movement usually occurs in a vehicle when some of wheels are jammed/broken. In such case we can easily explain circles. If for example rover can only turn to one side because of defect in wheels/control system, then it needs to turn 360° around for being able to continue it's journey along planned straight path.
2. Hardware/Software bug in rover apparatus.
3. Deliberate movement in such way for achieving specific goals, such as getting most best panoramic pictures of a view, or for other planned reasons such as checking out the maneuverability of the rover.

I want to believe that true reason is (3), however given that lunar and cosmic missions are very complex and very prone to accidents, (1) and (2) may be also likely. Is there any more information about this?

• Rovers can turn 360 degrees on the spot. The front and back pair of wheels are steerable and can spin in different directions which is the reason why you see a closed circular tire track. – Star Man Feb 12 '20 at 23:07
• The main issue are not the circles, but why rover moves like a drunkard in arc-like segments ? – Agnius Vasiliauskas Feb 13 '20 at 8:33

## 1 Answer

I grabbed a couple pix from SkyAndTelescope which may help.
On a macro scale, you can see that the path is chosen to avoid craters and whatnot:

This next one is a better version of what you posted, and again it looks like the tracks are avoiding various craters or small dips in the landscape:

• I agree about macro scale, but here we are more concerned about mini-scale. However you have found an interesting picture, which shows that rover if required can perform a sudden $90°$ turn, not only arc-like ones. And indeed with this right angle turn it probably tries to avoid a couple of holes. Still after that it does again arc-turn later. But this time I don't see clearly what it tries to avoid. I think there is additional arc path reason - the ergonomic one(s). Probably it tries to change direction gradually, instead of sharp turns. – Agnius Vasiliauskas Feb 13 '20 at 13:21