Chang'e 3 landing and first lunar day of operations, Including landing site geology and localization Options

[dvandorn]

There was this descent camera image taken after landing, showing a footpad at far right. The camera on top of the lander can't see the footpads.

Phil

Oh, yes -- a sliver of the footpad is visible, and the ground around it is in deep shadow.

I guess what I was noting was a difference in philosophy between the American (and to a somewhat lesser extent Soviet) engineers and the Chinese engineers. On American unmanned landers, the cameras were specifically positioned to provide initial images of a footpad on a lighted surface. The Chinese did not specifically position their cameras to be able to do this.

I'd bet this is a sign of confidence in the current knowledge of surface conditions. On Surveyor, the flight engineers wanted an initial confirmation that their craft was planted firmly on the surface. The surface conditions were far less well known at that time, and an image showing the footpad firmly on top of (not hanging above and not sunk deeply into) the surface was an important confirmation of the potential for successfully completing the mission.

The Chinese, on the other hand, are starting out with a far better operating knowledge of the surface conditions, and with more sophisticated IMU-based navigation than was available to early Luna and Surveyor craft. Therefore, there is less of an urgency to position a camera just so it can give you a confirmation that a footpad is firmly resting on the surface. Other imaging priorities come in to play, and hence you don't get the classic footpad shot.

Again, just an observation.

-the other Doug

[Marvin]

The only dynamic I can think of that would preferentially throw soil outwards from each pad would be one where the gear actually flexed outward, away from the octagonal lander body, at touchdown and then recoiled back to their normal deployed position. As the gear and struts look rather similar to the Apollo LM arrangement, this doesn't sound like something they would be designed to do.

Just an observation...

-the other Doug

When I first saw the lander, only one pad was visible and I thought it may have bounced or skidded. But now that we can see more of the pads, I think you're right in describing what happened.

It was also intentional. According to spaceflightnow, "Chinese officials said they designed the craft's landing sets with impact suppressors similar to shock absorbers."

http://spaceflightnow.com/china/change3/13...g/#.UreIr7RjLnQ

[bobik]

Quite informative article about the lunar dust experiment on Chang'e 3 (in Chinese)

[kenny]

The only dynamic I can think of that would preferentially throw soil outwards from each pad would be one where the gear actually flexed outward,
away from the octagonal lander body, at touchdown and then recoiled back to their normal deployed position. As the gear and struts look rather
similar to the Apollo LM arrangement, this doesn't sound like something they would be designed to do.

The Apollo pads were on a ball-and-socket joint on the end of the legs, so they could swivel and conform to any orientation of surface upon landing.
I wouldn't be surprised if the Chinese adopted this aspect of the design also, as they appear to have copied the rest of the Apollo strut/ leg arrangement.

So the quick flipping of those rotating pads upon impact would be the simplest explanation for throwing the dirt.

I noticed those clumps too, and was thinking it's a pity they didn't photograph them more closely from the Rover. A good chance to make an observation
about soil dynamics and granularity. See also how deep the tracks gouged into soft soil where Yutu did its turn in front of the lander.

[djellison]

and was thinking it's a pity they didn't photograph them more closely from the Rover...

They may very well have done so - I'd think we've seen only a tiny fraction of the total number of images taken.

[pospa]

Yutu's robotic arm successfully deployed (in Chinese) http://www.chinanews.com/gn/2013/12-23/5653502.shtml
Night hibernation will start around Dec 26th and lasts about two weeks.

[SFJCody]

Haven't seen this pic posted previously.

http://roll.sohu.com/20131223/n392264881.shtml



There also seems to be some new footage in this youtube video:

https://www.youtube.com/watch?v=R9qhPWbwwhc

[walfy]

I'm surprised they haven't immediately pounced on the rocks, soil just in front of them on the crater edge to at least get some observations with the instruments. One never knows when our robots decide to shut down for good! Perhaps it bespeaks of great confidence with the health of the machine.

[Explorer1]

Amazing how far the mast can 'lean' forward; though it doesn't tell us how far it can tilt up. An Earth image from either lander or rover would be astounding....

[Thorsten Denk]

The most urgent usually is taking a picture of the flag...

Night hibernation will start around Dec 26th and lasts about two weeks.

CalSky gives the following table for physical ephemeris:

Date: 2013, Dec 26:
Time Sub-Solar
UTC ..... Lat Lon
hh:mm .... o .... o
13:00 +1.32 251.1
13:15 +1.32 251.0
13:30 +1.32 250.9
13:45 +1.32 250.8
14:00 +1.32 250.6
14:15 +1.32 250.5
14:30 +1.32 250.4
14:45 +1.32 250.2
15:00 +1.32 250.1
15:15 +1.33 250.0
15:30 +1.33 249.9
15:45 +1.33 249.7
16:00 +1.33 249.6

Hence sunset should be centered around 14:15 UTC on Dez 26
(not taking into account the solar latitude ≠ 0).
And the subsequent sunrise will be around 09:00 UTC on Jan. 10.

Hope I'm not wrong.
Thorsten

[ugordan]

An Earth image from either lander or rover would be astounding....

... or underwhelming, depending on the angular resolution of the cameras...

[Hungry4info]

Amazing how far the mast can 'lean' forward; though it doesn't tell us how far it can tilt up.

Since the mast was originally stowed in the body of the rover (and can return there for lunar night?), I assume it can look "up" high enough to see Earth.

[Reed]

I assume it can look "up" high enough to see Earth.

Given that the HGA is fixed to the same mast, it better be able to aim at the earth

This suggests there should be earth photo ops every com pass, but perhaps they are still relaying through the lander? (edit: or the results are underwhelming as ugordan suggests)

[dvandorn]

Remember that the eye needs something to put an image into scale to make it appear impressive. Consider that while there are many images of Earth from cislunar space and lunar orbit, it's the ones framed against the lunar horizon that get put on postage stamps...

As Chang'e's landing site is at 45 degrees north and about 20 degrees west, I'd think that the Earth is no lower than about 45 degrees up in the sky at any given time. An image captured of it using Yutu's camera would likely show only the Earth, and nothing of the horizon below. In that way, it would be indistinguishable from a picture taken of Earth from lunar orbit which also included no portion of lunar surface in the frame. Just another pic of Earth from a lunar distance, nothing really special.

Now, if Yutu pulls up against a nice-sized piece of surface relief, spotting the Earth as it sits above a peak, or a rock, could be a dramatic shot. Not seeing anything in the near vicinity that would fill that bill (except maybe for heading down into a deep crater), I dunno when we might see that kind of photo op.

-the other Doug

[mcaplinger]

An image captured of it using Yutu's camera would likely show only the Earth, and nothing of the horizon below.

I could fix that problem in Photoshop in about 5 seconds

I tried to figure out how many pixels across an Earth image would be, but couldn't find the focal length or the FOV of these cameras. That could be guessed from the sizes and ranges of the hardware, but I'm too lazy.