What the Chinese Moon landing teaches us about American lunar orbiter


It’s probably because I really don’t know nearly enough about the moon and LADEE but what I got from Rick Elphic’s text is ‘our probe was too far from the landing site to be able to detect anything really’. Which isn’t a bad thing, you can’t expect to monitor anything when it’s out of the range of your equipment.

Two questions, though.
This reads like NASA knew the position of the landing site at least roughly in advance. Was that from tracking the probe’s flight and calculating predictions?
The LADEE’s orbit isn’t a secret. Was the landing site (among other reasons like playing it safe, fuel, etc.) maybe chosen deliberately not too close to LADEES observational range?

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Or maybe NASA’s orbiter just isn’t very good.

I assumed that the Chinese made that information public long before the mission.

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So the Chinese didn’t land on the moon either?

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Why the heck would you assume that? AFAIK, China doesn’t make much of anything about its space program public beforehand.

The moon has a tenuous atmosphere that continually escapes and is being replaced by other particles from the sun and elsewhere. A landing probe might be expected to kick up dust and turn over surface material, releasing stuff to the atmosphere. The escape velocity of the moon is 2.4 Km/sec, so it is likely that most of the solid stuff might fall back, but most models might predict the gases would hang around for a bit, and LAYDEE could detect them.

It turns out that LAYDEE did not detect them. This does not mean that LAYDEE does not work or it was in the wrong position ‘too far from the landing site’: it was in a position where the best models of the day predicted a detectable signal, so not finding one is a significant result.

‘Significant’ is not the same as ‘important’. It adds a bit to human knowledge. It prompts us to get in closer the next time do a similar experiment, Every little bit of extra data helps a bit. But please take any ‘scientists are baffled’ ‘this re-writes everything’ hype with a pinch of NaCl.

Without looking too hard, here’s an article from 2010, shortly after the launch of Chang’e-2, saying that the probe’s primary objective is to map out the Bay of Rainbows which is where they plan to land Chang’e-3:

[quote]Wu Weiren said Chang’e-2 would take high-resolution photos of the moon’s Bay of Rainbows area, the proposed landing ground for Chang’e-3.

Wu said four to five areas had been chosen for a landing ground for Chang’e-3, but the Bay of Rainbows would be the first choice.[/quote]

This is followed a month later by an article about the reveal of a Bay of Rainbows map from Chang’e-2 in a fancy ceremony. I don’t know if technical details of the mission were publicly released in the way that NASA tends to do that, but the basic information hasn’t been kept secret at all.

LADEE’s equatorial orbit is part of the mission design because Lunar atmosphere should be thickest around the equator. Wikipedia suggests that the design may have been around as early as 2008, but it looks like LADEE suffered some delays, so it’s rather doubtful that either NASA or CNSA would have expected at the time that the two missions would launch just a few months from each other in 2013.

Ah. So the model(s) used was flawed at some point, back to the whiteboards…
Question is, which part(s) of the model needs to be adapted. Could the surface dust in the landing area have different properties as assumed in the model?

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