China to land probe on the far side.

[Zakalwe]

Apart from the annoying "dark side" SNAFU, then this is a tidbit of really interesting news


http://news.xinhuanet.com/english/2016-01/15/c_135010577.htm

Any bets for the nationality of the next person to step on the Moon?

[bknight]

Apart from the annoying "dark side" SNAFU, then this is a tidbit of really interesting news


http://news.xinhuanet.com/english/2016-01/15/c_135010577.htm

Any bets for the nationality of the next person to step on the Moon?

It won't be an American for sure.

[Ishkabibble]

I haven't yet seen any discussion or information about a very important piece of information.

At some point, when entering lunar orbit, there is LOS. Because any communications, whether they be by laser, or by radio have to have line-of-sight in order to be receivable. So if they're going to the far side, unless they put a communications satellite at a LaGrange point near the moon, or in high lunar orbit, how are they going to get any information back?

I'd bet that this is the first of the landing site scouting missions. If they're on the far side, nobody can see what they're doing, unless a big program to put more recon satellites in orbit is instituted. They can fail, and nobody will know it until it is all over.

Regarding the "dark side" thing... Every single image I have ever seen of that other side of the sphere appears to show that the far side of the moon seems to have much darker regolith and surface features. Maybe they meant "dark-ER side" and just left off the "er"... 

[onebigmonkey]

To be fair, they did only say 'dark side' once, the rest of it is 'far'

Don't they still have a probe floating out there somewhere?

[gwiz]

Regarding the "dark side" thing... Every single image I have ever seen of that other side of the sphere appears to show that the far side of the moon seems to have much darker regolith and surface features. Maybe they meant "dark-ER side" and just left off the "er"... 

Not really.  The far side is more mountainous, with hardly any mare regions.  Mare regions are darker than mountains, so on average the far side is lighter than the near side.

[smartcooky]

Regarding the "dark side" thing... Every single image I have ever seen of that other side of the sphere appears to show that the far side of the moon seems to have much darker regolith and surface features. Maybe they meant "dark-ER side" and just left off the "er"... 

"There is no dark side in the moon, really. Matter of fact, it's all dark. The only thing that makes it look light is the sun."

Roger Waters (Pink Floyd) 1973

Actually, I think the "dark" side of the mood actually looks lighter

[bknight]

Regarding the "dark side" thing... Every single image I have ever seen of that other side of the sphere appears to show that the far side of the moon seems to have much darker regolith and surface features. Maybe they meant "dark-ER side" and just left off the "er"... 

"There is no dark side in the moon, really. Matter of fact, it's all dark. The only thing that makes it look light is the sun."

Roger Waters (Pink Floyd) 1973

Actually, I think the "dark" side of the mood actually looks lighter

Indeed as the moon receives sunlight as it rotates during its orbit.  When the "new moon" is visible to the Earth the Sun is nearly inline with the Moon/Earth Illuminating the side we don't see.

[Ishkabibble]

Apparently, everyone missed the  I had at the end of my post.

Note to LO: Is there a way that we can make emoticons about 10-15 times bigger than they are? 

[bknight]

Apparently, everyone missed the  I had at the end of my post.

Note to LO: Is there a way that we can make emoticons about 10-15 times bigger than they are? 

  I saw it.

[Ishkabibble]

And still went to the trouble to be scientific about it, without recognizing the facetiousness... 

What does a guy have to do around here to be allowed to poke fun at the writer of an article? 

[ka9q]

So if they're going to the far side, unless they put a communications satellite at a LaGrange point near the moon, or in high lunar orbit, how are they going to get any information back?

That's just it. My choice would be a relay satellite in a "halo" orbit around the earth-moon L2 point. You'd want to use a halo (instead of just sitting at L2) because otherwise the moon would permanently block it from seeing earth.

There's a similar reason why the spacecraft "at" the earth-sun L1 point are actually in halo orbits around it: otherwise the spacecraft would appear directly in front of the sun as seen from earth, and the sun's radio noise would make it difficult to hear.

[Ishkabibble]

So if they're going to the far side, unless they put a communications satellite at a LaGrange point near the moon, or in high lunar orbit, how are they going to get any information back?

That's just it. My choice would be a relay satellite in a "halo" orbit around the earth-moon L2 point. You'd want to use a halo (instead of just sitting at L2) because otherwise the moon would permanently block it from seeing earth.

There's a similar reason why the spacecraft "at" the earth-sun L1 point are actually in halo orbits around it: otherwise the spacecraft would appear directly in front of the sun as seen from earth, and the sun's radio noise would make it difficult to hear.

I suppose they could put a relaysat in lunar polar orbit, but they would have to put it at a high altitude, else they could only land at points close to the "edge" of the far side. I don't really know how to explain what I'm thinking, other than to imagine a flat image of the far side, and land along the "edges" that still have line of sight to a polar orbiting relaysat.

[Dalhousie]

Nice summary here:

https://theconversation.com/chinas-plan-to-be-first-to-far-side-of-the-moon-could-unveil-inner-lunar-secrets-53253

This Chinese website mentions the SPAB and has a drawing of a relay satellite based on Chang'e 1 and 2, with a large Galileo-style antennae.

http://www.guokr.com/post/716318/

Worth remembering that there will be a sample return mission before this, sometime next year.  There is probablygoing to be a follow-up to this, so maybe that too will go to the far side in about 2020.

[bknight]

That's just it. My choice would be a relay satellite in a "halo" orbit around the earth-moon L2 point. You'd want to use a halo (instead of just sitting at L2) because otherwise the moon would permanently block it from seeing earth.

There's a similar reason why the spacecraft "at" the earth-sun L1 point are actually in halo orbits around it: otherwise the spacecraft would appear directly in front of the sun as seen from earth, and the sun's radio noise would make it difficult to hear.

I was going to ask what is  halo orbit until I read the link in Dalhousie post.
I don't understand

"However, this can be solved by causing the relay satellite to follow a “halo orbit” around the L2 point. "

how is this accomplished?

[ka9q]

The Lagrange points are where the gravitational potential gradient is zero in an orbital system with two massive bodies. In English, those are points in space where the gravity of the two objects (e.g., the sun and the earth, or the earth and the moon) cancel and you can stay there more or less indefinitely.

There are 5 such points, numbered L1 through L5. L1 is along the line between the two bodies where their gravitational attractions match. The earth-sun L1 point, about 1.5 million km toward the sun from earth, is now well used; the most recent addition to the fleet there is DSCOVR, the spacecraft that returned that great sequence of the moon moving past the earth last summer. It joins ACE, SOHO and a bunch of others.

But none of the spacecraft are actually at the L1 point, because that would put them right in front of the sun as seen from earth. The sun generates radio noise, and this would interfere with reception of the satellite's signal. So they are slowly moved around the actual L1 point so that, from earth, they appear to slowly circle the sun, far enough from it that the dish antennas on earth can exclude the sun. (I think it's once per year, but I'm not sure). It does take fuel to do this, but with careful planning you can keep station for years. That's a halo orbit.

The L2 point is on the same line but not between them; it's closer to the smaller body. Similarly, L3 is on that line but closer to the larger body. (There was once a whole genre of science fiction about a "parallel earth" situated at the Sun-Earth L3 point, placing it permanently on the other side of the sun where we cannot see it. Unfortunately, our fantasies were dashed when our spacecraft saw nothing there, just as they show a lifeless, desolate desert on Mars, and an uninhabitable hell on Venus...)

L4 and L5 are in the orbit of the smaller body, 60 degrees behind and ahead of it (or maybe it's ahead and behind, I can never remember). These are the only two Lagrange points that are dynamically stable, i.e., you could put a rock there and it would stay indefinitely. The other three are metastable, kind of like balancing on a fence; it takes active control to stay there, but as long as you keep fairly close it doesn't take much energy.