
Chinese rover powers up devices in pioneering moon mission - dnetesn
https://phys.org/news/2019-01-chinese-rover-powers-devices-moon.html
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Baeocystin
Does anyone know why a halo orbit was chosen for the relay sat instead of a
regular, lunar orbit?† I know that due to the moon's lumpy gravitational
field, there are only a few stable orbits available, but anything orbiting a
Lagrangian point is going to require stationkeeping adjustments regardless,
right?

†I understand that that would put the lander out of contact during that part
of the relay-sat orbit, but it would also completely rule out a major source
of potential radio interference during observational periods, which strikes me
as an even more important consideration. Data can be stored and batched, after
all.

~~~
snops
I think orbiting around L2 would ensure the satellite was at a higher angle in
the lunar sky for most of the time, and hence the lander can be in contact for
longer, as low angles may be blocked by boulders or crater walls etc. The
radio to the satellite would normally use high frequencies so you can have a
focused beam for power saving, so it needs to be line of sight. You could
transmit faster, but this would take more power.

In addition, there is a little rover[1]. NASA rovers since Pathfinder have had
some automated driving, I imagine the Chinese can easily do the same, but
manually steering is still nice and hence the rover is more useful if you can
be in "live" contact with it for longer.

[1]
[https://en.wikipedia.org/wiki/Chang%27e_4#Yutu-2_rover](https://en.wikipedia.org/wiki/Chang%27e_4#Yutu-2_rover)

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craz8
The article you linked makes it clear why L2 was chosen - this orbit allows
_continuous_ communication between Earth and the lander. If the satellite was
_at_ L2, this would not be the case, as the moon would be in the way, so it
has to be far enough away to see both the lander location and Earth at the
same time

Also, orbiting the moon would give you coverage much less than half the time,
and you’d need to track the satellite across the sky from the lander

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superkuh
Just to be clear here because all the press releases are intentionally
ambiguous about it: the only serious radio astronomy instruments are the
Netherlands-China Low Frequency Explorer (NCLE) package on the relay sat in
the L2 halo orbit _always_ in line of sight of Earth. Not the lander, not the
rover. The relay sat there is the step towards lunar far side radio astronomy
but so far that is not actually going on.

It's a cool instrument in that it's antenna are stored as a flat roll but
extend out as hollow, rigid tubes.

~~~
dane-pgp
The article says:

"Harvard University astronomer Avi Loeb noted, however, that the relay
satellite needed to send back information from the far side also contaminates
the sky."

Does that mean the international community needs to agree a protocol to
establish periods of radio silence for objects on the far side of the moon,
and for lunar orbiting satellites, so as not to interfere with future radio
astronomy instruments?

~~~
superkuh
I don't think it is that serious yet but hopefully in time we will need to
create ITU region 4,
[https://en.wikipedia.org/wiki/ITU_Region](https://en.wikipedia.org/wiki/ITU_Region)
. The link back to Earth is relatively narrow beam width and it's doubtful a
simple dish/feed setup has significant sidebands and even then at only a
couple frequencies (probably ~7-8 GHz and ~2 GHz).

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Havoc
What's with the rubbish photo quality?

This is 2019 after all and I'm pretty sure the Chinese know a thing or two
about manufacturing cameras.

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JumpCrisscross
> _What 's with the rubbish photo quality?...I'm pretty sure the Chinese know
> a thing or two about...cameras_

The Chinese also know a thing or two about power budgets, bandwidth
limitations and optimising between function and vanity. Low quality rover
photos show they’re optimising for function, not propaganda value. That’s
good. (They’re also awesome pictures.)

~~~
emilfihlman
Just no.

The issue is not power budget, bandwidth or optimisation between function and
vanity. Moon has plenty of sunlight, the bandwidth on an Earth-Moon link is
very good and there's really no difference between vanity and function in
terms of implementation here.

The real reasons here are a) the Space Grade™ plague, b) radiation hardening
and durability and c) limited value in high quality photos.

non-web engineering on big total budget but limited per part projects is very,
very conservative.

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JumpCrisscross
> _the bandwidth on an Earth-Moon link is very good_

The rover is on the far side of the moon. It relies on a single relay
satellite at the Earth-Moon L2 [1]. This relay satellite had to be installed
specifically for this mission.

> _Moon has plenty of sunlight_

Spaceflight is expensive. Every watt for a better camera means a watt away
from scientific equipment. Power on such missions is micromanaged by
necessity.

The functional purpose of the camera is in assisting dis-mounting and post-
dismounting inspection. It did that. It also sent home good pictures.

[1]
[https://en.m.wikipedia.org/wiki/Chang%27e_4#Components](https://en.m.wikipedia.org/wiki/Chang%27e_4#Components)

~~~
TeMPOraL
> _Spaceflight is expensive. Every watt for a better camera means a watt away
> from scientific equipment. Power on such missions is micromanaged by
> necessity._

Also every watt that you can add to the system without taking it away from
something else is another watt you need to radiate away after it's done its
job. Thermal management is paramount in space missions.

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jstanley
Where's the best place to go to look at more pictures from this?

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newnewpdro
The lunar surface is more brown in these photos than the ones from Apollo,
which is more accurate?

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Theodores
Your comment reminds me of comments made about the colour of Mars. Allegedly
it wasn't red enough and looked too much like Arizona so - allegedly - they
made it to the expected red colour and kept this up over a series of missions.

This does not answer your question, however, 'white balance' is a thing when
it comes to space.

~~~
newnewpdro
That's funny, but this is a little different since I'm comparing it to the
Apollo mission photos.

The last thing I expected to see was a brownish lunar surface, considering one
of the most notable things about the Apollo photos is their B&W appearance
except for the lunar lander and american flag colors.

[https://www.flickr.com/photos/projectapolloarchive/210374815...](https://www.flickr.com/photos/projectapolloarchive/21037481544/in/gallery-
flickr-72157659397648815/)

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daniel_iversen
That picture with all the brown dirt totally looks like it was taken on a
desert here on earth ;)

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newnewpdro
China faked the landing, it's propaganda. (I'm at least half joking)

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Entangled
I've been combing the web for new pics but have found nothing. Anything new?

