Author Topic: LIVE: Chang'e-3 lunar probe and rover, CZ-3B - Xichang - December 1, 2013  (Read 316229 times)

Offline Apollo-phill

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I found this information by members from the National Laboratory of  Space Intelligence Control,
Beijing Institute of Control Engineering in an Abstract of a  paper on "AUTONOMOUS NAVIGATION AND CONTROL  FOR PINPOINT LUNAR SOFT LANDING".

This probably refers to spacecraft of the Change'3 class ?

Attitude control and orbital manoeuvres by a set of thrusters and main thrust engine.

Attitude and orbit determination and hazard detection by star sensors, inertial measurement unit (IMU), altimeter, velocimeter, sun sensors and  lunar imaging sensors.

Orbit control adopts a throttleable thrust explicit guidance and gravity turn guidance .

Measurement data from three dimensional (3D) imaging sensor and a visible imaging sensor are combined for faster autonomous hazard detection at the landing zone. Hazard avoidance manoeuvres are performed by fast,open-loop control and pinpoint closed-loop  control.

Main operational modes for the GNC are powered descent , attitude adjustment, hovering and hazard avoidance and the terminal landing.

Looking forward toward this weekend's Change'3 descent to the lunar surface in the Bay of Rainbows and Yutu rover deployment.


Phill Parker

Offline jumpjack

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dropping the last 4 feet seems risky... how does this compare to other lunar landings? I didn't think the Apollo LEM cut engines that high up at all...

It was a bit of a drop on Apollo to be sure... check out what happened to 15's engine bell (top right) from the drop: http://commons.wikimedia.org/wiki/File:Apollo_15_Engine_Bell.jpg
Looks like it was by design quite weak, to be used as a shock absorber:

Thickness from 0.010 to a max of 0.060 inches! (0.2 to 1.5 mm)

I think it would have collapsed under descent module weight even at 0 m/s vertical speed!
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Offline jumpjack

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By the way, same document above is useful to compare engines powers:

Apollo: variable thrust between 1000 and ~10000 lbf (~ 4400 to 44000 N)
Chang'e3: 1500 to 7500 "cattle cows" (lbf or N??) ; weight = ?

From this interseting table http://history.nasa.gov/SP-4029/Apollo_18-37_Selected_Mission_Weights.htm  (or better from this summary... http://www.braeunig.us/apollo/LM-descent.htm  ) we see that upon landing, the Apollo descent module weighted 8300 kg.

Apollo weight at landing = 8300 kg
Chang'e  weight at landing =?

Gravity on Moon surface is 1,6249 m/s2

If I remember correctly, terminal velocity in vacuum from height H should be v = sqrt(2*a*H) (as H = 1/2 * a * t^2) and v = a * t)  , where a = 1,6249 m/s2 on the moon.

This just reminds me that object mass does not affect terminal velocity in vacuum... :-)

So we have:
v =  sqrt (3.2498*H) = 1.8 * sqrt(H)

For H=4 meters we have:

v= 1.8 * 2 = 3.6 m/s = 13 km/h

Can anybody confirm my calculations?


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Offline Blackstar

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These are some nice-looking models. But I wonder how the color scheme matches the actual vehicle.

Alas, I don't read the language, so I'm wary of trying to order anything. I wish they were on eBay or had an overseas distributor.

Online Lar

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dropping the last 4 feet seems risky... how does this compare to other lunar landings? I didn't think the Apollo LEM cut engines that high up at all...

It was a bit of a drop on Apollo to be sure... check out what happened to 15's engine bell (top right) from the drop: http://commons.wikimedia.org/wiki/File:Apollo_15_Engine_Bell.jpg

Wow, but isn't that due to decreased clearance (bell extension) ? That's what the WP article implies.

However I guess I shouldn't be as surprised as I was. 4-5 feet isn't that far to fall in lunar gravity I guess. Depending on what vertical velocity the craft has at engine cutoff anyway, if zero then not much at all. (non zero in either direction will make for a harder landing of course)


For H=4 meters we have:

v= 1.8 * 2 = 3.6 m/s = 13 km/h

Can anybody confirm my calculations?

Wait, 4 meters or 4 feet? That's quite a difference!
« Last Edit: 12/11/2013 12:44 PM by Lar »
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Offline jumpjack

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I should check back old posts or look back for original sources, anyway it should be 4m / 12ft Chang'e 3 and 1,7m / 5 ft Apollo.

Which units are in use in China? Imperial or metric?
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Offline jumpjack

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This is barely inteligible, but look like the're talking about 4 meters rather than feet, so I don't know...

Landing the ladder down to the lunar surface , the rover was to go down. According to
Plan, " rabbit " lunar rover will be on December 15 when 38 points to 04 to 06 21
Points, to achieve the separation of the lander . Although the " off " in height from only
About two meters , but will have to spend nearly two hours , the difficulty is evident.
According to the plan , at 15:21 on December 15 to 23:38 , the
Lu , a nine hours after the rover separation , the two devices will begin Lee
With their own camera , captured in pictures for each other lunar surface.
http://www.planetary.org/blogs/emily-lakdawalla/2013/12060741-change-3-has-arrived-at-the-moon.html
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Offline jumpjack

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Wait, here they are some very clarifying posts in REAL english rather than Google-English!
We should keep an eye on this Cheng user!




cheng: 12/08/2013 12:01 CST
发射段:一箭入轨
Chang'e 1: GTO to phasing orbit to TLI orbit.
Chang'e 2: directly to TLI orbit
Chang'e 3: over a ton heavier than Chang'e 2, directly to TLI orbit.

cheng : 12/08/2013 12:06 CST
近月刹车:直接进入圆轨道
chang'e 3 is equipped with a newly designed variable thrust rocket engine to directly transfer the payload from tli orbit to the circular lunar orbit. in comparison, chang'e 1 and 2 were transfered from tli orbit to the elliptical lunar orbit then to the circular lunar orbit. this is due to limited fuel availability.

cheng: 12/08/2013 12:16 CST
软着陆:下降有动力
after 4 days in circular lunar orbit, chang'e 3 will transfer to an elliptical lunar orbit with the perilune point at 15km and the aposelene point at 100km. chang'e 3 will begin its descent at 15km at around 11:22PM~11:35PM 12/14/2013, (I believe the time is UTC+08:00. The descent engine will be ignited at 15km to decelerate, above 2km it'll have pointed its main engine downward, below 2km it'll be slowly descending. At 100m (328.084 feet) the payload will be hovering without receiving control from beijing. it'll utilize its camera and computer to identify the surface, and automatically select a plain to land on. at 4m (13.1234 feet) the descent engine will turn off, and the payload will land with a free fall.

cheng: 12/08/2013 12:22 CST
落月:9小时候月面留影
after the soft landing, first the lander will charge and initialize the rover; then the rover will start the communication link with earth control, unlock the locking mechnism, and move to the transfer mechnism (ladder). Then the rover will control the transfer mechanism to descend to the surface of the moon, and drive itself away from the lander. yutu (jade rabbit, the pet of the lunar princess in chinese folklore) will be separated from the lander at 4:38~6:21 12/15/2013, the descend will only be around 2 meters (6'7) but the entire process will take around 2 hours. nine hours after the seperation, the lander and the rover will capture some photographs of each other using the equipped cameras. and both are painted with the national flag, therefore, a color photo of the chinese national flag on the moon can be captured.
« Last Edit: 12/11/2013 02:33 PM by jumpjack »
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Offline JohnFornaro

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Here "cattle cow" = Newtons  ;) 

As a rule of thumb for scale, the force of one Newton is about the weight of one apple on Earth. Good mnemonic trick.

JimO:  Heartfelt thanks for that mnenonic!
Sometimes I just flat out don't get it.

Offline JohnFornaro

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...the lander and the rover will capture some photographs of each other using the equipped cameras. and both are painted with the national flag, therefore, a color photo of the chinese national flag on the moon can be captured.

Told ya there'd be a flag.

Is it landing on December 15th?
Sometimes I just flat out don't get it.

Offline jumpjack

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Offline savuporo

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So they must be currently imaging the landing area - and they probably have done health checks for various cameras already too. Have any of the photos gotten out yet ?
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Offline plutogno

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So they must be currently imaging the landing area

nope they can't. go outside tonight and look at the moon. you will notice that it's still night at the landing site

Offline Prober

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Is there a shop in Beijing where you can buy these models from (And space envelopes?)

I'm going  Beijing soon

A-P
A simultation model of China's first moon rover - "Jade Rabiit" - is displayed at a market in Yiwu city, East China's Zhejiang province on Dec 3, 2013. (Photo/China Daily)
http://english.people.com.cn/90882/8475036.html

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Offline Comga

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So they must be currently imaging the landing area

nope they can't. go outside tonight and look at the moon. you will notice that it's still night at the landing site

The Earth is always overhead from the landing site. There must be Earthshine from the "quarter-Earth" at this time of the month.   This is much brighter than illumination on the Earth's surface from the full Moon.   Note that this illumination would be fairly diffuse and from a high angle, which is not optimum for finding rocks and other obstacles.

I have no information on the sensitivity of their cameras, but it is possible to image the surface without direct sunlight.
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Online Phillip Clark

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I would doubt very much indeed that Earthshine would provide enough illumination to perform any significant imaging of the Chang'e 3 landing site.
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Offline plutogno

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yep. that would be unprecedented. plus, I don't see the interest since CE-2 mapped the area at 1.5 m resolution

Offline Blackstar

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yep. that would be unprecedented. plus, I don't see the interest since CE-2 mapped the area at 1.5 m resolution

Are there high-res LRO maps of that area?

Offline jumpjack

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...the lander and the rover will capture some photographs of each other using the equipped cameras. and both are painted with the national flag, therefore, a color photo of the chinese national flag on the moon can be captured.

Told ya there'd be a flag.

Is it landing on December 15th?
As far as i KNEW,  landing is planned for 14:22 December 14th  Universal Time, but I just read now:
Landing is set for approximately 15:35 UTC.
http://www.spaceflight101.com/change-3-mission-updates.html

So I'm now a bit confused. A bit MORE confused...  ::)
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Offline EirikV

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I believe the landing window is 1522-1533 UTC

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