LIVE: Chang'e-3 lunar probe and rover, CZ-3B - Xichang - December 1, 2013

[Phil Stooke]

Certainly lunar landings are possible in the dark, but we know the landing is scheduled for Dec. 14th when the landing area will be sunlit.

Descent images have been taken by other missions but never so far have they been transmitted live.  There's a first time for everything and this might be it.  My impression, however, was that they would be used onboard for hazard avoidance and only transmitted later.  But I could be wrong.

Phil

[Phillip Clark]

Certainly lunar landings are possible in the dark, but we know the landing is scheduled for Dec. 14th when the landing area will be sunlit.
Descent images have been taken by other missions but never so far have they been transmitted live.  There's a first time for everything and this might be it.  My impression, however, was that they would be used onboard for hazard avoidance and only transmitted later.  But I could be wrong.
Phil

I was responding to Danderman's comment above.   Only the Soviet Union landed spacecraft on the Moon when it was locally dark.

[Apollo-phill]

Range and velocity measurements are also provided by a large-dynamic-range laser ranging system and a microwave range sensor that become active once the vehicle has reached a certain altitude and orientation above the lunar surface....
 Navigation data is provided by the lander's inertial guidance platform, a laser ranging system and a microwave ranging sensor. At a sensed velocity after a defined burn time, the lander starts the Quick Adjusting Sequence of the descent, performing attitude maneuvers as it closes in on the surface.

[/quote]

Reading above I would suggest that no images will be used - just instrument data readings from the Inertial Reference gyros on the "stable" platform  , the laser ranging system and the microwave range sensor.
I think the Descent Camera is just for taking descent images from various altitudes at time increments - which will be downloaded later. From these images they will be able judge where exactly on target zone they have landed in sinus Iridum and to - maybe - plot the Yutu rover path for first few "excursions" ?

But all this guessing comes from China not releasing more detailed information - at least not yet. There IS a lot of information coming out but via many different media outlets - be better if it came from the space agency itself in form of press/media kit ? Maybe they can work on that one for next time :-)

Phill

[plutogno]

IIRC only Luna 20 landed in daylight (and is also the only one for which pictures have been published)

[plutogno]

I think the Descent Camera is just for taking descent images from various altitudes at time increments - which will be downloaded later. F

as I understand it, the camera is mainly for feeding data to a real-time 3D terrain reconstruction algorithm that is used for obstacle avoidance

[savuporo]

Reading above I would suggest that no images will be used ..

No, they have said in multiple instances that the landing is guided by visual obstacle detection

http://www.spaceflight101.com/change-3.html

Once in its hovering segment, about 100 meters above the surface, the lander will start acquiring images using its descent camera. The computer will be using a newly developed obstacle-recognition algorithm using optical images and 3D elevation data. Flying horizontally, the lander autonomously finds a flat spot for landing, avoiding any obstacles that can be detected using its systems.

It is not a "blind" landing - i.e. they basically have equivalent of ALHAT capability.

The previous maximum resolution for the terrain map they achieved was up to 1.5 meters per pixel. That is not sufficient for safe landing.

BTW, note that no previous planetary landing has had autonomous hazard avoidance capability so far.

EDIT: and here are some insights of how it might work
Paper published by JPL, in 2008
http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/41368/1/07-4233.pdf

Paper published at CAST, 2010, citing the previous one
http://www.cast.org.cn/n35081/n11219166/n11219211/n11799877/n12217613.files/n12217625.pdf

as I understand it, the camera is mainly for feeding data to a real-time 3D terrain reconstruction algorithm that is used for obstacle avoidance

From the brief read over the badly translated chinese paper here ( and other chinese papers citing these) , it looks like it would be a fairly common approach used in modern robotics of multi sensor fusion, with optical sensor being the primary high frequency input.

[Apollo-phill]

This question of drop height by Change'3 lander of 4 meters.

Remember that USA's first soft lander spacecraft - Surveyor 1 (launched 30 May 1966 ) - had its retrorockets turned off at a height of about 3.4 meters above the lunar surface. It landed safely and started science operations shortly afterwards.

Really getting a "buzz" now about Saturday's descent - the first one since the Russians  did the last soft landing all those decades ago !

Phill

[Garrett]

Lacking updates, I'm posting this:
As I don't have a great view of the Moon right now, according to this U.S. Naval Observatory simulator (see attached image), it is now dawn at the Chang'e 3 landing site (Sinus Iridum, circled by me)

Edit: forgot to post the link: http://aa.usno.navy.mil/imagery/moon

[Blackstar]

it is now dawn at the Chang'e 3 landing site

So the sun is coming up.

[Phil Stooke]

Re: earlier night landers.  Luna 16, 18, 20 carried cameras, Luna 23, 24 did not (redesigned sampler instead).  Luna 16 landed at night, took pics anyway to see if Earthshine was OK for imaging.  Pics showed small glints off rocks, but were considered useless and were never published.  I would sell my grandmother for access to the digital data (sorry, Gran) - with modern techniques we could do a lot with it.  Luna 20 - in daylight with pics released.  The others - I haven't checked landing times.

Phil

[AJA]

I don't expect images from the descent camera to be streamed live. that's a lot of data to transmit, and there are surely more urgent engineering data to relay to Earth during the phase....

Actually, i would think exactly the opposite. Remember, this is mostly an engineering validation mission first, and the most risky part is the landing. In the landing phase, it would apprear that camera is their primary guidance sensor. Should something go wrong and it goes splat, you want to have the critical sensor data available to reconstruct what might have happened.
They are using X-band which gives you a pretty wide link budget, and if they are using digital video compression at all you can easily fit low resolution video layer in the bandwidth.

But precisely because it's an engineering validation mission, you'd want the numbers - as perceived by the sensors on the spacecraft - and the numbers input into the control programs, and the corresponding responses from the thrusters. If an anomaly were to occur, how much can you tell with defocused, under/over-exposed images - assuming a fast anomaly[1]? All you'll have is a full field lunar image (surely no anomaly is going to be so bad as to cause tumbling!), without any idea of scale, and you won't even be able to tell how high up the craft was. Sure, you can compare the images to the images from the orbiter, and try to work out a scale, but the orbiter's resolution's limited, and it'll only help give you an upper bound for the height - by correlating features. If the spacecraft tumbles, then this becomes made a lot more complex - estimating rates from image data alone.

In any case, even if you're able to extract precise information - time, height and attitude: without other data, you're only speculating and extrapolating backwards - as to the cause of the problem.

[1] Plus - If the anomaly's a "slow" one - say... overdrawing current from the batteries, an SEU/SEL at an unpleasant time, overheating of the sensors, etc. etc. - and you actually manage to land - there's a problem simmering under the surface, and you don't initiate safe mode (if the S/C may not be able to initiate it etc. etc.)

As regards all the Apollo comparisons, I don't think, with the presence of the CSM overhead, that link budget was a limiting factor? Transmit all data in real time (hedging against any malfunction, and possible later inability to transfer) from LEM to CSM, archive the imagery aboard the CSM, transmit other essential data back to Houston. (Processing power may've been a factor though?)

[AJA]

BTW, note that no previous planetary landing has had autonomous hazard avoidance capability so far.

Chang'E 3 media sound-byte?


cf. http://mars.jpl.nasa.gov/msl/mission/technology/insituexploration/edl/descentimaging/


JPL themselves say that the MARDI on MSL wasn't used for ALHAT...
But look at the caption to the image of an MER MARDI image on the same page.

This image simulates how the descent imager for the Mars Exploration Rovers took three pictures of the surface and compared high-contrast features (e.g., craters) to determine the spacecraft's horizontal velocity during entry, descent, and landing. This measurement helped determine which transverse rockets should be fired to keep the spacecraft within its planned landing area.

That qualifies as rudimentary ALHAT to me.


In any case, what did the various Luna landers use then? For their night landings? Supreme confidence in their orbital imagery, and the onboard IMU, coupled with copious hydrazine reserves for the lander, and copious vodka reserves for the controllers?


Also. how would a descent camera distinguish between really smooth, uniform terrain, and a unfocused/ non optimally exposed image? Or even between really smooth terrain and a "greyout" readout/conditioning electronics failure?

[savuporo]

But precisely because it's an engineering validation mission, you'd want the numbers - as perceived by the sensors on the spacecraft - and the numbers input into the control programs, and the corresponding responses from the thrusters....

Yes, i wasnt saying you should discard the rest of the telemetry stream in favour of video, and bandwidth wise all other sensor and checkpoint data in telemetry frames would probably not make up even 1% video bitrate.

This image simulates how the descent imager for the Mars Exploration Rovers took three pictures of the surface and compared high-contrast features (e.g., craters) to determine the spacecraft's horizontal velocity during entry, descent, and landing. This measurement helped determine which transverse rockets should be fired to keep the spacecraft within its planned landing area.

That qualifies as rudimentary ALHAT to me.

Not really - this is a form of visual odometry that helps the position estimate, i.e. backup data stream for IMU. It is not active hazard avoidance , which is what ALHAT does.

In any case, what did the various Luna landers use then? For their night landings? Supreme confidence in their orbital imagery, and the onboard IMU, coupled with copious hydrazine reserves for the lander, and copious vodka reserves for the controllers?

I didnt dig out the books that i have on the subject, but from what i recall they were mostly banking on their landers mechanical robustness - and lots of blind luck. Orbital imagery would have given no confidence at the time, as it doesnt today - the resolution is not there.

Also. how would a descent camera distinguish between really smooth, uniform terrain, and a unfocused/ non optimally exposed image? Or even between really smooth terrain and a "greyout" readout/conditioning electronics failure?

These are common problems that robotic vision systems have to deal with - for intro, see the english paper i linked to above. Basically you do sensor fusion from multiple sources and a lot of signal filtering to discard low confidence inputs. Unfocussed and nonoptimally exposed frames are the least of the problems there.

[Galactic Penguin SST]

In other news tomorrow's landing time seems to have shifted again - there are news reports giving a ~13:40 UTC (8:40 am EST) landing time. I honestly do't know which one to believe in...

[jumpjack]

This weird (as usual) translation suggests two different engines being onboard:

When Chang E III hover in the 100 meters, in addition to the main engine, the soft landing engines work. Use of reverse thrust engine ignition, and slowly let it down.

Could this be true?!?

About obstacle avoidance it says:

However, in order to allow Chang E III to better avoid these dangers, the lander is also equipped with "eyes", ie ranging speed sensitive instrument. During landing, it can quickly scan the surface of the moon, or even draw a three-dimensional images of the lunar surface for program analysis and judgment, and hover height of 100 meters, the final level of the Chang-e III moved over the best landing point.

[Garrett]

In other news tomorrow's landing time seems to have shifted again - there are news reports giving a ~13:40 UTC (8:40 am EST) landing time. I honestly do't know which one to believe in...

I am actually quite amazed that very few mainstream news outlets are following the story. I honestly (naively?) expected the first Moon landing of the 21st century to be creating a much bigger stir. Sure, tomorrow evening there will be a headline or two, but I expected (or hoped) for more, even though it's not a manned landing.

Maybe actually imagery from the Moon's surface will wake folks up a bit. Maybe.

[QuantumG]

In other news tomorrow's landing time seems to have shifted again - there are news reports giving a ~13:40 UTC (8:40 am EST) landing time. I honestly do't know which one to believe in...

I am actually quite amazed that very few mainstream news outlets are following the story. I honestly (naively?) expected the first Moon landing of the 21st century to be creating a much bigger stir. Sure, tomorrow evening there will be a headline or two, but I expected (or hoped) for more, even though it's not a manned landing.

Maybe actually imagery from the Moon's surface will wake folks up a bit. Maybe.

Will there be live coverage somewhere? CCTV perhaps?

[Galactic Penguin SST]

In other news tomorrow's landing time seems to have shifted again - there are news reports giving a ~13:40 UTC (8:40 am EST) landing time. I honestly do't know which one to believe in...

I am actually quite amazed that very few mainstream news outlets are following the story. I honestly (naively?) expected the first Moon landing of the 21st century to be creating a much bigger stir. Sure, tomorrow evening there will be a headline or two, but I expected (or hoped) for more, even though it's not a manned landing.

Maybe actually imagery from the Moon's surface will wake folks up a bit. Maybe.

Will there be live coverage somewhere? CCTV perhaps?

There should be on CCTV - not sure when does it starts on the English channel, but on the Chinese side a special program should start at 11:00 UTC.

[jumpjack]

Found a very interesting and very active Chinese forum!

From rover thread (http://bbs.tiexue.net/post_6941624_1.html):
Weight: 140 kg
Operating temperature range:-180°C/+150°C
Internal controlled temperature: +20°C/+50°C
Gradeability: 20°
Obstacle height: 20cm
Visual capabilities:  three-dimensional optical imaging, infrared spectroscopy


Chang E II lunar Rainbow Bay local image maps http://bbs.tiexue.net/post_4596431_1.html
China canceled manned lunar program http://bbs.tiexue.net/post_7006575_1.html
Landing failure prediction    http://bbs.tiexue.net/post_7007285_1.html
New electric propulsion engine   http://bbs.tiexue.net/post_7011243_1.html
Nuclear devices on Chang'e 3   http://bbs.tiexue.net/post_6987138_1.html
"Black 750 seconds"   http://bbs.tiexue.net/post_7012426_1.html
"Moon race"   http://bbs.tiexue.net/post_7003966_1.html
Redirecting Chang'e 2 to Mars?   http://bbs.tiexue.net/post_7004959_1.html
Chang E II lunar satellite has 32G terrestrial transmission of scientific data   http://club.china.com/data/thread/12171906/2718/69/65/5_1.html
Chang E II lunar Rainbow Bay local image maps   http://bbs.tiexue.net/post_4596431_1.html

[Chris Bergin]

Ok cool. So we need a live thread for the coverage and be on standby for the live webcast at 11am UTC.

All in work, including an article from Rui.