Author Topic: Chinese Mars Mission  (Read 53855 times)

Offline hop

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Re: Chinese Mars mission
« Reply #60 on: 03/25/2016 08:00 pm »
Of course you can always just roll the dice and hope for the best, if you don't NEED to be SURE.
HiRISE class imagery doesn't get you to SURE either, because every landing site has a significant amount of non-survivable terrain on it. Every Mars landing to date has been rolling the dice and hoping for the best.

CE-3 had autonomous hazard avoidance, which no US Mars lander has ever used. Assuming they do the same for Mars and it works reasonably well, it would improve the odds significantly.

edit: Though if they are using airbags as suggested up thread, that's probably not the case.
« Last Edit: 03/25/2016 08:12 pm by hop »

Offline Dalhousie

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Re: Chinese Mars mission
« Reply #61 on: 03/25/2016 08:29 pm »
While the higher the resolution the better, you don't need HiRISE. The Vikings and Pathfinder landing sites were chosen without any high resolution imagery.
Yeah, you pretty much do need HiRISE to be sure that your selected site is safe.  The Vikings worked basically because they got lucky.  See this discussion of the Viking landing site selection process for details.

Of course you can always just roll the dice and hope for the best, if you don't NEED to be SURE.

Landing site safety is always comes down to probabilities, even with HiRISE.  For example the rock height requirement for MSL was defined as "Probability that a rock >0.55 m high occurs in random sampled area of 4m2 should be <0.50%"

Remember that HiRISE can't usefully see individual rocks much smaller than 1 m (three pixels).  That's why radar scatterometry and polarimetry is used  because it enables estimates of surface roughness cto be made, though not able to locate individual boulders.  Viking used Aricebo radar for this, we now have MARSIS and SHARAD in Mars orbit, as well as ground based instruments to fall back on (including FAST as of this year, with a diameter 60% greater than Aricebo)
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Offline Blackstar

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Re: Chinese Mars mission
« Reply #62 on: 03/26/2016 12:28 am »
CE-3 had autonomous hazard avoidance, which no US Mars lander has ever used. Assuming they do the same for Mars and it works reasonably well, it would improve the odds significantly.


Has that system ever been described in detail?

As a US spacecraft engineer pointed out to me, the Moon is a much less rocky surface than Mars, so hazard avoidance in general is easier. Designing a hazard avoidance system for Mars is tougher than one for the Moon, and so the Chinese may still want to opt for a smoother surface rather than leave it to the autonomous system to handle the risk. In addition, if you're carrying a rover, you don't want to put it down in a very rocky area or it won't be able to get out.

(I heard an interesting discussion about using hazard avoidance on Europa, where you may have really poor imagery of the surface. The challenges of designing that kind of system are substantial.)

Offline hop

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Re: Chinese Mars mission
« Reply #63 on: 03/26/2016 12:56 am »
Remember that HiRISE can't usefully see individual rocks much smaller than 1 m (three pixels).
This is true in the sense of actually *imaging* rocks, but that's not the only way estimate hazards.
Quote
That's why radar scatterometry and polarimetry is used  because it enables estimates of surface roughness cto be made, though not able to locate individual boulders.
You can get roughness at significantly better than meter scale from HiRISE imagery (e.g. www.hou.usra.edu/meetings/8thmars2014/pdf/1182.pdf)

Contrary to your suggestion, my understanding is that MSL rock hazard analysis relied primarily on HiRISE data. See http://link.springer.com/article/10.1007/s11214-012-9916-y

Offline hop

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Re: Chinese Mars mission
« Reply #64 on: 03/26/2016 01:07 am »
Has that system ever been described in detail?
Not that I've heard of. Hence the "if it works well" caveat.
Quote
As a US spacecraft engineer pointed out to me, the Moon is a much less rocky surface than Mars, so hazard avoidance in general is easier. Designing a hazard avoidance system for Mars is tougher than one for the Moon, and so the Chinese may still want to opt for a smoother surface rather than leave it to the autonomous system to handle the risk.
Agreed. The main point I was trying to make is that high res orbital imagery isn't the only possible way to manage the risk.

Offline Dalhousie

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Re: Chinese Mars mission
« Reply #65 on: 03/26/2016 08:09 am »
Remember that HiRISE can't usefully see individual rocks much smaller than 1 m (three pixels).
This is true in the sense of actually *imaging* rocks, but that's not the only way estimate hazards.
Quote
That's why radar scatterometry and polarimetry is used  because it enables estimates of surface roughness cto be made, though not able to locate individual boulders.
You can get roughness at significantly better than meter scale from HiRISE imagery (e.g. www.hou.usra.edu/meetings/8thmars2014/pdf/1182.pdf)

Interesting approach, but they are assuming that brightness variation at the pixel scale is due to roughness.  there may be other reasons.  I guess it does provide a conservative estimate.  But I would be looking at other evidence to back it up.

Contrary to your suggestion, my understanding is that MSL rock hazard analysis relied primarily on HiRISE data. See http://link.springer.com/article/10.1007/s11214-012-9916-y

Thanks for the link, I have been using the parallel paper by Grant and others on the science process but had not seen that one.  It's most useful.  It clearly shows that multiple methods are used and compared.

Note that in sections 5.2 and 9.6 it talks about using the spread of the laser returns in MOLA to determine roughness, and scattering of X and S-band radar returns in sections 5.5 and 9.6.  Imagery (HiRISE and HRSC) is discussed in the context of constructing DEMS to examine relief at the 1-1000 m scale (sections 5.2 13), and in imaging of larger rocks (section 2.4), inferred as being larger than the rover belly pan (~1.64 m across) and higher than the 0.55 m clearance of the rover.  Section 9.4.2 discusses the ability to recognise shadows as small as three pixels to map rock distributions (3 X 0.24 m = 0.72 m).

I don't want you to think I disagree with you.  I think we both agree that there are multiple sites with good HiRISE coverage for the Chinese to select a landing site from, that HiRISE is not the only data set used in assessing landing sites, and, in the unlikely event of them wanting to land somewhere where there is no HiRISE coverage, it is not the be-all and end-all of site selection, very useful though it is.  In the extremely unlikely event that the Chinese decide to land in an area with no HiRISE coverage, they still won't be landing blind.


« Last Edit: 03/27/2016 12:32 am by Dalhousie »
"There is nobody who is a bigger fan of sending robots to Mars than me... But I believe firmly that the best, the most comprehensive, the most successful exploration will be done by humans" Steve Squyres

Offline Blackstar

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Re: Chinese Mars mission
« Reply #66 on: 03/26/2016 11:23 am »
An interesting question--that I'll see if I can get an answer to this week--is if the prohibition on talking to the Chinese about space stuff prevents NASA from talking to them about planetary protection. It would be not good if a future American spacecraft brought back signs of microbial life on Mars that were taken there by a Chinese spacecraft. And certainly the Chinese would benefit from finding out how the Americans do planetary protection. But I suspect that there's no direct communication and that any communication is done through international forums like COSPAR.

Offline Infinitesky

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Re: Chinese Mars mission
« Reply #67 on: 03/26/2016 07:17 pm »
But I suspect that there's no direct communication and that any communication is done through international forums like COSPAR.
A very interesting question, I think China will pay attention to avoid the Mars microbial contamination.
It is a pity that NASA was banned from all forms of direct communication with China.

Offline Dalhousie

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Re: Chinese Mars mission
« Reply #68 on: 03/27/2016 12:37 am »
But I suspect that there's no direct communication and that any communication is done through international forums like COSPAR.
A very interesting question, I think China will pay attention to avoid the Mars microbial contamination.
It is a pity that NASA was banned from all forms of direct communication with China.

Two Chinese authors contributed to this international document on planetary protection from 2014 http://iaaweb.org/iaa/Scientific%20Activity/Study%20Groups/SG%20Commission%203/sg320/sg320interimreport.pdf The other contributors were from the US (six), Europe (three), Russia (three) and India (one).
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Offline Blackstar

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Re: Chinese Mars mission
« Reply #69 on: 03/27/2016 11:21 pm »
But I suspect that there's no direct communication and that any communication is done through international forums like COSPAR.
A very interesting question, I think China will pay attention to avoid the Mars microbial contamination.
It is a pity that NASA was banned from all forms of direct communication with China.

NASA is allowed to participate in multilateral communications with the Chinese. However, planetary protection issues are really obscure and complicated. They're just... WHOA! They're like, WOW! Complex, dude! You think other things are complicated? They ain't nothing compared to this stuff!

Sorry, got a little carried away there...

Anyway, this is the kind of subject where it seems like sharing as much information and talking as much as possible is in the best interests of everybody. NASA's been doing this stuff for a very long time and certainly understands it better than anybody. So the ability to share that knowledge shouldn't be constrained. But I bet it is.

Offline Blackstar

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Re: Chinese Mars mission
« Reply #70 on: 03/28/2016 10:38 pm »
So, I talked to a coworker who said that last Friday was a multilateral discussion in Paris about planetary protection issues. China, Russia and ESA sent representatives (I was a little unclear, but I think that he said that there were no NASA people there, which I find a little odd--but it may be that the U.S. was represented by non-government people). He confirmed that NASA cannot communicate directly with China on this issue. He did say he got some material about the Chinese program that he will share and I'll post here.


Offline Phil Stooke

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Re: Chinese Mars mission
« Reply #71 on: 03/29/2016 03:48 am »
Back to the rock hazard topic - the other approach to estimating rockiness, which was essential for Phoenix and has been used elsewhere, if thermal inertia, derived from the Mars Odyssey THEMIS instrument and available globally now.

Solid chunks of rock conduct heat into their interiors during the day and release it slowly at night, as it conducts back out.  Dust and sand act more like insulators, getting hot at the surface during the day but not conducting much heat downwards.  Then they cool off fast at night by radiation.  By comparing day and night temperatures with THEMIS we get a pretty good measure of thermal inertia and can use it to identify rocky areas.

Phoenix site selection was going on when there was not much HiRISE to use, so it helped identify rock-free areas.  HiRISE then imaged primarily the sites already chosen on the basis of THEMIS data.  HiRISE also showed that areas chosen on the basis of other morphological clues were often rockier than expected, causing a late change to the preferred area.

For the Chinese lander, going to an area with good coverage by HiRISE seems sensible, but they, like everybody else, have access to all the data now via PDS, JMARS etc. 

Offline Blackstar

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Re: Chinese Mars mission
« Reply #72 on: 03/29/2016 12:54 pm »
Here you go.

Offline plutogno

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Re: Chinese Mars mission
« Reply #73 on: 03/29/2016 05:07 pm »
CE-3 had autonomous hazard avoidance, which no US Mars lander has ever used. Assuming they do the same for Mars and it works reasonably well, it would improve the odds significantly.


Has that system ever been described in detail?

yep. although all the papers I can find on the subject are in Chinese. the algorithm is described in the paper attached, for example

Offline Infinitesky

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Re: Chinese Mars mission
« Reply #74 on: 04/02/2016 09:53 am »
So, I talked to a coworker who said that last Friday was a multilateral discussion in Paris about planetary protection issues. China, Russia and ESA sent representatives (I was a little unclear, but I think that he said that there were no NASA people there, which I find a little odd--but it may be that the U.S. was represented by non-government people). He confirmed that NASA cannot communicate directly with China on this issue. He did say he got some material about the Chinese program that he will share and I'll post here.
Yes, I know that although CASC can not communicate directly with NASA, but it is said that they can participate in the multilateral communications.Perhaps a large part of them are from the U.S. non-governmental organizations.(Maybe Mars Society?I seem to have heard that there was a Chinese student there before. )
Thank you very much for file sharing,I'm familiar with the contents of the past missions, but I also have found something new about the future Mars missions.It is surprising to learn from this channel rather than from domestic.
« Last Edit: 04/02/2016 10:07 am by Infinitesky »

Offline savuporo

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Re: Chinese Mars mission
« Reply #75 on: 04/02/2016 04:49 pm »
Yes, I know that although CASC can not communicate directly with NASA..

Speaking of communications. I wonder if this thing would speak fully standard CCSDS 0x1ACFFC1D dialect. Chang'e 1/2 almost did. But i'm wondering if ESA is doing any prep work with CNSA to be able to relay through Mars Express or TGO. That would be a tricky conversation to have, because Electra
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Offline Dalhousie

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Re: Chinese Mars mission
« Reply #76 on: 04/03/2016 01:19 am »
Yes, I know that although CASC can not communicate directly with NASA..

Speaking of communications. I wonder if this thing would speak fully standard CCSDS 0x1ACFFC1D dialect. Chang'e 1/2 almost did. But i'm wondering if ESA is doing any prep work with CNSA to be able to relay through Mars Express or TGO. That would be a tricky conversation to have, because Electra

Why would that be any more tricky than anything else?
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Offline savuporo

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Re: Chinese Mars mission
« Reply #77 on: 04/03/2016 02:29 am »
Why would that be any more tricky than anything else?

NASA is still prohibited from directly collaborating with CNSA, it would be just odd if NASA contributed asset would end up helping the Chinese mission. ESOC contributing their own assets to Chang'e missions is obviously not under any of these restrictions, so that's probably procedurally easier.
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Offline Blackstar

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Re: Chinese Mars mission
« Reply #78 on: 04/03/2016 03:06 am »
So, I talked to a coworker who said that last Friday was a multilateral discussion in Paris about planetary protection issues. China, Russia and ESA sent representatives (I was a little unclear, but I think that he said that there were no NASA people there, which I find a little odd--but it may be that the U.S. was represented by non-government people). He confirmed that NASA cannot communicate directly with China on this issue. He did say he got some material about the Chinese program that he will share and I'll post here.
Yes, I know that although CASC can not communicate directly with NASA, but it is said that they can participate in the multilateral communications.Perhaps a large part of them are from the U.S. non-governmental organizations.(Maybe Mars Society?I seem to have heard that there was a Chinese student there before. )
Thank you very much for file sharing,I'm familiar with the contents of the past missions, but I also have found something new about the future Mars missions.It is surprising to learn from this channel rather than from domestic.

Not Mars Society. That is a group of amateurs. They don't have any involvement in current robotic programs.

Offline Dalhousie

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Re: Chinese Mars mission
« Reply #79 on: 04/03/2016 03:46 am »
Why would that be any more tricky than anything else?

NASA is still prohibited from directly collaborating with CNSA, it would be just odd if NASA contributed asset would end up helping the Chinese mission. ESOC contributing their own assets to Chang'e missions is obviously not under any of these restrictions, so that's probably procedurally easier.

Mars express is not a NASA mission, nor is the TGO, both of which you specified, so why is this a problem?
« Last Edit: 04/03/2016 03:49 am by Dalhousie »
"There is nobody who is a bigger fan of sending robots to Mars than me... But I believe firmly that the best, the most comprehensive, the most successful exploration will be done by humans" Steve Squyres

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