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Unmanned Spaceflight.com > Earth & Moon > Lunar Exploration > Chang'e program
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Phil Stooke
The new map is very nice. I have just put a comment on LPOD about this but I'll repeat it here. The zoomable map works like the LROC Quickmap, except it does not have the extra level of detail provided by the LROC NAC frames. But when I zoom in on areas I know very well, I can see that the new Chinese map is better than the LROC WAC mosaic. The sun angle is higher, so topography is not so clearly seen, but the resolution is better than LROC WAC.

Phil

Paolo
according to the google translation of a post on a Chinese forum http://www.9ifly.cn/forum.php?mod=viewthre...e=104#pid203109

QUOTE
The CE-2 in April, has left the L2 to probe asteroid is expected to close rendezvous with an asteroid in January next year.


the same forum points at main belt (3179) Beruti as the target. sounds strange, I would rather have expected a NEO!

I am hoping they got confused with (4179) Toutatis! I have been waiting to see Toutatis ever since the first radar images were released 20 years ago!
Paolo
it now seems that Toutatis is indeed the target! the flyby will occur just weeks after the NEO has made a close approach within 0.046 AU of Earth.
I was wondering whether the Chinese have developed a moving target tracking algorithm to collect any data from the flyby or they will have to image all of the uncertainty volume of the asteroid in order to be sure of capturing it as Galileo did. any idea?
of course such software is not needed for a lunar orbiter...
Phil Stooke
Very interesting. There is a mirror-image ambiguity in the radar image reconstructions, and it will be very interesting to see it resolved in optical images. I think the ambiguity continues into the shape models as well, certainly in the earlier versions.

Phil

yaohua2000
Here is the full video of the presentation by Ouyang Ziyuan:

http://www.cas.cn/zt/hyzt/16thysdh/zb/fdsp...4_3598219.shtml
Paolo
more info from NASAspaceflight forum, where I first saw the new, to give them proper credit (I am user plutogno) http://forum.nasaspaceflight.com/index.php?topic=19644.225
CE2 left the Lagrangian point on 15 April and will flyby Toutatis on 6 January next year
tedstryk
I sure hope this is true (and, if so, successful) http://translate.google.com/translate?hl=e...26prmd%3Dimvnsu
elakdawalla
According to a commenter on my blog who says he speaks Chinese and listened to the presentation, the future encounters (Tukmit, Apophis, etc) are for future missions, not Chang'E 2.
Paolo
to answer my question about autonomous tracking, I asked JPL's Horizons the 3-sigma error ellipse semiaxes in right ascension and declination for the day of the encounter for an observer located at the center of the Earth. It turns out Toutatis' orbit is extremely well known (thanks to radar observations, no doubt) and probably CE will simply need to point at the spot in the sky where the asteroid is supposed to be.
The orbital elements in fact have very small 1-sigma uncertainties (down to 1E-10 for the semimajor axis and eccentricity): http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=4179...cad=0#discovery
From Horizons, it turns out the 3-sigma error ellipse on encounter day is a mere 0.025 x 0.010 arcseconds wide. That is 1.21E-7 x 4.85E-8 radians. The distance from Earth at that time will be 0.1887 AU or 28.2 million kilometers.
From simple trigonometry, the error ellipse is just 28.2E6 sin (1.21E-7) = 3.4 km wide at maximum.
did I make any mistake? am I missing something?
Paolo
while waiting for details and news on the Toutatis mission (note that it's been more than a week since the story was leaked, and Chinese mainstream press has not yet picked it up), I have found an interesting if quite technical paper on Moon-to-L2 navigation
Pre-LOI trajectory maneuvers of the CHANG’E-2 libration point mission
Paolo
at last the story has been picked up by Chinese news sites!
http://tech.sina.com.cn/d/2012-06-27/14427317706.shtml
nothing new as far as I can tell from the Google translation, beside the first mention of a planned flyby distance of 1000 km. I also find it interesting that they mention a flyby near the end of this year or early next year, as if the date was not yet fixed
Paolo
still nothing new on CE-2 to Toutatis, so I was performing some calculation.
I found the specs of the camera in the paper Overall scheme and on-orbit images of Chang'E-2 lunar satellite CCD stereo camera.
It is quite different from the camera on CE-1. It consists of a refracting optics mated to two 6144 pixel linear arrays: a forward looking and a rearward looking one. at a distance of 1,000 km from Toutatis, each picture will be 430 km wide and will have a resolution of 70 m per pixel. Unfortunately, the linear array camera is well suited for an orbiter, but not for a flyby probe. either CE-2 will have to rock back and forth to build images, or it will have to collect long swaths as the asteroid crosses the field of view. Moreover, it is not particularly suitable for optical navigation. In any case, I would not expect more than a handful of pics.
Data return should be slow but not painfully so. At L2 CE-2 returned data at 750 kilobits per second, and some 20 times more distant at Toutatis it should return at several kilobits per second, comparable to Stardust.
Paolo
I am puzzled... Chinese news sites are now reporting a Toutatis flyby in March next year instead of January!
see for ex http://news.sina.com.cn/c/2012-07-25/021924837262.shtml
Phil Stooke
That must be wrong - Toutatis will be very far away by then. I would guess a reporter misunderstanding. I am assuming the spacecraft will remain in the vicinity of Earth and probably return to the Earth-Moon system later, though no idea yet what its fate will be.

Phil
tolis
QUOTE (Phil Stooke @ Jul 24 2012, 09:17 PM) *
That must be wrong - Toutatis will be very far away by then. I would guess a reporter misunderstanding. I am assuming the spacecraft will remain in the vicinity of Earth and probably return to the Earth-Moon system later, though no idea yet what its fate will be.

Phil



Hopefully adding some confidence to the details of the encounter:

The event is mentioned in the Goldstone radar's schedule:

http://echo.jpl.nasa.gov/asteroids/Toutati...2_planning.html

It must be on then..

Regards to All,

Tolis.
Paolo
actually, I wrote an email to the guy who maintains the JPL asteroid radar site last month and he told me that he has no first-hand info. all he knows about the flyby is what can be learned from Emily's blog
elakdawalla
OK, that's funny. The Wikipedia effect at work.

I have spoken with American scientists working with the Chinese on this flyby, so it is for real, but I have no more details than I did before.
SFJCody
PanSTARRS observations of Chang'e suggest it will be at Toutatis by December.

http://www.projectpluto.com/pluto/mpecs/cheprobe.htm
Paolo
QUOTE (SFJCody @ Aug 15 2012, 04:55 AM) *
PanSTARRS observations of Chang'e suggest it will be at Toutatis by December.


thanks! solid info at (long) last!
Paolo
the Project Pluto page has been updated:

QUOTE
You can fit an orbit to the current (as of 18 August) observations and get a positional match, at 08:27 UT on 13 December, within better than an arcminute, with a close match in distance as well. Toutatis comes to its closest approach to earth (0.046 AU) on the preceding day.


meanwhile I have received an email from a Chinese engineer working on orbit design for CE-2. although he did not give me the precise date, nor the targeted flyby distance, he told me that the encounter is expected to take place 7 million kilometers (0.0468 AU) from Earth, which closely fits the 13 December date.
Some more details on orbital design: CE-2 entered solar orbit directly from L2, without any Moon or Earth flybys, with a delta-v of several m/s. At the end of the L2 "excursion", the remaining delta-v was about 120 m/s. Four course corrections will precisely target the Toutatis flyby and establish a geometry that's convenient for imaging and communications. The relative speed at closest approach will be about 11 km/s.
climber
QUOTE (Paolo @ Aug 20 2012, 01:43 PM) *
. The relative distance at closest approach will be about 11 km/s.

Interesting info biggrin.gif
Phil Stooke
We should probably move this section of the thread to a dedicated asteroid section.

Phil
Paolo
QUOTE (climber @ Aug 20 2012, 04:55 PM) *
Interesting info biggrin.gif


oops...
Paolo
google translation of an interview with Ouyang Ziyuan on Chang'e 1 and 2 lunar science and data mining
http://translate.google.com/translate?hl=e...ved=0CE8Q7gEwAg
Paolo
and a related youtube video
http://www.youtube.com/watch?feature=playe...;v=w58_INahqpk#!
it looks like poster presentations at some kind of congress
yaohua2000
Massive radio telescope to assist China’s moon missions: http://www.globaltimes.cn/content/740942.shtml
Phil Stooke
Very interesting news - thanks for posting these links.

Phil

Paolo
developing a Chinese "Google Moon" using Chang'E data:
Interactive visualization of 3D lunar model with texture and labels, using Chang’E-1 data
Paolo
meanwhile, Chang'E 1 is still producing a few papers: The improvement of cross-calibration of IIM data and band selection for FeO inversion
elakdawalla
Folks, I've just done some long-overdue forum housekeeping: I created a new subforum for the Chang'e program.

I split this very long Chang'e thread into four:
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