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Unmanned Spaceflight.com > Other Missions > Cometary and Asteroid Missions
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Paolo
I thought it was time to split the subject from the Moon forum.
Admins, can you move the relevant messages here?

anyway, just out: an interesting blog article by Bill Gray explaining how he recovered the probe and how he computed the orbit yielding the 13 December flyby date
Chang'e 2: The Full Story
Paolo
a few more observations of Chang'e 2 (designated 2010-050A by the COSPAR) in solar orbit were made last saturday by the Catalina Sky Survey
http://www.minorplanetcenter.net/iau/DASO/...DASO_000449.txt
I hope Bill Gray will soon be using them to update its orbit determination and encounter estimates
TheAnt
Interesting story thank you for sharing.
Mr Gray seem to be quite the detective and he do use the word 'sleuth' as well. =)
rlorenz
I don't suppose they'll rename the spacecraft 'Obelix'....
Paolo
I have got a copy of this paper presented at last week's IAF Congress
Low energy trajectory optimization for CE-2ís extended mission after 2012
I will not share the paper, but I can tell you something more about the Toutatis flyby

- first of all: 13 December 2012 is confirmed as the date. no distance nor relative speed or other details are given
- we are told that the Beijing Aerospace Control Center called for proposals on a mission beyond L2 in January 2012.
- there were lots of interesting proposals including one that would flyby Earth and Moon repeatedly, visit the L1 and L2 Lagrangian points, flyby a hundred-meter sized asteroid and finally explore the L4 Sun-Earth point in 2017 (the paper states that CE-2 would have been the first mission to do so. I think one of the two Stereos was first)
- in March 2012 the Toutatis flyby, proposed by the Chinese Academy of Space Technology was selected
- in a non-optimized form, the mission would have cost 107.5 m/s of the remaining 120 m/s delta-v budget
- a 6.2 m/s correction on 15 April "was mainly used to keep the Lissajous trajectory". it was previously reported as the date CE-2 was maneuvered out of the L2 halo orbit
- trajectory optimization was only carried out starting on 16 April. After optimization, an additional 22 m/s delta-v was gained that could be used to ensure a successful flyby
- the first targeting maneuver was carried out on 31 May (32.9 m/s)
- the second targeting maneuver (46.5 m/s) was to be carried out on 24 September
tolis
According to JPL's HORIZONS ephemeris service,

(Some of) The vital statistics of Toutatis on the 13th December 2012 are as follows:


Epoch (UT) () Geocentric distance () Apparent Magnitude () Solar Elongation
() (AU) () () (deg)
13/12 00:00 () 0.0466 () 10.73 () 125
13/12 12:00 () 0.0471 () 10.65 () 128
14/12 00:00 () 0.0478 () 10.59 () 132


Toutatis will be east of the sun and so an evening object in the sky. Judging from the magnitude and
solar elongation, I would say that it is well within reach of backyard observers (including myself).

Regards to All,


Tolis.
Paolo
I saw it in November 1996 using a small, 114 mm telescope. under dark skies, it was easy to spot and it was amazing to see it clearly glide against the background stars
Paolo
today on arXiv: Composition of Near-Earth Asteroid (4179) Toutatis

tolis
QUOTE (Paolo @ Oct 10 2012, 04:15 PM) *
I saw it in November 1996 using a small, 114 mm telescope. under dark skies, it was easy to spot and it was amazing to see it clearly glide against the background stars


It will be moving quite fast on this occasion too, about 1/3 degree per hour.
Paolo
to answer Phil Stooke's question in another thread http://www.unmannedspaceflight.com/index.p...st&p=193809 about the CE-2 end of mission I noted playing with the orbital elements published by Bill Gray that the orbital period of the probe is now 1.044 years that is it will trail behind the Earth by 15 degrees every year. in four years that is in July 2016 it will pass close to the trailing Lagrangian point L5. It will then be back in the vicinity of Earth in 24 years.
I pointed this out to someone in China who worked on orbit design for the Toutatis flyby but he told me that this is a pure coincidence and that it was not done on purpose
BTW I posted this graph of the orbit of CE-2 up to the end of 2016 in a fixed Sun-Earth reference to the NASAspaceflight forum a few weeks ago. L5 is the red dot.
Phil Stooke
Excellent - thanks for this.

Phil

Tom Tamlyn
The link to Bill Gray's August 25 planetary.org article in post # 1 is broken.

I found the post at:

http://www.planetary.org/blogs/guest-blogs...full-story.html
Paolo
just tweeted by @asrivkin at the AGU meeting

QUOTE
In asteroid news, China's Chang'E 2 will fly by the asteroid Toutatis in a few weeks. My (USA) source tells me it'll get 2 images


which to me confirms the difficulty of imaging Toutatis with a push-broom camera instead of a proper 2-dimensional CCD
Phil Stooke
Check out this e-poster from the current AGU meeting:

http://fallmeeting.agu.org/2012/eposters/eposter/p31a-1873/

This is about radar imaging of Toutatis. Even if we only get a couple of reasonably well resolved images of Toutatis, it will be a big help in interpreting the radar images which contain complex ambiguities. There is a detailed shape model, but such models are also not without problems. Plus of course, there will be some information (we would hope) about albedo variations etc. which the radar does not give.

Phil

Paolo
I saw it. It's a pity that 2 pics will not be enough to reveal the complex spin of Toutatis
Phil Stooke
No, but radar does that very well.

Phil

Paolo
speaking of which, the first radar image of the 2012 flyby
http://echo.jpl.nasa.gov/asteroids/Toutati...2_planning.html
Paolo
from this post to the mpml asteroids and comets group http://tech.groups.yahoo.com/group/mpml/message/27635 the two pics will be taken one on the inbound leg, the other on the outbound leg. my Chinese sources say the targeted distance will be 1000 km.
I guess what this means is that CE2 will aim at the point in space where Toutatis is supposed to be and wait for it to cross the field of view of its push-broom camera at the correct angular rate. then it will be reoriented to take a second picture with the same technique on the outbound leg
machi
So we can expect images with resolution ~100 m/pix at best. This isn't much for such small body like Toutatis (~2.5 km diameter), but still it can be very interesting.
~25 image elements per diameter is enough for major units, like albedo regions or big craters and it's sufficient for Emily's size comparison poster.
Explorer1
So the images will be the equivalent of what Deep Space 1 did, assuming they pull them off?
machi
Deep Space took images of Braille with resolution around 180 m/pix. Braille is two times smaller than Toutatis. So with some luck, we can expect images four times better than those of asteroid Braille (4◊ more pixels across diameter of asteroid).
This is what we can expect, if everything goes well and image will be taken close to 1000 km flyby distance.
Paolo
anyway, as the camera has two linear CCDs, a forward looking and a rearward looking one I would rather expect two couples of pictures instead of two pictures
Phil Stooke
Machi, that is Steins, not Braille.

And Paolo - doesn't that suggest the forward camera will take one and the rearward camera will take one? Otherwise you seem to be suggesting the spacecraft reorient itself during each sequence.

And there's another new image here:

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



Phil
machi
QUOTE (Phil Stooke @ Dec 7 2012, 03:11 PM) *
Machi, that is Steins, not Braille.

Yes, I know.
That is image of Steins from Rosetta used for demonstration as Toutatis may appear from CE-2.
I thought that I wrote this clearly, if not my apologies, it was lost in translation. smile.gif
In fact this image was uploaded with name "Steins_as_Toutatis_from_Change2", but evidently forum system still uses some kind of thumbnail with different name even for small images.
Paolo
QUOTE (Phil Stooke @ Dec 7 2012, 03:11 PM) *
And Paolo - doesn't that suggest the forward camera will take one and the rearward camera will take one?


the camera has two parallel CCDs, one looking 8 degrees forward of the nadir (when in lunar orbit), the other 17.2 degrees to the rear. To me the most logical sequence would be one where Toutatis crosses the field of view of the first CCD almost perpendicular to it and then about one minute later (the exact timing depends on the encounter geometry, which is not known) that of the second sometime on the inbound leg. Around closest approach the probe is reoriented so that Toutatis crosses again both fields of views in the outbound leg. this gives two pairs of images.
If no reorienting is done, you get only one pair of images a few tens of seconds apart
Paolo
third radar picture http://echo.jpl.nasa.gov/asteroids/Toutati...32Hz.s439.b.gif
it's amazing how the quality and resolution of these images has increased since 1992
machi
According to this page, flyby distance will be around 300 km.
If it's true, then images from CE-2 will much better than in my simulated image (maybe 4◊ better).
tasp
I'm not thinking of any other 'rocks' imaged with ground based radar getting a nice visible light camera flyby. (It is REALLY early for me though, and no coffee yet) (we need a 'sleepy' emoticon)

Anyone recall any others?


Paolo
Itokawa had been imaged by radar before Hayabusa arrived
machi
QUOTE (tasp @ Dec 9 2012, 02:21 PM) *
I'm not thinking of any other 'rocks' imaged with ground based radar getting a nice visible light camera flyby...
Anyone recall any others?


Not exactly "rock", but also comet Hartley 2 was imaged by radar.
Here is article about "Radar observations of asteroid 25143 Itokawa".
Phil Stooke
Comparing the Itokawa radar images and shape model with the spacecraft images shows the limitations of using low resolution radar data. The basic size and elongation are well established but the two-lobe shape is not seen. For Hartley-2 two lobes are also resolved but not much more. But for Toutatis we have high resolution radar data and a detailed shape model, and nothing with that kind of radar data has been visited by a spacecraft. So this will be a very interesting encounter.

Phil

JimOberg
Technical info is great. Hsieh hsieh.

Big picture question: has anybody received any word about the health of the spacecraft in the past two months?

We're only days from the encounter. Is the absence of any news from China something to worry about?
Explorer1
The absence of news is business as usual over there. Has there even been an official announcement of this flyby yet from CNSA in Beijing?
JimOberg
QUOTE (Explorer1 @ Dec 9 2012, 09:38 PM) *
The absence of news is business as usual over there.


I beg to differ. When things have been going well, China has released a stream of information, even ahead of actual events. They have been far more open then the Soviets were in Space Race days. I remember and can compare/contrast.

This silence is unusual.

Explorer1
Yes, I've read Don Mitchell's page on the old Soviet missions to the Moon and Venus, and the lengths he had to go to. I'm not sure if he posts on here, but I;m sure has has good insights too.
I'm just saying we should not get our hopes for a real crisp and immediate release like we've become used to from NASA or even ESA. I'd even be happy with a Halley's nucleus type blur.
Paolo
there was a long article on the development of CE-2 on a Chinese site recently
http://zh.cnr.cn/2100zhfw/zhhz/201211/t201...511342196.shtml and http://zh.cnr.cn/2100zhfw/zhhz/201211/t201...1342196_1.shtml
at a certain point it is stated (my adaptation of a google translation):

QUOTE
According to the latest news, Chang E 2 successfully completed further extend the test a second halfway correction, the whole control process satellite subsystems work properly, in good condition. Until October 9, Chang'e II satellite in orbit flight 736 days, has 2.61 million kilometers from Earth. Follow-up will be used to track and test our new two deep space monitoring stations and to carry out the technical test.
JimOberg
QUOTE (Paolo @ Dec 10 2012, 09:15 AM) *
there was a long article on the development of CE-2 on a Chinese site recently


Thanks, Paolo, that's encouraging.

I also found this more recent URL but I can't get my translators to work:
http://news.e23.cn/content/2012-12-10/2012C1000084.html

Paolo
another long article in Chinese linked today on the 9ifly forum
http://y234.cn/?p=6128
JimOberg
QUOTE (Paolo @ Dec 10 2012, 07:01 PM) *
another long article in Chinese linked today [url="http://bbs.9ifly.cn/thread-9843-109-1.html"]on the 9ifly forum [


I see a picture of chang'e-2 but can't get translator to work. Any help?

stevesliva
^ Google Translate
... seems to be a blogger asking similar questions. It appears based on english articles, so you get what we already know translated to chinese and then google-translated back. Wouldn't assume that will do anything but subtract information.
elakdawalla
Google translate worked for me. There's no new information in here -- in fact it links to Bill Gray's guest blog on planetary.org and to MPML. It provides background on Toutatis and on NEOs. Mostly it asks why the national space agency isn't ballyhooing this more, and then answers the question by explaining that Chang'E 2's ability to get good data on the encounter is limited, concluding that while any data will be interesting, the significance of this is more as an engineering test of the Chinese ability to make the encounter succeed, providing "valuable experience." Seems like a very nice explainer -- hopefully the author will get some traffic from Chinese readers smile.gif
JimOberg
QUOTE (elakdawalla @ Dec 10 2012, 09:13 PM) *
Google translate worked for me.


thanks. i agree that the technology demonstration of the SEL2 dwell, and the departure to the toutatis intercept point, are awesome new levels of space navigation capabilities. it would be nice to get images but your own blog put that in perspective.

i'm working to get my own media clients to appreciate the accomplishment and not to set artificially high success criteria.

would clementine have faced the same problem with asteroid imaging, or was its survey camera of a different design?

mcaplinger
QUOTE (JimOberg @ Dec 10 2012, 02:17 PM) *
would clementine have faced the same problem with asteroid imaging, or was its survey camera of a different design?

The Clementine cameras were all framing cameras with filter wheels, so no.

That said, slewing a pushbroom imager is not that big a deal; see http://mars.jpl.nasa.gov/mgs/msss/camera/i..._98_phobos_rel/ Of course I don't know how CE2's attitude control system works.
Phil Stooke
http://echo.jpl.nasa.gov/asteroids/Toutati...2_planning.html


New images appearing on this site now - one other difference between radar and CE2 images, worth remembering - the visible images will have MUCH better signal to noise - radar images are speckly and show very little detail near the terminator (except bits of it which are tilted towards the radar, like a crater rim) - in fact it's sometimes hard to see where the radar terminator is. So the new images really will be complementary in many ways.

Phil

machi
Very interesting images. Here is image pair from 9. December in more "visible" look:
Phil Stooke
15 years ago I made a map of Toutatis, using an experimental image interpretation method. It was never published because of a dispute about the validity of the concept I had devised. This is the map, in case anybody is interested. Apart from the concept I used to convert the geometry of radar images to the equivalent of visible images for mapping (that's where the dispute came in) I also tended to push my interpretation of craters too far in those days. Every little hollow became a crater in my map. Now I would be more cautious in my interpretation. (Note - rotation is about the long axis - and because of ambiguity in the images, this might be a mirror image of the real surface)

Phil

Click to view attachment
Paolo
anybody knows whether ESA is providing tracking support to CE-2?
otherwise, has anybody tried computing the windows of visibility for the Chinese Deep Space Network stations? just to know when we can expect to have some news of the flyby
Greenish
The images at http://echo.jpl.nasa.gov/asteroids/Toutati...2_planning.html get better every day. Will be really interesting to see how the delay-doppler representations compare to the visible light ones.

I just noticed the following on that page: "Scheduling update: due to an equipment failure, radar observations of Toutatis at Arecibo were cancelled." Not sure when this appeared... Can anyone explain what the potential impact could be on the observing campaign? Not that I'm complaining, the Goldstone quick results are great and impressive on their own.
Phil Stooke
I don't see anything in the online chinese press yet.

Phil

Paolo
I have seen a release (in Chinese) on the site of the Chinese Academy of Sciences.
I don't have a link at hand, but it really didn't say anything new.
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