China to the Moon - Chang'e program, Chinese unmanned lunar mission Options

[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

[Phil Stooke]

Chang'E-3 landing area:

http://meetingorganizer.copernicus.org/EPS...C2012-151-1.pdf

Phil

[Phil Stooke]

The landing area shown in that abstract is plotted here as a red box on a Quickmap background:



So not necessarily literally in Sinus Iridum, it may be outside but nearby. I don't know of other areas with the very high resolution coverage, so Chang'E 4 may be targeted for the same region, and maybe even the later sample return missions. Still quite a lot of scope for different sites and surface compositions here.

Phil

[tolis]

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]

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:

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]

. The relative distance at closest approach will be about 11 km/s.

Interesting info

[Phil Stooke]

We should probably move this section of the thread to a dedicated asteroid section.

Phil

[Paolo]

Interesting info

oops...