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Mercury Flyby 3
tanjent
post Sep 17 2009, 01:00 AM
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The mission website discussion of the orbital phase does not say much about how the mission will end.

http://messenger.jhuapl.edu/the_mission/orbit.html

Maintaining the orbit will require continued fuel consumption.
The page does not reveal if, after 12 months or 2 solar days they expect to simply run the tank dry and
lose contact with the spacecraft, or what other sort of ending will follow. I have heard no
proposals for extending the mission, but somewhere near the end - after completion of all the major objectives
a moment may come when otherwise unacceptable risks can be considered. My little suggestion represents just one
possibility - maybe not a very strong candidate, but if the mission can end with an attention-grabbing "goodbye" shot,
there would be some value in that.

Dmuller, thanks for pointing out the big advantage in apparent size still enjoyed by the sun at the present time.
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tedstryk
post Sep 20 2009, 12:56 PM
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While we are waiting, I have added my Mariner 10 set to my blog http://planetimages.blogspot.com/2009/09/m...at-mercury.html


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4th rock from th...
post Sep 21 2009, 11:58 AM
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ExcellentMariner 10 images! And a very nice job of bringing out the subtle color differences from a very limited dataset. They match very well with the Messenger global views.


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tedstryk
post Sep 21 2009, 02:26 PM
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Thanks. I made them just before the first Messenger flyby. The correlation isn't perfect, but the filter combinations here are much more blue-shifted. The south pole view is just a rough overlay based on the color seen in the first two images.


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Greg Hullender
post Sep 21 2009, 06:15 PM
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James Leary has discussed a possible extended mission:

http://www.nasa.gov/missions/highlights/we...transcript.html

However, all he said was that they mght get the spacecraft into a slightly lower orbit so as to get slightly better pictures. He didn't suggest that Messenger would ultimately impact Mercury.

Solomon's "Mercury After Messenger" is a very cool read all by itself, and he suggets an XM for Messenger might be just a single Earth year:

http://www.spacepolicyonline.com/pages/ima...n_MESSENGER.pdf

Despite the title, it's mostly about what Messenger will do at Mercury, but it suggests that after Messenger and Bepi-Colombo, there won't be a lot gained by another orbiter. The next step would have to be a lander or sample-return mission.

--Greg
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Greg Hullender
post Sep 22 2009, 03:48 PM
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The Messenger team will be doing a press conference tomorrow to discuss next week's flyby:

http://messenger.jhuapl.edu/news_room/details.php?id=130

QUOTE
WASHINGTON -- NASA will host a media teleconference at 1 p.m. EDT on Wednesday, Sept. 23, to preview MESSENGER's third and final flyby of Mercury.


This appears to be limited to press, but perhaps someone like Emily will be able to report back to us. :-)

--Greg
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Greg Hullender
post Sep 22 2009, 03:56 PM
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There is a nice map, just posted today, showing the planned imaging coverage:

http://messenger.jhuapl.edu/gallery/scienc...mp;image_id=326

Note that this suggests that Flyby #3 will cover more than half of the never-seen terrain.

I also note that the areas marked for Flyby #1 and Flyby #2 are backwards. Flyby #1 coverage is actually the area outlined in red on the image and Flyby #2 is outlined in blue, as we can see from the Flyby #2 coverage plan:

http://messenger.jhuapl.edu/gallery/scienc...erage_Sep08.jpg

We knew that this flyby would be very similar to Flyby #1 -- so much that some of us had worried there would be nothing new to see at all. What's surprising (to me, anyway) is that the coverage on approach is much larger and significantly shifted compared to flyby #1 (and this is where almost all the new coverage comes from) but the coverage on departure is almost the same as for Flyby #1. Wonder why so much difference between the two?

--Greg
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elakdawalla
post Sep 22 2009, 04:18 PM
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QUOTE (Greg Hullender @ Sep 22 2009, 07:48 AM) *
This appears to be limited to press, but perhaps someone like Emily will be able to report back to us. :-)

Gosh, I'd missed the fact it was a telecon, not TV briefing. I'm glad you mentioned it -- got my request for the phone number in in time! I'll certainly be reporting on it. Today I'm working on my usual preview timeline.

--Emily


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elakdawalla
post Sep 22 2009, 06:51 PM
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QUOTE (Greg Hullender @ Sep 22 2009, 07:56 AM) *
I also note that the areas marked for Flyby #1 and Flyby #2 are backwards. ...
I don't think so. According to my notes, it's flyby 2 and 3 that had the same geometry:

QUOTE
Flyby 1: January 14, 2008
» Sun illuminates 95 to 275°E
Flyby 2: October 6, 2008
» Sun illuminates 273 to 93°E
Flyby 3: September 29, 2009
» Sun illuminates 270 to 90°E


The two maps you point to are just centered on different longitudes.

I think maybe the reason the approach crescents are different is because on flyby 2 MESSENGER was coming in from a direction farther from the Sun -- its orbit has shrunk since then. But I don't have the best instinct for orbital geometry. If I don't think of a better question to ask, I may ask this one tomorrow.

--Emily


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Greg Hullender
post Sep 22 2009, 07:35 PM
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QUOTE (elakdawalla @ Sep 22 2009, 10:51 AM) *
I don't think so. According to my notes, it's flyby 2 and 3 that had the same geometry:

The two maps you point to are just centered on different longitudes.


Oops!

QUOTE (elakdawalla @ Sep 22 2009, 10:51 AM) *
I think maybe the reason the approach crescents are different is because on flyby 2 MESSENGER was coming in from a direction farther from the Sun -- its orbit has shrunk since then. But I don't have the best instinct for orbital geometry. If I don't think of a better question to ask, I may ask this one tomorrow.


Actually, taking a look at the plots of the orbit, I think I can see it now:

This was flyby #2

http://messenger.jhuapl.edu/the_mission/ME...rthPoleFull.jpg

And this is flyby #3

http://messenger.jhuapl.edu/the_mission/ME...rthPoleFull.jpg

The orbit "bends" a good bit more this time -- which makes sense, as Messenger is losing energy with each flyby. It's probably just a coincidence that the outbound path seems to be more or less the same (with respect to the planet surface) as it was for flyby #2. Especially since this flyby seems to be about 25 degrees further around Mercury's orbit than the last two were.

http://messenger.jhuapl.edu/the_mission/trajectory.html

Shoot. Just as I typed all this, the Messenger folks released this:

QUOTE
Because the spacecraft velocity relative to Mercury is about one-third slower at Mercury flyby 2 than at Mercury flyby 2, the gravity-assist turn angle to the spacecraft’s trajectory increases from about 27° to nearly 50°,” explains Jim McAdams, the MESSENGER mission design lead engineer. “This greater bend in the trajectory provided by the gravity of Mercury offers the spacecraft its first opportunity to view a small portion of Mercury’s surface twice with different vantage points and nearly identical lighting conditions just a few hours apart.


So I guess that's the answer. I'd still like to know exactly what percentage of Mercury will remain unimaged after this flyby . . .

--Greg
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dmuller
post Sep 23 2009, 01:08 AM
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Does anybody have the flyby timeline in spreadsheet form? Going through the encounter sim just drives me nuts, plus it doesn't match with any other info i have :-(


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Greg Hullender
post Sep 23 2009, 06:26 PM
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Another press release today:

http://messenger.jhuapl.edu/news_room/details.php?id=132

A couple of things I hadn't realized before:

1) This is their last chance to study the magneto tail in the equatorial plane.
2) The flyby images are higher-resolution near the equator than any pictures Messenger will take later.
3) They are still looking for possible moons, down to radius 100m.

--Greg
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Greg Hullender
post Sep 25 2009, 06:24 PM
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Another Messenger update, this one has a new photo.

http://messenger.jhuapl.edu/mer_flyby3.html

Given the approach image we saw before, I think that means the lighted part of this crescent is mostly terrain that has never been imaged before, so that's kind of cool. Interesting-looking bright crater near the top.

--Greg
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kohare
post Sep 26 2009, 12:56 AM
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QUOTE (gndonald @ Sep 17 2009, 01:15 AM) *
Preparations for the third flyby

They still have not released a press kit for this. It looks like it won't be released until the 23rd when they have the teleconference.

MESSENGER Mercury Flyby 3 Press Kit (PDF) now available. File title seems to indicate it's draft 3 from 23 September, so maybe it will be updated in a a final release??
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dmuller
post Sep 26 2009, 01:56 AM
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I have uploaded Emily's flyby blog onto my realtime simulation at http://www.dmuller.net/messenger. Less than 4 days to go.


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