Mercury Flyby 3 |
Mercury Flyby 3 |
Jul 3 2009, 09:27 PM
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#1
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Senior Member Group: Members Posts: 1018 Joined: 29-November 05 From: Seattle, WA, USA Member No.: 590 |
We're now just one Mercury year (88 days) from flyby #3, which happens on September 29, 2009, so this seems like a good time to start a thread about it.
http://messenger.jhuapl.edu/index.php For comparison purposes, it'd be nice if someone (probably someone on the Messenger team) put together a Mercury Map showing what areas will get better coverage from this flyby than from the previous ones. I realize it'll be very similar to flyby #1, but it won't be exactly the same. After that, it's a long wait until MOI on March 18, 2011. Curiously, that's the same date the New Horizons crosses the orbit of Uranus. http://pluto.jhuapl.edu/mission/passingpla...ets_current.php --Greg |
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Sep 22 2009, 03:56 PM
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#2
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Senior Member Group: Members Posts: 1018 Joined: 29-November 05 From: Seattle, WA, USA Member No.: 590 |
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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Sep 22 2009, 06:51 PM
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#3
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Administrator Group: Admin Posts: 5172 Joined: 4-August 05 From: Pasadena, CA, USA, Earth Member No.: 454 |
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 -------------------- My website - My Patreon - @elakdawalla on Twitter - Please support unmannedspaceflight.com by donating here.
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Sep 22 2009, 07:35 PM
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#4
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Senior Member Group: Members Posts: 1018 Joined: 29-November 05 From: Seattle, WA, USA Member No.: 590 |
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! 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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