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Mercury Orbit Insertion, Events and Discussion leading up to MOI
stevesliva
post Mar 7 2011, 05:00 AM
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I thought we had established that Dione is totally boring.
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Bjorn Jonsson
post Mar 7 2011, 11:27 AM
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There's not even a single planet/satellite/asteroid/comet that is boring in my opinion (and BTW I suspect you are confusing Dione with Rhea).

There are already some hints from the Messenger flyby data that Mercury is more interesting/complex than previously expected.
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JohnVV
post Mar 8 2011, 05:09 AM
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QUOTE
I thought we had established that Dione is totally boring.

well the voyager teem thought that the Jovian moons would be "the moon" boring and boy were they wrong
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volcanopele
post Mar 8 2011, 05:24 AM
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Nope Rhea is boring. But it's monotonous surface does make for nice desktop backgrounds. So it's good for something.


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Astro0
post Mar 8 2011, 11:02 AM
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I've been rummaging through some boxes and found a bunch of old NASA/JPL newsletters.
Thought that the covers of these might help wet your appetites for MESSENGER's pending MOI. smile.gif

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Explorer1
post Mar 8 2011, 10:53 PM
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I wonder what happens if you dial that number at the bottom...
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Phil Stooke
post Mar 9 2011, 01:10 PM
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I used to do that! For Voyager, not Mariner 10, but it was the same thing. Don Bane from the Public Affairs Office would record a phone message, updated every week during slow times, and daily or more often for busy times like a flyby. It was the equivalent of checking into UMSF every morning.

I'm at LPSC this week... I'll post a few pics when I get back... but regarding Mercury, I asked Sean Solomon if his spacecraft was going to impact on Mercury at the end of the mission so I could have a point to plot on a map. I think he preferred not to think about that just yet... but yes, it will. Still not clear to me if it will be a controlled impact, or just left to strike at an unknown location.

Phil


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kwp
post Mar 10 2011, 02:22 AM
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QUOTE (Phil Stooke @ Mar 9 2011, 05:10 AM) *
I asked Sean Solomon if his spacecraft was going to impact on Mercury at the end of the mission so I could have a point to plot on a map. I think he preferred not to think about that just yet... but yes, it will.


Hadn't occurred to me before, Phil, quite how morbid your interests can be. With regard to the demise of MESSENGER, do we know enough about Mercury's gravitational field to be able to estimate how stable the MESSENGER orbit will be? I assume Mercury's gravity is more homogeneous than the Moon's, but perhaps that is counteracted by Solar effects and light pressure?

-Kevin
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nprev
post Mar 10 2011, 02:41 AM
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I'd hardly call that a "morbid" interest, kwp. Phil has been diligently mapping space hardware/man-made crash sites on the Moon, and high-speed impacts are obviously of scientific interest since they frequently expose fresh subsurface material. Knowing Messenger's final impact region would greatly facilitate spotting the nice fresh crater it will make from some future Mercury orbiter (Bepi-Columbo?)


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Hungry4info
post Mar 10 2011, 07:32 AM
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QUOTE (kwp @ Mar 9 2011, 08:22 PM) *
...do we know enough about Mercury's gravitational field to be able to estimate how stable the MESSENGER orbit will be?
I'm almost certain we know next to nothing about it. All the flybys so far have mostly been equatorial to stay in the plane of Mercury's orbit for alignment with another flyby. And of course there's only been a handfull of flybys.


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tasp
post Mar 10 2011, 02:06 PM
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The Pioneer Venus craft experienced large perturbations from it's proximity to the sun at Venus distance. That affect will be worse at Mercury, and with the Mercurian orbital eccentricity, the effect will be variable over time, too.


(I am deliberately neglecting Messenger altitude and eccentricity, it is still early here)
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DFinfrock
post Mar 11 2011, 12:59 AM
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QUOTE (nprev @ Mar 10 2011, 02:41 AM) *
Knowing Messenger's final impact region would greatly facilitate spotting the nice fresh crater it will make from some future Mercury orbiter (Bepi-Columbo?)


I wonder if Messenger can survive in orbit long enough to wait until Bepi-Columbo's arrival, before taking that plunge to the surface. We could get a lot more science out of Messenger's demise, if it could remain in orbit that long, and allow Bepi to watch from orbit as the new crater forms.
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gndonald
post Mar 12 2011, 03:04 PM
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She's getting closer


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kwan3217
post Mar 13 2011, 05:36 AM
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QUOTE (Hungry4info @ Mar 10 2011, 01:32 AM) *
I'm almost certain we know next to nothing about it. All the flybys so far have mostly been equatorial to stay in the plane of Mercury's orbit for alignment with another flyby. And of course there's only been a handfull of flybys.


From http://messenger.jhuapl.edu/orbit_insertio...tionkeeping.htm

QUOTE
...and staying there

After MESSENGER arrives in the primary science orbit, small forces, such as solar gravity – the gravitational attraction of the Sun - slowly change the spacecraft's orbit. Although these small forces have little effect on MESSENGER's 12-hour orbit period, they can increase the spacecraft's minimum altitude, orbit inclination, and latitude of the surface point below MESSENGER's minimum altitude. Left uncorrected, the increase in the spacecraft's minimum altitude would prevent satisfactory completion of several science goals.

To keep the spacecraft’s minimum altitude below 500 kilometers (310 miles), propulsive maneuvers must occur at least once every Mercury year - one complete revolution around the Sun, or 88 Earth days. The first, third, and fifth maneuvers after Mercury orbit insertion will occur at the farthest orbital distance from Mercury where a minimum amount of propellant will slow the spacecraft just enough to lower the minimum altitude to 200 kilometers (124 miles). The act of lowering the spacecraft’s altitude in this way has an unavoidable side effect of also lowering orbit period by 13-15 minutes. The second and fourth maneuvers after orbit insertion will increase the orbit period back to about 12 hours by speeding up the spacecraft near its closest distance from Mercury. Because the sunshade must protect the main part of the spacecraft from direct sunlight during propulsive maneuvers, the timing of these maneuvers is limited to a few days when Mercury is either near the same point in its orbit as it was during Mercury orbit insertion or near the point where Mercury is on the opposite side of the Sun from that for orbit insertion.


Since the spacecraft will be in a long equatorial orbit, it will spend most of its time relatively far from Mercury, where the local lumpiness in the gravity field matters less and the gravity from the Sun and planets matter more. This is how the station-keeping maneuvers can be planned before the gravity field is mapped out. Of course if the gravity field turns out to be much much different from the expectation, they may have to change their plans, but I am sure that mission ops is flexible enough to handle it.
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As old as Voyage...
post Mar 13 2011, 08:43 AM
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QUOTE (DFinfrock @ Mar 11 2011, 12:59 AM) *
I wonder if Messenger can survive in orbit long enough to wait until Bepi-Columbo's arrival, before taking that plunge to the surface. We could get a lot more science out of Messenger's demise, if it could remain in orbit that long, and allow Bepi to watch from orbit as the new crater forms.


About 5 years ago I proposed to Paul Helfenstein (Cassini science team member) that at the end of its useful life Cassini could use its remaining fuel to leave Saturn orbit and drop Sunwards to impact on Mercury; the impact to then be observed by Bepi-Columbo. He was interested but I doubt it'll happen.


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