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MESSENGER ARRIVES, Mercury Orbit Insertion
MahFL
post Mar 29 2011, 01:13 PM
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QUOTE (Anders @ Mar 29 2011, 10:42 AM) *
I am curious about the orbital period of the MESSENGER spacecraft. Is it exactly 12 hours? If so, how was it chosen?



"The MESSENGER team designed the orbit to optimize the scientific yield of the mission and data transfer to Earth, while addressing thermal environment concerns.".

MESSENGER spends most of the time away from the surface to transmit data back to earth, and not to overheat due to reflected heat.
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Holder of the Tw...
post Mar 29 2011, 01:59 PM
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"Finnegan told Spaceflight Now the spacecraft is in an orbit with a closest approach 128.5 miles above Mercury's surface and a high point of 9,482.7 miles. The orbit is inclined 82.5 degrees to Mercury's equator and it takes MESSENGER more than 12 hours to complete one circuit of the planet, according to Doppler tracking data."

So it's more than twelve hours, but they don't say how much more.
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Anders
post Mar 29 2011, 04:30 PM
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QUOTE (Holder of the Two Leashes @ Mar 29 2011, 03:59 PM) *
So it's more than twelve hours, but they don't say how much more.


Thank You,
I got the impression that it was exactly 12 hours. That would have been an interesting trade-off.
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Phil Stooke
post Mar 29 2011, 04:41 PM
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Twelve hours period, with a major data downlink every other orbit, would simplify operations by having the same DSN coverage each day.

From the mission design page:

"After MESSENGER arrives in the primary science orbit, small forces, such solar radiation pressure – the force exerted by sunlight - 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 certain science goals.

To keep this minimum altitude below 500 kilometers (310 miles), propulsive maneuvers must occur in pairs once every Mercury year - every 88 days. The first maneuver in each pair increases the orbit period to 12 hours, 15 minutes by speeding up the spacecraft at its closest distance from Mercury. Two-and-a-half orbits later a maneuver at the farthest distance from Mercury slows the spacecraft just enough to adjust the orbit period back to 12 hours and return the minimum altitude to 200 kilometers (124 miles). 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 near the same point in its orbit as it was at Mercury orbit insertion."

So the current period might not be exactly 12 hours but that's immaterial, the intention is to keep adjusting it to stay around 12 hours all the time (and the correct altitude etc.).

Phil


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ugordan
post Mar 29 2011, 05:20 PM
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QUOTE (Holder of the Two Leashes @ Mar 29 2011, 03:59 PM) *
"Finnegan told Spaceflight Now the spacecraft is in an orbit with a closest approach 128.5 miles above Mercury's surface and a high point of 9,482.7 miles.


Those orbital parameters translate to 12 hours 4 minutes period if I got it right. You can never tell with "miles"...


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Hungry4info
post Mar 29 2011, 08:21 PM
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From here


Attached thumbnail(s)
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charborob
post Mar 29 2011, 08:26 PM
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Messenger took 363 images after that first one. More images to be posted tomorrow at 2 pm EDT.
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Bjorn Jonsson
post Mar 29 2011, 08:50 PM
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The image is centered at approximately 15°E and 55°S. This is a major improvement over earlier imaging coverage in this area and of course there are going to be narrow angle images as well. At a quick glance nothing that looks especially interesting. There are fairly strong contrast/brightness variations associated with some of the craters. Many scarps. And there is an interesting looking crater plus some associated features at (280,255).
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ugordan
post Mar 29 2011, 09:00 PM
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Looks good, nice to see the WAC behaving as if nothing happened. smile.gif


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volcanopele
post Mar 29 2011, 09:23 PM
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Here is the image laid on top of the released footprint map. The blue outline is the area that was blank on the map to this point. The blue dot is the south pole.
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Anders
post Mar 29 2011, 09:29 PM
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QUOTE (Phil Stooke @ Mar 29 2011, 06:41 PM) *
Twelve hours period, with a major data downlink every other orbit, would simplify operations by having the same DSN coverage each day.

Interesting point about DSN, I didn't thought about that.
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Phil Stooke
post Mar 29 2011, 09:39 PM
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Very rough fit of the image to a colorized version of the pre-orbit mosaic, south polar view. (only adding the bit which improves on the previous coverage)

Phil

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brellis
post Mar 30 2011, 03:56 AM
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I read an article saying thrusters have to be fired every few months to keep MESSENGER from floating into a higher orbit by the Sun's gravity. I don't get that, since it's in a polar orbit.

Oh, wait -- the Sun is ALWAYS tugging on things, and at the proximity of Mercury, it gets taken into account throughout the orbit, on a scale similar to instances where the ISS fires thrusters to stay at altitude versus miniscule atmospheric drag. Okay, I get that.

When it doesn't have any fuel left, will it get sucked into the Sun?

LOL! The mission science is just beginning, I'm already wondering what's going to happen to our intrepid spacecraft when it runs out of fuel! sad.gif
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eoincampbell
post Mar 30 2011, 04:04 AM
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It really is astounding science, all hail MESSENGER team,
cue: heavy orchestral sounds for MESSENGER images smile.gif


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Hungry4info
post Mar 30 2011, 04:44 AM
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QUOTE (brellis @ Mar 29 2011, 09:56 PM) *
When it doesn't have any fuel left, will it get sucked into the Sun?

The plan is for an impact on Mercury. But hypothetically, if they were to refrain from adjusting the orbit, and if MESSENGER left Mercury's hill sphere, it would orbit the sun.


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