Mercury Orbit Insertion, Events and Discussion leading up to MOI |
Mercury Orbit Insertion, Events and Discussion leading up to MOI |
Nov 25 2009, 05:30 AM
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Senior Member Group: Members Posts: 1018 Joined: 29-November 05 From: Seattle, WA, USA Member No.: 590 |
Excerpts from a new press release from the Messenger Team:
QUOTE Deep-Space Maneuver Positions MESSENGER for Mercury Orbit Insertion The Mercury-bound MESSENGER spacecraft completed its fifth and final deep-space maneuver of the mission today, providing the expected velocity change needed to place the spacecraft on course to enter into orbit about Mercury in March 2011. . . . today's maneuver began at 4:45 p.m. EST. Mission controllers at The Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., verified the start of the maneuver about 12 minutes, 49 seconds later, when the first signals indicating spacecraft thruster activity reached NASA's Deep Space Network tracking station outside Goldstone, Calif. "The team was well-prepared for the maneuver," said MESSENGER Mission Systems Engineer Eric Finnegan, of APL. "Initial data analysis indicates an extremely accurate maneuver execution. After sifting through all the post-burn data I expect we will find ourselves right on target." --Greg |
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Mar 9 2011, 01:10 PM
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#2
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Solar System Cartographer Group: Members Posts: 10229 Joined: 5-April 05 From: Canada Member No.: 227 |
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 -------------------- ... because the Solar System ain't gonna map itself.
Also to be found posting similar content on https://mastodon.social/@PhilStooke Maps for download (free PDF: https://upload.wikimedia.org/wikipedia/comm...Cartography.pdf NOTE: everything created by me which I post on UMSF is considered to be in the public domain (NOT CC, public domain) |
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Mar 10 2011, 02:22 AM
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Junior Member Group: Members Posts: 23 Joined: 30-June 05 Member No.: 422 |
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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Mar 10 2011, 07:32 AM
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#4
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Senior Member Group: Members Posts: 1452 Joined: 26-July 08 Member No.: 4270 |
...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.
-------------------- -- Hungry4info (Sirius_Alpha)
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Mar 13 2011, 05:36 AM
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#5
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Junior Member Group: Members Posts: 89 Joined: 27-August 05 From: Eccentric Mars orbit Member No.: 477 |
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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