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 15 2011, 04:43 AM
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Member Group: Members Posts: 599 Joined: 26-August 05 Member No.: 476 |
The orientation of the day side is to the right vs. to the left in Where is Messenger? page on the Messenger website. I had wondered about the latter since Messenger is ahead of Mercury in its orbit waiting for the planet to "catch up" to it. EOTSS appears to have the view in accord with the convention of North pointing up.
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Mar 15 2011, 03:05 PM
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Member Group: Members Posts: 146 Joined: 31-October 08 Member No.: 4473 |
The orientation of the day side is to the right vs. to the left in Where is Messenger? page on the Messenger website. I had wondered about the latter since Messenger is ahead of Mercury in its orbit waiting for the planet to "catch up" to it. EOTSS appears to have the view in accord with the convention of North pointing up. Actually, Messenger is catching up with Mercury, with higher ellipticity in its current (not for long!) orbit, Messenger's speed at perihelion is greater than Mercury's. |
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Mar 16 2011, 03:54 AM
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Member Group: Members Posts: 599 Joined: 26-August 05 Member No.: 476 |
Actually, Messenger is catching up with Mercury, with higher ellipticity in its current (not for long!) orbit, Messenger's speed at perihelion is greater than Mercury's. Agree Messenger velocity at perihelion is higher than Mercury. But, it appears to me that Messenger's orbit angular velocity is less than that of Mercury at the rendezvous. The Mercury flybys and DSM burns are tailored to put Mercury and Messenger in near-resonant orbits with each flyby and DSM burn reducing the ratio of the resonance. After the last flyby, Mercury completes 6 orbits and Messenger completes 5 orbits before the rendezvous for the orbit insertion burn. So it appears to me that Mercury is catching up with Messenger. Would someone who knows the astrodynamics please correct this? |
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Mar 17 2011, 03:10 AM
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#5
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Senior Member Group: Members Posts: 1018 Joined: 29-November 05 From: Seattle, WA, USA Member No.: 590 |
Agree Messenger velocity at perihelion is higher than Mercury. But, it appears to me that Messenger's orbit angular velocity is less than that of Mercury at the rendezvous. . . .Would someone who knows the astrodynamics please correct this? Here's a way to think about it that might be helpful. Imagine three probes. Two of them in very different circular orbits (say, one with a 1-year period and another with a 2-year period) and the third probe in an elliptical orbit that just touches the inner probe's orbit at perihelion and which just touches the outer probe's orbit at aphelion. At perihelion, probe #3 has to be moving faster than probe #1, and at aphelion, probe #3 has to be moving slower than probe #2. I assume you already know this is because probe #3 has more total energy (kinetic + potential) than probe #1 and less total energy than probe #2. The reason that the angular velocity as perihelion is greater than the angular velocity of probe #1 is simply because at perihelion, probe #3 is moving tangent to the orbit of probe #1. It has zero radial velocity at that point; ALL of its velocity is angular for that one instant. --Greg |
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