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Mercury Orbit Insertion, Events and Discussion leading up to MOI
Ron Hobbs
post Mar 16 2011, 04:44 AM
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nprev,

The milestone is that every planet known to the ancients, all the classical planets, will now have been the host of an orbiter from Earth. I think this is a very significant milestone. I find it interesting that Mercury was the last of the classical planets to be explored by an orbiter.

We are nearing the end of the initial reconnaissance of the Solar System. What a time to be alive!

Ron
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Holder of the Tw...
post Mar 16 2011, 05:45 AM
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QUOTE (mchan @ Mar 15 2011, 09:54 PM) *
Agree Messenger velocity at perihelion is higher than Mercury. But...


Planet and spacecraft are both pretty close to perihelion, Mercury already overtook and briefly passed MESSENGER, and now the probe is faster and closing in.
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nprev
post Mar 16 2011, 06:11 AM
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QUOTE (Ron Hobbs @ Mar 15 2011, 08:44 PM) *
We are nearing the end of the initial reconnaissance of the Solar System. What a time to be alive!


Very true. It took us something like 200,000 years to do that for Earth alone...around 60 years to do the same for the rest of the Solar System.

We make progress of sorts. wink.gif


--------------------
A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
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nprev
post Mar 16 2011, 07:43 AM
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And apologies for those who have seen this before, but Ron reminded me just how significant Messenger's impending detailed of exploration of Mercury really is in the Big Picture; here's a column I did once upon a time for Rui Borges' spacEurope blog:

http://spaceurope.blogspot.com/2008/05/map...-previsich.html


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A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
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tasp
post Mar 16 2011, 12:27 PM
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nprev:

The galaxy beckons.


wink.gif
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Greg Hullender
post Mar 17 2011, 03:10 AM
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QUOTE (mchan @ Mar 15 2011, 08:54 PM) *
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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