Mercury Orbit Insertion, Events and Discussion leading up to MOI |
Mercury Orbit Insertion, Events and Discussion leading up to MOI |
Mar 13 2011, 12:16 PM
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#61
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Solar System Cartographer Group: Members Posts: 10229 Joined: 5-April 05 From: Canada Member No.: 227 |
Ingenious idea but impossible! Remember, we didn't have a rocket big enough to get Cassini to Saturn without several gravity assists to help it, so the reverse is bound to be impossible with a little bit of residual fuel. And Cassini's fate is decided - burn up in Saturn's atmosphere.
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 13 2011, 04:39 PM
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#62
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Senior Member Group: Members Posts: 2173 Joined: 28-December 04 From: Florida, USA Member No.: 132 |
Ingenious idea but impossible!... Yeah. I know next to nothing about the mechanics of getting from one planet to another but look at how 'hard' it's been getting Messenger from Earth to Mercury. I don't see why it would be any easier to get from Saturn to Mercury and with a craft not designed to do that. |
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Mar 13 2011, 04:52 PM
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#63
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Merciless Robot Group: Admin Posts: 8785 Joined: 8-December 05 From: Los Angeles Member No.: 602 |
If I understand things correctly (and I probably don't), it might actually be easier in terms of delta-V to crash into Mercury from the outer Solar System. Saturn's heliocentric orbital velocity is much lower than that of the Earth, so presumably that means less thrust would be required to negate it & 'fall' into the inner system.
However, we're still probably talking about a change in velocity of several (if not tens) of km/sec, plus escaping from Saturn orbit. I doubt that Cassini could have done this even if it was fully fueled at the beginning of the maneuver. -------------------- 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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Mar 13 2011, 07:13 PM
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#64
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Senior Member Group: Members Posts: 2106 Joined: 13-February 10 From: Ontario Member No.: 5221 |
The sun-grazer and long-period comets are an extreme example of this right? A tiny nudge in the Oort cloud is more than enough to send them in a more or less straight line sunward.
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Mar 13 2011, 09:25 PM
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#65
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Merciless Robot Group: Admin Posts: 8785 Joined: 8-December 05 From: Los Angeles Member No.: 602 |
Yeah, basically. The stuff way out there is barely moving in comparison to the planets; probably doesn't take much to negate their orbital motion at all (e.g., gravitational nudges from passing stars over long periods of time, perhaps occasional outgassing from the cometary bodies themselves?)
-------------------- 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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Mar 14 2011, 03:14 AM
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#66
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Member Group: Members Posts: 128 Joined: 10-December 06 From: Atlanta Member No.: 1472 |
If I have calculated correctly, you need a delta-V of 5.4 km/s to go from Saturn's orbit into a Hohmann transfer orbit intersecting Mercury. Dawn could have done it (ignoring distance from Sun issue), but I doubt if Cassini ever had that much of delta-V.
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Mar 14 2011, 06:06 AM
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#67
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Member Group: Members Posts: 146 Joined: 31-October 08 Member No.: 4473 |
At the present time (this Sunday Evening), Mercury would appear from Messenger to be about the same size as the Moon from Earth, with the Sun looming 3 times that diameter.
I think Messenger must halve its current distance to Mercury to enter the Hill Sphere... Soon! |
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Mar 14 2011, 08:54 AM
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#68
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Member Group: Members Posts: 340 Joined: 11-April 08 From: Sydney, Australia Member No.: 4093 |
The cheapest (in terms of energy) way to get a spacecraft very close to, or into, the Sun is indeed a Jupiter flyby. Scientifically not very interesting because the spacecraft would not spend much time near the Sun during periapsis. See the Solar Probe Plus trajectory options at
http://solarprobe.jhuapl.edu/mission/docs/...018missions.pdf pages 3 and 4. The Jupiter flyby option requires by far the least C3. -------------------- |
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Mar 15 2011, 04:16 AM
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#69
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Senior Member Group: Admin Posts: 3108 Joined: 21-December 05 From: Canberra, Australia Member No.: 615 |
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Mar 15 2011, 04:43 AM
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#70
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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, 04:55 AM
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#71
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Founder Group: Chairman Posts: 14434 Joined: 8-February 04 Member No.: 1 |
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Mar 15 2011, 03:05 PM
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#72
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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 15 2011, 07:57 PM
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#73
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Senior Member Group: Admin Posts: 4763 Joined: 15-March 05 From: Glendale, AZ Member No.: 197 |
Not far now! If it were green, Messenger would look just like that little android character that keeps popping up on my new phone. -------------------- If Occam had heard my theory, things would be very different now.
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Mar 16 2011, 03:54 AM
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#74
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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 16 2011, 04:03 AM
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#75
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Merciless Robot Group: Admin Posts: 8785 Joined: 8-December 05 From: Los Angeles Member No.: 602 |
A minor milestone just occurred to me: Not only will Messenger become the first spacecraft to orbit Mercury, but for the first time we will have orbited every terrestrial planet in the Solar System...in fact, we will have active spacecraft orbiting every major body in the inner Solar System.
Maybe that's not such a minor milestone, actually... ...wow! -------------------- 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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