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How far will NH pass by Pluto?, - and will it be possible to effect a meaningful course change?
Guest_Oersted_*
post Apr 16 2008, 02:16 PM
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So, from what I gather, NH will pass by Pluto at a speed of around 14 km/s. I know it won't be able to slow down in any way, and will continue into deep space afterwards, but is a substantial course change envisaged at Pluto, or will it fly by so far away that the course change will be negligible?

I realise that the instruments must be optimised for a pass at a certain distance, but what distance is that and could it possible by reduced with no ill effects?

It would be mindblowing if a low pass over Pluto could be planned so that NH will fly close by Charon as well, wouldn't it? - Or maybe even - to go really out on a limb - a few high-speed figure 8's around both bodies, before the probe continues on its merry way. smile.gif Would that even be physically possible?

At least I'm not suggesting aero-braking if Pluto turns out to have a tenuous atmosphere. blink.gif
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djellison
post Apr 16 2008, 02:32 PM
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QUOTE (Oersted @ Apr 16 2008, 03:16 PM) *
Would that even be physically possible?


No.

It's fly in, fly out, at high speed, and balancing range for time and coverage.

Doug
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ugordan
post Apr 16 2008, 02:38 PM
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QUOTE (Oersted @ Apr 16 2008, 04:16 PM) *
... if Pluto turns out to have a tenuous atmosphere.

This is already an established fact. The atmosphere is currently (or should be in the not-so-distant future) in the process of re-freezing to the surface as Pluto moves away from the Sun.


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jamescanvin
post Apr 16 2008, 02:50 PM
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NH trajectory through the Pluto system (from NH website)




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john_s
post Apr 16 2008, 02:58 PM
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Last fall we changed this slightly, updating the closest approach distance from 10,000 km to 12,500 km. This buys us a bit more time near close approach, at the expense of a little spatial resolution. Going much closer wouldn't improve our resolution much because images would be smeared, and we wouldn't have time to cover much territory.

I guess we need to update that graphic!

John.
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Alan Stern
post Apr 16 2008, 03:03 PM
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QUOTE (john_s @ Apr 16 2008, 03:58 PM) *
Last fall we changed this slightly, updating the closest approach distance from 10,000 km to 12,500 km. This buys us a bit more time near close approach, at the expense of a little spatial resolution. Going much closer wouldn't improve our resolution much because images would be smeared, and we wouldn't have time to cover much territory.

I guess we need to update that graphic!

John.



Here's the updated version.


Attached thumbnail(s)
Attached Image
 
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Greg Hullender
post Apr 16 2008, 03:04 PM
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QUOTE (Oersted @ Apr 16 2008, 06:16 AM) *
Or maybe even - to go really out on a limb - a few high-speed figure 8's around both bodies, before the probe continues on its merry way. smile.gif


I remember how disappointed I was when I learned that a figure 8 isn't a possible orbit. (Neither is a spiral, for that matter.) If we could just post equations in here, maybe we could have a thread on orbital mechanics . . .

--Greg
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Alan Stern
post Apr 16 2008, 03:04 PM
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QUOTE (Alan Stern @ Apr 16 2008, 04:03 PM) *
Here's the updated version.



This is better.
Attached File(s)
Attached File  Encounter_Flyby.ppt ( 105.5K ) Number of downloads: 448
 
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jamescanvin
post Apr 16 2008, 03:12 PM
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QUOTE (Oersted @ Apr 16 2008, 03:16 PM) *
but is a substantial course change envisaged at Pluto, or will it fly by so far away that the course change will be negligible?


Clearly the deflection by Pluto (+moons) is going to be tiny - but I'd be interesting to know just how tiny is it?


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jamescanvin
post Apr 16 2008, 03:21 PM
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I hope Alan doesn't mind but here is that Powerpoint image in png format.


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Guest_Oersted_*
post Apr 16 2008, 06:38 PM
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QUOTE (Greg Hullender @ Apr 16 2008, 05:04 PM) *
I remember how disappointed I was when I learned that a figure 8 isn't a possible orbit. (Neither is a spiral, for that matter.) If we could just post equations in here, maybe we could have a thread on orbital mechanics . . .

--Greg


Why isn't a figure 8 or just an S-shaped orbit physically possible? (as opposed to just being not desirable for coverage reasons).

Thanks for all the replies and graphics, enlightening indeed! - And not just for me, I'm happy to say, since we seem to have an update on the pass parameters.
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JRehling
post Apr 16 2008, 06:44 PM
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QUOTE (jamescanvin @ Apr 16 2008, 07:12 AM) *
Clearly the deflection by Pluto (+moons) is going to be tiny - but I'd be interesting to know just how tiny is it?


Well, Pluto has 0.2% the mass of Earth, and New Horizons will pass 12,500 km away. That means the max acceleration due to gravity will be 0.0005 g, or about 0.005 m/s^2. Calculus or modeling are required to get a true answer, but if we assume that that acceleration were in effect for 1500 seconds, it would impart a total delta-v of 7.5 m/s. That should be the right order of magnitude. That is 0.0005 of the velocity of NH (more or less to right angles to its path), which would alter NH's heading by 0.03 degrees. Close enough to zero for you?
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ugordan
post Apr 16 2008, 07:21 PM
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My ballpark calculation assuming the impact parameter B is ~= C/A distance and v(c/a) ~= v(inf) and that there's no Charon around gives a deflection angle of 0.02 deg which agrees with JRehling's calculation nicely. For all practical purposes you can neglect Pluto has any mass.


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nprev
post Apr 16 2008, 07:40 PM
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Kinda figured as much...it's not very large, and is mostly made of not-so-massive stuff.

One thing I'd like to know is how much maneuvering propellent NH is currently estimated to have post-Pluto for the KBO encounter, and how large a conic section of space she can feasibly reach (by this I mean total potential delta-V vs. power supply endurance, comm range, etc. if there are any other limiting factors). Also, are there any tentative plans to conduct a retargeting maneuver to reach a KBO prior to the Pluto encounter, or will all this take place afterwards? (I'm guessing that the latter is far more likely based on current planning as shown, plus there's no gravitational assist potential at Pluto to speak of).

A Plutino would presumably be the ideal target in terms of feasiblity; IIRC, most of these are approximately coplanar with Pluto's orbit?


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siravan
post Apr 17 2008, 01:35 AM
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Looking at the encounter image, it seems that the trajectory is designed such that at closest distance to Pluto, NH is essentially 180 degree off Charon. I guess the design has scarified imaging resolution for the chance of doing radio science during occlusions. Is this the main reason or are there other considerations that forced the trajectory to be where it is? Also, is it possible for Pluto to have any rings (vis-a-vis Rhea)? And if so, is there any planning to look for them (long exposures and such)?
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