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dartmanx
2006-Feb-01, 04:54 PM
Once again, forgive my amatuer questions.

NH, according to the mission page (exact link: http://pluto.jhuapl.edu/mission/images/pluto_encounter3.jpg), is expected to coast about 10000 kilometers.

Now, how hard would it have been to coast slightly closer to Jupiter and cut this distance a bit for better observation? Or would that have been impossible due to the mechanics of the gravity assist?

stu
2006-Feb-01, 05:03 PM
One of the mission scientists is down the hall ... but she's not in now so I can't ask her. I would guess that it has to do both with the gravity assist (if you fly closer, then your orbit would be more perturbed so your angle change would be too much and you'd miss Pluto) and the heavy radiation environment around Jupiter, where the closer you get, the more radiation you receive and your instruments would need to be more heavily shielded.

01101001
2006-Feb-01, 05:35 PM
Yeah, I don't think Jupiter is the place for that sort of fine tuning of close-approach distance. There are undoubtedly trajectory correction maneuvers planned after the Jupiter assist, that set the flyby distance.

I also suspect that the mission is not all about closeup images of Pluto. The 10000 kilometer closest-distance is likely a compromise based on the needs of all the instruments on board. Further, there are objectives other than Pluto. They need to plan the cruise so that after close measurements of Pluto, they cruise near Charon, they pass through Pluto's shadow, and they pass through Charon's shadow, all without large maneuvers.

I'd bet the figure of 10000 is not the final one, but approximate, too. It sounds too round. In reality it will probably be refined a little to best accomplish all the goals, with more precise knowledge of the way things are moving, gained on the way in. (Oh, it even implies that on the graphic: "The New Horizons team will develop plans to observe Pluto's two smaller moons after addtional observations to refine each moon's orbit.")

By the way, the original link seems broken. It should be this:
Pluto-Charon Flyby: Closest Approach (July 15) (http://pluto.jhuapl.edu/mission/images/pluto_encounter3.jpg)

dartmanx
2006-Feb-01, 09:40 PM
One of the mission scientists is down the hall ... but she's not in now so I can't ask her. I would guess that it has to do both with the gravity assist (if you fly closer, then your orbit would be more perturbed so your angle change would be too much and you'd miss Pluto) and the heavy radiation environment around Jupiter, where the closer you get, the more radiation you receive and your instruments would need to be more heavily shielded.

I saw in another thread something about a correct burn near Jupiter possibly preventing a closer approach to Pluto.

But, I asked the question thinking "Hey, 1 kilometer closer to Jupier might mean 50 kilometers closer to Pluto...". Like alot of the public, I want to see the pretty pictures, after all.

ToSeek
2006-Feb-01, 09:44 PM
They could get as close to Pluto as they wanted to get - a tiny correction burn just past Jupiter would adjust the course by millions of miles, let alone thousands, by the time the spacecraft gets to Pluto. I'm assuming that there is good reason why they're aiming for a spot 10k km away, whether it's the instruments or the mission goal of witnessing the occultations.

stu
2006-Feb-02, 06:31 PM
One of the mission scientists is down the hall ... but she's not in now so I can't ask her.

According to Fran Bagenal, 10,000 km is at 32 Jupiter radii from the planet, which is a compromise distance to be outside the radiations belts, still get good data from Jupiter, and get the right gravity assist to get to Pluto.

tony873004
2006-Feb-02, 08:34 PM
I agree with ToSeek. It would only take a very small change in the Jupiter distance to equate to 10,000 km by the time it got to Pluto.

And a correction burn after the Jupiter encounter would only have to provide about 3 or 4 cm/s of delta-V to make a 10,000 km difference 9 years later (assuming linear:) )

Whatever distance we get to Pluto will be what ever distance we desire. Crashing into it would be an option if that's what we wanted to do.

scottmsg
2006-Feb-03, 05:13 AM
I believe 10,000km flyby is a requirement for the radio science part of the mission. From what I've read, there are to be occultations of the Sun and Earth by both Pluto and Charon.

Here is a post by Alan Stern, the Principal Investigator, on the timing of the mission, on unmannedspaceflight.com (http://www.unmannedspaceflight.com/index.php?showtopic=675&st=360&p=30783&#entry30783).

yaohua2000
2006-Feb-03, 06:37 PM
Flyby at 10000 kilometers allows the spacecraft occulted by both Pluto and Charon seen from the Earth. This is one of the mission goals.

http://commons.wikimedia.org/wiki/Image:View_of_Earth_from_New_Horizons_-_20150714.gif

publiusr
2006-Feb-09, 09:56 PM
New Horizons info:
http://forum.nasaspaceflight.com/forums/thread-view.asp?tid=1311&posts=13