Author Topic: New Horizons updates  (Read 172681 times)

Offline Dappa

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Re: New Horizons update
« Reply #80 on: 07/13/2012 05:06 PM »
New Horizons Doing Science in Its Sleep
Pluto-Bound Spacecraft to Collect More Data When ‘Hibernating’

http://pluto.jhuapl.edu/news_center/news/20120709.php

Offline cleonard

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Re: New Horizons update
« Reply #81 on: 07/13/2012 06:30 PM »
A 5th moon discovered... Wow. Looks like the New Horizons team has to go back to the drawing board and revise the Pluto encounter sequence (obviously) :)

This makes it very likely that there are more moons and maybe even rings.  The mission may change a lot.  Expect images looking for a safe path during approach and a likely last minute maneuver with the associated real fast revisions to the encounter.  I have a feeling that they will be busier than expected for those several weeks leading up to the flyby.

About the best they can do is target a radius from Pluto that is a disadvantageous resonance from Charon orbit.  Basically, shoot for the spot least likely to have another moon or significant debris.  Might not be the best from a science perspective, but you sure don't want it to go boom.

Offline Star One

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Re: New Horizons update
« Reply #82 on: 07/13/2012 06:51 PM »
A 5th moon discovered... Wow. Looks like the New Horizons team has to go back to the drawing board and revise the Pluto encounter sequence (obviously) :)

Covered in this article.

http://www.space.com/16548-pluto-fifth-moon-new-horizons-spacecraft.html

Offline Silico

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Re: New Horizons update
« Reply #83 on: 09/02/2012 12:54 AM »
How essential to making the New Horizons mission feasible is the fact that Pluto is crossing the plane of the solar system? Just bonus good luck that makes the mission a bit easier, or would it be much harder if history had turned out differently and the same spacecraft had to encounter Pluto in 1950, when it was at its greatest angle?

Offline ugordan

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Re: New Horizons update
« Reply #84 on: 09/02/2012 10:08 AM »
Bonus good luck. With Pluto that far out, the Jupiter flyby could have flung it out out of ecliptic plane by the required angle easily, although that would probably have required a closer flyby (potentially nearing Jupiter's radiation belts).

Offline Silico

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Re: New Horizons update
« Reply #85 on: 09/02/2012 10:39 PM »
Bonus good luck. With Pluto that far out, the Jupiter flyby could have flung it out out of ecliptic plane by the required angle easily, although that would probably have required a closer flyby (potentially nearing Jupiter's radiation belts).

That's right, the Voyager probes did out-of-plane slingshots to encounter Titan and Triton. NASA was actually considering sending Voyager 1 to Pluto.

Looks like the good timing for NH saved a few years in cruise and a more risky Jupiter slingshot.

Thanks for the reply.

Offline Dappa

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Re: New Horizons update
« Reply #86 on: 09/02/2012 11:14 PM »
Looks like the good timing for NH saved a few years in cruise and a more risky Jupiter slingshot.
This was indeed the most optimal timing for NH, but another launch window wouldn't have used more risky slingshot. In fact, it would not have done any slingshot maneuver, delaying NH's arrival at Pluto by 2-4 years. Besides, Pluto's orbit is quite slow, so Pluto wouldn't have moved very much out of the ecliptic a few years later. 
« Last Edit: 09/02/2012 11:14 PM by Dappa »

Offline ugordan

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Re: New Horizons update
« Reply #87 on: 09/03/2012 07:43 AM »
That's right, the Voyager probes did out-of-plane slingshots to encounter Titan and Triton.

Well, the out-of-plane for Voyager 1 was a result of the Titan flyby before encountering Saturn, not a prerequsite. Flying by Titan meant Saturn would be the final destination visited - losing Pluto, etc., but that was a trade that had to be made.

Offline Solman

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Re: New Horizons update
« Reply #88 on: 09/07/2012 07:34 PM »
 Could NH be capable of astrometry - the long baseline would allow best ever parallax measurement of distance to nearby stars if camera capable of this kind of precision wouldn't it?

Offline Robotbeat

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Re: New Horizons update
« Reply #89 on: 09/07/2012 08:32 PM »
Could NH be capable of astrometry - the long baseline would allow best ever parallax measurement of distance to nearby stars if camera capable of this kind of precision wouldn't it?
You should be able to figure this out yourself, given the aperture of the NH telescope and the baseline and some basic geometry, etc. ;)
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Offline Solman

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Re: New Horizons update
« Reply #90 on: 09/08/2012 09:27 PM »
Could NH be capable of astrometry - the long baseline would allow best ever parallax measurement of distance to nearby stars if camera capable of this kind of precision wouldn't it?
You should be able to figure this out yourself, given the aperture of the NH telescope and the baseline and some basic geometry, etc. ;)

 Don't you need to know the pointing accuracy of the telescope? I suppose I should have said useful parallax measurement - isn't it all about precision?

Offline Solman

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Re: New Horizons update
« Reply #91 on: 09/08/2012 09:43 PM »
 To clarify - what I mean is that the orientation of the spacecraft and thereby the telescope, has to be known to extreme accuracy to measure the parallax angle change to the required precision relative to a telescope on Earth doesn't it?

Offline Comga

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Re: New Horizons update
« Reply #92 on: 09/08/2012 10:22 PM »
To clarify - what I mean is that the orientation of the spacecraft and thereby the telescope, has to be known to extreme accuracy to measure the parallax angle change to the required precision relative to a telescope on Earth doesn't it?

A priori knowledge of the spacecraft pointing is not necessary.  It can be determined from the images.  However, the angular accuracy is going to be some fraction of the pixel Instantaneoud Field of View.  This is 20 microradians, about 4 arc seconds, for Ralph, and about 10 microradians for LORRI.  One might be able to get centroid determination down to 10% or that, maybe better.  However, the accuracy for Hipparcos was way beyond that, so even with a 2 AU baseline it is hard to beat.

Plus the baseline is in only one direction so the accuracy would be maximum for a perpendicular plane.  The targets it needs to see are nearly straight ahead, KBO's, where the baseline doesn't help.
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline simonbp

Re: New Horizons update
« Reply #93 on: 09/09/2012 04:04 AM »
For reference, LORRI has better-than-Hubble resolution for the Pluto system at two weeks out. So, it's not really useful for astronomy.

Ralph is a scanline imager (each column on the CCD is a different filter, meant for sweeping), so not capable of imaging astronomical targets.

They are extremely propellant-limited, and so will only spin down to three-axis stabilized a month-or-so out from the flyby.

There are lots of astronomers on the New Horizons team (my boss included), and believe me, if there were some way to get science out of the cruise phase without affecting the primary mission, they would have done it.
« Last Edit: 09/09/2012 04:06 AM by simonbp »

Offline ugordan

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Re: New Horizons update
« Reply #94 on: 09/09/2012 11:50 AM »
Consider the data volume as well. Data rates that far out are low and they would need to compete for DSN time with many other missions.

Offline Solman

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Re: New Horizons update
« Reply #95 on: 09/10/2012 11:33 PM »
 Thanks for the generous responses to this amateur's "bright idea".

Offline Comga

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Re: New Horizons update
« Reply #96 on: 09/11/2012 04:37 AM »
For reference, LORRI has better-than-Hubble resolution for the Pluto system at two weeks out. So, it's not really useful for astronomy.

Ralph is a scanline imager (each column on the CCD is a different filter, meant for sweeping), so not capable of imaging astronomical targets.

They are extremely propellant-limited, and so will only spin down to three-axis stabilized a month-or-so out from the flyby.

There are lots of astronomers on the New Horizons team (my boss included), and believe me, if there were some way to get science out of the cruise phase without affecting the primary mission, they would have done it.

This has some errors.

Ralph is a Time Domain Integration (TDI) imager.  It has several (16 IIRC) fully populated rows in each 5.7 degree wide 20 microradian IFOV array.  The electronic signal version of the image is clocked in synchronization with the rotation of the spacecraft to build up an image.  There are two panchromatic arrays and four arrays with color filters: red, blue, Near IR, and a wavelength range that corresponds to absorption by solid methane.   It darned well takes astronomical images, and quite good ones for such a small, light weight, low power, instrument.  It also does imaging spectrometery, recording hyperspectral data cubes from 1.2 to 2.4 microns across about a square degree FOV.   It also has a panchromatic frame transfer array with 128 rows (IIRC) that is the navigation sensor for the flight.

Hubble's ACS High Resolution Camera has 0.13 microradian IFOVs or 153 times that of Ralph, 76 times that of LORRI.  Pluto is about 30 AU away from Earth and Hubble.  LORRI's IFOV matches ACS HRC at 30/76=0.40 AU. New Horizons is under <8.3 0 AU from Pluto, with 1038 days to go, so at 50 days out it should be at said 0.4 AU.  That's seven weeks, not two, and reality is slightly better than this linear model.

I don't think that the statement about being "extremely fuel limited" can be supported.  As stated, the don't "spin down" to take all of their images.  In fact, New Horizons spins in the direction of its maximum moment of inertia (pitch) to take images and spectra with Ralph.  "Flat spins" (yaw) are for hibernation or other cruise phases where they want to maintain high gain antenna pointing towards the Earth with minimum action and interaction, and to hold the Student Dust Counter into the direction of travel. 

They have just despun New Horizons, run through an entire encounter sequence at full rotational speed I believe, as a practice.  They may do this again before encounter if new discoveries, such as the fifth moon P5, cause them to extensively rearrange the encounter sequence.  This will use fuel that would otherwise be available for a divert maneuver to target a KBO after the Pluto encounter, but they are not "fuel starved".
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline Comga

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Re: New Horizons update
« Reply #97 on: 09/11/2012 04:43 AM »
Consider the data volume as well. Data rates that far out are low and they would need to compete for DSN time with many other missions.

It's not a "fair competition". :-)

New Horizons needs to clear its memory at a specific time before closest encounter to maximize the available volume for data that may not be available again in the lifetimes of our great grandchildren.  Then it needs to send down some data right after closest approach to clear volume for science data on departure.  These are precisely scheduled and very high priority.  The DNS is not going to ignore these broadcasts or tell NH to limit its Pluto data.

edit: Pluto is moving away from the Sun.  Sometime in the next decade or so, the atmosphere will freeze out, snowing down on the surface and obscuring surface features until the next Pluto spring, some major fraction of 248 years from now.  This mission is our only chance to see the surface.
« Last Edit: 09/11/2012 04:45 AM by Comga »
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline ugordan

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Re: New Horizons update
« Reply #98 on: 09/11/2012 07:23 AM »
You are missing my point. Of course the Pluto flyby data is of the highest importance, I'm saying that allocating precious DSN time (which will support only low bitrates with NH anyway due to the vast distance) is a waste of DSN time for measuring something (star parallax) which is certainly not very high priority/mission critical data.

Offline Chandonn

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Re: New Horizons update
« Reply #99 on: 09/11/2012 08:46 AM »
Hey, can we please get this UPDATES thread back to UPDATES and move the DISCUSSION to a more appropriate thread?

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