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Posted by: ToSeek Jan 20 2006, 07:44 PM

We have a contrarian over on the http://64.207.216.12/showpost.php?p=660245&postcount=21 asking if it would have made more sense to have skipped the Jupiter flyby. Yes, it would take longer for the probe to get to Jupiter, but presumably it will be going slower when it gets to Pluto and could therefore do more science.

Any comments?

(I did search this time to see if this question had been answered. My apologies if it has, and I missed it.)

Posted by: Rob Pinnegar Jan 20 2006, 08:06 PM

That is an interesting point.

Aren't there some concerns here, though, regarding the memory storage of New Horizons? I vaguely remember that, as things stand, some of the images are going to have to be compressed to save memory, even with the shorter flyby of the Jupiter-assisted flight path.

This suggests to me that a slower flyby might have resulted in more images, but those images would contain less information due to increased compression.

Is this correct?

Posted by: Chmee Jan 20 2006, 08:08 PM

Actually, I just thought the same thing this morning in manner of "well, if the launch was delayed and NH was forced to go direct, at least they would have a longer encounter at Pluto.

Of course arriving a few years later the RTG would have that much less power, so less science might be accompished.

Posted by: Toma B Jan 20 2006, 08:13 PM

How much memory is actually on the New Horizons?

Posted by: helvick Jan 20 2006, 08:52 PM

There are two 8GByte solid state data storage units (one is a redundant backup).
Pre flight estimates of archive data volumes:
Jupiter Science - 43GBytes
Pluto/Charon - 13.5GBytes
From http://pds-smallbodies.astro.umd.edu/missions/newhorizons/new_horizons_pdmp.pdf
I'm assuming that lossless compression of the imaging data products accounts for most of the variance, there will be some pre-encounter data returned but I'd be very surprised if it was >5GBytes.

I don't think a slower flyby would make enough of a difference to justify the longer wait. We would lose all that Jupiter science too and that alone will more than make up for any marginal extra data that might be gained at Pluto.

Posted by: Bob Shaw Jan 20 2006, 08:52 PM

I seem to remember 2 x 4Gb solid-state memory assemblies (much tougher than those in PCs, so don't make hasty comparisons!).

Although it may be true that a Pluto encounter *would* take longer at a slower speed, the practical answer is 'not by much' when you're close. In addition, NH is billed as a mission to a variety of worlds, not just one - a slow trajectory eats into KBO time, costs money, and means that we lose time which should have been spent on that l-o-o-o-o-n-g slow cruise to the heliopause.

Good to see NH is on the way, and as *fast* as possible!

Bob Shaw

Posted by: ljk4-1 Jan 20 2006, 09:23 PM

Keep in mind that by 2015 there will likely be even better ways to retrieve, compress, and store spacecraft data.

That's how NASA/JPL was able to have Voyager 2 work at Neptune in 1989, a destination only considered as a possibility when the probe was first launched in 1977.

I am also sure the NH team doesn't mind having a set of worlds to "practice" on before Pluto and the other KBOs. Amazing that we are living in a time of planetary exploration where the Jupiter system is considered a necessary "detour" rather than the destination.

One of my wishes for the Jupiter encounter: Will NH be able to image Europa sufficiently to see if any of the surface ice has shifted since Galileo? Will the probe also be able to look for any Europan geysers?

Are there any pre-Pluto planetoids or comets on NH's flight path close enough to examine?

Posted by: JRehling Jan 20 2006, 09:37 PM

I kind of doubt that there will be appreciably better ways in 2015 -- I think we probably passed the "elbow" in the image-compression curve between 1977 and 2000.

If there are significant improvements to be made, they would probably be lossy compression routines special-cased for this mission's kind of imaging, distinct from the Internet-viewable JPEGs that image compression technology has developed around. For example, many images scanning for new moons would be predominantly black. Other opportunities would key on the fact that mosaics of Pluto would contain overlap between frames -- if the team is "gutsy" enough, they could choose to only transmit one copy of the overlap. Note that video compression takes advantage of the fact that similar frames of the same scene separated in time by very small intervals tend to share lots of image that thus only needs to be transmitted once. It's conceivable that multispectral sequences could take advantage of the considerable overlap (often: black space on the edge, light disc sector in the middle, same shadows due to topographical shading).

Indeed, 9 years is a long time to have to play with this stuff -- but you want to make sure that you don't miss some data if Pluto happens to be, in any way, psychopathic in its various spectral/spatial properties. For example, if a geyser plume were fast-moving.

Posted by: djellison Jan 20 2006, 11:57 PM

Remember - the further out you push the Pluto encounter, the thinner the atmosphere is likely to be.....and the less power you'd have...and the less fuel...thus less opportunity to visit KBO's etc etc

Getting there sooner rather than later makes sense in its own right, before you add the bonus of Jupiter science.

Doug

Posted by: tedstryk Jan 21 2006, 12:04 AM

"In a system as complex as a spacecraft, finding hardware and software problems during ground testing is commonplace. Last month, spacecraft testing revealed a hardware problem in one of the 64-gigabit Solid State Recorders aboard New Horizons. These flash memory devices, called SSRs, are the memory banks on which the spacecraft stores all of the scientific and engineering data it generates. For redundancy purposes, New Horizons carries two SSRs, and we require that both be operational at launch. The problem with our sick SSR is probably related to a manufacturing defect on a single circuit card, and is not expected to be hard to repair. The sick SSR will have to be removed from the spacecraft and repaired after New Horizons emerges from the vacuum chamber in September. The repaired device must be successfully tested on its own and on New Horizons before it can be certified as flight ready."
http://www.spaceref.com/news/viewsr.html?pid=17594
Based on this, it seems 64-gigabits per recorder, which would I believe be 8 gigabytes per recorder.

Posted by: Bob Shaw Jan 21 2006, 12:11 AM

Ted (etc):

Interesting to know just *what* the numbers are, but it certainly would appear that getting there faster is better, and cheaper. Now, where have I heard something like that before?

Bob Shaw

Posted by: Tom Tamlyn Jan 21 2006, 03:12 AM

The question posed is an interesting one. I suspect that the fact that the probability of "atmospheric collapse" increases with time (due to Pluto's orbital position moving further away from the sun) was a key reason for embracing the Jupiter maneuver. Also, I would think that there would need to be a very substantial increase in the length of closest approach to make up for the various risks and costs of a longer mission, to say nothing of the team's perfectly legitimate interest in designing a mission which they would live to complete.

Shamefully, I lack the physics skills to attempt even an approximation of the impact on the flyby speed of the slower cruise. However, a 2003 mission description paper available http://www.boulder.swri.edu/pkb/Antofagasta.doc on the Science Team's website states (emphasis added):

"The spacecraft-planet relative flyby speed for the planned Pluto-Charon encounter will be approximately 12 km/sec (depending on the launch date, this can vary by up to 20%). Nominal closest approach distances of 10,000 km are planned for Pluto and KBOs, but closer approaches are under consideration."

This suggests to me that the slower cruise would not produce substantial benefits in the form of a more leisurely closest approach. Also, I suspect that altering the approach distance would be a more useful way to optimize the flyby campaign.

It would be interesting to hear from someone who understands the orbital mechanics well enough to give an informed analysis.

TTT

Posted by: edstrick Jan 21 2006, 09:38 AM

"...Also, I suspect that altering the approach distance would be a more useful way to optimize the flyby campaign..."

Altering the flyby distance is probably minimally possible due to other constraints.

NH is targeting for radio occultation by both Pluto and Charon. There are probably a limited number of distances from Pluto that yield a good occultation by both objects.

Posted by: RNeuhaus Jan 23 2006, 08:50 PM

I remember, that the main reason is that NH must be by Pluto before than 2015-2016 because after that time Pluto will undergo an atmosphere changes becoming even freezer. So they want to study Pluto atmosphere before that time.

Rodolfo

Posted by: BruceMoomaw Jan 24 2006, 02:18 AM

There are actually three reasons for getting NH to Pluto as fast as possible, despite the higher flyby speed. First is indeed the risk that the atmosphere may be about to freeze out, in which case every year's delay is crucial. Second is the fact that, as Pluto moves slowly away from its equinox (which, by an interesting coincidence, is at about the same time as its perihelion), more and more of its south polar region is being shrouded in permanent shadow and thus not observable by sunlight (although you can get a dim look at it by reflected Charon light).

Third, of course, is that the longer it takes to get to Pluto, the higher the operating costs, and the higher the risk that it will fail before getting there. The whole reason I pushed this mission with fanatical determination in "SpaceDaily" is that it's one of those extremely rare cases in space exploration when delay means a serious loss of science and increase in cost DESPITE whatever new improved technologies are discovered with time. (Had we launched the damn thing in November 2003, as any sane NASA Administrator would have, we would have done still better in both the science and cost respects -- and we would also have been able to make a close flyby of Io, with possible great science returns from that.)

Posted by: disownedsky Jan 24 2006, 09:42 PM

A fourth reason is that the RTG powering NH loses about 3 Watts per year. This would have started to limit what she could do at Pluto, and possibly severly limit any Kuper belt encounters. As it is, power has to be managed actively during the Pluto Encounter. NH has to maintain a certain power "floor" or she freezes her hydrazine, which is end of mission since thrusters are her only actuators for attitude control. The instruments, however, largely do not contribute to this because they are outside the thermos bottle. So, as power drops, instruments have to go off.

Posted by: mars loon Feb 11 2006, 10:43 PM

Plus the added time at Pluto close approach is only increased by minutes. Not worth the loss in atmospheric data or KBO encounters and the rest mentioned earlier.

Posted by: Tom Tamlyn Feb 12 2006, 12:39 AM

Loon,

Thanks _very_ much for that information. I suspected that that might be the case but I don't know enough physics to begin to have a useful intuition.

Is the minimal difference due to influence of Pluto's gravity well at closest approach, or because there's no such thing as an orbit that can reach Pluto which isn't PDF ("pretty darn fast") at closest approach? or both, or something completely different?

Tom Tamlyn

Posted by: tedstryk Feb 12 2006, 02:19 AM

The problem is with slowing down. A slower flyby could be made, if we were willing to use nearly the entire spacecraft mass and then some for fuel to break. Or if we were willing to take a trajectory that took forty years to get there, we would get a slower flyby. But, as it stands, in order to get to Pluto in a reasonable amount of time (and with the atmosphere possibly freezing, time is crucial), NH will be travelling so fast that it simply will not be able to slow itself down when it gets there.

Posted by: ljk4-1 Jun 11 2006, 05:06 PM

Had we put our money, time, and effort more into space probes than cars,
we could have been to Pluto and back many times by now:

"On an average day, American drivers eat up nearly 7 billion miles of
pavement - roughly the distance to Pluto and back."

Posted by: Comga Jun 25 2006, 12:20 AM

I would like to throw some cold Hydration on this question and Nix it entirely. (Just can't reisit those awful, awful moon name puns.)

Bruce , and disownedsky, are precisely correct, as is the issue of the limit on science being the SSR capacities. There are even more risks and costs to delays. Look at Dawn and SOFIA, which nearly got cancelled for a few tens of millions of dollars, and are still fighting for their lives. As Alan Stern and others have said, New Horizons is in its native element, deep space. Where, I might add, the odds of collision with a rock are way, way less than the odds of colliding with politics here on Earth.

IIIRC, the boost at Jupiter is ~4 km/sec. Arrival speed is >11 km/sec. However, that does not mean that a flight without a Jupiter flyby would arrive at 7 km/sec. The difference would be less than 4 km/sec, because the trajectories would cross at sharger angles. So the increased time close to Pluto would be, as suggested, not significant.

In addition, Alan says that New Horizon's "dirty little secret" is that it will return more science data from Jupiter, due to the "short" range of only ~5 AU. Pluse NH flies down Jupiter's magnetotail to 1000 Rj, which will data not collected at any planet including Earth. And the Jupiter encounter is great practice, a good chance to wring out an encounter sequence.

How could it be any better than with the Jupiter flyby? (I am sure someone will have a suggestion.)

Posted by: edstrick Jun 29 2006, 02:22 AM

Various spacecraft, including the early interplanetary Pioneers, made "accidental" or outbound encounters with Earth's magnetotail at distances of up to hundreds, if not a thousand Earth radii.

Posted by: Comga Jul 1 2006, 03:13 AM

Yes, but New Horizons will pass staight down Jupiter's magnetotail, not cut across it, IIRC. At least I was told the path will be unique.

Posted by: edstrick Jul 1 2006, 08:41 AM

Sounds good!... Oh.. Voyagers also had distant encounters with the flapping magnetotail as Jupiter finally went into solar conjunction as they slowed down during the post-flyby cruise to Saturn.