Should Have Skipped Jupiter Flyby?, More time at Pluto Options

[ToSeek]

We have a contrarian over on the BAUT Forum 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.)

[Rob Pinnegar]

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?

[Chmee]

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.

[Toma B]

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...

How much memory is actually on the New Horizons?

[helvick]

How much memory is actually on the New Horizons?

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 New Horizons Data Management and Archiving Plan
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.

[Bob Shaw]

How much memory is actually on the New Horizons?

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

[ljk4-1]

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?

[JRehling]

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

[djellison]

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

[tedstryk]

"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.

[Bob Shaw]

"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.

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

[Tom Tamlyn]

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 here 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

[edstrick]

"...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.

[RNeuhaus]

We have a contrarian over on the BAUT Forum 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.)

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

[Guest_BruceMoomaw_*]

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.)