The Grand Tour, A proposal that ended with Voyager 1 & 2 Options

[Bob Shaw]

Hmmm... ...an outer planetary mission with a self-testing and repairing computer system aboard. Sounds fine until the AE35 unit enters a predicted failure mode.

'OK, STAR, let's take those pictures!'
'Shan't. Won't. Can't make me. N'yahh, n'yahh, n'yahh!'

[Guest_Myran_*]

Hehe! I see that Bob Shaw have seen the 2001 movie. (Yes me too.)

In reality it wouldnt be such a bad thing to have, not even for our MER rovers. Remember when Spirit was brought to a complete standstill due to one overfilled flash memory. So self test, diagnostics and automatic correction/repair is something that still could save the operators from sleepless nights.

[Bob Shaw]

Myran:

They said that about XP!

Bob Shaw

[Guest_Analyst_*]

Besides the paper „Who killed the Grand Tour?“ published in JBIS the following monograph gives a good overview of the Voyager program from a management point of view. You can compare it with SS’s recent book about the MER missions. It starts with the program genesis and hurdles and continues to building and lauching the spacecraft. The important resuls from the flybys are given and some facts about the current interstellar mission.

“Voyager’s grand tour: to the outer planets and beyond“
by Henry C. Dethloff and Ronald A. Schorn
ISBN 1-58834-124-0

Highly recommended. Read this and SS’s book and you know what roadmaps and long term plans are for.

Analyst

[ljk4-1]

I don't think Voyager 1 @ Titan was a bust. It provided radio occultation data that pegged the surface temperature and pressure so accurately that Huygens scarcely improved the measurement -- THAT is saying something. (I'm sure Huygens shrank the error bars...) That occultation also pegged the mean molecular weight. And Voyager images of Titan in the orange filter DID show surface features, though that fact was recognized only 15 years later.

It is subject to debate if the same information could have been had using later stellar occultations. The key question would be if Cassini/Huygens design was improved in any way owing to the Voyager 1 pass -- could be a PhD thesis to try to shake that out. Extra credit for assessing whether V1's probing of the bow shock would have been altered in the other plan.

Taking the counterfactual too literally, we could say that with Cassini there now, we would have all of the Voyager 1 discoveries in our pocket by today's date anyway, so in a sense, we got nothing from it that we wouldn't have had by 2005, and could only have gained by swapping it for Pluto. Then again, New Horizons would not have been approved if we'd had a Voyager flyby of Pluto, and NH certainly has a superior instrument payload thanks to 28 years of technical improvements. So come 2015, it may be said that *Pluto* science owes a lot to Voyager 1 not having flown by it!

Are those surface images of Titan from Voyager 1 available somewhere? I can't recall ever seeing them before, just the big fuzzy orange tennis ball ones.

What do folks here think of the assessment that Voyager 2's exploration of Triton in 1989 was equivalent to a flyby of Pluto?

[tedstryk]

One thing that has always puzzled me is why no attempt was made to have Pioneer 11 do a Titan occultation, since that could have been done even at a long range -- after all, Pioneer 10 did it for Io.  Apparently there was no way to combine it with the proper trajectory for a rehearsal of Voyager 2's close brush past the rings, but I don't know the details.

I know that at the time of the Titan encounter, Pioneer's communications with earth were so disrupted by the fact that it was almost in solar conjunction that a lot of data was lost. So perhaps they figured they wouldn't have a good enough signal to make it worth it.

[Bob Shaw]

Are those surface images of Titan from Voyager 1 available somewhere?  I can't recall ever seeing them before, just the big fuzzy orange tennis ball ones.

What do folks here think of the assessment that Voyager 2's exploration of Triton in 1989 was equivalent to a flyby of Pluto?

On the first point, yes, I'm also fascinated to hear that some surface features may have been visible - that's news to me!

And as for Triton, it may be the yardstick by which we judge Pluto, so it certainly was worthwhile having a good hard look at!

[edstrick]

Pioneer's Saturn flyby was "forced" onto a trajectory that took them through the ring-plane at the approximate radius where Voyager 2 would have to cross to go on to Uranus and beyond. The actual trajectory crossed the ringplane inbound, reached periapsis literally under the ring-plane, and crossed the ringplane outbound at a similar radius as the inbound crossing.

Encounter was only about a week before conjunction, and communications rapidly deteroriated after Saturn, but they didn't lose that much data, they did have to cut data-rates, especially outbound.

The alternate trajectory being considered was "inside" the rings, through the ringplane close to Saturn's equator...through part of the "D" ring. Given that a "D" ring had been claimed and named, even if it was highly debatable, it was not at all clear what Pioneer's chance of survival were. The science on the outside rings crossing was nearly as good, except for gravity studies of Saturn. Given the importance of verifying the survivability of the Voyager trajectory, the recommendation was the outside crossing.

Titan was "behind" Saturn and in a really poor location for any possible encounter. On the departure trajectory, they got low resolution full disk images that weren't much better than Earthbased images at the time, but they did see the north/south brightness assymetrys... opposite (I think) to what Voyager saw, which indicated seasonal or meteorological effects. The infrared radiometer got very rough thermal measurements on the (for it) unresolved disk which crudely supported "weak or no greenhouse" models of the atmosphere.

[JRehling]

Are those surface images of Titan from Voyager 1 available somewhere?  I can't recall ever seeing them before, just the big fuzzy orange tennis ball ones.

What do folks here think of the assessment that Voyager 2's exploration of Triton in 1989 was equivalent to a flyby of Pluto?

The Titan-from-Voyager work is here. That includes some best-yet looks at the northern latitudes! Add 'em to the map!

http://www.lpl.arizona.edu/~jrich/vgertitan.html

A close look at Triton is in no way equivalent to a Pluto flyby. The two worlds appear to be very similar in bulk composition, but the same could be said of Venus and Earth. Admittedly, no one would expect the two to turn out to be as different as Venus and Earth, but we won't know until we see Pluto.

Pluto should experience harsh seasons and some level of atmosphere freeze-out, while Triton (most latitudes, anyway) maintains more constant illumination from a very constant distance from the Sun. Pluto is in stationary lock with little Chiron while Triton faces tides from massive Neptune. And even without those two things, the worlds may have evolved differently for other reasons.

We don't know enough about Pluto to know how similar the two worlds might be, but for now, we have to assume that there are significant differences. Of course, they're liable to be more like one another than either of them is like some other randomly-chosen world...

[Bob Shaw]

The Voyager Titan surface images are remarkable! It's astonishing that after a quarter of a century the old data can still reveal so much (though we've seen elsewhere on the board that Surveyor, Mariner 69 and the Phobos mission all had many hidden gems, too - not to mention the super-resolution Viking views, or the Pioneer Io image). I suppose this shows the true value of properly archived data, and the false economy of disposal. I don't especially rate the 'Pioneer Anomaly' argument, but these Titan pictures certainly do show that a scientific consensus can shift over time, and that the new paradigm can make effective use of old data.

So: Let's hear it for saving the data, folks!

And: Let's spread the word of these happy outcomes!

[Guest_BruceMoomaw_*]

Ah. I had forgotten that Pioneer 11 flew through the ring plane at Voyager 2's planned distance TWICE (which I preseume was intended as an additional check on the rings' safety) -- which would have slapped far more limits on its trajectory than a single ringplane pass at that distance. I did know about the alternative plan to fly through the D Ring, which almost all the scientists backed but which NASA HQ vetoed (correctly, I think) because of the need to check the safety of Voyager 2's extension to Uranus. (By the way, brief consideration was given to extending Pioneer 11 on to a Uranus flyby, although it was quickly rejected and I don't know the details.)

As for Triton being an acceptable substitute for Pluto: no way. Triton, having been initially captured into a highly elliptical orbit around Neptune, then underwent really massive tidal heating while its orbit was being circularized -- heating intense enough that it's thought likely that ALL its ice melted into liquid, producing massive chemical changes as well as erasing its original physical structure. And, indeed, both chemically and in terms of their albedo patterns, Triton and Pluto bear little resemblance. If you want a reliable look at a KBO in its original form, the New Horizons mission is a necessity.

[ljk4-1]

The famous August, 1970 issue of National Geographic Magazine depicts the flyby routes of the two probes meant for the Grand Tour, plus it contains a fictional ship's log of what those probes and others then planned for the coming decades were believed to find as they journeyed through the Sol system.

http://solareclipsewebpages.users.btopenwo...LGEOGRAPHIC.htm

[tedstryk]

The only investigation that was a "bust" was surface geology investigation.. but.. then, that was a "bust" too for Jupiter, Saturn, Uranus, and Neptune!

When I made that comment, I was mixing it up with Pioneer 11 where the data return was messed up by solar conjuction. Sorry, I am scatterbrained. It is a shame Pioneer 11 wasn't sent on to Uranus and or Neptune. It could have been, but it wasn't thought that it would survive long enough, plus the Voyager team was first-hungry. While I am not sure if it could have imaged such dark worlds as all, a second pass through their magnetospheres and occultation data would have no doubt been helpful.

[gndonald]

Apologies for bumping a really old thread, but I have managed to locate the report into the Thermo-Electric Outer Planets Spacecraft from which I've managed to copy the attached images.

Interstingly the report claims that the only spacecraft built was going to be ground test model to develop technology for the coming Grand Tour.

A link to the report (155mb) is below.

TOPS - Final Report, 1st of April 1973

Attached thumbnail(s)