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

[Guest_Myran_*]

Seeing descriptions and even images of old projects that never did get underway, my memory was stimulated into remember 'The grand tour' plans.

Back in the 1960 the proposal was to fly no less than 4 spacecrafts, each with atmospheric probes for the four gas giants and one even with a flyby of Pluto after swinging past Jupiter and Uranus.

The proposal for this project did fare the same way as many other ambitious plans, that of limited funding but it was skillfuly advocated and eventually ended up with the dual Voyagers (which btw originally only was planned for flyby's of Jupiter and Saturn).

Regardless, if anyone remember some tidbits or even sits on more specific information I would be happy to have my memory refreshed. Thank you in advance!

[Guest_BruceMoomaw_*]

There was a nice detailed article on it -- and its demise -- in the Journal of the British Interplanetary Society about 7 years back. I have a photocopy, and will reread it to refresh my memory. (I don't recall it including atmospheric entry probes, though.)

Two of the craft would have been launched in 1977 to fly by Jupiter, Saturn and Pluto; the other two in 1979 to fly by Jupiter, Uranus and Neptune (thus both stretching out the financing and allowing avoidance of the Saturn-to-Uranus trajectory, which was thought to brush dangerously close to the outer edge of Saturn's rings). The craft would hve been distinctly more complex than the final Voyagers to ensure long lifetimes -- including, in particular, computers with triple components each of which would take a majority vote on their decisions.

Even after GT's 1972 cancellation and replacement by Mariner Jupiter/Saturn (renamed "Voyager" in 1977), NASA had a fallback plan: launch the third, backup Voyager by itself to Jupiter and Uranus (with an extended mission to neptune if it was still working) in 1979. "Mariner Jupiter/Uranus", as it was then called, would have had minor modifications: a set of reaction flywheels to allow it to slew around faster and more accurately to rapidly observe different targets during its fight through the Uranian system; replacement of its vidicon cameras by CCD cameras with near-IR sensitivity; and replacement of the IR spectrometer by one with greater sensitivity to longer wavelengths to examine the cold outer planets better. But that, too, got the axe in 1975, simply because of the never-ending funding demands of the Space Shuttle -- plus the fact that NASA wanted no extension of the expendable rocket program into 1979, which is the same reason they vetoed all proposals to launch Galileo on a Titan booster in 1982. They had a really major fraud to perpetrate on the taxpayers, after all, and any slipup like that could have bollixed it. So Voyager 3 hangs on the Air & Space Museum wall instead (near the third Viking lander and the backup to Mariner 10).

Had Voyager 3 been flown, I think it very likely NASA would also have extended Voyager 2's mission to proceed on from Saturn to Pluto -- which it would have reached a month or two before Voyager 3 reached Neptune, thus getting a good look at that planet when it was near both perihelion and equinox to provide the best possible scientific view of it (and also allowing Clyde Tombaugh to get a closeup look at the planet he had discovered). No such luck.

[tedstryk]

Had Voyager 3 been flown, I think it very likely NASA would also have extended Voyager 2's mission to proceed on from Saturn to Pluto -- which it would have reached a month or two before Voyager 3 reached Neptune, thus getting a good look at that planet when it was near both perihelion and equinox to provide the best possible scientific view of it (and also allowing Clyde Tombaugh to get a closeup look at the planet he had discovered). No such luck.

I don't think that was possible. It was Voyager 1 that could have been retargeted to Pluto.

[Guest_BruceMoomaw_*]

You may be right -- but one of them could certainly have been retargeted to Pluto.

[tedstryk]

You may be right -- but one of them could certainly have been retargeted to Pluto.

The choice had to be made...Send Voyager 1 on to Pluto or have a close Titan flyby. The Titan flyby, thanks to the clouds, was largely a bust, so in 20/20 hindsight, it is a shame it didn't go on to Pluto.

[JRehling]

The choice had to be made...Send Voyager 1 on to Pluto or have a close Titan flyby.  The Titan flyby, thanks to the clouds, was largely a bust, so in 20/20 hindsight, it is a shame it didn't go on to Pluto.

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!

[edstrick]

The Voyager 1 Titan flyby was enormously successful. The surface radius was established, the atmosphere structure was determined with such precision that the Huygens probe was possible. Atmosphere composition and haze physical properties were determined with considerable precision. Before Voyager, it was unknown whether there was a significant greenhouse effect, or whether the surface was only 0.1 atmosphere pressure with a temperature of around 80 K.. essentially at the tropopause. Some of this would have been determined by Earthbased observations in the 2+ decades since Voyager, but a lot would not have been.

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

[Guest_Myran_*]

Thank you BruceMoomaw for your reply.
Yes I distictly remember it was supposed to be four probes, and not two which is said on some sources like Wikipedia. For the number of only two I think theres some confusion with the dual Pioneers that also was a spinoff of sorts from the early Grand Tour proposals. But in the end it was the Voyagers that carried out the plan and did so very well, getting us a clear look at the moons of Jupiter and Saturn but also the only clear views of Uranus and Neptune that I will ever get.
But I agree its a pity we did miss out on Pluto, the opportunity was there. It will be a close call for me with New Horizons in 2015, lets try!

Regardless, I do remember a plan that involved cone shaped atmospheric probes in regard with the first four probe plan, and I remember that one well since it had a graph. But that proposal might not have been one AMES or JPL proposal at all but originated somewhere else like at some university. After 40 years things in my memory tend to blend somewhat.

[dvandorn]

Exactly -- each mission does, indeed, build upon what we learned from the last one. Without the Pioneers, we might not have designed the Voyagers to properly withstand the radiation environments at Jupiter and Saturn. Without the Voyagers, we wouldn't have had nearly as good an idea of which instruments would give us the best scientific return from Cassini. (For example, had we not done the Titan flyby during Voyager 1, we might not have included RADAR on Cassini.)

My memory of the whole Grand Tour concept is that, sometime in 1968 or 1969, I saw a proposed plan for two Grand Tour spacecraft that would require Saturn V boosters. They would take advantage of the late-70s launch windows to send both spacecraft to each of the outer planets in turn, with entry probes for the gas giants and, IIRC, a Titan hard-lander.

When NASA decided to shut down the Saturn V production line in late 1969, the people at JPL proposing the Grand Tour mission took it rather poorly, insisting it was total madness to pass up an opportunity like this. They made some enemies at other NASA centers with their vehemence. For a while, no plans for late-70's outer Solar System exploration were allowed to have the words "Grand Tour" in them -- it got that bad.

Pioneers 10 and 11 were already in the pipeline, and a follow-on mission, consisting of similar Jupiter/Saturn flybys *only*, was being developed that later became the twin Voyagers. But during the process of designing the Voyager missions, the Grand Tour aspects were played WAY down. It was as if the JPL teams were told that bringing up Grand Tour was a good way to kill the Jupiter/Saturn flybys. But, at the same time, they designed both spacecraft with enough power and maneuvering gas to handle the full Grand Tour -- with a little bit of luck.

So, at least the way I remember it, we got almost all of our Grand Tour mission by selling it as *only* a set of Jupiter/Saturn probes, and sneakily adding the Uranus and Neptuine encounters only after the spacecraft were in flight. Even though the Grand Tour was implicitly designed-for during spacecraft and mission development, it was simply not discussed in detail for fear that those who thought they had "killed that Grand Tour nonsense" wouldn't notice until it was too late...

-the other Doug

[Guest_BruceMoomaw_*]

The article I was after is D. Rubashkin's "Who Killed the Grand Tour? A Case Study in the Politics of Funding Expensive Space Science", in JBIS, Vol. 50, pg. 177 (year 1997). Unfortunately, it isn't available on the Web.

The short version is that Grand Tour was like Rodney Dangerfield -- at the time, it got shockingly little respect from ANYBODY. The Space Studies Board (aka COMPLEX) took a surprisingly dim view of it (as compared to the intensive exploration of Jupiter alone), and in fact recommended it be flown only if NASA's space science budget got a 50% hike for the rest of the decade -- which everyone knew wouldn't happen. Sen. Clinton Anderson of NM (then chairman of the Senate Aeronautical and Space Sciences Committee) took a very dim view of it because it was bleeding off funds from the NERVA nuclear rocket program, which he fiercely defended because Los Alamos was associated with it; no other member of Congresss seems to have any fondness for it; and Pres. Nixon had no intention of funding anything that would interfere with the Space Shuttle's development.

Anderson used the idea that NERVA and other nuclear rockets might allow space probes to be launched DIRECTLY to the three outer planets to bash Grand Tour mercilessly in 1971. By mid-1971 GT was already virtually moribund (and NASA had already dropped its plans to launch a preliminary test of the craft in 1975 that would fly by Jupiter and then go sharply out of the ecliptic, and had also delayed the launch of the first of the two Jupiter-Saturn-Pluto craft, which was originally supposed to fly in 1976 instead of 1977).

The last straw came in October 1971, when Nixon decided that in order to properly fund Shuttle he had to cancel either Apollo 16 and 17 (which he initially leaned toward doing), or GT (which NASA and COMPLEX persuaded him to do instead). At the same time, ironically, the White House zapped NERVA, briefly mollifying Sen. Anderson (who retired only a year later) with a smaller nuclear propulsion program which they also cancelled as soon as he was safely gone. The moment GT was cancelled in Dec. 1971, however, NASA and the White House replaced it with Mariner Jupiter/Saturn, which by contrast everyone -- COMPLEX, the White House and Congress -- immediately and enthusiastically endorsed, largely because it would cost less than half as much. (NASA still hoped from the start to fly at least one such craft to Uranus and Neptune, but without the "Self-Test And Repair" computer that was a major feature of the GT craft.)

The article doesn't say anything about the sequel to this story: NASA's brief hopes of flying Mariner Jupiter/Uranus in 1979. I'll do a bit more digging on that subject, but the main story is very simple: as with so much else, the Shuttle ate it. (And I have still seen no sign that GT was intended to carry any entry probes -- indeed, I very clearly remember that the detailed description of the GT craft in "Astronautics and Aeronautics" magazine at the same time included no mention of any entry probes.)

[edstrick]

The vehicle for grand tour was for a while at least known as "TOPS": The Outer Planets Spacecraft. Bruce: There was a substantial article in either Space Aeronautics or Astronautics and Aeronautics on the proposed mission in the 1970-71 time frame. I can't get at my brother's copies now to find and ID it.

The de-scoping of the mission also had the effect of descoping the instruments to Mariner Jupiter Saturn requirements. Their sensativities in many respects at Uranus / Neptune were crummy compared to what would have been flown <bigger apertures, etc> on TOPS.

The real loss, of course, was the third spacecraft. We, also of course, were lucky. Both Voyagers survived their primary mission and into extended missions. If Voyager 1 had failed to do it's required science at Titan and the critical ring radio occultations, Voyager 2 would have recovered those observations and there would have been no Uranus-Neptune mission.

[Bob Shaw]

I thought TOPS was Thermo-electric Outer Planetary Spacecraft?

[Guest_Myran_*]

Thank you dvandorn, you nailed it there. The timeframe of 1968 or 69 is just about right, since my recollection of the proposal fits with other memories from my personal life of that time.

The four probe proposal had blended in my memory with the two probe one.
I think so since you stated one thing I failed to mention, that the proposal included the option to have one atmospheric probe swapped for a Titan lander. So you did indeed remember correctly.

BruceMoomaw set the record straight for me, yes somehow I must have had the Mariner Jupiter/Uranus proposal in the back of my head when I wrote the original post. But also brought up another tidbit for my original interest for the Grand Tour and that was the 'Self-Test and repair' ability plus the other autonomous abilities they would have been given. If they had flown they would have been true robotic ambassadors for the human race.

[edstrick]

Mariner Jupiter/Uranus was sunk by both the Shuttle, and as I recall, by the Ford Administration's utter indifference. Remember "WIN: Whip Inflation Now" buttons?

The shuttle... and Jimmy Carter sunk the Hally's Comet Rendezvous mission when they refused to fund development of SEPS.. the solar-electric propulsion system and flight test it so it'd be mature technology for a major solar electric system that could do a Hally rendezvous.

One of many reasons I regret being stupid enough to vote for "Malaise Jimmy".. I wanted something better than "King Log" and voted for "King Stork" ......

[Guest_BruceMoomaw_*]

You may rest assured that either one of them would have been suckered by the Shuttle; I doubt there would have been any significant difference in their space policies.

That article you're thinking of was definitely in "Astronautics and Aeronautics"; I read it at the time, although I can't quite remember whether it was in 1970 or 1971.

Regarding Mariner Jupiter/Uranus' instrumentation: I mentioned that it would have carried both CCD cameras and an improved version of the IRIS spectrometer of its two predecessors. NASA made a considerable effort to get a copy of the latter ("MIRIS") onto Voyager 2, given its hoped-for Uranus and Neptune flybys; but in the end they weren't quite able to qualify it in time.

As for Voyager 1's close Titan flyby: there was absolutely no question that it was worth attempting, even if you had to give up an optional Pluto flyby in the process. Quite apart from the far better (and crucial) atmospheric data obtained from such a close flyby, before the flyby there was a good chance that Titan's atmosphere and clouds would be thin enough to provide a view of the surface -- in fact, chief camera PI Bradford Smith bet that such would be the case.

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.