Mariner Mars 1964, Mariners 3 and 4 to Mars: imaging plans? Options

[Phil Stooke]

I am currently working on a book about lunar exploration, but looking ahead to the next one, which will cover Mars. One question to which I think I have an answer - but I'd like to see what my fellow Mars enthusiasts think - is this:

Mariner 3 failed to leave Earth. But if it had flown successfully, what area on Mars would it have photographed?

My understanding is that there was no specific plan. The MM64 press kit, for instance, says nothing about image coverage for either Mariner 3 or Mariner 4. I believe that navigation to planetary distances was still so uncertain that the flight team could not predict at launch the sub-spacecraft point at closest approach - uncertainties included the exact time of the flyby, the distance and the point at which the spacecraft would pass through the target plane. These things would be known closer to the flyby but they weren't precisely predictable at launch, so Mariner 3 never got to the stage of having an imaging plan.

Am I right?

Phil

[Guest_BruceMoomaw_*]

Well, actually it DID leave Earth -- it just left Earth still wadded up inside its nose cone (and missed Mars by several tens of millions of km as a result of the added mass...)

I can confirm -- having followed the US space program pretty closely since the end of 1964 (in fact it was the 1964 Mariners that turned me into a fanatic on the subject) that there was no specific target planned for either of the 1964 Mariners. The 1969 Mariners were the first to have such a goal.

I imagine they would indeed have played it by ear for the 1964 Mariners, taking into account both the initial trajectory onto which the Mariners were injected by their Atlases and the serious needs of the non-imaging experiments (atmospheric occultation, flight through Mars' solar wind shock). I also know that any flyby distance between 3600 and 8600 miles was considered acceptable for the Mariners -- Mariner 4 was eventually targeted for a flyby at 5400 miles range, but due to a slight midcourse error actually flew at 6100 miles. As you say, their targeting accuracy at that time was not high enough that they could afford to get seriously persnickety over which part of Mars they tried to photograph with the two Mariners. It's likely that they would simply have assumed that, as long as the two Mariners photographed different parts of Mars, ANY two such different parts were acceptable. (I have, by the way, never been able to discover where the remaining 1969 Mars Mariner would have been retargeted had one of them failed early on.)

Personally, if Mariner 1 had succeeded, I wonder whether one of the 1962 Venus Mariners might have tried a radio occultation of Venus' atmosphere -- although Arvydas Kliore seems to have started pushing that experiment only in early 1964. I do know that this was actually the single highest-ranked experiment on Mariner 5.

And while we're taking a stroll through Space Memory Lane, remember that until Mariner 2 succeeded NASA was planning two more Mariner R spacecraft to be launched on Venus flybys in March 1964 -- with some science instrument modifications (improved microwave radiometer and magnetometer; ion chamber and cosmic dust detector replaced by the same UV photometer that got kicked off the 1964 Mars Mariners because it caused TV camera arcing, and finally DID get flown to Venus on Mariner 5. See "JPL Space Programs Summary #37-19".) I wonder if, had they been flown, THOSE Mariners would have carried out a radio occultation of Venus -- they even had high-gain antennas designed from the start to be smoothly tiltable, whereas Mariner 5's fixed high-gain dish had to add a feature allowing it to suddenly be tilted into a new fixed position to partially compensate for Venus' atmospheric refraction of its radio beam. (Since the 1964 Mariners had Earth sensors mounted on their high-gain dishes to aim and tilt them, they might even have been able to pull off another experiment very seriously considered but finally rejected for Mariner 5: an Earth sensor to measure the altitude of Venus' cloud tops.)

Coming soon, if you're all nice to me: a brief report on how NASA came within one month of trying to launch a VENUS ORBITER in June 1959 (although it definitely would have failed had it been launched). One of the most bizarre forgotten episodes of the early Space Age.

[The Messenger]

In 1964, the question of whether there were 'canal' on Mars was still open, and although the Mariner 4 photos produced no evidence of canal, there was enough graininess to leave the question open - at least for the 'Hoaglandites'.

With both Mariner 3 and 4, they were hoping to get as close as possible, within NASA planet contamination control constraints, which was about 6000km.

http://ntrs.nasa.gov/archive/nasa/casi.ntr..._1968009274.pdf