Mariner 4 Alternate Universe, What if...? Options

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What if Mariner 4's flyby had occurred right across Tharsis & Coprates Chasma, showing volcanoes & canyons instead of heavily cratered terrain? (I understand that trajectory determinants prevented this from happening, of course, but still...). Do you suppose that Mars exploration would have been thrown into hyperdrive during the heady '60s, perhaps enough to sustain manned efforts beyond Apollo?

Doug, my apologies if this is OT for this section...there seem to be some interesting implications here for the imaginative, though.

[edstrick]

Mariner 2 flew with a lot of luck, but it was the real working prototype (based on Ranger) for the Mariner series, starting in mature form with Mariner Mars 64. The near total success of Mariner 2 proved that the essential design was right, and just needed maturing.

There were two real problems on Mariner 2. The Microwave Radiometer was apparently damaged during launch, I think they suspected a thermal shroud was damaged. One of the 2 channels was greatly reduced in sensitivity, and it's response was actually reversed! The other worked reasonably well. This sort of problem was instrument-specific, of course.

The spacecraft overheated badly, and failed not long after the Venus encounter, quite likely due to the overheating. Getting thermal control "right" took time. Modeling was not adequate, and in-space behavior of materials didn't match predictions as they outgassed, changed color, whatever. Mariner 4 actually carried an engineering experiment, besides it's science instruments and the experimental solar light pressure stabilization paddles. It carried a small set of candidate thermal control "plaques" on the sun-facing side of the main body of the spacecraft, with a temperature sensor behind each one to monitor it's temperature changes relative to predicted values as the mission proceeded.

Teeny-tiny "micro-experiments" like that can often be fitted on missions and return significant value for the future. The Magnets on Mars landers are also "micro-experiments", as was Geoff Landis's (I think) dust accumulation experiment of the Sojourner rover.

[Guest_DonPMitchell_*]

Mariner 2 flew with a lot of luck, but it was the real working prototype (based on Ranger) for the Mariner series, starting in mature form with Mariner Mars 64. The near total success of Mariner 2 proved that the essential design was right, and just needed maturing.

Mariner-2 was a repurposed ranger probe, yes. And the ranger series had a long history of failure. The lunar missions didn't work until Ranger-7 in 1964. Heads rolled over this, and there was a congressional inquiry. Mariner-2 suffered a number of systems failures:

1. Failure of one solar panel very early in the mission.

2. Failure of the temperature control system (a bad design, not a failure to function). By the time of Venus encounter, the spacecraft was over 100 C. I say "over" because the thermometers were off scale by then.

3. The optical navigation sensors used for attitude control were slowly going blind, only a few percent of normal signal by the time it reached Venus.

JPL was "Just Plain Lucky" as they joked at the time.

THe probe passed Venus at a rather great distance, which reduced the value of its magnetometer, but it got close enough to tell that Venus did not have as strong a field as the Earth. Venera-4 provided the first accurate measurement of the field.

The most important experiment of Mariner-2 was the mesurement of microwave limb darkening. Most historians fail to mention that one of the two microwave channels did not actually show limb darkening. And in fact, this measurment was performed from Earth by radio telescopes several months before the Mariner encounter.

OK, I'm beating a dead horse here. Mariner-2 still deserves an important place in history, as the first spacecraft to reach another planet and return data.