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

[edstrick]

Mariner 4 had a scan platform, and one option they had was to do the flyby with the platform in a slow back-and-forth <I think> scanning mode, maybe within a limited angular range. The pre-encounter decision was, as I recall, to set the platform at an angle that gave a "best" single swath of pictures across the planet: Middle of the illuminated limb, approximately across the sub-spacecraft point, and on to the terminator.

Arrival date would have set the hemisphere covered. If Mariner 3 had not been enshrouded at launch, Mariner 4 would have launched earlier and imaged some other strip, possibly hitting more interesting features, possibly somewhat less.

[peter59]

Mariner 4 had a scan platform, and one option they had was to do the flyby with the platform in a slow back-and-forth <I think> scanning mode, maybe within a limited angular range.  The pre-encounter decision was, as I recall, to set the platform at an angle that gave a "best" single swath of pictures across the planet: Middle of the illuminated limb, approximately across the sub-spacecraft point, and on to the terminator.

Arrival date would have set the hemisphere covered.  If Mariner 3 had not been enshrouded at launch, Mariner 4 would have launched earlier and imaged some other strip, possibly hitting more interesting features, possibly somewhat less.

You are right about Mariner 4 scan platform. A few hours before planetary encounter "NRT" (nonreal-time) power is turned on to energize the TV and scan platforms. The scan subsystem initiates a "search mode" of operation, causing the scan platform to oscillate such that the TV and scan sweep an arc approximately perpendicular to the motion of the spacecraft. When the planet comes in view of the scan subsystem sensor, the scan subsystem switches to a "tracking mode" in which the sensor and the platform is kept pointing at the planet.



More about Mariner 4 original telemetry data at Mariner 4 data analysis