Venus landing sites Options

[Guest_PhilCo126_*]

Didn't notice any topic on the landing sites on the sister-planet of our Earth, so I started a topic on landing sites on Venus
Looks like the Soviet-Russian Venera 14 (landed March 1982) and American Pioneer Venus 2 day probe (landed December 1978) came 'close' together:

[JRehling]

I never worked out the details, but I assume that the narrow longitudinal range among most landing sites is an artifact of the near-synchrony between Venus's rotation and the synodic period between Earth and Venus. What this means is that for the minimal-energy trajectory, Venus is always oriented about the same way (WRT the Sun and the Earth) every time. The only desirable landing sites are in the longitudes that face the Earth and are also in daylight (to enable surface imaging). Venus was about half-full when VEx arrived, so that should have been the same situation when all previous landers have arrived, effectively limiting the landing sites to about 1/4 of the planet, with further constraints on latitude, and still further longitudinal constraints owing to entry mechanics.

By expending a bit more energy for the cruise phase, or by taking a more roundabout path, a craft could meet the daylight+Earth contact constraints and land elsewhere. A relay satellite could also provide that flexibility. Or, as was done with one of the Pioneer probes, dropping it into the night side.

[edstrick]

The early venera landers, #'s 3 through 8, were "lob it at the planet" designs, went in on high inclination cannonball trajectories. The later Veneras, I suspect but haven't checked, probably came in at shallower angles, though they still used spherical entry shells.

[Phil Stooke]

My version of the map. The sites aren't really so clustered.

Phil

[JRehling]

All told, they're pretty well distributed, but the four Veneras that returned surface imagery are within a mere 19 degrees of longitude of one another. It's this slice of the planet where I think most craft that have the same goal would end up landing unless a specific effort is made to diversify.