Soviet Imagery from the "Mars" Series Options

[Phil Stooke]

Speaking of Soviet Mars probes - well, this is Mars 4, but I'll add something on Mars 3 soon...

Here's a map showing the coverage of Mars 4 images, two long scanned images and a mosaic of individual frames. Part of one scan extends into the other hemisphere. Ted Stryk provided the scans, I made the mosaic from images provided by Don Mitchell.

Phil

[Geert]

Speaking of Soviet Mars probes - well, this is Mars 4, but I'll add something on Mars 3 soon...

Great work Phil!

Looks like they were targeting the Mars 6/7 intended landingsites but just missed both of them.
Any known pictures from Mars 5 of those same landingsites?

Pictures got me thinking...

They were taken close to the closest approach (2200 km more or less), which should have been close to the moment of orbital insertion (which could not be performed as engine could not be commanded). Both Mars 4/5 were to function as relays for the Mars 6/7 landers, and they were targeted for an orbit with a period of one sol, in order to pass over the landingsites every day at the same time. This works only if your longitude of ascending node is 90 deg from the longitude of landingsite, in other words the longitude of your periapsis is same as the longitude of the landingsite.

Orbital inclination of Mars 5 was 35 degrees, which is nicely in between the latitudes of the intended landingsites (Mars 6 at 24 S and Mars 7 at 50 S) so one orbiting relay could have served both landers (but probably not both at the same time... landers had to be targeted for more or less the same longitude otherwise this trick won't work).

From the pictures it looks like Mars 4 also passed more or less along 35 S on its closest approach, so targeted for the same orbit as Mars 5.

If you target your relay-orbit with a period of one sol and with the periapsis close to the landingsite, then your point of orbital insertion NEEDS to be over the intended landingsite as well (given that no major orbital maneuvering is done after insertion). Am I correct in this?

This would explain why the close approach images of Mars 4 show the strip in between both landing sites.

I'm still trying to work out whether Mars 5 was above the horizon (although dead) during the descent of Mars 6, given the orbital period and the arrival times I would say it had just passed the landingsite and was not in line of view, but all this orbital data is so vague that it's hard to be sure.