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

[Phil Stooke]

Mars 5 did image the Mars 6 landing site. I will post a map of Mars 5 coverage later. I have matched all Mars 5 images to modern maps now.

My puzzle at the moment concerns the Mars 7 target. I have shown it on the map as it is reported. But why land there? It's a rough area on the edge of the large crater Galle, not at all a suitable site, I would have thought. And there is another curious fact (stop me if you've heard it before). The Soviets asked NASA to provide Mariner 9 images of the Mars 6 site, and USGS made a map of the stated site (Mare Erythraeum). That map was published in a paper on Mars 6 in Cosmic Research, with the Mars 6 target and landing points shown, so all these facts fit together. But USGS also made a map of an area south of Mare Erythraeum, a sheet called Nereidum Montes, at the same time. Galle is just outside that map sheet. The middle of that map sheet would be at the northern edge of Argyre, a much better landing site, I would think. So was that the real Mars 7 target?

Phil

[Geert]

My puzzle at the moment concerns the Mars 7 target.

Fully agree with you regarding the doubts about the Mars 7 target. I searched my own archive, but can't find any other reference coordinates then 50S 28W which indeed don't make much sense given the data requested from the USGS.

Only reason that I can think of is that Nereidum Montes is too far west (44 W). It might be that Mars 4 was intended as relay for Mars 7, and Mars 5 as relay for the Mars 6 lander. After Mars 4 failed to orbit, they had to plan the landingsite in such a way that one orbiter (Mars 5) could relay for both landers. That means that both landingsites had to be close together in longitude (the orbiter was in an orbit with a one sol period, so it's groundtrack was more or less fixed and unless it would execute a phasing-manoeuvre inbetween both landings the landers had to land close together to have the same relay). Furthermore, Mars 7 arrived 3 days earlier then Mars 6 and with the Mars seasons this translates in a more southerly landingsite (although 50S sounds too far south for me).

They may have been forced to shift the Mars 7 landingsite further east after Mars 4 failed, in order to work the relay via Mars 5, that's the only reason I can think of.

I can't find any info that further maps were requested after the Mars 4 failure, so did they plan the move to an alternative site based on Mars 5 images?

The exact fate of Mars 7 is also a bit in doubt. It is usually stated that its solid propellant rocket didn't fire, where after it passed Mars. However, the only transmitter on Mars 6/7 active during EDL only started transmitting once the parachute was deployed, so there can't have been any transmission from the lander after separation from the orbiter, so how can they be sure the engine didn't fire?? Only known fact is that nothing was ever heard of the lander after its separation (similar to Mars 2). It might be that the lander separated too late from the flyby bus (see Ulivi/Harland Robotic Exploration of the Solar System, page 165, stating the first command to separate the lander was not acknowledged by the fly bus and the lander separated only at the second try) in which case the solid propellant engine might not have been able to get the lander on the correct entry trajectory, but the statement that the engine didn't fire seems weird given that there was no communication with the lander...

[tedstryk]

The problem is that the Mars-7 descent craft was released from the flyby bus 4 hours early causing it to miss Mars by 1300 km.
I am not sure what the big unknown is here.