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

Click to view attachment

Great work Phil! To clarify, the images from the scanning cameras are from me (I was afraid someone might think that the word scan referred to me with a scanner).

Yes, I could have been a bit more precise there. "Ted operated the scanning camera as he cruised past Mars"

Phil

I just thought it sounded like it said that I scanned images from Don Mitchell.

I understand your concern. It's interesting to compare your files and Don's - yours cover a slightly larger area, so they are clearly not from the same source. But I still like to think of you actually operating the camera.

Phil

Mine are from about a half dozen sources, all cobbled together. I also have a ton of raw scans I did in 2002 and 2007 (I think) of the film camera images...I just haven't gotten around to doing anything with them.

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.

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

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...

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.

That's according the Wikipedia:



However, this doesn't make sense, all those landers separated aprox. 4 hours prior encounter, that's the standard procedure, so if it separated 4 hours prior encounter, then it did not separate prematurely.

Furthermore, if it separated prematurely and it's rocket did fire, it would result in an too steep angle on entry and burn up, certainly not miss the planet (the rocket fired perpendicular to the flight path, reducing the passing distance). If it separated too late and the rocket did fire it might indeed have missed Mars, and idemdito if the rocket did not fire (but then again, how can we be sure as there wasn't any comms with the lander after sep).

Ulivi/Harland seem to imply it separated too late instead of prematurely, as stated above that would make sense although the passing distance of 1300 km still does not make sense, even then, if the rocket worked it should have been a lot closer. I guess 1300 km is the distance the fly-by bus passed Mars and nobody is sure where the lander ended up.

Actually it is from the NSSDC's page. I know that in the case of Mars-4, they had it conduct flyby science because they knew that it could no longer be maneuvered to go into orbit. It is possible that they realized that the Mars-7 descent module was also unable to maneuver before it separated from the flyby bus.

Meaning they knowingly separated a 'dead' lander, that's indeed a possibility, I don't know how much self-checks there were build in regarding the lander, from all stories it seems a highly automated sequence without much advanced electronics, all gunpowder engines and timers, no computers, so I don't know whether the landers were also effected by the wrong chips or whether this only effected the flyby-bus (and orbiters).

Only trick with this: if they knew prior separation that the lander was dead, why separate and announce it? They could just have mentioned that the mission was only intended as a fly-by... (although they did mention on launch that Mars 6 and 7 were identical). They must have had some hope that it would work, or there must have been some other reason why it had to be separated from the flyby bus.