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I have a two part question in reference to the answers provided for the linked question below:

Why did the Venera missions land so close together?

The answer stated:

”Not only did they land near local noon for the best possible natural lighting but they included halogen lamps (that went unused thanks to sunlight)3.”

First, why was it necessary for the Russians to land at local Noon on those days? Venus is Sun synchronous, making only one rotation every 243 days. That’s longer than the 225 days it takes for Venus to travel around the Sun. If Earth only rotated once during it’s 365 day year, any spot on the planet that you chose would have 6 months of light, then 6 months of day. So, in the timeframe of the landings, there wasn’t a night and day like there would be on Earth. They could easily pick a spot with 6 months of constant light. Why was local noon a concern for them?

The second part to this question-

You stated:

”On the other hand, they were using spherical entry capsules with no ability to steer during entry then parachutes in the higher altitude region of the atmosphere (where the wind speeds reach 100 m/s5) so it's possible they vaguely aimed at easy to hit (based on ballistic constraints) apparently flat regions then examined the radar maps closer for the areas where they actually landed.”

I remember the Venera Probes used 3 parachutes simultaneously to slow descent, at which point, the capsule detached from the parachutes and fell to the planet. This doesn’t make sense. The winds in the Venutian atmosphere reach 225mph and faster. That’s considerably faster than the 157mph winds of a category 5 hurricane. Parachutes do not functional well, if at all, in hurricane speed winds. How did they manage to successfully land? Also, I vaguely remember that the altitude at which the capsule detached from the parachutes was a considerable distance from the surface. Do you know the altitude? I’ve looked in every Venera photo that was made available, but I can’t find one that shows the parachutes- or burning/ dissolving remnants of- in the sky or on the ground in the distance. Clouds of sulfuric acid would not be good for parachutes, but we should still see something left of the chutes.

One last thing: I am pretty ignorant of E.M. wavelengths, so how did the Russians manage to get a radio transmission back out of the atmosphere, when we didn’t even have the technology to map the surface until 1976? We couldn’t penetrate the dense atmosphere. How did they do it?

I would greatly appreciate any knowledge you could provide on that subject. Please don’t take my question the wrong way. Although the possibility remotely exists that the landings were faked, I seriously doubt that they were. The US and Soviet Union were at odds and had just entered a space race at that time. We would have loved for them to fail. I don’t see the possibility of the US finding out that the Russians faked the landings, and not skewering them in the media and in front of the world. I just don’t understand how they managed to do it?

Thank you for your time, Matt Brubach

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    $\begingroup$ Thanks for converting this to a question! Welcome to space stack exchange. $\endgroup$
    – Organic Marble
    Commented Jun 11, 2021 at 21:25
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    $\begingroup$ Thank you for letting me know. Much appreciated. $\endgroup$
    – Matthew Brubach
    Commented Jun 11, 2021 at 22:26

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There are some very different concerns here, but I think I can address a couple of them:

First, why was it necessary for the Russians to land at local Noon on those days?

Noon is the time of day were the least amount of atmosphere is blocking the Sun. One of the findings of Venera 8, which did not land at noon, was that there is sufficient light on the surface to do photography.

The effect of opaque media is considerable as absorption grows exponentially with thickness, which is much more prominent on Venus than on Earth since a much larger fraction is absorbed.

Not getting good pictures would have been a disappointment, and landing in the middle of the day gave better light for the cameras.

This doesn’t make sense. The winds in the Venutian atmosphere reach 225mph and faster. That’s considerably faster than the 157mph winds of a category 5 hurricane. Parachutes do not functional well, if at all, in hurricane speed winds

Wind speed is not very important for parachutes (though turbulence is). A falling object will converge towards relative horizontal airspeed of zero, and as far as it is concerned, it is the ground that's travelling at 225mph (360km/h). Parachutes deal with that magnitude of relative airspeeds anyway. The main parachutes of the Apollo spacecraft activate at 200km/h, and that is while caring for passengers. The drogue chutes slowing Apollo down before that is also a parachute.

But: Those wind speeds are only found high up in the atmosphere. Near the ground, winds on Venus are very calm.

Also, I vaguely remember that the altitude at which the capsule detached from the parachutes was a considerable distance from the surface. Do you know the altitude?

At least for Venera 9, parachutes were cut at 50km.

One last thing: I am pretty ignorant of E.M. wavelengths, so how did the Russians manage to get a radio transmission back out of the atmosphere, when we didn’t even have the technology to map the surface until 1976? We couldn’t penetrate the dense atmosphere. How did they do it?

The atmosphere of Venus is not impenetrable to EM radiation. In particular, it has a "radio window", just like Earth, where the signal does not get too much weaker. The main leap to mapping the planet by radio waves is to have an orbiter, as radio altimetry of Venus is a slow process of measuring the height of the ground directly below you, requiring many revolutions to make a complete map (Which Magellan did in the 90s). That is something a flyby mission can not do.

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    $\begingroup$ SE, Thank you for answering my questions, I greatly appreciate it! I didn’t even think about the Apollo parachutes for some reason?? I still don’t understand the landing time though. It’s really not an important detail, just doesn’t make sense. When you say “landing at Noon gives the most light”, that point of time in the day on Venus is measured in days or months. Because the Sun doesn’t reach a high point in the Venutian sky every 24 Earth Hours. A Venutian day = 243 Earth Days. So that’s 121.5 Earth Days of constant light at any given point on Venus. But it’s not relevant. Thank You. $\endgroup$
    – Matthew Brubach
    Commented Jun 12, 2021 at 17:06
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    $\begingroup$ @MatthewBrubach It is indeed measured in days. They could miss the noon point by hundreds of kilometres and still be fine. But of those 122 days of light, the 50 first and 50 last are very dim. A day at Venus is dim, with a sharp top of daylight in the middle. A day at Earth is bright with dim edges. $\endgroup$
    – SE - stop firing the good guys
    Commented Jun 12, 2021 at 17:12
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    $\begingroup$ I think I finally understand what you mean. To arrive at the time the Sun is directly above a landing point on Venus, you would have a 10 Earth day window. The Venutian equivalent of our Noon hour would be equal to approximately 10 Earth days (If we divide the Venutian day into 24 increments. We wouldn’t have to worry about seasons, because Venus rotates on a 177.x degree axis, 2.x degrees from ecliptic (almost perfectly upside down). The very long sunrise would start in the west, and the sun would move toward the east. So the Russians planned the landings to occur in that 10 day window. Cont. $\endgroup$
    – Matthew Brubach
    Commented Jun 12, 2021 at 18:36
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    $\begingroup$ The date which that 10 day window occurred for a particular landing spot, would change from year to year, because the Venutian day is longer than the Venutian year. $\endgroup$
    – Matthew Brubach
    Commented Jun 12, 2021 at 18:37
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    $\begingroup$ @MatthewBrubach Venus's sidereal day of 243 earth-days with a retrograde rotation and its sidereal orbital period of 225 days combine to result in a Venusian solar day that's a bit under 117 days long, for about 58 earth days of sunlight and 58 earth-days of night, with a shade under two solar days per year. Still a long time, admittedly. $\endgroup$
    – notovny
    Commented Jun 13, 2021 at 10:25

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