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This is a question about early planetary missions. It looks like there was only one early (unsuccessful) landing mission to Mars and that subsequently Venus became the target for interplanetary landings. Here's my question:

Why was Venus prioritized when (at least with modern technology) the surface of Mars seems way easier to explore, and e.g. send back amazing images? Does this have something to do with the difficulty of getting there? Something with the fact that we didn't know about the extremeness of Venus' atmosphere? Or was there a non-technology related reason that deemed Venus as the more exciting destination?

Mazura
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user2705196
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4 Answers4

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The reason is delta-v, which is a crucial concept in Spaceflight. It means change in velocity, and is the primary 'currency' that space mission have to expend in order to reach places in the solar system. On earth, if you want to go anywhere, you can get there at any speed, it just takes longer. Unfortunately, that is not how it works in space, because the body you come from and the body you want to reach both cycle the sun at very large speeds. After getting into orbit, you need to accelerate by another 3.21 kilometers per second to escape the gravity influence of the earth completely.

In order to get to Mars from this point, you would need to accelerate another 1.06 km/s, so that the orbit of your spacecraft crosses the orbit of Mars. Alternatively, to achieve the same with Venus you would need to accelerate by only 640 meters per second. Already, it is cheaper to go to Venus than Mars, but it gets better:

As I said above, your spacecraft's orbit now crosses the orbit of your target planet in one point. However, the orbital speed is still quite different. With Mars, the spacecraft would crash right into the surface, and you need to accelerate another 4.28 kilometers per second in order to reach the surface safely*. If you went to Venus, you can enter the planet's dense atmosphere to cushion the impact. As a result, you don't need to carry any rocket fuel to make a landing.

This makes Venus a low hanging fruit. At a favorable constellation, Venus is the planetary body that takes the least delta-v to reach. That even includes our moon. Heck, it takes less delta-v to reach than geostationary orbit.

In fact, the Russian Venera Probes slammed right into the Venerean atmosphere from an interplanetary trajectory (11km/s). This caused a deceleration exceeding 300G and a heat shield temperature of 11,000 °C, but that didn't destroy those probes.

The diagram below shows different places in the solar system and rough estimates of how much delta-v you need to reach them. It all still depends on the exact constellation and the maneuver you use, so use these as ballpark estimates.

enter image description here

Copyright as noted in the image.

*Actually a bit less, because Mars also has some atmosphere that can help you with the landing.

Rikki-Tikki-Tavi
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We didn't know how hostile Venus's surface was, until we had landed there. The atmosphere of Venus makes it easier to land there than Mars. From Wikipedia, we learn:

Before radio observations in the 1960s, many believed that Venus contained a lush, Earth-like environment.

While there was some concept that Venus was hot, and had a high pressure, the exact amount as to how hostile it was wasn't really known until we had sent a lander there.

PearsonArtPhoto
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    Many early (40s and 50s) Sci-fi had human colonies on Venus, described as having a tropical atmosphere. – GdD Apr 04 '16 at 16:28
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    Public perception is a powerful thing. If Venus is popular or cool in the public mind, it will be high on the list. – wedstrom Apr 04 '16 at 18:15
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    Wow, 455 °C to 475 °C and 75 to 100 atmospheres of pressure (I think that means 1,100 to 1,400 PSI) that's pretty hostile compared to the inside of an oven, would burn and crush my dinner – Xen2050 Apr 04 '16 at 18:30
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    Venus is quite nasty. But we didn't really know how nasty it was until we landed something there, so... – PearsonArtPhoto Apr 04 '16 at 18:31
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    I think clouds of Venus are a still a better bet for colonization. Abundant energy, free industrial chemicals, actually having an atmosphere, near earth gravity, easier water manufacture [2(H2SO4) + heat = 2(H2O + SO2) +O], not being colder than Antarctica etc etc etc. I think venus fell into disfavor because it was a Soviet project and the West staked its claim on Mars. – King-Ink Apr 04 '16 at 21:12
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    The early craft were not sent unprepared! That it was hot enough to melt solder was known during the planning stages. radio observations, remember, not touching it and saying "ow". – JDługosz Apr 04 '16 at 22:02
  • @Xen2050 would burn and crush my dinner even if it didn't would you have liked to eat dinner laced with sulphuric acid? – cst1992 Apr 05 '16 at 08:45
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    ...and then we performed the most extreme, expensive and remote measurement of hardness of a lens cover. – SF. Apr 05 '16 at 16:34
  • @SF. That was a mistake. Give the poor guys a break. – cst1992 Apr 06 '16 at 12:14
  • @cst1992: The experiment didn't go as planned, sure, but I'm still curious about the results! What happens to hardness of a lens cap after several months in space, descent through Venus atmosphere and being thrown onto its ground... was it a putty due to heat or did it harden due to the pressure or did it crumble after months of radiation and cold followed by hot acid treatment? – SF. Apr 06 '16 at 22:32
  • It was a titanium lens cap, so I'm sure it'd have been fine. – cst1992 Apr 07 '16 at 05:18
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One picture is worth all your base to us.

Before we sent probes to Venus we had no pictures of its surface. Whether it lands or not you have to penetrate the atmosphere of Venus to take pictures of it, whereas the surface of Mars can be easily seen through its weak atmosphere from afar.

Most of the information about Venus has been derived from the intensive Soviet study of the planet. The only existing images from the surface were returned from four of their landing craft. –unbelievable-facts.com

It should be noted that the explorations of Venus and Mars both began ca. 1960. Venus is just the one that you have to land on (soft or hard) to gather any meaningful data*:

enter image description here

** Pics, or it didn't happen.

Although I can't rule out militaristic reasoning, I think it's more about the Space Race as a whole. During which, other than landing twelve people on the moon, the Soviet space program (notable firsts) beat the Americans' at nearly every conceivable turn. Including as a shining example: to this date theirs is the only country on Earth to ever take pictures of Venus' surface.

We hadn't seen it before nor have we seen it since. That's pretty exciting to me. CCCP-1, USA-0.

Mazura
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    I don't think it's arguable that the Soviet space program beat the Americans. Leaving out the moon, there were successful US Mars landers & orbiters (Soviet ones all basically failed, IIRC), the Pioneer & Voyager missions to the outer planets (no Soviet equivalent that I know of), Mariner 10 to Mercury, and successful Venus orbiter and landers (though they didn't take pictures): https://en.wikipedia.org/wiki/Pioneer_Venus_Multiprobe Indeed, going by Wikipedia's list of space probes, about the only thing the Soviets led in was failed missions. – jamesqf Apr 05 '16 at 04:59
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    @jamesqf "The Space Race [1957-1975] spawned pioneering efforts to launch artificial satellites, unmanned space probes of the Moon, Venus, and Mars, and human spaceflight in low Earth orbit and to the Moon." Voyger1 was launched in 1977; a day late and a dollar short. Besides, I'm counting achievements not failures. Here's a rather impressive list of the Soviet's Notable Firsts. – Mazura Apr 05 '16 at 05:09
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    Why, the OP asks? "... not because they are easy, but because they are hard." – Mazura Apr 05 '16 at 05:20
  • When you say "Soviet space program", I take that to mean the whole space program up until the collapse of the USSR in 1989. Seems rather unfair to pick an arbitrary end date. – jamesqf Apr 05 '16 at 05:41
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    On July 17, 1975 the Space Race ended when an astronaut and a cosmonaut made "the first international handshake in space." The Soviet list goes on up till 1987. I'm having trouble finding a similar list for NASA's firsts... – Mazura Apr 05 '16 at 05:58
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    @Mazura It would be more useful to give as much info as possible that has to do with the question than a debate of which space program was better or which one won.So paragraphs of cheering for USSR, US or other countries are'nt necessary since here it is not a forum for football clubs and cheering for them by giving our oppinions which one is better even if we are reffering historic facts,since the question has not to do with this.I suggest you to edit last part of your answer since the purpose of this site is giving arguments that answer the question not including enthusiastic paragraph – Mark777 Apr 05 '16 at 16:51
  • @Mazura: Who sez, you? I'd also point out that there's a major difference between doing something first, and doing it well. As for instance the Soviets landed a probe on Mars which IIRC didn't even manage to send back a full picture before failing. NASA's Vikings lasted for years, doing science other than just pictures. – jamesqf Apr 05 '16 at 17:37
  • @MarkBoghdani - The last part of my answer address the OP's last question: Or was there a non-technology related reason* that deemed Venus the more exciting destination?"* Yes, to WIN every possible facet of the Space Race. For which I would feel remiss if I didn't admit the fact that they basically did. – Mazura Apr 05 '16 at 22:46
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    @jamesqf, first satellite in orbit? USSR. first living being in space? USSR. first man in space? USSR. first space walk? USSR. first satellite to orbit the moon? USSR. first soft lunar landing? USSR. first lunar mission to return samples to earth? USSR. first manned mission to the moon? USA (yay finally!! good work USA) – Octopus Apr 05 '16 at 23:12
  • Also, "enthusiasm" is integral to this question. It is after all, called the Space Race. If we're going to answer Why, we need to know what we're talking about. And what we're talking about had its first preparations made for sometime during WWII: The Cold War. - I'd suggest the question be edited, to remove the (last) part of it that belongs on History.SE, except that I see no call for that at all. It's just that we need to have some understanding of 1960s Earth to explain all of the reasoning behind this why. – Mazura Apr 05 '16 at 23:21
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Scientists were unaware of how hostile Venusian surface conditions were til the probes they put there, were destroyed. Venus is a notorious probe destroyer. It's actually easier to go to Mars despite being farther away. Mars is a freezer Venus is a pressure cooker

LazyReader
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  • As noted by other answers, it is actually much easier to get to Venus than it is to get to Mars. I think what you may mean is that it is easier to survive for any reasonable amount of time on Mars than it is on Venus – Kevin Sep 21 '20 at 20:18