One of my earliest contacts with the concept of orbital mechanics was learning about the four cosmic velocities. They were in my primary school handbook. They were referenced in amateur astronomer's guidebook. They appeared during the university lectures. I believe they appeared in some sci-fi novels from the eastern bloc. They are the "daily bread" to anyone interested in space exploration around here.

  • First cosmic velocity is the minimal velocity to orbit the planet.
  • Second cosmic velocity is the minimal velocity to escape the planet's gravitational influence.
  • Third cosmic velocity is the minimum to escape the planet's solar system.
  • Fourth cosmic velocity is the minimum to escape the galaxy.

(and it was a bit of a pain to find any - even as simple and crude as the linked one - English language reference to these.)

The Wikipedia article is only available in Russian, Belarussian, French, Polish, Armenian and Bulgarian. And I've never seen anyone on this site ever mention "first cosmic velocity".

Is there any specific reason why this set of terms, so common and fundamental in the former eastern bloc is absolutely nonexistent in the western space exploration community?

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    $\begingroup$ "Cosmic" doesn't seem to have the same implications to Westerners that it does to you. In a 30 year aerospace engineering career I have literally never seen that word used in a technical sense except in literature translated into English by Russians. $\endgroup$ – Organic Marble Dec 28 '16 at 3:27
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    $\begingroup$ Dictionary definition: Definition of cosmic. 1 a : of or relating to the cosmos, the extraterrestrial vastness, or the universe in contrast to the earth alone b : of, relating to, or concerned with abstract spiritual or metaphysical ideas. $\endgroup$ – Organic Marble Dec 28 '16 at 3:32
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    $\begingroup$ @OrganicMarble: Maybe the translation could pick a different word, without such implications; regardless, the four velocities do form a neat natural progression and I found it quite surprising that this grouping is not present in western space culture at all, regardless of the naming convention used. $\endgroup$ – SF. Dec 28 '16 at 4:59
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    $\begingroup$ @OrganicMarble: BTW... Cosmic background radiation, Cosmic rays...? $\endgroup$ – SF. Dec 28 '16 at 5:04
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    $\begingroup$ Just read two translated books by Liu Cixin where these phrases were used. No idea if it is common in Chinese (the original language), or just this translation, but interestingly enough, as with other hard to understand translations in the books, the translator had added a footnote explaining what the phrase meant. $\endgroup$ – Innovine Dec 29 '16 at 14:50

I think this boils down to a difference of scientific pedagogical culture. In general, science is so international that we are used to terminology translating easily from one language to another. But, especially during the Soviet era, there was less scientific communication across the boundary between the Russian sphere and the rest of the world. The idea of the four cosmic velocities sounds like something that was introduced by a particular author at a particular point in time, as a way of emphasizing how much more is required to achieve each new "level of escape" in space exploration. People probably found it vivid, and it became a part of the culture.

But the books where that idea was spread were all Eastern European books. People didn't read them in the west, or at least not in English, and so the idea didn't make it here. People just talked about orbital velocity and escape velocity in general, as concepts that can be applied to anything with gravity.

Apparently, the concept did make it to Germany, but that makes sense, as part of Germany was once part of the Soviet sphere. Here is an article where it is discussed, and Russian scientists are credited with inventing the concept.

So, basically, you don't find it here because it just didn't (or hasn't yet) spread here from its birthplace in Russia.

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    $\begingroup$ Yes, it is used in Germany. The German Wikipedia entry about Escape Velocity notes it's also called "zweite komische Geschwindigkeit" = "second cosmic velocity". It also seems to be used in academics at least sometimes. Even though I grew up in what was West Germany, I've heard that term before; but it don't remember if that was before or after reunification. It really is possible the term came from Russia via East Germany. $\endgroup$ – DarkDust Dec 28 '16 at 19:27
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    $\begingroup$ Interestingly, the Fluchtgeschwindigkeit entry mentioned that the term cosmic velocity originated in the middle of the 19th century in discussions about meteors (a paper by Schiaparelli was mentioned but I didn't find a searchable translation). It's unclear to me whether that already was the concept of the four cosmic velocities. $\endgroup$ – DarkDust Dec 28 '16 at 19:29

There's a similar and unrelated terminology difference in statistics: what in Russian (at least in my university) is usually called "type I error" and "type II error" [1], in English is more often referred to as "false positive" and "false negative". I find the latter terminology superior: the names are descriptive, there are no arbitrary numbers to remember. I feel the same way about the cosmic velocities: the names "orbital speed" and "escape velocity" just seem more descriptive.

Since there doesn't seem to be much value in numbering these velocities (as long as each of them has some name), it's not surprising that this terminology didn't spread from eastern Europe to the rest of the world.

[1] https://en.wikipedia.org/wiki/Type_I_and_type_II_errors

  • $\begingroup$ Yes, the "numbered" approach always seemed a bit wrong to me. The logic behind 1st and 2nd velocity seems different from 3rd. And 4th is bonkers. I'm glad quite a lot of people were spared from this terminology. $\endgroup$ – kubanczyk Dec 29 '16 at 14:14

I could only find the Western counterpart of second cosmic velocity: https://en.wikipedia.org/wiki/Escape_velocity

  • $\begingroup$ Pretty sure SF. knows what it is called, but doesn't know why it's not called by the translated term mentioned. $\endgroup$ – Nathan Tuggy Dec 28 '16 at 7:40
  • $\begingroup$ Escape Velocity applies to the third and fourth cases too, not just the second. $\endgroup$ – Innovine Dec 28 '16 at 8:44

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