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I noticed to my surprise today that the very early Soviet flights were to a very high inclination - all the Vostok flights were between 64.9° and 65°, and the Voskhod flights were at 64.7° and 64.8°.

After this, Soyuz 1 was at 50.8°, and subsequent flights seem to have been at or around a standard 51.6°. The only exception appears to be Soyuz 22, which went to 64.75°. On the American side, all orbital Mercury flights were at 32.5°; early Gemini flights were the same before dropping to 28.8°. Apollo lunar flights used a parking orbit around 32.5°, and Skylab was at 50°. Several Shuttle flights went to 57°, and STS-36 made a rather complex flight to 62°. Vandenberg launches would have gone to nearly 90°, but they were cancelled.

Generally speaking, the high-inclination flights seem to have been aiming for earth observation opportunities (or in the case of STS-36, to deploy an earth observation satellite). Wikipedia explicitly mentions this reason for Soyuz 22.

However, it's not clear why it was used for the earliest Vostok/Voskhod flights - was it to support earth observation objectives? Was there a political justification, to ensure it could be observed as widely as possible? Was it a quirk of the launch system which made this inclination easy to achieve?

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I have a few suspicions, but I can't find a really good source that outlines exactly what. Here's a few bits of information:

  1. The Vostok rocket was used to launch spy satellites, which would be a higher inclination.
  2. Being only 1 orbit, the inclination could have been determined to allow for the uncertainty ellipse of landing to happen over Russia in a key part of the country, where it would be unlikely to damage anything when it landed, yet remain accessible.
  3. I suspect the ground track was made to avoid certain places, not fly deliberately over them.
  4. The communication network might have only been set up to support a higher inclination launch, likely due to #1.
  5. It could be to give really wide berth to China. I'm sure that the launches weren't as accurate as today, but I find it hard to believe they had a 10 degree inclination uncertainty. Still, it is possible...

Here's an image of the ground track:

enter image description here

Note that the higher inclination puts it clearly over Russia for most of it's early flight, and has it over the main part of Russia during re-entry. They probably wanted to avoid the Black Sea as a potential landing spot, as the vehicle could not land.

So, I suspect the main reason was that most launches to test the Vostok were spy satellites, which benefit from a higher inclination, and the communication network was set up to support such. Given the secrecy of the early Soviet space program, the exact answer might not be known to the public...

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    $\begingroup$ This makes sense, especially #1 - if Baikonur was set up for launches in that direction, you'd want to use the existing telemetry infrastructure. And it keeps you safely clear of China in case of launch aborts... $\endgroup$ – Andrew Aug 28 '15 at 20:44
  • $\begingroup$ I considered the China situation as well, I don't think that was as much of a concern, although it is certainly a possibility... $\endgroup$ – PearsonArtPhoto♦ Aug 28 '15 at 20:45
  • $\begingroup$ After looking at it for a bit, that ground track image is a bit skewed - the southernmost part is passing over the tip of Tierra del Fuego, ~56°S, while the northernmost bit is just by the Sea of Okhotsk, which would make it ~62°N. Interesting! $\endgroup$ – Andrew Aug 28 '15 at 20:49
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    $\begingroup$ How about high latitude of the launch site, avoiding overflying of China, and LV performance? $\endgroup$ – TildalWave Aug 28 '15 at 20:52
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    $\begingroup$ For Vostok 1, the track goes over ocean in the western hemisphere, as opposed to going over USA. In case something went wrong and Vostok had to de-orbit early, they wanted it to land in international waters. Landing in USA would have been much more "sticky". At least, that is what I remember from some book somewhere. BTW, by 1961, the sino-soviet split was already very real between Khrushchev and Zedong. It was very important to avoid a track over China. $\endgroup$ – DrZ214 Mar 4 '17 at 23:38
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Baikonur is at 46 deg. latitude. You can lift the most payload by going into an inclination that equals your launch latitude.

ISS ended up at 57 deg., so Shuttle flights needed to launch close to that to be able to rendezvous.

A consideration is where debris might go for a launch failure, so you don't have low inclination launches from Vandenberg. For the Shuttle, a consideration was what could be reached in case of an abort. Easter Island was the plan if SLC-6 at Vandenberg had ever been used.

Early Soviet launch vehicles had limited or no capability to gimbal the engines, so would set azimuth by rotating the entire stack on the launch pad.

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  • $\begingroup$ ISS is actually at 51.64 degrees. Mir before it was in the same inclination. $\endgroup$ – DrZ214 Mar 4 '17 at 23:40

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