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While looking for the Earth satellites at the highest orbit I found mention of the Vela 1A.

Wikipedia's High Earth Orbit page indicates a perigee of 101,925km and apogee of 116,528km, however heavens-above indicates a perigee of 43,087km and an apogee of 174,729km.

I can understand that different sources have numbers that vary a bit, but in this case the ellipse is very different, I can't figure out why. So which one (if there's one) is right, and optionally why is the other wrong ? Has the initial orbit been modified ?

Note that I've already looked at the NASA page but didn't found information about the orbit.

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    $\begingroup$ Do we have a policy on decimal and thousands separators? This question was very confusing because to an American, these numbers describe prompt-reentry orbits rather than high orbits. $\endgroup$ – Russell Borogove Sep 20 '18 at 0:48
  • $\begingroup$ @RussellBorogove Good point, sorry for that. It was actually a mistake to use dots. I don't know which separator is the most appropriate (I'd use ' now) but since the comma is used on Wikipedia let's keep it as it is. $\endgroup$ – Tim Sep 20 '18 at 4:27
  • $\begingroup$ @RussellBorogove On Meta.SE: Should the network use thousands separators in numbers? $\endgroup$ – Jan Doggen Sep 20 '18 at 7:36
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Interestingly I can't find any TLEs for Vela 1A (1963-039C, 00692) between April 1968 and October 2014! It was inserted into the nearly circular orbit described in your Wikipedia article, but when it re-appears in the catalog, it has an eccentricity in the 0.54 to 0.57 ballpark.

So the Heavens-Above site is using the last available TLE from mid-2017, and this will be the best value to use. Of course the orbit will change over time and this is no longer accurate.

As an aside, there seems to be two naming conventions. Two spacecraft were launched each time. One convention calls them A and B, the other n and n+1. So Vela 6A and 6B are also called Vela 11 and 12.

Heavens-Above TLE for Vela-1A

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    $\begingroup$ Thank you for this detailed answer. Any idea how it went from a ~0.07 to a ~0.6 orbit eccentricity? $\endgroup$ – Tim Feb 13 '18 at 13:17
  • $\begingroup$ @Tim All twelve of them have behaved similarly. I don't know yet but I'd like to find out. My guess is that it is a natural process, but I'm not sure if its related to the shape of the Earth, or to effects of the Sun and Moon. I was going to post another question about this in a little while. $\endgroup$ – uhoh Feb 13 '18 at 13:22
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    $\begingroup$ @Tim I've just asked What is the basic mechanics behind the way the orbits of the twelve Vela spacecraft evolved over decades? I am not sure if it will receive a helpful answer, or if it will need more work, but let's see what happens! This has turned out to be a really interesting question! $\endgroup$ – uhoh Feb 13 '18 at 14:30
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    $\begingroup$ Thank you for that, I will follow your question attentively, it's really bugging me now. $\endgroup$ – Tim Feb 13 '18 at 14:32
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This object was "lost" for some decades. In October 2014, the Palomar Transient Factory (which was looking for near-earth asteroids that might hit us) recovered it. That was apparently enough to get the Space-Track folks back on it again.

The near-earth asteroid folks stumbled across it again in November 2017, so we now have a pretty good orbit for it.

Further details, and a plot of perigee height and inclination vs. time from 1969 to the present, are at

https://www.projectpluto.com/pluto/mpecs/63039c.htm

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  • $\begingroup$ Welcome to StackExchange and thank you for this answer and the great explanation on your answer about the Kozai mechanism! This topic is even more fascinating than I expected! $\endgroup$ – Tim Sep 21 '18 at 6:50

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