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While browsing a space object visualisation service, AstriaGraph, I see a large number of objects occupying a specific MEO orbit, and I want to understand the name and purpose of this orbit, and what these objects might be.

There are several hundred objects, with no IDs, classifications or details on this particular platform, in a ~6900x34500 km orbit, with a period of 12 hours. It looks a little like a Molniya orbit, but the inclination - just 24 degrees - appears very low, and they appear to apogee dwell over the south Atlantic, which seems odd.

Does anyone know what this orbit - or these objects - are?

Illustration of the orbit in question (from UTex AstriaGraph)

Russell Borogove
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alexandicity
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  • What kind of coordinate system is this? co-rotating with Earth? – asdfex Dec 09 '23 at 09:31
  • Unsure. I'd instinctly say it was inertial, as I don't think orbits like that can be co-rotating. I realise my question (with the geographical dwell), implies co-rotating, but I'm not sure either way. – alexandicity Dec 14 '23 at 11:59

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Answer: Space junk in Geosynchronous Transfer Orbit.

As PearsonArtPhoto explained in the answer to the linked question (and again elsewhere), these are upper stages of GEO launch vehicles. The perigee appears to be over Cape Canaveral (Lat 28*N) so we know who is holding the smoking gun.

Woody
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  • Placing GEO satellites in 23deg inclination (initial orbit) sounds quite inefficient. Not answered in the other question as to why they chose to do so (i.e. rocket not correcting for the "natural inclination" when launched from 28degN). – AJN Dec 09 '23 at 05:22
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    Inclination changes are expensive, but less so when the spacecraft is further from the Earth, slower, and when it has lower mass. Maybe doing the burn with the kicker, after ditching the upper stage, saves propellant ??? I think another question is needed – Woody Dec 09 '23 at 18:49
  • Indeed, the inclination gives us a likely launch site, and the eccentricity looks like GTO. Plane changes are indeed relatively cheap when at GEO. Not efficient, but it's the best that can be done from the US. Apogees isn't high enough for a regular GTO, but that may just be a different launch profile.

    The first linked answer is for a different orbit (that is clearly GTO), but the second one is indeed relevant. It explains the quantity of objects in such a tight orbit well. All that debris from a single launch - wow. Thank you!

     – alexandicity Dec 14 '23 at 12:03
  • May I ask how you found these linked answers? I did a search beforehand but couldn't find these same topics (sorry - SE newbie here!) – alexandicity Dec 14 '23 at 12:07
  • @alexandicity ... can't remember. I was trying to learn about launching to GEO so I was surfing around. I'm still not clear on the trade-offs of different strategies. – Woody Dec 14 '23 at 17:01