A quote near the end of the BBC's article 'Disco ball' put into space from NZ says:

Jonathan McDowell, a satellite-tracker and astronomer at the Harvard-Smithsonian Center for Astrophysics, commented: "The irony is that it's poorly placed for observation right now - low on the horizon for evening passes in New Zealand and not visible from the USA until March - if it stays up that long."

N2YO says that it is 43166, 2018-010D, in a 299 x 532 km orbit at 82.9°. This LEO orbit has a mean motion of close to 15.5 per day, is there some freaky resonance that puts it over the US only during the daytime somehow?

Question: How could it remain invisible from North America (or USA at least) for two months?

A secondary question would be if this is intentional - is this a side-effect of making its visibility somehow more from New Zealand?

  • $\begingroup$ Your recent edit really is a separate question. Space Track hasn't yet released the names for the objects, so it isn't certain if it is 10D or 10F, they are just guesses, unless someone actually called JSPOC and asked them. As it doesn't have a payload, it would be very difficult to track except with Radar, and thus might not be obvious to anyone yet. The better tracking will be available soon, but in any case, I doubt the objects have separated enough to really know yet. $\endgroup$
    – PearsonArtPhoto
    Jan 29, 2018 at 3:51
  • $\begingroup$ @PearsonArtPhoto that edit was accidentally saved, I've already split it out as a separate question. space.stackexchange.com/q/24656/12102. & rolled back. $\endgroup$
    – uhoh
    Jan 29, 2018 at 4:10
  • $\begingroup$ @PearsonArtPhoto D and F objects certainly well separated, and Humanity Star probably has a whopping and distinctively pulsing radar cross-section - compared to the other 2018-010 payloads. $\endgroup$
    – uhoh
    Jan 29, 2018 at 4:42

1 Answer 1


The mean motion isn't really what causes it to not be visible for a long time, but the nodal precession. High inclination orbits tend to have a slower rate of nodal precession, which is why Sun Synchronous orbits are nearly completely polar. Using this calculator, and calculating for a 400 km orbit, I calculate a precession of about a degree per day. That being the case, if they launched it poorly, it could indeed take months to switch to a more favorable viewing location.

I don't think this was intentional. It largely depends on the time of day they launched the rocket.

For such a nearly polar orbit, the satellite will basically pass over twice per day, separated by 12 hours. The launch happened at 2:43 PM in New Zealand. The orbit happens a few minutes later, so let's say 2:00.

Actual pass times are closer to 12-2, AM and PM. The exact time can vary. For a really good New Zealand pass, it will just clip the sun at the earlier portion of the window. Due to the fact that New Zealand is far south, the "twilight" period where the satellite is in sun, but the Earth in shadow, is expanded more then normal, and allows for it to be seen, barely in middle of the night passes, as can be seen at Heavens-Above.

In the US, it is the winter. This time of the night has no visibility. Thus, it is pretty much a guarantee that the satellite is eclipsed when it will pass overhead.

The only thing that could have been done differently would be to launch at a different time. I assume at this was a test flight, they choose to launch at a time of day that they could clearly see what was happening.

  • $\begingroup$ I see, for such a low orbit, it's only when the passes soon after dusk or before dawn that the spacecraft is illuminated by the Sun. That's why for example this pass i.stack.imgur.com/cxsGJ.jpg chosen from your link cuts out so quickly. If the orbit where much higher (or the spacecraft had it's own light source) the window would be wider. The only thing that will increase coincidence with the dawn/dusk lines is the unfortunately slow nodal precession. Got it! $\endgroup$
    – uhoh
    Jan 25, 2018 at 21:45

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