# Tag Info

21

As of this point we do not have actual footage of the reentry. It occurred somewhere over the Pacific Ocean, there is very little to no population there. Almost no planes were at the reentry point. Maybe per coincidence some fisherman or island inhabitant just happened to catch it, but I think it is unlikely. There is some fake footage, mostly consisting ...

15

It was done with one single dish, ...in Ku-band (16.7 GHz) and ... currently equipped with a high target resolution. The Fraunhofer Institute for High Frequency Physics and Radar Techniques (FHR)'s March 21, 2018 press release - the original source of the picture in the question - links to an introductory description of their Space observation radar TIRA (...

15

This issue was discussed recently in SpaceDaily where it explains why this is a known unknown: Right now, it's impossible to make an educated guess on even a rough "window" for Tiangong's return. The orbit is still high. Unpredictable factors such as solar activity will influence its orbital decay. We won't have an estimate until it starts to fall much ...

11

Okay, first of all, let's assume that the two space stations are aligned properly. How often does this happen? The key thing is that each satellite will drift westward each day, due to what is known as Nodal Precession. Wikipedia gives us an approximate formula: $\omega_{p} = -\frac{3}{2}\frac{R_E^2}{(a(1-e^2))^2} J_2 \omega \cos i$ That gives each of ...

10

Is it because the Earth is not exactly a sphere and also due to uneven mass distribution? Yes! Is it an atmospheric effect? No. Earth's large J2 or oblateness term is always trying to perturb satellite orbits, and the effect is strongest in LEO. In this answer for example, I show how J2 constantly advances the argument of perigee of an elliptical ...

5

Tiangong-1 will deorbit sometime in late 2017 As recently reported in Popular Mechanics The China National Space Agency recently announced that Tiangong-1 will deorbit sometime late in 2017, although they can't say exactly when or where the former space station will fall. Source

5

After the uhoh's excellent answer, there’s no need for another answer, but with a simulation we can see the effect of the Earth's oblateness and of the atmosphere. The simulation includes the Newtonian and the relativistic accelerations of all the planets, Sun and Moon. The Earth's gravity field is modeled with the SGG-UGM-1 gravity model (computed using ...

3

Seems to be a mistake based on both common sense and backup from @OrganicMarble's comment above - not to imply that the later is not also a subset of the former :) Apparently, not everything on the internet is always correct.

3

No-one knows for sure where it will come down: there are still wide margins on the estimates. But it's not looking likely to be the US. You can see a graphic of one estimate here (click for the latest update): As you can see, the tracks do not go near the US in the relevant timeframe.

3

Looking at STK and the public elements for each object. Unfortunately I can't do a conjunction report, as I can't seem to get JUNO into STK unfortunately... But here's a few photos: Juno Flyby: ISS/Tiangong at the time of closest approach: Given this, hands down the answer is Tiangong. I don't have an exact distance for you, but it will be within 4 track ...

3

There's a "Global Infrasound Network" that monitors for nuclear explosions. If a reentry is big enough, I expect they'll "hear" it. It might have to be pretty big, perhaps larger than the the vast majority of meteors and satellites, but they did detect the 2013 Russian meteor. NASA provides a summary of "fireballs" seen by &...

3

(Posting as an answer so I can insert images) Lending credence to the idea that this is "sensitive response to measurement noise", consider these two plots from SatFlare.com (arrows added). They show just one datum that dropped in perigee and went up in apogee; the next measurement was back on the smooth track. Perigee:

2

The Fraunhofer Institute for High Frequency Physics and Radar Techniques near Bonn, Germany released a picture from a distance of 270 kms. There is some interesting information about how they tracked it in space.com

2

Edit: The question has been updated and the plot showing a "blip" in inclination which has the same shape as the "blib" in eccentricity. I've incorporated my comments here: The only phenomenon I'm really proposing is that when limited measure data is fitted and parameters are extracted, there are sources of noise in the extracted parameters, and the noise ...

2

I'll elaborate on @pericynthion's answer a bit, with regard to what the "noise" may be, and speculate on the cause. Despite the visual appearance in the question, a plot of apogee is not any smoother than one of perigee. Currently you show one plot with a range of 24 kilometers and the other with a range of 1,000 kilometers. Below, I've plotted the ...

2

The perigee altitude for PSLV-C39/IRNSS-1H is very low (< 200 km) in the timespan you selected. This makes it much more sensitive to atmospheric drag than an object at higher altitude. Atmospheric drag is notoriously difficult to predict due to atmospheric density fluctuations and spacecraft attitude variation. Also, the lower altitude means fewer ...

1

@RussellBorogove's comment is fairly conclusive. ...I note that Celestrak was established in 1985, at which point Salyut 7 was up, but Skylab was not. The Archived TLE data page says 1980-2004, but there's a link to request earlier data. Skylab reentered the atmosphere before 1980 and Tiangong-1 and Tiangong-2 were both launched after 2004. And, as ...

1

Several satellite radar tracking stations are being used to track the doomed station. This .png is updated every few minutes by The Aerospace Corporation. In the lower left a list of tracking radars and their future observation windows are shown.

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