# Tag Info

33

Starlink (and other satellites) categorically do not have exterior lights or illumination, that would be a waste of power for no particular benefit. The reason that we can sometimes see satellites or other spacecraft at night is because the spacecraft is still exposed to daylight. Here is an image describing this phenomena: (image credit: Gary Meader; ...

10

A starting point for checking orbital stability is the Sphere of Influence for short term stability (or rather, to select a suitable frame a reference in the patched conic approximation), and the Hill sphere for more long term stability (satellites). $$r_{SOI} \approx a\left(\frac{m_{satellite}}{m_{parent}}\right)^{2/5}$$ For a reference spacecraft, I'm ...

9

I'm going to answer a slightly different question from the other answer: "why are Starlink satellites so visible, compared to other satellites?" The answer is that they're very close to the earth; the lower edge of what might be considered a viable long-term orbit is 300 km, and some have recently been deployed at 280 km. They are boosting to a higher ...

7

Is this method correct ? Not quite. You are assuming that $\hat r$ and $\hat v$ are orthogonal. A quick check shows that this is not quite the case. The ISS's orbit is not quite circular. This means that while your $\hat y$ points in the right direction, it is not a unit vector. You can make it a unit vector by dividing by the magnitude. Then you can ...

5

Looks right to me to a first approximation. One useful sanity check is that X comes out close to V (because the orbit is close to circular and thus V was already almost perpendicular to R to begin with). Another is to note that the ISS was about to cross the equatorial plane (the ITRF $z$ coordinate of R is almost zero) and moving in a direction a little ...

4

Part of what makes satellites expensive is all the R&D, careful manufacture, and extensive testing that goes into them before launch. The end goal is to make them as reliable as possible, so things don't go wrong and require fixing (or at least the probability is minimized). Satellites are typically built with a predetermined lifespan; part of that is ...

4

Here is a simulation to predict the reentry date. 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 EGM2008 derived gravity anomaly and GOCE observation data) truncated to the degree and order 15 (to save the running ...

3

My bet would be on needles of the Project West Ford experiment, launched 9 May 1963. a ring of 480,000,000 copper dipole antennas (needles which were 1.78 centimetres long [...] was placed in orbit to facilitate global radio communication. Fifty years later, in 2013, some of the dipoles which had not deployed correctly still remained in clumps, ...

3

I looked more carefully at my source, which is plots using STK, and here is a recent closely zoomed in plot. Note that for some reason it uses a different perigee and apogee on a regular basis, which seems a bit odd, to say the least... I'm using the classical orbital parameters, mean of epoch. I switched this from the "Apogee Altitude" to the "Apogee ...

3

They are some weird processing artifacts. Here is the correct plot for KMS-4 (ID 41332) obtained from the TLEs downloaded from www.space-track.org and processed with the CSpOC library (downloadable from the same link): the shape is incredibly smooth and there are no evident secondary perturbations (surely there are several small components of perturbations,...

2

The language here tends to get in the way a bit. Generally “reaction wheels” are used for pointing: you turn them, then stop turning them once the satellite is pointing as desired. They’re not meant to spin rapidly to soak up a bunch of angular momentum. If you just need to control pointing, a reaction wheel system isn’t going to be able to absorb the ...

2

With everything in space the answer is complicated. Yes they have sent humans to space to fix or capture satellites but it's usually cheaper to build and launch a new one than fix it in orbit. Though that's not always the case. For example the Hubble Space Telescope was serviced 5 times in space (1993/4, 1997, 1999, 2002, and 2009). Another time Space ...

1

I can't answer you fully why Celestrak is wrong, but the correct number is 44972. It seems like this was updated in the other source. New objects are around 45000 right now, they shouldn't be much larger than that.

1

Read the file using Python Python has a library, py5 that can read and write these types of files. There are good introductions and instructions in https://www.christopherlovell.co.uk/blog/2016/04/27/h5py-intro.html and https://stackoverflow.com/questions/28170623/how-to-read-hdf5-files-in-python Sample code import h5py import pandas as pd f = h5py....

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