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### How to calculate the planets and moons beyond Newtons's gravitational force?

The question Calculating the planets and moons based on Newtons's gravitational force was pretty much answered with two items: Use a reasonable ODE solver; at least RK4 (the classic Runge-Kutta ...
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### How often does the ISS orbit align with the day/night terminator?

In the following image (coming from SAT-Flare) you can see the orbit of the ISS (in red) and the day/night terminator (in blue). The terminator separates night from day along the surface of the Earth. ...
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### Was Alexander Gerst the first man to have bare skin exposed to the vacuum of space and live?

On August 30, 2018, a hole was found in the Soyuz Orbital Module on the ISS. Astronaut Alexander Gerst initially plugged it with his thumb, meaning a part of his bare skin touched space. I can't find ...
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### How to generate TLE file?

Subsequently to this answer: What is the way of generation of TLE file for a satellite? How to deal with BSTAR drag term, mean orbital elements, etc.? The generated TLE will be used as the input for ...
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### Physical meaning of perigee advance

I'm starting to study orbital perturbations and I can't find any physical explanation about the perigee advance (apsidal precession) when considering Earth oblateness effects. Can someone give a ...
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### Is SGP4 propagation necessarily more accurate near the epoch chosen for TLE generation?

This interesting answer includes a quote from Space-Track: From Space-Track.Org FAQ TLEs can contain future epochs. About 20 satellites are categorized as "multi-day objects" ...
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### What is the reason for secondary oscillations in apogee and perigee plots for objects 41332 and 41333?

This answer provides quite interesting plots of apogee and perigee for objects 41332 and 41333. The primary (sine wave -like) oscillations are probably due to perturbations caused by potential ...
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### Equation for orbital period around oblate bodies, based on J2?

In this answer I point out that the period of items (ring particles, moons, spacecraft, etc.) around an oblate body will not scale exactly as $a^{3/2}$ because the closer you are to the planet, the ...
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### How do “Deep space” corrections in SGP4 account for the Sun's and Moon's gravity?

The [Simplified Perturbations model][1] SGP4 is used to calculate Earth satellite state vectors (position and velocity) using standard ephemeris data encoded as TLEs (Two Line Elements). According to ...
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### Do orbits change over a period of time, especially when the Star is not at the center (example: Didymos)?

Consider a celestial body, say the asteroid Didymos for example, with an elliptical orbit around the Sun. Now since the Sun has a huge gravitational pull and mainly because it is not at the center of ...