795 views

### What does it take for a craft to perform a flight simulating weightlessness without having to fly a steep parabola/ellipse?

Alright, I'll try to ask a better question on what I mean so that we figure out how one becomes weightless in a craft without having to fly steep parabolae. Other than flying parabolae or nose-down ...
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### Can the Right Ascension and Argument of Perigee of a spacecraft's orbit keep varying by themselves with time?

I came across the orbital data for a low Earth orbit spacecraft and one thing which I am not able to understand is why does its Right Ascension of ascending node and Argument of Perigee keep changing ...
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### How fast do Starlink satellites (SpaceX new satellites) rotate around the earth?

I'm specifically interested in knowing how long they take to do a full circle around the earth but don't find any info. Could anyone help me?
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### Determine orbit type from TLE

I was wondering if, and how, one can tell from the values in a TLE whether an orbit is LEO, MEO, HEO, or GEO. I'd like to do this in code eventually, so any formulas or threshold values would be much ...
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### In "spacecraft talk" is nadir just a fancy word for "down"?

Assume the approximation that the Earth is spherically symmetric — without higher order gravitational multipoles, and other effects that might be related to gravity from other bodies or the ...
550 views

### Which satellite constellations are already operational in LEO (Low Earth Orbit)?

I am researching information on active and operational constellations in LEO (Low Earth Orbit) but from what I can see, many missions are still only planned (e.g. OneWeb, Amazon) and the only one ...
1k views

### Help understanding negative apogee coinciding with exact center of Earth (Mars InSight launch)

Watching the NASA JPL video NASA Launches InSight to Mars (Part 2) after MECO-2, the orbital parameters shown in the video don't make sense to me; specifically the apogee altitude. At this point in ...
2k views

The recently launched Starlink satellites are designed to use their HAL Ion thrusters to seek their own independent orbits, evade collisions, and de-orbit at the end of their lives. That's a lot of ...
301 views

### Deviation of semi-major axis

If I calculate the semi-major axis of Molniya-1T with $a = \sqrt[3]{\dfrac{GM}{n^2}}$ with $n=3.18683728\text{ }d^{-1}$, I get another apoapsis ($a=19505.7$ km) as noted at Heavens Above: apogee ...
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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 ...
541 views

### Did Tiangong-1 turn the engines on?

The following graph shows the Tiangong-1 radius vector at the perigee, semi-major axis and apogee (scaled to 6371 km just to show an approximate altitude) and its orbit eccentricity: I used the SGP4 ...
737 views

### What is the Fischer 1960 Mercury Ellipsoid, and why is it called that?

Don't be distracted by the 1960 Mercury shown below. Reading about Irene Fischer (also here, and mentioned in this answer) and seeing the Fischer 1960 Mercury Ellipsoid turn up in tables of ellipsoid ...
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### How to read stuffin.space data?

In a comment to this question, @PcMan suggested my stuffin.space for satellite data. Now I am not quite sure of how to interpret the data, take for example the following screenshot: Why is the ...
375 views

### How large would be the seasonal variation of eclipse duration for a spacecraft in LEO?

The question How long will a 500 km altitude satellite spend in Earth - shade per orbit has several answers, and there is some discussion of constraints related to maximum eclipse, due to some issues ...
156 views

### Failing at getting apogee and perigee from TLE

At Celestrak, the current orbit for ISS is currently listed as 423x417 km, but if I'm getting the TLE data from Celestrak and use orb.get_lonlatalt(now) from ...
121 views

### Mechanics of Sun-Synchronous Orbit & North Korea's KMS-4

QUICK QUESTION: Is North Korea's KMS-4 in a proper Sun-synchronous orbit? https://www.n2yo.com/?s=41332 2016-009A FOLLOW-UP QUESTION: How do I tell? I want to understand the mechanics. RESEARCH:...