Brandon Rhodes
  • Member for 6 years, 11 months
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Is 75 meters an exceptionally close distance for two satellites to pass at >6,000 m/s?
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32 votes

No, 75 meters is not exceptionally close — several satellites show predicted passages that close or closer every single week of the year. But it is close enough to potentially appear in the top 10 ...

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How to obtain UTC of the epoch time in a satellite TLE (two line element)?
11 votes

The best guess available about the time scale used in TLE files is from the epic Revisiting Spacetrack Report #3 report from Celestrak, which they have put online here: http://www.celestrak.com/...

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How to get earth-centered, earth-fixed coordinates from Skyfield?
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9 votes

Skyfield ≥1.34 The most recent versions of Skyfield introduce an explicit itrs reference frame that rotates with the Earth. You can learn about it starting here: https://rhodesmill.org/skyfield/...

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Time, UTC, Julian Date, TLE epoch - how are they related quantitatively?
8 votes

I often have to go read the Skyfield guide to dates and times to keep everything straight, but, briefly: A Julian Date is simply a rival way to name moments, that is simpler than our customary date-...

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Nuances of the terms (mean / osculating / Keplerian / orbital) elements
4 votes

I find these terms easiest to explain using an analogy. Let’s take these 5 points in the x,y plane: (1,1) (2,3) (3,4) (4,4) (5,3) We can perform the following operations on them in a Jupyter Notebook ...

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Why can n2yo somehow interpret this TLE but Skyfield can't? Why does it return nans and zeros for position?
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3 votes

The n2yo web site might be calling the SGP4 routine and, instead of checking its error code output and disregarding the coordinates that it returned, it might use the coordinates as though they are ...

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How to calculate cone angle between two satellites given their look angles?
2 votes

Computing the angle between two vectors is going to be difficult if you first transform their x, y, and z coordinates into angles, because you'll then need to dive in the formulae of spherical ...

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Ephemeris for lunar body-centered body-fixed coordinates?
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1 votes

Using Spice data files, the Skyfield library for Python can now report lunar libration as the sub-longitude and sub-latitude of the point on the Moon facing the Earth. To take an example from its ...

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How to (correctly) rotate this data so the Ecliptic is in the XY plane?
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1 votes

You should be able to fetch ecliptic coordinates with: x, y, z = venus.at(t).ecliptic_position().km Here is the current documentation — it is a bit brief, so I will try adding an example to them ...

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Asteroid 2013 TX68 March 5, 2016 close approach, and calculating with Skyfield
1 votes

The error IndexError: tuple index out of range is simply because I mistyped the two indexes in the error message in that source file. Python is zero-indexes so I ought to have typed: IOError('cannot ...

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