268 lines
6.9 KiB
Markdown
268 lines
6.9 KiB
Markdown
# Spacecruft Celestia GNSS
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Celestia is a "real-time space simulation that lets you experience our
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universe in three dimensions".
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The present repo contains the `tle2ssc` Python script which converts
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NORAD Two-Line Element sets (TLE) from CelesTrak into into
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Solar System Catalog (SSC) files that can be read by Celestia.
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The `tle2ssc` script is set by default to retrieve the latest orbits
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for various GNSS ("GPS") satellite systems.
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It could be easily updated for any other source of TLEs.
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*Celestia Animated Time Lapse GNSS Orbits*
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# Quick & Dirty Install
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If you just want to import the pre-generated file into Celestia for
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a look, just copy these files into your `extras` folder or similar.
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```
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# crufty below, private dir better
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sudo mkdir -p /usr/share/celestia/extras-standard/gnss/models/
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# Whatever user...
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sudo chown -R debian:debian /usr/share/celestia/extras-standard/gnss
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# Get SSC file
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wget -O /usr/share/celestia/extras-standard/gnss/gnss.ssc \
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https://spacecruft.org/spacecruft/celestia-gnss/raw/branch/main/extras/gnss/gnss.ssc
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# Get 3D model
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wget -O /usr/share/celestia/extras-standard/gnss/models/galileo-gnss.cmod \
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https://spacecruft.org/spacecruft/celestia-gnss/raw/branch/main/extras/gnss/models/galileo-gnss.cmod
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# Then (re)start Celestia.
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```
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# Install celestia-gnss
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Install thusly to generate your own `.ssc` files.
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```
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git clone https://spacecruft.org/spacecruft/celestia-gnss
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cd celestia-gnss
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sudo apt update
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sudo apt install python3-pip python3-virtualenv
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# Many ways to do python setup, here is one:
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virtualenv -p python3 env
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source env/bin/activate
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pip install --upgrade pip
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pip install -r requirements.txt
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```
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# Run celestia-gnss
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Example (crufty example, if you have perms):
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```
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./tle2ssc > /usr/share/celestia/extras-standard/gnss/gnss.ssc
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```
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# Use in Celestia
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Use thusly, hooman.
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*Celestia Showing GNSS Satellites with Labels*
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Then copy the satellites you want into your Celestia extras dir.
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Crufty bad way to do it, example:
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```
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sudo cp -a extras/gnss/gnss.ssc /usr/share/celestia/extras-standard/
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```
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Each system, GPS, Galileo, Glonass, Beidou, can be used,
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or the GNSS files which include all four, plus more regional systems.
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# Screenshots
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Screenshots of running Celestia with GNSS satellites.
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*GNSS Satellites Orbiting Earth*
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*Celestia with Moon orbit, Earth, and GNSS satellites.*
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*Celestia MultiView.*
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# See Also
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## Spacecruft
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Spacecruft:
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* https://spacecruft.org/spacecruft/gnss-earth
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* https://spacecruft.org/spacecruft/celestia
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## Celestia
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Upstream Celestia:
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* https://celestia.space/
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* https://github.com/CelestiaProject/Celestia
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Celestia forum thread about celestia-gnss:
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* https://celestia.space/forum/viewtopic.php?f=6&t=22559
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## TLE Conversion
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TLE Conversion Spreadsheet by Grant Hutchison from July 2003,
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the basis for the formulas in the `tle2ssc` script.
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* https://www.classe.cornell.edu/~seb/celestia/hutchison/spreadsheets.html
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* https://www.classe.cornell.edu/~seb/celestia/hutchison/tle-xls.zip
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Useful formula from here too:
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* https://kaitlyn.guru/projects/two-line-elements-tle/
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I had this exact printout on my desk (trimmed to size!) when I came across
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this gem from @fisadev via Poliastro docs:
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***How are satellite orbits disseminated?***
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<img src="pics/wtf-tle.jpg" width="600">
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* https://docs.poliastro.space/en/latest/examples/Loading%20OMM%20and%20TLE%20satellite%20data.html
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Perhaps from page 7 of the PDF,
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*Strategic Center for Networking, Integration, and Communications
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Orbit Propagation Front-End Software Development*.
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* https://ntrs.nasa.gov/citations/20180008672
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Not used, but perhaps could be useful from Libre Space Foundation:
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* https://gitlab.com/librespacefoundation/python-satellitetle
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## Solar System Catalog
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*"Solar System Catalog" files are primarily used to define the objects which
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can be found in a stellar system, such as planets, moons, asteroids, comets,
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and spacecraft. They also have four other uses: they can define alternative
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surface textures, locations on or near an object, and orbital reference points.
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An SSC file can also edit objects which have been defined in other SSC catalog files.*
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Info on `.ssc` files:
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* https://www.classe.cornell.edu/~seb/celestia/creating-ssc-files.html
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* https://en.wikibooks.org/wiki/Celestia/SSC_File
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In Celestia the name "Galileo" is used for the *other* spacecraft, not
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for the EU GNSS. So the name used in here adds `-gnss`,
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ala, `galileo-gnss.ssc`, whereas the other GNSS don't have it appended.
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Example `.ssc` file contents:
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```
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"GSAT0101 (PRN E11)" "Sol/Earth" {
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Class "spacecraft"
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Mesh "galileo-gnss.cmod"
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Radius 0.005
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EllipticalOrbit {
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Epoch 2459722.35154914
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Period 0.58659637
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SemiMajorAxis 29600.176
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Eccentricity 0.00041090
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Inclination 56.9865
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AscendingNode 22.0582
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ArgOfPericenter 29.0248
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MeanAnomaly 331.0391
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}
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Obliquity 56.9865
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EquatorAscendingNode 22.0582
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RotationOffset 296.9294
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# Orientation [ ]
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}
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```
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## TLE Sources
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GNSS (All)
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* https://celestrak.com/NORAD/elements/gnss.txt
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Beidou (China)
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* https://celestrak.com/NORAD/elements/beidou.txt
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Galileo (Europe)
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* https://celestrak.com/NORAD/elements/galileo.txt
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Glonass (Russia)
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* https://celestrak.com/NORAD/elements/glo-ops.txt
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GPS (USA)
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* https://celestrak.com/NORAD/elements/gps-ops.txt
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## Spice
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Spice TLE:
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"Evaluate NORAD two-line element data for earth orbiting spacecraft."
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* https://naif.jpl.nasa.gov/pub/naif/toolkit_docs/FORTRAN/spicelib/evsgp4.html
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## SGP4
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SPG4
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* https://pypi.org/project/sgp4/
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## Skyfield
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Skyfield
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* https://rhodesmill.org/skyfield/earth-satellites.html
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# 3D Models
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Celestia uses an old 3D proprietary format from an old 3D application in
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`.3ds` format. It also has it's own format `.cmod`.
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## Galileo
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Galileo 3D models are from the ESA:
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* https://gssc.esa.int/education/galileo3d/
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## 3D Model Conversion
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The `galileo.obj` file from the ESA can be read by `cmodview` in
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the `celestia-tools` package. The file can be saved in `cmodview`
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as `galileo-gnss.cmod` and then read by Celestia.
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The ESA supplies textures, but the aren't applied in the Celestia model (yet).
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### Blender
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`blender-2.79b` didn't work to convert a `.obj` file to `.3ds`
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that rendered in Celestia.
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# TODO
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Do.
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* All GNSS satellites are using the Galileo 3D model.
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* Textures need to be added to 3D models.
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* Orientation of satellite 3D models is incorrect.
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* Confirm orbits are reasonably correct.
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# Status
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Alpha, under development.
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Output works in Celestia. Orbits are not confirmed correct.
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# License / Copyright
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Upstream sources under their respective copyrights.
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Copyright (C) 2022, 2023 Jeff Moe.
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License: GPLv2 or any later version.
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