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sattools/README-skymap.md

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skymap Mini HOWTO

HOWTO find a particular satellite for viewing with skymap for use with stvid imaging.

From notes by Cees Bassa mixed with my misunderstandings. This example will use the Bluewalker 3 satellite, with NORAD ID 53807.

First a TLE is needed. I get this from Celestrak, ala:

wget -O ~/devel/spacecruft/TLE/bluewalker3/bluewalker3.tle \
  "https://celestrak.org/NORAD/elements/gp.php?CATNR=53807"

Should look something like this:

BLUEWALKER 3            
1 53807U 22111AL  22323.16311390  .00001894  00000+0  10565-3 0  9997
2 53807  53.2016 312.3504 0014195 129.0685 231.1577 15.18596984 10510

Run skymap (with my branch):

#!/bin/bash

LENGTH=86400
TIME="2022-11-19T17:20:45.000"
TLE=~/devel/spacecruft/TLE/bluewalker3/bluewalker3.tle
SITE=9990
LAT="40.568912"
LONG="-105.225852"
# Set elevation in data/sites.txt
# 9990 JM  40.568912  -105.225852     1843    Jeff Moe
#ELEVATION="1843"

skymap									\
	--no-stars							\
	--width=1600							\
	--height=1000							\
	--all-objects							\
	--nmax=128							\
	--length=${LENGTH}						\
	--catalog=${TLE}						\
	--latitude="${LAT}"						\
	--longitude="${LONG}"						\
	--time="${TIME}"

skymap tutorial main

That's a 24h prediction for BW3 for the example location.

  • Grey tracks are in the shadow.
  • Orange tracks are in sunlight but during daytime.
  • Yellow tracks are in sunlight but during night time.

The example has two passes during night time:

  • Low South East.
  • Low South West.

skymap tutorial south east skymap tutorial south west

In interactive mode, use l to change the track length to 3600 secs (1 hour). To use skymap in interactive mode, launch skymap from the command line. When you hit l in the graphical display, the prompt will be in the terminal window.

Then use . to move time forward with these 1 hour steps. It makes it faster if skymap is run without drawing stars until needed, especially during frequent re-renders. Disable viewing stars with shift-Q.

skymap tutorial timestep

At some point you'll get the first pass. Then use < a few times to reduce the timestep size to something like 450 seconds. Then step forward with . until it is above the horizon.

Moving time forward to 00:37:37: Pressing i with the cursor near 53807 gives you the az/el and RA/Dec to read off.

Cees dumped the TLE for 53807 into a text file with

tleinfo -i 53807 >53807.txt

This results in two TLEs, though ? XXX compare with TLE from above.

BLUEWALKER-3            
1 53807U 22111AL  22291.57105995  .00000747  00000+0  51211-4 0  9998
2 53807  53.2021  96.3521 0013619  43.3355 316.8709 15.18466480  5717
0 BLUEWALKER 3
1 53807U 22111AL  22291.57105995  .00000747  00000-0  51211-4 0  9999
2 53807  53.2021  96.3521 0013619  43.3355 316.8709 15.18466480  5717