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.

TLE

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

Skymap Script

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 Window Overview

Below is a 24 hour (38400 seconds) prediction for Bluewalker 3 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 West.
Low South East.

Skymap Interactive

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.

At some point you'll get the first pass.

Use < a few times to reduce the timestep size to something like 450 seconds.
Step forward with . until it is above the horizon.
In example, move time forward to 00:37:37.

Skymap Satellite Info

Press i with the cursor near 53807. It gives this output:

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

Age: 0.9 d

x:   +5351.2801 km; vx: -0.38650 km/s
y:   -2422.0234 km; vy: +6.04035 km/s
z:   +3590.7817 km; vz: +4.61568 km/s
r:    1633.97 km; v:  -0.343 km/s
l: -92.78; b:  31.44; h:     506.35 km

R.A.:  01:13:17.38  Decl.: -19:10:17.4
R.A.:  01:12:10.33  Decl.: -19:17:33.2 (J2000)
Azi.: 127.8 Alt.: 11.3

Phase: 53.17
Magnitude: 6.25
Angular velocity: 0.2593 (deg/s)

This gives you the Az/El and RA/Dec to read off.

TLE with `tleinfo`

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

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