sattools/README-skymap.md

# 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](img/skymap-tutorial-main.png)


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](img/skymap-tutorial-south-east.png)
![skymap tutorial south west](img/skymap-tutorial-south-west.png)

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](img/skymap-tutorial-timestep.png)

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
```