Satellite Chaser

manual

V 1.1

August 2019
Contents
1 Introduction and general remarks 2

2 What do I need to run this software? 2

3 Settings 2

4 The Camera Tab 3

4.1 Star Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

5 The Mount Tab 4

6 The Setup Tab 4

6.1 Callibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
6.2 Satellite Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
6.3 Satellite Catching Coordinates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
6.4 Platesolving . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

7 The Guide Tab 5

8 The Cockpit Tab 6

9 Quick start 6
9.1 Test Run . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
9.2 Real Pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

10 Aknowledgements 8

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1 Introduction and general remarks
Up until now there were no ”complete” packages available for a typical satellite tracking workflow.
This program intends to fill this role. It provides tools for all stages of satellite tracking, from setup
to guiding, combined with a modern and intuitive UI.
It should be noted that this software was created with ISS tracking in mind, but theoretically it
can be used with any satellite that has a TLE.

The program aims to provide clear visual feedback before and during the satellite pass, as often
time is sparse and mistakes can easily be made:

• In a typical workflow the tabs will be worked through top-to-bottom, left-to-right. Note that
this is not always the case and that some parts can be skipped under certain circumstances,
more on that in the specific sections.

• Every crucial task has a red background, as soon as the task is done the background turns
green. When everything is green the user is safe to press the start button as soon as the
satellite crosses the screen.

Something to watch out for: This software does not care what side of pier your mount is. It will
track past the meridian until stopped by other means. Always have an eye on your telescope during
tracking and do test runs if you are unsure whether your telescope is going to hit the tripod.

2 What do I need to run this software?

• An ASCOM compatible equatorial or Alt/Az mount. Regarding equatorial mounts: A fork
mount would be best, as it avoids meridian flips, but a german equatorial mount works too.
Whether you can track entire passes without meridian flip or not depends on your setup.

• A main camera with a telescope and a guide camera with a guide scope. An off-axis guider is
not going to work, as the guide cam needs to see the satellite. This software works using
DirectShow, you need to install the DirectShow Drivers of your cameras.

• All sky Plate Solver, an external platesolving program. You need to have the appropriate
star catalogues for you guide scope focal length installed.

• A 64 bit windows. Tested on windows 10.

3 Settings
Settings can be accessed from the top right, by clicking on Settings.

Setting are separated into 2 sections, essential and advanced settings. Essential settings are as
they suggest critical for correct operation of the software.

• Longitude and Latitude are both in degrees. They should be fairly accurate, as they are
used for prediction of the satellite coordinates. These can vary greatly for small changes in
location.

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 • Arcsec/Pixel, Focal Length and Pixel Size are used for Platesolving and calculation of the
correction vectors during guiding. If you don’t know these values, there are plenty online
calculators available.

• The path to All Sky Plate Solver must include the PlateSolver.exe

• The temp path will be used for Snapshots, a testfile.txt which shows velocity of RA and DEC
during the pass and images to be platesolved by ASPS. Usually you will only need this folder
for the snapshots. The testfile.txt can be useful if you want to know at what point your
mount will no longer be able to track the satellite if the max speed warning is given or if you
want to plot the curves.

• The max speed will be used for determining wheter the mount is capable of tracking. If this
value is exceeded a warning will be given. Tracking can still be done, but the user should
keep in mind that this could damage the mount.

• The Equatorial or Alt/Az setting should be set once and then left. Affected are callibra-
tion, satellite calculation, GOTOs and tracking. In the guide and cockpit tab RA is
equivalent to Az and DEC is equivalent to Alt.

The advanced settings are for situational non satellite tracking related purposes. The platesolving
live-adjust feature turns out to be quite the reliable tool for exact framing. If a user wants to frame
the telescope according to specific coordinates, they can be entered and the platesolving live-adjust
feature will correct for those instead of the satellite.
The gain functions determine the range of the PID rulers in the Cockpit tab. Values from x=0 to
x=1000 are used for the rulers. By default the range is from 0.05 to 22, which should be sufficient
in most cases.

4 The Camera Tab

Here the Guide camera and the main camera(the one that is connected to the telescope) can be
managed. The cameras are connected via DirectShow, which only allow exposure increments in
exponential steps, hence why the exposure is in these units. The exposure in seconds can be derived
by 2x , for example 2−3 = 1/8 of a second.

4.1 Star Detection

Star Detection should always be turned on eventually, but the option to turn it off is included as
it can be quite resource intensive.

• The Threshold value determines the cutoff for star detection. Values below this value will
not be considered. Generally this value will have to be adjusted the most.

• The Blur value applies a gaussian blur to the image. This can be useful to prevent noise from
being detected as stars. Generally this value can be left at its default.

• The MinArea value determines how large a structure needs to be to be considered a star. The
default value should be good.

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The Finish Scope Alignment button should be pressed when a new main scope/guide scope align-
ment has been performed, or if this is the first time using the software.
Restoring the scope alignment will retrieve the crosshair from the last session(not including nudges
from the guiding phase).
No matter which button is pressed, the screen from the main camera will disappear, the main
camera will be freed, and the next phase can be started.

5 The Mount Tab

This tab is rather self explanatory. Choose and connect your mount via the ASCOM interface.
Make sure to press the connect button after choosing a mount. No other protocols are supported
at this point. The mount controls can be used for centering the telescope during Live Adjusting.

6 The Setup Tab

The setup tab is used to prepare your mount for the satellite pass. Perhaps the most complicated
tab, it callibrates the telescope and frames the target.

6.1 Callibration
Callibration is necessary for guiding (although not for tracking). Using the callibration the mount
knows where the RA and DEC axis are pointing and can give adequate guiding commands. Calli-
bration requires that star detection is activaed and a star selected. It will move the star in both axis
for a distance of 100 pixels, so it is advisable to choose a star near the center. Alternatively, the last
callibration can be automatically restored or a manual one can be entered(which can be retrieved
from the logs, this could be handy if switching PCs). Generally you have to redo callibration after
a meridian flip or if the orientation of the guide sensor has changed.

6.2 Satellite Calculation

This does all the necessary math concerning the target satellite pass. After entering the 3 lines of
the TLE and the approximate start time, 5 passes will be calculated. After selecting the correct
pass and entering the altitude at which the satellite will be intercepted and pressing Calculate the
program will calculate the movement vectors for the pass. This is a CPU intensive task and can
take a while. On an cheap laptop it tends to take about 1 to 2 minutes. The program won’t
lock, other things can be done during this time. The window will turn from yellow to green when
finished. Additionally the satellite catching coordinates will be populated.

6.3 Satellite Catching Coordinates

This field will be populated as soon as the Satellite calculations are done. The RA and DEC
correspond to the satellite coordinates at the point of the chosen altitude. Additionally the time at
which point this will happen is displayed. You can issue a GOTO command or convert the numbers
to the sometimes convenient HH:MM:SS format. This will not affect the calculations.

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6.4 Platesolving
This tool does not work with Alt/Az mounts.
Platesolving in combination with the Live-Adjust feature is a tool which perfectly centers the satel-
lite pass in your crosshair. It requires calibration data and active star detection. It should be noted
that the live adjust feature only works if the target satellite position is already somewhere on the
screen, as in the telescope should already be rather accurately pointed to the target.
The frame currently displayed(without the crosshair and all the circles) will be used for ASPS
platesolving when pressing the solve button. If the solves succeeds the RA and DEC fields will be
populated. When pressing the Live-Adjust button a single yellow circle will appear on the screen
if the satellite position is within the frame. This represents the point which the satellite will be at.
When clicking on a star an adjustment procedure similar to sharpcap polar alignment will appear.
The star must be brought to the green circle using standard RA and DEC movements. If the yellow
line goes out of the screen a new star can be selected by pressing stop and repressing Live-Adjust.
After this procedure the frame can be platesolved again to check accuracy. The yellow circle should
now be very close to the crosshair.

Do not redo the Live-adjust process without a new platesolve! Platesolve data used for Live-
adjust becomes invalid as soon as the mount is moved.
Directly after a platesolve the Satellite Trail button can be pressed. It will show the path the
satellite will take. Each circle represents 1/10th of a second.

The platesolving and Live-Adjust feature can be redone as often as necessary. Generally once
for correcting and once for checking accuracy should suffice.

7 The Guide Tab

Here guiding will be started. Check if all the warnings are green, if that is the case the Start button
can be pressed once the satellite crosses the screen. Next to the start button is a clock so that it
is clear when this should happen. Be wary though: The TLE data are generally very precise, but
the computer clock can be off. Before setting up make sure to sync your computer clock.
If this is your first pass it is recommended to perform a dry run and check the Invert checkboxes
accordingly. This can be done during the day without a telescope:

• Roughly slew the mount to the catching position of the satellite pass. Press the start button.
The mount should start tracking. It should become obvious if one of the axis is tracking in
the wrong direction. You can stop the tracking at any point. Afterwards check the invert RA
or invert DEC checkboxes accordingly.

• Restart(this is important!) the program and redo the dry run. Now the mount should track
the theoretical satellite correctly. Relevant for equatorial mounts: The configuration should
always be valid at this side of the pier. If you are at the other side you need to invert
the setting of the DEC axis.

If everything works, the satellite should appear close to the predicted time and it should move
accurately towards the crosshair. Depending on the amount of backlash in your mount you need to
press the start button a bit before it crosses the crosshair. It’s recommended to leave the guiding
turned off until the start button is pressed and the satellite selected, as else it will try to guide
on whatever is selected when the start button is pressed(probably a star). As soon as guiding is

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turned on, the satellite should start moving towards the crosshair. Guiding speed can be modified
in the Cockpit tab. If it is obvious that guiding is inverted, as in the satellite is being guided out
of the frame, you need to check the invert RA/DEC guiding checkboxes accordingly. Pay close
attention to your telescope during tracking. The software does not do meridian flips,
and will track past the meridian until stopped by other means.
If you see that the satellite is not centered in the main camera, you can try nudging the crosshair
with the controls. Each press will move the crosshair by one pixel. If your setup suffers from flexure
this can come in handy.

8 The Cockpit Tab

This tab displays guiding errors and a tunable PID controller. PID controllers are very widespread
in the industry and often used for control systems. There are a lot of good resources online about
PID controllers, so I will not go into detail about how they work here. The gains each have 2
trackbars assigned to them. One for rough tuning(upper) and one for fine tuning(lower). If you
want a different gain range you can set a custom function for the trackbars in the settings. Values
from x=0 to x=1000 are used.
Although there are only 3 values to be adjusted it is not a trivial task to find optimal gains. They
can and should be adjusted during guiding. I’ve experimented with different combinations and I
find a P gain around 1, I around 0.1 and D around 0.5 to be a good starting point.

9 Quick start
9.1 Test Run
If this is your first time using this software it’s recommended to make a test run with a hypothetical
satellite pass to figure out whether you need to invert an axis.

• Go to the setup tab and click on calculate satellite data. Enter the TLE and pass time and
press calculate. Choose the right pass and choose your desired starting altitude. Calculate
the vectors.

• Roughly place the mount at the catching position of the satellite pass. You can do this with
just the mount, you don’t need a telescope.

• Press the start button. The mount should start tracking. It should become obvious if one of
the axis is tracking in the wrong direction. You can stop the tracking at any point. Afterwards
check the invert RA or invert DEC checkboxes accordingly.

• Restart the program and redo the routine, but check the correct checkboxes this time. Now
the mount should track the hypothetical satellite correctly. Relevant for equatorial mounts:
The configuration should always be valid at this side of the pier. If you are at the other
side you need to invert the setting of the DEC axis.

9.2 Real Pass

Here is a typical workflow from the perspective of a first time user. If you have already done this
once you can skip the guide scope callibration and mount callibration by just restoring the values

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from the last session.

This assumes that the mount is polar aligned and pointing roughly in the direction of the satellite.
• Connect the guide cam and the main cam
• Adjust Exposure and gain on both and activate star detection
• Adjust the Threshold until stars are reasonably detected
• Slew to an easily identifiable star and center it in the main scope(check Show Crosshair)
• Locate the star in the guide cam view to the left and click on it
• Press finish Scope alignment
• Connect the mount if you haven’t already
• Click on a star close to the middle and press callibrate
• After it’s done click on satellite calculations
• Input the TLE and time,click on Calculate, wait until the process finished. Then select the
correct pass, enter the altitude at which tracking should start and click on calculate vectors.
• After this is done remember the catching time and slew to the target coordinates. Keep in
mind which side of pier you want to be on.
• Try platesolving. Try increasing gain/exposure if it doesn’t work. If it succeeds click on
Live-Adjust. There should be a yellow circle on the screen. If there isn’t slew more precisely
to the target coordinates and do another platesolve.
• Imagine a line from the circle to the crosshair. This line will be attached to the star you click
on. If the line goes out of the screen press stop and live-adjust again, then click on another
star.
• Use the mount RA DEC controls to bring the selected star to the green circle. No need to be
extremely precise.
• You can check if everything is aligned by doing another platesolve and pressing live-adjust
again. If the yellow circle is near the crosshair everything is correct. You can also press
satellite trail to check the path of the satellite.
• Go to the guide tab and check that the axis inversion are correctly checked. Remember to
start capture with the main camera in a different capturing software about 1 min before the
pass. Check that no other software is connected to the mount. Check that everything is
green. Leave guiding unchecked. Wait for the satellite to cross the screen. Use the time next
to the start button as reference when this should happen.
• When the satellite is close to the crosshair press start( hotkey Ctrl+Shift), click on the satellite
and start guiding.
• Check that the satellite appears in the main cam, adjust settings etc. If the satellite is not
centered nudge the crosshair with the controls(every click is 1 pixel). Adjust gains in the
cockpit tab.
• Keep an eye on your telescope, this software does not do meridian flips!

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10 Aknowledgements
This software uses the following libraries: Alglib,emgucv,Directshowlib and pyephem.