like to watch
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- [aaaa/attitude-adjustment](aaaa/attitude-adjustment)
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- [aaaa/digital-filters-meh](aaaa/digital-filters-meh)
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- [aaaa/like-to-watch](aaaa/like-to-watch)
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- [aaaa/seeing-stars](aaaa/seeing-stars)
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- [comms/56k](comms/56k)
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- [ground-segment/phasors-to-stun](ground-segment/phasors-to-stun)
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# I Like To Watch
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**Category:** Astronomy, Astrophysics, Astrometry, Astrodynamics, AAAA
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**Points (final):** 37
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**Solves:** 126
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>Fire up your Google Earth Pro and brush up on your KML tutorials, we're going to make it look at
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>things!
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## Write-up
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by [haskal](https://awoo.systems)
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A netcat endpoint is provided, and when you connect it provides the following info:
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```
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We've captured data from a satellite that shows a flag located at the base of the Washington
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Monument.
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The image was taken on March 26th, 2020, at 21:54:33
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The satellite we used was:
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REDACT
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1 13337U 98067A 20087.38052801 -.00000452 00000-0 00000+0 0 9995
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2 13337 51.6460 33.2488 0005270 61.9928 83.3154 15.48919755219337
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Use a Google Earth Pro KML file to 'Link' to http://18.191.77.141:26963/cgi-bin/HSCKML.py
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and 'LookAt' that spot from where the satellite when it took the photo and get us that flag!
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```
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Additionally, an example KML file is provided
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```xml
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<?xml version="1.0" encoding="UTF-8"?>
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<kml xmlns="http://www.opengis.net/kml/2.2">
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<Folder>
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<name>HackASatCompetition</name>
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<visibility>0</visibility>
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<open>0</open>
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<description>HackASatComp1</description>
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<NetworkLink>
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<name>View Centered Placemark</name>
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<visibility>0</visibility>
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<open>0</open>
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<description>This is where the satellite was located when we saw it.</description>
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<refreshVisibility>0</refreshVisibility>
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<flyToView>0</flyToView>
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<LookAt id="ID">
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<!-- specific to LookAt -->
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<longitude>FILL ME IN</longitude> <!-- kml:angle180 -->
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<latitude>FILL ME IN TOO</latitude> <!-- kml:angle90 -->
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<altitude>FILL ME IN AS WELL</altitude> <!-- double -->
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<heading>FILL IN THIS VALUE</heading> <!-- kml:angle360 -->
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<tilt>FILL IN THIS VALUE TOO</tilt> <!-- kml:anglepos90 -->
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<range>FILL IN THIS VALUE ALSO</range> <!-- double -->
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<altitudeMode>clampToGround</altitudeMode>
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</LookAt>
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<Link>
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<href>http://FILL ME IN:FILL ME IN/cgi-bin/HSCKML.py</href>
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<refreshInterval>1</refreshInterval>
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<viewRefreshMode>onStop</viewRefreshMode>
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<viewRefreshTime>1</viewRefreshTime>
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<viewFormat>BBOX=[bboxWest],[bboxSouth],[bboxEast],[bboxNorth];
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CAMERA=[lookatLon],[lookatLat],[lookatRange],[lookatTilt],[lookatHeading];
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VIEW=[horizFov],[vertFov],[horizPixels],[vertPixels],[terrainEnabled]</viewFormat>
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</Link>
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</NetworkLink>
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</Folder>
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</kml>
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```
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We can use [gpredict](http://gpredict.oz9aec.net) to figure out where the satellite was by loading
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the TLE (one way is to create an http endpoint with the TLE in a txt file, and then add the URL in
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the gpredict settings). However, gpredict will refuse to load this TLE. It turns out the checksums
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are incorrect, and if we calculate them according to the TLE spec, we get these lines with fixed
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checksums
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```
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REDACT
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1 13337U 98067A 20087.38052801 -.00000452 00000-0 00000+0 0 9992
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2 13337 51.6460 33.2488 0005270 61.9928 83.3154 15.48919755219334
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```
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Now, gpredict loads the data (if not, close gpredict, clear the cache with `rm
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~/.config/Gpredict/satdata/*.sat`, start gpredict, and select `Update TLE data from network`). The
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next step is to create a location for the washington monument. The monument is located at
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-77.0354,38.889100. Finally, use the gpredict time controller to pause real time, then set the time
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to March 26th, 2020 at 21:54:33.
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We can see that (in the ground reference frame) the satellite is at azimuth 35.52 degrees and
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elevation 58.18 degrees. Additionally, it has a line-of-sight range of 488 km.
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To make our lives easier you can notice in Wireshark that Google Earth Pro simply makes HTTP
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requests to the given endpoint with parameters given in the KML file, like this
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```
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http://server/cgi-bin/HSCKML.py?BBOX=...;CAMERA=...;...
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```
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So we can use plain curl to avoid messing with the Google Earth Pro GUI a lot. We need the following
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parameters: the bounding box of the view, the camera parameters, and the view parameters.
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For the bounding box, we create a reasonable box around the location of the washington monument
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```
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BBOX=-77.035378,38.889384,-77.035178,38.889584
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```
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For the camera parameters, we look directly at the base, but we need to provide a heading and tilt.
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The Google Earth KML reference has a handy diagram of the reference frame needed
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Since gpredict is in a ground reference frame, we need to add 180 to the azimuth to get the heading,
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and subtract 90 - elevation to get the tilt. With these calculations and the monument coordinates we
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have (note the range is in meters, not km, so we multiply by 1000)
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```
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CAMERA=-77.035278,38.889484,488000,31.82,215.18
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```
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Finally, for the view we chose some reasonable parameters that seemed to work. This part doesn't
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seem to be very important
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```
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VIEW=60,60,500,500,1
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```
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Putting it together, the full URL is
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```
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http://theserver/cgi-bin/HSCKML.py?BBOX=-77.035378,38.889384,-77.035178,38.889584;
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CAMERA=-77.035278,38.889484,488000,31.82,215.18;VIEW=60,60,500,500,1
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```
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Requesting the URL reveals the flag
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```xml
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<?xml version="1.0" encoding="UTF-8"?>
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<kml xmlns="http://www.opengis.net/kml/2.2">
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<Placemark>
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<name>CLICK FOR FLAG</name>
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<description>flag{juliet71739hotel:GNeeb.....}</description>
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<Point>
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<coordinates>-77.0354,38.889100</coordinates>
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</Point>
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</Placemark>
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</kml>
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```
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## Resources and other writeups
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* <http://gpredict.oz9aec.net/>
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* <https://en.wikipedia.org/wiki/Two-line_element_set>
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* <https://developers.google.com/kml/documentation/kmlreference?csw=1#range>
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