like to watch

README.md

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 - [aaaa/attitude-adjustment](aaaa/attitude-adjustment)
 - [aaaa/digital-filters-meh](aaaa/digital-filters-meh)
+- [aaaa/like-to-watch](aaaa/like-to-watch)
 - [aaaa/seeing-stars](aaaa/seeing-stars)
 - [comms/56k](comms/56k)
 - [ground-segment/phasors-to-stun](ground-segment/phasors-to-stun)

aaaa/like-to-watch/README.md

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+# I Like To Watch
+
+**Category:** Astronomy, Astrophysics, Astrometry, Astrodynamics, AAAA
+**Points (final):** 37
+**Solves:** 126
+
+>Fire up your Google Earth Pro and brush up on your KML tutorials, we're going to make it look at
+>things!
+
+## Write-up
+
+by [haskal](https://awoo.systems)
+
+A netcat endpoint is provided, and when you connect it provides the following info:
+
+```
+We've captured data from a satellite that shows a flag located at the base of the Washington
+Monument.
+The image was taken on March 26th, 2020, at 21:54:33
+The satellite we used was: 
+
+REDACT
+1 13337U 98067A   20087.38052801 -.00000452  00000-0  00000+0 0  9995
+2 13337  51.6460  33.2488 0005270  61.9928  83.3154 15.48919755219337
+
+Use a Google Earth Pro KML file to 'Link' to http://18.191.77.141:26963/cgi-bin/HSCKML.py
+and 'LookAt' that spot from where the satellite when it took the photo and get us that flag!
+```
+
+Additionally, an example KML file is provided
+
+```xml
+<?xml version="1.0" encoding="UTF-8"?>
+<kml xmlns="http://www.opengis.net/kml/2.2">
+  <Folder>
+    <name>HackASatCompetition</name>
+    <visibility>0</visibility>
+    <open>0</open>
+    <description>HackASatComp1</description>
+    <NetworkLink>
+      <name>View Centered Placemark</name>
+      <visibility>0</visibility>
+      <open>0</open>
+      <description>This is where the satellite was located when we saw it.</description>
+      <refreshVisibility>0</refreshVisibility>
+      <flyToView>0</flyToView>
+      <LookAt id="ID">
+        <!-- specific to LookAt -->
+        <longitude>FILL ME IN</longitude>            	<!-- kml:angle180 -->
+        <latitude>FILL ME IN TOO</latitude>              	<!-- kml:angle90 -->
+        <altitude>FILL ME IN AS WELL</altitude>              		<!-- double -->
+        <heading>FILL IN THIS VALUE</heading>                <!-- kml:angle360 -->
+        <tilt>FILL IN THIS VALUE TOO</tilt>                     <!-- kml:anglepos90 -->
+        <range>FILL IN THIS VALUE ALSO</range>                     <!-- double -->
+        <altitudeMode>clampToGround</altitudeMode>
+      </LookAt>
+      <Link>
+        <href>http://FILL ME IN:FILL ME IN/cgi-bin/HSCKML.py</href>
+        <refreshInterval>1</refreshInterval>
+        <viewRefreshMode>onStop</viewRefreshMode>
+        <viewRefreshTime>1</viewRefreshTime>
+        <viewFormat>BBOX=[bboxWest],[bboxSouth],[bboxEast],[bboxNorth];
+CAMERA=[lookatLon],[lookatLat],[lookatRange],[lookatTilt],[lookatHeading];
+VIEW=[horizFov],[vertFov],[horizPixels],[vertPixels],[terrainEnabled]</viewFormat>
+      </Link>
+    </NetworkLink>
+  </Folder>
+</kml>
+```
+
+We can use [gpredict](http://gpredict.oz9aec.net) to figure out where the satellite was by loading
+the TLE (one way is to create an http endpoint with the TLE in a txt file, and then add the URL in
+the gpredict settings). However, gpredict will refuse to load this TLE. It turns out the checksums
+are incorrect, and if we calculate them according to the TLE spec, we get these lines with fixed
+checksums
+
+```
+REDACT
+1 13337U 98067A   20087.38052801 -.00000452  00000-0  00000+0 0  9992
+2 13337  51.6460  33.2488 0005270  61.9928  83.3154 15.48919755219334
+```
+
+Now, gpredict loads the data (if not, close gpredict, clear the cache with `rm
+~/.config/Gpredict/satdata/*.sat`, start gpredict, and select `Update TLE data from network`). The
+next step is to create a location for the washington monument. The monument is located at
+-77.0354,38.889100. Finally, use the gpredict time controller to pause real time, then set the time
+to March 26th, 2020 at 21:54:33.
+
+![Gpredict showing the satellite pass at that time](gpredict.png)
+
+We can see that (in the ground reference frame) the satellite is at azimuth 35.52 degrees and
+elevation 58.18 degrees. Additionally, it has a line-of-sight range of 488 km.
+
+To make our lives easier you can notice in Wireshark that Google Earth Pro simply makes HTTP
+requests to the given endpoint with parameters given in the KML file, like this
+
+```
+http://server/cgi-bin/HSCKML.py?BBOX=...;CAMERA=...;...
+```
+
+So we can use plain curl to avoid messing with the Google Earth Pro GUI a lot. We need the following
+parameters: the bounding box of the view, the camera parameters, and the view parameters.
+
+For the bounding box, we create a reasonable box around the location of the washington monument
+
+```
+BBOX=-77.035378,38.889384,-77.035178,38.889584
+```
+
+For the camera parameters, we look directly at the base, but we need to provide a heading and tilt.
+The Google Earth KML reference has a handy diagram of the reference frame needed
+
+![KML docs showing the tilt parameter](kml1.png)
+
+![KML docs showing the heading parameter](kml2.png)
+
+Since gpredict is in a ground reference frame, we need to add 180 to the azimuth to get the heading,
+and subtract 90 - elevation to get the tilt. With these calculations and the monument coordinates we
+have (note the range is in meters, not km, so we multiply by 1000)
+
+```
+CAMERA=-77.035278,38.889484,488000,31.82,215.18
+```
+
+Finally, for the view we chose some reasonable parameters that seemed to work. This part doesn't
+seem to be very important
+
+```
+VIEW=60,60,500,500,1
+```
+
+Putting it together, the full URL is
+
+```
+http://theserver/cgi-bin/HSCKML.py?BBOX=-77.035378,38.889384,-77.035178,38.889584;
+CAMERA=-77.035278,38.889484,488000,31.82,215.18;VIEW=60,60,500,500,1
+```
+
+Requesting the URL reveals the flag
+
+```xml
+<?xml version="1.0" encoding="UTF-8"?>
+<kml xmlns="http://www.opengis.net/kml/2.2">
+<Placemark>
+<name>CLICK FOR FLAG</name>
+<description>flag{juliet71739hotel:GNeeb.....}</description>
+<Point>
+<coordinates>-77.0354,38.889100</coordinates>
+</Point>
+</Placemark>
+</kml>
+```
+
+## Resources and other writeups
+
+ * <http://gpredict.oz9aec.net/>
+ * <https://en.wikipedia.org/wiki/Two-line_element_set>
+ * <https://developers.google.com/kml/documentation/kmlreference?csw=1#range>