Keywords: space situational awareness
Summary
The purpose of this demonstration is to show how to use the DIRSIG platform motion model to track a moving space object in geosynchronous orbit. The space object of the demo is a simplified model of the Anik F1 telecommunications satellite launched by Telesat from Canada.
The following AMOS conference paper has measured data of the same object, on the same day, from the same ground location of this demo: http://www.amostech.com/TechnicalPapers/2009/Poster/Scott.pdf
Details
The imaging platform is located on the ground at a static (fixed) location but it will track the target satellite in it’s geosynchronous orbit. The Two-Line Element (TLE) used in this simulation for the Anik-F1 satellite is included below:
1 26624U 00076A 14071.62213340 -.00000092 00000-0 00000+0 0 2575 2 26624 0.0179 165.5599 0001149 199.2228 282.0497 1.00273915 48818
The ground oberving platform is located in Canada at 45.317 +North latitude and 75.667 +W longitude. The simulation tracks the satellite over an 8 hour period (UTC 2.0 to 10.0 on 17 Mar 2009). The target satellite is dynamically positioned in the simulation using the TLE directly and the observing platform tracks the satellite by pointing at the location defined by that same TLE.
Important Files
This section highlights key files important to the simulation.
Materials
The material properties in the demo are notional and derived from real space material measurements, but not the actual measurements of the Anik F1 satellite.
Target Satellite Geometry and Motion
The geometry for the Anik F1 satellite is defined in the file
anik_f1.obj. That OBJ file is then added to the scene and put into
motion in the anik_f1.glist file. The dyanmic location uses the
Flexible Motion model to directly utilize the TLE. The orientation
is defined such that the satellite always looking at the center of the
Earth (the ECEF origin).
<geometrylist enabled="true">
<object>
<basegeometry>
<obj><filename>anik_f1.obj</filename></obj>
</basegeometry>
<dynamicinstance>
<motion type="flexible">
<locationengine type="sgp4">
<data source="internal">
<tle1>1 26624U 00076A 14071.62213340 -.00000092 00000-0 00000+0 0 2575</tle1>
<tle2>2 26624 0.0179 165.5599 0001149 199.2228 282.0497 1.00273915 48818</tle2>
</data>
</locationengine>
<orientationengine type="lookat">
<locationengine type="fixed">
<location type="ecef">
<x>0.0</x><y>0.0</y><z>0.0</z>
</location>
</locationengine>
</orientationengine>
</motion>
</dynamicinstance>
</object>
</geometrylist>Imaging Platform
The imaging platform is not modeled after a real-world sensor. The sensor features a 2D array focal plane with RGB and Near-IR channels. The read-out rate of the focal plane is 0.001 Hz, which results in a period of 1000 seconds or just over 15 minutes. Over the 8 hour collection, 29 frames are acquired.
Platform Motion (Tracking)
The track.motion file is used to drive the motion of the imaging
platform by configuring the Flexible Motion model to track the
target satellite in orbit. The location of the platform is static
(fixed) at the observer latitude and longitude defined earlier.
The orientation is defined so that the imaging platform tracks the
satellite orbit by telling it to "look at" the locations defined
by the satellite’s TLE:
<motion type="flexible">
<locationengine type="fixed">
<location frame="geodetic">
<latitude>45.317</latitude>
<longitude>-75.667</longitude>
<altitude>0</altitude>
</location>
</locationengine>
<orientationengine type="lookat">
<locationengine type="sgp4">
<data source="internal">
<tle1>1 26624U 00076A 14071.62213340 -.00000092 00000-0 00000+0 0 2575</tle1>
<tle2>2 26624 0.0179 165.5599 0001149 199.2228 282.0497 1.00273915 48818</tle2>
</data>
</locationengine>
</orientationengine>
</motion>|
Important
|
For DIRSIG5, the ability to have an SGP4 positioned scene object isn’t fully supported yet. For the time being, there is a 2nd simulation setup that uses a fixed ECEF position for the satellite. |
Options (DIRSIG4 only)
This demo also makes use of the advanced user options for the atmosphere
in the demo.options file:
atm.sourceupdatedelta-
Override the default time delta for when the Sun location is recomputed. Changed from the default of 900s (15 min) to 30s.
atm.verbose-
Print verbose messages related to atmospheric updates. In this case, it allows the user to verify that the Sun has moved for each frame.
Simulations and Results
There are two simulation scenarios in this demo:
-
A single-frame simulation
-
For DIRSIG4, use
demo.sim -
For DIRSIG5, use
demo.jsim
-
-
A multi-frame (video) simulation
-
For DIRSIG4, use
video.sim -
For DIRSIG5, use
video.jsim
-
Running the Single-Frame Simulation
This single-frame simulation produces a single image file. To run the simulation, perform the following steps:
-
Run the DIRSIG
demo.sim(ordemo.jsim) file -
Load the resulting
demo-t0000-c0000.imgfile in the image viewer.
The simulation produces a single-frame simulation shown below. The satellite has some strong specular glints, so the image is best displayed using the Selected Two Percent Scaling when using the DIRSIG built-in image viewer.
Running the Multi-Frame Simulation
The multi-frame simulation produces 41 image files. To run the simulation, perform the following steps:
-
Run the DIRSIG
video.sim(orvideo.jsim) file -
Load the resulting
demo-t0000-c0000.img,demo-t0000-c0001.img, etc. files in the image viewer.
The imaging instrument is setup to use the "file per capture" output schedule. As a result, the simulation produces 29 separate image files for the 29 captures. The animation below was created from these 29 frames imaged during the 8 hour collection. The satellite is nearly stationary above the Earth, an the shadows change due to the Earth’s position relative to the Sun.
