Keywords: space situational awareness

Summary

This demo shows how to setup an imaging platform in a GEO orbit that is tracking a satellite in a LEO orbit.

Details

Some of the key elements of this simulation inolve the positioning of the two orbiting satallites. The location of both satellites is setup using the Flexible motion model and the Two-Line Elements (TLEs) for two real satellites. The imaging satallite is using the orbit for the Canadian Anik-F1 telecommunications satellite. The target satellite is using the orbit for the NASA EO-1 satallite.

The TLE for the GEO imaging satellite is (recent Anik-F1 is used):

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 TLE for the LEO target satellite is (recent EO-1 TLE is used):

1 26619U 00075A   14086.18494821  .00002663  00000-0  52402-3 0  4248
2 26619  97.9906 145.4495 0008900 226.0780 133.9706 14.63359462711179

Important Files

The goal of this demo is to show how to use a a TLE to define the motion of the target satellite and and to tell the imaging platform what to track. Therefore, the materials used in the scene are miminal to help the user visualize the simulation.

Target Satellite

A very low resolution geometry model for the EO-1 satellite is used (see the geometry/eo1_simple.obj file).

geometry/eo1_simple.png
Figure 1. The simple geometry model for the EO-1 satellite.

The EO-1 target satellite OBJ model is positioned and oriented within the geometry/eo1_simple.glist file:

<geometrylist enabled="true">
  <object>
    <basegeometry>
      <obj><filename>eo1_simple.obj</filename></obj>
    </basegeometry>
    <dynamicinstance>
      <motion type="flexible">
        <locationengine type="sgp4">
          <data source="internal">
            <tle1>1 26619U 00075A   14086.18494821  .00002663  00000-0  52402-3 0  4248</tle1>
            <tle2>2 26619  97.9906 145.4495 0008900 226.0780 133.9706 14.63359462711179</tle2>
          </data>
        </locationengine>
        <orientationengine type="velocity">
          <up frame="ecef" vector="0,0,1"/>
        </orientationengine>
      </motion>
    </dynamicinstance>
  </object>
</geometrylist>

The <motion> description uses the EO-1 TLE for the location and uses the velocity to define the orientation (the vehicle points along spatial velocity). In order to make the orientation robust at locations far from the Scene ENU origin (both satellite are very far away), we have explicitly specified that we want to use the ECEF +Z vector to constrain the orientation.

Imaging Platform

Because we wanted to be able to image the EO-1 satellite from our GEO orbit, a very high resolution camera is setup. The angular extent of the EO-1 satellite when viewed from a GEO altitude is 50 nanoradians (5.0e-08 radians), which is very small. The camera has 10 micron pixels and a 2,000,000 mm or 2,000 m focal length. The camera has a 0.05 Hz frame rate. The capture method is setup to save a file per capture, which means a separate imge file we be generated for each image frame.

Important
 Obviously this is a fictional imaging system created for demonstration purposes.

The platform motion configuration is contained in the demo.motion file. It uses the SGP4 location engine and the Anik-F1 TLE to position the imaging platform. The orientation of the platform is defined so that it is always looking at the location of the EO-1 satellite, but specifying the TLE for that satellite:

<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="sgp4">
      <data source="internal">
        <tle1>1 26619U 00075A   14086.18494821  .00002663  00000-0  52402-3 0  4248</tle1>
        <tle2>2 26619  97.9906 145.4495 0008900 226.0780 133.9706 14.63359462711179</tle2>
      </data>
    </locationengine>
    <up frame="ecef" vector="0,0,1"/>
  </orientationengine>
</motion>

Again, in order to make the orientation robust at locations far from the Scene ENU origin (both satellites are very far away), we have explicitly specified that we want to use the ECEF +Z vector to constrain the orientation.

Tasks

The simulation is setup for a very specific time window where EO-1 decends across the northern hemisphere (passing over Rochester, NY).

geometry/eo1_track.png
Figure 2. A visualization of the EO-1 track in STK

The start time for the acquisition is 11 March 2014 14:47:00 UTC and the end time is 11 March 2014 14:51:00 UTC. The demo.tasks file has this 14 minute long window defined. Given the 0.05 Hz read out rate, this results in 41 frames.

Setup

There are two simulation scenarios in this demo:

  1. A single-frame simulation

  2. A multi-frame (video) simulation

Running the Single-Frame Simulation

This single-frame simulation produces a single image file. To run the simulation, perform the following steps:

  1. Run the DIRSIG demo.sim file

  2. Load the resulting demo-t0000-c0000.img file in the image viewer.

Running the Multi-Frame Simulation

The multi-frame simulation produces 41 image files. To run the simulation, perform the following steps:

  1. Run the DIRSIG video.sim file

  2. Load the resulting demo-t0000-c0000.img, demo-t0000-c0001.img, etc. files in the image viewer.

Results

Single-Frame Simulation

The simulations produces the single-frame simulation shown below:

images/demo.png
Figure 3. Output of the single-frame simulation (two sigma scaling).

Multi-Frame Simulation

The output of the multi-frame simulation is 41 individual image files. The frames can be scaled and encoded into a video format for viewing using a variety of 3rd party software tools (ffmpeg, mpeg_encode, etc.).

images/video.gif
Figure 4. An animation of the 41 frames produced by the multi-frame simulation.