ODTK Adding Known Maneuvers

You want to process tracking data from a LEO satellite that performed a maneuver within the reference period. You believe the satellite is performing a Hohmann transfer. You believe the semimajor Axis from 7000 to 7100 km. You also know the firing times and the amount of delta V consumed to perform the two maneuvers.

Create a New Scenario

Let's start by creating a new scenario and defining it's properties.

  1. Create a new scenario ().
  2. Rename the scenario Rising.

Add a Generic Observation File

  1. Double-click the Scenario to open the scenario's properties.
  2. Expand the Measurements attribute under the Scenario heading.
  3. Double-click the Files value under Measurements.
  4. Click the Add button.
  5. Double-click the Filename value.
  6. Browse to the student files provided for this exercise (Typically, <install Directory>\AGI\ODTK 6\ODTK\UserData\TrackingData).
  7. Change the file type to GOBS File.
  8. Select RisingSatellite.gobs.
  9. Click Open.

Set the Measurements Span

  1. Set the StartMode to Start Time.
  2. Enter the Start Time to 01 Apr 2014 10:13:30.000 UTCG.
  3. Set the EndMode to Stop Time.
  4. Enter the End Time to 03 Apr 2014 10:13:30.000 UTCG.

Set Up the Tracking System

  1. Select Rising () in the Object Browser.
  2. Extend the File menu.
  3. Select the Import option.
  4. Select the Import Object option.
  5. Change the Files of Type to Tracking System Files (*.tso).
  6. Browse to the location of the tracking system database.
  7. Insert the GroundStationNetwork.tso tracking system (). (Typically, <install Directory>\AGI\ODTK 6\ODTK\UserData\TrackingStations)
  8. Click Open.
  9. Locate the Measurement Statistics value.
  10. Double-click the Measurement Statistics value to view the tracking system.

Preview the Measurements

Let's take a quick look at the Measurements for data in the Static Product builder.

  1. Click the Preview Measurements () button.
  2. Open the Static Product Builder ().
  3. Create a Measurements by Tracker graph.

Model the Satellite

Let's take a moment and model the satellite in ODTK.

  1. Insert a new Satellite () named RisingSatellite.
  2. Open RisingSatellite's properties.
  3. Locate the MeasurmentProcessing field.
  4. Set the TrackingID to 1001.

Set the Initial State

You can set the intial state of the satellite using an external HTML page.

  1. Bring the OD Launchpad to the front.
  2. Expand the Installed Utilities option.
  3. Launch the InitialStateTool.htm.
  4. Browse to the location of the RisingSatellite.e file. (Typically, <install Directory>\AGI\ODTK 6\ODTK\UserData\Ephemeris).
  5. Leave the other properties.

Create a Filter

  1. Insert a new Filter () called RisingSatFilter.
  2. Open the Filter's () properties.
  3. Locate the Output field.
  4. Set the SmootherData Generate option to True.
  5. Run () the Filter.

Run the Filter Graphs

Residual Ratios Graph

  1. Open the Static Product Builder ().
  2. Click the Add a New Product ().
  3. Rename the Product to Residual Ratios.
  4. Set the Output to Residual Ratios.
  5. Set the Input to the filrun file.
  6. Run graph.

Position Uncertainty Graph

  1. Open the Static Product Builder ().
  2. Click the Add a New Product ().
  3. Rename the Product to Position Uncertainty.
  4. Set the Output to Position Uncertainty.
  5. Set the Input to the filrun file.
  6. Run graph.

It seems you have a maneuver that you didn't model yet that is causing the residuals to be rejected and the uncertainty to grow. Let's model those maneuvers.

Add Maneuvers

ODTK has the capability of performing orbit determination through maneuvers with no need to restart OD after the maneuver. Maneuvers can be modelled as an instantaneous or finite maneuver. An instanteous maneuver has no duration, but instanteously changes the satellites velocity. A finite maneuver models the acceleration throughout the maneuver. ODTK also provides the capability of calibrating the maneuver from the tracking measurements.

Maneuver Description
Instant
  • Great for short maneuvers, especially when no tracking data is available
  • Easy to calibrate
  • Treated as impulsive where you specify the epoch and delta-V
  • Implicit mismatch between the impulsive assumption and reality
Finite
  • Appropriate for long maneuvers or when you have data during the maneuvers
  • Harder to calibrate
  • Great flexibility
  • Adds magnitude and direction states into the state space. You can specify the uncertainty in each and since they are Gauss-Markov processes, they are time varying.
  • Can share common states across maneuvers
  • Useful for recovering unknown accelerations like mismodeled SRP or drag

ODTK makes available four types of impulsive maneuvers, each defined by a different model:

Maneuver Description
Velocity Change (InstantManDeltaV) A physically non-realistic method that treats the Delta V as instantaneous *(adequate for short-term thrusting)
Acceleration History (InstantManAccelFile) A time history of acceleration of the satellite during the maneuver
Constant Thrust (InstantManConstThrust) Holds the thrust constant, thereby increasing acceleration as mass decreases (a=F/m)
Constant Acceleration (InstantManConstAccel) Holds acceleration constant, thereby decreasing force as mass decreases (F=ma)
  1. Open the satellite's () properties.
  2. Locate the ForceModel field.
  3. Locate the InstantManeuver field.
  4. Click to Add maneuvers.
  5. Add the two maneuvers described into the RisingSatellite_maneuvers_summary.txt file. (Typically, <install Directory>\AGI\ODTK 6\ODTK\UserData\Ephemeris). Ensure the maneuvers are in m/sec. The result should be something like this:
  6. Rising Maneuver

    Option Value
    DeltaVX -49.4131 m*sec^-1
    DeltaVY 4.44297 m*sec^-1
    DeltaVZ -32.1698 m*sec^-1

    Circularize

    Option Value
    DeltaVX 51.2087 m*sec^-1
    DeltaVY -3.28619 m*sec^-1
    DeltaVZ 37.1909 m*sec^-1
  7. Run () the filter.
  8. Check the results by running the Residual Ratios graph again.

Add a Smoother

  1. Add a Smoother () object.
  2. Open the Smoother's () properties.
  3. Set the Input File to the *.rough file created by the previous Filter run.
  4. Run () the smoother.
  5. Generate a Position Uncertainty plot.
  6. Create an Instant Maneuver Summary report using the *.smtrun file generated from the smoother and check it for reference.

Generate a Filter Smoother Consistency Plot

  1. Open the Smoother's () properties.
  2. Click the Add a New Product ().
  3. Rename the Product to Position Consistency.
  4. Set the Output to Position Consistency.
  5. Set the Input to the difrun file.
  6. Run graph.

ODTK 6.5