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Need some tracking data? Use the Simulator!

By: Giuseppe Corrao

One of the most common issues for analysts/operators involved in the orbit determination process is the availability of tracking data. Tracking data input is needed for all objects (IOD, LS, Filter) devoted to the state estimate, but in many cases, they are difficult to get or they are too few to start practicing with the tool. 

ODTK provides an ad-hoc object (the Simulator) that is able to generate any type of simulated tracking data (e.g., Range, Doppler, Right Ascension, and Declination) in multiple formats, ready to be ingested by the  objects mentioned above. There are multiple reasons for having simulated tracking data available. 

Become an expert user 

  • Verify instruments bias errors effects on OD results. 
  • Emulate residuals signatures accordingly with different initial conditions. 

Pre-mission analysis capabilities 

  • How quickly we can get an accurate estimate? 
  • How accurate will the estimate be? 
  • What can I do to get a better estimate (e.g., add more tracking stations)? 

Ground station and satellite design 

  • What kind of tracking data will meet mission requirements? 

Ground station scheduling 

  • How much tracking data do I need to schedule to meet accuracy requirements? 

Being the tracking station biases and the force model parameters described through statistical parameters (mean, sigma …), the Simulator has the ability to produce random deviations accordingly with the stochastic model used to configure the tracking station biases and the force model coefficients. The following parameters can be affected: 

  • Initial orbit 
  • Force models (solar pressure, atmospheric density) 
  • Measurement and Transponder biases 
  • Measurement white noise and time-varying biases 
  • Clock (frequency white noise and random walk) 
  • Maneuvers (magnitude and direction) 

Each deviation is independent from the other, and can be scaled to a specific weight factor. 

The tracking data generation can also be limited to a predetermined tracking schedule that takes into account visibility constraints (thanks to STK’s access capabilities) and more generic unavailability, such as station maintenance.

The Simulator can produce tracking data relevant to any Satellite in the scenario as generated from any available Tracking Station object. By default, the measurements are created in the Generic Simulation (.gobs) format, but there are many other formats available.

When the Simulator is started, it propagates the satellites under consideration by using the same propagator (HPOP) used in STK, and then starts emulating measurements taken from the Tracking Station with respect to the satellite’s state at any specific epoch. As result of a random error distribution, each Simulator run will produce a slightly different trajectory that is saved as an ephemeris (.e) file to be used as reference. 

Have an happy OD with the Simulator!

Posted: 3/18/2019 8:00:00 AM


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