SkyMon PED - Passive Ephemeris Determination

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The objective of the activity is to determine satellite ephemeris data (orbital parameters describing the trajectory of a satellite) for the purpose of improving the accuracy of geolocation systems and tracking of satellite orbits.

The following objectives are met: 

  • To provide a product ready for the market able to satisfy the market’s demand for accurate satellite ephemeris data 

  • To continuously determine satellite ephemeris data for the purpose of providing a tracking system for GEO, MEO and LEO satellites. 

  • To provide very accurate satellite ephemeris data as input for geolocation systems for the purpose of improving their accuracy 

  • To predict the trajectory of a satellite based on historical ephemeris data

In addition, this data can be used for:

  • Traditional satellite ranging activity (supporting flight dynamics operators to prepare satellite manoeuvres and calculate the state vector before/after the manoeuvre) 

  • Collision and interference avoidance (e.g., coordination of co-located satellites) 

  • Space situational awareness activity 

  • •    Remote sensing applications.


The key challenge of the project is to determine the orbital position with an accuracy better than traditional ranging systems. This requires to trigger the measurement on several ground stations at exactly the same time for calculating the Time Difference of Arrival (TDOA).

  • By using PED, the customer is independent from cooperation with other sources providing ephemeris data (e.g. Satellite Operator)

  • Precise knowledge of satellite manoeuvre situations

  • Immediate Measurement: No need to wait until precise ephemeris data may be provided (if provided at all) from other sources (e.g. Satellite Operator). The interference situation may have disappeared or changed in the meantime.

  • No need to know and receive additional reference signals to counteract impact of ephemeris error.

  • Determining Orbital Elements (Ephemeris Data) with an accuracy of less than 600m

  • Support of different formats, like Cartesian (ECI, ECF), NORAD-TLE

  • Detection of satellite manoeuvres

  • Support of GEO, MEO and LEO satellites

  • Calculate and display of satellite trajectory

System Architecture

Main Elements

  • Rx Stations (minimum 3)

    • Small Size (1.2m)

    • Signal Sampling (USRP, B210)

    • 1PPS Synchronization (GNSS Receiver)

    • Antenna Control (ACU)

    • Transfer of IQ Samples to Central Station (SkyMon PED, SkyMon ILS)

  • Central Station (SkyMon PED)

    • Controlling & Triggering Rx Stations

    • Computing TDOA/FDOA

    • Calculating Satellite State Vectors

    • Determining Orbital Elements


The project is done in three phases: First phase is to develop a Simulator for verifying the reachable accuracy of the system for different scenarios (# of Rx stations, orbital position, signal characteristic, etc.). The outcome of the Simulator defines the product specification and the basic design. In the second phase, the main algorithms are developed as well as the user frontend. In the third and last phase, the system accuracy and performance is verified.

Current status

The project has been kicked off and the simulation work package has been started. The main design has been defined and all relevant documents for the CDR review meeting are currently prepared.