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EPTOS project had the objective of developing a flight dynamics product able to optimize the orbital transfer trajectory, focusing in the typical commercial telecom GEO satellites LEOP from the orbit after separation from the launcher to their final GEO position by using low-thrust electric propulsion.

The final product has been integrated in GMV’s commercial focusleop product, part of GMV’s focussuite flight dynamics system, flight-proven and highly reliable software devoted to ground control of commercial satellites during LEOP. The new development is applicable for both mission analysis and operations activities.


The big challenge of this project was to evolve focusleop product to support full-electric missions by developing a new optimizer considering a full operational set of requirements:

  • Solve minimum transfer time problem and minimum propellant problem by using thrust/coast arcs
  • Consider operational constraints such as maximum attitude rotation rate, eclipses, GEO belt crossings, Van Allen radiation dose or thrusters’ degradation over time
  • Compute re-optimization of a previously planned strategy with updated data from orbit determination at an intermediate point of the transfer
  • Obtain good results with the minimum user intervention and within small responses time making it useful for operation purposes

GMV in collaboration with ESA has contacted commercial GEO satellite operators in order to define the users’ requirements to be verified in this project as close as possible to the actual market needs.


EPTOS function is integrated in the existing focusleop product as an additional function establishing the corresponding interfaces with the rest of functions. Additionally some of the existing functions will be properly modified to accommodate Electric propulsion strategy. With this design, it has possible with a small effort to make EPTOS:

  • Use common interfaces for main satellite parametrization (mass, engine properties, propagation perturbations, physical constants, verbose control, etc.)
  • Share interfaces with other LEOP strategy design and operations modules to ease the configuration (initial orbit from launcher, reference orbit file, target in GEO, etc.).
  • Compute electric propulsion orbit raising in different scenarios:
    • GTO or SSTO (or any other orbit) from the launcher
    • Intermediate TO after chemical propulsion phase, thus allowing for hybrid strategies
    • Any intermediate state during operations, for instance, from an updated orbit coming from an orbit determination
  • Use EPTOS outputs in other functions of the system for further analysis purposes such as launch windows opportunities, geometrical events verifications (eclipses, sensor blindings, interferences, antenna coverage, etc.) or ground station coverage.

The product EPTOS consists of the focusleop infrastructure including a new module called EPTOS for supporting Electric Propulsion Transfer Optimization Software. focussuite framework is a consistent and coherent set of integrated components designed to develop and customize flight dynamics systems making special emphasis in easing the integration of new applications, while providing powerful and advance data manipulation and visualization means, and automation capabilities. These components can either be deployed as stand-alone components or integrated so that they can interoperate and collaborate among them. The system allows easy extension to external applications like computational modules written in any programming or scripting language.

The new EPTOS module is in charge of computing the optimized strategies and generate as main outputs the orbit file (satellite position and velocity from separation to station acquisition), the list of manoeuvres (defined by start and end epochs, and thrust profile) and the attitude law.

EPTOS performs very well overall, being able to return a trajectory which is optimized and also flyable. This approach has been successfully tested giving good results and showing good software performances in the more relevant scenarios:

  • Transfer time optimization
  • Final mass optimization
  • Final longitude constraint

EPTOS can be used integrated inside the focusleop application with a user-friendly interface (client/server infrastructure, easy data modification through panels, undo/redo options, plots visualization, possibility to import/export data sets, etc.).

EPTOS can use common databases and data files shared with other computational programs, such as an orbit determination result. This will allow, among other benefits, computations for hybrid transfers having first a chemical manoeuvres part and then the EP orbit raising, and re-optimization of the trajectory during operations at any intermediate point of the transfer.

EPTOS outputs (orbit file, manoeuvre file, attitude profile and mass evolution file) can be easily used in other modules of focusleop for additional computations such us orbital events predictions, ground station coverage, launch windows computation, etc.

This easy interaction and sharing of common databases between EPTOS and the rest of the modules, will allow the user to use EPTOS fully integrated in the application for both mission analysis and also operations procedures.

System Architecture

focusleop as part of focussuite product has being designed to accommodate new functionalities in a very easy and simple manner. focussuite infrastructure will provide a very user-friendly interface with many advantages as they are:

  • Advanced off-the-shelf, multi-mission, multi-satellite flight dynamics solution for flight dynamics satellite control that sets a new standard in functionality, reliability, flexibility, and user friendliness.
  • Capability to provide full lifecycle flight dynamics operations support through our unsurpassed collection of flight-proven mission independent and mission specific functionality. Flight-proven support of commercial satellite platforms is provided with accuracy fully consistent with native systems.
  • Availability of a large collection of plug-and-play components providing unprecedented functionality and being able to customize the system to fit your specific needs. GMV provides custom solutions with strong customer focus and customer support.
  • Provision of a generic framework that allows further product development and evolution, including the ability to integrate external applications with unprecedented ease. Our open framework dramatically boosts productivity, system usability, accessibility and stability.

focussuite has therefore been conceived as a real framework as it is demonstrated by its major functionalities: a computation layer based on the extensive reuse of existing and improved software, a client/server architecture, a database driven system, an advanced GUI (based on desktop applications philosophy: “everything-in-one-working-area” and “all-one-click-away” and using a GUI toolkit that allows a development of GUIs through configuration files rather than through code), procedures automation capability through the autofocus extension (based on a dedicated language SOL -Spacecraft Operations Language), advanced graphical capabilities, portability (e.g. Windows / UNIX / Linux), extensibility (any extra functionality following certain I/O rules can be easily integrated via configuration files) and finally, capability to perform unlimited Undo/Redo operations.


The project was developed in two different phases: Phase 1 for prototyping EPTOS algorithms and Phase 2 for its implementation inside a commercial operational tool. For each of both phases, the following milestones have been successfully passed:

  • Kick-off (KO): Project start
  • Preliminary Design Review (PDR): A preliminary architectural design of the software is elaborated.
  • Critical Design Review (CDR): The design process is completed and the software tool is fully developed.

Acceptance Review (AR): All verification and validation tests have been successfully completed and the report finalized.

Current status

The project has been completed and the product is available as part of GMV’s COTS product focusleop (focussuite Flight Dynamics solution for LEOP mission analysis and operations).

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