Airbus Defence and Space


CAP propulsion analysis tool

CAP is a simulation software developed by Airbus Defence and Space in order to design and optimise spacecraft propulsion systems.


CAP is intended for a quick design of propulsions systems (A phase) as well as for in-flight performance prediction of detailed subsystems. The program is able to simulate all kinds of propulsion systems: monopropellant, bipropellant operating in pressurised or blow-down mode and systems including ion thrusters.


CAP is integrated into a user friendly graphical framework. In particular a Schematic Editor as well as a Mission Editor gives to the user a high level of flexibility for taking into account design changes that occur during the development phase.

CAP detailed presentation

Features / technical details

The input data that are required for running a simulation gather the followings :

  • The subsystem data describe the propulsion architecture in term of component characteristics and flow scheme. They are generated through the Schematic Editor. ·
  • The mission data describe the subsystem mission along the time in term of thruster actuation, valve opening/closing orders ...etc. They are generated through the mission editor or are automatically issued from in-flight telemetry data. ·
  • The ambient data include the interface data with the external environment of the subsystem such as thermal fluxes and temperatures. They are generated from other software packages or from in-flight telemetry.

The output data are closely related to the mathematical models that predict the performance of individual component. However typical time dependant results are presented hereafter :

  • Tanks: pressure, propellant/pressurant masses and fluxes, temperatures, etc...
  • Thrusters: inlet pressure, propellant mass fluxes, thrust, specific and total impulses, temperatures, etc...
  • Spacecraft: thrust, speed increment and impulse along the three axes, mass, etc...


The CAP software is used within the Ariane 5 program as well as on telecommunication satellite programs (TELECOM 2, HISPASAT, ST1, WORLDSTAR, HOTBIRD…) for propellant budget, mission analysis and manoeuvres optimisation.

Several validation campaigns of the mathematical models have been performed using the Telecom 2 in-flight data as well as Ariane 5 flight data. These validations have shown the great capabilities and accuracy of the CAP simulations.

Reference customers

ESA, CNES, Intelsat, Inmarsat, Eutelsat, Hispasat, ...