Hardware in the loop test campaign for e-st@r cubesat

The paper describes the Hardware-In-the-Loop (HIL) simulation methodology used in the development of the e-st@r cubesat, which is one of the cubesats chosen by the ESA Education Office for the Vega Maiden Flight. The e-st@r program is carried out by students and researchers of the Department of Mechanical and Aerospace Engineering at the Politecnico di Torino, and the cubesat has been successfully launched into orbit in February 2012. The HIL methodology has been applied to the space segment composed by a payload (an Active Attitude Determination and Control System) and a satellite bus (an On Board Computer, an Electrical Power System and a Communication System). The simulation tests campaign objective is to investigate and evaluate the e-st@r performances during its operative life by including the main hardware of the satellite in the loop. Simple and very low cost solutions must be taken into account in order to satisfy the requirements and the constraints of the e-st@r mission. HIL simulation includes the models of 1) sensors (an Inertial Measurement Unit and a Magnetometer), 2) actuators (three magnetic torquers), 3) solar panels (five couples of GaAs TJ solar cells), 4) thermal behaviour of the satellite, 5) orbit, 6) dynamics and kinematics of the satellite. The satellite behaviour during all mission phases, the uplink and downlink communications, and the performances (such as pointing accuracy and orbital manoeuvre capability, batteries charge/discharge time, power consumption) are the main features and high level functional requirements investigated and tested during the HIL verification campaign. Data acquired during the tests both by the simulator PC and by the Ground Station allow to compare the hardware behaviour and the simulated response obtained from the global simulation model. The results of the verification by means of the HIL strategy are consistent with the expected values in any operative condition, thus validating the methodology. Moreover, it has been verified that testing via HIL simulations may efficiently support the design and verification of a small satellite program, reducing the time and the cost of the development phase, while at the same time increasing the effectiveness and reliability of the satellite. The methodology tested on the e-st@r cubesat may be tailored also to other similar projects, thanks to its versatility given by its inherent modular structure