Mission analysis
STECCO mission was simulated using GMAT and in-house codes. The aim of these studies is to estimate the time-variation of the orbit parameters, the decay time and the thermal loads onto the satellite. Data collected from TLE and the on-board sensors will be used to validate the models used and improve the guess on the drag coefficient CD for this class of satellite.
STECCO Mission
Orbit: SSO 550x540 km
SMA: 6916 km
ECC: 0.002
INC: 97.6 deg
LTAN: 11 am
Orbit period: 5723 sec
Decay time: 12 years
Satellite Laser Ranging
Satellite Laser Ranging (SLR) allows precise positioning of the satellite with respect to a laser ranging ground station, by means of the Cubic Corner Reflector (CCR) mounted on the tip faces of STECCO. Unlike other tracking and positioning systems that use microwaves, the SLR uses the optical spectrum of electromagnetic waves. The precision of ranging with the nowadays stations of the International Laser Ranging Service (ILRS) is below the cm. Because of the relative velocity between the satellite and the ranging station, the laser pulses reflected by the satellite are deflected away from the station (in the direction of the satellite). The angular deflection of the beam is a function of the orbital altitude (h) of the satellite, of the complementary of the elevation angle (θ) of the satellite with respect of the zenith of the tracking station, and of the azimuthal angle of the velocity with respect to the plane defined by the position vector of the satellite (ω). The velocity aberration of STECCO are compensated using CCRs with a diameter of 25.4 mm (1 inch). The CCRs that are used are commercial-of-the-shelf (COTS) units. The use of COTS reflectors has been approved by ILRS and tested on small university mission, and has been approved for the ASI LARES 2 scientific satellite.
Attitude Determination and Control
TRIAD
The TRIAD algorithm is implemented on-board the FPGA section of PHOEBE OBC. The algorithm provides Attitude Determination from the input of the 12-bit MEMS three-axis magnetometer and gyroscope and geomagnetic field extracted from the IGRF model and stored on-board.
CCR
The use of two COTS CCRs makes possible to estimate the Attitude of STECCO from ILRS data. In particular, the angle from nadir direction and the angular rates of STECCO can be extrapolated from SLR and propagated to infer the whole attitude state of STECCO. Feasibility studies have been performed to verify the suitability of the technique, that will be validated during the flight of STECCO.
MARD
STECCO will validate in space the Magnetic Attitude and Rate Determination (MARD) algorithm, which allows estimating the attitude and angular rates of the satellite based on the data of a single three-axis magnetometer. The algorithm studied and Hardware-in-the-Loop simulations were performed using the Helmholtz cage at the School of Aerospace Engineering.
The "EGG"
The attitude control of STECCO is performed by means of passive techniques including gravity-gradient stabilization and viscous damping. The effectiveness of a viscous damper, named the "EGG", capable of storing the angular momentum of the satellite and dissipate its rotational kinetic energy, will be tested in-orbit.
