Final phases of the STECCO Flight Unit integration
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STECCO is equipped with innovative attitude control devices, aimed at controlling its angular velocity and enhancing gravity gradient stabilization, leading the satellite long axis to align along nadir. Radio-amateur will be capable of monitoring the spacecraft attitude (pointing direction) and see the effect of attitude control on it. In addition STECCO is equipped with two Corner Cube Retroreflectors (CCR) for laser ranging experiments from ground.
Payload: Four payloads are included. (1) Two cubic corner reflector (CCR), installed at the satellite extremities, which allow satellite laser ranging whose data will be used for estimating the attitude of STECCO without the use of on-board sensors. (2) A passive viscous damper whose goal is dissipating STECCO rotational kinetic energy. (3) A new OBC (PHOEBE) developed at the School of Aerospace Engineering which can be reconfigured in orbit. A magnetometer-only attitude determination algorithm, implemented on FPGA, which allows determining the attitude of STECCO based on the use of only one three-axis magnetometer.
Telemetry, Tracking & Control (TT&C): TT&C is composed of STECCO radio and antenna, and it communicates with the ground station at the School of Aerospace Engineering in Rome, which receives telemetry and data and send uplink and downlink commands, and with radio amateurs, who receive telemetry and data.
On-Board Data Handling (OBDH): OBDH is managed by PHOEBE OBC, which includes a three-axis magnetometer and a three-axis gyroscope. Data from sensors are collected, stored and transmitted. The magnetometer measurements are processed by a FPGA module on which the attitude determination payload is implemented. The allocation of attitude estimation and sensors data, together with the beacon and the data transmission is managed by the OBC. PHOEBE features in-orbit reconfigurability possibility which will be used to test several architectures including RISC V.
Electrical Power System (EPS): All power for the STECCO spacecraft is provided by twelve body-mounted solar cells, placed on the larger surfaces of the spacecraft. The cells are connected in series of three and strings from opposing sides are connected in parallel: the resulting connection is a total of two solar arrays connected as 3s2p. A protection diode is included in each string. Each solar panel consists of three CESI CTJ AI triple junction solar cells, custom cut to 27.5cm2. At AM0 reference conditions the maximum power point of the cell is at Vmp = 2.33V and Imp = 0.475A. The expected working temperature is lower than 40°C. Considering the connection and the diode loss, in the most favourable attitude the peak power in AM0 condition is 4.4W at BOL.
The energy storage is based on a 2S2P battery consisting of four Lithium-Ion VARTA LPP443441S cells having a capacity of 2.5Wh each, for a total of 10Wh. The cells are singularly protected against over-charge, over-discharge and over-current conditions.
The solar array is interfaced to the battery by a MPPT PCDU, also performing battery management. The unregulated bus at nominal 7.2V is used to directly supply the battery heater (1Wmax) and a redundant dc-dc converter driving a regulated 3.3V bus, distributed to all systems and payloads. The peak bus current is less than 1.5A, for a total peak power absorption lower than 4W. The whole STECCO EPS fits in a 0.5x2 P (25x100 mm).
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