Scuola di Ingegneria Aerospaziale

TigriSat

Tigrisat is a 3U CubeSat built by Italian and Iraqi students at Sapienza University of Rome in the framework of the first “High Level Postgraduate Course in Aerospace Engineering” supported by the Italian Ministry of Foreign Affairs and the Iraqi Ministers of Science and Technology, High Education and Transport.

The satellite has been entirely designed by the students with the support of the professors of the School of Aerospace Engineering of Sapienza University of Rome. The satellite has been then built and tested in the laboratories of the School of Aerospace Engineering. The main target of the Tigrisat project was definitely its educational value. The nominal mission target was the test of a payload for the monitoring of dust storms above Iraq based on a high performance RGB camera and a commercial single board computer running a custom scripted algorithm for dust detection. Nonetheless other important mission objectives have been targeted including the validation of a novel attitude determination and control algorithm implemented on the FPGA of the ABACUS on-board computer, the test of novel technical solutions (e.g. the solar panels with embedded coils for the attitude control) and a novel S-Band antenna.

Characteristics

Deployable UHF antenna for telemetry, telecommand and beacon;
Modular structure which simplifies the mounting and testing of the satellite. Tigrisat
Complies to the cubesat standard in the 3-unit format: it weighs 4 Kg and its size is 100mm x100mm x 340mm

On-Board Computer

A custom on-board computer named ABACUS (Advanced Board for Active Control of University Satellites) developed at the School of Aerospace Engineering of Sapienza University of Rome. ABACUS is based on fault-tolerant design and a reliability enhancing architecture. ABACUS implements hardware redundancy, provided by a microcontroller and an FPGA, distributed in two independent but cooperative sections. Technology diversity grants common mode fault tolerance.

S-Band Antenna

An ad-hoc designed S-band antenna for payload data downlink. A novel S-band patch antenna system suited for Earth-observing cubesat satellites has been designed. The antenna consists of four rectangular patches that, properly excited, can achieve different radiation pattern shape, in order to satisfy requirements depending on the mission of the satellite. In particular, the correct phasing of the excitation signals for the four patches is achieved with a RF distribution network patterned on the opposite side of the same substrate. The antenna has a compact size and its geometry and characteristics are compatible with any cubesat standard structure. A 57 mm wide square window allows to accommodate imaging system optics in its center, leading to a very compact overall system. Measurements confirmed that the antenna achieves good impedance match, well below −10 dB at the operational frequency of 2450 MHz. The antenna gain ranges from 3.7dBi to about 8dBi, depending on the selected configuration of the supply signals.

Smar Solar Arrays

Solar panels with embedded coils for the actuation of the magnetic attitude control and with on-board sensors for attitude determination and health monitoring. The coils are mounted on a frame (yellow parts in the pictures) and are then mounted in a trench made in the printed circuit boards. Each of the four side boards also hosts a sun sensor, two temperature sensors and the connectors for the sensor signals and for the power that comes from the solar cells that are mounted on the opposite side of the boards.

Attitude Determination and Control System

A novel magnetic attitude determination and control algorithm to achieve nadir pointing attitude. The algorithm combines B-dot and proportional control. High gain values ensure a fast decrement of the initial kinetic energy while approaching the required attitude. Low gain values as soon as the switching point is achieved ensure a nadir pointing maintenance. The proposed switching function is proportional to kinetic and potential energy. The entire ADCS is coded in the ABACUS FPGA section.

Launch

Tigrisat has been successfully deployed in a sun-synchronous orbit ranging from 550km to 610km at perigee and 620km to 715km at apogee. Tigrisat has been released in orbit by Unisat-6 on June 20th 2014 at 21:07 UTC, 25 hours and 38 minutes after the separation of Unisat-6 from the Dnepr Launch Vehicle that was launched from the Yasni cosmodrome in Russia on June 19th 2014 operated by Kosmotras. Although the nominal mission duration was six months, Tigrisat is still operating correctly after more than five years in orbit.