Small Satellite Attitude Determination With RF Carrier Phase Measurement

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1 Politecnico di Torino Electronics Department IAC-09.C1.6.9 Small Satellite Attitude Determination With RF Carrier Phase Measurement Danilo Roascio, Leonardo M. Reyneri, Claudio Sansoé, Maurizio Bruno International Astronautical Congress 2009 Daejeon, Republic of Korea October 15th

2 Outline Overview of the AraMiS architecture Existing attitude determination systems RF tracking with phase measurements Phase measuring receiver Antennas considerations Conclusions IAC-09.C1.6.9 D. Roascio, L.M. Reyneri, C. Sansoé, M. Bruno Politecnico di Torino 2/17

measuring receiver Antennas considerations Conclusions IAC-09.C1.6.

3 ARAMIS Concept Tiles Common satellite subsystems: Power conversion/storage/management Attitude determination/control Housekeeping On-board spacecraft control Telecommunication Gathered and split in two types of Tiles: Power Management Tile (PMT) TT&C and AOCS Tile (TTC) IAC-09.C1.6.9 D. Roascio, L.M. Reyneri, C. Sansoé, M. Bruno Politecnico di Torino 3/17

Gathered and split in two types of Tiles: Power Management Tile (PMT) TT&C and AOCS Tile

4 ARAMIS Concept - Tiles Power Management and AOCS Tiles Payload OBC and TT&C Tile IAC-09.C1.6.9 D. Roascio, L.M. Reyneri, C. Sansoé, M. Bruno Politecnico di Torino 4/17

5 Modular Architecture Smallest cube 5 PMT (>20 W solar power, >95 W peak power) 1 TTC Rectangular Box 20 PMT; 2 TTC Up to cm 2 payload-specific openings Hexagonal prism with 20 cm optical telescope payload Solar Panels array IAC-09.C1.6.9 D. Roascio, L.M. Reyneri, C. Sansoé, M. Bruno Politecnico di Torino 5/17

openings Hexagonal prism with 20 cm optical telescope payload Solar Panels array

6 Power Management Tile Thermomechanical subsystem: 1.6 mm thick halodined Al frame Power subsystem: triple junction GaAs solar cells (4.2 W) two Li-Ion batteries (14.4 Wh) Double redundant 14 V distributed power bus Attitude determination sensors Inertial (yaw gyroscope) Magnetic (2-axis magnetometer) Optical (sun and earth sensor) Attitude control actuators Reaction wheel: 3-4 rpm typical Active magnetic with coils for despinning Standard housekeeping Test connector IAC-09.C1.6.9 D. Roascio, L.M. Reyneri, C. Sansoé, M. Bruno Politecnico di Torino 6/17

4 Wh) Double redundant 14 V distributed power bus Attitude determination sensors Inertial (yaw gyroscope) Magnetic (2-axis magnetometer)

OBC & TT&C Tile Thermomechanical subsystem: 5 mm thick halodined Al frame 4 stands for payload support Dual Telecommunication subsystem: 437 MHz, 9.6 kbps AFSK, Omnidirectional PCB antenna 2.

7 OBC & TT&C Tile Thermomechanical subsystem: 5 mm thick halodined Al frame 4 stands for payload support Dual Telecommunication subsystem: 437 MHz, 9.6 kbps AFSK, Omnidirectional PCB antenna 2.4 GHz, up to 500 kbps FSK, Omni- or directional patch array 33 dbm TX power, -110 dbm RX sensitivity User-defined protocol (e.g. AX-25) Dual-redundant on-board computer and on-board data bus. Central opening for earth observation equipment. IAC-09.C1.6.9 D. Roascio, L.M. Reyneri, C. Sansoé, M. Bruno Politecnico di Torino 7/17

4 GHz, up to 500 kbps FSK, Omni- or directional patch array 33 dbm TX power, -110 dbm RX sensitivity User-defined protocol (e.g.

8 Attitude Determination Systems Common attitude determination systems applied to small satellites: solar cells (low accuracy if used for power generation) sun sensors (good accuracy but not available in eclipse) star trackers (big optics needed) magnetic field sensors (low accuracy, subject to disturbances from satellite subsystems) GPS sensors (complex hardware) IAC-09.C1.6.9 D. Roascio, L.M. Reyneri, C. Sansoé, M. Bruno Politecnico di Torino 8/17

trackers (big optics needed) magnetic field sensors (low accuracy, subject to disturbances from satellite

9 RF tracking Techniques for object tracking with RF signals are well known in radar systems: simultaneous lobing monopulse radars: the reflected pulse is received by two antennas and is combined with an interference network at RF level to obtain ΔAz and ΔEl the interference network is narrowband and increases complexity in the RF stage phase comparison monopulse radars: the reflected pulse is received by two antenna and an actual measurement of the phase difference is used to obtain ΔAz and ΔEl IAC-09.C1.6.9 D. Roascio, L.M. Reyneri, C. Sansoé, M. Bruno Politecnico di Torino 9/17

narrowband and increases complexity in the RF stage phase comparison monopulse radars: the reflected pulse is received by two antenna and an

10 Phase Measurement This approach allows to use the existing antenna and COTS components Phase shift (R d): Δφ = 180 (multi-cycle delays not considered): d = λ/2 Δθ = 90 d 7 cm Δθ 63 IAC-09.C1.6.9 D. Roascio, L.M. Reyneri, C. Sansoé, M. Bruno Politecnico di Torino 10/17

delays not considered): d = λ/2 Δθ = 90 d 7 cm Δθ 63 IAC-09.C1.6.9 D.

Patch radiation pattern Observable Δθ also limited by patches radiation pattern Cavity model: L λ g /2, ε r = 2.

11 Patch radiation pattern Observable Δθ also limited by patches radiation pattern Cavity model: L λ g /2, ε r = θ = 60 G E -3 db, G H -7 db G H = -3 db Δθ 41 IAC-09.C1.6.9 D. Roascio, L.M. Reyneri, C. Sansoé, M. Bruno Politecnico di Torino 11/17

94: @ θ = 60 G E -3 db, G H -7 db G H = -3 db Δθ 41 IAC-09.C1.

12 RF splitting Signals from antennas are split with hybrid power dividers Phasing section applies proper delay to antenna feeds to obtain the desired beam Coupling factor < -3 db to avoid waste of power in transmission Measurement system works in parallel with and independently of existing transceivers IAC-09.C1.6.9 D. Roascio, L.M. Reyneri, C. Sansoé, M. Bruno Politecnico di Torino 12/17

of power in transmission Measurement system works in parallel with and independently of existing

13 Phase Measuring Receiver (I) S-band signal, FSK, up to 500 kbps. Different techniques can be used to measure phase shifts: Interference approach implies sums and differences with hybrid circuits frequency specific, poor noise rejection Active shifting at RF level with programmable phase shifters may indirectly provide a measurement and also apply some degree of beam steering requires ad-hoc RF components, added complexity The signals are then downconverted for processing at lower frequencies (retaining their relative phase.) IAC-09.C1.6.9 D. Roascio, L.M. Reyneri, C. Sansoé, M. Bruno Politecnico di Torino 13/17

noise rejection Active shifting at RF level with programmable phase shifters may indirectly provide a measurement and also apply some degree of beam

14 Phase Measuring Receiver (II) Common superheterodyne structure (good interfering signals resilience, easily tunable.) How to measure phase shifts? PLL loop locked on first signal (reference), phase detectors (PFD) provide phase evaluation directly at IF level. With proper PLL loop filter, the system keeps working also with modulated data. COTS components (-90 dbm sensitivity, 3 db NF, incl. losses.) IAC-09.C1.6.9 D. Roascio, L.M. Reyneri, C. Sansoé, M. Bruno Politecnico di Torino 14/17

PLL loop locked on first signal (reference), phase detectors (PFD) provide phase evaluation directly at IF level.

15 Antennas Considerations Antenna arrays usually not desirable in small satellites (higher gain useless if tumbling or without ground station tracking) Other solutions possible higher gain at horizon, lower gain at zenith: 2 2 array + out-of-phase center element not compatible with the AraMiS architecture double 2 2 array (8 patches ring) leaves room for the center hole good simmetry (circular polarization) 6 dbi directivity at θ = 45 IAC-09.C1.6.9 D. Roascio, L.M. Reyneri, C. Sansoé, M. Bruno Politecnico di Torino 15/17

element not compatible with the AraMiS architecture double 2 2 array (8 patches ring) leaves room for the center hole good

16 Conclusions The RF tracking methods used historically in radars can be applied with COTS components to the AraMiS architecture and to small satellites in general. Unlike radars, the control on the test signal in satellites is quite limited. This lead us to a downconverting system stronger to interfering signals. The proposed system remains totally independent from existing transceivers and will also work with modulated signals. Simulation of the overall accuracy is difficult since it will be set by the circuit non-linearities (jitters, PFDs, IMP, etc.) Actual performances of the attitude determination system are being evaluated on the first prototypes. The RF carrier phase tracking system should be able to fill the gap between coarse solar cell systems and accurate sun/star trackers. Without additional structural requirements other than the ones already present for antennas. IAC-09.C1.6.9 D. Roascio, L.M. Reyneri, C. Sansoé, M. Bruno Politecnico di Torino 16/17

The proposed system remains totally independent from existing transceivers and will also work with modulated signals.

17 Thank You For Your Attention! Questions? IAC-09.C1.6.9 D. Roascio, L.M. Reyneri, C. Sansoé, M. Bruno Politecnico di Torino 17/17

C-S TEAM. Page 1 of 5

C-S TEAM. Page 1 of 5 Title: Medium/large vehicle tracking system Primary POC: Jacoba Auret Organization: C-S Team (Cape Peninsula University of Technology-Stellenbosch University) POC email: 14807599@sun.ac.za Need We exist