Attitude Determination and Control Subsystem

Star Tracker

(Power Conditioning Unit)

The Star Tracker is a robust and modular opto-electronic sensor compatible with different space orbits. Thanks to it's modular structure, it satisfies attitude determination needs of different Attittude and Orbit Control Systems (AOCS).

stars img 2

Star Tracker Features

Key Features

  • 1 electronic unit can be connected to up to 3 optical units via the fast SpaceWire interface
  • HAS-2 CMOS APS sensor with thermo-electric cooler (TEC)
  • Electronic unit embedded software capable of processing multi-optical unit data
  • Electronic unit embedded software with autonomous orientation acquisition, tracking algorithms and star catalog
  • Delivery of the fused attitude quaternion to the flight computer

Optical Unit Features

Spherical lenses, rad-hard glass material
70 mm focal length, f/1.4
15 x 15 degree field of view
Light curtain protecting the sensor from unwanted light (from the Sun and Earth)
Radiation tolerant APS CMOS HAS-2 sensor, 1.024 x 1.024 sensor resolution

Optical Unit Budgets

Supply: Power supply is provided through the electronic unit.
Power Power supply is provided through the electronic unit.
Size: 159 mm x 130 mm x 343mm (W x L x H)
Weight: 3 kg

Electronic Unit Features

Dual Core, High Reliable LEON3FT Based Microprocessor
RTEMS Real Time Operating System
CCSDS and ESCC Compatible TM-TC
Bootloader, Drivers and Board Support Packages, Star Tracker Software
8 MB SRAM, 256 MB SDRAM, 2 MB PROM (All ECC protected)

Electronic Unit Budgets

Supply: 28V nominal (16V - 40V Input voltage range)
Power: 20W (nominal)
Dimensions: 308 mm x 279 mm x 148 mm (W x L x H)
Mass: 7.3 kg

Optical Unit Interfaces

3 x 2 SpaceWire
3 x 2 Power and Time Synchronization Interface (RS-422)

Electronic Unit Interfaces

Bus: 2 x 2 CAN
2 x 1 JTAG
Synchronization : 2 x 2 PPS Input (RS-422)
Power Interface : 2 x 2 Main Power Input

Heritage / Platforms


Environments / Reliability

Thermal:-20 to +50 C
Lifetime: 5 to 15 years
SEU tolerant
Latchup Immune

Sun Sensor

(Power Conditioning Unit)

The Sun Sensor is an instrument to detect the position of the Sun to be used for attitude control in satellites. They are especially important during the launch and early orbit phase, emergency cases and in case attitude determination sensors like star trackers does not operate correctly.

The Sun Sensors make use of various analog or digital detectors to indicate the Sun angle vector typically with low accuracy. Our domestically developed the Sun Sensor is a fully digital, high-performant, high accuracy instrument that is tolerant to harsh environmental conditions.


Sun Sensor Features

Key Features

  • FPGA-based and radiation-resistant electronic processing unit
  • High resolution radiation tolerant CMOS detector
  • ±64° field of view in two axes
  • High precision Sun vector estimation with 0.1º angular resolution
  • In-house developed optical design and digital algorithm using expanded grid
  • 5 Hz output frequency
  • Domestically produced optics (OPMER)

Reliability and Fault Detection, Isolation and Recovery Features

Electronical processing unit with high reliability
Internal Temperature Monitoring
Internal Current and Voltage Monitoring
Redundant data bus
FDIR enabled algorithm


Supply: 28V (IMECE), 100V (TURKSAT 6A)
Power: 3.2 W (IMECE); 3.7 W (TURKSAT 6A)
Size: 100 x 100 x 40 mm (IMECE), 124 x 106 x 42 mm (TURKSAT 6A)
Weight: 550 g (IMECE), 800 g (TURKSAT 6A)


TM-TC : 2 x CAN ISO (warm redundant)
Pin redundant power interface

Heritage / Platforms


Environments / Reliability

Thermal:-20 to +50 C
Lifetime: 5 to 15 years
SEU tolerant
Latchup Immune

Global Positioning System

(Power Conditioning Unit)

The receiver is designed such that it can receive and process GPS L1, L2 and L5 and GALILEO E1 and E5a signals. It utilizes 36 channels that can be activated simultaneously to support multi-constellation and/or multi-frequency applications. It is qualified with both on-ground qualification tests according to ECSS and has been flown on a high-resolution Earth observation satellite in LEO. The general features and specifications of the receiver are given in the following table where position and velocity accuracy are provided in 90% spherical error probable (SEP).

GPS Features

Parameter Value
Position Accuracy (m, % 90 SEP) < 10
Speed Accuracy (m/sec, % 90 SEP) < 0,01
Time Accuracy (nsec) < 500
PVT Solution Algorithms Least Squares, Kalman Filter (Main)
Full Convergence After Cold Start < 1.5 Orbits
Possible GNSS Signals GPS L1 C/A, L2C, L5 I/Q
Total Channel Number 36
Measurement Data from Each Channel Code Phase, Carrier Phase, Pseudorange, Doppler, C/N0
Solution Performance Data GDOP, Number of Satellites
Configuration 2 x Antennas (Ant.) 2 x LNAs 1 x Electronic Unit (EU)
Effective Antenna Field of View (°) 140
Minimum Visible Satellites in LEO 4
Mass (kg) Antenna: 0.5
LNA: 0.1
EU: 3.8
Dimensions (mm) Antenna < Φ 165, 70
LNA < 55 x 40 x 20
EU < 300 x 300 x 100
Input Voltage (V) 28 ± 5
Max. Power Consumption (W) < 15
Data Interface MIL-STD-1553
PPS Interface RS422
Other Features An embedded radiation dosimeter is available

Reaction Wheel

(Power Conditioning Unit)

Reaction Wheels are momentum changing components, which are comprised of a high inertia rotor (flywheel) coupled to an electric motor and are used for the precision control of attitude and stabilization of satellites. Reaction Wheels must not only provide the precise attitude control but also operate almost without interruption during the satellite's lifetime. Therefore, the lifetime of the the spacecraft generally depends on the performance of the reaction wheels. Usually, four Reaction Wheels (for redundancy purposes) are required to control the spacecraft in 3-axis.
Orientation control and stability in three axes can be achieved by using multiple (usually 4, at least 3) Reaction Wheels.

The Reaction Wheel, developed by TUBİTAK UZAY, provides satisfying performance in terms of momentum storage, torque, and wheel speed measurement, as well as zero-crossing and micro-vibration features.

reaction wheel img 1

Reaction Wheel Specifications

The Reaction Wheel comprises two units: 1) Electrical Unit and 2) a Mechanical Unit. The main features of the Reaction Wheels are:

  • Angulan momentum storage >15Nms,
  • Reaction Torque > 200 mNm,
  • Total mass 8.5 kg.


  • İMECE : 1 Structural Thermal Qualification Model , 1 Qualification Model, 1 Flight Model
  • TURKSAT 6A: 1 Structural Thermal Qualification Model, 1 Qualification Test Model, 1 Engineering Model, 1 Flight Model
  • AYAP -1 Lunar Research Project: 1 Structural Thermal Qualification Model , 1 Qualification Model, 4 Flight Model
Features Unit Remarks
Reaction Torque 250 mNm
Angular Momentum Storage 15 Nms @ 4000 rpm
Speed range ± 4000 rpm
Nominal Voltage (LEO) 28 V (23 -35 V)
Nominal Voltage (GEO) 100 V (95-105 V)
Interface CAN 20 Hz TM/TC interface
Mass 8.5 kg Total for Wheel Unit and Electronics Drive Unit
Protection Features Overspeed, Over Current, Over/Under Voltage, Over Temperature
Lifetime 7 years (LEO), 15 years (GEO)
Stand-by Power Consumption < 10W
Highest Power Consumption < 125 W
Operating Temperature '-20 C / 50 C