Motivation

Navigation systems play an important role in aerospace, in seafaring, in autonomous mobility and in navigation devices for both smartphones and cars. The STARS Laboratory (Laboratory for Sensor Testing and Assessment on a Rotation Simulator) supports the development of highly accurate navigation systems.

The development of a navigation system can be separated into different phases, starting from the requirements definition to the final tests. In the early phases of the development, Software-in-the-Loop Tests (SiL Tests) are used. They allow to adapt the filter algorithm and to verify the performance of the navigation system. An important part of the SiL Test is the mathematical model of the sensors. One task of the GPS/INS Test- and Verification Laboratory is the exact characterization of the sensors. This data provides the foundation for the mathematical sensor model used in the simulations, which turns into a higher accuracy of the navigation solutions.

Later in the development, the simulated sensor data will be exchanged with the real sensor data to verify the performance of the navigation system. These tests are called Hardware-in-the-Loop Tests (HiL Tests). To support the SiL and HiL Tests, the GPS/INS Test- and Verification Facility was build. The lab may also be made available for external customers.

The Laboratory

The laboratory is operated by the Department of Guidance, Navigation and Control Systems at the DLR Institute of Space Systems. One of the duties of the department is to design and build navigation systems for spacecrafts. These systems often consist of several accelerometers and gyroscopes which are combined to an inertial measurement unit (IMU); additional sensors (e.g. GPS receivers, star trackers and/or Sun sensors) can be included as well. The characterization of the sensors as well as the determination of mathematical models for the sensors are key-tasks of the laboratory. These models are used in the SiL Tests to create a realistic simulation. The real sensor data is used in the HiL Tests to verify the results from the SiL Tests. For HiL testing, the laboratory offers the possibility of stimulating the sensors using the equipment listed below.

Description of the Equipment

Rotation table ACUTRONIC AC3347

Rotation table with Rocket Mount Unit (RMU)

The rotation table in combination with the real time system, provided by the company dSPACE, is used for the stimulation of the different sensors. Through this combination, it is possible to move the sensor using programmed positions, rotation rates or trajectories in real time and collect the synchronized data of the rotation table and sensor. This setup can be used to characterize gyroscopes, accelerometers or IMUs as well as provide measurements for Hardware-in-the-Loop Tests. A set of large doors can be opened to allow an unobstructed view of the night sky for the verification of star trackers.

Specification of the rotation table:

• Continuing rotation around three axes with max. 1000 °/s
• Max. rotational speed acceleration between 400 and 30000 °/s²
• Orthogonality errors of the axes < 3 arc seconds
• Position accuracy < 3 arc seconds
• Position resolution 0.00001 °
• Rotational speed solution 0.0001 °/s
• Temperature stabilization through climate chamber with CO2 cooling between -50 °C and +80 °C
• Connection over SCRAMNet+ to the real time simulation platform dSPACE
• 450 mm diameter of inner rotary plate
• 15 kg specified test object mass (other masses possible)
• GPS antenna line and other electric connections on the rotary plate

GPS Simulator Spirent GSS 7700

The GPS simulator offers the possibility to test GPS receivers. Additionally, by connecting the GPS simulator to the real-time system and the rotation table, it is possible to test more complex systems.

Specification of the GPS simulator:

• 4-32 channels
• GPS L1 supports C/A + P Code + M-Noise
• GPS L2 supports C/A or p Code + L2C + M-Noise
• GPS L5 supports L5 I and L5 Q
• Complete flexibility through SimGEN software
• Real time remote control and simulated flight path for hardware-in-the-loop testing
• Output of different RF signals L1/L2
• Interference of up to 16 channels on L1 band

Sun Simulator neonsee

Sun simulator with collimation camera on the rotation table

The sun simulator can be used in combination with the rotation table to test and characterize Sun sensors.

Specification of the Sun simulator:

• Usable illumination field: 200 x 200 mm
• Adjustable collimation angle from 0.368 ° (Venus) to 0.051 ° (Jupiter)
• Adjustable irradiance from 1780 W/m² to 162 W/m² with a specified spectrum or down to 2.5 W/m² without a specified spectrum

Possible Services

• Characterization of gyroscopes inside a thermal chamber and determination of the sensor characteristics according to the IEEE Standard
• Characterization of accelerometers inside a thermal chamber and determination of the sensor characteristics according to the IEEE Standard
• Characterization of inertial measurement units (IMUs) inside a thermal chamber and determination of the sensor characteristics according to the IEEE Standard
• Characterization of Sun sensors with an AM0 spectrum and different collimation angles and irradiance levels
• Test and calibration of GPS receivers
• Flight path simulation for gyroscopes and GPS receivers using pre-set trajectories
• Hardware-in-the-loop tests via a real time capable dSPACE system
• Thermal testing between -50 °C and +80 °C
• Characterization of angle and inclination measurement systems