CNES’s CESARS Center Makes Access to Satellite Communication Easier
The CNES, also called the National Center for Space Studies, is a French agency dedicated to space studies which operates under the supervision of both the Ministries of Economy, Defense and Research. One of its missions is to develop and present the French Spatial Program to the national government and to execute it. The CNES focuses on 5 strategic areas: Ariane (Launchers), Sciences, Observation, Telecommunications, and Defense. The CNES created the center CESARS in order to spread and increase the usage of Satcom in any new kind of application. CESARS welcomes freely companies, laboratories, collectivities, to give them advice, feedback on technologies, assist them by performing tests, and giving access to the technical platform in itself, including the hardware.
A Combined Solution for Enhanced Real-Time Control for UAV Navigation
Before going through with a project, the team working in the center CESARS usually runs tests on ground to check and verify the equipment. Here, the goal was to confirm the compatibility between Cobham’s AVIATOR UAV 200 and SBG Systems’ Ellipse-D Inertial Navigation System.
Ellipse-D is a miniature Dual-Antenna Inertial Navigation Systems that provides highly accurate navigation and orientation data even in the most challenging environments. Like all SBG’s sensors, this INS/GNSS is extensively tested and calibrated from -40°C to 85°C to ensure optimal performance.
The AVIATOR UAV 200 is a compact all-in-one Satcom terminal (antenna + modem included) that fits in a small UAV. It allows the connection between a UAV and a satellite, which acts as an intermediary between the UAV and the ground control. Cobham’s solution may be used to send information, such as videos, at a very low data rate (200kbps), from the UAV to the ground control. The AVIATOR UAV 200 enables the UAV to fly longer and further away from the control room via BLOS (Beyond Line of Sight) communication.
How do they work together?
The inertial sensor sends roll, pitch, yaw, heading, and position inputs to the AVIATOR UAV 200. These data are then used to steer the AVIATOR UAV 200’s antenna beam towards a telecommunication satellite, and continuously and precisely track it, to maintain an optimal data transmission. The more accurate the antenna pointing is, the more stable the satellite link will be.
Thanks to its dual antenna GNSS receiver, the Ellipse-D is able to provide a precise and reliable heading at start time, which is critical for this kind of applications. During the flight, the Inertial Navigation System will provide the UAV motion and position information to help the AVIATOR UAV 200 to adjust and keep the link with the satellite. In case of spoofing, the INS will help maintaining a robust heading thanks to the Extended Kalman Filter.
Stationary and OTM (On-The-Move) Tests in Ground Configuration
In October 2020, the CNES conducted a few tests within the CST (Toulouse Space Center).
First, the hardware and software were taken in hand in the laboratory. The hardware was then integrated into the Oscar truck (OSCAR is a “mobile laboratory” on which OTM antennas are set and tested, on the roads). After checking that it was working properly in stationary mode, OTM tests inside the CNES were run to attest the compatibility between the inertial sensor and the terminal.
Configuration of the Equipment
During the test in stationary mode in the laboratory, the CNES used the sbgcenter software that comes with the Ellipse-D INS/GNSS to configure the equipment to best fit their application. This software provides different motion profiles to adjust the Extended Kalman Filter parameter and deliver the best performance for the conditions of use.
Chosen settings on sbgcenter software:
- Profile choice: “general purpose”. It was the most suitable for the behavior of the Oscar truck. For an integration on a UAV, a UAV profile must be chosen.
- Configuration of the 2 GNSS antennas: must be at more than 45 cm from the Cobham terminal, and in a similar “environment” (close enough, no obstacles between them, must undergo the same dynamics).
- Alignment of the vehicle in relation to the control unit entered (in our case they are oriented along the same axis).
- If other sensors are placed on the carrier, they can be entered too (pitot tube, accelerometer…).
- The com port A of the Ellipse-D (the “main”) is connected to the PC to visualize the information received on the sbgcenter. Port E is connected to the Cobham terminal. Both are configured at 115200 bauds.
- As far as the data output is concerned, the transmission frequency of the AT_ITINS messages must be at 50Hz maximum.
Integration and OTM Test
Two “On-The-Move” tests were conducted on the same circuit. The test circuit includes straight lines and traffic circles and the maximum speed to complete it was 30km/H.
The first test revealed that settings adjustments were necessary, especially the transmission frequency which was set too high.
During the second test the connection was stable, even when changing direction, validating the settings. The ping passed correctly, and the longest latencies observed are those following a passage near a building (possible masking of the LOS). On the Aviator UAV 200 interface, everything worked (signal level >50dbHz, GPS fix).
By recording the test sessions, the sequences can be replayed on the sbgcenter through different options:
- Position view: It shows a figure with animations where you can follow the vehicle’s path.
- Cockpit View: A graphical user interface with visualization of the carrier’s attitude data.
After all those tests, CNES’ Cesars center team came to the conclusion that SBG Systems’ Ellipse-D Inertial Navigation System is compatible with Cobham’s AVIATOR UAV 200 terminal, in a “ground” configuration. This conclusive test brings a wide panel of opportunities to UAV users.