Unmanned Systems Technology 011 | C-Astral Bramor ppX | IMUs | Autonomous farming | UAV Turbines UTP50R | London Show report | Advanced materials | Las Vegas Expo report

26 Dossier | C-Astral Bramor ppX Gen4 cells are 30% lighter than its Gen3 counterparts, and weigh just 170 g/m 2 before encapsulation, boosting the power- to-weight ratio from 1.4 to 2.3 kW/kg. The LRS variant will feature Gen4 panels. Launch and recovery The standard catapult offered with the Bramor ppX is an elastic-powered device with a hand winch, but a pneumatic alternative is also available as an option. This is recommended for cold weather operations down to -40 C, and includes a compressor and an electronically controlled valve. Both catapults have a lightweight folding aluminium structure. As well as the parachute deployment system, C-Astral also developed the parachute itself, with a circular canopy made from a lighter grade of the same material used for manned chutes. Most operators can ensure that the UAV touches down within 30 m of the ground control station, although greater accuracy can be achieved with practice. Explaining C-Astral’s thinking behind in-house parachute development, Trost says, “In 2006, when we started, there was absolutely nothing on the market, plus we like to test things by ourselves in real scenarios. Of course weight is the main driver, and our engineers are good at doing this stuff.” Flight control and navigation The autopilot is a joint development between Lockheed Martin Procerus and C-Astral, and is based on Kestrel 2 hardware, with the software written by C-Astral. The effort took several years, with a focus on complete integration of the imaging sensors with the flight control system to ensure that the vehicle always follows a flight path that puts the sensor field of view over the area the operator wants to survey. Altitude is measured simultaneously by a static pressure sensor and the GNSS, while a digital terrain model – a virtual landscape, Aster GDEM 2, programmed into the navigation system – provides an estimated distance to the ground. The survey-grade GNSS comes from Septentrio, with whom C-Astral has a close working relationship. Septentrio’s AsteRx-m GNSS receiver for UAVs offers centimetric RTK precision with or without a real-time data link, features camera shutter synchronisation and low and scalable power consumption. AsteRx-m is built around the GReCo3 GNSS chip set running Septentrio’s own ‘GNSS+’ algorithms that calculate the receiver’s position in three dimensions from multiple satellite signals. It supports the L1 and L2 signals broadcast by both GPS and GLONASS spacecraft, and includes three channels for satellite- based augmentation system tracking, so it can make use of corrections provided by the EGNOS, WAAS, GAGAN, MSAS and SDCM systems. A total of 132 hardware channels support simultaneous tracking of all the visible satellites in both constellations. Also among Septentrio’s suite of proprietary algorithms are LOCK+, which maintains satellite tracking during heavy vibration or turbulence, and IONO+, which compensates for disturbances to the signal caused by conditions in the ionosphere. To deal with the multipath problem created by reflections of the satellite signals from buildings and the like, AsteRx-m uses an advanced A-posteriori multipath estimator technique that includes both code- and phase-based mitigation schemes. To detect errors in signals from individual satellites so that it can either exclude them or compensate for them, AsteRx-m includes receiver-autonomous integrity monitoring technology that uses redundant signals – any above the minimum number needed to work out the receiver’s position – to calculate multiple pseudo-ranges, and then applies a statistical function to determine whether a fault can be associated with a particular signal. AsteRx-m achieves its centimetre-level RTK accuracy while consuming less than 600 mW of power using GPS alone and less than 700 mW with both GPS and GLONASS. To simplify the AsteRx-m’s integration into the UAV, Septentrio enables direct connection to the autopilot, while the receiver’s 6-30 V power conditioning circuitry enables it to run directly from the vehicle’s electrical bus, and an event marker is provided to synchronise a camera shutter with GNSS time – another touch to ensure imagery includes accurate time and position. As an option, the AsteRx-m can be supplemented by a survey-grade inertial measurement unit (IMU), such as the VN- 300 from VectorNav. This has an onboard extended Kalman filter running at 400 Hz December/January 2017 | Unmanned Systems Technology Supplied with a rugged tablet computer, the Pilot C3P software allows the operator to plan a mission quickly with just tap-and-pinch gestures on the screen