Unmanned Systems Technology 006 | ECA Inspector Mk2 USV | Antenna systems | Northwest UAV NW-44 | Unmanned ground vehicles | Navigation systems | Lunar X challenge

68 boards as surface-mount components for ease of manufacture, and multi-GNSS modules with integral antennas can be made very small, the smallest measuring 10 x 10 x 5.9 mm and weighing 2.5 g. The latest multi-GNSS processors at the heart of such navigation modules use a system-on-chip architecture known as wafer-level chip-scale packages. They typically integrate a GNSS radio, a GNSS engine, a power management unit, a phase-locked loop frequency synthesiser and an auxiliary subsystem on a CMOS die. The GNSS radio provides a single input and dedicated receive paths for GPS, GLONASS and other GNSS signals, while a state-of-the-art GNSS engine, for example, consists of a navigation subsystem and a measurement subsystem. The navigation subsystem in turn consists of an ARM CPU that calculates the position, velocity and time solution, with memory in both ROM and RAM form, along with host interfaces such as UART, SPI and I2C, and drivers for them. The measurement subsystem contains a digital signal processor, also with ROM and RAM chips. Navigation subsystems that combine multi-signal, multi-GNSS receivers and inertial sensors are likely to prove popular with engineers looking to make mapping from small UAVs more efficient – especially in the absence of satellite signals – as well as less expensive. For example, a new generation of compact Lidar sensors capable of generating high-resolution 3D maps is opening up new markets, but operators need accurate geo-referencing for them and want to reduce the need for pre- surveyed ground control points – or preferably eliminate them altogether – to reduce the need for lateral overlap (sidelap) that must be flown to ensure there are no gaps in coverage. One approach is to integrate a precision differential GNSS receiver and MEMS inertial sensors onto a single- board module and provide software that can compensate for errors in the MEMS inertial units before fusing them to provide a final solution. Such a solution, augmenting the MEMS inertial sensors with GNSS-derived correction data, enables survey-grade position and orientation information to be derived from low-cost systems, and post- processing software can boost accuracy further. This combination of sensors also provides very accurate orientation measurement and real-time kinematic (RTK) positioning to enable UAVs to make precision landings. (RTK uses measurements of the phase of the signal’s carrier wave and relies on a reference station or a network of them to transmit real-time corrections over a radio link between base station and mobile receiver, potentially achieving centimetre-level accuracy.) Using the SPS, such systems are claimed to achieve positional accuracies of between 1.5 and 3 m, improving to 0.5-2.0 m with differential GPS (DGPS) augmentation and to between 0.02 and 0.05 m with RTK or post-processing. In terms of velocity measurement, the accuracy is 0.05 m/s with SPS – with or without DGPS – February/March 2016 | Unmanned Systems Technology Hemispherical resonator gyros have proven extremely reliable in spacecraft applications, thanks in part to a lack of moving parts to wear out (Courtesy of Northrop Grumman) This GNSS module has an integrated antenna and is the smallest such module so far, according to the manufacturer (Courtesy of Origin GPS)