ResQu Revisited

ResQu Revisited

Project ResQu, which concluded in 2014, comprised four project streams designed to bridge the gaps between research, industry implementation, and public uptake.

Two key areas of the project were the migration of the DAA system, first developed in Smart Skies for a Cessna-scale platform, to the 20 kilogram ScanEagle UAS, as well as the development of an Automated Emergency Landing System (AELS). The AELS could enable the safe operation of the UAV over populated areas in the event of a failure such as communication breakdown or engine failure.ResQu 1

Dr. Dmitry Bratanov, research engineer with ARCAA, joined the Project ResQu engineering team in 2013 to support the DAA advancement for UAS. The DAA migration effort included the selection, design, and integration of new hardware, algorithm, and software optimization, as well as the comprehensive testing of the integrated system.

Two other streams were also part of Project ResQu, although not part of this article. These streams included the development of an unmanned aircraft system for performing Miconia weed surveys (led by CSIRO) and a focus on appropriate regulations to provide assurances for safe UAS operations (lead by BR&T-Australia and QUT).

Downsized and Optimized

Clearly, a critical component of the safe use of UAS in controlled and uncontrolled, or unsegregated, airspace is reliable DAA technology.

The existing DAA technology used on ARCAA’s Cessna 172R (the ASL) relied on the IMU-FSAS, a tactical grade inertial measurement unit from iMAR GmbH. As part of the aircraft’s GNSS/INS positioning technology, the IMU-FSAS forms an extremely accurate, integrated positioning system. However, the IMU weighs more than two kilograms; not ideal for this application.

Bratanov says, “The role of the IMU in DAA is crucial for intruder detection. The IMU data is used initially to compensate for aircraft motion in real-time; then an advanced temporal and spatial filtering is in charge of detection and tracking of targets. We needed an iMAR-like capability but at much lighter weight, size, and power.”

As part of the IMU selection process, the research team conducted a comprehensive trade study of currently available products that might meet the size, weight, power, and cost requirements with comparable iMAR capabilities for the UAS market. Apart from specific accuracy criteria essential for the DAA, the team sought a system that could provide operational robustness and interoperability for the onboard system of a highly dynamic UAV.

Throughout the study, the Project ResQu team flight-tested a number of solutions, including the system they selected: a NovAtel OEM615 dual-frequency, SPAN®, RTK capable GNSS receiver along with Analog Devices ADIS 16488 microelectromechanical system (MEMS) IMU.

The ADIS 16488 IMU features low noise gyros and accelerometers in a small, lightweight, environmentally sealed enclosure. When integrated with NovAtel’s SPAN technology, it enables precision measurements for applications that require low cost, high performance, and rugged durability in a very small form factor.

With tightly coupled SPAN integration, NovAtel is able to provide a low cost, lightweight MEMS solution to achieve superior positioning performance in open sky situations.

Traditionally, accurate navigation using inertial technology was only possible with high-end ring-laser or fiber optic gyroscope technology. New applications are increasingly requiring smaller, lighter and more cost effective solutions for use on smaller vehicles or within sensor assemblies. MEMS technology has improved dramatically over the last few years to answer this need. Compared to their higher grade counterparts, MEMS sensors have relatively large error characteristics that need to be accurately estimated before they can be used in a navigation solution. Key error sources include bias, bias instability, scale factor, and angular or velocity random walk errors. Using a tightly–coupled approach, NovAtel is able to effectively estimate these errors and provide an accurate position, velocity, and attitude solution.

“Compared to other solutions tested during the initial study, the NovAtel SPAN-ADIS solution was the best performer for our particular requirements,” said Bratanov.

The team also used NovAtel’s Waypoint® Inertial Explorer® for reconstruction of the most accurate solution by processing airborne and ground data in differential mode. Waypoint’s Inertial Explorer maximizes the performance of GNSS/INS hardware by ensuring position, velocity, and attitude accuracy.

The tightly–coupled integration of GNSS and IMU data delivers precise results, even when lower grade inertial sensors are used. “Waypoint provided valuable reference data to evaluate required and demonstrated real-time capabilities,” Bratanov said. “The technology provided us with a critical functionality for the range of applications that we’re considering.”