A parallel evolution is also being experienced in the civil/military Air Traffic Management (ATM) field, where the extensive introduction of advanced Communication, Navigation and Surveillance (CNS) technologies, including digital data links, satellite services and Automatic Dependent Surveillance–Broadcast (ADS-B) is supporting the transition to the Next Generation Air Transportation System (NextGen). However, the international aviation community (both civil and military) is now facing important technological and operational challenges to allow a proper development and deployment of the CNS/ATM and Avionics (CNS+A) innovations announced by the US NextGen, the European SESAR (Single European Sky ATM Research) and other programs such as CARATS (Collaborative Actions for Renovation of Air Traffic Systems) in Japan and OneSky in Australia. In particular, it is essential to address global harmonisation issues and to develop a cohesive certification framework for future CNS+A systems simultaneously addressing safety, security and interoperability requirements. Important research efforts are also necessary to demonstrate the feasibility of avionics and ATM technologies capable of contributing to the emission reduction targets set by ICAO, national governments and various large-scale international research initiatives. Therefore, a growing emphasis is now being placed on environmental performance enhancements, focusing on Air Traffic Flow Management (ATFM), aircraft trajectory optimisation, airport operations and dynamic airspace management technology enablers including, in a near future, urban environments.
Another major area of current research in the CNS+A context is addressing the development of UAS Traffic Management (UTM) technologies and the associated regulatory framework to allow unrestricted access of UAS to all classes of airspace, including very low-level and Beyond-Line-of-Sight (BLoS) operations. Recent developments in communications, navigation and Sense-and-Avoid (SAA) technology are progressively supporting UAS operations in medium-to-high density operational environments, including urban environments.
In addition to CNS+A technologies for air operations, space cyber-physical systems are also being researched for a wide range of practical applications including near-Earth commercial satellites, space transport/tourism, and interplanetary scientific missions. In this context, it is anticipated that economically viable and reliable cyber-physical systems will play a fundamental role in the successful development of the space sector and significant research efforts are needed in the field of reusable space transportation systems, Space Traffic Management (STM), and Smart Satellite Systems (SmartSat).
Based on these premises, our current research efforts in Avionics, CNS/ATM and Space Systems (ACASS) are focussing on the following key topics:
- Future Air Traffic Management Systems
- Intelligent Navigation and Guidance Systems
- Adaptive Sensor Networks and Multisensor Fusion
- UAS Traffic Management and Urban Air Mobility
- BLoS Communications and Surveillance
- Integrated Vehicle Health Monitoring Systems
- Space Transport and Smart Satellite Systems
- Space Stuational Awareness and Space Traffic Management
Air Traffic Management Systems
NextGen is intended to meet the air transportation needs of the US in the 21st century – in particular, a significant growth in demand for air traffic services, possibly on the order of three times today’s demand levels. Similar challenging objectives are set for the European SESAR program, which is also focusing on ATM fragmentation issues more severe in the European Air Space. With both R&D programs under way, it is fundamenotal to make clear how the enabling technologies will be deployed in the two continents in the near and mid-terms, and where the main synergies and differences lie between the European SESAR and US NextGen ATM programs. There are significant (technical, operational and legal) challenges for the NextGen and SESAR deployments, and to allow harmonization and integration of the two programs into the Global ATM Framework. Coordination is also fundamental between SEASAR/NextGen and other national/regional ATM modernisation initiatives (e.g., OneSky in Australia and CARATS in Japan). This will include exchange of results, simulations tools and research methodologies, to allow a proper integration and rapid fruition of the key enabling technologies. This research is focusing on the following topics:
- Communications, Navigation and Surveillance Systems Performance Metrics
- Flow Management, Decentralization and Collaborative Decision Making
- 4D Aircraft Trajectory Optimisation and Time Based Operations
- Performance Based Navigation and Intent Based Operations
- Gate-to-Gate Optimisation Problems for SESAR/NextGen and CleanSky
- Dynamic Airspace Management (Time-Based and 4D)
- ATM Route Planning (ARP) and Flight Management Systems (FMS)
- HMI aspects of 4DT Management in Manned and Unmanned Aerial Vehicles
The objective of our research is to develop innovative technologies which have the potential to be used in the next generations of ATM route planning, strategic/tactical intent negotiation and avionics Flight Management Systems (FMS). Current research projects (supported by various industrial partners) include:
- Harmonization of SESAR and NextGen in the Global CNS/ATM Network
- Next Generation FMS for 4D Trajectory Planning, Monitoring and Negotiation
- Next Generation 4D Route Planning, Negotiation and Validation Systems
- Dynamic Airspace Management (Time-Based and 4D) Models and Software
- Human-Machine Teaming – Cognitive HMI2 (CHMI2) for ATM 4D IBO
- Human-Machine Teaming – CHMI2 for Manned/Unmanned Aircraft 4D IBO
Integrated Multisensor Systems
Military aircraft and UAS are already equipped with ISR sensors (RADAR/LIDAR, SAR/ISAR, VIS/IR/EO sensors, laser rangefinders, etc.), SATCOM, GNSS, a variety of inertial sensors including platform/strap-down Inertial Navigation Systems (INS) and/or low cost MEMS, plus high throughput RF data links (for high data rate applications like free-stream video transmission) and conventional tactical data links for communications with legacy air, ground and see platforms in current network-centric scenarios. Using the information already provided by the on board avionic systems/sensors (i.e., imaging, ranging, velocities, linear and angular accelerations, attitude angles, angular displacement with respect to known reference points and co-operating platforms) will offer significant cost-advantages, allowing the implementation of suitable data fusion algorithms for accurate navigation and real-time platform guidance. The concept of integrated multisensor navigation is no way limited in application to military avionic systems. There is a growing number of civil applications, where information from multiple sensors is combined to improve performance, provide redundancy management, increase robustness, or achieve graceful degradation when sensor failures (or outages) occur. Although the sensor integration possibilities are expanding very rapidly today, this research will focus on integration of GNSS, INS and other sensors, such as RADAR, LIDAR and other Forward Looking Sensors (FLS), which are an important subset of modern aerospace avionic systems.
Flight vehicle operation depends primarily upon accurate and continuous knowledge of vehicular position and attitude. In case of an aircraft, this is required primarily to provide guidance information to the pilot. Similarly, in the case of UAS, continuous and accurate position and attitude data are required to allow platform control. Technical requirements for air navigation systems primarily include accuracy, physical characteristics such as weight and volume, support requirements such as electrical power, and system integrity. One of the most important concepts is to use a multisensor integrated system to cope with the requirements of long/medium range navigation and landing. This would reduce cost, weight/volume and support requirements and, with the appropriate sensors and integration architecture, give increased accuracy and integrity of the overall system. The best candidates for such an integration are indeed the GNSS (and DGNSS) and the INS. The use of barometric altimeter output is also desirable to provide a robust bounding signal to the INS vertical channel and to support platform-level GNSS integrity monitoring functions. Moreover, current RADAR and LIDAR systems can provide accurate ranging (and height) information and high-resolution images which can be used for navigation update, obstacle avoidance and, in military aircraft, for targeting and other applications. The traditional limitations of laser systems (atmospheric propagation and eye-safety) are greatly reduced by state-of-the-art techniques (e.g., multi-source systems, frequency-shifting, etc.). There are still important issues for a laser sensor as an active angle (azimuth, elevation) and range sensor for all-weather applications that need to be investigated. However, in principle, the integration of laser sensors can provide the highly accurate/reliable information required for an effective integration with DGNSS and INS, particularly useful for navigation and landing applications.
In military applications, further possibilities are also offered by Link 16 and other tactical data links. As the current standard for military anti-jam digital communications, Link 16 has been implemented in the JTIDS and MIDS/JTRS terminals. These systems provide Anti-Jam (AJ) communications using Frequency Hop and Pseudo Random Noise (PRN) spreading techniques. As a result, there are accurate time-of-arrival (TOA) measurements between the transmitting terminals. It is therefore important to develop an integrated navigation filter capability, which optimally integrates MIDS/JTRS data with other sensors (e.g., GNSS, INS, FLS), providing a robust navigation solution in GNSS-denied conditions. Based on the above discussion, this research addresses the following challenges:
- FLS and AI/ML for Future Intelligent Navigation Systems
- UAV Navigation and Guidance using On-board C4ISR Sensor Resources
- Data Links and Relative Navigation for Multi-sensor Navigation Systems
- GNSS Integrity Augmentation for Mission- and Safety-critical Applications
Optimal control theory is used today in a wide range of engineering problems. It deals with finding optimal control laws that minimize a certain performance criterion (cost functional) of a dynamic system through mathematical optimisation techniques. The optimisation process involves translating the system (e.g., aircraft or spacecraft) dynamics and its desired objectives into the abstract language of mathematics, which give rise to what is called a control problem, and then to find the solution to this problem. Such a solution is also called optimal control and the path followed by the aircraft/spacecraft to reach the desired goal is called the optimal trajectory. The physical system which is represented by a mathematical model, consists of a set of relations between the system states and its control inputs. Physical restrictions on the control inputs lead to a finite set of admissible inputs or controls. The solution of a control problem is to determine the admissible inputs which generate the desired output and which, in doing so, minimize the cost functional.
Traditionally, optimal control problems were solved using indirect methods, applying the calculus of variations or Pontryagin’s maximum principle to satisfy first-order necessary conditions for optimality. These methods are characterized by explicitly solving the optimality conditions stated in terms of the adjoint differential equations, the maximum principle, and associated boundary conditions. This is practical for classical problems and some special weakly non-linear low dimensional systems. However, to obtain a solution of dynamic systems described by strongly non-linear differential equations, it is necessary to use numerical methods. Even so, these methods suffer from the fact that adding new constraints can require deriving new necessary conditions. Also, in many complex problems, getting the necessary conditions in a useful form can be a very difficult task. As problems became more complex, indirect methods became increasingly harder to use, eventually being replaced by the more computationally intensive direct methods. Direct methods transcribe the continuous optimal control problem into a parameter optimisation problem. Satisfaction of the system equations is accomplished by integrating them stepwise using either implicit or explicit rules; in either case, the effect is to generate non-linear constraint equations that must be satisfied by the parameters, which are the discrete representations of the state and control histories. The problem is thus converted from the original infinite dimensional optimal control problem into a finite Non-Linear Programming (NLP) problem which can be solved using standard NLP solvers.
UAS Developments and Applications
Several research initiatives are currently underway in the US, Europe and Australia to help the FAA, EUROCONTROL and CASA define safety thresholds and develop policies, procedures and systems that would make UAS unrestricted airspace access a reality. Before unrestricted UAS operations become possible in the US, European and Australian airspaces, assurances must be made that they can operate safely. Of the many challenges facing the aviation research community, developing a certifiable Sense and Avoid (SAA) capability for UAS is viewed as one of the most fundamental and yet most elusive tasks to be accomplished. For manned aircraft, one of the basic obligations of the pilot is to “see-and-avoid other aircraft.” The see-and-avoid procedure has the advantage of not relying on any cooperative equipment in the threat aircraft. While see-and-avoid is subject to human limitations, it is proving difficult to develop a practical suite of sensors/systems that can provide anything nearly equivalent to human vision and associated decision making. SAA can be defined as the capability of a UAS to remain well clear from and avoid collisions with other airborne traffic. SAA provides the intended functions of self-separation and collision avoidance as a means of compliance with the regulatory requirements to “see and avoid” compatible with expected behaviour of aircraft operating in the airspace system. From a conceptual point of view the SAA capability performs the following sub-functions:
- Detect – Determine presence of aircraft or other potential hazards
- Track – Estimates position and velocity of intruders based on surveillance reports
- Evaluate – Assess collision risk based on intruder and UA positions and velocities
- Prioritize – Determine which intruder tracks have met a collision risk threshold
- Declare – Decide that action is needed
- Determine Action – Decide on what action is required
- Command – Communicate determination action
- Execute – Respond to the commanded action
Many manned aircraft have transponders that offer cooperative detection by ground-based radar and airborne collision avoidance systems. Existing regulations require the use of a transponder in certain airspace and when operating under instrument flight rules. There is, however, substantial airspace where transponders are not required for operations. There are also many aircraft registered in Australia, in the United States and in Europe without a transponder or an altitude reporting transponder, either because their aircraft cannot support them or their owners elected not to equip. About half of these aircraft do not have electrical systems (e.g., some gliders, balloons, and classic aircraft). These non-cooperative aircraft are largely relegated to flying under visual flight rules and in lower altitude airspace (gliders are an exception), where many small UAS will likely want to fly. Even if UAS could count on all aircraft having transponders, cooperative detection of these transponders based on the TCAS design would require active interrogations and a directional antenna, both of which are likely not practical on a space and power limited small unmanned platform.
Another and perhaps more practical approach to SAA is through the adoption of ADS-B cooperative surveillance. ADS-B can be thought as an electronic beacon that is continually broadcasting position, velocity and ID information for the benefit of any receiver in range. If UAS could rely on all aircraft to have such a beacon, the physics of the SAA detect/track tasks would be reduced to a receiver that decodes the ADS-B messages and a computing system that processes ADS-B surveillance reports in order to allow the other SAA sub-functions (evaluate, prioritize, declare, determine action, command and execute). Conceptually, these sub-functions are applicable to the entire UAS and, therefore, may be allocated to any element within the UAS to include the following:
- Unmanned Aircraft (UA)
- Control station and associated data and communication links
- UAS flight crew (UAS pilot/observer – visual or electronic)
- Associated procedures needed to operate in the airspace
- Equipment needed to manoeuvre the UA
This research is concentrating on these fundamental issues in the attempt to identify sensors, systems and data fusion techniques suitable for current and likely future UAS applications. Additionally, besides addressing SAA problems and current challenges of UAS Integration into the ATM Networks, this research is focusing on the unique aspects of UAS design, verification and certification for global operations including specific issues related with integrated CNS/ATM systems.
Integrated CNS/ATM Systems
To cope with the rapid growth of air traffic in the Asia-Pacific region, the Australian ATM system is evolving into a highly integrated network where civil, military and remotely piloted aircraft will continuously and dynamically share the common airspace in a highly automated and collaborative decision-making environment. To meet the goals of enhanced flight safety, environmental performance and efficiency while simultaneously meeting the demands of future traffic growth, several key policy directions have been identified by the Australian government: robust and integrated planning, adoption of advanced technology, international harmonisation of ATM systems, enhanced regional aviation safety, and environmental impact mitigation. In this context a key strategic priority for Australia is to plan, develop and implement a new ATM platform that meets the future needs of both civil and military aviation, and to enhance ATM business competitiveness by addressing service capability, continuity and environmental sustainability. The OneSKY project focuses on a joint operational system that harmonises Australia’s civil and military ATM systems to provide national solutions replacing or enhancing current systems. With Australian air traffic expected to grow by more substantially in the anticipated life of the new transport aircraft, and with the introduction of new concepts to improve airspace organisation and airport operations, this programme will be a significant milestone in Australian aviation. Research is therefore needed in Australia to develop a new ATM regulatory framework and new systems for dynamic airspace management, free-flight and intent-based operations. This also encompasses the development of innovative methods and algorithms for the dynamic allocation of civil/military airspace resources and of Communication, Navigation, Surveillance and Avionics (CNS+A) technologies enabling the unrestricted access of Remotely Piloted Aerial Systems (RPAS) to commercial airspace.
Ground-based Automatic Dependent Surveillance Broadcast (ADS-B) currently provides nation-wide surveillance coverage, including those vast areas of the Australian continent that are not under primary radar or Secondary Surveillance Radar (SSR) coverage. The Civil Aviation Safety Authority (CASA) has approved radar-like separation standards for tracks under ADS-B surveillance and issued the first ADS-B fitment mandate in December 2013. A Receiver Autonomous Integrity Monitoring (RAIM) system enables controllers to anticipate and plan for a reversion to procedural separation if a GPS outage is predicted. For areas that are under radar surveillance (major air corridors and terminal manoeuvring areas) sensor-fused radar and ADS-B data has proved to be superior to radar data alone, particularly for tracking manoeuvring aircraft. Space-based ADS-B promises to expand the benefits of ADS-B to oceanic airspace and addresses the low reporting rate of Automatic Dependent Surveillance Contract (ADS-C). Optimised ATM procedures such as Tailored Arrivals and the Brisbane Green RNP project have been trialed or implemented in Australia. These national initiatives are now aligned with those of the Asia Pacific region with Australia’s involvement in the Asia and Pacific Initiative to Reduce Emissions (ASPIRE).
Australia’s National Operations Centre (NOC), based in Canberra, employs several techniques to optimise air traffic flows. Optimised Flextracks allow long-haul traffic to benefit from favourable winds. Slot management is performed to optimise the allocation of airport and Air Traffic Control (ATC) slots, while traffic management initiatives such as ground delays programs tackle critical congestion situations, thereby reducing fuel consumption, noise and gaseous emissions at the same time. Collaborative Decision Making (CDM) procedures improve common situational awareness and permit pre-tactical slot swapping. Current initiatives include User Preferred Routes (UPRs) and the extension of national CDM and Air Traffic Flow Management (ATFM) operations to support long-range ATFM strategies for the Asia-Pacific region. Australia is involved in the International Civil Aviation Organization (ICAO) Asia-Pacific ATFM Steering Group, which aims to develop an Asia-Pacific regional ATFM operational concept based on a multi-nodal network of national ATFM centres. Conducting ATFM across national borders will improve its effectiveness, particularly for commercial airline companies. For example, delay can be absorbed en-route or allocated as ground delay if congestion is anticipated at the destination airport several FIRs away. Achieving this in the Asia-Pacific region without a single regulatory authority like Eurocontrol or the Federal Aviation Administration (FAA) is one of the issues to be addressed but the benefits are evident. Early regional CDM trials between Bangkok and Singapore have proved promising, and it is clear that interoperability and harmonisation of standards will be key factors moving forward. In the next few years, new high-integrity and safety-critical CNS+A systems will have to be developed and deployed for strategic, tactical and emergency ATM operations, and in particular:
Civil/Military Dual-use CNS+A Technologies, including a secure and reliable network infrastructure and airborne data-link for information sharing and CDM, network-centric ATM technologies for strategic and tactical ATFM, Dynamic Airspace Management (DAM) and real-time Four-Dimensional Trajectory (4DT) operability.
CNS+A Technologies for RPAS, reliably meeting the Required Communication, Navigation and Surveillance Performance (RCP, RNP and RSP) standards for unrestricted access of RPAS to the national airspace (non-segregated operations). In this perspective, essential steps are the adoption of fused cooperative/non-cooperative surveillance systems, Beyond Line-of-Sight (BLOS) communication systems, high-integrity navigation systems and integrated avionics architectures.
Satellite-based CNS Systems, such as multi-constellation Global Navigation Satellite System (GNSS) and space-based data-link and ADS-B, for improved coverage of remote and oceanic airspace, precision approach and auto-land.
Airport ATM Systems, mainly consisting of safety-nets for ground and air traffic operations, Remote Tower Systems (RTS) and new standardised ATC Operator (ATCO) work positions. In particular, the Advanced Surface Movement Guidance and Control System (A-SMGCS) will also provide runway incursion and excursion detection and alerting similarly to the Airport Movement Area Safety System (AMASS) and Runway Awareness and Advisory System (RAAS) developed in Europe and in the US.
High-integrity, high-throughput and secure data-link and ground network infrastructure for civil/military dual usage and System Wide Information Management (SWIM) system will be developed to allow a greater sharing of ATM information, such as weather, airport operational status, flight data, airspace status and restrictions. Web service technologies for mobile, internet-based access will also be included to flexibly expand the number of participants in CDM processes. Business intelligence and Big Data will also be implemented as part of SWIM for enhanced data mining. The implementation of enterprise-wide data warehouses by ANSPs, including Airservices Australia, will enable ATM to move beyond post-event reporting and mine years of historical data to determine underlying traffic flow patterns and emission levels and derive enhanced models to address them. Automated ATFM (A-ATFM) systems will enhance the continuous balancing of air-traffic demand with capacity to ensure the safe and efficient utilisation of national airspace resources. Automated Dynamic Airspace Management (ADAM) will enable the seamless optimal allocation of airspace resources. Real-time multi-objective 4DT optimisation and negotiation/validation algorithms, implemented in the next generation ground-based and airborne CNS+A systems, will promote a continuous reduction in environmental impacts which will be particularly significant in severe congestion and weather conditions. To enhance the efficiency of Australian aviation at a regional and global level, it is essential to address the interoperability of the Australian ATM regulatory framework evolutions with the rest of Asia-Pacific region and with the European/US frameworks (i.e., SESAR and NextGen). This will likely contribute to the global ICAO initiatives in this domain, such as the Aviation System Block Upgrades (ASBU). From a technological perspective, interoperability is also required at various levels, including Signal-in-Space (SIS), system level and Human-Machine Interface and Interaction (HMI2).
Space Transport and Smart Satellite Systems
Progress in spaceflight research has led to the introduction of various manned and unmanned reusable space vehicle concepts, opening up uncharted opportunities for the newborn space transport industry. For future space transport operations to be technically and commercially viable, it is critical that an acceptable level of safety is provided, requiring the development of novel mission planning and decision support tools that utilize advanced Communication, Navigation and Surveillance (CNS) technologies, and allowing a seamless integration of space operations in the current Air Traffic Management (ATM) network. Key areas of research concentration include:
Emerging (“New-entrant”) platform operational concepts and capabilities, highlighting both the challenges and the opportunities brought in by the integration with conventional atmospheric air transport.
Common launch and re-entry planning methodologies, where the physical and computational limitations of these approaches are identified and applicability to future commercial space transport operations are assessed.
On-orbit phase, where the unique hazards of the space environment are examined, towards identifying the necessary elements required for space object de-confliction and collision avoidance modelling.
Regulatory framework evolutions required for spacecraft operations with a focus on space debris mitigation strategies and operational risk assessment.
Atmospheric flight phases, where possible extensions and alternatives to the conventional airspace segregation approaches are investigated, including promising Air Traffic Flow Management (ATFM) and Dynamic Airspace Management (DAM) techniques, to facilitate the integration of new-entrant platforms.
Advanced modelling approaches to meet on-orbit risk criteria and evolutionary requirements to improve current operational procedures.
As an integral part of the RMIT University contributions to the SmartSat Cooperative Research Centre, the CPS Group is currently performing research in the following key areas:
Distributed and Intelligent Satellite Systems. Development of next generation systems to enable intelligent behaviour and autonomous decision making and operation by satellites and satellite constellations (artificial intelligence and machine learning software solutions). Novel systems for detection and characterisation of threats from Resident Space Objects (RSO) including autonomous capability and Space Traffic Management.
Advanced Communications, Connectivity and Internet of Things (IoT) Technologies. Development of algorithms and technologies for laser communication links with high data transfer rates. Development of adaptive intelligent radio technology allowing sensing and flexible use of spectrum. Development of systems that allow seamless connectivity between satellite and terrestrial communications.
Next Generation Earth Observation Services. Development and delivery of industry specific EO sensors (e.g., smart LiDAR and passive IR technologies) and data analytics services for multiple applications, including: Agriculture, Mining/Resources, Transport and Logistics.