Iris Precursor - SESAR (Single European Sky Air Traffic Management Research) Program
The ARTES Satellite Communication for Air Traffic Management element, or Iris, aims to supply a validated satellite-based communication solution for the European Air Traffic Management System. It is implemented in close collaboration with the SESAR (Single European Sky Air Traffic Management Research) Program launched in 2006 by EUROCONTROL and the European Community. 1)
Table 1: Some background of the Iris program 2)
Overview of Iris development within ESA's ARTES 10 Program
Iris, element 10 of the ARTES program, aims to supply a validated satellite-based communication solution for the European ATM (Air Traffic Management System). It is implemented in close collaboration with the SESAR (Single European Sky Air Traffic Management Research) Program launched in 2006 by Eurocontrol and the European Community. ARTES 10 is the ESA program to support the development of a satellite-based communication system for the European ATM. 3)
The Iris Program is a new type of initiative for ESA, where the space component is one of the component in a much larger system, tuned to the needs of external partners and end-users who are not always familiar with satellite technology. Because of this, a long-term, incremental approach is necessary.
Iris will complement existing and planned systems, supporting the growth of worldwide air traffic. It is anticipated that Iris will be fully operational in 2028, with deployment of a precursor service foreseen for 2018.
Iris will enable 4D trajectory management via satellite, for both continental and oceanic airspaces, as a safe and reliable service. Communications will take place via robust data links and will ultimately be used by the vast majority of aircraft, complemented with conventional voice communications between pilots and controllers. To achieve this goal, Iris will also develop and validate a new standard for satellite communications that can be used for ATM in any region of the world.
Iris is part of a much broader push to modernize how air traffic is managed in close collaboration with the SESAR Joint Undertaking launched in 2006 by EUROCONTROL and the European Union. The new communication system will be standardized by EUROCAE (European Organization for Civil Aviation Equipment) and the ICAO (International Civil Aviation Organization).
The objective of the SESAR program is to develop a high-performance ATM system to enable the safe and environmentally-friendly development of air transport. The SESAR program is defining and evaluating two different communication technologies that will be used in parallel for this system. A new terrestrial data link, with antennas on-ground, and a satellite-based service. This multi-link will offer the safety and capacity requirements for tomorrow's ATM systems.
ESA's objective is to help aviation authorities to deploy a global service supplied by multiple parties. ESA activities belong to the satellite technology domain; the SESAR Joint Undertaking will then use this technology for the operational service verification, before the final deployment.
• July 12, 2018: Engineers are shown testing Iris equipment to exchange messages in real-time with a flight control facility from a Cessna plane, which took off from Amsterdam Schiphol airport and flew over the Netherlands and the North Sea for three hours to test the system's connection. 4)
- Iris will provide a safe and secure text-based data link between pilots and air traffic control (ATC) networks using satellite technology.
- The program is developed under a public-private partnership between ESA and Inmarsat, and will help relieve pressure on the aviation sector's congested radio frequency communication channels.
- It is part of the European Commission's SESAR (Single European Sky ATM Research) masterplan to modernize Europe's air traffic management.
Figure 1: Iris flight trial in a Cessna plane which took off from the Amsterdam Schiphol Airport and flew over the Netherlands and the North Sea for system tests (image credit: ESA)
• January 17, 2018: ESA has signed a €41.3 million contract with Inmarsat to help get more flights in the air with fewer delays, increased safety and reduced carbon dioxide emissions. 5)
- The program will introduce a safe and secure satellite-based air traffic management data link between aircraft and ATC (Air Traffic Control) to relieve the congested radio frequencies used today.
- The contract was signed this month during a ceremony in London. ESA, Inmarsat (GB), Thales Alenia Space (IT), CGI (GB) and an industrial consortium will now start finalizing the technology and preparing the implementation across Europe.
- Iris supports the SESAR (Single European Sky ATM Research) Master Plan for the next-generation of air traffic management. SESAR provides recommendations on how to deliver security, capacity, safety and efficiency benefits for European air traffic. This is crucial, as the number of flights in European skies is expected to grow by 50% over the next 20 years.
- Satellite data links between aircraft and ATC are currently mainly used as support over oceanic airspace. The already-congested European continent still relies on radar- and radio-based ATM systems, which require aircraft to be separated by a certain distance or time to ensure safety. Poor weather conditions can also hamper pilots' and ATC's ability to navigate the skies safely, and necessitate even larger gaps between flight paths.
- These limitations have brought Europe's airspace to near-saturation, resulting in mass flight delays and cancellations and wasting untold amounts of time and money. As our skies become busier, the terrestrial data link systems will reach full capacity by 2025–30, which is why SESAR has recognized the need for a complementary technology solution.
- ESA and Inmarsat have been testing and developing the Iris ground network and cockpit terminals that will help to do just that. Iris technology will relay vital aircraft information and safety services to air traffic control using satellites, creating a secure satcom-based solution that will relieve pressure on existing data link communications. Controller-pilot communications will increasingly move to digital text instead of voice, improving speed and accuracy.
- Iris is also designed to enable initial ‘4D' trajectories, pinpointing an aircraft in four dimensions: latitude, longitude, altitude and time, which is one of the major concepts defined in SESAR. This will enable precise tracking of flights and more efficient management of traffic through TBO (Trajectory-based Operations). TBO allows pilots and controllers to collaborate on flight trajectories and calculate the shortest available routes, cruise at optimum altitudes, and use continuous climb and descent paths, saving fuel and improving the environment.
Figure 2: Iris, element 10 of the ARTES program, aims to develop a new air-ground communication system for air traffic management. It is the satellite-based solution for the SESAR (Single European Sky ATM Research) program. By 2020 it will contribute to the modernization of air traffic management by providing digital data links to cockpit crews in continental and oceanic airspace (image credit: ESA, P. Carril)
- Iris will also define how modernization programs can evolve to enable full 4D trajectory management over airspaces across the globe, with satellite data link becoming a primary means of secure communications between controllers and aircraft.
- Magali Vaissiere, ESA's Director of Telecommunications and Integrated Applications, said: "It is hard to overstate the impact this new application of satellite technology will have on modern air travel. We have been working on the Iris program with Inmarsat and our other partners since 2012, and are happy to now be able to implement the result of this extensive research and development to improve both the European economy and the lives of European citizens in this very tangible way."
- Rupert Pearce, Chief Executive Officer of Inmarsat, said: "This is an incredibly important project for us, but more importantly, it is fundamental to the future of European aviation. Europe's aviation industry is under intense pressure due to limited airspace capacity. The advanced capabilities of Iris will mark a step change, helping to address the limitations of today's legacy protocols and paving the way for more efficient, cost-effective air traffic management."
• December 20, 2016: ESA recently completed its first flight trials using satellites to help bring Europe closer to its goal of modernizing air traffic control. The trials are part of the public–private partnership between ESA and UK satellite operator Inmarsat to deliver high-capacity secure digital data links via satellite for air–ground communications for cockpit crews over European airspace under ESA's Iris Precursor program. 6) 7)
Figure 3: The routes for four recent Iris Precursor flight trials (image credit: ESA, Inmarsat)
- By 2019, Iris Precursor will provide air–ground communications for initial ‘4D' flight path control, pinpointing an aircraft in four dimensions: latitude, longitude, altitude and time. This will enable precise tracking of flights and more efficient management of traffic.
- An aircraft from the Netherlands Aerospace Center carried a prototype Iris terminal connected to Inmarsat's next-generation SB-S (SwiftBroadband-Safety) satellite service as it took off from Amsterdam. During four flights to different destinations in Europe, the connection between the aircraft and ground networks was tested extensively and air traffic control messages were exchanged. The connection was maintained even when the aircraft switched satellite beams.
- "ESA's Iris program is forging ahead as part of Europe's long-term goal to modernize air traffic control. A stepped approach and good collaboration between public and private partners is bringing excellent results," commented Magali Vaissiere, Director of Telecommunications and Integrated Applications at ESA.
• On Sept. 15, 2016, ESA and the SESAR Joint Undertaking signed an agreement to foster even closer ties between their technical programs and align key milestones. The SESAR (Single European Sky ATM Research) program promises to boost efficiency, capacity and performance for managing air traffic worldwide. ESA's Iris program will provide the satcom technology for this. 8)
- By 2018, Iris will provide air–ground communications for initial ‘4D' flight path control, pinpointing an aircraft in four dimensions: latitude, longitude, altitude and time. This will enable precise tracking of flights and more efficient management of traffic. High-capacity digital data links via satellite carrying this information to cockpit crews in continental and oceanic airspace are expected to become the norm, with voice communications used only for specific operations.
Figure 4: By 2028, the Iris long-term service will enable full 4D management over airspaces across the globe and the data link will be the primary means of communications between controllers and cockpit crews (image credit: ESA)
• March 9, 2016: Together with the Netherlands Aerospace Centre (Nationaal Lucht- en Ruimtevaartlaboratorium; NLR), the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) has become a member of the EU Single European Sky ATM (Air Traffic Management) research program, known as SESAR 2020. 9)
• March 8, 2016: ESA and UK satellite operator Inmarsat are forging ahead with the development of air–ground communications via satellite as part of Europe's plan to keep our skies safe as air traffic increases. A new partnership between ESA and Inmarsat secures the modernization of ATM (Air Traffic Management) and will build on developments already under way in Europe. 10)
- On Feb 23, 2016, the Iris Precursor operated a first test flight between Toulouse and the Balearic Islands passing above Madrid, performing initial 4D flight path control and controller–pilot data link exchanges with the Maastricht Upper Area Control Center.
- By 2018, in an essential milestone for Iris, the Precursor service will provide air–ground communications for initial 4D flight path control, pinpointing an aircraft in four dimensions: latitude, longitude, altitude and time. This will enable precise tracking of flights and more efficient management of traffic so that flight plans can be continually updated during flight to maintain an optimal trajectory to destination. These trajectory management concepts will allow air traffic control to offer better routings, sequence aircraft far in advance and maximize airport and airspace capacity.
- The planned evolution of datalink service provision in European airspace is based on incremental steps, from current services for clearances, to initial 4D (i4D) trajectory management services and, ultimately, to full 4D services to be defined in SESAR.
• In July 2015, a safer airspace over Europe by 2018 is materializing as ESA's Iris precursor project began development. The PPP is looking to satellites to make aviation safer through modern communications. With the design phase completed, Iris Precursor will now develop an improved satellite network to overlay existing terrestrial VHF networks to carry air traffic management communications across European skies. 11)
• November 26, 2014: A contract was signed today in London in the presence of Greg Clark, UK Minister for Universities and Science. The Iris PPP (Public–Private Partnership) between ESA and UK satellite operator Inmarsat will become an integral part of Europe's future air communication infrastructure by ensuring that such satellite-based traffic management systems meet stringent international standards. Iris is part of a much broader push driven by the European Commission to modernize air traffic management in support of the Single European Sky. 12)
- Iris Precursor is a milestone in this direction, modernizing air traffic management and ultimately making data links the primary means of communication, eventually replacing voice reports from pilots. This signature is a first step in a partnership that will provide long-term approaches to air traffic management.
- It is based on SwiftBroadband Safety, a service currently offered by Inmarsat that provides aircraft with an ‘always-on' data connection and is an extension of the company's 20 years of experience as the leading provider of safety communications to 98% of airlines. Hawaiian Airlines recently began flight trials of SwiftBroadband Safety as part of achieving approvals for oceanic operations.
- Thanks to the Iris Precursor upgrade, the service will reach the required level of safety for use in safety-critical applications over continental airspace and provide a satellite overlay to terrestrial networks.
- The contract is the result of a major funding commitment approved at ESA's 2012 Ministerial Council, with the UK as the main contributor followed by Denmark, Norway, the Netherlands, Ireland and Portugal.
Figure 5: Schematic of digital data links via satellite in air traffic control (image credit: ESA)
SESAR (Single European Sky Air Traffic Management Research) Vision
Within the framework of the Single European Sky (SES), the European Air Traffic Management Master Plan (hereafter referred to as ‘the Master Plan') is the main planning tool for defining ATM (Air Traffic Management) modernization priorities and ensuring that the SESAR (Single European Sky ATM Research) Target Concept becomes a reality. The Master Plan is an evolving roadmap and the result of strong collaboration between all ATM stakeholders. As the technological pillar of the SES initiative, SESAR contributes to achieving the SES High-Level Goals and supports the SES regulatory framework. 13)
The Master Plan details not only a high-level view of what is needed to be done in order to deliver a high-performing ATM system, but also explains why and by when. It therefore sets the framework for the development activities performed by the SJU (SESAR Joint Undertaking) in the perspective also of the deployment activities to be performed by all operational stakeholders under the coordination of the SESAR Deployment Manager and in accordance with the Deployment Program to ensure overall consistency and alignment.
ATM is a critical element in the European air transport value chain and key to connecting regions and making Europe a global hub for mobility and prosperity. To ensure the sustainability and competitiveness of aviation, Europe needs to have a clear vision on how to deliver a high-performing ATM system.
Since the 2012 edition of the Master Plan, several significant developments have taken place, such as the availability of the first SESAR Solutions, the start of deployment activities and the significant change to the long term traffic forecast. ATM modernization therefore needs to reflect a greater focus on increased efficiency and effectiveness while sustaining or even improving the levels of safety and security. At the same time, it must also recognize the need to provide solutions to address critical capacity bottlenecks.
Mindful of these developments, this edition of the Master Plan:
• introduces a vision for the future European ATM (Air Traffic Management) system;
• presents the first wave of SESAR deployment, such as the PCP (Pilot Common Project) 14), and details the Key Features of R & D activities (SESAR 2020);
• provides new deployment scenarios for elements that are sufficiently mature to be brought into the deployment pipeline;
• makes explicit reference to RPAS (Remotely-Piloted Aircraft Systems) and rotorcraft as airspace users, as well as to cybersecurity elements within ATM;
• incorporates the results of a more comprehensive military involvement;
• reflects synergies and consistencies with the Deployment Program and the Network Strategy Plan.
The Master Plan vision builds on the notion of ‘trajectory-based operations' and relies on the provision of ANS (Air Navigation Services) in support of the execution of the business or mission trajectory — meaning that aircraft can fly their preferred trajectories without being constrained by airspace configurations. This vision is enabled by a progressive increase of the level of automation support, the implementation of virtualization technologies as well as the use of standardized and interoperable systems.
The system infrastructure will gradually evolve with digitization technology, allowing ANSPs (Air Navigation Service Providers), irrespective of national borders, to plug in their operations where needed, supported by a range of information services. Airports will be fully integrated into the ATM network level, which will facilitate and optimize airspace user operations. Going beyond 2035 towards 2050, performance-based operations will be implemented across Europe, with multiple options envisaged, such as seamless coordination between ANSPs or full end-to-end ANS provided at network level.
Furthermore, it is widely recognized that to increase performance, ATM modernization should look at the flight as a whole, within a flow and network context, rather than segmented portions of its trajectory, as is the case today. With this in mind, the vision will be realized across the entire ATM system, offering improvements at every stage of the flight.
Figure 6: Improvements at every stage of the flight (image credit: EU, Eurocontrol, Ref. 13)
NextGen (Next Generation Air Transportation System) of USA
NextGen is an effort begun in 2003 whose goals include improving the capacity, efficiency, and safety of the U.S. air transportation system and also enabling reduction in noise, pollution, and energy use. FAA (Federal Aviation Administration) and various stakeholders, including equipment providers, airlines, and contractors, are currently implementing both near-term and mid-term NextGen capabilities. The Federal Aviation Administration Modernization and Reform Act of 2012 calls for the NRC (National Research Council) to examine NextGen's enterprise software development approach and safety and human factor design. The NRC assembled a committee of experts to study the issue. 15)
In the course of the committee's study, it became clear that "NextGen" means different things to different people, ranging from a wide-ranging transformational vision to a much more concrete set of phased incremental changes to various parts of the NAS (National Airspace System) . In the committee's view, NextGen is a set of programs to implement a suite of incremental changes to the NAS.
Table 2: Some background of FAA's modernization efforts for ATC (Air Traffic Control) 16)
Figure 7: Improvements to phases of flight expected under NextGen (Next Generation Air Transportation System), image credit: FAA
An important and necessary part of NextGen is addressing urgent requirements to replace aging equipment. NextGen also includes efforts to further deploy performance-based navigation, to redesign certain aspects of the airspace, to equip aircraft with technology that can form the basis for future capabilities, and an additional broad range of activities. However, NextGen does not set out a series of planned steps toward a fundamentally-transformed end-state.
Enterprise Architecture: An enterprise architecture supports and documents existing systems and business processes. The current NextGen enterprise architecture appears to be a set of functional enclaves that are providing individual services, described in a set of documents at the NAS enterprise architecture level. This tacit architecture is bottom-up and program-driven. This approach to enterprise architecture is not an adequate technical foundation for steering NextGen's technical governance and managing the inevitable changes in technology and operations.
System Architecture: A system architecture models and defines the structure and behavior of a system in a way that supports reasoning about the system and its characteristics. A system architecture for the NAS should help ensure proper operation of the system, allow proper analyses for prediction of system behavior, performance, and so on, and ensure future evolvability. The current NAS system architecture is not well-developed, though this is difficult to discern because of the nearly exclusive focus by the FAA on the enterprise architecture.
NextGen capabilities continue to bring positive effects to the aviation industry and the flying public all across the National Airspace System (NAS). The FAA and the aviation industry work together through the NAC (NextGen Advisory Committee) to identify high-benefit, high-readiness NextGen capabilities for implementation in the near term. This work began in 2014 by identifying four focus areas — Multiple Runway Operations (MRO), Performance Based Navigation (PBN), Surface Operations and Data Sharing, and Data Communications (Data Comm). The FAA and the aviation industry identified specific capabilities to implement at specific locations in the 2014–2017 timeframe and documented both FAA and industry commitments in the FAA's NextGen Priorities Joint Implementation Plan. 17)
The FAA and industry are committed to jointly evaluating the effects of these commitments on the NAS through the work of a JAT (Joint Analysis Team). This helps the FAA and industry understand the value of implementations in this plan.
Given the success of this collaboration, the FAA and industry agree to keep collaborating through the NAC to update the commitments each year and roll the plan forward biannually. The commitments in this plan reflect the culmination of work through 2019. Both the FAA and industry have identified specific commitments within each of the four focus areas to implement capabilities at specific locations by specific dates to increase safety, reduce aviation's impact on the environment, enhance controller productivity, and increase predictability, airspace capacity and efficiency. The FAA and industry will continue to monitor joint progress and be agile and flexible to make necessary adjustments to commitments.
Accomplishments were realized in all four focus areas:
• The FAA made substantial progress on Wake Recategorization (Wake RECAT) implementation at locations with simultaneous approaches to parallel runways by reducing separation criteria for multiple runway operations. RECAT was refined with additional separation reductions that are currently implemented at all RECAT sites across the NAS. The FAA also successfully addressed separation standards for multiple dependent and independent parallel operations at numerous locations and completed safety analyses for a variety of other separation standards. To date, the Wake RECAT capabilities identified positive effects on the NAS with capabilities delivering benefits as anticipated. For example, the JAT's operational performance findings on Charlotte's Wake RECAT implementation estimated $237,000 in total annual savings in airborne and taxi out time.
• In the critical area of PBN, the FAA increased its community outreach at Charlotte by holding two public workshops to discuss flight path changes for routes northeast and southeast of the city. The FAA implemented 11 procedures at Charlotte, with 10 more to be implemented in early 2017. The agency also completed a Metroplex implementation at Northern California, implemented Established on RNP (EoR) capabilities at Denver, published the EoR National Standard, and conducted a single site assessment for Las Vegas.
• As an early implementation activity, the Terminal Flight Data Manager (TFDM) Program funded the Traffic Flow Management System (TFMS) Release 13 to enable the addition of new surface data elements. This modification was implemented in April 2016 and included changes to the data use hierarchy so that near-term "early implementation" benefits in TFMS will be realized. The FAA is now able to ingest and use several data elements in TFMS that will yield TFM (traffic flow management) benefits with better traffic management initiatives and increased predictability for the customers and the system. The FAA made the investment in early implementation given industry's commitment to provide the data, and there is a concerted effort underway with industry to provide data. The FAA also deployed electronic flight strips at Newark, Las Vegas and San Francisco.
• The FAA has made significant progress in Data Comm and is on track to complete Departure Clearance Tower Services at 56 airports by the end of Calendar Year 2016. Our industry partners are well on their way toward the goal of 1,900 Data Comm-equipped aircraft operating in the NAS by the end of CY 2019. More than 900 Data Comm-equipped aircraft currently operating (as of August 2016) were equipped through the FAA's Data Comm equipage initiative.
Harmonization between NextGen and SESAR
As two of the major aviation modernization programs in the world, the NextGen program of the FAA (Federal Aviation Administration) and SESAR have a shared interest and responsibility in harmonization as a means of ensuring global interoperability. The two programs have common challenges and a similar conceptual and performance-driven approach. It is widely understood that systems will not be completely identical but harmonized and interoperable at the standard level. SESAR and NextGen advocate a ‘not-one-size-fits-all' approach in both the US and in Europe as well as at ICAO (International Civil Aviation Organization) level. This is globally accepted and the aim is to achieve the degree of harmonization necessary to:
• ensure aircraft can operate in all regions (without requiring additional equipment);
• ensure that common standards are available when needed and in time for both development and implementation planning;
• optimize development and implementation costs through the sharing of effort and results.
The scope of what should be harmonized is derived from the agreed ICAO global ATM operational concept developed by the entire global aviation community and complemented with new requirements expressed by the ATM stakeholders, in particular airspace users.
The US-EU MoC (Memorandum of Cooperation) on civil aviation research and specifically Annex 1 on SESAR-NextGen interoperability is the important vehicle for harmonization between these two major modernization programs and their results directly contribute to the development of global harmonization initiatives under the umbrella of ICAO, the industry standardization bodies of RTCA (Radio Technical Commission for Aeronautics) and EUROCAE (European Organization for Civil Aviation Equipment), as well as with other relevant international standardization organizations. The MoC as such also constitutes the collaborative framework within which the US and the EU develop and establish joint or supporting positions on standards and priorities in the ICAO work program, while allowing other regions to share information and where possible participate in the different domains of the MoC.
The SESAR and NextGen programs are aligned with and support ICAO's GANP (Global Air Navigation Plan) and the ASBUs (Aviation System Block Upgrades). The two programs both impact and are impacted by the GANP in terms of ICAO priorities. Looking ahead, the focus is to further align the two programs' priorities supporting a further evolution of the GANP, namely its update in 2016 and 2019 (Ref. 13).
High-level frameworks have been established and are now being complemented with further agreements at a more detailed level (e.g. harmonized planning and standard proposals to industry standardization organizations and ICAO).
1) "Satellite Communication for Air Traffic Management (Iris) Overview," ESA ARTES Applications, URL: https://artes.esa.int/iris/overview
2) "Iris - the satellite-based communication solution for the Single European Sky Air Traffic Management Research program," ESA brochure, 2010, URL: http://www.evolvsys.cz/files/brochures/esa/Iris.pdf
4) "Iris flight trial," ESA, 12 July 2018, URL: http://m.esa.int/spaceinimages
5) "ESA to clear congested skies with Iris," ESA, 17 Jan. 2018, URL: http://m.esa.int/Our_Activities/
6) "Preparing for air traffic control via satellite," ESA, Dec. 20, 2016, URL: http://m.esa.int/Our_Activities/Telecommunications
7) "Inmarsat and European Space Agency Complete First Test Flights for Air Traffic Modernization Project," Dec. 20, 2016, URL: http://airfax.com/blog/index.php/2017/01/02/inmarsat-and-european
8) "European cooperation for safer skies," ESA, Sept. 15, 2016, URL: http://m.esa.int/Our_Activities/Telecommunications_Integrated
9) "Single European Sky – DLR and NLR join the 2020 SESAR research program," DLR News, March 9, 2016, URL: http://www.dlr.de/dlr/en/desktopdefault.aspx
10) "Space keeps us safe as air travel rises," ESA, March 8, 2016, URL: http://www.esa.int/Our_Activities/Telecommunications
11) "Europe advances with safer air travel," ESA, July 14, 2015, URL: http://www.esa.int/Our_Activities/Telecommunications_Integrated
12) "Building a safer airspace for Europe," ESA, Nov. 26, 2014, URL: http://www.esa.int/Our_Activities/
14) Commission Implementing Regulation EU No 409/2013 specified the requirements for common projects. Common projects aim to deploy in a timely, coordinated and synchronized way ATM functionalities that are mature for implementation and that contribute to the Essential Operational Changes identified in the European ATM Master Plan (2012 edition). The first of these common projects is the PCP (Pilot Common Project).
15) "A Review of the Next Generation Air Transportation System: Implications and Importance of System Architecture," Computer Science and Telecommunications Board , Division on Engineering & Physical Sciences, May 2015, URL: http://sites.nationalacademies.org/cs/groups
16) Bill Shuster, Peter De Fatio, Frank LoBiondo, Rick Larsen, "Air Traffic Control Modernization - Progress and challenges in implementing NextGen," United States Government Accountability Office, Report to Congress, August 2017, URL: https://www.gao.gov/assets/690/686881.pdf
17) "NextGen Priorities Joint Implementation Plan, Rolling Plan 2017-2019," 23 Sept. 2016, URL: https://www.faa.gov/nextgen/media/NG_
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (firstname.lastname@example.org).