DLR (CC BY-NC-ND 3.0).
Proba-V integrated view
Satellite-based air traffic control with ADS-B
Satellite based air traffic control with ADS-B
An A320 overflying Scotland was the first aircraft 'seen' from space by a receiver developed by the German Aerospace Center (DLR), proving that tracking aircraft from space is possible. The ESA PROBA-V satellite has been orbiting Earth since 7 May 2013, and is equipped with a receiver that detects aircraft ADS-B signals (Automatic Dependent Surveillance – Broadcast). The device was operated for the first time on 23 May 2013, and recorded over 12,000 ADS-B signals within two hours at an altitude of 820 kilometres. According to the DLR Project Manager, Toni Delovski, "this was the first experiment of its kind, anywhere in the world – and now we have evidence that it works".
Once the receiver was switched on, scientists were able to locate more than 100 aircraft during the first pass over the British Isles, East Asia and Australia. ADS-B signals, which include position and speed information, are broadcast by aircraft every second. An aircraft's identifier (its so-called registration plate) is also transmitted. However, once aircraft fly out of the range of the ground radar stations, continuous air traffic surveillance is no longer possible. For example, aircraft travelling from Europe to Brazil disappear from the radar over the Atlantic and will only be detected again by ground radar shortly before reaching South America. At the moment, continuous radar-based air traffic surveillance is not possible in oceanic airspace or in regions with limited air traffic surveillance infrastructure. But tracking from space could close this gap in future. 'ADS-B over satellite' is a joint project of the DLR Institute of Space Systems and the DLR institute of Flight Guidance, in cooperation with the Luxembourg partner SES TechCom Services. DLR developed the satellite payload, and SES TechCom developed and implemented the ground data processing centre.
Air traffic control – radar vs. space
Air traffic is continuously increasing, and is currently being monitored by Air Traffic Management (ATM) systems that are predominately based on radar. In some instances, ADS-B has been, or is being, introduced, which regularly transmits the position of the aircraft, as well as other flight information, via the aircraft's Mode S transponder, which is then received by the ground station. In regions where the air traffic control infrastructure is well established, radar or ADS-B coverage overlaps. This ensures that there is full coverage and visibility over all air traffic. Nevertheless, this continuous surveillance is not available everywhere due to the limited range of the radars located on the edge of regions that have good air traffic control infrastructures.
On the other hand, in oceanic airspace, regions with less advanced infrastructure, and in regions where there is political unrest, continuous air traffic control is not in place, either because it is not physically possible to build air traffic control stations that fully cover those areas, or because it is too expensive, technologically challenging, or due to the political situation, which results in an unreliable service that does not meet the necessary international standards. In regions with no radar coverage, Non-Radar Airspaces (NRA), flight surveillance occurs procedurally. In other words, pilots radio in or use data links to report to the relevant control station when they reach certain checkpoints, informing them of their position. The distance between these data links is, however, relatively large due to technical and financial reasons, meaning that there is no continuous surveillance of air traffic.
Improving search and rescue measures in emergencies with real-time positioning
To ensure flight safety, large separation distances are mandatory in flight paths passing through NRA. But due to the rise in transoceanic air traffic, a smaller than normal separation distance is already being permitted in some cases.
Much worse than this, though, are the consequences of not being able to make contact with air traffic control during a transoceanic flight in the event of an emergency or crash. The lack of continuous surveillance means that, if a pilot fails to make contact with the control station long after expected, and contact by the station cannot be established, an accident must be assumed. Further delays in implementing rescue and salvage measures occur due to the inability to pinpoint the exact location of an accident, which, as a result, then requires the deployment of an extensive search operation.
Global air traffic control from space
DLR recommended that global air traffic be monitored from space in future, which would resolve the issues of non-continuous surveillance in flights within NRA outlined above. This could be achieved by satellites intercepting the information broadcast by aircraft, in this case data from the Automatic Dependent Surveillance - Broadcast (ADS-B), which can then be transmitted to existing ground infrastructure. Given that Mode S transponders are compulsory for commercial aircraft, global coverage of all air traffic could be ensured by using satellites. Using ADS-B, DLR has demonstrated the feasibility of this concept.