3.4.2 Electronic Order of Battle
The EOB is defined as a list of the locations, identifications, functions, and capabilities of electronic equipment employed by a military force [41]. This information is made available to the pilot during the pre-flight preparation of the aircraft. Information about the planned route and current equipment and ammunitions on the aircraft may also be loaded electronically to an aircraft computer. The planned route will often be described using a fixed number of locations. Such a location is known as an Intermediate Point (IP).
The inventory consisting of countermeasures and weapons is based on theEOB. Since countermeasures and weapons will often have to share the same stations placed under the aircraft the more countermeasures that are deemed necessary the fewer weapons may be carried. Generally the assessment of the battlefield will lie within one of the categories given below. While battlefields within some of these categories are estimated as being unlikely, they are mentioned here for completeness.
• The battlefield contains no known threats and the aircraft is not equipped withECM.
• The enemy has passive missiles only (e.g. MANPADS) and the aircraft will be equipped with flares.
• The enemy has active missiles only and the aircraft will be equipped with chaff. This situation is unlikely.
• The enemy has active missiles only. These missiles may be jammed and the aircraft is equipped with both chaff and jammer. This situation is unlikely as well.
• The enemy has multiple types of weapon or the composition of weapons is unknown. The aircraft is equipped with chaff, flares, and a jammer.
• The enemy has passive missiles only or missiles that may be jammed. The aircraft is equipped with jammer and flares. This situation too is unlikely.
3.5 System Data Flow
The basic data flow for the working environment of theDSSis shown in Figure 3.2. At the left hand side data is fed to theDSSfrom different systems on-board the aircraft. With the aid of a knowledge base and the constructed SA the
30 Decision Support System in a Fighter Aircraft
DSSfinds a solution. This solution can then be presented to the pilot, and/or automatic responses from other on-board systems can be initiated.
Figure 3.2: Data flow. Data is coming from sensors on the left hand side of the figure. Decisions from theDSSinfluence the subsystems on the right hand side.
The pilot is continuously gathering information from the on-board systems to improve and revise his Situational Awareness (SA). In order to support the pilot theDSS needs to build and maintain its ownSA. When a solution is found by theDSS it must be executed. One way to do this is to present the solution to the pilot and let him execute the actions suggested. Since one of the reasons for introducing aDSSis to reduce the workload of the pilot theDSSmay be linked directly to relevant subsystems for automatically deploying countermeasures, possibly in conjunction with proper evasive manoeuvres.
Decision making in military domains are often described by the four actions:
Observe, Orient, Decide, Act (OODA). These actions are performed repeatedly in what is known as the OODA loop [5, 37]. When engaged by a missile the fighter pilot will first observe the missile; he will determine if the missile is posing an immediate threat; if it is he will decide on proper evasive actions;
and finally he will act to avoid the impact of the missile. If the fighter pilot is to be aided by a DSS it will itself run through the first three phases of the
OODAloop before a decision is presented to the pilot. If a proper response must be found no later than 200 milliseconds after a threat occurs, according to the requirements mentioned in Section 3.3, the DSS must perform a loop at least five times a second.
3.5 System Data Flow 31
3.5.1 Acquiring Data
In order to decide on actions to suggest to the pilot the system needs input from various sources. In most fighter aircraft these sources will be systems connected to a data bus on-board the aircraft. In many aircraft this bus will comply with the MIL-STD-1553B standard [4].
On a MIL-STD-1553B bus the communication is controlled by abus controller.
Data can come from a number of remote terminals, and it can be read by a number ofbus monitors. The bus controller serves as an arbiter that allows the remote terminals to use the bus one at a time. Data on the bus is transmitted as datagrams from one remote terminal to one or more bus monitors. The format of a datagram is described in an Interface Control Document (ICD), and since every remote terminal may use a specific format for every bus monitor receiving data from the terminal, a large number of ICDs may be needed to describe communication on the bus. Since a DSS may need input from many remote terminals, and these may vary from one aircraft to another, the DSS must be designed so it can be easily adapted to a comply with new sets ofICDs.
Most datagrams are transmitted with a relatively low frequency. If allowed by the bus controller a typical datagram will have a transmission frequency in the order of 1 to 20 per second, depending on the assessed importance of the datagram. Combined with a relatively low clock frequency controlling the bus, a slack time in the magnitude of 0.1 to 0.5 seconds may well appear between the time a sensor system has detected a threat till a bus monitor (e.g. theDSS) receives notification about it. This slack leaves only a short period of time for theDSSto find and suggest an action to the pilot.
Besides on-board sensor systems data to the DSS may be supplied through a tactical data link. Link-16 is a standard for such a tactical data link, and it is used for sharing information (e.g. identification and voice commands) between allied units (aircraft, ships, etc.) in the battlefield. A DSS may benefit from data given through Link-16 to maintain a model of threats, their tracks, sizes, numbers, and positions.
The sensors and sources for detecting threats on-board the aircraft differ in sev-eral aspects. They operate in different bands of the electromagnetic spectrum, use different methods to determine the threats, and since they may interpret their analogue input differently, they may not agree on the threats found. To give theDSSa single ”ground truth” to work with, it may be essential that data from the different kind of sources are fused before handed to the system.
32 Decision Support System in a Fighter Aircraft
3.5.2 Threat Evaluation
Not all changes to the threat scenario will require theDSSto suggest new actions.
Throughout a mission one of the goals of theDSSis to minimize the workload of the pilot. Therefore, when the aircraft flies over friendly territory, and no threats are imminent, no actions must be suggested by the DSS. As soon as theMWSissues a warning, or theRWRdetects radiation from a possibly hostile radar, the territory can no longer be considered friendly, and the system will suggest actions to the pilot.
Even while flying over enemy territory theDSSmust only suggest evasive actions when necessary. To determine when e.g. warnings from the RWR stem from previously undetected radar system, or if the radar has just reappeared on the
RWRafter being lost for a moment, athreat evaluatorsubsystem may be added to theDSS. Such a subsystem will have to base its evaluation on a registration of recent warnings. TheRWRmay loose track of radar systems if the aircraft is positioned such that either itself or the terrain underneath it prevents the radar from being detectable by the RWR antennas. For theMWSsome warnings can be ignored too. If a warning is issued for a fraction of a second only, it is likely to be caused by e.g. a reflection that is visible only for a moment, instead of by a missile following the aircraft. If the threat evaluator has to compare every warning to previous warnings, the first warnings of a threat will be ignored.
When warnings are no longer ignored even less time is left for theDSSto find a solution.
3.5.3 Executing Decisions
In general aDSSwill support a decision maker in deciding proper actions. When the suggestions from a fighter aircraftDSS is presented to the pilot, the pilot will have to decide on the actions to perform before carrying them out. Since a limited time is available for the pilot to do this theDSScan perform the actions itself; even without the consent of the pilot. Most fighter aircraft use fly-by-wire control, i.e. all controls are entirely electronic. This means that the DSS can take control of the aircraft and perform the proper manoeuvres while dispensing expendables. While this may be technical feasible it is not necessarily a situation wanted by the pilot. According to [39] nine of ten interviewed pilots said that having the aircraft taking control was anathema to them.
Having theDSSworking in interaction with some of theECMsystem on-board the aircraft, without taking complete control, may still improve the survivability of the aircraft. TheDSSmay e.g. notify the jammer aboutRFthreats not detected