Argumentation is presented on the need to adapt spacecraft orientation systems in emergency situations through rational control. Rational control is based on the intelligent diagnostic and recovery functions automation. The problem statement of choosing restoration tools in the block diagram of a rational control system is considered. The dynamic knowledge base of recovery tools is presented. The methods for choosing the tools of restoring of rational control object operability under destabilizing influences are described. rational control object, efficiency, destabilizing effect, dynamic knowledge base, restoration, The space missions' duration increase has led to the emergence of new scientific and technical problems to ensure the operability of onboard systems and in particular spacecraft attitude control systems. In a long-term space flight in addition to the traditional perturbing effects of the external environment, failures, malfunctions and equipment faults of the internal environment affect the attitude systems. External and internal influences are essentially destabilizing factors that disrupt the orientation systems performance. To parry destabilizing influences more developed of orientation systems functional tools are needed that provide autonomous and operational adaptation to changing operating conditions. Such adaptation can be provided by automating such intellectual abilities of a person as the ability to find the cause of emergency situations by consequences, i.e. to diagnose and, knowing the diagnosis, to choose the tools of restoring the efficiency of the orientation system.
2022 Copyright for this paper by its authors.
the principle of management by diagnosis. The use of this principle allows us to formulate a new
structure of rational control [
The object of rational control in this structure must have the properties of diagnosability and recoverability, which make it possible to ensure adaptability to destabilizing influences.
A necessary condition for the recoverability of an object of rational control is the absence of an excess amount of reserve tools. After fault state diagnosis is stated, one of several possible tools is required to implement procedures for restoring the operability of a rational control object.
The paper presents the results of solving the problem of choosing the tools of restoring the efficiency of a rational control object using a dynamic knowledge base of possible diagnoses and the corresponding tools of restoration.
Consider, using the example of a block diagram of a rational orientation control system, the problem statement of choosing recovery tools.
To control the attitude of a spacecraft under conditions of destabilizing effects, according to the principle of control by diagnosis, a certain composition of functional elements is required (Figure 1).
For rational control of the spacecraft relative to the center of mass, a redundant structure sensor
unit and a redundant structure drive unit are used. The object of rational control is affected by many
types of destabilizing influences that violate its orientation, i.e. workable state. The operability status
is analyzed in the diagnosis unit using information from the sensor unit and drive unit, and a diagnosis
̂ is formed [
Further in the control unit upon information being received about a appeared fault in the rational control object, a specific tool among the recovery tools available on the spacecraft board should be chosen promptly and in such way the operability is restored.
When designing an object of rational control for each type of destabilizing effect di ∈ D, i = ̅1̅̅,̅q̅ tools of parrying it vj ∈ v̅, j = ̅1̅̅,̅μ̅ are formed based on the possibilities of the design, the existing structural redundancy, taking into account the limitations of weight and size, energy and cost. Mathematically, this can be represented using the mapping F: D → v. This relationship can be represented graphically using Table 1, where the types of destabilizing effects are placed by rows, and the tools of recovery v used to neutralize them are placed by column. In accordance with the requirement of multifunctionality such tools are chosen that can parry several types of , which is reflected by the Boolean variable , which takes the value "1" if it is possible to neutralize the type of destabilization using the recovery tool or "0" if not. Rank 1 . . . . … … … … … … … …
Parameters , numerically equal to the count of "1" in the column, characterize the rank of recovery tools. The more types of destabilization can be neutralized by using the tools , the higher its rank .
The parameter , numerically equal to the sum of "1" in the row, characterizes the destabilization recoverability level. The higher , the more tools available for rational control object operability recovering in the case of the destabilizing effect appearance. The lower , the smaller amount of tools are available for restoring working order. Parameter 0 characterizes the general level of the object recoverability and is equal to the sum of the ranks . recovery tools, based on the limitations on operational characteristics.
The Table 1 is formed from the condition of satisfying the following criteria of recoverability: ∀ ≥ , = ̅1̅̅,̅̅ and ∀ ≥ , = ̅1̅̅,̅̅ . Here is the required value of the recovery level, based on the tactical and technical requirements for the attitude control system, and is the allowable rank of
In the course of functioning of system of rational management Table 1 should reflect the current state of available recovery tools, i.e. each time is selected and used, the recovery tool removes the corresponding column from the table and recalculates the level values . In fact, the table is a dynamic structure of the knowledge base of recovery tools for types of destabilizing effects of the form ∈ . The production rules in the equivalent format of the production knowledge base for restoring operability are formed according to the rows of the table as follows: “if the diagnosis is , then available recovery tools correspond to it are those, for which = 1”. Further it is necessary to select only one from these recovery tools for its use in the procedure for restoring the operability of a rational control object.
For each row of the dynamic knowledge base, there is a subset ⊂ of recovery tools. From this subset, it is necessary to choose one tools vj ∈ V , which will be the best from the point of view of some criterion. Depending on the criterion, an appropriate algorithm for choosing the best recovery tool is also formed. 4.1.
The rank numerically reflects the weight of each recovery tool. To each matches a subset and, accordingly, a subset of ranks ⊂ , where is the set of all ranks . The set is the set of natural numbers. Among these numbers it is necessary to find one that satisfies the selected criterion.
In traditional practice, the use of redundant recovery facilities on spacecraft applies the principle of frugality. This principle lies in the fact that to parry the current contingency, the simplest backup tools is used, i.e. the lowest ranking agent, assuming that the worst off-nominal situations may be in later phases of the flight and will require higher ranking recovery agents to parry them. Therefore, in relation to the
Table 1 needed nonnumeric subsets to find the lower numerical edge. Mathematically, this is described as follows: ∀ ∈ < . Then is the optimal tool for recovery in a current case.
To find the smallest number in the subset, it is necessary to use a method that allows performing search in the optimal way. For the dynamic knowledge base the criteria for method optimality might be time and memory storage volume.
If the count of tools for recovery is more than 100 and information renewed rarely then it could be better to store data sorted by rows in ascended order according to . In this case first founded = 1 in a row will give the number of tool with the minimal rank. Additional memory is unneeded, time complexity of search will be O(n) and processing time will be less in better cases. However it is need additional operating time, when knowledge base is restored.
In other cases it will be reasonable just to combine search in a row using both criteria: = 1 and
< . Then procedure of search will be following: = = _ , = 1 Repeat for <=
If
= 1 and <
is the optimal tool for recovery destabilization . Additional memory 4.2.
It is great possibility that the rank of several tools in the subset could be the same. So we may improve the automatic recovery tool choice in the rational control system by adding some other criteria. As shown in Table 2 there are several parameters that could be estimated for each tool: • • • 1 1 1 1 1 2 2 2 2 2 2 … … … … … … … … … … … = [ , , , … ] of them or some subset ′ ⊂ .
In any case we have a statement of the multi-criteria problem of choosing the best option
∈ according to the set of criteria . It is usually solved in classical decision-making theory
using one of the developed methods [
The main advantage of the methods of multi-criteria decision-making is that they allow obtaining
the best alternatives having contestant criteria represented in different scales (from rang to absolute)
close to those that could be chosen by excellent expert human who is objective without any biases.
But it must be mentioned that the major procedures are automated, not automatic, and need a lot of
customizations during the process [
In the work it is propose to apply in parallel modified method ELECTRE – ELECTRE GR [
( ) = ∑ ∈ − ( ) , ∈ .
The scheme of the proposed method is represented on Figure 2. (1) 1 ⊂ | ∀ ∈ ( ) < , (3) is a threshold given by the decision maker or set by default in a case of automatic where procedure:
= min( ) + 0.1(max( ) − min ( )). (4) In this case the subset of the best tools for restore will be found as:
= 1 ∩ . (5)
The rational control system based on such techniques will be able to run in pure automatic mode after criteria ranking. The thresholds as it was mentioned may be set by default. The best final alternative could be define in two ways: • using (2) and procedure as in the case of single-criterion choice, defined above; • using (3) and (5) with gradually changing beginning from maximum until | | = 1.
The theoretical studies carried out on the dynamic knowledge base processing for tools choosing have shown the possibility of the spacecraft control intellectual procedure automation. The results obtained during research allow proceeding to the development of software modules for a dynamic knowledge base and the choice of tools for restoring the operability of rational control objects.