2 PROBLEM DESCRIPTION AND
PROPOSED APPROACH TO ITS
SOLUTION
The task of constructing a schedule for target
application of space systems for conducting
operational object sounding is as follows: based on
applications from users for monitoring agricultural
fields during a specified period with the given
frequency, and taking into account restrictions on
image characteristics, the system forms a
comprehensive plan for execution of applications,
satisfying the given requirements (Darnopykh,2004).
Complexity of this task lies in heterogeneity of
technical characteristics and principles of organization
of onboard equipment of the satellite, as well as in large
dimensions: dozens of satellites and ground stations
are used, and a large number of point-type observation
objects is specified. The period for performing
shooting or data transmission operations is limited by
a non-permanent visual contact between satellites and
observation objects, as well as by the radio contact
between satellites and ground stations.
Limitations on technical characteristics of onboard
equipment and external restrictions (cloudiness,
illumination, etc.) are constraining performance of
operations. The presence of several devices increases
the number of potentially possible surveys of ground
objects, which leads to multivariance of shooting
plans. It is necessary to ensure prompt decision-making
without recalculating the entire schedule when a new
event appears in multi-criteria environment.
Traditional centralized planning is based on
mathematical methods: branch and bound method,
nonlinear programming, mathematical and dynamic
programming, discrete optimization, constraint
programming, genetic algorithms.
Disadvantages of centralized planning are the
following: determinacy and complexity of taking into
account rapidly changing conditions, lack of reliable
information about the current situation, loss of
schedule adequacy over time. It is possible to
overcome these disadvantages through the use of
distributed approach, in particular, multi-agent
approach to planning.
The Distributed Constraint Optimization Problem
(DCOP) methodology implements the use of agents in
optimization problems with constraints in distributed
systems (Meisels, 2008). The algorithms take into
account the network structure of the problem. The
general principle of such algorithms is decentralization
in decision-making, dynamic nature of emerging
decisions and gradual striving for equilibrium in
conditions when in the presence of external influences
the multi-agent system finds a new equilibrium
position. However, a disadvantage of distributed
algorithms is exponential growth either of the number
of messages exchanged by agents or of their volume
(Yokoo, 2001, Petchu, 2009). To reduce growth
various heuristics are used.
(Pinto, et al., 2018) discusses a method for
optimizing planning of interaction in a group of
satellites and ground stations, taking into account
priorities and operational constraints. In (Wörle, et al.,
2015), a system of incremental mission planning for
spacecrafts is described, in which operations are
rescheduled in the shortest possible time to meet new
restrictions and rules.
For practical solution of the planning problem for
survey schedule, it is proposed to divide the planning
process into two stages:
1. Conflict-free planning, the goal of which is to
obtain initial acceptable schedule.
2. Proactive planning that tries to improve the
resulting schedule.
When planning, it is necessary to dynamically
adjust the schedule of target application of the space
system as new applications are received, application
parameters or composition of the space system change,
or unpredictable events, related to meteorological
conditions or equipment failures, happen.
Thus, the planning system for target application of
the Earth remote sensing satellites can be attributed to
complex adaptive systems, for efficient management
of which the principle of adaptive restructuring of
decisions and action plans for real-time events is
proposed (Rzevski, 2014).
For the second planning stage, a multi-agent
approach has been chosen, since it has proven practical
effectiveness in tasks requiring operational solutions
(Wooldridge, 2009, Shoham, 2009, Skobelev, et al.,
2016).
As a result of agent interaction, the plan obtained
at the stage of conflict-free planning is adaptively
adjusted by resolving conflicts and re-planning of tasks
in order to achieve the best option for their possible
placement compared to the current one, in order to
improve the quality of the whole schedule (Skobelev,
et al., 2016).
3 DESCRIPTION OF THE
PLANNING PROBLEM
To build a schedule for target application of a swarm
of satellites, a simplified mathematical model of the
ERS space system is used.
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