  A concept of the ground-based optical astronomical observations efficiency is
considered in this paper. We believe that a telescope efficiency can be
increased by properly allocating observation tasks with respect to the current
environment state and probability to obtain the data with required properties
under the current conditions. An online observations scheduling is assumed to
be essential part for raising the efficiency. The short-term online scheduling
is treated as the discrete optimisation problems which are stated using several
abstraction levels. The optimisation problems are solved using a parallel
depth-bounded discrepancy search (PDDS) algorithm [13]. Some aspects of the
algorithm performance are discussed. The presented algorithm is a core of
open-source chelyabinsk C++ library which is supposed to be used at 2.5 m
telescope of Sternberg Astronomical Institude of Lomonosov Moscow State
University.
