Computational Intelligence - November 2013 - 23

power that must be charged before the rover
The Mars Sample Return (MSR) problem generator
goes off-duty. In fact, this power (which
might otherwise be used to perform a numwas developed with the twofold aim of (i) creating
ber of pre-dusk activities that have to be
well-founded benchmark problem instances with
inevitably postponed to the following day)
particular reference to the MSR domain addressed
must be saved to guarantee the equipment's
proper heating during the longer nights.
in this work, (ii) and establishing an initial stable
With regards to the average battery power
reference to be exploited by other authors aimed
utilization (see both Bat avg (%) columns), we
at addressing similar problems.
observed a rather regular trend which confirmed that the shorter the martian days' duration, the higher is the battery average power
sequences) is related to the fact that, since each problem
demand. While this result may seem quite straightforward (e.g.,
instance always has 4 sequences characterized by a deadline
more battery power is required to safely "survive" the longer
(regardless of its size), the presence of such deadlines
nights), the fact that approximately the same amount of power
become more relevant for the instances where the conis used for both the baseline and makespan-optimized solutions
strained/unconstrained sequences ratio increases.
is puzzling.
One possible explanation may be directly derived from the
formula used for the Bat avg assessment, as we can see that
V. Conclusions and Future Work
while shorter plans should require less battery power (e.g., the
In this paper we presented last results on delivering advanced
distance traveled are shorter), the Bat avg value is inversely proautonomous reasoning capabilities to robotic planetary exploration. In our current work, we were inspired by the requireportional to the makespan (i.e., an optimized makespan
ments of a particular rover-based Mars exploration mission,
increases the Bat avg value). Despite all of the above, the very
namely, the Mars Sample Return (MSR) mission concept.
strict correspondence of values in all the cases remains howOne of the contribution of this work is to integrate the most
ever to be fully explained.
significant MSR mission requirements into a scheduling
Finally, the average rover cache utilization data (both
problem model, the Power Aware Resource Constrained
Cache avg (%) columns) deserve some attention. Looking at
Mars Rover Scheduling (PARC-MRS) problem. Following
the Cache avg (%) columns, a decreasing utilization of the
the proposed model, we presented a scheduling algorithm
cache can be observed as the seasonal situation move from
aimed at synthesizing complete plan sequences that span the
the summer to the winter daylight conditions. This can be
whole mission horizon by reasoning upon a wide set of realnoticed for all the MSR 40 - 25 -) and the MSR 40 - 30 -)
istic mission requirements. More concretely, the reasoner we
benchmark sets, and the same behavior applies to both the
propose focuses on a number of results belonging to previous
feasibility and the optimization assessment data (even
research, and provides an extension of a well-known conthough it can be observed that in the makespan-optimized
straint-based, resource-driven procedure which exploits
solutions the average cache utilization tends to increase).
power aware reasoning capabilities within an integrated resoThis circumstance is easily explained as a direct conselution strategy, where a wide variety of complex temporal
quence of the longer times necessary to complete the same
and resource constraints are considered, with special attention
missions under less favorable power charging conditions
paid to the energy requirements. Indeed, one of the main
(i.e., longer plan makespans entail a less efficient cache utilicontributions of this work is the successful exploitation of a
zation). Yet, it can also be obser ved that in the
well known methodology to represent renewable resources by
MSR 40 - 25 -) case, the previous regular trend is not folmeans of a classical cumulative scheme, to model and solve
lowed: as the lighting conditions worsen, there is an "counthe PARC-MRS problem. We also conducted an experimenterintuitive" behavior where the average cache utilization
tation assessment to evaluate the efficiency of our solution
seems to increase, before definitely falling to the expected
algorithm, as well as the effectiveness of an optimization
values. This "anomaly" on the general trend might be
schema in providing minimum-makespan solutions. We proexplained with the influence of the maximum time winposed a study of the benchmarking problem tailored to the
dows on the execution of some job sequences, which may
MSR domain, and produced a methodology to generate
cause the rover to decide not to release all of the acquired
meaningful PARC-MRS problem instances. As a result of this
samples at the AV location before heading for a new experistudy, we have created a benchmark library using baseline
ment's location, in order to satisfy some experiment-related
parameter values which were carefully selected from recent
deadline constraint. It is straightforward that in all such cirreal-world mission specifications. More concretely, we have
cumstances, the cache utilization tends to increase as the
based our benchmark production on one of the rover models
cache itself remains occupied by the unreleased samples. The
offered by the ESA's 3DROV simulator, an advanced and
reason this phenomenon becomes evident only with the
realistic planetary robot design, visualization, and validation
smaller instances (i.e., those composed of 20 experiment

November 2013 | Ieee ComputatIoNal INtellIgeNCe magazINe

23



Table of Contents for the Digital Edition of Computational Intelligence - November 2013

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