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FAST, CHEAP AND OUT OF CONTROL: A ROBOT INVASION OF THE
RODNEY A. BROOKS and ANITA M. FLYNN
MIT Artificial Intelligence Lab*, Cambridge, MA, USA.
Complex systems and complex missions take years of
planning and force launches to become incredibly
expensive. The longer the planning and the more
expensive the mission, the more catastrophic if it fails.
The solution has always been to plan better, add
redundancy, test thoroughly and use high quality
components. Based on our experience in building ground
based mobile robots (legged and wheeled) we argue here
for cheap, fast missions using large numbers of mass
produced simple autonomous robots that are small by
today's standards (1 to 2 Kg). We argue that the time
between mission conception and implementation can be
radically reduced, that launch mass can be slashed, that
totally autonomous robots can be more reliable than
ground controlled robots, and that large numbers of
robots can change the tradeoff between reliability of
individual components and overall mission success.
Lastly, we suggest that within a few years it will be
possible at modest cost to invade a planet with millions
of tiny robots.
1 . INTRODUCTION
Over the last four and a half years the MIT Mobile Robot
Group has pursued the goal of building totally
autonomous mobile robots for a variety of tasks. We
have refined hardware and software tools so that we can
quickly build robust interesting robots. For instance
Genghis, a six legged walking robot shown in Fig. 1
was completed 12 weeks after initial conception, in
response to a JPL workshop on micro spacecraft . The
robot [2,3] was principally built and debugged by two
people, with occasional supporting help from about half
a dozen others. The robot weighs less than a kilogram
and can scramble over very rough terrain. A follow-on
vehicle  will be able to climb metre high rocks, and
travel at around three kilometres per hour. Such easy to
build high performance robots suggest some new ways
of thinking about planetary exploration.
Two of the principal costs in planetary surface
exploration missions arise from the mass of the
planetary rover upon launch, and hand construction of
the unique vehicle itself. In this paper, we demonstrate
that technology has progressed to the stage where we
can tackle both of these problems simultaneously by
creating swarms of totally autonomous microrovers in
the I to 2 Kg range. This way, total mass delivered to the
planetary surface is minimised and in addition, the
multiple copies of the rovers increase the chance of the
mission's success. Cost savings in terms of construction
dollar per Kg result, due to the opportunity to apply
mass production techniques to the roved manufacture.
[Genghis is a 1 Kg six logged robot. It can
walk and climb over rough terrain It has four
onboard processors, twelve actuators with force
feedback, six pyroelectric sensors two whiskers ,
and pitch and tall inclinometers Total time for the
project between initial conception and completion
of the robot was twelve weeks.]
Total autonomy actually increases mission reliability.
Out of control of ground based operators, the robots can
use force control with tight sensing feedback loops.
This is in contrast to the minutes to hours long position
control feedback loops of long delay teleoperation.
Force control is the key to reliable performance in the
face of any uncertainty. By completely removing all
ground based control of the rovers, their complexity
goes down drastically as there is no need for much of the
communications equipment, and no need for the ground
support maintaining communications. Simplicity
increases reliability. In fact, the resulting reduced
complexity of the overall mission will allow complete
programs to be conceived, researched, developed and
launched on time scales more reminiscent of the sixties
than those of today.
In the last part of this paper we present some radical
ideas on how to scale down the size of planetary rovers
even further, to the milligram range inspiring missions
which will capitalise on thousands or even millions of
rovers roaming a planetary surface.