Environmental Engineering Reference
In-Depth Information
6.6.8 Spacecraft as Agents
While spacecraft share many of the properties of the agents described above,
the unique environment in which they operate makes unusual demands on
their design. Since spacecraft are mobile, self-contained, and externally fo-
cused, they are often viewed as space-based robots, but this is not the com-
plete picture.
While mobile, a spacecraft consumes much less of its time and resources
for navigation than does a comparable robot. Navigation usually happens at
only a few fixed points in the mission and the spacecraft is focused on other
issues the rest of the time. In addition, the external orientation of a spacecraft
is primarily for the use of science sensors whose data are usually shipped to
earth and not used directly by the spacecraft. Most of the other sensors can
be viewed as internally focused, distributed throughout the vehicle, and their
purpose is housekeeping or health management of the craft. They perform
activities to manage power, manage angular momentum, and keep the craft
correctly positioned. This internal focus has led some to argue that spacecraft
should be viewed as immobots. Certainly, some immobot technologies should
be included in future spacecraft designs.
As autonomous spacecraft become more common, they will find themselves
in the role of determining which science goals to pursue based on the current
situation. If, for example, a pursued science goal cannot be met because of
external events or an internal failure, the spacecraft will choose between the
other available goals to maximize the science returned. Analyzing and pri-
oritizing the information returned to humans is a primary area of research
in software agents. In addition, software agents are a principal focus in the
effort to build cooperative capabilities. In the future, it is likely that groups
of spacecraft will work together to achieve larger science goals. These tech-
nologies, first worked out in software agents, need to be included in spacecraft
designs.
While all of these agent technologies represent elements of the whole pic-
ture, NASA has the burden to evaluate them and adapt the technologies for
spacecraft use. There are many ways that space-mission agent technologies
differ from nonspace agent technologies. Most software agents are ephemeral;
their only goal is to acquire, manipulate, and exchange information, and the
only resource they consume is computation. Spacecraft are not ephemeral.
They exist in the real world and their primary resources are sensors and ac-
tuators. Actions consume tangible resources, and many of these resources are
irreplaceable.
Actions in a spacecraft are usually costly, and once an action is taken,
it may not be reversible. This makes it necessary for planning to factor-in
the resources used and future cost carefully if the action cannot be retracted.
These issues are usually ignored in software agents. Even most robots and
immobots are not as deeply concerned about these issues as are spacecraft.
