Environmental Engineering Reference
In-Depth Information
likely recurring theme in future missions. These are among the principal
factors that make autonomy and autonomicity an increasing necessity in many
future space missions.
New scientific discovery is enabled by observing deeper into space using
instruments that are more sensitive and complex, by making multiple obser-
vations simultaneously with coordinating and cooperating spacecraft, and by
reacting to the environment or science of opportunity more quickly. All of
these capabilities can be realized either through the use of autonomous sys-
tems and autonomic properties or by having a human onboard the spacecraft
or, except in the case of very remote assets, by having a suciently large oper-
ations staff at the mission control center. In some missions, a human onboard
the spacecraft would not be able to react fast enough to a phenomenon, or
maintain required separations between spacecraft. In other missions, such as
missions to another planet or the asteroid belt, a crewed spacecraft would be
infeasible, too dangerous, or too costly.
We also saw in Chap.
3
that adding autonomy to missions is not new.
Autonomy or automation has been an increasing aspect of flight and ground
software with the gradually increasing complexity of missions and instruments
and with ongoing budgetary pressures. This trend is continuing into future
NASA missions, more particularly robotic (un-crewed) missions.
11.2 Reliability of Autonomous and Autonomic Systems
In NASA missions, software reliability is extremely important. A software
failure can mean the loss of an entire mission. Ground-based systems can be
tended by humans to correct any errors. In unmanned space systems, with
only a few exceptions (e.g., the Hubble Space Telescope, which was designed
to be serviced on orbit by space-walking humans), any corrections must be
performed strictly via radio signals, with no possibility of human presence.
Therefore, software and hardware for space missions must be developed, veri-
fied, and tested to a high level of assurance, with a corresponding cost in time
and money.
Because of the need for high assurance, one of the challenges in adding
autonomy and autonomicity to spacecraft systems is to implement these con-
cepts so they work reliably and are verifiable. The software must be robust
enough to run on a spacecraft and perhaps as part of a community of space-
craft. Further, the software must be implementable in a reasonable timeframe
and for a reasonable cost (relative to the type and importance of the mission).
Autonomous systems often require flexible communication systems, mo-
bile code, and complex functionality, not all of which is always fully under-
stood at the outset. A particular problem with these types of systems is
that such systems can never really be tested to any degree of suciency,
as an intelligent system may adapt its behavior on every execution. New ways
of testing and monitoring this type of software are needed to give mission
