  The controversial hypothesis that 'Oumuamua (1I/2017 U1) was an alien craft
dominated by a solar sail is considered using known physics for the two
possible cases: controlled and uncontrolled flight. The reliability engineering
challenges for an artifact designed to operate for 10^5 - 10^6 yr are also
considerable. All three areas generate research programs going forward. The
uncontrolled case could be either "anonymous METI" (messaging extraterrestrial
intelligence) or "inadvertent METI". In the controlled case the nature of the
origin star, trajectory guidance from the origin star to the Sun, and the
identity of a destination star are all undecided. The "controlled" case has
more strikes against it than the "uncontrolled" case, but neither suffers a
knock-out blow, as yet. Some of the issues turn out not to be major obstacles
to the alien craft hypothesis, but others weaken the case for it. Most,
however, imply new studies. Some of these, e.g., intercept missions for new
interstellar objects, are concepts being developed, and will be of value
whatever these objects turn out to be. Overall, these considerations show that
a many pronged, targeted, research program can be built around the hypothesis
that'Oumuamua is an alien craft. The considerations presented here can also be
applied to other interstellar visitors, as well as to general discussions of
interstellar travel.
