I've read sci-fi in which a starship bridge synthesized smells. E.g.
burning insulation smells when there was burning insulation in the
engine core at the far end of the ship.
What would be the standard thing to do? A yellow "check engine" light
on the dashboard? It might go unnoticed, although the very large
explosion a short time later won't. A loud alarm? That would be
typical, but how the hell are the officers supposed to discuss and
work on solving the problem with that kind of a racket drowning them
out?
There are multiple considerations to take into account here, and I
believe the number of crewmembers is crucial to selecting the correct
feedback mechanisms. Some thoughts:
- You don't want to overwhelm any one single sense, so you want to
distribute your feedback (if there's a lot of it) throughout the
various senses of the operator. You would use all of sight, hearing,
feeling (e.g. force feedback) and even, as you suggest, smell. I don't
quite see taste being used, but the balance sense is a definite maybe.
- You probably do not want to use loud, audible alarms on a bridge
with two or more crewmen when those crewmen depend upon vocal
communication to work the problem.
- The more crewmembers you have, the less you will have to use
additional senses, since each crewman can be given a very focused task
and each will independently be able to assess when a situation is
grave enough to have to alert their superior. The lone crewman,
however, will have to process all incoming information himself and so
you want to use as many of his senses as possible. The lone crewman
example is therefore, I believe, the most interesting one in this
regard since it poses the biggest challenge in categorizing
information and synthesizing useful feeback.
- It is important that the computer is able to correctly categorize
various pieces of information and assign each a suitably subtle or
obvious sensory feedback mechanism. (I should add that I could see a
similar development happening for the modern infantryman: modern
battlefield technologies make available to him a staggering amount of
information but he can't possibly process it all on his own. I imagine
a team of 1-5 people dedicated to each infantryman, processing
information and presenting the salient bits to him through various
pieces of non-intrusive feedback apparatus.)
A smell can directly talk to the hindbrain and produce a visceral
awareness of danger, something wrong, or something off, or just
information. A rotten smell to indicate a biohazard detection; smoke
when there's fire; vague sea-breeze air-freshener type smells might
indicate the outside environment is pressurized and safe to breathe;
and so forth.
I expect that some of these will tend to be at the forefront of the
crew's mind at the time when they become relevant. That is, if you
intend to leave the starship you're going to manually inspect the
environment readouts first anyway and even if you don't, the ship is
likely to give you a warning if you try to operate the airlock when it
has detected adverse conditions outside.
Smells are probably best used for low-key, lasting conditions that
aren't particularly critical but which you will eventually want to get
around to addressing. A low but measurable pressure loss perhaps, or
some small anomalous drift that thrusters can easily compensate for.
It seems dangerous to overload smells that might otherwise be natural
to the surroundings though. For instance, if smoke smell is
synthesized to warn of a fire elsewhere in the ship, then this might
conflict with the natural smell of smoke that would develop when
there's a fire on the bridge.
And these don't obstruct communication even though they
don't risk going unnoticed -- aside from the relatively innocuous
ones, where their not being noticed doesn't mean not being alerted to
a hazard, but instead perhaps assuming more hazard than is there,
which is the safe way to err.
There would need to be logic in place so as to escalate the feedback
level of the more hazardous events. So a pressure loss smell might be
promoted to an audible alarm if you're in danger of losing all your
atmosphere within an hour. (That being said - I can't imagine what
might motivate anyone to enter space combat with a fully pressurized
starship anyway, but this /is/ fiction we're talking here.)
A few additional things to keep in mind:
1) Smells don't necessarily mix well, so you might be limited to one
at a time.
2) You'll want to have a fairly effecient ventilation system so as to
be able to get rid of a smell quickly once its cause has been dealt
with or a new, more important, smell needs to be substituted.
3) You want to avoid unpleasant smells since they may negatively
affect the performance of the crew.
Cheers
Bent D