[extropy-chat] FWD [forteana] Re: Are dwarfs better for long duration spaceflight?]

[Terry W. Colvin]

On Tue, 30 Aug 2005 23:31:00 -0700,

"Terry W. Colvin" <fortean1 at mindspring.com> fnarded:

>There is a professional society of which I have been a member
>for over 20 years, SAWE, the Society of Aerospace Weight
>Engineers.  We sit around and argue about stuff like this.  Really.

<snip>

>If you take issue with any of these concepts, do speak
>up and state your reasoning.

There are a lot of interesting points presented here, but I do have
some concerns about going small and light-weight for crew selection
on future manned missions.

Designing for absolute minimum weight aerospace vehicles is fraught
with problems. Current aircraft have a great deal of work done to
define the performance criteria of the vehicle, the loading it is
expected to encounter and such like - referred to as its
"design envelope". Many moons ago I worked on a British military
aircraft that had undergone a drastic weight reduction exercise,
that employed a variety of techniques (using minimum thickness skins,
scalloped edges to cleats and plating, punched and dished holes,
the works). While a measure of weight as saved, it made the vehicle
so difficult to manufacture that the cost increases by far outweighed
any operational savings. it also wrapped the structural capability of
the aircraft very close to its performance envelope - thinner skins
oilcanned and flexed, the scalloped edges around fastener holes
reduced the fatigue life, and so on.

In a nutshell, while there are advantages to making stringent size and
weight requirements on your crew, simply making a tight, lightweight
design is not the complete answer.

I also have a bit of a problem with the physical requirements placed
on a crew. You have also to be concerned with whether or not a given
cew member can coe with possible extremes that could be encounteed
on a long-term mission. Coping with extremes of temperature, air
pressure, acceleration and the like, must also be considered when
choosing a crew. Would, for example, a person of a more delicate
stature be capable of enduring a longer or more rigorous work schedule?
Where does the cut-off occur between body size and work rate?
Simply saying "Astronaut A is thirty percent lighter than Astronaut B,
so has a sixty percent less consumable rate" doesn't mean much if
Astronaut B can do twice the work in a given time and needs to take
fewer rest breaks.

Okay, sitting in the cabin of a spacecraft on a zero-g coast between
Earth and Mars is going to favour the lightweight crew member. But
lugging bits of gear about on the surface of Mars when they get there
is going to put a much greater strain on the smaller guy. The
enclosed-volume-to-mass of a big space suit going to be a lot easier on
the big guy than the little one, especially if things like backpacks and
power supplies are standardised.

I worked on the design of the cockpit of the Royal Australian Air Force
Hawk fast jet trainer. Up until then most of our customers had been on
the small side, and in the "one size fits all" aircraft our major worry
was whether we could wind the rudder pedals far back enough for the
aircrew to reach them. It was a bit of a culture shock to suddenly have
to find room in this little aircraft for the six-footers that the Aussies
were recruiting into their air force. As it is, I'm still worried that their
heads are a touch too close for comfort to the explosive cutting strips
fitted to the inside of the canopy

Like they say, size (in either direction) isn't everything.

Just a thought.

Robin Hill, STEAMY BESS, Brough, East Yorkshire.



-- 
"Only a zit on the wart on the heinie of progress." Copyright 1992, Frank Rice


Terry W. Colvin, Sierra Vista, Arizona (USA) < fortean1 at mindspring.com >
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