Newsgroups: sci.space
Path: utzoo!henry
From: henry@zoo.toronto.edu (Henry Spencer)
Subject: Re: LNLL Inflatable Stations
Message-ID: <1990Nov15.045618.18276@zoo.toronto.edu>
Organization: U of Toronto Zoology
References: <7154@hub.ucsb.edu> <9011122154.AA02573@iti.org> <2732@polari.UUCP> <1990Nov14.223219.17751@wdl1.wdl.fac.com>
Date: Thu, 15 Nov 90 04:56:18 GMT

In article <1990Nov14.223219.17751@wdl1.wdl.fac.com> jwm@wdl76.wdl.fac.com (Jon W Meyer) writes:
>Just speculation, but although the lighter station is more susceptable to
>drag, wouldn't the lighter weight also be a benefit?  What I'm talking
>about is that it will take less fuel to accelerate a lighter station
>X meters per second than it would to accelerate the heavier station by
>the same amount.  Perhaps these effects could balance each other...

It turns out that the mass of the station is entirely irrelevant, to a good
first approximation, to the reboost fuel requirements.  A heavier station
needs more fuel to reboost but needs it less often.  The requirement is that
the thrust of the reboost engines, averaged over the period between reboosts,
equal the average air-drag forces.  Said forces are influenced heavily by
frontal area and somewhat by shape but not at all by mass.  Other things
being equal -- which they probably aren't -- the LLNL station will probably
need somewhat more reboost fuel because it is bigger.  However, I dimly
recall that it is meant for a somewhat higher altitude, which will help.
Its spin will also help; Fred, in a gravity-gradient orientation, would
always be broadside-on to the "slipstream", while the LLNL station will
spend much of its time at an angle.
-- 
"I don't *want* to be normal!"         | Henry Spencer at U of Toronto Zoology
"Not to worry."                        |  henry@zoo.toronto.edu   utzoo!henry