Re: Serious propulsion

From: Earl Colby Pottinger (earlcp_at_idirect.com)
Date: 02/20/05 

Date: Sun, 20 Feb 2005 09:04:51 -0600
To: sci-space-tech@moderators.isc.org

schillin@spock.usc.edu (John Schilling) :

> alexterrell@yahoo.com writes:
>
> >Henry Spencer wrote:
> >> In article <1108143123.041040.288750@g14g2000cwa.googlegroups.com>,
> >> <alexterrell@yahoo.com> wrote:
> >> >> the problem is not the solar cells but the structural dynamics of
> >> >> enormous lightweight solar arrays...
> >> >> ...Solving either in the next 20 years is conceivable, but not
> >> >> a small project...
>
> >> >But if you have lots of ion thruster, you can have lots of solar
> >> >arrays, each flying independently, powered by four ion thrusters.
>
> >> If they're connected by cables or structural elements, they are *not*
> >> flying independently, and the dynamics problems have *not* gone away.
> >>
>
> >As long as the electrical cable is not taut, they are flying in
> >formation, but exerting no force on each other.
>
>
> The electric cable can only be "not taut", if the cable is massless
> and/or the spacraft are not accelerating. Otherwise, the cable is
> under at least enough tension to supply the force accelerating the
> mass of the cable. While that force may be small, if the other
> part of your system is a swarm of middling large but featherweight
> gossamer structures, it's enough. Henry is right, this is a Hard
> Problem. Almost certainly harder than making one huge solar array,
> and that's not easy.
>
> There may be some merit to a swarm of modestly sized flying solar
> arrays using *beamed* power transfer, whether microwave or laser,
> and I have seen the idea proposed here and there. But it also is
> rather beyond the state of the art.

Don't forget to add in the problem if one of the thrusters fails. With a
large array of thrusters (100+) it would be silly to shut the rest down as
the loss of one thruster would make very little diffirence the flight
profile. But that thruster and it's array will for sure start tensioning the
cables.

Worse would be a thruster with a bad connection to it's power cables, the
engine could start to pogo, and what would be needed to fix the problem even
if the bad engine is turn off would very complex indeed.

               Earl Colby Pottinger 

-- 
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