From: dillard@ccwf.cc.utexas.edu (Alex Dillard)
Newsgroups: rec.arts.sf.science
Subject: Re: Ringworlds
Summary: Radiation measurement is a bad way to keep the Ringworld centered
Date: 3 Sep 92 23:23:06 GMT
Organization: The University of Texas at Austin, Austin TX

In article <2gsy8cq@rpi.edu> kasprj@rpi.edu writes:
> Radiation detectors placed along the ring detect an increase of the solar 
>flux above acceptable levels.[1] Too much solar energy coming in means that
>that section of ring is too close to the sun, so it's time to fire the 
>attitude jets. 
> 
[excellent discussion of attitude jet control system deleted]
> 
> [1]: Niven never mentions these detectors, but their existence is the 
>simplest way to assure that the system works. Note that these "detectors"
>could be mechanical devices or living protectors; given what we know of 
>the Pak, I wouldn't be surprised if the original design had a childless
>protector stationed at each ramjet. 
> 
> [4]: I just realized that you could "fool" a mechanical system into 
>firing when it wasn't supposed to by bombarding the detectors with 
>simulated solar radiation. A living protector wouldn't fall for this, 
>of course. Maybe a better system would be to link all the detectors 
>and have the thrust vary based on the differential between the closest
>and the farthest points. Anyhow, I think that the last surviving 
>protectors would have set up something reasonably foolproof if they'd
>had time.

   There is a problem with using radiation as the basis for determining distance
from the sun, solar radiation flux is neither constant nor uniform.  Solar 
flares, sunspots etc. (what else might effect this is beyond my knowledge, but
you get the idea)  change the ammount of radiation coming out of various parts
of the sun.  (btw, when I say 'sun' I mean the star around which the Ringworld
is built, not Sol)  A much better system for finding the right position for the
Ringworld would be to measure the curvature of spacetime.  If the curvature of
spacetime is greater than the average value, push that part of the ring away 
from the sun.  If the curvature is less, push toward.  How do we measure the 
curvature of spacetime? Simple, have an _extremely_ accurate clock at the 
control station for each thruster.  Each controller sends out a timing pulse to
it's neighbors.  The controller compares it's clock with the times given to it
by it's neighbors, and if it sees that it is faster, it fires it's thruster away
from the sun, pushing it's segment of the Ringworld back down the curvature of
space-time around the sun. If it's clock is slow, it pushes away from the sun,
decreasing the curvature of space-time in it's vicinity and speeding up it's 
clock.  
   A sampling of many of the neighbor clocks would help improve the space-time
curvature measurement, but would slow down the response time, as the controller
has to do more calcualtions to make the measurement.  Looking at one neighbor
further away (say the tenth neighbor to each side) would make the accuracy 
requirement for the clocks less stringent, but the timing of the signal path 
would have to be more stable.  I guess superconductor would be stable enough.
  To initialize the system, some other form of heloicentricity would determine
that the Ringworld was spot-on centered, and then each controller would send a 
timing pulse.  The neighbors recieving the timing pulses would record the 
difference between them, so that differences in signal path length or time would
be removed.  The controller would then fire when the difference between it's 
neighbor's timing pulses changed.  
  Well, now we have the control system, let's build it. 

-- 
 \ _
 - o  We were once so close to Heaven, Peter came out and gave us medals,
  ^   declaring us the nicest of the Damned. - They Might Be Giants
        Alex  dillard@doc.cc.utexas.edu 
Newsgroups: rec.arts.sf.science