Re: Long term viability of geosynchronous orbits

From: Andrew Coyle (andrewgcoyle@yahoo.com)
Date: Fri Dec 07 2012 - 23:09:46 UTC

  • Next message: Jonathan W: "Re: Long term viability of geosynchronous orbits"

    Interesting.  Very interesting that all measurements are done in the classical geocentric math - we measure bodies in space from the non mobile perspective.  Is quantum theory useful?
    
    Andrew
    
    
    On Dec 7, 2012, at 6:00 PM, Jonathan W <tlj1899@gmail.com> wrote:
    
    > George (and everyone else),
    > 
    > Thank you for your very through responses.  I knew that the atmospheric
    > drag at 22,300 miles is very low, but I didn't realize that it is
    > practically zero.  I also appreciated the comments on why we don't have any
    > tiny moons at this moment in time.
    > 
    > Jonathan
    > 
    > On Fri, Dec 7, 2012 at 1:52 PM, George Roberts <gr@gr5.org> wrote:
    > 
    >> I thought that by now Ted would say something but I guess he hasn't been
    >> reading this thread.
    >> 
    >> GEOSYNCHRONOUS VERSUS GEOSTATIONARY
    >> 
    >> First of all, the orbits are called geosynchronous, not geostationary.
    >> Geostationary refers to a particular geosynchronous orbit that doesn't
    >> deviate north or south from the equator.
    >> 
    >> Geostationary is unstable even over one year due to the moon and requires
    >> fuel to maintain.  Pretty quickly dead satellites start to drift north and
    >> south by up to some amount (23 degrees maybe?) then drift back into
    >> geostationary again, then back to non stationary.
    >> 
    >> The orbit form earth looks like the satellite moves north and south along a
    >> line perpendicular to the equator.
    >> 
    >> This doesn't answer the question about viability as geosynchronous can be
    >> stable for I'm sure thousands of years.
    >> 
    >> DRAG
    >> Another issue discussed was drag at that altitude.  Yes, there's drag but
    >> it's probably too small to worry about.  Someone correct me.
    >> 
    >> TIDES
    >> I've read that ignoring drag, anything orbiting completely inside
    >> geostationary distance will have it's orbit decay due to tides.  Anything
    >> outside that distance will increase it's orbit due to tides.  The moon is a
    >> good example.  It is outside that distance (by a factor of about 10) and
    >> has
    >> been moving farther and farther away from the earth despite drag.  The
    >> energy to move the moon to a higher orbit came from the earth's rotation -
    >> the earth is rotating slower and slower as the moon's orbit is lifted
    >> higher
    >> and higher.  But the closer you are to geosync, the smaller the effect.
    >> Which leads us to graveyard orbits.
    >> 
    >> GRAVEYARD ORBITS
    >> http://en.wikipedia.org/wiki/Graveyard_orbit
    >> When a geosynch sat gets down to 3 months left of fuel they usually send it
    >> into a Graveyard orbit which is *higher* than geosynch.  The goal is for
    >> all
    >> dead geosynch satellites to go there but only 1/3 or so make it.  The
    >> reason
    >> for moving it higher versus lower is so that it is out of the way of new
    >> geostationary sats on their way to their new orbit.
    >> 
    >> HOW LONG?
    >> But none of this answers the question, how long would a geosynch sat last?
    >> I don't know the answer.  I suspect it's much less than 100 million years.
    >> If it was that long then I would expect us to have lots of other small
    >> moons
    >> up there.  I suspect it's more like thousands of years but I really don't
    >> know.   Maybe 100,000 years.
    >> 
    >> A two body orbit is amazingly stable.  Add a third body (like the moon) and
    >> things are very unstable.  There aren't very many (any?) stable orbits left
    >> inside the orbit of our moon.  Otherwise we would have more moons.
    >> Including only Earth, Moon, Sun, Jupiter and trying to find a stable orbit
    >> inside the moon's orbit that lasts more than a million years is probably
    >> impossible.
    >> 
    >> So I don't think this photo-disc-message will last long enough for aliens
    >> to
    >> find it.  It would have been better to put it on the moon.
    >> 
    >> - George Roberts
    >> http://gr5.org
    >> 
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