From: burrynulnulfour@ppllaanneett.nnll   
      
   On 17.09.19 2:03, eripe wrote:   
   > On Tuesday, September 17, 2019 at 5:09:00 AM UTC+7, Bob Jenkins wrote:   
   >> Space elevators won't work.  Well maybe they will but they're more   
   complicated than we've been thinking.   
   >>   
   >> A space elevator would be anchored at one point on earth, usually over the   
   ocean on the equator, then would extend straight up to about 1/5th the   
   distance to the moon.   
   >>   
   >> A minor overlooked matter is the moon.  It's 1/81th the mass of the earth,   
   and on average 10x further from the elevator than the earth, so the elevator   
   would be pulled up at 1/8000th its weight when the moon is overhead.  So the   
   connection to earth    
   has to be strong enough to resist a force of 1/8000th the elevator's total   
   mass pulling up.  Like tides, it'll be 1/8000th heavier when the moon is   
   opposite the elevator, so it's more like 1/4000th fluctuation daily.   
   >>   
   >> But the major overlooked matter is that the earth's equator is not aligned   
   with the moon's orbit.  It's off by 18 to 29 degrees.  Two issues.   
   >>   
   >> 1. The elevator's orbit wants to be in the plane of the moon's orbit,   
   because the moon tugs it that way once a day.  On planets without a moon, the   
   sun will have a similar effect.  The plane of the earth's orbit around the sun   
   and the plane of the    
   moon's orbit around the earth are pretty close, off by about 5 degrees.  If   
   the elevator isn't in the moon's plane, it'll fall towards it, and keep   
   falling past it then fall back, oscillating back and forth.  "Precession."    
   From earth this looks like    
   tilting north, then south, then back to north, once a day.  If you start with   
   an elevator pointed up, after a few years it'll have fallen 2*29 degrees to   
   the side, forming a 32 degree angle with the ground, then it'll rise back to   
   straight up, back and    
   forth.  If you want to prevent it from precessing, you have to actively push   
   it sideways, which is a thrust of about 1/100000th the elevator's mass times g   
   all the time.  I can't see doing that.  So instead you'd build the elevator in   
   the moo   
   n's orbital plane in the first place, and it would tip north and south daily   
   by 18 to 29 degrees.   
   >>   
   >> 2. The elevator no longer goes straight up from the nearest point on earth:   
   the connection oscillates north and south from the nearest point between -18   
   to -29 and 18 to 29 degrees daily.  This implies a change of up to 800km of   
   elevator length twice    
   daily.  Perhaps you could spool it up then reel it out again.  You could drive   
   a power plant off of reeling it out.  The elevator cable will be moving pretty   
   fast: 800km in 12 hours is an average of 66km/hour.  Alternatively, you could   
   keep the elevator    
   connection fixed, just tugging harder when the attachment point is pulling in   
   and tugging less when the attachment point is going out.   
   >>   
   >> Any pictures of a space elevator going straight up from earth are as wrong   
   as a stopped clock: they're only right for an instant twice daily.   
   >   
   > The force from the moon is tiny compared to the self correcting force to the   
   rotating plane. If the station is 1° off that plane it will be pulled back by   
   a force of sin(1)= 1,7% of its mass.   
   > The moon can only make it wobble a widdle.   
   >   
   There is no cable able to carry its own weight , and a few percents will   
   make   
   no difference whatsoever.   
   Any cable of any type of matter will break.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)