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    The telescope collapsed  on 01dec20 at 7:52:27.6  (last communications with the tilt sensor running in the dome). This page has info on things that occurred after the collapse.

Links:

• list of drone videos after the collapse
• Monitor the stability of the platform and azimuth arm on the ground.
• Some photos after the collapse
• 201208 : measure distance to span the moat under the dish.
  

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Monitor the stability of the platform lying on the ground

    Every day felix and I shoot 5 points on the platform and 2 points on the end of the azimuth arm to see if the debris is moving. We sit at the helipad  and shoot across the dish to the platform and az arm on the far side of the dish (about 350 meters). We are measuring to a reflectorless surface (no prisms). We've chosen mainly bolt heads for the points.

    The points are label P1-P5 on the platform, and P6-P7 on the end of the azimuth arm. The images below show the locations of the points.

• P1-P5 on platform (.jpeg)
• P6-P7 on end of azimuth arm (.jpeg)

 The plots show how far (radial distance) the points have moved from the first measurement day,

     How the platform/azarm has moved as they sit on the ground (.ps) (.pdf)

• The vertical axis is the  distance each point has moved from the first measurement (02dec20f for platform, 4dec20 for az arm end)
• The colors separate out the points measured.
• Page 1 radial motion points.
• Top - radial motion of platform points  P1-P5
  
• bottom - radial motion of the az arm tip, points P6-P7
• Page 2,3 x,y,z motions of platform (page 2) and tip of azimuth arm (page 3)
• X-east, Y north, Z up vertically
• The reference prism that set the theodolite  azimuth 0 was measured to be 65 deg east of Magnetic north
• I've used magnetic north 13deg west of true north.
• Page 4: diagnostic looking at the azimuth angle for the measured points and the reference prism.
• Top,Middle, change of the azimuth angle for the platform and az arm points
• Bottom: stability of the northern reference prism that is used to define azimuth 0
• The az 0 is  set by looking at the northern reference prism
• After measuring the platform,azimuth points, we remeasure the northern reference prism
• If nothing has changed, this should still be at az=0
• The bottom plot shows the azimuth angle of the 2nd measurement of the reference prism.
• 7dec20 morning has a large offset (40 asecs)
• This is the only set of points that were measured around sunrise.
  
• More measurements at this time will show whether this is a temperature affect (or just that phil screwed up ..)
• 08dec20. phil screwed up by using an aluminum tripod. the problem is differential heating of the tripod legs at sunrise.
• I could see the tilt change as the east leg heated before the other 2. Need to switch to wooden tripod (but will mess up reference point).
  

Measurement errors:

• TM50 errors:
  
• Angle error: .5 asec --> .8 mm At 350M.
• Our angle error is much larger:
• we don't have a prism we are shooting off of, so aligning with the bolt visually causes extra error.
• Distance error:
• on reflectorless measurements: 2mm + 2ppm . at 350 meters->2.7mm
• Our distance error will be worse since we may not perfectly center on the bolt head or auxpin center. The laser spot size is larger than the bolt head.
  
• Size of laser beam at 350 meters.
• the laser beam spot size is 5.6 x 8.75 cm at 350 meters.
  
•  I assume that the receive ccd will find the center of the returned signal to a lot better than this.
• Position, level/tilt adjustment of the theodolite
• We position the theodolite above the survey marker at the helipad with the tm50 positioning laser.
• The tm50 is then leveled using its digital bubble
• The measurements are then automatically corrected for any level errors during shooting.
  
• Reference frame error.
• We are using a tripod with prism on top to set our azimuth for each day of shooting.
  
• This may move a bit in the wind (1mm?)
  
• The tripod is about 17 meters away. a 1mm error at the tripod would make a 2.5 cm error at 350 meters.
• What is the largest error?
• My guess is that our ability to manually center on the points causes the largest error.
  
• When the bolts are shadowed or when there is bright specular reflection, it is harder to center on them.
• Looking at the images that accompany each measurement, you can see that we are occasionally offset from the center of the bolt head.
• 08dec20: found that largest error for morning shots is the aluminum tripod we are using. At sunriset the legs are heating differentially causing tilt errors.
  

processing: x101/survey/pltlow/pltdat.pro, getdata.pro

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201208 Distance needed to span the moat

The location of 4 tiedown blocks were measured to see what was needed to span the moat.
The block orientation is

	distance Feet	block 1	block 2
SE to NE distance	49.7	SE image	NE image
SW to NW distance	50.4	SW image	NW image

The cross hair shows where on the block the measurement was made.

processing: x101/survey/moat/printmoat.pro

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Some photos after the collapse

date	object	links	notes
201204	tops of tower 4,8	t4LowRes t4Hires t8lowRes  t8Hires	Shows loose rocks at the top. taken with theodolite from helipad
201208	T4auxN on dish T4AuxN end in dish	lowres      hiRes .jpeg	Want to save end of this cable for analysis. taken with theodolite from helipad Shows end hanging in dish
201208	lead blocks under dish	.jpeg	by  end of azimuth arm.