tower 4 auxiliary main cable comes loose from the socket.

10aug20

Links:

Platform positions after the cable failures
monitor the platform corners


cable tensions from p50 sagsurvey

Photos of the damage (available to all)
photos of the cable sockets

11aug20: tiedown tensions and telescope position as we moved to hurricane stow position.
13aug20: measure the distance between the auxmain connection points.
12nov20: measure distance t4 tdmast to broken cable (to check if helicopter winch cable will work)
12nov20: measure distance from winch mount points to top of tower 4 (to raise t4auxNorth cable)

NSF_engineering report on damage to AO (19nov20)

index to some drone photos
 
Notation:




 Intro

  On 10aug20 at 02:35:55 ast the auxiliary main cable from tower 4 (north aux main cable #301) came out of the socket at the tower and fell into the dish.
When the cable fell, the operator stopped the telescope. A few minutes later the operator commanded the telescope to continue tracking. It continued tracking for about 20 minutes.
07nov11 update:
On 06nov20 at 19:39 tower 4 main cable south broke. I've updated the plots to start at 06nov20..
Unfortunately the distomats are no longer hitting the retroreflector on platform corner 4 (dist 3, south side). The plots will show no reading until we realign the distomat).

The plots show the telescope position and tiedown cable tensions when the break occurred (.ps) (.pdf)

SUMMARY:


processing: x101/200810/aux4.pro

Compare platform position after 2 failures

The plots show how the platform moved before and after the cable failures (.ps) (.pdf)

Note: i will update the plot when more data becomes available.

processing: x10/201120/telrotlr.pro


Monitor platform corners

    After 06nov20 cable failure, distomats 3 and 1 no longer hit the retro reflectors. On 20nov20 they were realigned.

The plots show the corner positions of the platform (.ps) (.pdf)

Also take a look at position change during failures;



What was on this page Prior to 06nov20 cable failure :

The telescope is currently positioned at:

Every two minutes the distomats measure the distance to the corners of the platform.
After each reading, a  plot is generated showing the position of the corners (.ps) (.pdf)
( to the following plot, you may have to refresh the page).

The auxmain4North cable was attached about 60 feet before the corner 12 vertex. It was carrying about 100Kips of vertical load.
When the cable let loose

Note: if you seen horizontal lines in all the traces.. this will be missing data when the computer failed to read the distomats.

Table of when things occurred that may affect the position

date
day on plot
description
200812 13:00
0.5
repositioned distomats so they would hit reflectors on triangle corners. started recording.
200820
14:00
8.6
moved the az,dome,ch (a few tenths of deg) to insert the stow pins
200822
10
tropical storm laura approaches ao.

11aug20: moving the telescope to stow position

    On 11aug20 we moved the dome and azimuth arm from the location after the failure to close to the hurricane stow position.

The plots show the telescope motion and the change in the tiedown cable tensions.
Note that positive azimuth angle increases Clockwise (north to east).

Plot 1:overview of telescope positions (.ps) (.pdf)

Plot 2: 11aug20 showing the telescope motion and td tensions (.ps)     (.pdf)

processing: x101/200917/telescopePos.pro, 200811_poskips.pro


13aug20: measuring the distance between the auxmain connection points

    On 13aug20 felix and I used the tm50 theodolite to measure the distance between the connection points of some of the auxmain cables to verify how long any replacement cable needs to be. This will be an approximate value since the platform is currently not in the standard position  (see monitor positions above)... but the cables are currently spanning the distances we measured.

    The technique was:

The table below contains the results:

  Notes:


processing: x101/survey/200813/


12nov20 - distance top of corner 4 td mast to broken cable

    The distance from the top of the platform  corner 4 tiedown mast to the  platform corner 4 broken main cable was measured to see if the helicopter cable has enough reach to lower a person to cut the cable.
Felix and i measured the distances from the helipad on 12nov29 using the tm50 total station. The table below has the results as well as pictures of the measured points.
In the pictures, the crosshair shows the measurement point.

Location
measured x,y,z  points
(from tm50  position)
Distance  from Top point
feet
overview
img
hires
img

x
Feet
y
Feet
z
Feet




top of Mast
302.568
557.392
278.302

.jpg
.jpg
cable socket
299.002
559.302
199.197
79.21
.jpg .jpg
level with bottom of ubolt
298.191
559.688
186.894
91.54
.jpg .jpg

Notes:


processing: x101/survey/201112/t4mast/cmpdist.pro


12nov20 - distance from winch base to top of T4

    Winches will be used to raise the failed T4auxNorth cable. On 12nov20 we measured the distance from the center of the
cement block used to mount the winch to the top of tower 4. We measured two blocks:

The table below shows the distances. It includes pictures of the site line from the block to the tower top.

location
measured x,y,z points
(from tm50 location)
Feet

distance to T4 top
Feet
overview
img
hires
img
Notes

x
y
z




from helipad  block
-460.325
-254.328
321.221
616.25
.jpg
.jpg
1
from block by T4
48.96
-67.231
260.848
273.79
.jpg
.jpg
2
from block by T4
to M1 cable at handrail
46.993
-72.409
266.431
280.07
.jpg
.jpg
3

Notes:

processing: x101/survey/201112/t4auxn/cmpdist.pro
home_~phil