Procedure to Remove 2.5m Secondary Truss
Prepared by Russ Owen, French Leger, and Larry
Carey
Reviewed by Mark Klaene
Maintained by Gretchen Van Doren
Last modified on 2001-10-03 at 10:10
Cautionary Notes
- This operation requires 5 people.
- If the telescope runs away at any time, engage an e-stop
button immediately.
- The following weather conditions must be met:
- No threat of precipitation
- Sustained wind speed < 35 MPH for 15 minutes
- Wind gusts for instrument changes < 25 MPH
- Dew point depression: >= 4°F or 2°C
- Dust count < 10,000 units
- Check for condensation regularly when the dew point
depression is less than 8°F or 6°C. Close the
enclosure if condensation is found on rails, building skin, or
the top of the doghouse.
- Do not push the dust limit and the dew point limit at the
same time. If the dust counts are near the stated limit, it is
best to have a dew point depression of > 18°F or
20°C.
- Safety wear (recommended): rubber-soled shoes, hard hat.
- Only people trained by observatory staff may execute this
procedure.
Equipment Required
Wind Baffle Pendant Control; Location: 2.5m
enclosure
Wheels; Location: 2.5m storage trailer
Support Brace; Location: 2.5m storage trailer
Spreader Bar (for wind baffle counterweights);
Location: behind the Machine shop.
Wind Baffle Counterweight Mounting Blocks; Location:
2.5m enclosure cabinets.
Pallet Jack; Location: 3.5m enclosure ground
level
Lumber (to stack counterweights); Location: Garage;
Appearance: 4"x4"x24"
Scrap wood to protect the floor when setting down
counterweights.
Primary Mirror Hard Covers; Location: 3.5m enclosure
ground level
Initial State of Telescope
- All instruments removed (excluding the spectrographs) and
safely stowed.
- Spectrograph corrector removed and safely stowed.
- Wind baffle removed and wind
baffle support frame secured (tied down and supported with
jackscrews).
- M2 removed and
safely stowed.
- Engage at least one E-stop.
Procedure
Note: stow all items mentioned in procedure in the plug plate
lab.
- Attach two sets of wheels to the east end of the secondary
truss.
- If any accessible wires run to the truss, detach them (we'll
get the wires inside the truss later).
- Rig the secondary truss to the overhead crane. Run two 12 foot
straps to the east corners (one strap per corner), double them and
connecting the ends to a large shackle at the crane hook. Run two
8 foot to the point where the east conical baffle mount attaches
to the truss, again doubling them and connecting the ends to the
large shackle at the crane hook. This should center the load
adequately.
- Take up some weight with the crane by monitoring the tension
on the straps.
- Remove the secondary truss alignment pins, as follows: run a
nut down a few turns with a wrench to begin to pull the pin. Then
back the nut off a bit and pry the nut and pin out with a
marlinspike. This avoids tightening the nut so far that it jams on
the pin.
- Loosen the bolts holding the secondary truss.
- Adjust the crane to take the weight of the truss.
- Remove the screws holding the truss.
- With the overhead crane, move the truss slightly east, away
from the PSS.
- Detach all wires running through the truss.
- With the overhead crane, move the truss far enough east to
clear the wind baffle frame.
- Attaach the west wheel to the truss. Rotate the truss a bit if
required, being careful not to hit the primary baffle or anything
else.
- Lower the truss onto its wheels and detach it from the
crane.
- Attach a support brace at the PSS end of the truss, connecting
the upper and lower ends.
- Roll the truss out of the enclosure.
- Remove the wind baffle counterweights:
- Rig the overhead crane with the wind baffle
counterweight spreader bar. If using the old spreader bar (an
improved one is planned), use two doubled 8 foot straps (load
capacity of 1500 lb minimum) to attach the bar to the crane.
Suspend 6 foot straps from the ends of the spreader bar to
attach to the counterweights.
- Attach the wind baffle counterweight mounting blocks to the
front of the wind baffle frame.
- Remove the two thinnest blue wind baffle counterweights (40
lbs each) by hand and stow.
- Remove the next thinnest blue wind baffle counterweights
(70-80 lbs each) by hand or crane and stow.
- Remove the remaining two pairs of blue wind baffle
counterweights by crane. Set on 4x4s and stow with the pallet
jack.
- With the crane and spreader bar set-up, remove the outer
white wind baffle counterweights. Set on 4x4s and stow with the
pallet jack.
- With the crane and spreader bar set-up, remove the middle
white wind baffle counterweights. Set on 4x4s and stow with the
pallet jack.
- With the crane and spreader bar set-up, move the inner
white wind baffle counterweights to the mounting blocks at the
front of the wind baffle frame.
- Remove all rigging from the crane and raise the crane out
of the way.
- Move all four telescope counterweights to the top of their
range (approximately number 750).
- Check the balance of the wind baffle plus telescope (the two
are turnbuckled together and act as a unit):
- Attach the wind baffle pendant control.
- Station one person in the lower level to watch the torque
reading on the wind baffle altitude motor amplifier.
- Make sure the wind baffle tie-down strap allows about one
foot of motion.
- Remove the west jackscrew (the one preventing the wind
baffle from going up).
- Release all E-stops.
- Release the altitude brake.
- Move the wind baffle slightly up and down. The torque
reading (which is in percent) should be no higher than number
60 in both directions. If it is higher, press an E-stop and
rebalance the telescope.
- Engage an E-stop.
- Remove the wind baffle tie-down strap and the jackscrews.
- Release all E-stops and raise the wind baffle and telescope to
zenith. Monitor the torque as you go: if it exceeds number 80,
engage an E-stop and rebalance the system.
- Pin the telescope at zenith. Pushing the pin in engages an
E-stop, so if the pin jams you'll have to use the turnbuckles (not
the pendant) to free it.
- Engage an E-stop.
- If you are done, set the hard covers on the primary mirror. If
you are planning to remove M1 now, leave the covers off and
proceed with M1 removal.
- Later, when you are done working in the enclosure, store the
truss sideways inside the enclosure.
Document History
2001-08-10 first public release. R. Owen.
2001-08-16 edits F. Leger, R. Owen.
2001-08-28 edit M. Klaene, add crew.
2001-08-29 web page created; format edits by GVD
2001-08-29 edit R. Owen.
2001-09-05 web update GVD
2001-09-05 R. Owen: restore list formatting and improve HTML
conformance.
2001-10-03 R. Owen: minor improvements based on recent
removal.