Procedure to Remove
the 2.5m Primary Mirror (M1)
Prepared by Russ
Owen, French Leger, and Larry Carey
Reviewed by Mark Klaene
Maintained by Gretchen Van Doren
Last modified on 2004-06-24 at 10:00
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
M1 Crate; Location: stored at American Storage
in Alamogordo; Appearance:
yellow
M1 Lifting Spider; Location: stored at American
Storage in Alamogordo; Appearance:
green
M1 Hard Covers; Location: 3.5m enclosure
ground level; Appearance: white
M1 Guide Rods; Location: 3.5m enclosure
observing level; Appearance: threaded rod approx 5'
M1 Support Pedestals (with foam pads); Location: 3.5m enclosure ground level; Appearance:
black steel with white foam pads on top.
Eight pieces of 4x6 wood, 6 feet long; Location: Garage
Support Platform (or extension ladder if platform
not available).
Work Light for the person in the center of M1.
Flashlights; (4) rubber-coated
Common Corrector Crate; Location: stored
at American Storage in Alamogordo;
Appearance: black
Common Corrector Cover (with bolts and Delrin washers);
Location: stored in the common corrector crate
Hydraset; Location: 3.5m enclosure ground
level; Appearance: black on rollers
Astigmatism Corrector Tools; Location: storage
trailer on site; Appearance: L-shaped tool and rod puller.
Braided Rope; Location: 2.5m enclosure storage
cabinets; Appearance: 50 feet of 1/2"
Protection Tubes for Axial Actuator Quills; Location: storage trailer on site
Rigging straps; Location: 2.5m enclosure
storage cabinets; Appearance: variety of sizes
Plastic guide strips; Location: 2.5m enclosure
storage cabinets; Appearance: 3/16" x 2" x 4' white vinyl
Initial
State of Telescope
Procedure
Note: stow all items mentioned in procedure in the plug
plate lab.
- Set up barriers
to control personnel traffic.
- Determine
lead person and review procedure with crew before commencing
- Remove hardware
around the front circumference of M1:
- Remove
the witness samples and aperture stop/earthquake ring. The aperture stop
is in four pieces and requires a 5/32" Allen wrench. Be careful not
to touch the fronts of the witness samples.
- Remove
top earthquake bumpers. This requires a 1/8" Allen wrench.
- Set one
hard cover on the south third of M1.
- Rig the
support platform across the south side of the PSS (above the portion of
the mirror protected by the hard cover.)
- Remove the
M1 light baffle:
- Rig the
M1 light baffle to the overhead crane using an 8ft. strap.
- Position
somebody wearing a non-scratchy hat or cap and carrying a work light up
inside the center hole of M1 (standing on the floor). Be very careful
not to touch the common corrector. This same person does all the detaching
mentioned in the next steps and attaches the lifting spider.
- Rotate
the rotator until the light baffle bolts are visible by looking through
access holes in the common corrector mount.
- Unscrew
the M1 light baffle mounting bolts. These are captive bolts; leave them
captured for now.
- Using the
crane, hoist the M1 light baffle out and over the WB frame and stow.
- Install the
remaining M1 hard covers.
- Remove the
common corrector:
- Using the
crane and 3 point rigging, hoist the common corrector cover onto the common
corrector.
- Attach
the corrector cover to the common corrector using the bolts and Delrin
washers.
- Detach
the common corrector from its mounting ring.
- Using the
crane, hoist the common corrector out of the telescope and crate it.
- Retrieve
the brass spacer washers that go between the common corrector and its
mounting ring. (At some point these spacers may be permanently attached.)
- Stow the
crated common corrector.
- Remove
the support platform from the PSS.
- Remove the
common corrector mounting ring (black cylinder in center of M1):
- Rig the
common corrector mounting ring to the crane using an 8 ft. strap through
holes on the ring.
- Detach
the common corrector mounting ring from the rotator.
- Using the
crane, hoist the common corrector mounting ring out of the telescope and
stow in the plug-plate lab.
- Remove
the captive bolts that held the M1 light baffle.
- Attach the
M1 lifting spider:
- Rig the
M1 lifting spider to the crane with a Hydraset.
- Adjust
the Hydraset so it is nearly fully compressed (piston within body).
- Using the
crane, hoist the M1 lifting spider into the center of M1 and attach to
the M1 lifting fixture.
- Remove actuators
and gauges:
- Home M1
actuators A, B, C, and D (see the Galil
Mirror Controller manual for instructions).
- Turn off
the support
system air.
- Disconnect
astigmatism actuator air.
- Remove
the transverse vertical actuator (actuator D).
- Remove
the transverse vertical Mitutoyo linear gauge (Y axis gauge), and remove
the three small black screws on inner plate.
Do not remove the main plate or detach the gauge from the inner
plate or else “absolute” position will be lost.
- Detach
the lateral links at the mirror.
- Remove
the two lateral Mitutoyo linear gauge hard points (the blocks the gauges
touch), using a 0.050" allen key. Note: the gauges themselves
cannot be removed with the mirror in.
- Remove the
astigmatism corrector actuators and rods:
- Turn the
rotator as needed to expose access panels for the various astigmatism
corrector actuators. Rotator positions for removing astigmatism
actuators: 2o,
28o, 72o,
95o, 115o,
158o, 182o.
- Use the
L-shaped tool to pry each rod loose at the actuator end.
- Detach
the actuator from the PSS (squeeze to release).
- Use the
rod puller to detach the rod at the mirror end.
- Turn the
rotator to 0 degrees.
- Position
the three M1 support pedestals, setting them on pairs of 4x6s to distribute
the weight on the floor.
- Detach the
lifting fixture (inside M1) from the PSS.
- Position
four people with rubber-coated flashlights and plastic guide strips on the
PSS to watch the mirror as it comes up.
- Have each
person place guide strip between the PSS and M1. Move it around to check
for obstructions, and then hold it upright while M1 is raised.
- Position
one person inside the M1 central hole. This person controls the crane and
watches the under side of the mirror.
Note: all lifting is done using the crane, not the Hydraset. The Hydraset
acts as a force gauge, shock absorber, and safe way to set the mirror back
down on the PSS (should that prove necessary).
- Using the
crane, raise the lifting fixture just enough to free it.
- Hydraset
- Raise the
lifting fixture a few inches and extend the Hydraset piston.
- Assign
one of the four people on the PSS to watch the Hydraset force gauge. When
lifting the mirror, watch the Hydraset at all times. It should read approximately
2250 lbs when the mirror is raised.
- Install the
mirror guide rods.
- Using the
crane, raise the lifting fixture, until it contacts the mirror. IMPORTANT:
make sure the fixture is seated correctly on the glass, and there is nothing
between the lifting fixture and the glass. Any error could destroy the mirror.
- Raise M1
about a foot.
- Detach all
4 thermometer cable connectors.
- Raise M1
slowly. Be especially vigilant as the bottom of the mirror reaches the tops
of the vent tubes, as the vent tubes have shoulders.
- When M1 has
cleared the PSS, remove the guide rods.
- When M1 is
high enough to clear the wind baffle support frame and flat field lamps,
attach two tag lines around its circumference. Give one rope to somebody
at the west end of the PSS and the other rope to somebody on the floor at
the east end of the telescope.
- Hoist the
mirror over the wind baffle support frame and lower onto the M1 support
pedestals.
- Inspect the
mirror.
- Place protective
tubes over the axial actuator quills.
- Remove the
extension rods from the three axial Mitutoyo linear gauges.
- If you are
going to leave the mirror on the pedestals for any length of time, keep
1200 lbs of force on the crane hook.
- Crate M1:
- Place the
open M1 crate on the back of the pickup truck.
- Back the
truck up to the west edge of the concrete apron.
- Raise the
mirror off the M1 support pedestals.
- Use the
enclosure and crane to move M1 into its crate.
- Roll the
secondary baffle back into the enclosure; note that it fits best sideways.
Document History
2001-08-10 first public release R. Owen.
2001-08-16 F. Leger, R. Owen: corrected M1 guide rods.
2001-08-29 R. Owen: misc. edits.
2001-08-29 web page created; format edits by GVD.
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
M1 removal.
2004-06-24 SDSS Engineering Staff:
minor improvements based on last M1 removal.
2004-06-25 Download to web site; archived old
procedure: GVD