Procedure to Remove
the 2.5m Secondary Mirror (M2)
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 10:10
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
M2 Crate; Location: stored at American Storage
in Alamogordo; Appearance:
yellow
M2 Belly Band; Location: inside M2 crate;
Appearance: polished metal circular band.
M2 Spreader Bar for crane with down-straps attached;
Location: 3.5m enclosure ground level; Appearance: green.
Force Gauge for crane (500 lb.); Location:
3.5menclosure; Appearance: black
Hydraulic Damper for crane; Location: 2.5m
storage cabinets.
Ladders; Location: 2.5m enclosure; Appearance:
4 ft. step.
Plastic Sheeting; Location: Garage; Appearance:
1/4"
Rigging straps; Location: 2.5m enclosure
storage cabinets; Appearance: variety of sizes
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).
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 the
M2 light baffle:
- Remove
all four M2 light baffle side plates; be careful of the delicate 1/4-turn
quick-release screws.
- Rig the
M2 light baffle to the overhead crane with 8 ft. straps (400 lb capacity
min), and take up some weight.
- Station
one person on each side of the mirror to control the light baffle.
- Loosen
the M2 light baffle and adjust the crane to just take up the weight.
- Unscrew
the light baffle and remove it.
- Stow the
light baffle.
- Rig the overhead
crane with (in order from the hook): hydraulic damper, 500 lb. force gauge
and M2 spreader bar.
- Install the
M2 belly band:
- Place the
belly band around the M2 with the latches on top. Off-centered
trunnions to be positioned toward the front plate of mirror. Hook the
latches but do not close them yet.
- Connect
the spreader bar to the trunnions on the belly band.
- Take up
90-100 lb. of force on the crane hook.
- Put a light
weight level on the spreader bar and level the spreader bar by sliding
the belly band around the mirror.
- Close the
belly band latches.
- Prepare M2
for removal:
- Turn off
24V to Galil
- Detach
all wires coming from the mirror and piezos and make sure they are untangled
and can easily be removed with the mirror.
- Tape thermometer
cables to the back of the mirror with aluminum tape.
- Remove
the Heidenhain encoders and flexures. The flexures are very fragile. If
they are bent, discard them.
- Tape the
Mitutoyo linear gauges fully retracted.
Place a small piece of tape, ends facing each other, to prevent
adhesive from touching the Mitutoyo actuator.
- Lay the big
sheet of plastic on the floor of the enclosure, under M2 and up against
the lip of the enclosure.
- Lay the lid
of the M2 crate, foam side up, on sheet of plastic under M2.
- Take up the
weight of M2: approximately 270 lb. on the force gauge.
- Find at least
two Allen wrenches to fit the set screws that hold the axial actuator flexure
to the actuator (at least one should be L-shaped) and a wrench to fit the
screws holding the anti-rotation link.
- Position
one person, wearing a face mask, in front of the mirror, pushing it east
with gloved hands against the outer edge of belly ban to hold it in place.
Position two people behind the mirror to detach the axial actuators. Have
a fourth person ready to take parts and tools.
- Detach the
axial actuator flexures at the actuator end by loosening (but not removing)
four set screws per actuator.
- Remove the
anti-rotation link (detach at both ends and stow). Warning: the axial
flexures are very vulnerable with the anti-rotation link removed. Do not
allow the mirror to rotate or tip.
- Position
two people in front of the mirror, one at either side, to keep the mirror
vertical. Position one person behind the mirror to feed cables and make
sure the actuator flexures don't hang up on anything. Have a fourth person
control the crane. The combined
weight of the spreader bar, belly band, and mirror is approximately 280-290
lbs. 275 lbs. is the true weight
number.
- Move the
hoist west to gently pull the mirror off its center rod. Be sure to hold
the mirror vertical (it will try to swing) and watch that nothing hangs
up in back of the mirror.
- Verify that
all cables are detached and that the actuator flexures are clear of the
M2 cage.
- Keeping the
mirror vertical, lower it to a few inches above the lid of the mirror crate.
- Double
check the belly band latches.
- Rotate the
mirror face-side down (90 deg.). Note: the rivets on the belly band may
hang up on the lifting fixture.
- Rotate the
mirror about its vertical axis until the trunnions are at the corners of
the crate lid.
- Lower the
mirror into the crate lid.
- Remove the
whiffles. Stuff Kimwipes into mirror holes to keep screws from falling inside
and have a grabber ready. Stow the whiffles (with attached axial actuator
flexures and all fasteners).
- Lay two strips
of plastic outside the enclosure, as skids for the M2 crate lid.
- Slide the
crate lid out from under the truss.
- Place the
main body of the crate on top of the crate lid, being careful to align the
holes in the foam with the mounting pads glued to the back of the mirror.
- Close the
crate latches.
- Double check
the latches. Sometimes they look latched but the hook has not properly engaged
in the slot.
- Do not
rely on the M2 crate latches to support the weight of the mirror. Both
the crate lid and the crate body have handles. Only lift by the lower set
of handles!
Document History
2001-08-10 first public release R. Owen.
2001-08-16 F. Leger, R. Owen.
2001-08-28 edits M. Klaene: add gloves, sheeting, actuator
positioning.
2001-08-29 web page created; format edits by GVD.
2001-08-29 R. Owen: misc. edits.
2001-09-05 web updates GVD.
2001-09-05 R. Owen: restore list formatting and improve
HTML conformance.
2001-10-03 R. Owen: minor improvements based on recent
M2 removal.
2004-06-21 SDSS Engineering Staff:
minor improvements based on last M2 removal.
2004-06-25 Downloaded proceudre to web site;
archived old procedure: GVD