Goals:

To bring all segment piston relations to with in +/- 10 microns of segment 43.

Equipment and Conditions Required:

small basket on JLG
handheld spherometer
RS232 cable from JLG basket to control room or primary mirror platform
Styrofoam pad
safety harnesses for JLG people
3 radios
lap top computer or RS232 terminal

Personnel Required: 3
JLG driver
measurement person
ground support, operate Sps and structure

Frequency:

Responsible Party:

Procedure:

1. The day before (or early in the morning) change to the small JLG basket.

Verify that JLG is full of gas. Test the spherometer for proper operation with the RS232 interface. Connect to lap top or terminal. Turn on, verify that measurements are sent when the button is pressed. Check battery, if display is fading or reads bp, replace battery. The battery is model CR2450, 3v lithium. Verify that a hard rubber tip of some sort is on the micrometer tip. Verify that spare batteries are on hand.

2. The night before the last thing the night staff should do is to stack the array as well as possible. The air conditioning should then be turned on and set for the current truss temperature.

3. The day of pistoning, gather up tools and equipment. Pistoning should be planned to start in the early morning or the shortest time from the stack.

Connect the spherometer and a laptop or terminal server to the RS232 cables. The protocol is 1200 baud, 8 bits, 1 stop bit, no parity. Test the connection by turning on the spherometer and pressing the RS232 cable button. A reading should appear on the terminal.

4. The measurement person will need to lay down in the JLG basket so the styrofoam pad is for them to lay on. Test spherometer prior to going up. JLG personnel should go to the bathroom prior to going up. All equipment should be removed from pockets.

5. The JLG should be maneuvered into the structure and piston measurements should be started at segment 43. Follow the map to piston all segments.

Piston measurements:

Measurements are made between a reference segment and a test segment.

See piston measurement graphic

1. Calibrate the spherometer prior to each measurement by placing all four legs on the reference segment and pressing the reset button on the micrometer. This can be very awkward for some segments.

2. Place the three plastic feet close to the edge of the reference segment.

3. Gently lower the micrometer leg onto the test segment. Use the weight of the spherometer and light pressure to hold the micrometer down. Firm hand pressure will cause 5-10 microns of piston in the segments giving a bad reading. Keep you hand still. Avoid any dragging of the micrometer tip over the surface. No only will it potentially scratch the surface but even a very small drag will cause the micrometer to read improperly at the 5 micron level.

4. Without moving the spherometer, press the button on the RS232 cable three times in order to send three readings to the person on the ground. These readings should match to 1 micron. The ground person should average these readings. This reading is know as the forward reading.

5. Lift the spherometer turn around. Repeat steps 3-4 but place the plastic feet on the test segment and the micrometer on the reference segment. This is know as the reverse reading.

6. The required piston is calculated as Piston = (Forward - Reverse) / 2. The ground person should record this reading and apply it via the PMC interface.

7. Repeat steps 3-6 to measure residual piston. If required, insert additional piston until residual is under 10 microns or so.

8. Do this for all segments working out from segment 43.

Safety Precautions:

Notes:

History: