The Telescope (pointing)

1. Pointing background Current pointing errors. Some problems with pointing. Can we point during the painting project. For more info: http://www.naic.edu/~phil The Telescope (pointing)

2. BeamWidths: lband:200”, xband:30” A 1/8 inch offset at focus = 5” error. A 1 lambda motion in focus = 3 db gain loss 5 deg F moves the platform 1 inch vertically Adding weight to the platform: 8/(24) kips lowers platform 1 inch tiedowns Retensioned/(Not retensioned) Pointing model removes time invariant errors. Tiedowns, distomats used to remove time variable errors (from temperature changes). Positioning specs

3. 13 term model in az & za with za lookup tbl. Current model created May 2004 after: Alfa installation Kevlar cables installed in dome New compressors on dome Dome side rollers tightened on 1 side Pointing errors immediately after the models: New pointing model needed after painting. The pointing model

4. AUSAC Meeting · January 16-17, 2007 Current pointing errors • Pointing errors Jan06 to Sep06. • 1 azimuth term in errors • probably coming from a tiedown at the wrong height • Could also be caused by weight being rearranged on the platform • Appeared close to mar05 when td12 jack was replaced. • Structure in az errors  add an az encoder table

5. AUSAC Meeting · January 16-17, 2007 Some problems we’ve had • 2005 distomat failures solved after distomat windows replaced. • Az encoder failures sept,nov06 • Corrosion inside encoder • New encoders installed after fixing rfi • Re-installing encoder uses a mechanical index. • A .1 inch error at 60 feet (index position) is a 5 asec error on the sky.

6. AUSAC Meeting · January 16-17, 2007 Tiedowns losing tension • Tiedowns can lose tension when the dome points at or away from a tiedown. • 27may04 calibratoin run. • 10Am, 84degF, za=16.5 az=155. • Sept06 A2221 (galfa HI halo clouds). • sat at az=0 and drove between za 12 and 19 deg. • Took data 8:30 to 9:30 am. Temp=80 F. • Lost tension on at least 7 days.

7. AUSAC Meeting · January 16-17, 2007 Tertiary drive to move between 2 positions • New tertiary drive system to be installed during painting project. Move between standard and longer optical path (set and leave it). • You lose some gain since out of focus. • We need to: • figure out the new position and any pointing corrections it will entail. • The online software needs to be able to control this. • We need hardware indices to verify that things are in the correct position (in case of encoder failure).

8. AUSAC Meeting · January 16-17, 2007 How much torque to tilt Platform?(or can we paint and point..) • Look at height of platform corners vs az sep06-dec06 • 0 offset occurs when az perpendicular to tower. • Fit line to points when azimuth points at a tower. • Given dome, ch, and counterweight weight, compute the corner deflection vs torque. • cornerHghtIn=.908 - .0003312*torq(kip-ft). • Since corners are 124 feet from the center: platRotAngle(Amin)=2.1 - .00077*torque(kip-ft)

9. AUSAC Meeting · January 16-17, 2007 How much sky motion when platform rotates? • Platform probably rotates about maincable connections. • The sky angle gets larger as you move out in za (for a fixed platform rotation). • You get about an 8 Asec pointing error for a 1000 kip-feet torque. This would be from placing 10 kips near the corner of the triangle. The result is linear in the torque. • The dome at 20 deg would give a 3 Amin error if the elevation rails were not shimmed.

10. AUSAC Meeting · January 16-17, 2007 Sband tx horn • New sband transmit horn installed may06 • Wanted to over illuminate the tertiary. • Increases the gain • Increases Tsys (we don’t care for tx horn) • Increases the kilowatts of power spilling over the tertiary. • The gain increased by about 4% (.4 K/Jy) • New sband receive dewar/horn to be installed soon. • …that’s it….