Transcript AMiBA: Hexapod Commissioning and Pointing

Array for Microwave Background Anisotropy
AMiBA hexapod commissioning and pointing
AMiBA team
ASIAA
NTU Physics
On-site control room:
Remote TCS
2005: on-site testing
Antenna control computer
Example: identification of oscillation problem
and debugging
(ACU)
Mount
 assembly and
intstallation of optical
telescope (OT)
 from oscillations to
smooth trajectories
 from hard limits to
working safety checks
Pointing control computer
commanding possibilities:
• preset az el pol
(PTC)
• startrack ra dec skypol
(hexpol=const or skypol=const)
• program track: ‘any trajectory’
 from manual operation
to automatic schedule
 from no star images to
correct star positions
 ...to smooth operation
Pointing error model: a 2-step approach
1st pointing run: all known pointing corrections activated (PTC)
→ ccd star position error as a function of mount position
→ separate average mount error from optical telescope (OT) error
mount error = left-overs interpolation table
Pointing error corrections
define telescope pointing!
jack corrections:
jack pitch error compensation
(“geometry”)
temperature compensation
2nd pointing run: all known pointing corrections + interp. table
jack rotation correction mode
→ check improvement
•Expected
ujoints locations and jack lengths
support cone compensation mode
pointing accuracy:
ujoints
jacks
telescope corrections: RF/optical refraction mode
without laser system: 12 arcsec
OT correction → dominant correction
with laser system: 6 arcsec
error table interpolation → “left overs”
2006: Improvement in optical pointing performance with interpolation table
azimuth signature
perfect axes
mount axes
without interpolation table
mount/cone tilt
 automatic pointing schedule:
OT axes
1 hour ~ 100 star images
(const. solid angle distribution
over accessible sky)
 ccd image analysis: split error
into azimuth and elevation error
with interpolation table
 identify main OT signature
(solid green line)
and remaining pointing errors
(red scatter)
 one iteration with interpolation
table:
pointing error in az, el reduced
from 0.8 to 0.4 arcmin rms
cone N misorientation
N
2006: radio pointing: drift scan versus offset tracking
A) drift scan
B) offset tracking
step patterns of 2
arcmin offset
Ideally the centers of
cut intersections should
approach a specific line...
compare maximum
to find relative
misalignment of
different antennas
Ant 1
Ant 7
elevation signature
Ongoing efforts and next steps
 use each dish to
measure total power of
the Sun
 A) cut the saturated
power curve horizontally
to find the center, vs.
 B) scan around the Sun
by offsets and compare
their step-like patterns
to find relative
misalignment
Polarization pointing
1-night-tracking
Long-term stability and repeatabilty
of pointing model
2nd,3rd iteration for interpolation table
(goal: 10 arcsec pointing accuracy)
 radio alignment: goal : 2 arcmin relative
alignment w.r.t central reference antenna
 integration of 2nd and 3rd OT