Coarse phasing JWST using NonRedundant Tilts (NRT) in TFI
a back-up method requiring no extra hardware
Anand Sivaramakrishnan
JWST TFI Science Team (NRM lead)
JAM team lead
Stony Brook University Physics & Astronomy Department
Peter G. Tuthill
University of Sydney & JAM Team
D. Scott Acton
Ball Aerospace
1
STScI TIPS JIM November 18 2010
JWST Commissioning
2
Exit gate: no segment deviates in piston from
the mean piston of all segments by >~ 300nm
Baseline method: Dispersed
Hartmann Sensing
•Well-understood
•Works well on WFSC testbed
•Two of them in 2 NIRCams
•STScI expert Erin Elliott
•Looks good
3
Why develop back-up?
•Comfort
•Uses different instrument than NIRCam SW
•Flexible diagnostic tool, mitigate risks
•No new hardware required
•Look at the NRT idea for show-stoppers
4
Image Stacking before Coarse
Phasing
•segment images must be moved to fall at a common
location on one of the NIRCam SCA’s - “Stack Center”
•Large moves inaccurate, small moves accurate (details
ITAR)
5
Groups of three segments
6
Groups of four segments
7
NRT PSF
8
Spectral Bandwidth
9
Filters
Capture range
L = lc/b = R.l
TFI R=100 4-5um
NIRCam LW
R=100 4 filters
2np ambiguity:
3 wavelengths
10