TIPS/JIM
16 July 2009
Status of focus and pointing during SMOV4
M. Lallo for TEL
TIPS/JIM
16 July 2009
SMOV Focus & Plan
1.) Focus of ACS/WF channel determined by TEL Group indicates a defocus
equivalent to –2.5 microns of HST Secondary Mirror despace. (Coarser SBC
measurements consistent with this).
2.) WFC3 & COS focus and optical alignment activities carried out by Hartig. During
this process, they were offset last week by the equivalent of this –2.5 micron
amount. This move has left the two new SIs slightly off their best focus but achieves
practical confocality with ACS.
3.) A movement of the HST Secondary Mirror of +2.5+0.5 = 3.0 microns will occur
this Monday (July 20th) and should leave the three SIsʼ focii ~ +0.5 micron.
• Restoration of optimal focus for WFC3 will precede WFC3 PSF specification tests, Early
Release Science, and Cycle 17.
• WFC3 wishes to maintain focus comfortably within 2 microns
• Leaving the OTA focus at +0.5 microns should result in passing through best focus (0) in
cycle 17, and not reaching –2 microns until mid-2012
• STIS slit focus should remain within typical ranges seen in the past since STIS was
originally optimized with OTA at comparable focus values.
TIPS/JIM
16 July 2009
Long-Term Trend of the HST OTA
·Phase retrieval focus results from WF/PC,
WFPC2/PC, & ACS/HRC images since HST
launch culled together, averaged per visit and
put onto same frame (WFPC2/PC focus)
·Secondary mirror moves have been removed
to present continuous curve.
·Curve shown is a fit double exponential:
-5.04 + 56.26e–t/364.53 + 106.24e–t/2237.2
·RMS residuals 2.7 microns
·Asymptote of -5 mic
TIPS/JIM
16 July 2009
SMOV Pointing & Plan
1.) FGS2: has been aligned (for now) with solution good to ~ 90 mas 1 sigma.
• Alignment found ~9” from pre-flight operational values. Not unexpected.
• Updates to scale have also been made.
• Higher order distortion currently assumed as ground-tested. Will be calibrated later.
• Scale and Alignment calibrations have brought the total position error from max of ~22 arcsec
to ~ 90 mas. Will change!
• FGSs 1 & 3 believed to be remained calibrated with total position errors ~50 mas.
2.) SIs: Calibrating the alignment of the SIs to the FGSs determines their location in V2,V3.
Solutions have been worked by TEL & SI teams:
• WFC3:
UVIS, Preliminary results indicate a shift of ~3”, with small orientation change (<0.1 deg
TBD). Not unexpected based on past SIsʼ gravity release, latch uncertainty, and pre-flight model
accuracy. IR, Currently being worked. Larger shift expected due to optical adjustment of channel.
Updates to Ground Systems database on Aug 3 SMS (215)
• COS: Aperture found within 1.8” of pre-flight estimate. Since then aperture has been intentionally
moves significantly as optical alignment is performed. Total shift being determined by COS team.
Values will be used to update Ground Systems database on Aug 3 SMS (215)
• ACS: ACS shift was (–0.55,–0.41) arcsec V2V3. Early 2007 checks gave (–0.32,–0.36). Ground
Systems database update planned for ~Aug 10 (SMS 222)
• STIS: position determined (+0.233, –0.062). Ground Systems database update TBD.