18 May 2006 Slide 1 of 10 STScI TAGFLASH Ground System Development Current ground system could support immediate COS launch Current ground system could support immediate COS launch Functionality of all existing science/calibration modes has been tested and reported upon at MSRs prior to January 2004 Functionality of all existing science/calibration modes has been tested and reported upon at MSRs prior to January 2004 COS TV testing in 2003 revealed spectral drift caused by OSM motions COS TV testing in 2003 revealed spectral drift caused by OSM motions Drift occurs after grating-grating changes on OSM1 or OSM2 Drift occurs after grating-grating changes on OSM1 or OSM2 No significant drift found for small OSM motions (i.e, central wavelength changes or FP-POS motions on a grating) No significant drift found for small OSM motions (i.e, central wavelength changes or FP-POS motions on a grating) Tests were conducted during the COS TV in October 2003 to characterize the drift behavior Tests were conducted during the COS TV in October 2003 to characterize the drift behavior Drift is correctable if PtNe lamps are flashed periodically during science exposures Drift is correctable if PtNe lamps are flashed periodically during science exposures COS CALWG met at STScI in January 2004 and recommended that a TAGFLASH observing mode be implemented COS CALWG met at STScI in January 2004 and recommended that a TAGFLASH observing mode be implemented High-level requirements review completed in December 2005 Front end detailed requirements completed February 2006 STScI detailed development schedule presently being refined Planned completion: June 2006 Flash duration and separation specification needed STScI and IDT in CALWG splinters and telecons Test at Thermal-Vac II Bench Testing of Commanding (T. Wheeler) Bench Testing of Commanding (T. Wheeler) TAGFLASH and previously developed Target Acquisition components Late spring 2006 Essential for SMGT-readiness certification

18 May 2006 Slide 2 of 10 STScI TAGFLASH Ground System Development TAGFLASH Mode TAGFLASH Mode STScI detailed development in progress and on schedule Planned completion: June 2006 STScI and IDT refined flash duration and frequency specifications in CALWG splinters and telecons Test at Thermal-Vac II Bench Testing of Commanding (T. Wheeler) Bench Testing of Commanding (T. Wheeler) TAGFLASH and previously developed Target Acquisition components Late spring 2006 Essential for SMGT-readiness certification

18 May 2006 Slide 3 of 10 CBA CBA PtNeWavecalExternalScienceNUVMAMA FUV MCP (1 of 2 segments) External Science Internal PtNe Wavecal COS Spectral Layout for Simultaneous Internal Wavecals and Science Spectra Obtain (continuous or flashed) internal PtNe spectra at same time as science exposure Track internal PtNe lines and apply shifts to science spectrum (all events time-tagged) in COS data pipeline Scattered light from internal wavecal at position of science spectrum is negligible (<1%).

18 May 2006 Slide 4 of 10 Spectral Drift Examples G160M # G285M # G140L # Drift exceeds 1 resolution element Steep Rise Plateau Drift exceeds 1 resolution element

18 May 2006 Slide 5 of 10 Spectral Drift Correction Correction needed to meet Level 1 requirements Correction needed to meet Level 1 requirements Spectral resolution (and perhaps more importantly, line shape) Wavelength zero point Simple correction could be done with existing wavecal capabilities outside science exposures if necessary Simple correction could be done with existing wavecal capabilities outside science exposures if necessary Wavecal at beginning and/or end of science exposure Following charts show this is not satisfactory for long exposures Long exposures could be broken into shorter exposures with additional overhead (~4 min per wavecal, or about 8% observing efficiency loss per wavecal assuming 52 minute orbital visibility) TAGFLASH would embed wavecals in science time TAGFLASH would embed wavecals in science time No overhead for wavecals at all CALCOS to be updated to correct for drifts

18 May 2006 Slide 6 of 10 OSM Drift (G285M) Linear Drift Correction No correction, line is offset and skewed Better shape but still offset by almost a resolution element Linear approximation (beginning and end) Actual motion 1 resel

18 May 2006 Slide 7 of 10 “Optimal” approximation (4 flashes) Actual motion Correction improves shape and offset OSM Drift (G285M) Optimal Drift Correction 1 resel

18 May 2006 Slide 8 of 10 Flash Frequency and Exposure Times Flash Frequency (after major OSM move) Flash Frequency (after major OSM move) First orbit (4 flashes) Flash at beginning exposure as reference Intermediate flash early (~600 sec) to follow fast drift Intermediate flash after another ~1800 sec to follow change in drift slope Flash every 2400 sec thereafter If CVZ, then flash again after another 2400 sec, etc Exposure times Exposure times NUV settings <10 seconds if all three stripes considered in cross-correlation FUV settings 5-30 seconds, or less if both segments considered together Exposure time of at least 5 seconds recommended even in cases where times as short as 1 second would suffice to be certain the lamp flashes

18 May 2006 Slide 9 of 10 Lamp Lifetime Reduced lamp flash durations Reduced lamp flash durations G130M will be workhorse grating (longest lamp exposures) But other gratings might be used with more OSM motions e.g., extended NUV wavelength coverage Assume 1000 COS orbits per year Assume 4 flashes per orbit (4000 flashes per year, probably high) Assume 15 seconds per flash Assume 10 milli-amp current setting On-orbit Usage On-orbit Usage 8 amp hr lifetime budget per lamp (2 lamps available) In one year, use 4 x 1000 x 0.01 x 15 / 3600 = 0.17 amp hr /yr A 10 year mission => less than 2 amp hr of on-orbit usage => Lamp on-time should not be a lifetime issue

18 May 2006 Slide 10 of 10 TAGFLASH Testing Tests during TVac-II Tests during TVac-II SMOV tests SMOV tests Determine drift character on-orbit for suite of OSM motions Allows changes for on-orbit understanding of drift Early pattern will probably be conservative (more flashes)