SPACE TELESCOPE SCIENCE INSTITUTE Operated for NASA by AURA COS TAGFLASH System Requirements Review COS Lamp Lifetime Estimates for TAGFLASH Scenarios Steven Penton Center for Astrophysics and Space Astronomy University of Colorado at Boulder 14 December 2005

University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates 2 University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates Requirements Requirements COS Calibration Optics Review COS Calibration Optics Review Lifetime Estimates from FOS and GHRS Lifetime Estimates from FOS and GHRS Lifetime Estimates from COS 2003 Thermal Vacuum Testing Lifetime Estimates from COS 2003 Thermal Vacuum Testing Implications for COS TAGFLASH Operations Implications for COS TAGFLASH Operations Detector Issues ? Detector Issues ? Recommendations Recommendations Presentation Overview

University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates 3 University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates Requirement : The calibration lamps must support a 5-year on-orbit mission (but the goal is 8 years). COS contains two internal Platinum-Neon (PtNe) wavelength calibration (wavecal) lamps, and two flatfield Deuterium lamps on the calibration platform. Additional Lamp Requirement

University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates 4 University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates COS Calibration Subsystem

University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates 5 University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates COS Calibration Subsystem

University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates 6 University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates COS PtNe Wavecal Lamp - Side View

University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates 7 University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates COS PtNe Wavecal Lamp - Front View

University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates 8 University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates Based upon George Hartig’s analysis of the FOS (PtCrNe) and Dennis Ebbets’ recollection of GHRS (PtNe) lamp performance, concludes that the COS PtNe lamps should degrade at 15% per Amp-Hour (A-Hr). After 8 A-Hr, estimates that the COS lamp output would be down to 27% of its original output. Concludes that COS has 2x8 = 16 Amp-Hrs of lifetime wavecal exposure available, a safety margin of 2:1 (Based upon 1000 orbits/yr x 5 yrs x 6 min/orbit.) As pointed out by Ken Sembach on December 15, New Estimates by Florian Kerber, et al. ( ) indicate GHRS degradations on the order of 25% / (50 hrs * 10mA) = 50% per Amp-Hr. Initial Lamp Lifetime Estimates Ball SER No. SYS-039

University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates 9 University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates DRM Scenarios (Design Reference Mission) Science Operations Requirements Document (OP-01) Lifetime. The wavelength calibration subsystem shall be designed to provide the required data for the entire lifetime of the COS instrument. The COS shall be designed for a minimum of five years on-orbit operating life and a minimum of ten years calendar life (CEI Sec ). The pre-launch testing and calibration may represent the equivalent of one year of operations. The Design Reference Mission estimates that COS may be prime instrument for up to 10,000 orbits, with as many as four wavelength calibration exposures per orbit. The DRM also estimates that approximately individual targets will be observed with COS over its lifetime. Each on- board target acquisition may require at least one exposure of the calibration lamp. The above estimates imply approximately 40,000 wavelength calibration exposures. If each exposure requires one lamp to be on for 3 minutes the requirement is for 120,000 minutes (2000 hours) of use. These estimates imply approximately 40,000 turn-on cycles. 10,000 orbits x 4 wavecals/orbit x 3 min/wavecal x 0.01 Amp = 20 A-Hr 10,000 orbits x 6 wavecal mins/orbit x 0.01 Amp = 10 A-Hr, 5 A-Hr per lamp

University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates 10 University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates Looks OK, BUT there is one under “appreciated” aspect and one assumption (15 % per A-Hr) that complicate matters. Estimates of the actual lamp degradations (% per A-Hr) have been measured from Appendix B “Repeatability Monitor” data and will be presented later. First, we need to consider the obvious implication of lamp degradation, one needs to constantly increase the exposure time and/or lamp current to maintain a constant signal-to-noise in the wavecal spectra. Assume 1,000 orbits/yr, 6 wavecal mins/orbit, split between lamps. Complications of Previous Estimates

University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates 11 University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates

University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates 12 University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates 15% per A-Hr + 6 min/orbit = ~ 7 years lifetime

University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates 13 University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates 25% per A-Hr + 3 min/orbit = ~ 7 years lifetime

University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates 14 University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates 5 Repeatability Monitors (Test #850) : Sequenced observations of all gratings with one of the PtNe lamps + FUV and G185M flatfield observations. Each observation fully corrected: Background subtracted FUV : Thermally and Geometrically Corrected Each extracted spectrum cross-correlated to the first observation to ensure only identical spectral regions were tracked. ALL COS exposures examined to determine actual A-Hr used for each lamp (included those observed in pseudo TAGFLASH). The output of the lamps over the 2003 thermal-vac was tracked to quantify actual lamp degradation in % per A-Hr. Appendix B - Lamp Degradation Analysis

University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates 15 University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates t G130M Example

University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates 16 University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates t G185M Example

University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates 17 University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates Results (1000 orbits/yr x 6 min/orbit)

University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates 18 University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates Results (1000 orbits/yr x 3 min/orbit)

University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates 19 University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates PtNe #1PtNe #2 NUV Spectral Stripe ABCA+B+CABC G185M G225M G285M G230L FUV Segment ABAB G130M8050 G160M G140L800 COS Wavecal Count Rates (counts/sec)

University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates 20 University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates COS Wavecal Exposure Times (seconds to 1,000 cts) PtNe #1PtNe #2 NUV Spectral Stripe ABCA+B+CABC G185M G225M G285M G230L FUV Segment ABAB G130M G160M G140L 1.3

University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates 21 University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates The NUV/FUV detectors exhibit efficiency reduction with usage (local gain sag). The figure of merit is total lifetime counts in any spot (fluence). Count Rates < 100 per sec for G130M < 600 per sec for G160M < 800 per sec for G140L/A Max Count Rate per line < 2 per sec G130M/A ; < 1.2 per sec G130M/B < 2 per sec G160M/A ; < 20 per sec G160M/B (2/3 of max allowed) < 6 per sec G140L/A Max Counts per year per line : 1,000 orbits/yr X 6 min/orbit x 60 sec/min x 20 cts/sec = 7.2 million cts/yr per line (1/3 of max allowed) Detector Issues ?

University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates 22 University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates ItemFUVNUVRationale Minimum Count rate: Minimum of 5 lines in each exposure 0.33 cts/sec/line Count rate integrated over emission line : 100 counts in 5 minutes. Maximum global count rate (Time Tag) < 21,000 cts/sec global Time-tag < 21,000 cts/sec global Time-tag Maximum time-tag count rate limited by on-board data processing Maximum count rate in one pixel 5 cts/sec/pixel200 cts/sec/pixel Charge replenishment + uniform image illumination Maximum count rate in one emission line 75 cts/sec/resel800 cts/sec/resel Local bright object protection, max rate derived from CARD limits: FUV: 1500 cts/sec/resel / 20 NUV: 300 cts/sec/pixels x (2x2) optimistic resolution Accumulated counts in one emission line per year 2.2 x 10 7 cts [1000 five min 75 cts/sec/] 2.4 x 10 8 cts [1000 five min 800 cts/sec] Threshold for onset of gain sage: FUV 10 9 counts/mm 2 NUV counts/mm 2 No obvious Detector Issues Count Rate Limits

University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates 23 University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates Don’t Panic The lamp degradation look problematic, but are measured over very small baselines ( A-Hr) We are in the process of organizing an in-depth lamp analysis with non-flight lamps to determine the actual lifetime/degradation rates of COS PtNe lamps Use shorter exposure times for each wavecal (1,000 cts) Use all NUV stripes in cross-correlation Strive to keep lamp usage to < 3 min/orbit Recommendations

University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates 24 University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates Separate wavelength calibration templates are needed for each lamp (PtNe #1, PtNe #2). The lamps are unique, have different usage, and follow different optical paths Wavelength calibration templates MUST evolve with time (at least annually). The line ratios of the lamps change with usage history and current setting Minimize the wavecal local rate check exposure times (1 min x 1,000 orbits x 0.01 mA x 5yrs = 1 mA = -25%) (6 sec x 1,000 orbits x 0.01 mA x 5yrs = 0.1 mA = -2.5%) Recommendations

University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates 25 University of Colorado - Boulder COS Lamp Lifetimes Steven Penton December 14, 2005COS Lamp Lifetime Estimates Investigate whether unique exposure times are needed for (some) NUV FP-SPLIT positions (1 step = 50 p) Investigate whether the lamps can be run at the ‘LOW’ current settings (3mA for PtNe#1, 6mA for PtNe#6) to conserve lifetime (Thermal Vac II, Appendix C) ?? Future Tasks

Tagflash- NUV The Movie 4 minutes of wavecal over 4000 sec (10 sec bins)