Monthly Observatory Report
                                          for
                                   September 1994

1. MONTHLY HIGHLIGHTS:

   1.1 Summary of major accomplishments

   COSTAR:

   There was no COSTAR activity during this reporting period. The instrument remained in HOLD mode and was stable.

   WFPCII:

   WFPCII continues to operate nominally throughout the month of September.

   The 12 hours monthly decontamination on day 267 restored UV throughput to nominal values (~1 normalized).

   Science and Calibration observations continue to execute successfully.

   FOC:

   FOC is continuing the normal science program with GO and GTO cycle 4 proposals using the f/96 relay without problems. For a picture of the Faint Object Camera click here.

   FOS:

   The FOS continued to execute a variety of GO, GTO, and CAL proposals during the month of September.

   GHRS:

   Both side 1 and side 2 of the GHRS are running without problems.

   1.2 Summary of major problems

   COSTAR:

   On day 94264 limit violations were reported for several COSTAR voltage monitors and one current monitor. The instrument was in hold mode and the out-of-limits condition lasted for one sample of the telemetry. Some of the monitors read high, others read low. Each monitor appeared to report nominal readings after these violations occurred. All of these monitors are associated with the same minor frame in the telemetry. An internal COSTAR telemetry page counter also reported an anomalous reading coincident with the reported violations. We believe that these out-of- limits conditions were caused by a telemetry glitch and did not reflect any physical problem of the COSTAR.

   FOC:

   In general: No major problems with FOC operations during the reporting period. Electrical and thermal monitors of the Instrument continue to show nominal values after the Servicing Mission. On day 256 ( September 13, 1994) one FOC observation was lost out of proposal FOC 5469 due to a STR track change during the Science Data dump. No HSTAR were filed against the Instrument hardware or its operational software.

   FOS:

   A software fix of the handling of the take-data flag by the DF224 has been completed and tested on the simulator at Goddard. Once this fix is installed at the end of November, the new FOS Peakup algorithm will work correctly.

   During the past month there were four Binary Search target acquisition failures. Two of these failures resulted when the target was found to be fainter than expected. Another had an error in the initial coordinates specified for the target. The final failure was caused by an improperly calculated exposure time. There were no instrumental errors associated with these failures.

   GHRS:

   Monitoring of GHRS carrousel reset activity is continuing. During the month of September there was one reset event for 195 commanded positions. Figure ghrs-f4 contains a plot which shows the accumulated number of times the carrousel is commanded to a new position and compares this rate to the accumulation of carrousel resets. The trend of both of these data sets is similar. Figure GHRS-F4 also includes a bar chart which associates reset activity to specific locations on the carrousel. This chart shows that the rate of reset events is higher at the lower region of the carrousel step scale. The rates shown in the region of the G140M grating are mis-leading since this is a little used optical element. A single reset in this region is rated higher than it would be in a more commonly used region.

   WFPCII:

   On day 248 proposal 5446 (Nearby SO & Spiral Galaxies) was scheduled during an earth occultation (HSTAR 4906). This was attributed to a software scheduling problem.

   On day 249 proposal 5092 (GTO Low Latitude Parallel) failed to acquire its target due guide star acquisition failure. The failure was caused by an erroneous preceding FHST roll update. An attitude reference update was uplinked in real time to correct the FGS pointing.

   On day 264 at 18:52:22 WFPCII flagged a UERRMSG1=010014B4 (hex) for one major frame. The error was a microprocessor timing error in which a minor frame sync pulse was not detected at the expected RTI count. The microprocessor registers showed no indication of an internal timing problem. The missing minor frame sync pulse was seen twice by WFPCI in the past, and may indicate that the anomaly occurred between the CU/SDF and RIU interface (external to WFPCII). Further analysis will be done.

2. OBSERVATORY PERFORMANCE

   2.1 Pointing and guiding

   The alignment matrices of FHST were updated on day 157 (June 6) this year. This has led to a reduction in the average guide star acquisition miss distance of 5 milli-arcseconds.

   The sky distribution of pointings in this month is shown in Fig. 2.1. Fig. 2.2 shows the monthly average pointing miss for primary guide start acquisitions and reacquisitions. The pointing miss is measured from the location of the guide star found during search compared to the predicted position (start of the search). table 2.1 describes the statistics of guide star acquisitions. It takes into account both primary acquisitions and reacquisitions. "No lock" means that coarse track cannot be established or maintained. "Degraded mode" refers to the cases where the guiding mode falls back to coarse track when the commanded mode of the find lock cannot be established or maintained. "Search rad exc" refers to cases where the guide stars are not found.

   The distribution of guiding modes by Science Instrument during scheduled exposures is given in table 2.2. for each scheduled exposure, the actual guiding mode is obtained from the engineering telemetry. The scheduled exposure time is subsequently summed up by guding mode for each SI to produce the distribution.

   The full-width at half-max (FWHM) of jitter during observations are plotted as a function of the magnitude of the dominant guide stars in Fig. 2.4. the jitter is obtained from the motion of the dominant guide stars in the FGS. The rms of jitter along V2 and V3 axes is also calculated for each observation. The average of FWHM and rms of jitter over all observations in each month is given in Fig. 2.3 and shows no obvious trend.

   For each observation, the PMT sensitivity is calculated for each FGS in fine lock based on the PMT count rates and magnitude of the guide stars. The sensitivity is expressed in total counts of the 4 PMTs per 25 milli-seconds normalized for a 13th magnitude star with the FGS filter in pupil position. Fig. 2.5 shows the average sensitivities of each month since Janurary, 1991. The is no obvious trend. The variation of the sensitivities appears compatible to the error of the guide star magnitude.

   2.2 Observations

3. OBSERVATORY TRENDING

   3.1 Telescope:

   The temperature fluctuations of critical spacecraft components are shown in Figure 3.1. All temperatures are nominal.

   3.2 Costar:

   the costar trending program is being developed. Table costar-t1 has been included to document current mechanism positions associated with the COSTAR mirrors.

   3.3 WFPCII:

   tables wfpc-ii t1, t2, t3 and Figures WFPC-II F3-F9 show the September instrument statistics and profiles for cycle usage, power and temperature. All values are nominal and within limits unless otherwise noted.

   table t1 shows the cycles of various mechanisms and power supplies.

   table t2 shows the lvps, mechanism, and tec voltage and current outputs.

   table t3 shows the bays, optical bench, Bulkheads, Cold and Hot junctions, Camera Heads, Attach points, AFM, and Radiator temperature values.

   Figure f3 shows the frequency for various shutter close/open and open/close flight times.

   Figure f4 shows the cold and hot junctions, Camera Head, and Radiator temperatures.

   Figure f5 shows the Bays, Optical Bench, and Cal Module temperatures. On day 245 the cal module reached its highest temperature value so far at 24.3 C. This was caused by the VIS lamps being turned On for 90 minutes instead of the usual 40 minutes.

   Figure f6 shows the mechanism, tec and 22 lvps voltages and current.

   Figure f7 shows the lvps, camera head, and UV Output Monitor voltages.

   Figure f8 and Figure f9 shows the afm voltages and current

   3.4 FOC:

   FOC: The f/96 relay of the Instrument continues to operate without problems after the installation of COSTAR: Evaluation of Error Logs show all voltages, currents, and temperatures within their nominal limits.

   Serveral plots of selected monitor points critical to the performance of the Instrument are an integral part of this report:

   Four critical temperatures are shown foc-p1:foc thermal plots reflecting the thermal profile during the reporting period.

   A set of three plots foc-p2:foc high voltage monitors illustrate the profile of the output voltages of the critical High Voltage Power Supplies for the FOC detectors. For a picture of the FOC Dectectors click .

   foc-p3:foc vpu noise and sds error log Both plots are focused on the health and safety of the Instrument. The Video Processing Unit (VPU) Noise level indicator summarizes the input signal as detected by the VPU. The peaks typically indicate passages throught the South Atlantic Anomaly (SAA).

   foc-p4:foc mode and observation profile shows the usage of the camera over the reporting period. A reading of the Thermal Control Table Number of "2" flags the time the FOC has been in the High Voltage Mode using the f/96 relay. The value of "1" indicates a reactivation of the F/48 Camera section.

   Several Tables are inserted to keep track of operational statistics in particular of limited lifetime items: Table foc-t1 illustrates the statistics of the HV cycles and the hours the FOC was operated in the High Voltage Operate Mode. The same table foc-t1 shows the MIN/MAX/AVERAGE values grouped into the different operational modes: Safemode, Hold, and the High Voltage Operate Mode.

   The foc-t2: mechanism cycle/usage table summarizes the usage of the mechanism during the reporting period and adds up the total number of cycles during Ground Testing and In-Orbit use.

   A statistic on FOC f/96 Observations is given in Table foc-t2: mechanism cycle/usage table This table also keeps track of the number of loss of lock that occurred during a scheduled FOC observation time and adds up the time lost on target.

   For a picture of the optical path and the FOC mechanism click here.

   3.5 FOS:

   Table fos-t1 shows the Cycle, Voltage and Miscellaneous summaries for the FOS for the month of August. There were no health and safety of operational limit violations for the month. No additional diodes were disabled during the month.

   Table fos-t2 shows the thermal summary for the month. There were no health and safety or operational limit violations for the month.

   Figure fos-f1 is the standard plot of Collimator (predicted and actual) temperature (Y302) as a function of time. The predicted temperatures are based on algorithms for both the Operate (LVON) state and the Hold (LVOFF) states as a function of FOS aft shroud sink temperatures. The optical bench reacts in such a way as to be within +/- 1 deg C of equilibrium 24 hours after a transition. This plot suggests nominal thermal behavior for the detector as a whole even during the periods of continuous LVON.

   Figure fos-f2 shows a nominal optical bench gradient temperature for the month. Figures fos-f3 and f4 show the Red and Blue detector dark count data for the month. These plots are a representation of the Overlite counts from the FOS at all times that the detector is in Operate mode. Overlite is an engineering telemetry monitor of the total counts on the active detector array for the last 60 seconds. The data represented here occured after HV stabilization, after dead/noisy diode disabling, outside the SAA, with the FOS aperture door shut, and all lamps off. The data are therefore total dark counts in a 60 second period for all enabled diodes. Figures fos-f5 and f6 show the comparison of September's dark count data to August's. September's dark count data represent nominal performance.

   3.6 GHRS:

   All trended monitors appeared normal for this reporting period. The following tables and figures summarize activity of selected areas of the instrument.

   Table ghrs-t1 is a cycle and use summary of the instrument mechanisms as well as a statistical analysis of main bus voltages and currents.

   Table ghrs-t2 is a statistical summary of key instrument temperatures. All temperatures are within their normal range.

   Figure ghrs-f1 contains plots of key instrumental temperatures. The temperature profiles for each detector and the optical bench are shown since these temperatures can affect optical stability. The temperature plot for MEB 1 is also included since large operational gradients on this monitor contributed to the intermittant failure on the side 1 low voltage power supply.

   Figure ghrs-f2 shows the side 1 and side 2 power supply voltages for the month. These voltages remain very stable.

   Figure ghrs-f3 contains monthly power profiles for each side of the instrument as well as historical summaries of hours spent in OPERATE mode.

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