UV throughput was restored following the 6 hours CCD decontamination on day 289 (see Figure F2).
Science and Calibration observations continued to execute successfully.
For a picture of the Faint Object Camera click here.
Two calibration proposals have been successfully completed: "FOC F/96 cycle 5 Aperature Location Monitor" and the routine "UV Throughput monitoring".
1.2 Summary of major problems
All engineering plots do show missing data for 27 day of the month. Since the Instrument was NOT in operate mode during the time period and subsequent telemetry do show nominal values no further investigations are required.
On day 275 at 10:37 a GS acquisition failed to fine lock on FGS 3 only, affecting FOS proposal 6038. The subsequent FOS Binary search acquisition found a target and appears to have been successful. All of the following exposures executed in a nominal fashion.
On day 286 at 12:03:43Z a FGS LOL occurred which caused a chain of events that led to the loss of science for proposal 6155 and the issuing of a FOS status buffer message. At 12:05:07 the RTCS YSEPO was executed, it found that the TDF flag was down and set FOS event flag 13 and exited without opening the aperture door. Once flag 13 is set the aperture door will not open until it is reset at the end of the observational set, thus all of the following observations (3 FOS Peakups/dwell scans) were executed with the AD closed. At 12:08 the RTCS YPKUP (the 1st of 3 peakups/dwell scans scheduled) was activated (this RTCS coordinates the FOS dwell scan), after 60 seconds the HST was still not considered stable (ie TDF=0) and YPKUP entered an error path that output the FOS status buffer message 290 with the Parameter T24500UO, dumped the SHP and exited without executing the scan. The TDF came back up at 12:10:41 and the subsequent two peakup executed nominally except that the AD was closed. The cause of the FGS LOL is still under investigation.
On day 292 at 10:00:30 a FGS LOL occurred causing a FOS maneuver request to be rejected (FOS requested peakup). Two NSSC-1 STB Exec 20 were issued. The reacquisition of the GS was completed and the TDF was back up by 10:06:04, but not before FOS event flag 13 was set by RTCS YSEPO at 10:05:22, thus all of the subsequent observations were executed with the AD closed. Proposal 5831 was the proposal affected. The cause of the FGS LOL is still under investigation.
On day 299 at 20:09:19 a FOS Binary search onboard target acquisition failed. The NSSC-1 status message issued indicated that the failure occurred during part one of the acquisition (aperture mapping) because the field was to crowded (5 targets found). At 21:11:08 a LOL occurred during a type three slew. The recovery from LOL was completed at 21:14:06, but not before RTCS YSEPO set flag 13, thus all of the subsequent observations were executed with the AD closed. The cause of the BS TA failure and the FGS LOL are still under investigation.
1.2.2 Monitoring of GHRS carrousel reset activity is continuing. During the month of October there were 8 reset events for 418 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. This plot shows that the rate of resets was proportional to the number of times the carrousel was moved for the first few years of the mission. Over the last year, however, we see the rate of carrousel resets increasing. While the rate of reset events is still small, this trend represents a deterioration of the carrousel mechanism. 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.
2. Observatory Performance
1) For acquisitions on single GS: The acq will fail to gyro mode. 2) For acquisitions on an GS pair: a) Attempt to achieve coarse track on both guide stars in order to perform a coarse angle check. If coarse track cannot be achieved, the acq will fail to gyro mode. b) If the above coarse angle check passes, try to go to fine lock mode on single GS. The primary GS will be tried first. If fail to achieve FL on the primary GS, the secondary GS will be tried. If fail to achieve FL on the secondary GS, the acq will fail to gyro mode. c) If the above coarse angle check fails, the acq will fail to gyro mode. No acquisitions in coarse track or fallback to coarse track will be allowed.
During this month, search radius limit was exceeded on five different sets of guide stars, which caused 9 guide star acquisition failures. One GS pair was later acquired in coarse track mode. All 13 of the "no lock" and "degraded" acquisitions were due to double guide stars, and 6 different sets of guide stars were involved in these partial failures.
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.
3. Observatory Trending
Serveral plots of selected monitor points critical to the performance of the Instrument are an integral part of this report:
The f/48 relay is considered to be operational for the use of long slit spectrometer observations.
Several plots of selected monitor points critical to the performance of the Instrument are an integral part of this report:
Several Tables are inserted to keep track of operational statistics in particular of limited lifetime items:
For a picture of the optical path and the FOC mechanism click here.
