UV throughput was restored following the 6 hours CCD decontamination on day 347 (see Figure F2).
Science and Calibration observations continued to execute successfully.
For a picture of the Faint Object Camera click here.
Proposal FOC 6255 on day 338 ( December 4, 1995 ) was executed to perform a long-slit spectroscopy of the Center of M31 using the F/48 detector.
1.2 Summary of major problems
On day 318 starting at 03:19 FOS proposal 6125 (Imaging and Spectroscopy of SN 1885 in M31) which was WFPC-2 assisted was unsuccessful in finding its target. The data is currently being analyzed in an effort to determine the cause.
On day 334 at 17:00 a GS acquisition failed to fine lock backup (FGS1 dominate). This affected the FOS proposal 5781 (EMISSION LINE VARIABILITY IN THE LENSED QUASAR Q0957+561)
On day 338 at 03:28 a FGS LOL was observed (FGS1 was dominant). This occurred while the FOS was observing a moving target (proposal 5843, FIRST ULTRAVIOLET SPECTROSCOPIC SURVEY OF 2060 CHIRON). The FGS was unable to recover from the LOL before the beginning of the next FOS observation, therefore FOS event flag 13 was set and the remaining 8 hours of observations were lost. The DF224 vehicle control law will not service a FGS LOL recovery while it is busy. In the above described case there was not enough time available between slews during intervening observations for the LOL recovery to occur. The reacquisition after the V1 earth occultation was successful. All of the remaining FOS observations in this obs set executed with the aperture door closed. It was suggested to the FOS team that the RTCS YSEPO be modified to only set event flag 13 during mode 2 TAs. RTCS YSEPO is currently executed at the beginning of every observation. Its purpose is to insure proper pointing before opening FOS's aperture door. It does this by 1st checking event flag 13 ( if set the RTCS exits without opening the AD). It than checks the TDF, if it is set the RTCS opens the AD and exits, otherwise it set event flag 13 and exits (this prevent the AD from opening for all subsequent observations until the end of the OBS set when event flag 13 gets reset). It does not make sense to inhibit an entire set of observations just because the TDF was false at the beginning of one observation, unless that observation is a mode 2 TA. The proposed solution would require two versions of YSEPO. The first version would only be used before mode 2 TAs and would be identical to the current version used. The second version would check the TDF and event flag 13 before opening the AD but would not set flag 13 if the TDF was down.
On day 352 at 07:51 the status buffer message 3202 with a parameter of 10 was issued indicating a BS target acquisition failure. The cause of the failure was a lack of targets in the field. The proposal affected was 6007 (COMPARISON OF LARGE SCALE STRUCTURE IN QSO ABSORBERS AND GALAXIES AT THE GALACTIC POLES)
Starting on day 352 and progressing almost continuously through the end of day 358 two FOS HDF proposals were conducted (proposal 6339, VERIFICATION OF THE UV SPECTRUM OF HST BACKGROUND LIGHT AND A MODEL OF OTA- SCATTERED EARTHSHINE & proposal 6342, MEASURE OF THE INTEGRATED OPTICAL FLUX FROM THE DIFFUSE EXTRAGALACTIC BACKGROUND LIGHT (EBL)). Due to the operation nature of the FOS, the SDF (Science data formatter) science data output is required to be enabled the entire time the instrument is observing. This draws about 20 additional watts of power, significantly increasing its temperature. Starting on day 352 an increase was observed in the SDF A side temperature. Over the next several days it undulated between 58 and 62 degs C. On day 358 it peaked out at about 63 degrees, 2 degrees below its high yellow limits. Procedures were developed to safe the FOS and disable the SDF SD output in an effort to prevent the SDF red limit temperature (70 degs C) from being exceeded. This procedure would only be required if the SDF temperature was approaching 68 deg C (Key monitor COP 9.2 specifies that the Payload be safed if the SDF A temperature exceeds 68 degs C for 5 mins). Other SIC&DH thermal parameters were analyzed and were observed to be elevated but in no danger of breaking limits. One week later on day 365 the GHRS was observing in the CVZ for 5.5 hours continuously. The SDF A temperature rose to 65.5 degs by the end of the observation, breaking its yellow of 65 degs C. It should be noted that CVZ observations with the FOS and GHRS need to be watched closely for these types of temperature violations.
In support of the FOS instruments team's spectral dispersion curve study, magnetometer data has been retrieved from the engineering data archive. Data from as early as August of 1990 has be obtained.
FOS red diode 289 has been determined to be dead and will be disabled in the 029 SMS.
1.2.2 Monitoring of GHRS carrousel reset activity is continuing. During the month of December there was 1 reset event for 165 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. More recently, 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.
5384 Science data missing for U2574301 proposal 5972. 5396 WFPCII data dropouts in DCF observation 20/21.
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.
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
WFPCII Tables: T1, T2, T3 and Figures: F3-F9 show the December 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.
t3 shows the bays, optical bench, Bulkheads, Cold and Hot junctions, Camera Heads, Attach points, AFM, and Radiator temperature values.
The f/48 relay is considered to be operational restriced use to the use of long slit spectrometer observations; e.g. FOC proposal 6255 executed this month.
Serveral 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.
