Minutes
          Einstein Observatory Users Committee Meeting 
                         April 2, 1979

I. Status of Observatory

A. Spacecraft

Operations have been smooth. Observations have been conducted for all consortium
institutions and guest observers. No time has been lost due to failure to
receive SCP loads or the spacecraft being "lost. "

The overheated gyro has been replaced by a backup. There were no problems in
this transition.

An attempt was made to reactivate star tracker B, turned off two months ago
because of an apparent corona problem. It was hoped that this tracker would
outgas and, after some time had elapsed, would make a simple recovery. The star
tracker would not come on.- The problem two months ago probably Iy resulted in
permanent damage. The remaining two trackers are being watched very carefully.

CFA is writing software to make use of star tracker data when the trackers are
in map mode. This makes possible an aspect solution;\when the trackers are not tracking. CFA is also undertaking studies in X-ray navigation. If the remaining two trackers should fail, the intent is to use X-ray data from the imaging instruments to up-date the gyros so the position information is current and the telescope can be pointed successfully at new targets.

B. IPC

The IPC is working well except for the gain varying in flight. This variation is caused by differential gas loss through the window and a temperature effect. The counter is operated as a flow counter. The problem started December 12 during activation in orbit. The control leak rate declined and the gain increased. Since then, the control leak has stabilized at a flow approximately ha If the initial rate. The current mode of operation for each observing session is to fill the detector and then go to the focus. There is a temperature change upon going to the focus and the gain increases rapidly at first, and then stabilizes. The total gain increase is approximately 30% and occurs during the first 1. 5 days of observa
ion. We are scheduling short observations during the first day and then the
longer observations to use time when the gain is stable. Software is being
modified to handle this variable gain. We cannot now routinely derive energy
spectra from these IPC data.

C. High Resolution Imager

No problems. Operation has been nominal. Pictures are excellent.

D. Objective Grating Spectrometer

The OGS was used for the first time in the time period March 12-16. The
mechanism which inserts the grating is the same as that used for the filters.
Since one of the beryllium filter quadrants failed, we wish to minimize operation
of this type of mechanism. Accordingly, grating observations were scheduled so
that many targets could be observed during one grating insertion. Eleven strong
galactic X-ray Sources and stars were observed. Both 1000 and 500 line gratings
were used. Dispersed photons were seen showing that both sets of gratings
survived launch. No prominent lines have been identified in the quick look data.
Stars (where one expects to see lines) were extremely weak. Spectra from the
stronger galactic sources appear to be continuum. The grating production data are
necessary to fully evaluate this instrument. A second set of grating
observations is planned for mid-May.

E. Focal Plane Crystal Spectrometer

There have been no hardware problems. Some production data is available and has
been analyzed. 30,000 seconds of data for Cas A have been examined.
A silicon 13 feature has been seen. This line complex contains approximately 120
photons. An absorption feature apparently due to nickel in the mirror has been
seen in the spectrum of Cyg X-2. This instrument is apparently operating
nominally. Long observing times are necessary to obtain enough counts to study
spectral features.

F. Solid State Spectrometer

Ice is still the biggest problem. Temperature data from the flight have been
collected and will be used to make an accurate estimate of the detector lifetime.
The current operational procedure is to do a one day defrost, to cool down, and
then observe for two days. We think a Significant fraction of the ice has now
been driven completely out of the system. Consequently, as time goes on, fewer
defrosts will be necessary and longer observing sessions will be planned. This
will e1'..i:end the lifetime of the instrument somewhat.

II. Science

Three associations of O-stars have been observed; in Cygnus, Carina, and Orion.
Each of these fields has many sources, all associated with O-stars. We have also
seen many late stars as X-ray sources.

The Crab nebula has been observed. The pulsar shows as a strong point source and
diffuse emission associated with the main wisp is clearly visible. X-ray
pictures of Tycho's remnant and Cas A show shells with much structure, some
associated with optical filaments and some with radio emission. Approximately 50
X-ray sources have
been seen in pictures taken of M31 with the IPC and the HRI. One source
apparently coincides with the nucleus. Approximately 20 quasars have been
observed to be X-ray sources. The most distant one lies at Z = 3.1. Variability
has been observed in one quasar; about a factor of 2 in an hour. X-rays from
clusters have been observed out to Z '" 0.75.

After verifying the analysis techniques, the deep survey data is starting to be
resolved into point sources. Surveys are reasonably complete for the Draco field
and the Eridanus field. We find a number of faint stars, quasars, and perhaps two
clusters. The weakest source seen so far has a strength of '" 2 x 10-3 UFU. We
are close to the confusion limit in the IPC. We intend to pursue the deep
surveys. A deep survey takes approximately one week of satellite time.

The solid state spectrometer detects very prominent lines in supernova remnants.
Lines have also been seen in stars and in binary X-ray Sources. Some line
features are observable in clusters. No line features are seen yet in compact
extragalactic sources.

Ill. Scheduling and Momentum Management

Gas usage has averaged 2.3 lbs/week. At this rate, the predicted lifetime is 2.4
years. The effect of various observing strategies on gas consumption has been
extremely difficult to evaluate. Although we are nominally pursuing
active:momentum management, we are not sure that the other operational
constraints have given this Procedure a chance to operate properly. There is a
bias against doing short observations. Primarily the reaction wheel heating
constraint prevents us from doing more than approximately 12 observations a day.
Our original planning assumed we could do as many as 20 observations a day. Long
observations are also needed for backloads, times when the onboard spacecraft
programmer is loaded with the new observing schedule. These times typically
include three real time passes. Ideally, there would be one 7000 sec observation
every 12 hours to fulfill the backload requirement.

Bookkeeping to keep track of observing time is difficult and not strictly
accurate. USing the system which we have yields the following fractional time
usage for the period January 6 - March 28.

CFA    .46           IPC    .36
CAL    .05           HRI    .25
MIT    .11           SSS    .26
GSFC   .24           FPCS   .13
GO     .14                -----
     -----                 1.00
     1. 00

The useful observing efficiency may be as low as '" 0.46. OUr pre-flight
planning assumed a useful observing efficiency of 0.65.

Scheduling of observations is going more smoothly but momentum management has
not been applied effectively. Guide star selection which used to be a problem is
now almost automated and is not holding up scheduling. The SSS MOPS will be
increased to three days reflecting optimism about the ice build-up problem. IPC
MOPS are being made longer to take advantage of the gain stabilization occurring
after the first day and a half of observation.

There was much discussion about choosing targets and setting priorities. No
decisions were reached. The feeling was that during the first six months of
observation, high priority targets would be observed irrespective of the gas
usage. After the first six months, when all important targets have been available
at least once, minimum gas usage will become one of the foremost considerations.
This means that some observations may not be done until one year after scheduled
and that scheduling targets far in advance to be observed at specific times
(simultaneous X-ray/optical observations) may become very difficult.

On occasion it may be desirable to do observations outside of the ± 15° solar
constraint band. This was discussed. It is possible, but a burden on an already
overloaded operational system.

In view of the exciting results coming from the SSS and its. limited lifetime,
it was suggested that the time devoted to SSS observations be increased at the
expense of the other instruments, particularly the FPCS, since both SSS and
imaging observations are desirable in advance for efficient use of this
instrument. The consortium will consider this.

IV. Data Processing

We have received production tapes through day 73. We are not yet doing
"production" processing. HRI processing is being held up by attitude information.
We expect to start processing in one month, after insuring that the proper
bore-sighting, star tracker offsets, and temperature data have been put in the
programs. We will then use the map mode aspect programs to determine attitude
when the trackers are not in track mode. This is necessary for both HRI-2 and
HRI-3. IPC production processing is two months away from commencement. The IPC
gain is the main problem. We cannot now derive energy spectra routinely, and
software must be modified to handle the varying gain parameters.

V. Action Items

CFA will generate and distribute to the guest observers a list of all approved
guest observers, observations done, and observations in the observing catalog.
CFA will generate a schedule of future observations. Because the efficiency of
the observatory is less than pre-flight planning, observations in the red book
will take longer than the planned ten months to complete. CFA will calculate a
date for nominal completion of red book observations. CFA will continue to give
guest observations priority in order to spend 20% of the time on guest
observations. The main problems anticipated are the limitation on doing short
observations and a reluctance to observe too many targets in regions of high gas
usage.

After the red book observations are complete,' guest observer time will be
increased with a goal of eventually achieving 50% of the time for guest
observations. CFA will generate a new red book containing the consortium plan for
the second year of observation. It should be complete by June.

CFA will circulate a phone number for people to call to get the current detailed
observing plan (DOP). This phone number will be circulated with instructions for
calling to obtain the current schedule and observing times.

A number of changes to the red book observing program were presented. These
observations will be circulated to the Committee with these minutes for comments.

Attendees:
G. Branduardi
C. Canizares
P. Charles
G. Clark
R. Giacconi
S. Holt
J. Hutchings
K. Long
A .Opp
E. Schreier
F. Seward
H. Tananbaum

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