Minutes 
                 Einstein Observatory Users Committee Meeting
                                February 6, 1979

The agenda of this meeting was divided between a review of spacecraft operations
--from observation planning to final scientific results--and a general
discussion about how these operations might be improved, particularly those
concerning outside groups. Attendees were R. Giacconi (CFA, Chairman); H.
Tananbaum (CFA); W. Forman (CFA); G. Branduardi (CFA); K. Long (CAL); S. Holt
(GSFC); C. Canizares (MIT); T. Markert (MIT); A. Opp (NASA); F. Seward (CFA/Guest
Observers); P. Charles (Guest Observer Representative); J. Hutchings (Guest
Observer Representative).

Review of Operations

Spacecraft and instruments are operating as expected, except for the anomalies
to be noted. The resolution of the telescope is as expected. Images of point
sources have a FWHM of 4 arcsec. Accuracy of boresighting is a few arcsec and is
currently being improved.

Star trackers A and C are operating properly. Star tracker B is not. This
developed an apparent corona problem and has been turned off. We do not know if
there is permanent damage to this tracker since it apparently arced for three or
four days.  The two remaining trackers are being carefully monitored for sighs of
similar problems.

Soon after launch, it was found that the level of the bright object detector
(BOD) was set too low. For two weeks, the beryllium filters were inserted and
removed by the solar-protect system when the bright earth was observed. After
200-300 cycles, one quadrant stuck in an open position. The problem apparently is
with the motor that drives the mechanism. The solar detect logic has been
changed. The BOD no longer operates the filters. Because the insertion mechanism
is of the same type, we are being very cautious about the use of the aluminum
filters and gratings.

The FPTA (focal plane transport assembly) works just fine, and has been
operating approximately once every three days. Other eqUipment such as the South
Atlantic Anomaly detector, mirror heaters, etc. also work well.

One gyro has been heating, and we replaced it with a spare unit. There are six
gyros; three are necessary to run the spacecraft.

Observing time has been lost because of problems in uplinking and verifying
stored program loads. The spacecraft has also been "lost" three times. This
occurs because the star trackers cannot find the expected guide stars.
Consequently, there is no update to the gyro reference. By the time ground
controllers are aware of this, there has already been a maneuver to the next
target. The best solution is to maneuver to a safe target, one with clear cut
guide stars. The trackers are put into a map mode.  The measured position is used
to update the gyros and then the planned observation program is resumed. In
normal operations, sometimes there is no guide star lock, and the map mode is
used for these targets. Guide stars are third to ninth magnitude stars. The
problem is in the guide-star-selection software and not in the star trackers
themselves.

Use of the RCS propellant has been approximately 1/3 pound per day. This is
equivalent to a two-year lifetime. The spacecraft was operated for the first two
months using passive momentum management. Targets were picked that were close to
the plane of the orbit or close to the pole of the orbit. At the end of January,
active momentum management was initiated. Targets were selected to cancel the
build up of moments caused by gravity gradient torques. Gas consumption might be
reduced by a factor of 2 using this technique.

Solid State Spectrometer

Ice builds up on the face of the detector and frequent defrosts are necessary.
Currently the detector is being operated at the focus for two days and is
defrosted before the next use. After one day at the focus, there is one mean free
path of ice at 1.7 keV. Resolution of the detector is 150 EV, FWHM. Spectra were
shown from Cas A and Tycho's SNR. Lines from silicon and sulfur were very
prominent. Lines from calcium, magnesium, argon and iron were also seen. The
background is approximately 10 times higher than that listed in the red book, a,
problem when observing the faintest sources. Frequent defrosting will shorten the
lifetime. The experimenter estimates lifetime of this instrument is not much
more than 6 months. The instrument manufacturer estimates the lifetime as 8
months. The pre-launch lifetime estimate was 10 months. Each defrost costs one
day's lifetime.

Focal Plane Crystal Spectrometer

All sub-systems are nominal, backgrounds are as predicted, and the mechanism
which moves the counters and crystals has been operating as expected. MIT is
still working on data analysis software. The preparation of SCP.loads for
observations has been time consuming. Processed data for Cyg X-2 were shown.
There were only a few photons available from the quick look data.

Imaging Detectors

The high resolution imagers work well. HRI #2 developed a temporary high
background region which appears as a region of diffuse emission. HRI #3 is
presently being used.

Many pictures have been obtained with IPC-l. The gain of this detector has been
time variable. The control-leak rate has decreased from the nominal value and
differential transmission of the counter gas through the window causes the gain
to be higher than expected.

Approximately two dozen pictures were shown. Included were point sources such as
SS Cygni and the Vela pulsar; some fields containing many sources such as the
Cygnus OB association, Eta Carina, and M31; several active galaxies and quasars;
and some extragalactic extended sources such as M87 and A1367. The Draco Deep
Survey field was shown to illustrate the detection of extremely weak sources (2 x
10-3 UFU); the difficulties of finding such faint sources were discussed.

Data Processing

The computer and data reduction procedures at CFA were described. There are two
computers; one used for the processing of production data, the other as a user
computer devoted to software development and analysis of reduced data. In a given
data "run", the reduction machine can handle six orbits of data. It is necessary
to transfer data from a tape to the disk for processing and then eventually back
to tape with some archived information remaining on the disk. This can be done
twice a day. There are 15 orbits of production data and up to 6 orbits of quick
look data each day. Data processing is consuming more than real time, and unless
the operation becomes more efficient or the data storage capability of the
existing computers is increased (as has been requested), data processing is going
to fall more and more behind data acquisition. At present, processing of MPC
data and IPC spectral data has been omitted until software and instrument
problems have been settled.

Quick look data is currently delivered by airplane with a 24 hour delay. The
telephone line transmission of data was unsatisfactory due to the time and
manpower effort it required as well as hardware unreliability.

Processing software was described including archiving, handling of aspect data,
instrument data,  and the basic science analysis of the results.

CFA is currently devoting two people full time to the preparation of MOPS
and DOPS. The end result is a selection of instruments, targets, and observing
sequence which is transmitted to the observatory. Much of the selection is done
by the computer, limited, of course, to targets in the solar window. Human
intervention is necessary to assure that high priority targets are observed and
in the selection of guide stars for some targets.

First Month of Operation

The observatory has been operating "normally" for one month a In the 30-day
interval, 6 January to 4 February included, the IPC was at the focus for 16 days,
the HRI for 3 days, the SSS for 8 days, and the FPCS for 3 days. The pointing
time allotted to various organizations was CFA 41%, GSFC 26%, MIT 10%, CAL 13%,
GO 10%. In this time, observations were accomplished for approximately 20 guest
observers, including one simultaneous radio/optical/X-ray series of observations of HR 1099.

Guest Observer Program

Approximately 120 guest observer proposals were evaluated at the August and November reviews. Ninety of these were approved, requiring approximately six months observing time at a 20% rate. Use of the !PC was requested 69% of the time, the HRI 17%, and the SSS 14%. Proposals requiring the FPCS have been deferred by the committee until the sensitivity of this instrument is better understood. At this date, there are 45 more proposals for evaluation at the February 27 review.

Discussion

The general discussion was concerned with observatory operations, dissemination of information to the outside world, flexibility of the observing schedule, the ability to react to transient events, changes in the observing plan to follow up new discoveries, optical follow-up to X-ray observations, and the data format that would be most useful to guest investigators.

Action Items

(1) New observations. The consortium will add new observations to their program as dictated by scientific resu
ts. In particular, they will plan observations for the second year of
observatory time with a firm plan for 50% of the observatory time. Up to 50% of
the time will be available to guest investigators. Should the guest investigator
program not be able to support this much obserVing time, the consortium will have
contingency observations planned to fill up to 30% more of the time. The
consortium will prepare a new red book for the first six months of the second
year.

(2) The consortium will supply additional information concerning the observing
program at more frequent intervals. The first issue will be a list of approved
guest observers and their programs, a list of all planned targets listed by right
ascension, and some sort of communication serving as a newsletter. The
consortium will also investigate installing a telephone service or some sort of
expanded list concerning the exact
schedule of operations planned for the immediate future. This would interest
optical  and radio astronomers wishing to do simultaneous observations. This will
not be possible to do unless the making of DOPS can be speeded up. Up to now the
exact schedule is known only a day before the actual occurence of the
observation

(3) Quantitative information concerning the SSS ice problem will be distributed
by GSFC in order that potential observations of soft sources can be better
evaluated.

(4) CFA will investigate the possibility of sending guest observers part of the
production output of their observation as hard copy_ In this way, an observer
could learn something about the results before coming to CFA to work with his
data. There are judgments to be made before data proceSSing is complete that can
probably only be made using the interactive displays available at the CFA
computer. However, it was felt that some knowledge of the data beforehand would
allow the guest observers to work more efficiently while using the system.

(5) The next meeting of this committee will be some time between April 2 and
April 6.

FS:jk