Minutes
Einstein Observatory Users Committee Meeting
February 1, 1980
Distribution: Canizares, Charles, Giacconi, Grindlay, Helfand, Holt, Hutchings,
Kaluzienski, Schreier, Seward, Tananbaum
I. Spacecraft and Instruments
At the last meeting, the solid state spectrometer was known to be failing, and'
indeed it finally became too warm to be useful ~ October 20. Since 25% of the
observing time was used for this instrument, we have subsequently been able to
devote a higher fraction of observing time to the imaging instruments.
The two's bit in the HRI-3 voltage command failed, causing the high voltage to
drop and loss of some data. This problem was solved by changing the high voltage
step, and HRI-3 is now operating normally. Since the nominal mission lifetime was
one year, this may be an indication of a general mortality in the spacecraft
components. We might expect more failures like this as time progresses.
A discharge was observed in IPC-A. This appeared as a very soft source (50,000
cts/ sec) of duration 2 minutes. A second event also occurred at a level of 50
cts/ sec. There is some concern that there may be other weak events like this
which have been undetected as abnormal and may appear as weak serendipitous
sources. Recall that the operation of the IPC has been abnormal because the
controlled leak clogged early in the mission causing the quench gas to be lost
through the window more rapidly than other gas components. We have been plagued
with a variable gain since that time.
The controlled leak from the gas system of IPC-B was switched to IPC-A with
encouraging results. There has been no recurrence of the break-down problem. The
leak JS operating nominally, and a few weeks of operation has shown\\1']1 no sign
of clogging. Because of the increased gas flow through the counter, the gain has
been stable with only a 2% decrease in two weeks. We are continuing to monitor
performance carefully. There are only the two controlled leaks on the spacecraft.
There are no more spares.
Approximately two days of observation time was devoted to a series of short
observations to calibrate one of the star trackers and to calibrate the spatial
response of the IPC.
We have solved a problem which resulted in a smearing (a few arc-seconds) of
some of the HRI images. It was found that the measured separation of stars in the
f.o. v. of the star trackers depended on the magnetic field directed along the
pointing direction, and this effect was confirmed using the fiducial lights
attached to the instruments. We are changing the software used to calculate
spacecraft aspect so that star tracker data are corrected for this effect. A
reanalysis of several smeared
images has resulted in new images which are very close to the response expected
from point sources. We are now changing the production software and expect to
routinely process HRI data incorporating this change in about two months.
To summarize the aspect situation; we now have (a) a new calibration for tracker
C. (b) a calibration of the above mentioned magnetic effect in the star
trackers, and (c) a new set of bore-sights. Incorporating these three
improvements, we expect to determine the location of strong sources in the HRI to
about 2 arc-seconds. This is a factor of 5 better than the location accuracy
achievable in the past.
It is now necessary to take into account the fiducial light data between each
observation. These fiducial lights make it possible to observe 2-3 arc-second
movements between targets. These movements are due to thermal effects and to FPTA
motion This is precisely what the fiducial lights were designed to do, and only
now is our aspect determination accurate enough so that it is necessary to take
small motions into account.
The new IPC calibration will allow us to determine distortions in the IPC
measure ments accurately, and we expect to eventually achieve 30 arc-second
location accuracy of strong sources in the center of the IPC field.
II. Lifetime
The spacecraft, launched into a 290 n. m. circular orbit, is now at an altitude
of >::;j 270 n. m. If the solar activity continues to follow the presently
predicted level, the orbit is predicted to decay to an altitude of 200 n.m. in
Dec. 1981. If the solar activity is 20- above the predicted level, the orbit will
decay to 200 n. m. in April 1981. Re-entry will soon follow after the altitude
decreases to 200 n. m.
At the current rate of usage, 0.23 pounds/day, the attitude control gas will run
out December 1981. Gas usage at the start of the mission was 0.32 pounds/day and
dropped to 0.29 pounds/day when passive momentum management was implemented.
This dropped to 0.23 pounds/day when new software to calculate pairing
observations was used at GSFC. We want to decrease gas usage still more so we are
sure that the gas will last until re-entry.
III. Data Processing
The map mode aspect routine is now used routinely in data processing.
We have improved the software connected with the observing catalog. It is now
possible to search for conflicts and overlaps between observations with the
computer. This conflict program was used in preparation of the New Red Book and
before the December Guest Observer Review.
There was a delay in data processing over the Christmas holidays. We are now
processing data 10-11 weeks old. The normal processing delay is only 6-8 weeks.
The IPC spectral fitting procedures are still not understood. CFA will prepare a
short written description of the accuracy with which spectral information can be
obtained from the present IPC data and this will be distributed to Guest
Observers.
IV. Observing Program
The "second year" Consortium Observing Program was prepared, incorporated into
the "New Red Book," and distributed ~ Jan. 1. We have also prepared 1) a "Yellow
Book" containing the entire present observing catalog (both Consortium and Guest
Observers, observations both done and planned, and using all instruments) ordered
by right ascension; and 2) a complete list of approved Guest Observer projects.
These were mailed ~ Feb. 1, and with this information, Guest Observers will know
as much about the program as we do.
Table 1 lists statistics concerning proposals reviewed in the six NASA Guest
Observer Reviews. At the last review, the Review Committee considered 109
proposals and accepted 70. The observing time approved by the Committee every 3
months has been about 3 months Guest Observer time. Thus, about 18 months Guest
Observer time has been committed, and we anticipate 9 months Guest Observer time
still Uncommitted before April 1981. The fraction of time spent doing Guest
Observations has been increasing steadily. This is given in Fig. 1. We expect to
have averaged 20% Guest Observer time in the period Jan. '79-April '80. The Guest
Observer time is anticipated to increase to 50% by April 1981.
Table 1
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Total Guest Fraction of
Total Observer Time Three Months
Review Proposals Accepted Approved Observing
(104 s) Time
----------------- --------- -------- ------------ -------------
1 August 1978 68 43 57 .16
2 November 1978 60 47 64 .18
3 February 1979 63 46 94 .25
4 May 1979 43 28 55 .15
5 September 1979 69 44 120 .33
6 December 1979 109 70 186 .51
---- -----
412 278
An observing efficiency of 0.46 has been used to calculate the above fractions.
----------------------------------------------------------------------
Table 2 gives the division of time during 1979 between the various organizations
using the Einstein Observatory. We are not far from the time division expected.
The major perturbation was the SSS which was given a large fraction of the
observing time because of the short lifetime of the instrument.
Table 2
----------------------------------------------------------
Organization Planned Share of Time Fraction of Time
Jan. '79 - Jan. '80
------------ --------------------- -------------------
CFA .36 .364
CAL .12 .107
MIT .16 .135
GSFC .16 .220
GO .20 .165
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V. Miscellaneous
The Guest Observer Program was discussed in an att&mpt to assess the results of
the Program to date and to determine the direction which it should take in the
future. It was decided to conduct a poll of the Guest Observers to get their
reaction to the program. The G. O. representatives will draft a questionnaire. We
will ask for opinions of the program, for any positive or negative feelings, and
for suggestions for improvements.
The nature of the Guest Observer Program after the end of the mission was
discussed. There was unanimous agreement that the program should be continued
using the data base collected by the observatory. Eventually, all data should be
available to "all qualified observers." There was some discussion of the time
delay between the processing of data and the time at which it is available to all
comers with no clear resolution of this issue. CFA will prepare an outline of
the program for discussion with NASA.
Guest Observer representation on the Users Committee was discussed. Currently
there is one optical astronomer and one X-ray/ optical astronomer. It was
proposed to increase Guest Observer representation on the Committee by adding
another Guest Observer. NASA will search for a radio astronomer to serve as a
third member. It was the general opinion that rotation of Guest Observer
representatives was desirable without arriving at a definite length of time fOF
one person's service on the Committee.
The date of the next meeting will be negotiated later.
FS:jk