Compton Observatory Science Report #133
Thursday, August 19, 1993 
Eric Chipman, Compton Observatory Science Support Center

Questions or comments can be sent to the Compton SSC.  Phone 301/286-7764,
e-mail SPAN GROSSC::CHIPMAN, Internet chipman@grossc.gsfc.nasa.gov.  

The following note was sent in from NASA Hq:

Addendum to the Compton Observatory Science Report #132, August 12, 1993:

The last Science Report described how to communicate electronically with the
President of the United States.  I am sure that this was meant, in all
innocence, to inform the reader.  Just to avoid any misunderstandings, I want
to clarify that the message was not a solicitation to lobby for Integral, or
the Compton Observatory, or any other cause.  Individuals outside NASA are, of
course, free to use their own judgment and make statements of their own
choosing.  However, NASA does not solicit any such statements.

Guenter R. Riegler
Manager, Compton Gamma Ray Observatory Program


Science operations are continuing.  

As of August 12, 1993 the Compton GRO mean orbital altitude was 349.11 km.   

>From flight operations:  COMPTON GRO REBOOST OPERATIONS STATUS, 8/17/93

The second set of Compton GRO engineering test burns of the two B-side
orbit adjust thrusters (OATs) was successfully completed on August 17,
1993.

After performing a reaction-wheel attitude maneuver earlier in the day to
align the thrust vector with the orbital velocity vector, the solar arrays
were placed in the indexed position (facing the +X direction), and the
thruster burns were performed close to orbit noon.  While the spacecraft
was in thruster maneuver mode with the attitude control thrusters disabled,
the two B-side OATs were fired individually for approximately one second
with a 60-second wait between firings to allow any transients to dissipate.
The pattern of one-second firings was:  OAT 3, OAT 4, OAT 4, and OAT 3.
The high-gain antenna remained active during the event to provide high
quality telemetry required for frequency analysis.  The spacecraft was then
returned to wheel control and remaining body rates were removed.

The objective of these test burns was to observe the flexible body dynamics
as each OAT fired individually.  The data analysis is expected to provide
information for adjusting the structural resonance filter as part of the
ongoing evaluation of orbit reboost options.

Preliminary conclusions pending detailed data analysis from these burns
indicate that the OATs firings were nominal.

>From Wilson/LaVigna
   
There were two maneuvers performed on Tuesday, August 17, 1993.  These
were done to align the velocity and thrust vectors in preparation for the
OATS test burn that day, and then to return to the new science attitude for
viewing period 301.  The maneuver time for the first maneuver was 1416Z
to 1434Z, through an angle of 54.40 degrees, leaving a boom angle wrt the
equator of 10.42 degrees.  The second maneuver times were 2155Z to 2234Z, 
with a maneuver angle of 127.42 degrees, leaving an HGA boom angle from the
equator of 73 degrees. 

BATSE
-----
The hard x-ray pulsar GRO J1008-57 fell below the BATSE detection limit
on Aug. 10.

During viewing period 3-01 BATSE is collecting data for the Crab pulsar,
Her X-1, PSR1055-52, PSR1508+55, and PSR0525+21. The pulsar hardware is also
begin used to collect single sweep 31 ms resolution data for pulsar searches
using LAD 6.

COMPTEL
------- 
The COMPTEL instrument is performing well and continues routine
observations. 

During the period of the spacecraft thruster testing earlier in the
week by the Flight Operations Team at Goddard, the primary detector
high voltages of COMPTEL were switched off, as in previous tests of
the propulsion system.  The telescope was reactivated, and normal
operations resumed, without incident.

EGRET
-----
EGRET operations were normal this week.  During this week, 
work was centered on the papers for the Compton Symposium
and the sections of the sky papers that we are writing.  As
we near the end of phase 2, EGRET is seeing that the gamma
ray sky off the galactic plane is very different in phase 2
than phase 1.  New sources are being seen, and ones seen in
phase 1 frequently have different intensities in phase 2
than when originally observed.  Some of these results were
presented at the AAS meeting in June, and work on a large 
summary paper on AGN's is now in progress.

OSSE
----
OSSE operations are normal.  There were no difficulties entering or recovering
from the reboost practice.

For viewing period 301, the Z-axis target is the Vela pulsar (PI team), and
and the X-axis targets are QSO 1028+313 (GI: M. Maisack) and Mrk 279 (GI: A.
Porter).  The Sun is available on the OSSE scan plane, so slewing response
to BATSE solar flare triggers is enabled.

There have been no slews to the Sun since the last report.