Don Savage
Headquarters, Washington, DC          March 25, 1997
(Phone:  202/358-1547)

Tammy Jones
Goddard Space Flight Center, Greenbelt, MD
(Phone:  301/286-5566)

Ray Villard
Space Telescope Science Institute, Baltimore, MD
(Phone:  410/338-4514)

RELEASE:  97-54

HUBBLE SPACE TELESCOPE CHECK-OUT FINDS SUCCESSES, CONCERNS

    The Servicing Mission Observatory Verification
(SMOV) for NASA's Hubble Space Telescope (HST),
currently about halfway through its detailed check-out
prior to returning to scientific operations, has found
Hubble in overall excellent health, with seven of the
eight components replaced or installed during the
servicing mission functioning very well to date.
However, a few concerns with one of the science
instruments are being evaluated.

    "The Hubble Space Telescope is checking out
extremely well overall, and the few anomalies we see
give us no reason to believe we will not be able to
meet all our scientific goals," said Dr. Ed Weiler,
HST Program Scientist, NASA Headquarters, Washington, DC.

    "I'm very impressed that in just the few weeks
since the servicing mission, we've already seen Hubble
take the best images of Mars ever obtained from
Earth's distance.  Every observatory commissioning
encounters some problems, but we're on track to clear
up all our remaining concerns.  That's good news for
the many, many astronomers who are lined up for
observing time on Hubble."

    Earlier this month science observations with the
Wide Field and Planetary Camera-2 resumed, and on
March 10 the science team obtained images of Mars.
Also, further optimization and alignment of the
mirrors in the new Fine Guidance Sensor (FGS),
installed during the servicing mission, were completed
with excellent results following its first star
observation.  Project management officials say it's
clearly the best FGS aboard HST.

    Commissioning of the new Space Telescope Imaging
Spectrograph (STIS) has proceeded very well, according
to project officials.  In the coming two weeks team
members will test the instrument's ability to acquire
targets in the narrow slits.  Once this is
demonstrated, the instrument will be ready to begin
science operations.

    Checkout of the Near Infrared Camera and Multi-
Object Spectrometer (NICMOS), installed during the
second servicing mission, has provided both excellent
results and some areas of concern.

    The NICMOS, designed to observe the universe in
near-infrared light, contains three cameras and a set
of highly advanced light sensors which must be
maintained at a very cold temperature -- nominally 58
degrees Kelvin (-355 degrees Fahrenheit).  These
sensors, along with filters and other components, are
housed in a large cryogenic dewar (a high-technology
insulated bottle filled with about 225 lbs of solid
nitrogen embedded in aluminum foam).

    The NICMOS Principal Investigator, Dr. Rodger
Thompson, University of Arizona, said NICMOS high
resolution cameras 1 and 2 have shown excellent images
in preliminary focus tests.  However, these tests also
show that camera 3 focus is currently beyond the
range of the NICMOS internal mechanical adjustment
capability.  Analysis indicates the situation may be
due to unexpected thermal contact in the dewar, which
results in a slightly warmer cryogen temperature and a
subsequent reduction of dewar lifetime.

    The most likely explanation is that as the solid
nitrogen warms up it expands, and exerts pressure on
the internal structure of the dewar.  This expansion
resulted in an unwanted physical contact between two
internal structural components of the dewar, providing
a pathway for excess heat to travel from the warmer
outer structure of the dewar to its colder internal
parts, warming the solid nitrogen to a higher than
desired operating temperature.  This expansion also is
affecting the performance of Camera 3.

    The analysis team expects that the thermal contact
might release in the future, returning NICMOS to its
nominal state.  Under these conditions, analysts
predict that camera 3 should move back into the
instrument's range of focus.  Rearrangement of the
NICMOS observing schedule could allow the full
implementation of the NICMOS science program.

    It will take several weeks or months for team
engineers to be able to determine for certain the
amount of reduction in the lifetime of the cryogen;
however, the reduction can be compensated for by
rearrangement of observing schedules.

    Current plans call for SMOV activities to continue
for the next few weeks with results of the Early
Release Observation program available in early May.

    During the STS-82 HST Second Servicing Mission in
February, astronauts aboard the Space Shuttle
Discovery replaced two older science instruments
aboard Hubble with STIS and NICMOS, and also replaced
a Fine Guidance Sensor, a Reaction Wheel Assembly, a
Data Interface Unit, a Solar Array Drive Electronics
package, an Engineering/Science Tape Recorder, and a
Solid State Recorder.  In addition, the astronauts
performed other maintenance on the observatory,
including patching of some insulation and installing
covers on the Magnetic Sensing System.

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