Late Breaking News

NICMOS / NCS Safing and Status

As part of the preparations for Servicing Mission 4 (SM4), the flight software
for the spacecraft computer (NSSC-I) had to be updated in order to accommodate
the new instruments that will be installed. Since this computer manages the
health and safety of all the on-board instruments, including NICMOS and the
NICMOS Cooling System / NICMOS Cryo-cooler (NICMOS NCS/NCC), this involved
shutting down the NCS/NCC as part of the procedure, on Sep 10, 2008. After the
NSSC-I update, the NCS was restarted but went into safemode soon afterwards,
before the cooldown had completed. A project tiger-team was formed, including
staff at STScI and GSFC as well as the engineers who had designed and built the
NCS, and three more NCS restart attempts were carried out. In each case, the
NCS safed with telemetry that was suggestive of the possible presence of small
amounts of icy contaminants interfering with the circulator pump. The leading
theory suggests that small amounts of these contaminants, likely water ice,
became dislodged as part of the shutdown and restart process, and were
transported from benign areas to the location of the turbo circulator
mechanism and sensors, where they are interfering with the nominal operation
of the system.

There is no indication of any damage to the mechanical systems in the NCS/NCC
or to NICMOS itself, for the brief amounts of time that the system was running
during each restart attempt. However, continued operation in this state may
pose a significant health and safety threat, hence the decision has been made
across the Project to defer further restart attempts until the system has
warmed up sufficiently to enable the contaminants to thaw and reduce their
level of interference. With SM4 imminent, this means that the cooler will
remain off through SM4 (it would have had to be powered down during SM4 in any
case). The current plan is to restart it soon after SM4, as was also originally
planned, with the main difference being that the expected cooldown may take a
few weeks longer than originally planned, due to the warmer initial state of
the system. The net result is that the remainder of the Cycle 15 and 16 NICMOS
observations will be deferred for execution after SM4, and will execute along
with the rest of the observations currently planned for Cycle 17.

Summary of NICMOS SMOV4 Plans ISR Available

A new NICMOS Instrument Science Report outlining the NICMOS plan for Servicing Mission Observatory Verification 4 (SMOV4) is available. It presents the NICMOS requirements, the planned activities
to fulfill these requirements and a brief plan for the data reduction and analysis. It can be found on the NICMOS web site at http://w
ww.stsci.edu/hst/nicmos/documents/isrs/isr_2008_004.pdf.

Verifying the NICMOS Count Dependent Non-Linearity Correction ISR available

A new NICMOS ISR that re-investigates the NICMOS count dependent non-linearity, using the flat field lamps to
reach high count regimes is available. The NICMOS count dependent non-linearity has been previously
quantified and is currently corrected in NICMOS pipeline. In this document we show
that the count dependent correction is still accurate to within 1.2% of true linearity for
counts above 100 ADU independent of filter used. This is a response to the count-rate
dependent non-linearity investigations, to eliminate questions about the current count
dependent corrections.

It can be found on the NICMOS web site at http://w
ww.stsci.edu/hst/nicmos/documents/isrs/isr_2008_003.pdf.

New TIR about Light leaks from NICMOS flatfield lamps into WFPC2 is available.

A new TIR characterizing the light leaks from the NICMOS internal flat-field lamps into WFPC2
is available. A set of images is taken with WFPC2 using the F814W filter while having the NICMOS
lamp in both on and off mode. We find that there is a light leak from the NICMOS lamp
into WFPC2, increasing the overall background counts by ~25% in the F814W filter.
Using the WFPC2 ETC, we estimate the effects of this light leak for different sky
background levels and find an increase by almost a factor 2 in the case of a “low” sky
background, while the effect is ~20% for a “high” background case. The effects on
shorter wave-length filter observations are smaller, but may still increase the background
level significantly. For example, in the F555W filter, the increase is 2% and 16% for a
“high” and “low” sky background, respectively. Besides the overall increase in
background, there is also a particular feature, “dragon’s breath”, in WF4 with a
significantly elevated signal (factor ~3) in ~400 pixels. We conclude that the NICMOS
internal flat-field lamp should not be used while observing with WFPC2.

Improvements to Calnica ISR Available

A new NICMOS Instrument Science Report describing a number of improvements to Calnica is now available. The ISR reports two major
and a number of minor updates to calnica, the STSDAS task that performs routine instrumental calibration of NICMOS raw images.
It can be found on the NICMOS web site at http://www.stsci.edu/hst/nicmos/documents/isrs/isr_2008_002.pdf.

Bright Earth Persistence ISR Available

A new NICMOS Instrument Science Report showing the presence of image
persistence in NICMOS data due to prior saturation of
the array by the bright Earth as well as an algorithm to remove its impact, is
now available. It can be found on the NICMOS web site at http://w
ww.stsci.edu/hst/nicmos/documents/isrs/isr_2008_001.pdf.

NICMOS Safing and Recovery

The Near Infrared Camera and Multi-Object Spectrometer (NICMOS) entered safe mode on Saturday, September 1, 2007 at approximately 11:00 PM EDT (Day 245, 02:58 UTC). The safe mode cause was an apparent Analog/Digital FIFO read failure of internal engineering status by the Control Section flight software of the NICMOS main computer. NICMOS flight software is designed to trigger safing upon failure to properly read the status under the assumption that the inability to determine its own state presents a potentially dangerous condition for continued operation.

NICMOS safe mode entry occurred during orbit day outside the South Atlantic Anomaly. The spacecraft was in two-gyro mode following the successful transition from Zero-Gyro Sun-Point safe mode earlier that day. Although the NICMOS safing event occurred during the recovery to science operations from the Gyro #2 failure on August 31, the two events are unrelated. The leading candidate for the cause of the error was a single event upset affecting the special engineering data buffer, a CPU register, or a memory location. The HST Project proceeded accordingly to recover NICMOS from safe mode, with no reoccurrence of the error, on Tuesday, September 4, 2007 at about 1:00 PM EDT (Day 247, 17:10 UTC).

There are no NICMOS science observations planned for the current week (beginning September 2, 2007). Updates on the status of NICMOS instrumentation and NICMOS science observations will be posted as they become available.

Calibration Plans ISR Available

A new NICMOS Instrument Science Report detailing the NICMOS Cycle 15 Calibration Plans is now available. It can be found on the NICMOS web site at http://www.stsci.edu/hst/nicmos/documents/isrs/isr_2007_004.pdf.

Time Dependent Flat-fields ISR Available

A new Instrument Science Report is now available describing the creation of time-dependent flat-fields. The ISR is available at http://www.stsci.edu/hst/nicmos/documents/isrs/isr_2007_002.pdf. The time dependent flat fields are available at http://www.stsci.edu/hst/nicmos/calibration/reffiles/temporal_flat_files/index.html.

NICMOS Focus Update ISR Available

A new Instrument Science Report is now available describing the current focus status of NICMOS. The ISR is available at http://www.stsci.edu/hst/nicmos/documents/isrs/isr_2007_003.pdf

New SAAclean ISR Available

A new Instrument Science Report is now available for the new SAAclean PyRAF task, available as part of STSDAS. SAAclean removes the persistence from cosmic rays encountered during a passage through the South Atlantic Anomaly. The ISR is available at http://www.stsci.edu/hst/nicmos/documents/isrs/isr_2007_001.pdf

The NICMOS team encourages SAAclean users to submit any feedback on the task to the STScI Help Desk at help@stsci.edu.