STScI Logo

Hubble Space Telescope
NICMOS STScI Analysis Newsletter 41


| STScI Analysis Newsletter
| 23 January 2009
Visit the NICMOS web site 
"New in the Last 45 Days" for all new information about


After the previous restart attempt and subsequent safing of
the NICMOS Cooling System (NCS) in December 2008, an Anomaly 
Review Board was convened to examine the failure, which this
time was not due to the circulator pump but was instead
caused by a low speed limit violation of the Turbo 
Alternator, which helps to maintain the proper flow rate of 
coolant. After examination of the data, approval was given 
by HST Project for a restart attempt on Thursday, 15 January 
2009. The system initially restarted nominally, with the 
circulator pump motor behaving as expected and soon reaching 
a stable current level of around 62 mA, which it maintained 
for the next 24 hours. On Friday 16 January 2009, approval
was given to proceed with the cooldown phase which involved
activating the compressor and Turbo Alternator, this time 
with modified restart parameters. The cooldown proceeded for
about 10 hours until the Turbo Alternator safed, again with
a low speed limit violation similar to the signature seen in
December 2008. The HST Project has decided to defer 
subsequent NICMOS Cooling System startup attempts until 
after Servicing Mission 4, due to limitations on the amount 
of time remaining.
At STScI, the HST Mission Office and the Director's Office
were involved in these discussions and support this decision.
The NCS Anomaly Review Board is continuing its investigation
of the failed restart attempts and will prepare a recommended
plan of action for any future restart attempts after SM4.

For more detailed information and updates, please consult the
NICMOS webpages:

| Help:
| To subscribe or unsubscribe to the STAN, send a message
| to with the subject line blank and
| the following in the body: [un]subscribe nicmos_news
| The Space Telescope Science Institute is operated by the
| Association of Universities for Research in Astronomy,
| Inc., under NASA contract NAS5-26555.