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Subject: Good news: ACS High Resolution Channel
Date: Tue, 10 Oct 2006 16:26:16 -0400 (EDT)
From: Kenneth Sembach
Reply-To: Kenneth Sembach

Hello Everyone,

We have very good news to report to you regarding the status of the
Advanced Camera for Surveys High Resolution Channel [HRC] today.

As you may recall, the HRC suspended on September 23rd because
of a problem with one of the relays on a signal processing chain
board in the CCD detector electronics. Analysis of the condition
by the ACS Anomaly Review Board concluded that the most likely
cause of the problem was a bit of non-conductive debris between
two relay contacts that must meet to make a proper electrical
connection. After a thorough assessment of the risk to the HRC
and other ACS instruments, the Anomaly Review Board recommended
last week that the relay be toggled open to clear the debris
and then closed to reestablish the electrical connection.

Yesterday the two CCD detectors were powered down as part of normal
monthly operations. Last evening the suspect relay was toggled open
and closed. This procedure evidently cleared the debris because this
morning the missing +35V connection was restored when the low voltage
power supply for the the CCDs was turned on again. All voltages are
now in their normal ranges. As you can imagine, everyone involved
in the ACS recovery is delighted that the analyses and recovery
operation produced the desired effect.

The HRC will be monitored for several days before final approval
is given later this week by the HST Project to proceed with a series of
special commands to configure the HRC for science operations next week.
In the meantime, the HRC voltages are being watched carefully, and the
HST schedulers are working to incorporate HRC observations into next
week's observing plan. The other ACS CCD camera, the Wide Field Channel
[WFC], is operating nominally and fully functional.

Discussions about how to bring the final remaining channel
(the Solar Blind Channel [SBC]) back on-line have already begun.
Some changes to the instrument commanding may be needed to run the
SBC because its use has historically been tied to a set of commands used
to toggle the problematic relay in the HRC. Since it is quite likely that
the HRC relay will not be toggled again, an alternate approach to
operating the SBC is being developed. The SBC is fully functional,
and all expectations are that the SBC will be available for use in the
near future.

Please refer any external press/media questions to the STScI Office
of Public Outreach (Contacts: Ray Villard and Cheryl Gundy). The ACS
Team will post information about the status of ACS and information for
Guest Observers on the HST web page (http://www.stsci.edu/hst/) and the
ACS web page (http://www.stsci.edu/hst/acs/) as soon as it is available.


Sincerely,

Ken Sembach