Chandra completed its sixth year of successful scientific operations
on 23 July 2005, with the spacecraft and science instruments
continuing to perform in an outstanding manner. The 6-year
milestone was celebrated with the 6 Years of Science with
Chandra symposium held in Cambridge in November. The quality and
depth of the results presented at the symposium spoke to the
impact that Chandra is having on our field. Of particular note
was the number of papers that involved multiwavelength data from
Chandra, Spitzer and Hubble - NASA’s three Great
Observatories. As we head into the 7th year of observations, it
is not surprising that over-subscription rates remain very high
for the Chandra user research programs, including the General
Observer, archive research, and Directors Discretionary Time
programs, and the Chandra Fellows program, which is now in its
8th cycle. As the mission progresses, it is clear just how
important a role Chandra plays as NASA’s prime X-ray astronomy
asset.
The staff of the CXC worked hard during the last year to
maintain the high standards
met throughout the mission so far. Of particular note were the
increasing temperatures measured in all spacecraft subsystems
as the passive thermal insulation degrades due to continued
exposure to radiation. The rising temperature has resulted in
increasingly more complex mission planning constraints and has
started to have a measurable impact on the average observing
efficiency for the mission - down to 61% compared to 65% in
2004. As a result of the new thermal constraints, an
increasing number of observations are now being split into
multiple segments and scheduled with other observations or
segments that help ensure a favorable overall thermal
profile. The Flight Operations Team and the Science Operations
Team are monitoring the thermal situation carefully and
working to minimize the impact on the science return for the
mission.
The observing program transitioned from Cycle 6 to Cycle
7 observations in December,
although we expect a number of remaining Cycle 6 observations
to be interleaved with Cycle 7 observations through the first
quarter of the year. There were 7 schedule interruptions in
the last year due to high levels of solar activity, resulting
in an overall loss of about 3% of the scheduled observing
time. The mission planning team responded efficiently to all
the solar re-plans and minimized the science lost. Planners
also responded quickly to the 13 Target Of Opportunity (TOO)
observations that required schedule interruptions. Its
exciting to see so many TOOs being requested following
SWIFT’s launch in November
2004.
The
spacecraft continued to operate well overall with no
safe modes or major
anomalies. Operational highlights included completing the
earth eclipse seasons of summer 2005 and winter 2006 with
nominal power and thermal performance, and passing through a
lunar eclipse without incident on November 1.
The Flight Operations Team was also busy developing a number of
flight software patches designed to increase the safety and
science efficiency of Chandra. A patch was created to provide the
capability to transition to Normal Sun Mode following
execution of the Science Instrument safing actions (SCS 107)
in response to a high radiation event. The capability ensures
a favorable thermal attitude in cases when stopping the
command load would violate a propulsion line thermal
constraint. A second patch increased the value of the Electron
Proton Helium INstrument (EPHIN) E1300 channel threshold by a
factor of two. The new value will reduce the number of false
triggers of the science instrument safing sequence (SCS 107)
during periods of puffed-up radiation belts, and when EPHIN is
at high temperature. The change will also help with mission
planning by relaxing a thermal constraint. A third patch
modified SCS 107 to move the Science Instrument Module (SIM)
only once when SCS 107 is executed, rather than twice. The
previous implementation consisted of two moves, the first to
an intermediate position to allow the HRC camera door to be
closed, and a second to its final HRC-S position. Because the
HRC door is no longer closed during SCS 107 runs, the extra
movement could be eliminated, reducing the likelihood of
excessive SIM motor heating.
The science instruments also continued to operate well overall,
with only a small number of minor anomalies that had little
impact on the science return. ACIS experienced a recurrence of a
latch-up of the threshold crossing plane circuit that affected
one observation in July. The t-plane was cleared at the start of
the following observation by commands that reset the ACIS Front
End Processors. The reset commands are routinely included in the
loads in anticipation of an occasional occurrence of this
anomaly, the last having been in November 2001. ACIS also
experienced an unexpected power-down of its Digital Electronics
Assembly side-A. This event was thought to be due to a single
event upset.
HRC experienced nominal operations with the exception of a brief
episode of anomalous secondary telemetry in December. The
anomalous data were seen in the engineering portion of the
telemetry stream and had no impact on operations. No corruption
of the X-ray event data was observed.
A number of important changes to the Chandra Operations Control
Center ground system took place last year, including the
transition in July to a direct network link to JPL (previously
all mission data and communications had been routed through the
GSFC closed I/ONet), and the migration to a new version of the
ground system hosted on the Linux operating system. The ground
team worked hard to perform the required testing to ensure a
seamless transition from the old IRIX operating system and
Silicon Graphics hardware. The team also prepared carefully for
the 2005 leap-second and all systems handled the extra second on
December 31 without difficulty.
The Science Data Processing team continued their excellent record
for throughput of data, with the average time from observation
to delivery of data reduced to less than 2 days. The Chandra
archive holdings grew by 0.3 TB to 2.6 TB (compressed) during
the year and now consists of 9.6 million files. A new mirror
site for the archive was established at IUCAA in Pune,
India.
The Data System team released software updates in support of the
Cycle 7 proposal submission deadline and Peer Review, and for
the Cycle 8 Call for Proposals in December. Work has also
continued on preparations for the third full re-processing of
the Chandra archive.
The Education and Public Outreach team was very active with 24
press releases, a NASA Media Telecon and 10 additional image
releases. The interest in the Chandra web site and educational
products remained at near record levels last year.
We
look forward to continued smooth operations and exciting science
results.
Roger Brissenden