The Purpose and Organization of the Chandra X-ray
The CXC is based in Cambridge, Massachusetts, and is staffed by team members
from the Smithsonian
Astrophysical Observatory, the
Massachusetts Institute of Technology, and TRW. Chandra and the
CXC are managed by NASA-MSFC. The purpose of the
CXC is to provide the support required by the science community to
realize fully the potential of the Chandra X-ray Observatory (CXO).
The Chandra X-ray Center changed its
name from the Advanced X-ray Astrophysics Facility (AXAF) Science Center in December of 1998, as NASA
renamed AXAF in honor of Subrahmanyan Chandrasekhar.
The CXC has responsibilities in the following areas:
The Chandra Archive Operations Team is responsible for maintaining the
Chandra Data Archive. After data have been processed through Automated
Processing (AP) and passed Validation and Verification (V&V), their
ingestion into the Archive is overseen by the Chandra Archive
Operations Team. This group ensures the integrity of the archive
databases; maintains the AP status, Chandra bibliography, FITS
keyword, and operational databases; provides support to other CXC
groups, such as MP, CDO, and grants; is responsible for data
distribution; and controls the public release of proprietary data. In
addition, it maintains ties with other NASA data centers, provides
informational e-mails to users, works with the database team on the
development of archive interfaces, and supports mirror sites such as
Mirror Site at Leicester University (UK).
The frontier astrophysics which Chandra will accomplish requires that
the telescope, science instruments, and other spacecraft systems (such
as the aspect star camera) be fully calibrated on the ground and in
orbit. The CXC is responsible for collecting and archiving the
calibration data, coordinating the analysis of the data, archiving the
results of the analysis, and making the data and the analysis results
available to Chandra users.
For the Science Instruments (ACIS, HRC, HETG, and LETG) and the telescope,
the calibration activities are conducted in three sequential stages:
This stage involved the separate calibration of the science
instruments and the telescope. The calibrations included determinations
of the detectors' quantum efficiencies, spatial uniformity, and
count-rate linearity. The periods of the Low-Energy and High-Energy
Transmission Gratings were also measured.
Calibration at the X-ray Calibration Facility
The Science Instruments and the telescope together were
calibrated at the MSFC X-ray Calibration Facility (XRCF). At the XRCF,
X-rays from a particular target (e.g., aluminum), located 1700 feet
from the telescope, were focussed by the telescope onto a detector.
The XRCF calibration determined the effective area of the
telescope/detector combination, the instrument scale, the spectral
resolution, and the point response function as a function of energy
and angle from the telescope axis. The CXC received and archived
these calibration data and the analysis results, and makes them
accessible to users. Included in the results are models which are
used in the CXC-developed software to assist users in planning
proposals and analyzing data from observations.
The CXC performs the initial and on-going on-orbit calibrations. The
on-orbit calibrations involve observations of celestial sources, as
well as observations where the instrument is
not at the telescope focus, in order to measure instrument backgrounds
The CXC also generates and updates calibration models and
parameters. During on-orbit operations, periodic re-verification and
re-determination of the calibration models and parameters are
required to account for variations and aging effects in the telescope
system and SIs, and for unforeseen operating characteristics in the
space environment. The CXC monitors the state of calibration of the
instruments and telescope, and initiates calibration actions.
The Operations Control Center, located at a separate secure location in
Cambridge MA, houses the systems used to send commands to the Chandra X-ray
Observatory and receive the telemetry data for astronomy and engineering.
The Flight Operations Team (FOT) is responsible for the health and safety
of the spacecraft. Their Mission Planning section works with scientists and
engineers to produce a detailed operations schedule, liaises with NASA's Deep
Space Network to provide communications support and to prepare the command
loads. The FOT Operations Section performs the around-the-clock activities involved
with command transmission as well as telemetry monitoring and analysis. The FOT
Engineering Section deals with spacecraft problem resolution and on-orbit trend
analysis and maintenance tasks, and develops procedures for future
The Integrated Support Team configures and maintains computer and
equipment required for spacecraft operations. Their Ground Operations
Team is also responsible for setting up the communications links, ensuring
successful receipt of the telemetry data, and relaying it for
A Flight Director Board meets at the OCC on a weekly basis to review and
recommended changes to technical processes or operations procedures, and to
outstanding spacecraft issues.
Data Processing Operations Team
This Team processes the Chandra data after it has been received at the
Operations Control Center (OCC). Pipeline Processing
is used to convert the
data from its raw (telemetered) form into Level 2 science products (see the
Guide to Chandra Data
Archive Products.) All
resulting data products are ingested in the
Chandra Data Archive, and
following Verification & Validation, are distributed to the users.
This Team is also responsible for special processing of problem data, and
for the testing of the operational software.
Development and Operations Science Support
This group provided review of science instrument and aspect camera systems
requirements, design, development and verification prior to launch. They
worked directly with the IPI and contractor teams in many cases to
assist in calibrations and become familiar with the operation of the hardware.
They provide the primary technical CXC resource for the operation of
these instruments on-orbit, and perform monitoring and trends analysis of all
facets of on-orbit performance affecting the scientific return.
CXC Director's Office
The Director's Office represents the Chandra observers (GO and GTO)
and assists the Director in the running of the CXC. This group is
responsible for the following:
Coordination with the Chandra Users' Committee,
which is the
formal link between users and the Chandra project. Potential Chandra
observers may contact any member of the User's Committee to
communicate comments or concerns.
Working with other CXC groups to insure science analysis
software is accessible through a user-friendly interface.
observing-proposal submission and
review process, which includes: preparation of instructions given in
the CfP; the POG (Proposers' Observatory Guide); the
RPS software and the receipt and sorting of proposals; the formation of a
peer committee and the review of the proposals; preparing the results
for Mission Planning and for posting; and the receipt and peer review of
stage II cost-proposals.
In coordination with the Users Committee, The Science Working Group,
The Chandra Project Office, and NASA Headquarters, this group prepares
summaries of policies concerning the interaction of Users, the CXC,
and NASA. Subjects of concern are time allocations for GO, GTO, and TOO
targets, target scheduling, coordination with other observatories,
calibration data, proprietary data, analysis tools, peer review, etc.
Monitoring and oversight of observation status and completeness.
The CXC is responsible for ensuring that Chandra observations are carried
out in a manner which satisfies the science requirements of the
observers while maximizing the overall observing efficiency.
The scheduling of targets must take into account factors such as the relative
positions of the sun, earth, and spacecraft as well as any special observing
constraints. Examples of the latter could include simultaneous observations of
a particular object with another satellite/ground based observatory, or
several observations to monitor variability. The scheduling process must also
provide rapid response for "Targets of Opportunity", such as supernovae or
other episodic events. For information on user interaction with
Mission Planning, see the
Chandra Observation Scheduling page.
Science Data Systems
The remarkable science capabilities of the Chandra X-ray Observatory
require new, flexible, multi-dimensional
software for data analysis.
The Science Data Systems team (SDS)
is responsible for design, specification, and testing
of scientific data analysis software supporting the
needs of the Chandra X-ray Observatory users,
both for initial
reduction of the instrument specific data and for more advanced
The principal goal is to allow Chandra users to exploit
the richness of the Chandra data by building a data analysis system
that provides users with substantial
SDS has designed the
Analysis of Observations (CIAO)'' software which
is a system of tools that allows multi-dimensional
data analysis of Chandra data.
The software incorporates multi-mission analysis capabilities
including the Data Model library
for manipulating data files. A set of generalized modeling and fitting
tools allows users to construct complex models
and to fit them to multi-wavelength astronomical data in N dimensions.
The tools include error estimation based on advanced statistical
models. SDS works closely with the
Software Development team in developing
the pipeline processing tools and the data analysis software.
SDS has developed tools that provide access to calibration products
and integrate calibration data. As a result the users can obtain a
consistent up-to-date view of the
spacecraft geometry, HRMA, and detector and gratings characteristics.
SDS has developed utilities to carry out simulations and modeling of
spatial and spectral responses of the HRMA and detectors, and plasma
spectral models for interpreting the X-ray spectra.
The latter require compilation and maintenance of a significant atomic
SDS provides user support by producing extensive
software documentation, manuals, analysis guides and data analysis
threads. They also provide a
direct user support via technical backup for the
Helpdesk, and by answering questions from users requiring investigation
of subtle analysis issues.
SDS carries out a primary check of the
processed data for each observation verifying that the processing
has produced high quality products for the user, including
the best aspect solution.
Science Operations Team
The Science operations team is a superset of three Chandra teams, Mission
Planning, Calibration, and Development and Operations Science Support
(DOSS). The SOT's responsibility is to maximize Chandra science return
by optimizing spacecraft operations. It includes planning for and responding to
various failures and degradations, using on-board software and ground
operations software and procedures. They interface directly with the
Observers to assure the correct configuration of each observation.
They also directly support the reviews to assure that all detailed
planning and commanding of the spacecraft is correct.
The Hardware & Systems group supports CXC data processing and archive
operations, software development and science activities
by providing and maintaining hardware and operating systems for all these
functions. This group also support special CXC `off-site' events, such as
workshops, presentations and demos at conferences and peer reviews.