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:

1. Subassembly Calibration 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.
2. 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.
3. On-orbit Calibration 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 and characteristics.

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 Calibration Coordinator builds and manages the Chandra Calibration Database (CALDB) with help from the Calibration and Science Data Systems Groups. This database houses all publicly available calibration products used in Pipeline Processing as well as scientific analysis.

The Operations Control Center, located at a separate secure location in Burlington 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 operations.

The Integrated Support Team configures and maintains computer and communications 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 ground processing.

A Flight Director Board meets at the OCC on a weekly basis to review and approve all recommended changes to technical processes or operations procedures, and to track any outstanding spacecraft issues.

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.

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.

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:

• Oversight and maintenance of the CXC's Science Web pages.
• 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.
• Interfacing with users; includes disseminating Chandra Announcements, publishing the Chandra Newsletter, maintaining the CXC Helpdesk, organizing the science exhibits in the Chandra booth at the AAS, and organizing Chandra Workshops.
• The 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.
• Running the Einstein Fellowship program.
• 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.

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 scientific analyses. 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 analysis power.

• SDS has designed the "Chandra Interactive 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 database.
• 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.

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 Software Development Team provides software for a wide array of CXC activities, both internal and external. This includes software for Proposal Planning, Mission Planning, Data Receipt and Processing, Archive Databases and Functions, and Status Monitoring. This Team also writes much of the CIAO (Chandra Interactive Analysis of Observations) software in collaboration with the Science Data Systems (SDS) Team.

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.