The Purpose and Organization of the Chandra X-ray Center

The CXC is based in Cambridge, Massachusetts, and is staffed by team members from the Smithsonian Astrophysical Observatory, the Massachusetts Institute of Technology, and Northrop Grumman (formerly 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:

See also:

CXO Project Science at NASA-MSFC
Chandra X-ray Center (CXC) Scientist Directory

Divisions of the CXC

Archive Operations

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 the Archive 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:

  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.

Calibration Coordinator

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.

CXO Operations Control Center

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 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.

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:

Mission Planning

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 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.

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.

Software Development Team

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.

Hardware and Systems

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.

Last modified: 12/14/17