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Data Formats & SoftwareThe dilemma facing the HEASARC in 1990 was that every mission up until that point had produced data in a different format, with a different set of analysis software, and little or no documentation. At the end of each mission the data were in many cases scientifically useless. Combining data from different missions was hard and there was little reuse of software between missions. The HEASARC solution was to adopt a single, self-describing format for all missions: the FITS standard. At the time FITS had just been mandated as the standard for all NASA astrophysics data. But there had been little effort made to define standard data structures, or even decide which level of data should be formatted to this standard. HEASARC took the lead in defining these data structures for each level of data, a vital first step. More information on these standards can be found on the HEASARC FITS Working Group page.
The HEASARC worked with the next mission in line, ASCA, to create a FITS-based multi-mission analysis system. The HEASARC first provided a portable subroutine library to read and write FITS files. The package, known as FITSIO, was first released in early 1992. It formed the basis for all the HEASARC software and is now widely used throughout the world. The FTOOLS package was created to use FITSIO and so provide an operating system-independent data analysis package. The underlying structure utilized several ideas from IRAF and can co-exist with IRAF packages. The FTOOLS package is now effectively the HEASARC software archive and provides a reliable way to maintain and distribute the relevant mission software. The XANADU package (XSPEC, XRONOS, XIMAGE), already in wide use in the community in 1990, has been adopted and extended by the HEASARC to provide multi-mission high-level tools for spectral, image, and timing analysis.
At the time of the creation of the HEASARC it was controversial to propose reformatting the original raw telemetry to FITS. But the HEASARC and ASCA team took on this challenge and proved it was a very cost effective approach. The advantage of reformatting the raw data was that once in FITS, the basic data processing software could be reused for subsequent missions. The HEASARC now recommends that all missions distribute data in FITS format. If new standards are required then the HEASARC staff work with the particular project to define these. It has been a notable success for the HEASARC that smaller, less well funded missions have adopted the HEASARC software infrastructure "as is" and used it to produce a full analysis environment at minimal cost. The BeppoSAX mission and the USA instrument on Argos are examples of this. The adoption of the FITS standards has made possible a large suite of general purpose multi-mission tools, now called HEASoft, that combines FTOOLS, XANADU and several other useful packages.
When the Chandra, XMM-Newton and Suzaku missions were planning their data systems the HEASARC organized a series of workshops to facilitate communication between these missions. These proved to be very helpful and, e.g., ensured that the high-level Chandra and XMM-Newton data products could be read into the existing software packages. Both the Chandra and XMM-Newton data systems are FITS-based and follow very closely the "FTOOLS-approach" first developed by the HEASARC. Bringing these software systems into the HEASARC architecture should be relatively straightforward.
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