SSDOO Provides New Service for XTE: Mission Data Staging Service

Volume 11, Number 3, September 1995
By Roger Dilling and Joseph King
Owing to the very large data volume involved (2.5 GB/day), new systems and approaches have been prepared for the management, archiving, and dissemination of data from the X-Ray Timing Explorer (XTE) spacecraft by NSSDC, its sister organization the Astrophysics Data Facility (ADF), and the High Energy Astrophysics Science Archive Research Center (HEASARC) of the Goddard Laboratory for High Energy Astrophysics (LHEA). These organizations are partners in assuring effective public access to high energy astrophysics (HEA) data, and they support spaceflight projects in various ways.

XTE is a Guest Observer-mode spacecraft slated for launch on November 9, 1995. During its nominal three-year life it will observe and time astrophysical X-ray sources. It carries three instruments: the Proportional Counter Array (PCA), the High Energy X-Ray Timing Experiment (HEXTE), and the All Sky Monitor (ASM), provided by Goddard, the University of California at San Diego, and the Massachusetts Institute of Technology (MIT), respectively.

The XTE Science Data Center (XSDC), an element of the ADF, will receive XTE data from Goddard's telemetry capture facilities and will produce FITS-formatted calibrated data products for the XTE Project's Instrument Teams and Guest Observers. XSDC will also transmit these data files along with the uncalibrated files to a new NSSDC mass storage system, the Mission Data Support Service (MDSS), described further below. These data will adhere to XFF (XTE File Format) relative to directory/subdirectory structure. XFF was developed by the LHEA's XTE Guest Observer Facility (GOF), HEASARC, and XSDC. GOF and HEASARC personnel have developed software to access these data on the MDSS for validation and analysis purposes and anticipate creating new products that would also be input to the MDSS system.

Early network access to public data on the MDSS system will be through the interfaces developed by HEASARC. Further information on these interfaces is available through the XTE HEASARC WWW Home Page at With time these data will also become accessible through NSSDC's normal access paths. It should be noted that ASM data (plus some "verification data") will become public immediately, whereas there will be one year Guest Observer-proprietary periods for the PCA and HEXTE data.

The current hardware/software configuration for the MDSS is an SGI Challenge DM workstation running IRIX, and a Digital Linear Tape (DLT) jukebox managed by Unitree software. The jukebox can accommodate 244 DLT tapes of 10 GB capacity each (uncompressed), giving a total capacity of 2.4 TB plus any compression. There are three DLT tape drives in the jukebox, each rated at 1.25 MB/s transfer speed and each separately addressable on the Challenge's bus. The Challenge is connected to the local area network via Ethernet and FDDI.

Within Goddard's Space Science Data Operations Office, NSSDC has responsibility for the MDSS system, while ADF has responsibility for providing the lead scientific support and appropriate technical support.

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Author:Miranda Beall
Curators: Erin Gardner and Miranda Beall
Responsible Official: Dr. Joseph H. King, Code 633
Last Revised: 04 Dec 1996 [EDG]