Volume 16, Number 2, June 2000
By Edwin Grayzeck
[Ed. note NSSDC is part of a NASA space science data archive infrastructure providing both permanent archiving (NSSDC) and "active archiving" at sites with both science discipline and data management expertise. Staff members of active archives interact with projects and principal investigators in preparing data and ancillary material for archiving and in supporting researchers' use of archived data. NSSDC plays an active archive role for much of space physics and for several long-wavelength astrophysics missions. The Planetary Data System (PDS) is a distributed array of nodes responsible for active archiving of NASA planetary mission data. NSSDC receives data from PDS for permanent archiving and for dissemination to the general public. This article is intended to give NSSDC News readers a sense for PDS's approach to data provider interactions, use of standards, and peer-review of data and related materials prepared for archiving. E. Grayzeck is at the PDS Small Bodies Node at the University of Maryland. JK]
The Planetary Data System, through its Small Bodies Node (SBN) has just completed the initial data review for the Near Earth Asteroid Rendezvous (NEAR) mission automated delivery system to provide the level 1B archive. The NEAR Shoemaker spacecraft, launched in 1996, reached final rendezvous with the asteroid EROS in February 2000. With its suite of diverse instruments, including an imager, the spacecraft is expected to gather over 200 GB of data in the nominal one-year orbital phase. The mission is being managed by the Johns Hopkins University Applied Physics Laboratory, which has established a Science Data Center (SDC) to provide the data to the science teams and to PDS for distribution to the larger community of planetary scientists.
As the first in the Discovery series of missions, NEAR has worked closely with the PDS, which, as a distributed research archive of data that conform to format and documentation standards, has a well-defined set of procedures for the archiving of data. These steps can be categorized as Definition, Design, Production, and Distribution. In the initial stage documents such as the Project Data Management Plan and Archive Policy and Data Transfer Plan provide the basic outline of work and time lines for activities. The PDS has provided an outline to the planning process with suitable example checklists in the Data Preparation Workbook. By working with these guidelines, missions can draw on that experience and improve the quality of the resultant data sets as well as make use of technology that PDS pioneers. For example, the Archive Plan for the NEAR mission was prepared by the SBN with SDC input to identify the data products (and calibration information) for each instrument.
For the design stage the PDS provides documents that outline the Preparation of Data, which begins with a Quick Start Introduction to PDS Archiving. Although the PDS has a broad set of standards built around data objects and keywords for other missions, it is sometimes necessary to add or modify elements to accommodate specific data requirements. The PDS provides on-line documents that list the Standards and associated Data Dictionary. For the case of the NEAR archive, the SBN and SDC held monthly meetings or teleconference to hammer out how to use PDS services such as software tools to design and test data labels, metadata documents, and CD-ROM volumes. Since the NEAR mission had distinct phases, such as the 1997 fly-by of Mathilde and the Earth Swing-By in 1998, those collected data were used for a critical design of the archive elements. Following PDS procedures, staff reviewed these data and took appropriate actions to streamline the process.
The data collected at the asteroid EROS have also been broken into phases so that a basic organization of the archive by time was established with each period lasting approximately 30 d. For production the SDC has developed the PDS Archive Delivery System (PADS) that generates the CD-ROMs expected for each EROS phase of the mission, organized by instrument and time. The first CD-ROM volumes have now been reviewed both internally by SBN staff and by outside reviewers following PDS guidelines. Action items from that process are now being addressed over the next two months after which the SDC will commence with monthly deliveries of data until nominal mission end in February 2001.
The distribution of the archive to the larger scientific community is the responsibility of PDS. Since the estimate for data volume exceeds 260 GB for just the uncalibrated data, the SBN has worked with the Data Distribution Laboratory, affiliated with the PDS, to develop an automated conversion process to create a collection of DVD-Rs from the CD-ROMs. The DVD-Rs will be held on line at the PDS, which will be the main access point for users. In addition to the uncalibrated level 1B data the archive will also have higher level products and calibrated submissions from the science teams. The PDS is now developing procedures to implement standards on DVD-ROM products that will be used for the final NEAR archive. This process should begin during the calender year 2000.
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Author: Miranda Beall