This Legacy journal article was published in Volume 1, May 1992, and has not been updated since publication. Please use the search facility above to find regularly-updated information about this topic elsewhere on the HEASARC site.

NSSDC as an Element Of Support

for the HEASARC

James L. Green, Cynthia Cheung

and Jeanne Behnke



The High Energy Astrophysics Science Archive Research Center (HEASARC) is a responsibility that has been given to GSFC by NASA Headquarters. The purpose of the HEASARC is to support a multi-mission archive facility in high energy astrophysics for scientists all over the world. Data from spacecraft and space-borne instruments such as ROSAT, GRO, BBXRT, and XTE, just to name a few, will be made readily available along with multi-mission analysis tools and knowledgeable science user support staff. The HEASARC activity is being accomplished through a team effort between the Laboratory for High Energy Astrophysics (LHEA) and the National Space Science Data Center (NSSDC).

Figure 1 provides an overview of the roles of the LHEA and NSSDC. As shown in the figure, the LHEA is responsible for the individual science user support, which includes retaining an expert staff of astrophysicists cognizant of all the mission data that is supported within the archive. LHEA will maintain an active database, the HEASARC On-line Service, for rapid access and analysis of multi-mission high energy astrophysics data. In addition, the HEASARC science support staff will be developing software analysis tools which will facilitate the inter-comparison of high energy astrophysics data in the archive. It is envisioned that this extensive value-added service will primarily support researchers who are not knowledgeable about the appropriate use and analysis of high energy astrophysics data. Providing ease of access to disparate data sets by non-experts is one of the most important functions that the HEASARC will play in future years.

The role of the NSSDC is to maintain and provide a more routine access to the extensive physical archive that is being accumulated. This includes bulk data distribution and distribution to individual scientists who do not need the extensive user support contacts that are provided by the LHEA/HEASARC staff. The NSSDC will also work with scientists through the NSSDC/FITS office in order to meet their formatting needs. Additional NSSDC facilities will be used in order to produce and distribute HEASARC CD-ROMs. The first HEASARC CD-ROM is expected to be ready for distribution by mid-1992.

Figure 1 - HEASARC and NSSDC Responsibilities

Archive Data Availability

The NSSDC will support the HEASARC activities by migrating all key high energy astrophysics data to the NSSDC Data Archive and Distribution Service (NDADS) system. NDADS will provide the long-term management of the archive for the HEASARC. It is anticipated that the NDADS system will provide the HEASARC user support facility with quick and easy access to archived raw and processed data. The NDADS system is currently located in Building 28 at GSFC and supports the archiving, access, and retrieval of data from a bank of optical disk jukeboxes.

The following table provides an initial list of astrophysics data that either have already been archived, are in the process of being archived, or will be archived in the NDADS system.

Project		Data Set		Start-End Ingest Dates

High Energy Astrophysics data:

Vela-5B		X-ray All Sky			January 92 (Complete)

Ginga		Large Area Counter (LAC)	March 92
		Quick Look Data and
		Observing Log

HEAO-1		A-1 Pointed Observations &	March 92 - April 92
		Single Day Scan Maps
		A-2 Sky Maps			May 92 - June 91
		A-3 Source Catalog		When available
		A-4 Sky Maps			When available

HEAO-2		IPC Images			December 91 (Complete)
		IPC SLEW Survey			December 91 (Complete)
		HRI Images			December 91 (Complete)
		HRI Event Lists			April 92 - May 92
		SSS raw data			April 92 - May 92
		FPCS data			When available
		OGS, MPC data			When available

HEAO-3		C-1 data			March 92 (Complete)

OSO-8		Cosmic X-ray spectra		June 92 - July 92

GRO		BATSE, OSSE, COMPTEL,		June 92 - Completion
		EGRET data

ROSAT		HRI, PSPC data			August 92 - Completion

BBXRT		X-ray Spectra			August 92

SAS-1 (Uhuru)	X-ray All Sky			When available

SAS-2		Gamma-ray All Sky		When available

SAS-3		X-ray Spectra			When available

EXOSAT		Standard Processed Data		Fall 92

COS-B		Gamma-ray Sky Survey		Fall 92

Astro-D		Standard Processed Data		Spring 94

Other Astrophysics data: 

IUE		Current Processed Data		October 91 - Completion
		Final Archive Data		April 92 - 1994

EUVE		Standard Processed Data		May 93 - Completion

IRAS 		Deep Sky plates			August 91 - March 92 (Complete)
		Faint Source Survey		December 91 - May 92
		ISSA (Super Skyflux Images)	December 92 (Complete)

COBE		Infrared All Sky Survey		July 93 - Completion

ADC		Astronomical Catalogs		On-going

NIST		Atomic Physics Data		December 91 (Complete)

The NSSDC has played an important role in archiving the data from the International Ultraviolet Explorer (IUE) project. At this time NSSDC has archived all 12 years of the IUE mission data on platters in the optical disk jukebox. This data is not only being used in the normal archive and distribution activities, but is also used by other projects to test the capabilities of the NDADS system.

The ROSAT Project will deliver non-proprietary archive data to the NSSDC starting in August 1992.

The Gamma Ray Observatory Science Support Center (GROSSC) has been working very closely with the NDADS staff to develop mechanisms for ingesting GRO data into the NDADS archive. The GROSSC will deposit public data in specified areas on NDADS which will then be loaded automatically into the archive following verification procedures. The GROSSC is also building a user interface to provide scientists with the ability to browse the GRO data products and then access the actual archived data .

The table in this section is not complete, but it is expected to grow to meet the demands of the HEASARC support facility and the world community of scientists interested in rapid access to astrophysics data archived at the NSSDC. Space physics data (solar, space plasma, etc.) will also be stored in the NDADS system. The next few sections provide a brief overview of the NDADS system services and capabilities.

NDADS System Configuration

The NDADS system hardware is nearly identical to the Data Archive and Distribution Service (DADS) being acquired for the management and archiving of data from the Hubble Space Telescope. NDADS is a new capability in the NSSDC, and it will undergo rapid changes over the next two years as continual increases in services are planned. All users are being asked to provide constructive feedback to the NSSDC so that proper resources can be allocated to bring the system into complete operational status.

A schematic of the system is shown in Figure 2. There are four major software components in the system: the archiver/data ingest subsystem, the catalog subsystem, and the host/user interface subsystem. The system architecture provides a natural isolation between catalog and user interface and archive and user interface facilitating update of the archive without affecting the other components.

The NDADS facility is a Digital Equipment Corporation VAX cluster configuration with almost 1.2 terabytes of on-line optical disk storage. The hub of the system is a cluster of three VAX 6410 CPUs and one VAX 8250 CPU. One of the VAX 6410s operates as the CATALOG CPU and includes the database management subsystem and stores science and inventory information about data sets. The other two 6410 CPUs function as the user host CPUs, one for Astrophysics and one for Space Physics. These systems are the interactive access points for users. Some of the online information systems that currently run on the NDADS are the HEASARC On-line Service and the IUE Data Access system.

As shown in Figure 2, the VAX 8250 currently operates as the Data Archive CPU. This subsystem will be replaced later this year with a faster, more modern computer. This component archives data to optical disk and retrieves data from the archive. It is planned that this subsystem will connect to the GSFC Mass Data Storage and Delivery System (MDSDS) for archive backup. A crucial part of the archive subsystem is the mass storage component, two Cygnet optical jukeboxes, models 1802 and 1803. The jukeboxes are each configured with two SONY 6.5 gigabyte optical disk drives. Using 12-inch Write Once Read Many (WORM) optical platters, the SONYs will allow a read/write capability of 300 KB/second. The Cygnet 1802 holds 51 platters for a total of 334 gigabytes online disk space and the 1803 holds 131 platters for a total of 858 Gigabytes online disk space. The jukebox robotics are operated by Cygnet's JIMS (Jukebox Interface Management System) software. An APTEC IO Processor is used as a front end to the jukeboxes from the VAXes.

Other components of the cluster include magnetic tape drives, stand-alone optical disk drives, staging disks, multiple network access and a MicroVAX 3300 for overall system control and monitoring. One of the most promising features of the system architecture is its easy expandability to ten terabytes through the addition of more optical disk jukeboxes.

NDADS System Services

The NDADS system provides its users with a variety of both generic and specific services. Generic services include integrity and quality control, data ingest and retrieval, and ordering and delivery services. The NDADS will ensure that the data in the optical disk jukeboxes are stored redundantly and without error in order to maintain data integrity. The media will be checked periodically for degradation, and data will be copied to new media when appropriate.

In association with the HEASARC personnel, the NSSDC will ensure that the data and metadata ingested by the archive facility is correct. Data and metadata ingest is the NDADS function which loads the archive data into the optical storage system. The ingest mechanism is reserved for use by the NSSDC.

The NDADS facility provides the capability for users to retrieve data from the archive either interactively or remotely. A user may initiate a request from either one of the NDADS host computers or from his/her remote computer by using specific software packages. The data are quickly retrieved from the storage system and placed in one of several desired locations. The NDADS will provide services for data set and documentation ordering and distribution. These include services provided via networks, magnetic tape distribution, WORM optical disk, specific CD-ROMs and bulk distribution.

For users who interactively log onto NDADS, specific data set services include: access to catalog and inventory tables, identifiers and keywords, and browsing and visualization. A catalog of the entire NDADS archived collection will be available to all users and will be an important management tool for the operation of the archive. Each data set component will have an inventory table. In the case of an inventoried file component, the table relates the granule identifiers with the file on optical platter plus other relevant information. Identifying keywords and search capabilities will be applied to each data set to facilitate the retrieval of the data in the archive through the user interfaces.

It is planned that each data set component will have one or more interactive browsing tools. In the case of an inventoried file component, the browsing tool inputs a requested file and displays its contents to a user. For example, browsing tools for IUE spectra are available as an Interactive Data Language (IDL) script procedure which provide plots of the spectra. It is expected that the HEASARC will provide software for browsing high energy astrophysics data. These browsing tools, which are archived with the data, are also available to the science community as an archived product.

NDADS Automated Retrieval Mail System

Since December 1991, the Automated Retrieval Mail System (ARMS) system has been available on NDADS for direct data retrieval. Data requests are to be sent as an electronic mail message to the NDADSA:: ARCHIVES account. The subject line should give the project name, data type and data format (optional), and the data destination (optional). The body of the mail message should contain the list of requested data IDs. ARMS permits an average-size data request to be completed within minutes of receipt of message at the NSSDC. Over 3000 requests for IUE data have been filled by ARMS since its introduction. The following is an example of a mail message request:

Send to: NDADSA::ARCHIVES -or-

Subject: REQUEST Project_name Data_type [Data_format [Remote_access]]






A list of the valid project names, data types, data formats, remote access information and data IDs can be obtained by sending a message to NDADSA::ARCHIVES with the subject "SEND INFORMATION" or "HELP". No text is required in the body of message for this request. A list of the current NDADS holdings can also be obtained by sending a message with the subject "HOLDINGS" or "HOLDINGS Project_name".


The NSSDC and the Laboratory for High Energy Astrophysics will provide enhanced access and support to users of high energy astrophysics data. LHEA will provide expert user support to the astrophysics research community. The NSSDC will support the HEASARC effort by providing data management, bulk data distribution, and long term archiving of all HEASARC data and non-proprietary software products. The NSSDC will fulfill its responsibility through the NDADS system.

Figure 2 - NDADS Facility Configuration

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