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NSSDC as an Element Of Support
for the HEASARC
James L. Green, Cynthia Cheung
and Jeanne Behnke
NSSDC
Introduction
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-
ARCHIVES@ndadsa.gsfc.nasa.gov
Subject: REQUEST Project_name Data_type [Data_format
[Remote_access]]
Text:
Data_ID1
Data_ID2
.
.
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".
Summary
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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