A. Richmond, M. Duesterhaus, S. Yom
Hughes STX, GSFC/NASA, Greenbelt, MD 20771
E. Schlegel, A. Smale
NASA, Research Scientist, USRA, Greenbelt, MD 20771
N. E. White
NASA/Goddard Space Flight Center, Laboratory for High Energy Astrophysics, Greenbelt MD 20771
HEASARC was created by NASA in 1990 as a site for X--ray and Gamma-ray archive research. The total data volume will be of the order of 1Terabyte by 1995, available on-line for immediate access. HEASARC provides a multi-mission archive for data from the Röntgen Satellite, the Compton Gamma-Ray Observatory, the Astro 1 Broad Band X--ray Telescope, Advanced Satellite for Cosmology & Astrophysics, and XTE missions. This co-exists with the archival data from past missions such as HEAO 3, OSO 8, SAS 2 and 3, Uhuru, Vela5B, the second High Energy Astrophysics Observatory, and the first High Energy Astrophysics Observatory. Data from non-US missions (e.g., the European X-ray Astronomy Satellite and Ginga), is also provided as international agreements allow, along with data from Ariel-V, COS-B, EUVE, HST, IRAS, SMM, and TD1. The HEASARC is located at the Goddard Space Flight Center and is a collaboration between Goddard's Laboratory for High Energy Astrophysics (LHEA, responsible for the science content of the archive), and the National Space Science Data Center (NSSDC, responsible for the data archive management).
XTE is the X--ray Timing Explorer, categorized by (1) 1 microsec time resolution, (2) 2--200keV energy band covered, (3) 1.06microJy sensitivity at 5.2keV, (4) 1^o FWHM field-of-view, (5) all-sky monitor capability, (6) having more than 93% of sky visible, and (7) near real-time operation.
The WWW was chosen as the user interface to the XTE RPS to promote
The major limiting characteristic of HTTP is statelessness. For our StarTrax interface we want to engage in a dialog with the user which progresses from nothing, and builds up to a state where we have identified a target satisfying given constraints, and can offer associated data products. The WWW offers the opportunity to ``mix and match'' reusable components in a rapid prototyping approach; we were astonished in our early days (only 1 year ago!) at how quickly we could deliver useful functionality. Later we began to realize that some of our early optimism was perhaps too naïve: the need for good software engineering practices is probably even greater than before. There are many more components being interconnected and interfaced, and exponentially more failure points. Perl helps you to hack up something real fast without worrying too much about the engineering aspects until much too late.
In spite of the sometimes severe disadvantages, we believe the WWW is a very effective platform for rapid information systems development in astronomy and astrophysics. The WWW provides a substantial pre-existing infrastructure supporting a client-server architecture on the Internet, so one can deliver application functionality at a much faster rate---say, an order of magnitude faster. In the ``classical'' mode---in which we started this project---the developer(s) spend a great deal of time wallowing in relatively low level code. We have not yet achieved the goal of ``reusability,'' in spite of the promises of modern software engineering methodologies. Using WWW and HTML (Hypertext Markup Language) (and ideally, Perl), since you build on that infrastructure, you can deliver functionality very quickly. This not only delivers the promises of rapid prototyping (throw one away), but also of rapid development. The iteration cycle time was often of the order of minutes, rather than hours or days, as in the classical approach. This was partly due to the pre-existing WWW functionality, but to our choice of Perl rather than C. Perl is ideally suited to this kind of work, because it, too, provides a great deal of ready-made high-level functionality. For example, we converted some 30 lines of C code, for decoding URLs, into 3 lines of Perl.