A major question for astronomical users is how they will acquire data on SOFIA. Historically, airborne astronomy data have been obtained primarily by knowledgeable P.I. teams and their collaborators. With the advances in airborne instrumentation and associated software support, USRA, the prime contractor for SOFIA, felt that it should be possible to obtain some airborne data without collaborating with a knowledgeable P.I., so that any astronomer with a good proposal can obtain the data needed to do his or her science. To make this possible, the observatory must provide a framework in which the extraordinary complexities of infrared astronomy are handled in a routine fashion. With strong support from NASA, the USRA has chosen to enable this policy by developing several facility instruments which will be maintained and operated by USRA and its team at the SOFIA Science and Mission Operations Center (SSMOC) at Moffett Field. The first-light facility instruments were described in the previous newsletter. It should be noted that SOFIA will also have a number of PI instruments, including 2 German PI instruments, that USRA will support in a PI mode similar to what was done on the KAO.

To support the general investigator in obtaining data with the facility instruments in the airborne environment, it was realized that a number of software tools and associated environments were also required. The idea that general investigators would be interacting with the observatory in at least four important respects -- observing preparation, data acquisition, data reduction pipelines, and archival data access -- led to the expanded notion of a user support system that can assist the astronomer from start to finish: the "Data Cycle System", or DCS. The DCS is being developed by USRA using teams at the Rochester Institute of Technology, UCLA, and NASA Ames. It is supported strongly by NASA. Below, the developers of the SOFIA DCS describe the various components of the system. Although the DCS was originally meant to support the use of facility instruments, it is being developed in such a way that the DCS functionality can be applied to PI instruments later.

When most SOFIA users of facility instruments interact with the observatory during normal operations, their interaction will be mediated by an interface which is part of the Data Cycle System, or DCS. The DCS is not only an interface, however; it is the software system which provides users with most of the functionality that they will need at every step along the way to ultimately acquire their calibrated and reduced data. These functions include science planning, proposal preparation, pipelined data reduction, and archival storage and retrieval of SOFIA data.

The DCS was originally motivated by two considerations. The first was the recognition that a data archive is indispensable. SOFIA data will be unique and often unattainable elsewhere, so they represent a scientifically valuable heritage that can and should be usable by the entire community once the original investigator has had the opportunity to use those data for his or her project. Archival research flourishes as an important legacy of most space-based observatories, and SOFIA's 20-year legacy will long be a prime scientific resource to be used alongside the databases from HST, SIRTF, Chandra, Herschel and NGST, among others. The second consideration is the "democratization" of airborne astronomy. In contemplating how, for example, an X-ray astronomer or even a theorist might gather and reduce data, it became evident that observers should have the option of a highly automated procedure for using selected, commonly-used modes of facility instruments, and that the reduction of routine data from those instruments should be doable with a standard pipeline.

The distribution of the DCS development effort among several institutions -- both universities and research institutions -- reflects the broad scope of interest in the DCS. The "Core DCS", being developed at the Rochester Institute of Technology in New York, will reside both on the aircraft and at the SOFIA Science and Mission Operations Center (SSMOC) at NASA/Ames. It will ingest the astronomical observing requests -- filled-in astronomical observing templates containing all parameters necessary for the execution of an observation -- and distribute the information to the science instruments and to the mission control software (MCS). The Core DCS will also be the first repository for the science data, first allowing astronomers to use the facility instruments "quick-look" functions to monitor the incoming data, and then producing the pipelined, reduced data products, once all of the calibration and reference source data are in hand. At the SSMOC, or from any computer on the web, the Core DCS can be called upon by astronomers to use the data reduction modules appropriate to each science instrument in different ways than those assumed by the standard pipelines. In addition, astronomers can call upon the Core DCS to analyze archival data. The RIT development team consists of Robert Krzaczek, Joel Kastner, Ian Gatley, Scott Lawrence and Patrick Stein.

The SOFIA data archive is being developed at UCLA by the Data Management Team, consisting of John Milburn, Ralph Shuping, and Mark Morris, with strong advisory participation by Steve Lord, at IPAC (the Infrared Processing and Analysis Center, located on the Caltech campus). Each time SOFIA lands, the on-board data will be transferred to the SOFIA archive. The data will be organized within a sophisticated database management system (currently Informix), and they will be accessible on the web through a custom interface. It is our goal that the archive will contain the raw, untouched science and calibration data for all instruments, and the pipeline-processed data for the facility instruments. The complete archive will reside at the SSMOC, but we are also working with IPAC to have the pipeline-processed, "finished product", SOFIA images and spectra be accessible on-line via their Infrared Science Archive (IRSA). The IRSA provides the astronomical community with access to many major infrared databases, including those from IRAS, ISO, MSX, 2MASS, SWAS, SIRTF, and Herschel, and we expect that the scientific value of SOFIA data can be enhanced by the intercomparisons made possible in the context of the IRSA.

The SOFIA archive will also house all recorded auxiliary data from the observatory and aircraft -- the so-called "housekeeping data". The housekeeping data includes environmental data, aircraft coordinates, velocities and headings, telescope and instrument parameters, water vapor monitor readouts, and log entries by observers and the flight director. It will also include digitized guider camera images. The auxiliary data will be invaluable for detailed assessment of the science data products after the flight. In addition, much of it will be usable by the observatory staff for monitoring the health of the observatory, performing trend analyses, and tracking down anomalies.

An important part of the archive will be the interface which allows queries based on a variety of criteria. Any astronomer planning future research will be able to quickly learn what has already been observed with all instruments on SOFIA, and, when the facility-class instruments have been used, the resulting images and spectra will be readily accessible, once the validation period has elapsed. It is our goal that all raw data will be publicly accessible after the validation period, and after the first few years of operations, an active archival research program is expected. So far, no decisions have been made about archiving data from the German instruments.

Flight planning and scheduling are not part of the DCS, and presently the SOFIA flight planning is being done within the USRA development of the Mission Control Software. However, the DCS does support advanced research efforts at NASA/Ames Research Center by Jeremy Frank to explore how SOFIA could automate flight planning. One of the demands upon the observatory is that the flight hours be efficiently used to maximize the science return from the observatory. Doing so requires folding several science programs and several flights into the planning mix, so the algorithms needed to determine the maximal solution, given all the constraints on flight paths and flight durations, not to mention altitude constraints, can be quite complex.

The overall project management and software systems engineering of the DCS development activities is the responsibility of Fran Nelbach, the SOFIA Information Systems Development Manager at USRA. Goeran Sandell, a Senior Support Scientist at the USRA, oversees many of the DCS activities, calling upon his extensive experience in data systems at other observatories.

Eventually, the DCS will incorporate proposal preparation tools and observation planning tools, with links to major on-line databases for sky visualization and background estimation. Time estimators will be a part of the observation planning suite. Studies of how best to provide these capabilities, possibly through the use of non-developmental software, are being initiated. It is expected that existing software can be obtained and adapted in time to support the early rounds of proposals. For the components described above, the work is on track to be completed well in advance of first light. The DCS system will be based on the most modern tools and techniques available, and perhaps most important, is flexible enough to accommodate the dramatic changes that can be anticipated during the 20-year lifetime of the observatory.

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