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Spitzer Telescope Handbook
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2.3                 Principal Investigators, Science Team, and User Community

Initially, only six scientists were selected for the Science Working Group, three instrument PI’s and three at-large members.  These were:


Giovanni Fazio, Harvard-SAO, PI for the Infrared Array Camera (IRAC)

Jim Houck, Cornell, PI for the Infrared Spectrograph (IRS)

George Rieke, U. Arizona, PI for the Multiband Imaging Photometer for SIRTF (MIPS)

Michael Jura, UCLA, Interdisciplinary Scientist

Frank Low, U. Arizona, Facility Scientist

Ned Wright, UCLA, Interdisciplinary Scientist


In addition, these scientists were joined on the SWG by three ex-officio members:   

Nancy Boggess, NASA-HQ, Program Scientist

Michael Werner, NASA-Ames, Project Scientist and SWG Chair

Fred Witteborn, NASA-Ames, Deputy Project Scientist

2.3.1       Evolution of the Spitzer Science Working Group

The SWG remained remarkably stable over the ~20 years between selection and launch.  The only original member who left the group was Deputy Project Scientist Fred Witteborn, who did not make the move to JPL when the SIRTF project was relocated in 1989-1990.  However, several new members were added to the group – both to supplement the existing group and fill additional needs.  Thus at launch the SWG had expanded to 13, including the Project Scientist (Werner) and his new Deputy.  The new members were:


Dale Cruikshank, NASA-Ames, Planetary Science Representative

Robert Gehrz, U. Minnesota, Outreach Coordinator

Charles Lawrence, JPL, Deputy Project Scientist

Marcia Rieke, U. Arizona, Community Affairs Coordinator

Tom Roellig, NASA-Ames, Facility Scientist

Tom Soifer, Caltech, Director of the Spitzer Science Center [ex-officio]


In addition, the NASA Program Scientist has remained an ex-officio member of the SWG. A number of excellent NASA scientists, and detailees, have held that position over the years, and the SIRTF/Spitzer project has benefitted from their participation and oversight. They include Nancy Boggess , Bill Danchi, Jay Frogel, Jonathan Gardner, Fred Gillett, Doug Hudgins, Bill Latter , Dave Leisawitz, Keith MacGregor, Kartik Sheth, Eric Smith, Guy Stringfellow, Glen Wahlgren and Kimberly Weaver.


Although the instrument PI’s had a business and contractual relationship to the Project Office, the SWG as a group had only an advisory role.  Formally, the SWG makes recommendations to the Project Scientist concerning scientific and technical matters, and the Project Scientist passes these on to the Project manager, or brings to the SWG questions raised by the Project Manager. In practice, the non-PI SWG members were well-integrated into the activities of the Project Office and often headed important project-wide tiger teams and integrated product teams.  In addition, the SWG played an extremely important role in SIRTF advocacy.  Finally, each member of the SWG was allocated observing time on Spitzer (see below) and was responsible for defining scientific programs, analyzing data and publishing the results.

2.3.2       Spitzer Scientific Utilization

Most of the observing time on Spitzer during the cryogenic mission (82.2%) (and all the time during the warm mission) was awarded to the international astronomical community through the usual peer-review process, which was managed by the Spitzer Science Center.  Four somewhat distinct categories of observing time were identified in during the cryogenic mission: 


Guaranteed Time was awarded to the PIs on behalf of their instrument teams and to the other members of the SWG.  During the first 2.5 years of the cryogenic mission, each instrument team was granted 5% of the observing time, which was shared among the two-to-three dozen scientists who were affiliated with each of the instrument teams.  The non-PI members of the SWG, including the Project Scientist and his Deputy, shared equally in another 5% of the time.  Two and one-half years was singled out for this purpose because it was the Spitzer Level 1 lifetime requirement (considerably exceeded by the actual cryogenic lifetime).  Following the first 2.5 years, the instrument team share continued at 5% while the non-PI allocation ceased. 


Director’s Discretionary Time amounted up to 5% of the observing time.  It was awarded at the discretion of the SSC Director to facilitate observations of new or time-critical phenomena which cannot be deferred to the next annual proposal cycle.  In the warm mission Director’s Discretionary Time totaled 10% of the time observed (see the end of section 3.1 for more information).


Legacy Science Program is an innovation in community utilization that was pioneered by Spitzer.  The intent was to assure that Spitzer addressed critical scientific problems while producing a coherent legacy in the form of uniform, high quality databases of broad scientific interest.  This was done by inviting proposals for large programs and funding the selected teams both to produce scientific papers and to create higher order data products that go far beyond the standard data products produced by the Spitzer Science Center.  In the first Legacy selection, announced in 2000, six projects were selected and awarded a total of 3160 hours of Spitzer time, with over 700 hours going to the largest program.  These programs were largely completed during the first year of the Spitzer mission, and additional Legacy programs were selected and carried out annually for the next four years until the completion of the cryogenic mission. In total 8691.4 hours were allocated to 32 Legacy science programs. During the warm mission, the spirit of the Legacy Science program was carried on in the Exploration Science and Frontier Legacy programs.


General Observer (GO) projects.  All observing time on Spitzer not allocated into one of the previous three categories was awarded to General Observer projects, which cover a very wide range of scientific topics.  These can include joint projects with other NASA observatories.  The GO program continues during the Warm and Beyond Mission, utilizing all observing time (except the 10% Director’s Discretionary Time). 


In addition to these observational programs, Spitzer also had grants for theoretical research and programs doing archival research during the cryogenic mission. During both the cryogenic and warm missions, Spitzer offered joint time with observatories in some cycles, including the Hubble Space Telescope, Chandra X-Ray Observatory, NRAO and NOAO.


In aggregate 747 scientists from 38 countries were selected as Principal Investigators on Spitzer programs over the 5.7 years of the Spitzer cryogenic mission.  During the warm mission 335 scientists from 22 countries were selected as Principal Investigators.


During the warm mission there were five categories of observations. In addition to the General Observer (GO) and Director’s Discretionary Time (DDT) programs, three new program types were introduced:


Exploration Science Programs: The Exploration Science programs were science that required more than 500 hours of Spitzer observing time. Exploration Science programs provided an opportunity for large-scale investigations not practical during the cryogenic mission. In total 38,412.4 hours of Exploration Science in 42 programs were selected. The largest Exploration Science program selected was allocated 2108 hours.


Frontier Legacy Programs: Frontier Legacy programs were introduced in Cycle-13. The Spitzer mission began with Legacy programs - large, coherent science investigations that would provide a lasting legacy for the Spitzer mission in addition to the primary science goals of the program. The Frontier Legacy category was introduced to solicit programs that require substantially more time than the typical Exploration Science programs (which were introduced in Cycle-6). These programs were designed to create an important component of the legacy of the Spitzer mission. In total there were three Frontier Legacy programs with allocations totaling 8545.1 hours, the largest single program was allocated 5286 hours.


Snapshot Programs: As the warm mission progressed the downlink rate dropped and the program complexity increased as more exoplanet and time series observations were approved. It became necessary to encourage programs to fill the gaps between these heavily constrained observations. Snapshot programs were designed to provide a substantial number of hours of easy to schedule, lower data volume science and were selected with the understanding that only a sampling of the proposed sources might be observed.



Description automatically generated

Figure 2.6: Program types for science observations in the Spitzer mission. The cryogenic mission ran from August 2003 to May 2009, and the warm mission ran from July 2009 to Jan 2020. Legacy and GTO programs were cryogenic mission only, Exploration Science, Frontier Legacy and Snapshot programs were warm mission only. The dip in hours of observations during 2009 is due to IWIC. DDT time increased in 2014 for the Frontier Fields, and at the end of mission (see section 3.1)



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