Spitzer Documentation & Tools
Legacy History

Policies and background information for the Original Legacy program

The Chair of the Legacy Science Time Allocation Committee, when formally recommending the projects to the SSC Director, offered this statement:

"Taken together, the projects we recommend represent an exciting use of NASA's next major astrophysical observatory. Each of the projects will yield the superb science that we expect of a major investment of time in a NASA Great Observatory. A hallmark of each of these projects is that they fully exploit the unique and special capabilities of Spitzer that make it a major NASA mission and the highest priority space project of the 1991 National Academy of Sciences Decade Review."

Legacy Program Overview

The Legacy Program was motivated by a desire to enable major science observing projects early in the Spitzer mission, with the goal of creating a substantial and coherent database of archived observations that could be used by subsequent Spitzer researchers, including General Observers (GOs). Legacy Science projects are distinguished from GO investigations by the following fundamental principles:

  • They are large and coherent science projects, not reproducible by any reasonable number or combination of smaller General Observer investigations;
  • They are projects of general and lasting importance to the broad astronomical community with the Spitzer observational data yielding a substantial and coherent database; and
  • They are projects whose raw and pipeline-processed data enter the public domain immediately upon SSC processing and validation, thereby enabling timely and effective opportunities for follow-on observations and for archival research, with both Spitzer and other observatories.

Previous space astronomy missions have implemented variations on this theme, often as "Key Projects." Unlike those missions, however, the Spitzer Legacy Science Program did not pre-determine science topics or categories, and the Legacy Science Program was open to all credible science areas for which Spitzer could make a major contribution, and was open to all scientists on a competitive basis. Spitzer relied on the ingenuity of the user community and the peer-review process to guarantee that the approved projects maximize the scientific legacy of Spitzer.

The original Spitzer Legacy Science Program was comprised of six projects selected by the Spitzer Science Center (SSC) in November 2000 following a solicitation of proposals and competitive peer review. The six original projects used a total of 3160 hours of Spitzer observing time, primarily in the first year of the mission, and integrated substantial ancillary data from ground-based observatories and other space-borne telescopes. Each Legacy Science project developed post-pipeline data products and/or analysis tools that have been delivered to the SSC for wider dissemination to the community. These products, including catalogs and image mosaics, were invaluable to researchers planning future GO proposals. Enhanced Legacy science data product deliveries to the SSC started in October 2004. The data are available from the Infrared Science Archive (IRSA).

Additional Legacy programs were selected in subsequent observing cycles. The Legacy Science Program ended with the conclusion of the cryogenic mission.

A list of all of the Legacy programs, including abstracts, data delivery schedules, etc., can be found on the Legacy page.


As Spitzer underwent two fiscally-mandated redesigns in the early 1990s, project managers and engineers derived clever and ingenious schemes for protecting the scientific integrity and vitality of the program. As the original 5-year lifetime seemed to be sliced in half, scientists within the Project Office and throughout the external user community realized that they too would have to re-examine the way science is conducted with such a precious resource.

The apparent reduction in available observing time understated the true impact because of the need for "thinking time," that is, the time required for collection, analysis, and dissemination of data, followed by the subsequent proposing of additional follow-on investigations. The usual iterative cycle of

propose -----> observe -----> analyze -----> publish -----> interpret -----> re-propose

is too lengthy for a short cryogenic mission. The potential loss of scientific knowledge was particularly great for Spitzer, where the huge increase in "astronomical throughput" (sensitivity, efficiency, sky coverage) inevitably led to discoveries that are unexpected and/or unobservable by any other means. With this stark realization in mind, the Spitzer Project and its community-based advisory group at the time - the Community Task Force - formulated a unique and innovative program that seeks to establish an early and long-lasting heritage: the Spitzer Legacy Science Program.

Resources Available
The resources that were available to approved Legacy Science teams included observing time, funding, and technical assistance.

Observing Time
The high observing efficiency of Spitzer translated into an extraordinary amount of astronomical observing time annually. Apart from telemetry, routine calibrations and assorted engineering activities, it was estimated that more than 6000 hours of science observing time would be available annually. The SSC anticipated that ~3000 hours of observing time would be allocated to Legacy Science projects within the first year of the Spitzer mission. Depending on the nature and scope of submitted proposals, it was conceivable that an additional ~1000 hours might be devoted to Legacy Science investigations early in Spitzer's second year. Six Legacy programs were selected, for a total of nearly 3200 hours of Observatory time.

The SSC provided funding for approved Legacy Science investigators. The funding was offered in three stages, and was conditional on the demonstration of satisfactory progress during each stage.

Prior to Spitzer's launch, this funding was intended to support detailed observation planning, the collection of ancillary data, and the development of post-pipeline data processing algorithms and software. Following launch, funding supported a variety of activities, including: monitoring of observing program, validation of observing strategy and refinement of observing plans (as necessary), continued development of post-pipeline data products, extraction of early science results from data, and the delivery of higher-level data products to the SSC.

The SSC expected to offer a total of ~$20 million in investigator support for the multi-year Legacy Science Program, with a total of $2.5 million available before launch.

SSC Support
Each Legacy Science team had an SSC scientist designated to serve as their scientific and technical liaison. The SSC hosted a post-selection Legacy Science Workshop in January 2001 in Pasadena. This Workshop brought together members of the approved Legacy Science teams, the Spitzer Instrument Teams and SSC staff to discuss matters of mutual interest.

The SSC also formed a Legacy Science Working Group (LSWG), comprised of Legacy Science project investigators, Spitzer Guaranteed Time Observers (GTOs), and SSC scientists and engineers. The purpose of the LSWG was to provide a forum to:

  • Promote the common adoption of data reduction/analysis/validation and software standards & tools when it makes sense to do so
  • Facilitate cross-team intellectual exchanges & refinement of observing strategies/programs
  • Facilitate exchanges with GTOs, in pursuit of greater efficiencies and effectiveness of science programs

Responsibilities of Investigators

The Legacy Science teams were established and funded well before launch. The approved teams were expected to implement a multi-year investigation of their choice, and received conditional funding as they proceeded through the three stages of the Legacy Science Program. To proceed from one stage to another, the approved Legacy Science teams had to satisfactorily demonstrate competence in executing the tasks associated with each stage. The Spitzer Science Center assisted the teams during the course of their investigations, as needed, and conducted periodic assessments of progress.

Stage One
Stage One began when approved teams were initially funded in December 2000, and extended through the end of the nominal 60-day In-Orbit Checkout period, a total duration of 21 months. During this period, Legacy Science teams revised their proposed observing plans (i.e., target lists/fields and AORs), as necessary, in response to recommendations made by the TAC and the observing time allocated by the SSC Director. The teams submitted these revisions, including unambiguous descriptions of targets/fields, to the SSC by April 2001. The teams also delivered the detailed specifications of their observations to the SSC by October 2001. [Legacy Science proposals did not need to include a full set of completed AORs at the time of proposal submission.]

During Stage One, the teams also began to develop their project-specific post-pipeline data processing, if proposed. Finally, the teams utilized this period to prepare for the analysis of Legacy Science data and (if proposed) began to collect ancillary data to support their Legacy Science project. These ancillary data may have involved other space-borne or ground-based observatories. Researchers also began planning for complementary modeling and/or simulations in support of their Legacy Science investigation.

Stage Two
Stage Two began with Spitzer's science operations phase, and extended for a period commensurate with the scope and level of activities proposed. The precise duration of this stage depended on the nature and scheduling of the proposed observations and data processing activities associated with the project. The majority of Legacy Science projects were executed in the first year of the Spitzer mission, and the duration of Stage Two for such projects was not allowed to exceed two years after the launch of Spitzer. For the exceptional projects with a significant amount of second-year observations, either as a result of using second-generation observing modes or from second-look observations, the duration of Stage Two may have been extended for up to an additional year. This third year would be devoted primarily to producing post-pipeline data products based upon observational data taken during the second year.

During Stage Two, the teams first verified the soundness of the proposed observing strategy. This analysis was accomplished using pipeline data products produced by the SSC (and tools developed by the teams) and products derived from observations taken as part of their Legacy Science project early in the science mission and/or the Spitzer First-Look Survey. The teams also applied the algorithms and analysis tools developed by them and/or the SSC to the pipeline-processed data delivered to them by the SSC. If necessary, the teams modified their observing strategies and data analysis plans, algorithms and/or analysis tools in response to on-orbit performance data. The teams completely specified any observations utilizing the second-generation observing modes via submission of appropriate AORs. Furthermore, the teams planned any second-look observations that were part of their approved project.

Legacy Science teams delivered any post-pipeline data products and/or software analysis tools to the SSC. Incremental versions of these products should have been delivered to the SSC approximately every six months after the start of the science mission. During Stage Two, the teams also started to extract scientific results from their data.

Final data products and/or analysis tools must have been delivered to the SSC by the conclusion of Stage Two, accompanied by explanatory documentation. Products based on data from first-generation observing modes should have been delivered to the SSC within two years of launch, with incremental products delivered in time to affect planning for GO Cycle 2. Products based on data from second-generation observing modes (or from second-look observations, if executed in the second year of the Spitzer mission) should have been delivered to the SSC within a year of the completion of the second-year observations. These data products should have been delivered to the SSC no later than three years after launch, with incremental products delivered in time to affect planning for GO Cycle 3.

Post-pipeline data products developed by the Legacy Science teams and delivered to the SSC entered the public domain immediately upon SSC verification. The SSC also verified any software analysis tools delivered by teams, assessed its utility to the general user community, and planned for its release into the public domain.

Stage Three
Stage Three may have extended for an additional one year, and was contingent on the successful completion of Stage Two. During Stage Three, the teams continued to extract and publish scientific results based upon their Legacy Science data.

Progress Reviews

In order to maximize the likelihood of success for each Legacy Science project, the SSC conducted reviews at key points during the duration of each project. These reviews assessed the progress being made by the teams, identified any problems that arose, and identified remedial actions (as necessary).

An Observing Strategy Review took place at the SSC in September 2001. The purpose of this review was to assess the team's plan for conducting Spitzer observations, and to optimize the plan (where possible). This review occurred one month prior to the deadline for submission of completed AORs to the SSC. At a subsequent Data Plan Review, in May-June 2002, teams described their post-pipeline data processing plans (if proposed), and their development of analysis algorithms and/or software tools (if proposed).

A post-launch Progress Review occurred during Stage Two, approximately six months after the launch of Spitzer, or three months after commissioning of the relevant observing modes was completed. At this review, each team validated their observing strategy, based on the analysis of early data taken as part of their Legacy Science project. Each team should have also demonstrated progress towards their proposed higher-level data processing tasks, in the form of prototype analysis software.

In addition to these Reviews, teams should have regularly informed the SSC of progress towards their milestones during the intervening periods. For each project that proposed post-pipeline product development, the SSC also assessed each team's progress when receiving intermediate data products and/or software tools semi-annually.

A final Progress Review took place at the end of Stage Two, on a schedule that was unique to each Legacy Science team. At this review, each team delivered the final version of their committed post-pipeline processed data products (and explanatory documentation) to the SSC for verification and archiving. If the teams proposed to deliver higher-level data analysis software tools, the final versions of these products (and explanatory documentation) were also delivered to the SSC by the conclusion of Stage Two.