A GO proposal may be submitted for any amount of HST observing time, counted in terms of HST orbits. Chapter 6 of the HST Primer describes how the required number of orbits can be calculated for a particular set of observations. Programs that require fewer than 100 orbits are called Regular Programs (see Section 3.2.1), and those that require 100 or more orbits are called Large Programs (see Section 3.2.2). Programs in these categories can request observing time in future cycles when this is scientifically justified (see Section 3.2.4). The additional category of Treasury Programs (see Section 3.2.5) is designed to stimulate certain types of ambitious and innovative proposals that may not naturally fit in the Regular or the Large Program categories.

	Proposers are strongly encouraged to develop competitive Large and Treasury proposals.

Large and Treasury proposals will be evaluated by the TAC (see Section 6.1.2). Typically ~1/3 of the available time is allocated to these types of programs. In Cycle 20 existing Multi-Cycle Treasury programs account for part of that allocation, and about 600 orbits will be available for new Large and Treasury programs.

Proposers of Large and Treasury Programs should note that all HST observations are accepted with the understanding that the timescale on which the observations will actually be obtained will depend on scheduling opportunities and demands on HST resources. Experience has shown that programs with scheduling constraints may require execution over an extended period.

In general, proposals are either accepted or rejected in their entirety. Accordingly, you are urged to request the actual number of orbits required to achieve your science goals.

Regular GO Programs are programs that request 99 orbits or less.

Large GO Programs are programs that request 100 orbits or more.

Large Programs should lead to a clear advance in our understanding in an important area of astronomy. They must use the unique capabilities of HST to address scientific questions in a comprehensive approach that is not possible in smaller time allocations. Selection of a Large Program for implementation does not rule out acceptance of smaller projects to do similar science, but target duplication and overall program balance will be considered.

Proposers submitting Large Programs should consult the Large Program Scheduling User Information Report linked from the HST Documents page and the HST Orbital Viewing and Schedulability page. These documents contain necessary information for developing a Large Program that is feasible with respect to HST orbit scheduling. Investigators proposing Large Programs must select the Large Program flag on the cover page, use a visibility that enhances schedulability, and include additional technical detail in the "Description of Observations" section to provide information on the scheduling aspects of their program. The shorter visibility period will be enforced in Phase II for each approved GO program that is awarded 100 orbits or more in a single cycle.

Following the recommendations of the Space Telescope Users Committee, data taken for all Large Programs will have no proprietary period as a default. Proposers may request a proprietary period, and that request should be justified in the "Special Requirements" section of the proposal (see Section 9.3). Such a request will be subject to review by the TAC.

In Cycle 20, we anticipate the selection of four to eight Large Programs. For comparison, in Cycle 19 five Large Programs were accepted for a total of 676 primary orbits. Descriptions of these programs are available on the Treasury, Archival Legacy and Large (TALL) Programs Web Page. Most Large programs accepted in previous cycles were allocated between 110 and 150 orbits. It is also possible to propose a Large Program of 500 to 1000 orbits that extends across multiple cycles to address a high impact issue of broad scientific interest.

HST is a complex observatory, with many possible combinations of observing modes and spectral elements on each instrument. Calibrations and calibration software are maintained by STScI for the most important and most used configurations. However, STScI does not have the resources to calibrate fully all potential capabilities of all instruments. On the other hand, the astronomical community has expressed interest in receiving support to perform calibrations for certain uncalibrated or poorly calibrated modes, or to develop specialized software for certain HST calibration and data reduction tasks. In recognition of this, STScI is encouraging outside users to submit proposals in the category of Calibration Proposals, which aims at filling in some of the gaps in our coverage of the calibration of HST and its instruments.

	Calibration Proposals should not be linked explicitly to a specific science program, but should provide a calibration or calibration software that can be used by the community for existing or future programs.

Users submitting Calibration Proposals must contact the appropriate instrument group to discuss their program prior to submission.

Successful proposers will be required to deliver documentation, data products and/or software to STScI to support future observing programs or archival research. Funding is available to support Calibration Proposals in the same manner as for normal science programs, with the following exception:

	Scientists affiliated with STScI are not eligible for any funding to support their role (as PI or CoI) in a Calibration Proposal.

Calibration Proposals will be reviewed internally by the Instruments Division. The internal review will provide the TAC with an assessment of the feasibility of the proposal, how the proposal complements/extends the existing calibration program, and the type of science impacted by the proposed calibrations. Proposers should summarize the relevance and overall scientific utility of the calibration techniques and products described in their proposal.

A specific science program that has special calibration requirements is not a Calibration Proposal; such a proposal should be submitted as a normal GO proposal and the necessary calibration observations should be added to the science program as described in Section 4.3.

Investigators interested in the submission of a Calibration Proposal are encouraged to study the Instrument Handbooks to determine the level at which STScI provides calibration and characterization. Examples of the kinds of topics that have been addressed by calibration outsourcing programs of the type discussed here are

For a complete description of the instrument calibration plans/accuracies, and for other potential topics, please see the Scientific Instruments Web Page.

The data obtained for a GO Calibration Proposal will nominally be non-proprietary, as is the case for regular calibration observations. Proposers may request a proprietary period (which should be explained in the ‘Special Requirements’ section of the proposal; see Section 9.3), but such a request will be subject to panel- and TAC review and will be granted only in exceptional circumstances if exceedingly well justified. Calibration Proposals can also be submitted as Snapshot Programs (see Section 3.3.2) or Archive Programs (see Section 3.4.3). Archival Research proposals are appropriate in cases where the necessary data have already been taken, or for programs that do not require specific data but aim to develop specialized software for certain HST calibration and data reduction tasks.

	Calibration Proposals must be identified in the ‘Special Proposal Types’ section of the proposal (see Section 8.10).

Regular and Large GO Programs may request HST observing time for more than one cycle.

	Long-Term Programs must be limited to cases where long-baseline, multi-epoch observations are clearly required to optimize the scientific return of the project.

Long-Term Programs require a long time baseline, but not necessarily a large number of HST orbits, in order to achieve their science goals. Examples include astrometric observations or long-term monitoring of variable stars or active galactic nuclei.

You may request time in up to three observing cycles (20, 21, and 22). Long-Term Proposals should describe the entire requested program and provide a cycle-by-cycle breakdown of the number of orbits requested. The scientific justification for allocating time beyond Cycle 20 should be presented in detail. For Long-Term Programs, the sum of all orbits requested for Cycles 20, 21, and 22 determines whether the program is Large or Regular. Target of Opportunity Programs (see Section 4.1.2) are not eligible to be Long-Term Programs.

The Cycle 20 Review Panels and TAC will be able to award limited amounts of time to Long-Term Programs for Cycles 21 and 22. GOs with approved Long-Term Programs need not submit continuation proposals in the subsequent cycles (and hence, GOs who had Cycle 20 time approved in Cycles 18 or 19 do not have to submit a Phase I continuation proposal, although a new Phase II and budget submission will be required for each new cycle).

Starting in Cycle 11, the opportunities for large-scale research with HST were expanded with the introduction of the Hubble Treasury Program. This allows proposals for datasets of lasting value to the HST project that should be obtained before HST ceases operations. A Treasury Program is defined by the following characteristics:

•	The project should focus on the potential to solve multiple scientific problems with a single, coherent dataset. It should enable a variety of compelling scientific investigations.

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Enhanced data products are desirable to add value to the data. Examples are reduced images, object catalogs, or collaborative observations on other facilities (for which funding can be provided). Funding for the proposed data products will depend on their timely availability, as negotiated with the STScI Director. They should be delivered to STScI in suitable digital formats for further dissemination via the HST Data Archive or related channels.

•	Data taken under the Treasury Program will usually have no proprietary period (see Section 5.1), although brief proprietary periods may be requested if that will enhance the public data value.

The following additional characteristics are particularly encouraged:

•	Inclusion of an Education/Public Outreach component. A Phase I Treasury proposal only needs to summarize the planned E/PO component briefly; typically, one paragraph at the end of the Scientific Justification section. A detailed E/PO proposal should be submitted later as discussed in Chapter 11.

The emphasis in Cycle 20 remains on observations whose value is maximal if taken soon. However, Treasury Programs may request observing time to be distributed in future cycles with appropriate justification (similar to the situation for Regular and Large GO Programs; see Section 3.2.4). In addition, Treasury Programs may request observing time in future cycles if the requested number of orbits is large enough to make implementation in a single cycle impractical or impossible.

In this cycle approximately 600 orbits of HST time will be available for new Large and Treasury Programs. In Cycle 19 one Treasury Program was accepted; two Treasury Programs were accepted in Cycle 18. Descriptions of all Treasury Programs are also available on the HST Treasury, Archival Legacy and Large Programs Web Page.

Selection of Treasury Programs will be handled by the TAC as part of the normal peer review process (see Section 6.1.2). Successful proposals will be reviewed by STScI to ensure observing efficiency. STScI resources may be made available to approved Treasury Programs by decision of the STScI Director. In particular, some programs require substantial pipeline processing of their data to generate the final products. Examples are large mosaics for surveys, or co-additions of many exposures in deep fields.

If scientifically justified, it is possible to propose a Treasury Program of order 500 to 1000 orbits that extends to cycles beyond Cycle 20, with commensurate funding, to produce an enhanced dataset of high impact.

STScI reserves the right to conduct midterm progress reviews of Treasury Programs, to ensure that adequate progress is being made to achieve the goals of the project. Ongoing funding is contingent on the results of such reviews. For Treasury Programs above a certain cost threshold, STScI may require successful proposers to use professional project management personnel to aid the scientific team in such areas as planning, scheduling, budgeting, cost-control, and reporting.

Investigators proposing Treasury Programs must select the Treasury Program flag on the cover page, use a visibility that enhances schedulability, and include additional technical details in the “Description of the Observations” section to provide information on the scheduling aspects of their program. Note that a program can be both Large and Treasury, in which case both flags should be set. Proposers submitting Treasury Programs which are also Large Programs should consult the Large Program User Information Report, which can be found on the HST Documents web page (linked from the Cycle 20 Announcement Page). This document contains a discussion of the issues surrounding Large Program scheduling.

	Treasury Programs should be identified in the ‘Special Proposal Types’ section of the proposal (see Section 8.10).

The ‘Scientific Justification’ section of the proposal (see Section 9.1) should include a description of the scientific investigations that will be enabled by the final data products, and their importance. The ‘Description of the Observations’ section of the proposal (see Section 9.2) should not only describe the proposed observations and plans for data analysis, but should also describe the data products that will be made available to STScI and the community, the method of dissemination, and a realistic time line.