HST Call for Proposals and HST Primer for Cycle 24
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Hubble Space Telescope Call for Proposals for Cycle 24 > Chapter 3: Proposal Categories > 3.2 General Observer (GO) Proposals

3.2
A GO Proposal may be submitted for any amount of observing time, counted in terms of HST orbits. GO Proposals are classified as Small (1-34 orbits; Section 3.2.1), Medium (35-74 orbits; Section 3.2.2), or Large (75 or more orbits; Section 3.2.3). Chapter 6 of the HST Primer describes how the required number of orbits can be calculated for a particular set of observations. Proposals in each of these categories can request observing time in future cycles when this is scientifically justified (Section 3.2.5). The additional category of Treasury Proposals (Section 3.2.6) is designed to stimulate certain types of ambitious and innovative proposals that may not naturally fit into the Small, Medium, or Large Proposal categories.
Submitters of Medium, Large, and Treasury Proposals 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.
3.2.1 Small GO Proposals
Small GO Proposals are those that request between 1 and 34 orbits.
It is anticipated that 1800 orbits will be available to the review panels for allocation to Small Proposals in Cycle 24.
3.2.2 Medium GO Proposals
Medium GO Proposals are those that request between 35 and 74 orbits.
The Medium Proposal category was introduced to ensure that compelling science programs that demand a medium-size orbit request have a comparable chance of success as both smaller and larger observing programs. Medium Proposals are reviewed by the panels and ranked together scientifically with the Small Proposals,
but the panels are not charged for them. Each panel will have a specific quota dependent on the Medium Proposal pressure in that panel. It is anticipated that up to 650 orbits in total will be available for the allocation to Medium Proposals in Cycle 24. This nominal allocation is consistent with Cycle 23, when 13 Medium Proposals totalling 593 orbits were selected. However, the TAC has the ability to increase or decrease the Medium allotment to balance the over-subscription between Regular, Medium, and Large Proposals.
3.2.3 Large GO Proposals
Large GO Proposals are those that request 75 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 Proposal for implementation does not rule out acceptance of Small or Medium Proposals to do similar science, but target duplication and overall program balance will be considered.
Approximately 1000 orbits are available to new Large and Treasury Proposals in Cycle 24. For comparison, in Cycle 23 a similar number of orbits were awarded to 12 Large and Treasury proposals for a total of 974 orbits, and in Cycle 22 there were 12 Large and Treasury Proposals were accepted for a total of 1146 primary orbits. Descriptions of these programs are available on the Treasury, Archival Legacy and Large (TALL) Programs webpage. Most Large Proposals accepted in previous cycles were allocated between 100 and 150 orbits, though larger orbit requests are welcome if scientifically justified.
Data taken for all Large Programs 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.
Investigators submitting Large Proposals 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 submitting Large Proposals will find that APT automatically sets the ‘Increase Scheduling Flexibility’ flag in all observations. Proposers should include additional technical detail on the scheduling aspects of their program in the ‘Description of Observations’ section. The shorter orbital visibility will be enforced in Phase II for each approved Large Program.
3.2.4 Calibration GO Proposals
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 Calibration Proposals, which aim to fill in some of the gaps in our coverage of the calibration of HST and its instruments.
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:
Calibration Proposals will be reviewed internally at STScI 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 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 webpage.
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. Calibration Proposals can also be submitted as Snapshot Proposals (see Section 3.3.2) or Archival Proposals (see Section 3.4.3). AR 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.
3.2.5 Long-Term GO Proposals
Small, Medium, Large, and Treasury GO Proposals may request HST observing time in more than one cycle if a clear scientific case is made.
Long-Term Proposals 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 (24, 25, and 26). Long-Term Proposals should describe the entire requested program and provide a cycle-by-cycle breakdown of the number of orbits requested. The Cycle 24 review panels and TAC will only be able to award a limited amount of time in future cycles, so a detailed scientific justification for allocating time beyond Cycle 24 must be presented. Scheduling concerns are not a sufficient justification. The sum of all orbits requested in Cycles 24, 25, and 26 determines whether a Long-Term Proposal is Small, Medium, or Large (or counted against the Cycle 24 orbit pool in the panels). Target-of-Opportunity Proposals are eligible to be Long-Term if certain conditions are met (see Section 4.1.2).
GOs with approved Long-Term Proposals need not submit continuation proposals in the subsequent cycles (and hence, GOs who had Cycle 24 time approved in Cycles 22 or 23 do not have to submit a Phase I continuation proposal, although a new Phase II and budget submission will be required for each cycle).
Budget requests submitted for the first cycle of a Long-Term Proposal should include costs only for the effort to reduce and analyze the data obtained in the first cycle. Separate budget proposals are required in each subsequent cycle (see Chapter 11)
3.2.6 Treasury GO Proposal
Treasury Proposals are those designed to create 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:
Data taken under a 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. Such requests are subject to TAC approval.
The following additional characteristics are particularly encouraged:
The emphasis in Cycle 24 remains on observations whose value is maximal if taken soon. However, Treasury Proposals may request observing time to be distributed in future cycles if scientifically required (similar to the situation for Small, Medium, and Large Long-Term GO Proposals; see Section 3.2.5). In this cycle approximately 1000 orbits of HST time will be available for new Large and Treasury Proposals. Descriptions of previous Treasury Programs are available on the HST Treasury, Archival Legacy and Large Programs webpage.
Treasury Programs will be selected 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.
Investigators submitting Treasury Proposals must select the Treasury Program flag on the APT cover page, use an orbital visibility that enhances schedulability, and include additional technical details on the scheduling aspects of their program in the “Description of the Observations” section. Note that a proposal can be both Large and Treasury. Submitters of Large Treasury Proposals should consult the Large Program User Information Report, which can be found on the HST Documents webpage (linked from the Cycle 24 Announcement webpage.) This document contains a discussion of the issues surrounding Large Program scheduling.
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.

Hubble Space Telescope Call for Proposals for Cycle 24 > Chapter 3: Proposal Categories > 3.2 General Observer (GO) Proposals

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