This page walks the proposer through the various parts of the Astronomer's Proposal Tool (APT), the software through which HST proposals are developed and submitted.

As described in HST Guidelines and Checklist for Phase I Proposal Preparation, a Phase I proposal consists of a completed APT proposal form and an attached PDF file. The present chapter describes the items that must be filled out in the APT proposal form; this information is also available from the context-sensitive help in APT. Not every item described here needs to be filled out for every proposal. For example, some items are only relevant for observing proposals, while others are only relevant for archival proposals. APT will automatically let you know which items need to be filled out, depending on which proposal type you choose. HST Preparation of the PDF Attachment describes the items that must be addressed in the attached PDF file.

Proposal Information

Title

The title of your proposal should be informative, and must not exceed two printed lines. Please use mixed case instead of all upper case.

Abstract

Write a concise abstract describing the proposed investigation, including the main science goals and the justification for requesting observations or funding from HST. The abstract must be written in standard ASCII and should be no longer than 20 lines of 85 characters of text. This limit is enforced by APT.

Proposal Phase

No action is required by the proposer at this time. The Phase will automatically be set to ‘PHASE I.’ See HST Proposal Submission Policies for a description of the different phases in the HST proposal process.

Theory

Mark this keyword if you are submitting an AR Theory Proposal. This keyword appears in the APT form only for AR Proposals.

Legacy

Mark this keyword if you are submitting an AR Legacy Proposal. This keyword appears in the APT form only for AR Proposals.

Cloud Computing

Mark this keyword if you are submitting an AR Cloud Computing Studies Proposal. This keyword appears in the APT form only for AR Proposals.

Data Science Software

Mark this keyword if you are planning to request funding for the development of software products that will be made available to the community for the purposes of analyzing HST data. This keyword appears in the APT form only for AR Proposals.

Calibration

Mark this keyword if you are submitting a Calibration Proposal. This keyword can be set for GO, AR, and SNAP Proposals.

Treasury

Mark this keyword if you are submitting a Treasury GO Proposal. This includes Multi-Cycle Treasury submissions. This keyword appears in the APT form only for GO Proposals.

UV Initiative

Mark this keyword if your proposal is eligible for the UV Initiative. This keyword can be set for both GO and AR Proposals.

Fundamental Physics

Mark this keyword if your proposal is eligible for the Fundamental Physics Initiative. This keyword can be set for both GO and AR Proposals.

GO-Archival

Mark this keyword is your proposal combines a request for new data with significant archival research. This keyword appears in the APT form only for GO Proposals. Once checked, the set of flags for AR proposals will appear.

Cycle

For a Cycle 32 Proposal, enter '32' (this is the default).

Mid-Cycle

If you are submitting a Mid-Cycle GO proposal, please check the "Mid-Cycle" box. To learn more about the Mid-Cycle submission process, see the HST Cycle 31 Mid-Cycle Time Submission page.

Requested Resources

Number of Target-of-Opportunity Activations

For proposals containing Target-of-Opportunity observations, enter the number of times you will need to activate visits over the course of the program. An activation is defined as a formal request to STScI to execute one or more visits in a specific turn-around time in reaction to a new target or event. Enter the specific number of activations needed for Non-Disruptive, Disruptive, Ultra-Disruptive, and Flex Day requests in the corresponding boxes. To learn more about Target-of-Opportunity observations, see the Target-of-Opportunity (ToO) Observations section.

Primary and Parallel Orbits

This item appears in the APT form only for GO Proposals.

Enter the total number of orbits requested for Primary observations and the total number of orbits requested for Coordinated Parallel observations OR enter the total number of orbits requested for Pure Parallel observations. Only whole orbits can be requested, and only whole orbits will be allocated. In general, only the boxes for ‘This Cycle’ need to be filled out. However, Future-Cycle Proposals should provide a year-by-year breakdown of the orbits requested by also filling out the boxes for ‘Next Cycle’ (Cycle 33) and ‘After Next’ (Cycle 34). See the Future-Cycle Proposals section of the HST Proposal Categories page for more important instructions on how to enter future-cycle observations into APT.

Total Targets

This item appears in the APT form only for SNAP Proposals.

Specify the total number of targets requested. Multiple visits to the same source should be counted as multiple targets.

Exclusive Access Period

This item appears in the APT form only for GO and SNAP Proposals.

Enter the requested exclusive access period (formerly known as a proprietary period), of either 0, 3, 6 (months), that will apply to all observations in the program. The default exclusive access period is 0 for Calibration, Large, and Treasury GO Programs, 3 for Mid-Cycle Programs, and 6 for SNAP, Small GO, and Medium GO Programs. See Data Rights for more information. The benefits of or need for a non-default exclusive access period must be discussed in the ‘Special Requirements’ section of the proposal.

Scientific Category

Specify one Scientific Category from the list below. Please adhere to our definitions of these categories. If you find that your proposal fits into several categories, then select the one that you consider most appropriate. If you are submitting a Calibration AR Proposal, then choose the Scientific Category for which your proposed calibration will be most important. STScI reserves the right to re-assign proposals to categories to ensure the highest chance of the proposal being reviewed by the proper expertise.

• SOLAR SYSTEM ASTRONOMY: This includes all objects belonging to the solar system (except the Sun, Mercury, and Venus), such as planets, minor planets, comets, asteroids, planetary satellites, and Kuiper-belt objects.

• EXOPLANETS AND EXOPLANET FORMATION: This includes all objects belonging to known extrasolar planetary systems, and observations of their host stars, as well as all studies of circumstellar and proto-planetary disks.

• STELLAR PHYSICS AND STELLAR TYPES: This includes stars of all temperatures and evolutionary phases, including pre-main sequence stars, supernovae, pulsars, X-ray binaries, CVs, and planetary nebulae. It also applies to ISM and circumstellar matter in the Milky Way.

• STELLAR POPULATIONS AND THE INTERSTELLAR MEDIUM: This includes resolved stellar populations in globular clusters, open clusters or associations, and the general field of the Milky Way and other nearby galaxies. Studies of color-magnitude diagrams, luminosity functions, initial-mass functions, internal dynamics and proper motions are in this category.

• GALAXIES: This includes studies of the initial mass function, stellar content and globular clusters in distant galaxies, galaxy morphology and the Hubble sequence, and low surface-brightness galaxies. Starbursts, IR-bright galaxies, dwarf galaxies, galaxy mergers and interactions may fall under this heading. This category also includes studies of gas distribution and dynamics in distant galaxies. Starbursts, IR-bright galaxies, dwarf galaxies, galaxy mergers, and interactions may also fall under this heading if the emphasis is on the ISM.

• THE INTERGALACTIC MEDIUM AND THE CIRCUMGALACTIC MEDIUM: This category includes the physical properties and evolution of absorption-line systems detected along the line of sight to quasars, inflow and outflow of gas to the CGM/IGM, and other observations of the diffuse IGM, and the spectroscopy and imaging of damped Ly-alpha systems.

• SUPERMASSIVE BLACK HOLES AND ACTIVE GALAXIES: This encompasses active galaxies and quasars, including both studies of the active phenomena themselves, and of the properties of the host galaxies that harbor AGNs and quasars. The definition of AGN is to be interpreted broadly; it includes Seyfert galaxies, BL Lac objects, radio galaxies, blazars, and LINERs.

• LARGE SCALE STRUCTURE OF THE UNIVERSE: This includes studies of the structure and properties of clusters and groups of galaxies, strong and weak gravitational lensing, galaxy evolution through observations of galaxies at intermediate and high redshifts (including for example, the Hubble Deep Fields), cosmology in general, the structure of the universe as a whole, cosmological parameters and the extra-galactic distance scale.

These Scientific Categories will be used for review panel assignment.

Alternate Category

If your science goals straddle two separate science categories, users have the option to add an alternate category which will allow keywords from both categories up to a limit of 10 total keywords, thus providing more flexibility in where the proposal will be assigned for review.

Science Keywords

From the list of Science Keywords (see Appendix B: Science Keywords), please select those that best describe the science goals of the proposal. Your choice here is important. Based on the keywords that you specify, your proposal will be assigned to specific reviewers during the proposal review. Please give as many keywords as possible, but not more than five. You must give at least two.

Coordinated Telescopes

This item appears in the APT form only for GO Proposals.

JWST hours

If you are asking for both HST and JWST observing time then list the requested number of JWST hours. You should then also provide detailed information on the JWST observations in the ‘Coordinated Observations’ section of the proposal. If you are not requesting any new JWST observations (or if you have JWST time that has already been awarded), then leave it blank.

Chandra ksec

If you are asking for both HST and Chandra observing time then list the requested number of Chandra kiloseconds. You should then also provide detailed information on the Chandra observations in the ‘Coordinated Observations’ section of the proposal. If you are not requesting any new Chandra observations (or if you have Chandra time that has already been awarded), then leave it blank.

XMM-Newton ksec

If you are asking for both HST and XMM-Newton observing time then list the requested number of XMM-Newton kiloseconds. You should then also provide detailed information on the XMM-Newton observations in the ‘Coordinated Observations’ section of the proposal. If you are not requesting any new XMM-Newton observations (or if you have XMM-Newton time that has already been awarded), then leave it blank.

NOIRLab Nights

If you are asking for both HST and NOIRLab observing time then list the requested number of nights on NOIRLab telescopes. You should then also provide detailed information on the NOIRLab observations in the ‘Coordinated Observations’ section of the proposal. If you are not requesting any new NOIRLab observations (or if you have NOIRLab time that has already been awarded), then leave it blank.

NRAO Hours

If you are asking for both HST and NRAO observing time then list the requested number of NRAO hours. You should also provide detailed information on the NRAO observations in the ‘Coordinated Observations’ section of the proposal. If you are not requesting any new NRAO observations, then leave it blank.

TESS Targets

If you are asking for additional TESS short-cadence targets in addition to HST observing time, then list the requested number of additional TESS targets. You should also provide detailed information on the TESS targets in the ‘Coordinated Observations’ section of the proposal. If you are not requesting any new TESS targets, then leave it blank.

Proposal PDF Attachment

List the location on your computer of the PDF file to be attached to your Phase I submission. This file should contain the items described in HST Preparation of the PDF Attachment.

Team Expertise and Background

Selecting the arrow to the left of the items in the Tree Editor of APT will show subordinate sections that can be selected to enter additional information. For Proposal Information, this includes Principal Investigator and Co-Investigator information (see below), and the Team Expertise and Background selection. The Team Expertise and Background selection provides a free-format text box to enter the relevant information. See HST Anonymous Proposal Reviews for details on what information to provide here. Please note: the box supports ascii text. Special text markup and LaTeX characters will not show correctly.

Investigator Information

Principal Investigator

Enter the first and/or last name of the PI. Please use standard ASCII. Entering the first few letters (at least two) and pressing enter or tab will bring up a window containing a list of matches from our proposer database. Clicking on your entry will supply APT with the address information. For U.S. PIs, the institutional affiliation is defined as the institution that will receive funding if the proposal is approved.

If you are not in the database, click on "New Entry". If you are in the database, but the address information is incorrect, click on "Update This Address." Both clicks will take you to the MyST tool so you can be added to, or update information in, the database. Once you have entered your MyST, you must redo the database search and supply APT with the updated information.

APT will not compromise the anonymous status of the proposal. It will keep investigator and institutional information, as well as the separate Team Expertise and Background section, from the TAC and Panels until they are requested by an authorized person to be utilized in a last sensibility check.

If a proposal has a non-U.S. PI and one or more U.S. Co-Is, then you must select one of the U.S. Co-Is to be the US Admin Co-I, who will oversee the grant funding for U.S. investigators.

Phase I Contact

For Large and Treasury Programs, we will contact the proposer within 1-2 weeks of the submission deadline if we need to verify our understanding of the appropriate scheduling constraints. If a Co-Investigator is to serve as the contact for this verification, then the Phase I Contact box should be set accordingly. Any person may be designated as the Phase I Contact.

Co-Principal Investigators and Co-Investigators

Co-Principal Investigators (Co-PIs) and Co-investigators (Co-Is) can be added in APT as necessary in Phase I; once a program is approved (Phase II), Co-PIs and Co-Is can only be added with prior approval. By default, APT will provide one blank Co-I template. Please add other Co-PIs and Co-Is or delete as necessary. There is a limit of 999 Co-PIs and Co-Is on any proposal. For each Co-I, enter the name and select the correct person from the list of database matches. For each Co-PI, fill out a Co-I form and additionally check the box labeled “Co-Principal Investigator". As for PIs, new investigators or address updates should be submitted via MyST. For U.S. Co-PIs and Co-Is the institutional affiliation is defined as the institution that will receive funding if the proposal is approved.

Targets

Your proposal can include observations of fixed targets (i.e., all targets outside the solar system whose positions can be defined by specific celestial coordinates), generic targets (i.e., targets defined by certain general properties, rather than by specific coordinates), and solar-system targets (i.e., moving targets). Targets that have not yet been discovered or identified may generally be included only under special circumstances, and should be given generic target names.

GO Proposals must include a list of all targets. For proposals with a large number of fixed targets, there is a capability to ingest a comma-separated text file with the appropriate target information. See the HST Phase I Proposal Roadmap for details.

A complete list of targets is not required for SNAP proposals during Phase I. See Snapshot (SNAP) Proposals for more guidelines on crafting SNAP proposals.

Target Number

Each target in your proposal will be assigned a unique number by APT. A different target must be defined when different coordinates or a different target description are required. Separate targets should be defined and listed if observations are planned at several points within an extended object. For example, acquiring spectra at three different locations within the Crab nebula requires each point to have its own target number, name and coordinates, such as CRAB1, CRAB2 and CRAB3. However, if you are proposing a large field mosaic with the same exposures at each point, you may define one target for the object. You should specify in the Description of Observations the exact number of fields you plan to observe.

Target Name

The target naming conventions for HST are defined in detail in the HST Phase II Proposal Instructions (there are special conventions for Moving Targets). Please adhere to these naming conventions throughout your proposal. For generic targets use a short text description either of the target location (e.g., RANDOM-FIELD) or of the target itself (e.g., NEXT-SUPERNOVA).

Provisional Coordinates

Supply the coordinates for fixed targets only. In Phase I, target positions with accuracies of ~1 arc minute are sufficient for the TAC and panel review (except in crowded fields where the identity of the target may be in question). However, in Phase II significantly more accurate coordinates will be required, and it is the responsibility of the proposers to provide these. See the STScI Phase II documentation for details.

V-Magnitude

A magnitude or flux should be specified for every target. Supply the V-magnitude for the entire target (galaxy, planet, etc.), if known. In the case of observations with ACS/SBC, STIS/MAMA, or COS, specify the V-magnitude of the brightest object in the field of view (this may not be the primary target). For variable targets, give the brightest V-magnitude expected during the observations. The configurations mentioned above have detectors with bright-object safety limits, and observations that violate those limits are infeasible. See the Bright-Object Constraints section of the HST Primer, or the respective Instrument Handbook for details. With the exception of the safety checks, this information is used only for scientific review, not for exposure-time calculations. It is not required to specify the V-magnitude or flux for generic targets.

Other Fluxes

For each target you should specify either a V-magnitude or another magnitude or flux. For all MAMA (STIS and ACS) and COS instrument observations, a V-magnitude is required.

Supply the apparent total magnitude or flux in the relevant passband for the entire target (galaxy, planet, etc.), if known. For variable targets, give the brightest magnitude expected during the observations. This information is used only for scientific review, not for exposure-time calculations. The format is free text.

Observations

This item appears in the APT form only for GO and SNAP Proposals.

The "Observations Summary" (OS) in the PDF that the TAC reviews is generated from the information supplied in the Targets and Observations folders in APT. The OS lists the main characteristics of the observations that you propose to obtain. In general you must include in the OS all the configurations, modes, and spectral elements that you propose to use. Configurations or targets that are not specified in the Phase I proposal, but are included in Phase II, may delay the program implementation, and may be disallowed. Note the following:

• For Future-Cycle Proposals, the OS should include information for all the proposed observations, not just those requested in Cycle 32. See the Future-Cycle Proposals section of the HST Proposal Categories page for more important instructions on how to enter future-cycle observations into APT.
• Parallel observations must be included in the OS, and marked as such using the relevant Flags (see the table below).
• Target acquisition observations need not be included in the OS, unless they are themselves used for scientific analysis.
• Normal calibration observations that are often or routinely taken (e.g, fringe flats) need not be included in the OS. However, the OS should include any special calibration exposures of internal sources or external targets. Special internal calibrations should be listed separately from external calibration exposures. When these special calibrations require additional orbits, that should be specified and the orbits included in the total allocation. The need for these calibrations should be justified in the "Description of the Observations" section of the proposal.

All exposures of a given target made with a particular instrument may be summarized in a single observation; observations of the same target with a second instrument (e.g. coordinated parallels) must be specified in a separate observation.

Observations are numbered sequentially in the APT Phase I proposal form. Each observation should include the items that are listed and discussed below in separate sub-sections.

Target

Select the target from the pull-down menu. The menu will contain all the targets you have entered in the “Targets” folder.

Instrument

Select an instrument from the pull-down menu. The menu will contain all the available instruments. Only one instrument can be selected in each observation.

Instrument Setup(s)

Under “Instrument Setups” click on “Add.” This will bring up a pop-up menu which will allow you to select the parameters for an observation with the selected instrument (e.g., config, science mode, spectral elements). Note that you can create multiple Instrument Setup(s) for this instrument in one Observation.

Config

Enter the Scientific Instrument configuration. A pull-down menu shows the available and allowed options for the instrument you have selected.

Science Mode

Enter the science mode. A pull-down menu shows the available and allowed options (which depend on the choice of Configuration).

Coronagraphy

If you are proposing coronagraphic observations with STIS, then set this keyword to ‘yes.’ Coronagraphic observations with the ACS/SBC are not permitted (see Section 3.3.2 of the ACS Instrument Handbook).

Polarimetry

If you are proposing polarimetric observations with ACS, then set this keyword to ‘yes.’

Spectral Element

Enter the desired spectral elements (i.e., filters and gratings) using the ‘Spectral Element’ pull-down menus which show the available and allowed options (which depend on the choice of Configuration and Science Mode). Each Instrument Setup denotes a set of exposures with the same spectral elements. For example, if you are proposing for four exposures with the F555W filter and two with the F550M filter, one instrument setup would give the F555W filter as the Spectral Element, and a separate instrument setup would give the F550M filter as the Spectral Element.

Wavelength

If a COS or STIS grating is used, then first select the grating and subsequently give the central wavelengths in Angstroms for the exposures.

Orbits

Enter the number of orbits requested (i.e., the sum of the orbits required for all the instrument setups in the observation). Consult Orbit Calculation Overview for instructions on how to calculate the appropriate number of orbits for your observations.

Number of Iterations

If you require multiple sets of observations, enter the number of iterations (for example, if you will reobserve at a different time or if you have a large mosaic). This will automatically update the total number of orbits requested for the observation.

Special Requirements

Use these flags/checkboxes to set special requirements, if applicable. Note that these requirements must be set in the Phase I version of the proposal.The meanings of the checkboxes are indicated in the table below. For Snapshot observations, select only the 'duplication' or 'coordinated parallel' checkboxes.

Table: Summary Flags for the Observations

Flag/Checkbox	Corresponding Special Requirement
Coordinated Parallel	All of the exposures specified in this observation are to be done in Coordinated Parallel mode.
Pure Parallel	All of the exposures specified in this observation are to be done in Pure Parallel mode.
CVZ	Continuous Viewing Zone observations.
Duplication	Observations which duplicate or might be perceived to duplicate previous or upcoming exposures.
Target of Opportunity - Ultra-Disruptive	Target-of-Opportunity observations with turn-around time shorter than 2 days.
Target of Opportunity - Disruptive	Target-of-Opportunity observations with turn-around time shorter than 3 weeks.
Target of Opportunity - Non-disruptive	Target-of-Opportunity observations with turn-around time longer than 3 weeks.
Target of Opportunity - Flex Day	Special disruptive Target-of-Opportunity observations designed for the monthly Flexible Thursday opportunity.
Target of Opportunity - Carry-Over	Target-of-Opportunity observations that will carry over into the next cycle if not triggered, intended for rare events unlikely to trigger in one cycle. Note that Carry-Over Target-of-Opportunity requests cannot also be Flex Day requests.
Relative ORIENT Link	This observation will have a given spacecraft orientation relative to other observations
On Hold	This observation may be on hold until another observation executes.
Observations Grouped in Time	This observation will be grouped in time with other observations.
Sequential Observations in Time	Requiring that this observation will be taken in order within a given amount of time.
Non-Interruptible Sequential Observations	This observation will be taken back to back in a given amount of time and cannot be interrupted by an occultation of the telescope.

Scheduling Requirements

With the exception of observations of solar system or generic targets, proposers must provide any additional scheduling information or constraints in the Phase I proposal. This information will help STScI understand and assess the scheduling implications of your program. Be sure to read the Description of the Observations, Orbital Visibility and Scheduling, and Special Requirements sections, as those are the primary places for describing your observing strategy, including any justification for special requirements. Some special requirements are used when running the Visit Planner and others show up as flags only.

The following requirements, described in detail below, must be specified in Phase I to be implemented in Phase II:

SHADOW, LOW SKY, SAME ORIENT, BETWEEN, AFTER OBSERVATION BY, AND PERIOD.

For Large and Treasury Programs, STScI will contact the proposer within 1-2 weeks of the Phase II submission deadline if STScI needs to verify its understanding of the appropriate scheduling constraints. As noted previously, if a Co-I is to serve as the contact for this verification process, the Contact Co-I keyword box should be set.

NO SCHEDULING CONSTRAINTS

Setting this requirement means there are no scheduling constraints on the Observation.

SHADOW

Set this requirement when all exposures defined in the Observation are affected adversely by geocoronal Lyman-alpha background emission, and therefore need to be obtained when HST is in Earth shadow. This requirement complicates scheduling and reduces HST observing efficiency, and must therefore have adequate scientific justification in the Phase I proposal. SHADOW is incompatible with CVZ. This requirement should not be used if low continuum background is required: in that case use LOW SKY instead.

LOW SKY

Set this requirement when all exposures defined in the Observation are affected adversely by scattered light (e.g zodiacal light and earthshine), and therefore need to be obtained with minimal sky background. The continuum background for HST observations is a function of when and how a given target is observed. Observations can be scheduled when the sky background is within 30% of its yearly minimum for the given target, which is done by restricting the observations to times that minimize both zodiacal light and earthshine scattered by the Optical Telescope Assembly (OTA). To minimize the zodiacal light, the scheduling algorithm places seasonal restrictions on the observations; to reduce the earthshine, the amount of time data is taken within an orbit is reduced by approximately 15%. The former complicates scheduling, while the latter reduces the observing efficiency of HST. Therefore, using the LOW SKY restriction must have adequate scientific justification included in the Phase I proposal. With this restriction, the zodiacal background light for low-ecliptic latitude targets can be reduced by as much as a factor of 4. Avoiding the earthshine at the standard earth-limb avoidance angle (see the Pointing Constraints section of the HST Primer) can make a similar difference. LOW SKY is incompatible with CVZ.

SAME ORIENT

Setting this requirement means that all exposures defined in the Observation MUST be observed at the exact same ORIENT. This requirement is only meaningful if the observations are to occur in multiple visits (e.g. Number of Iterations is greater than 1, or if the Total Orbits is greater than 5).

ORIENT RANGE

Enter the ORIENT range that all the exposures defined in the Observation must be observed within. If multiple ORIENT ranges are acceptable, then enter all values. This requirement must be specified in Phase I to be implemented in Phase II.

BETWEEN

Enter the range of dates that all exposures defined in the Observation must be observed within. If multiple BETWEENs are acceptable, then enter all values.

AFTER OBSERVATION BY

Enter any timing requirements between Observations. Timing requirements between observations WITHIN an Observation do not need to be specified. This is intended to capture repeated visits with spacings of multiple days or greater, not timing requirements of less than 1-2 days.

PERIOD <time> and ZEROPHASE <date> and PHASE <number1> TO <number2>

Supplies the period and zero-phase for observations to be made at a specific phase of periodically variable target. <time> is the period in days, hours, minutes, or seconds, and <date> is the date of the zero-phase with respect to the Sun (i.e., HJD, not calendar date), <number1> is the start of the phase ranges, and <number2> should be between 0.0 and 1.0.

Verifying Schedule Constraints

If you have specified any scheduling constraints, you are encouraged to use the APT Visit planner to verify that your observations are indeed schedulable. While it cannot check that the total number of orbits you have requested are available, the Visit Planner will at least confirm whether or not there are days during the cycle when your target(s) can be observed with your imposed scheduling constraints. In general, the more days that are available, the more feasible your program. This is particularly important for Large Programs. Detailed instructions for performing this verification can be found in the HST Training Materials, in the "APT Analysis of Scheduling Constraints" Training.

If you find that any observation is not schedulable, and it is not scientifically possible to adjust any special scheduling constraints (e.g. a BETWEEN), then you can increase the scheduling opportunities by selecting the Increase Scheduling Flexibility flag in APT. Note that using this option may require you to ask for a larger orbit allocation, since setting the flag will reduce the orbital visibility for the observation; this reduced orbital visibility is automatically used for Large Programs. More information can be found in the HST Training Materials, in the "APT Analysis of Scheduling Constraints" Training.

Next: HST Preparation of the PDF Attachment

HST Filling Out the APT Phase I Proposal Form