You have been awarded time on HST. Now comes "Phase II," the time during which you transform your accepted Phase I proposal into a computer-readable program containing the detailed information needed for implementation and scheduling of your science program.

What you write in Phase II is essentially a high-level computer program. The elements and syntax of the language you use are described in the Phase II Proposal Instructions. We do not produce paper copies of this document, but it is available on-line in PDF format. The Phase II Proposal Instructions include a linked table of contents and an index.

You will be provided with Phase II support and information from STScI, much of which has been recently updated. Whether or not you are an experienced HST user, you should carefully review this package and the HST Phase II Proposal instructions before beginning to construct your Phase II program.

Getting Help

Each approved program has been assigned a Program Coordinator (PC) as identified in your acceptance letter from the STScI Director. Your PC will contact you to introduce themselves and help you get started with the Phase II process. He or she will provide you with your Phase II submission deadline and discuss our policies for delayed submissions and program changes. Please be sure to read this communication carefully and discuss any questions you may have with your PC.

As in previous Cycles, supplementary support to Canadian GOs is available directly from the Canadian Astronomy Data Center at DAO. While Canadian PIs receive full PC support at STScI, they are invited to take advantage of their local support group.

Preparing and Submitting Your Phase II Proposal

  1. Note the TAC Allocation and Comments:

    Read your notification letter, paying special attention to the approved allocation of HST orbits, any instrument and/or target constraints, and other mandatory or recommended changes.

  2. Read the Documentation:

    All of our user documents are available on-line from the HST Phase II Proposal page. If you need additional documentation, contact your Program Coordinator (PC).

  3. Install the APT Software:

    The Phase II release of APT is now available. APT is a suite of software tools for developing HST proposals. The release is a new version for Phase II proposals, and should be installed on your computer before beginning Phase II proposal development. For installation help, visit

  4. Prepare your Phase II File:

    Using the new Phase II Proposal Instructions and your copy of your submitted Phase I proposal, complete all information for the Phase II proposal and run the APT software (including both the Orbit Planner and Visit Planner ). APT uses xml files as input and output.

    One of the output products from this process will be an orbit-by-orbit description of the program you have developed. Your Program Coordinator is your primary contact for APT questions, and we encourage user feedback and suggestions on this software. Please review the general form and cover page text sections of your Phase II proposal for accuracy. These sections should be updated to reflect the current program contents. Be sure to insert the Phase II proposal number that was provided in your original acceptance letter.

    HST is a very complex observatory operating in low earth orbit. It is a delicate spacecraft that must be operated within a great many scheduling, pointing, orientation, solar power management, thermal, and other constraints. APT has been designed to model this system to a level of detail sufficient to allow the observer to create efficient, effective observing proposals. You should expect to take a week or more to prepare your program. Do not hesitate to contact your PC (or Contact Scientist if applicable) if you have any questions. We urge you to begin work on your program as early as you can. The last week before the deadline can be a very frantic time for all concerned!

    Please refer to The HST Phase 2 Target Coordinate Instructions for detailed instructions on measuring target coordinates for Phase II. This is especially important when sub-arcsecond coordinate inaccuracies can degrade an observation. The coordinates used to point HST need to be in the International Celestial Reference System (ICRS) frame. Ultimate responsibility for correct coordinates lies with the observer.

    Target coordinate confirmation charts will no longer be generated by your PC. These charts can now be generated within APT, and you are responsible for doing this step. (Confirmation charts are not possible for generic parallel targets.) You must generate the confirmation charts and verify the target pointing before submitting your Phase II proposal.

    All programs must accurately mirror the accepted portions of the Phase I proposal. New targets, instruments or wavelength ranges cannot be introduced without review and approval, nor can you submit a Phase II program that requires more time than allocated. If you encounter a scientific need to make such changes as a result of your Phase II work, you must contact your Program Coordinator and provide a justification for the change. All major changes of this nature also require Director's Office approval. Also, if you have changed your mail or e-mail addresses, you can update these through APT.

  5. Submit your Phase II Program:

    When you believe your APT Phase II proposal is complete and correct (i.e., the program proves to be syntactically correct, within TAC allocation, error free and schedulable based on the output from APT), submit your proposal using the APT submit tool in the graphical interface. As with previous steps, contact your PC if any problems are encountered. Your PC is prepared to help you create an error free and schedulable program if you encounter difficulties. For APT, the submitted file name does not have to conform to a specific format. That will be done upon receipt at STScI.

    Once a Phase II program has been submitted, you will receive an automatic reply that it has been received at STScI. The PC will then verify that it is error-free and within its allocation, the program will be considered "accepted," and implementation work will start. Proposals with errors that can be fixed by the PIs will be rejected and sent back for correction. Any programs that are more than the TAC allocation or partially submitted will also be rejected and sent back.

    It is essential to submit a clean, correct and complete observing programs before the submission deadline.

After You Submit Your Phase II Program

  1. Program Implementation:

    After submission, the PC will continue with the preparation and implementation of your program. Once the current cycle programs are initially processed, a Long Range Plan will be developed to provide planning windows for each program visit. Your PC will review these planning windows and the structure and content of your program visits with you as necessary during flight preparation.

  2. Final PI Walkthrough:

    When nearing the final stages of flight preparation, your PC will review your program one final time. You will be sent information regarding the current version of your program, including identification of significant changes that have been made and a review of your plan windows. For more complex programs, a teleconference may be requested to walkthrough the details of this package with you. We strongly encourage all PIs to actively participate in this phase. Failure to respond to the request to review the final program within one week will be taken as approval to proceed with flight preparation.

  3. Program Scheduling and Monitoring:

    Your PC (and Contact Scientist if assigned one) will continue to monitor your program as it is scheduled and executed, and will inform you of any difficulties. Do not hesitate to contact them if you have questions or concerns. You can monitor the progress of your program and obtain information regarding assigned Plan Windows via the HST Program Information web page.

  4. Making Changes to Your Phase II Program:

    Once your Phase II program has been submitted and accepted, changes may only be made with justification. First, contact your Program Coordinator and provide a description of the requested change and the reasons for it. The PC is allowed to approve minor alterations (such as exposure time adjustments or target coordinate updates). The PC may seek approval from the Contact Scientist or an Instrument Scientist if the changes might alter the scientific goals of the program (such as new targets, or different filters or observing modes). A change that is in conflict with the original TAC decision (such as the number of orbits used, or the primary instrument used) should be submitted using the Change Request Form (located at the bottom of the program information page for a given program) and will be formally reviewed by the Telescope Time Review Board.

    Justifiable changes can be accommodated up until approximately 4 weeks before the assigned Plan Window opens, resources permitting. Please notify your PC (and CS if applicable) immediately if you identify the need to change your program.

Policies for Phase II

To maintain a high observing efficiency and to have a seamless transition between cycles, we need to have clean (i.e., error free), complete Phase II programs. Also, to develop a reliable Long Range Plan, all the Phase II programs have to be in the database, which makes it essential that programs be submitted on time. The Phase II deadline for Cycle 32 is July 17, 2024.

Please note the following STScI policies concerning Phase II submissions:

  1. PIs are required to submit their Phase II programs ON TIME. Programs that are not submitted by the deadline are subject to forfeiture of the awarded orbits. 
  2. Your submission is not complete until it has been accepted by your PC. To be accepted, Phase II programs must be submitted with all expected targets listed and the total number of orbits required must be at or below the program's allocation. Partial or incomplete programs are not acceptable. An accepted program must be error free according to APT. In some cases we can accept a program with errors, but only with the approval of the PC.
  3. Observers must use the Phase II Proposal Instructions and APT that have been prepared for Cycle 30 in writing their Phase II programs. Many details of HST observing change each year as we improve and augment software, and it is vital that the current Instructions be used.
  4. Target of Opportunity (ToO) observations may only be activated if they occur during the above time interval for Cycle 30 unless they have been approved to span 2 cycles. Otherwise, ToO visits expire at the end of the Cycle and will be removed from the HST program at that time. GOs must repropose for ongoing ToO observations, if they were not previously approved for 2 cycles.
  5. The manner in which SNAPshot programs are executed is described in a User Information Report

Additional Recommendations

  1. Observers should be aware that in most cases the duration of an individual visit in your Cycle 30 proposal should be three orbits or less (see Visit Size Recommendations for details). Please check the updates for the instruments you are using.
  2. If you are having difficulties with your program or do not know how to correct your APT Phase II file, please contact your PC and discuss the issue.
  3. Note that changes to programs once they are submitted should be strongly justified (e.g., you need to correct an erroneous source position).
  4. We will check for duplications with all planned or executed programs. If duplications are found, and have not been justified in the Phase I proposal, the PI will have to prove the need for the observations before they are accepted for implementation.
  5. All accepted programs have been reviewed for technical feasibility and schedulability. The results of the review have been stored in the database and the programs will be tracked. Hard-to-schedule visits will be in the implementation pipeline for only one year. If these programs have not been scheduled after a year, they may be removed from the visit pool. This will allow us to limit the work spent on trying to implement unschedulable programs at the expense of other programs. It is therefore VERY IMPORTANT that PIs discuss issues with their PC/CS and solve problems as soon as possible.
  6. PI notification letters included information regarding budget preparation.

Please feel free to contact your PC if there is any help or assistance you need.

Look for other information at the APT Phase II and the Phase II Proposal pages.

Meeting our goal of excellence in user service depends on receiving feedback from you. Our team at STScI is excited about the prospects offered in Cycle 30 to advance toward that goal and we're ready to help you complete the next step as an HST observer.


HST Help Desk 

Please contact the HST Help Desk with any questions.