Phase I: Writing and Submitting a Proposal for HST Observing Time

A Phase I Proposal Provides:

  • A summary of the observing program.
  • The scientific justifications for the program.
  • A list of targets with their celestial coordinates.
  • The instrument(s) to be used with desired modes, filters, and dispersers.
  • An estimate of the number of spacecraft orbits needed to accomplish the observing program (a means to calculate this number is provided in the Phase I instructions).

Proposers should consult all relevant technical documentation about the capabilities and sensitivities of the instrument(s) to be used in their programs and should discuss the requirements of their observing programs with appropriate STScI experts. Contacts are provided via the STScI HelpDesk. To avoid duplication conflicts, proposers also should consult up-to-date exposure catalogs, available online at the STScI website.

Call for Proposals

DD Time Submission

Up to 10% of the available HST observing time may be reserved for Director's Discretionary (DD) allocation. Learn More

Mid-Cycle Submission

Up to 200 orbits per cycle will be available for Mid-Cycle GO programs. Mid-Cycle programs were initiated in Cycle 23 to provide the community with an opportunity to propose for in-cycle observations of recently-discovered, non-variable objects. As such, they complement Director’s Discretionary programs, which target unexpected transient phenomena and time-critical observations. Learn More

Completion of Phase I: The TAC Review of Phase I Submissions

A Telescope Allocation Committee (TAC), organized by the Space Telescope Science Institute (STScI), reviews and evaluates the submitted Phase I proposals. The TAC recommends a list of programs to the STScI Director for preliminary approval and implementation. Upon final approval by the Director, a successful proposal enters into the Phase II stage of proposal preparation.

Peer Review

Additional Resources

Please Contact the HST Help Desk with any Questions