STScI . ... Phase I Proposing . ... Astronomer's Proposal Tool . ... STScI solicits proposals for HST Observing, Archival Theoretical Research. ... HST Cycle 24 Phase II Proposal Deadline . The Call for Proposals (CP) invites the astronomical community to propose for observing time on HST in a given cycle (nominally one year in duration). It summarizes the policies and procedures for proposing in that cycle of HST observing, including requests for funding research on archival HST data. ...