Hubble Cycle 18 Proposal Selection


The 1,051 proposals submitted in Cycle 18 included 872 general observer (GO), 51 snapshot (SNAP), 75 archival, 10 legacy archival (AR), and 43 theory programs. Six hundred orbits were made available for proposals reviewed by the TAC, and 2,000 for the proposals reviewed by the 14 panels. Three hundred out of 2,000 orbits were reserved for medium-sized proposals (see table with summary of Cycle 18 results). The Cycle 18 panels and TAC recommended approving 196 programs, including 146 GO, 3 SNAP, 28 AR and legacy archival, and 13 theory programs. The recommended theory programs include one GO and five AR calibration programs. Two joint ChandraHubble, two joint National Optical Astronomy Observatories–Hubble, and one joint Spitzer–Hubble programs were awarded time by the panels.

Eight large and treasury programs were recommended by the TAC.

As a reflection of Hubble’s new capabilities, Cycle 18 has seen one of the highest oversubscriptions in the history of the telescope. About nine times more orbits were requested than were available, and six times more proposals were submitted than approved. Hubble is a joint NASA–European Space Agency (ESA) mission. ESA scientists were principal investigators (PIs) on 33 of the 196 accepted proposals, accounting for 14.8% of the orbits allocated and 16.8% of the proposals.

For Cycle 18, the TAC and the panels recommended 59% of the GO prime orbits—excluding orbits of parallel observations—for spectroscopy and 41% for imaging. WFC3 is the most widely used instrument in prime mode, with a usage of 42%, followed by STIS 26%, COS 23%, ACS 9%, and FGS <1%. If parallel orbits are included in the count, the statistics are WFC3 42%, ACS 24%, STIS 18%, COS 16%, and FGS <0.1%.