The Hubble Multi-Cycle Treasury Science Program

I. Neill Reid,, & Suzanne L. Hawley,


Servicing Mission 4 (SM4) had the prime goal of maximizing the scientific productivity of the Hubble Space Telescope for the subsequent five years. Following SM4’s successful completion, Hubble has its most powerful suite of instrumentation. The Call for Multi-Cycle Treasury (MCT) Programs issued in 2009 was designed to provide the community with an opportunity to exploit those enhanced capabilities, and to help achieve the overarching goal of SM4. The MCT Time Allocation Committee (TAC) met early this year, and recommended execution of three observing programs that incorporated science from four MCT proposals. The observing time for those programs, which includes contributions from both the general observer (GO) pool and Director’s Discretionary (DD) time, will be distributed over at least three cycles, starting in Cycle 18.


Hubble was launched in April 1990. During the succeeding 20 years, it has revolutionized our understanding in diverse fields, including: galaxy formation and evolution; the properties of active nuclei and the development of black holes; the structure and evolution of the intergalactic and interstellar media; stellar populations in different environments; Galactic and extragalactic star formation; the characteristics of circumstellar disks and exoplanet atmospheres; and the detailed properties of denizens of our own Solar System. This scientific diversity and impact reflect, at least in part, the way that Hubble time is allocated—with observing programs that range in scope from small, narrowly focused investigations of individual targets, to extensive survey programs that enable progress on multiple research topics.

From the outset of the Hubble program, there was clear recognition that different scientific questions demand a range of resources, and that Hubble would only reach its full potential if that concept was realized in the time-allocation process. Thus, in 1986 the Space Telescope Advisory Council recommended that time be divided equally among small, medium and large programs, where “large” programs were defined as those requiring more than 100 orbits. This directive was repeated in the first (and succeeding) Call for Proposals, but to little avail. As the Hubble Second Decade Committee (2DC) commented, in Cycles 1 to 8 only 18 of 2,173 GO programs received allocations of more than 50 orbits, and only 5 more than 100 orbits.

Formally, the Institute Director allocates time on Hubble, but generally does so based on recommendations made by the TAC. In these early cycles, all GO (and SNAP) proposals were graded and ranked by specialist panels, with the TAC merging proposals from the various disciplines. Selection committees have an inherent desire to try to please as many applicants as possible. Faced with a limited budget, there is a tendency to favor smaller proposals, as each panel is reluctant to allocate a significant fraction of its resources to a single proposal. Indeed, one can show statistically that the breakpoint comes where a proposal requires more than 20% of the orbits available to a panel.