STScI Newsletter
2023 / Volume 40 / Issue 02

About this Article

Science Mission Office and Hubble Mission Office (hubblereview[at]

A horizontal, undulating, linear structure resembling overlapping strings of yarn extends edge-to-edge across the frame, but takes up only a quarter of the width at its widest point. Mostly orange with some blue, these are filaments of glowing gases, which resemble lines in a wrinkled bedsheet.
Astronomers recently used the Hubble Space Telescope to zoom into a very small slice of the leading edge of an expanding supernova bubble, where the supernova blast wave plows into surrounding material in space. The bubble, called the Cygnus Loop, is about 120 light-years in diameter and has a width of six full Moons as seen on the sky.
Credit: NASA, ESA, Ravi Sankrit (STScI)

Multi-Cycle Treasury Programs were introduced into the HST lexicon over a decade ago, with the completion of Servicing Mission 4, the installation of Wide-Field Camera 3 (WFC3) and the Cosmic Origins Spectrograph (COS), and the successful repairs to the Space Telescope Imaging Spectrograph (STIS) and the Advanced Camera for Surveys (ACS). The primary aim was to provide an opportunity for the community to address high impact scientific questions that require observations on a scale that cannot be accommodated within the standard time allocation process. To that end, some 2200 orbits, distributed over Cycles 18 to 20, were assigned to three programs selected by peer review: the Panchromatic Hubble Andromeda Treasury program (PHAT), imaging a substantial fraction of the Andromeda disk; the Cluster Lensing And Supernova Survey (CLASH), mapping lensing in galaxy clusters; and the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey program (CANDELS), probing galaxy formation and evolution through deep imaging in five high galactic latitude fields. All three programs succeeded in establishing a major legacy for not just Hubble, but general astrophysics to build on in the succeeding years.

Fourteen years after SM4, Hubble is still going strong, with all four instruments from SM4 maintaining high performance. Following discussions with the Space Telescope User Committee, NASA and the Space Telescope Science Institute (STScI) believe that a call for a new set of MCTs is timely. Unlike in 2009, we do not plan to issue a separate call for MCTs, adding yet another deadline for the community. Rather, we will include MCTs as an option in the Cycle 32 Call for Proposals. Following precedent, the resources will be divided between General Observer and Director’s Discretionary time, with up to 250 orbits of GO and 250 orbits of DD time over Cycles 32-34 for a total of 1500 orbits.

As an initial guide to MCT program characteristics:

  • MCT programs must require at least ~350 orbits and may request more than 1,000 orbits.
  • MCT Programs must clearly specify why the science goals cannot be achieved through the standard TAC allocations.
  • MCT Programs will be reviewed and ranked by the Cycle 32 Executive Committee along with Large and Treasury programs, but with a separate pool of orbits.
  • MCT Programs may enable a broad variety of compelling scientific investigations; they may also focus on one specific issue or parameter.
  • MCT programs should expect to be scheduled over multiple cycles; however, they should only request time in future cycles if that scheduling is required to achieve the science goals.
  • MCT programs, as with all Treasury programs, should provide enhanced data products or software tools for the scientific community.
  • MCT programs will have no exclusive access period.

Full details on MCT program requirements will be included in the Cycle 32 Call. Depending on the response to the current call and the future health of HST, an MCT Call may be part of future cycles but not on a regular basis.


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