The FutureofSpaceImaging The Future of Space Imaging Report of a Community-Based Study of an Advanced Camera for the Hubble Space Telescope hen Lyman Spitzer first proposed a great, W earth-orbiting telescope in , the nuclear energy source of stars had been known for just six years. Knowledge of galaxies beyond our own and the understanding that our universe is expanding were only about twenty years of age in the human consciousness. The planet Pluto was seventeen. Quasars, black holes, gravitational lenses, and detection of the Big Bang were still in the future—together with much of what constitutes our current understanding of the solar system and the cos- mos beyond it. In , forty-seven years after it was conceived in a for- gotten milieu of thought, the Hubble Space Telescope is a reality. Today, the science of the Hubble attests to the forward momentum of astronomical exploration from ancient times. The qualities of motion and drive for knowledge it exemplifies are not fixed in an epoch or a gen- eration: most of the astronomers using Hubble today were not born when the idea of it was first advanced, and many were in the early stages of their education when the glass for its mirror was cast. The commitments we make today to the fu- ture of the Hubble observatory will equip a new generation of young men and women to explore the astronomical frontier at the start of the st century. 1 2 3 4 5 6 7 8 9 FRONT & BACK COVER 1.Globular clusters containing young stars at the core of elliptical galaxy NGC 1275. Credit: J. Holtzman, NASA. 2.Central core and accompanying jet of giant elliptical galaxy M87. Credit: Tod R. Lauer (NOAO), Sandra Faber (UCSC), NASA. 3.HST Deployment. Credit: NASA, Smithsonian Institution, IMAX. 4.Portion of Orion Nebula. Credit: C.R. O’Dell (Rice University), NASA. 5.Mars, image taken on December 30, 1990, at a distance of 85 million km. Credit: Dr. Philip James (University of Toledo), NASA. 6.NGC 2440 nebula with central hot star. Credit: S. Heap, NASA/Goddard Space Flight Center. 7.Cygnus Loop Supernova Remnant. Credit: J.J. Hester (Arizona State University), NASA. 8.Core of peculiar galaxy Arp 220. Credit: E. Shaya, D. Dowling (University of Maryland), WFPC IDT, NASA. 9.Core of galaxy NGC 4261 with giant disk of cold gas and dust fueling a suspected black hole. Credit: Walter Jaffe (Leiden Observatory), Holland Ford (STScI and JHU), NASA. INSIDE FRONT COVER 1.Photograph of pre-historic petroglyphs 1 by William K. Hartmann. 2.Gaseous ring around SN 1987A. Credit: NASA, ESA. 3.High resolution UV image of Io. Credit: Francesco Paresce (STScI), Paola Sartoretti (University of Padova), NASA, ESA. 23 4.Einstein Cross—gravitational lens G2237+0305. 45 Credit: FOC IDT, NASA, ESA. 5.“X” structure in core of M51, which is due to absorption by dust and gas, marks the location of a possible black hole. Credit: H. Ford (JHU/STScI), the Faint Object Spectrograph IDT, and NASA. Support for this research was provided by NASA under Contract NAS5-26555 and Grant NAGW-3135 through the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy. Design and production assistance was provided by Foxglove Communications. Executive Summary i The Future of Space Imaging Report of a Community-Based Study of an Advanced Camera for the Hubble Space Telescope Edited by Robert A. Brown Space Telescope Science Institute 3700 San Martin Drive Baltimore, Maryland 21218 October 1993 ii FOSI: Frontiers of Space Imaging Executive Summary iii Authorship This report is the product of the Future of Space Imaging study1 and of the subsequent preparation of the proposal of the Advanced Camera to the ESA M3 competition2, in which the following people participated or to which they contributed. It was our privilege to conduct this study and author this report on behalf of the international community of as- tronomers. We express our particular gratitude to our many colleagues who responded to the community survey. James Beletic1 Georgia Institute of Technology Pierre Bely1 Space Telescope Science Institute, ESA J. Chris Blades1 Space Telescope Science Institute Robert Brown1,2 Space Telescope Science Institute Christopher Burrows1 Space Telescope Science Institute, ESA Mark Clampin1,2 Space Telescope Science Institute France Cordova2 Pennsylvania State University Edward Cheng1 Goddard Space Flight Center James Crocker1,2 Space Telescope Science Institute Greg Davidson National Aeronautics and Space Administration Jean Michel Deharveng2 Laboratoire d’Astronomie Spatiale, Marseille Robert Fosbury1,2 ST-European Coordinating Facility, ESA John Hoessel1 University of Wisconsin John Huchra1,2 Center for Astrophysics Garth Illingworth2 Lick Observatory Rolf-Peter Kudritzki2 University of Munich Tod Lauer1 National Optical Astronomy Observatories Michael Lesser1,2 Steward Observatory Edwin Loh1 Michigan State University Duccio Macchetto2 Space Telescope Science Institute, ESA Aden & Marjorie Meinel1 Jet Propulsion Laboratory George Miley2 Leiden Observatory iv FOSI: Frontiers of Space Imaging Warren Moos1 Johns Hopkins University Jeremy Mould1 California Institute of Technology Susan Neff1 Goddard Space Flight Center Francesco Paresce2 Space Telescope Science Institute, Torino, ESA Ronald Polidan1 Goddard Space Flight Center Michel Saïsse2 Laboratoire d’Astronomie Spatiale, Marseille Francois Schweizer1 Carnegie Institution of Washington Donald York1 University of Chicago Executive Summary v Preface In March 1992, the National Aeronautics and Space Administration (NASA) Program Scientist for Hubble Space Telescope (HST) invited the Space Telescope Science Institute (ST ScI) to conduct a commu- nity-based study of an Advanced Camera (AC), which would be in- stalled on a scheduled HST servicing mission in 1999. The study had three phases: a broad community survey of views on the candidate sci- ence program and required performance of the AC, an analysis of tech- nical issues relating to its implementation, and a panel of experts to for- mulate conclusions and prioritize recommendations. An oral report was delivered in December 1992, at which time NASA made a second re- quest to ST ScI, to assist in preparing a proposal for the AC on behalf of the astronomical community to the European Space Agency (ESA) Call for Mission Ideas of 26 November 1992 (“M3 competition.”) A joint US- ESA science team was formed for this purpose, and the proposal was submitted in May 1993. This report—The Future of Space Imaging—is a compilation of the results of both the study and ESA proposal. vi FOSI: Frontiers of Space Imaging Executive Summary vii Introduction The Hubble Space Telescope (HST) is a cooperative program of the European Space Agency (ESA) and the U.S. National Aeronautics and Space Administration (NASA) to operate a long-lived observatory in space for the benefit of the international astronomical community. The three years since the launch of HST in 1990 have been momentous, with the discovery of spherical aberration and the search for a practical solu- tion. HST was designed for servicing in orbit by the Space Shuttle. NASA and ESA are now preparing intensively for the first shuttle repair mission scheduled for December 1993, which should obviate the effects of spherical aberration and restore the functionality expected for HST at launch. Despite spherical aberration, hundreds of astronomers around the world are analyzing HST data and reporting their discoveries. The early results of HST are outstanding, as is illustrated by the recently published proceedings of an international conference, Science with the Hubble Space Telescope.1 The HST program of astronomical research is un- matched by any ground-based telescope, and it refreshes the original vi- sion of what could be achieved by a great telescope unfettered by the Earth’s atmosphere—a vision postponed briefly but not foreclosed by spherical aberration. HST is now at a crossroads with respect to the second half of its de- sign lifetime—the period after 1997, when an advanced spectrograph and a near infrared camera will be installed on the second servicing mis- sion. In 1999, a third servicing mission will be required to restore the spacecraft orbit, which decays due to atmospheric drag. Owing to the long development time for space-qualified instruments, now is the time to make critical decisions with respect to what scientific instrument can or should be installed during the 1999 servicing mission. This instrument must be started now to be ready on time in 1999. Over the past year and a half, in consultation with the international viii FOSI: Frontiers of Space Imaging astronomical community, we have studied the issue of what best can be done with the 1999 instrument opportunity. We have asked if there is still a role for HST at the turn of the century. The answer is clearly: Yes! We are convinced that HST, properly instrumented, will make unique and important astronomical discoveries into the 21st century. This is be- cause no ground-based telescope, no matter how large nor how well equipped with adaptive optics, will match HST in terms of wavelength coverage and image quality over a wide field. We have asked what type of instrument will provide the greatest sci- entific benefit to astronomers. We are convinced that it should be a cam- era because otherwise an adequate optical and ultraviolet imaging capa- bility will not be assured in 1999. Furthermore, it should be advanced because detector and computer technology is now capable of deriving full value from a 2.4 m diffraction-limited telescope in space. What combination of scientific programs should define the priorities for the technical performance of the Advanced Camera (AC)? The breadth and depth of the highly competitive HST imaging science program. We have assessed the imaging tasks astronomers have proposed for or desired from HST, and we believe the most valuable 1999 instrument would be a camera with both near ultraviolet/optical (NUVO) and far ultraviolet (FUV) sensitivity, and with both wide field and high resolu- tion options.