HST & Beyond Study

Robert A. Brown

Space Telescope Science Institute
3700 San Martin Drive
Baltimore, MD 21218 USA

In the midst of celebrating recent Hubble Space Telescope (HST) results, we invite you to pause and reflect on the conditions, forces, and processes that gave rise to this magnificent research facility. For unlike the principles of nature, those factors are not immutable but are changing. When we consider what space observatories should follow HST, we must consider not only scientific needs and technical opportunities but also broadened concepts about the role of science in society, current fiscal constraints, and emerging public policies. Achieving this synoptic perspective has been the primary challenge to recent study activities in the United States pertaining to space astronomy following the prime mission of the HST in 2005.

Also, while in Paris celebrating the internationality of the HST Program, we invited our European colleagues to recognize certain differences in the processes of science funding in the United States as compared with other spacefaring countries. Among these differences are annual space budget debates in the United States Congress, compared with the long-term treaty commitments of the European Space Agency. We might also point out the 200-year debate in the United States about the benefits and desirability of publicly sponsored research, compared with an historical and cultural commitment to science in Europe. It is hard for most astronomers in the United States to recall a time when there was essentially no public funding of astronomical exploration, yet prior to 50 years ago that was the situation in our country.

In 1946, Lyman Spitzer first advocated a telescope in space to explore the cosmos with unprecedented clarity and spectral coverage. The chief contribution of such a radically new and more powerful instrument, he wrote, ``would be, not to supplement our present ideas of the universe we live in, but rather to uncover new phenomena not yet imagined, and perhaps to modify profoundly our basic concepts of space and time.'' One year before, Vannevar Bush, who led the wartime science effort in the United States, published what would become the charter of American science for the Cold War years, a monograph called ``Science, the Endless Frontier.'' It invoked the resonant myth of the American West, and provided a rationale for science funding in peacetime based on serendipitous benefits that historically have accrued from exploration, such as stimulus to education and discoveries leading to new products and processes for the marketplace. Bush's frontier metaphor was embraced by policy makers, with two important consequences: unprecedented investment in ground-based astronomical observatories and the advent of a cadre of skilled astronomers supported by the federal government to use these facilities for research. These commitments notwithstanding, the decision in the 1970s to build HST required an additional basis, for the concept of science for its own sake could not alone support such an investment---most of a million dollar outlay for every professional astronomer in the country. Fortunately, the Space Shuttle was a transportation vehicle needing an exciting science payload to demonstrate the utility of humans in space, and HST became the prized solution.

Today, while enjoying the success of HST, we all must recognize that the environment of the space and science programs in the United States has changed significantly from the conditions that created the astronomical facilities and professional circumstances of today. There is no longer a blind faith that federal funds for basic scientific research will produce more accomplished schoolchildren, assure competitiveness in global markets or otherwise ameliorate America's problems. Indeed, decision makers appear to have rejected `the endless frontier' as a useful public policy concept. Thus, the search is underway for some consensus rationale to continue funding space astronomy at levels comparable to the present.

The HST & Beyond Study, conducted by the Association of Universities for Research in Astronomy (AURA) with support from NASA, suggests such a qualitatively new rationale for public funding of space astronomy. What that rationale is, and the type of research program it calls for, is the subject of the remainder of this paper.

The charter of the study reads, "The HST & Beyond Committee is charged to study possible missions and programs for optical-ultraviolet astronomy in space for the first decades of the 21st century. It should initiate a process which will produce a new consensus vision of the long term goals of this scientific enterprise".

The membership of the HST & Beyond Committee is:

• Alan Dressler, Chair (Carnegie Observatories)
• Robert A. Brown (Space Telescope Science Institute)
• Arthur F. Davidsen (Johns Hopkins University)
• Richard S. Ellis (Cambridge University)
• Wendy L. Freedman (Carnegie Observatories)
• Richard F. Green (National Optical Astronomical Observatories)
• Michael Hauser (Space Telescope Science Institute)
• Robert P. Kirshner (Harvard University)
• Shrinivas Kulkarni (California Institute of Technology)
• Simon Lilly (University of Toronto)
• Bruce H. Margon (University of Washington)
• Carolyn C. Porco (University of Arizona)
• Douglas O. Richstone (University of Michigan)
• H. S. (Peter) Stockman (Space Telescope Science Institute)
• Harley A. Thronson, Jr. (University of Wyoming)
• John L. Tonry (Massachusetts Institute of Technology)
• James Truran (University of Chicago)
• Edward J. Weiler (NASA/Headquarters, ex officio)

The Committee met three (and one-half) times, in April 1994, September 1994, and May 1995, and then briefly in conjunction with the January 1995 meeting of the American Astronomical Society, where we opened the process to the community by inviting their comments on, and participation in, our debate and deliberations.

The Committee developed a variety of candidate astronomical themes that could define the space observatories to succeed HST. They elaborated these themes in terms of research issues, measurement requirements, and intellectual ramifications. We heard presentations about new technical capabilities such as adaptive optics, interferometry, and advanced mirror technology.

We also philosophized at length about the exact nature of our apparent opportunity to inform our community and influence the political environment regarding the future of space astronomy in the United States.

Finally, we assessed the themes---and the missions and programs to pursue them---according to scientific merit, technological readiness, and a non-scientific criterion: How will the taxpayer benefit from this astronomical research? A study asking that question is not entirely new. To its credit, the last Astronomy Survey Committee (Bahcall Committee) asked the same question for their 1990 report. They recognized that the benefits of space astronomy accrue to the human mind, as telescopes gather neither gold nor jewels except as people experience them in thought. To pursue those benefits, the Bahcall Committee recommended ``an education initiative in astronomy,'' which should feed the public's fascination with exotic discoveries and serve as a handmaiden to basic teaching and training of new scientists. Today, the national astronomy program is wrestling with the implications of this recommendation in terms of approaches and measurable outcomes.

The HST & Beyond Committee goes further than the Bahcall Committee, proposing to seize upon another educational opportunity uniquely accessible through astronomy: to address ancient questions about the origins of our cosmos, our world, and the life it contains. This new departure has to do with informing perspective and world view. Its distinctive quality is perhaps best appreciated by reflecting on the changes in the human mind inspired by Nicolaus Copernicus almost 500 years ago.

The Copernican revolution was not one but two revolutions. The first, the one with which scientists are most familiar, placed the Earth in its proper place in the skies, orbiting the Sun, not the other way around. This masterstroke inspired science as we know it. The scientific method itself was formulated in the process of sorting out where the planets are in three-dimensional space. Important tools, such as the calculus, were devised to assist the inquiry.

The second Copernican `revolution' affected vastly more people, for it impinged upon their world view. If the Earth was just another planet, then the human experience of Earth might or might not distinguish it from other worlds like it. What happened here on Earth might have happened in all those myriad `theres'. This ramification of science, this second revolution, has played itself out in nearly 500 years of robust philosophical debate about the uniqueness of Earth. Today, for the first time in human history, we can describe, design, and build the telescope---the interferometer---to discover other worlds orbiting nearby stars and measure their properties, including whether these worlds may be habitable.

The wider question of our cosmic place in time and space is another important extension of the Copernican revolutions. It is also a question that just in our time has become accessible with telescopes in space. We can describe, design, and build a telescope to look back in time to the earliest galaxies like our Milky Way, and follow the progression of events that gave rise to our galactic home.

HST has set the stage for this scientific opportunity with proof of the evolution of galaxies back as far as light in the visible spectrum can inform us, and with evidence of disks where planets may be building around young stars. These results encourage us to believe that some day we will be able to describe and understand in detail the cosmic events that led to the conditions suitable to our own existence.

Toward this end, and in line with the broader general discussion of the candidate astronomical themes, the HST & Beyond Committee has identified two major scientific goals, whose accomplishment will justify a commitment well into the next century: (1) the direct study of the birth and evolution of normal galaxies such as the Milky Way, and (2) the detection of Earth-like planets around other stars and the search for the evidence of life on them. Despite substantial progress in both areas in recent years, we have not achieved, nor have we at present the means to achieve, these two ambitious and crucial goals.

To further these two central scientific endeavors, and to simultaneously provide the broad capabilities of ultraviolet-optical-infrared astronomy in space that are necessary to advance the field on its many fronts, the HST & Beyond Committee recommends the following program:

(1) The HST should be operated beyond its currently scheduled termination date of 2005. An emphasis on ultraviolet imaging and spectroscopy, and wide-field, high-resolution optical-light imaging makes the HST a critical astronomical tool through the first decade of the next century. Present budgeting shows that this premier scientific tool could be operated in a ``no repair, no upgrade'' mode at approximately 20% of its present operation and maintenance cost, which would allow a highly cost-effective return on the investment in HST beyond 2005.

(2) NASA should develop a space observatory of aperture 4 m or larger, optimized for operation over the wavelength range 1--5 microns with imaging and spectroscopy. Extension of capabilities shortward to about 0.5 micron and longward to at least a 20 micron would greatly increase the observatory's versatility and productivity. The Committee strongly recommends this course, if it can be done without a substantial increase in cost. Such an observatory should be the first major astronomical ``facility class'' instrument in space to follow the AXAF and SIRTF programs. It will be an essential tool in an ambitious program of study in all areas of astronomy, especially in the origin and evolution of galaxies. The technology necessary for a cost-effective facility-class mission at these wavelengths---including ultra-lightweight precision mirrors and structures, advanced cooling systems, and ``smart'' controls---will be important for a variety of concurrent and follow-on programs, such as the imaging interferometry program discussed below. We believe that an approximate cost of $500 million for a 4-m version of this facility is a realistic and desirable goal.

(3) NASA should develop the capability for space interferometry. This will lead to a mission for astrometric observations in visible light at the 10 microarcseconds or better level, and the eventual construction of an imaging interferometer. The Committee recognizes this technology as a vital next step in pursuit of fundamental astrophysical questions and, specifically, sees IR interferometry from space as essential to one of our primary goals: the detection and study of Earth-like planets around neighboring stars.

Accomplishing these ambitious goals within the resources that are likely to be available in future years will require new space technologies hardware and innovations in the management of large projects, activities that are already advancing within NASA. International cooperation will be needed. By increasing their direct involvement in the building and operation of these facilities, astronomers can take a positive, active role in achieving these objectives.

Because the lead time for such challenging missions is long, two different kinds of activities must begin soon. First, the HST & Beyond Committee recommends that NASA set up study teams to investigate the technical issues involved in building and economical, large-aperture, near-IR-optimized space telescope. This effort will support and parallel the activities already underway within NASA to explore the possibilities for space interferometry. Improved information regarding capabilities, costs, and tradeoffs will be crucial to the deliberations of the next decennial survey report in astronomy and astrophysics.

The HST & Beyond Committee also recognizes that it is increasingly important for scientists to explain their motivations, goals, and results to the society that supports their research. The necessity of doing so is especially acute because, as we draw nearer to answering some of humanity's ancient questions, it would appear that competition for the resources available for scientific research will be stronger than at any time in the last half century.

It is not often given to science that it can inform directly a culture's attitudes and beliefs and an average person's self-understanding. The Apollo missions to the Moon were terrific scientific and technical accomplishments, yet their primary impact was beyond traditional science. That impact, epitomized in the magnificient pictures of the Earth as an island of life in space, was the realization that our common inheritance and destiny supersedes the divisions and distinctions between the people of the world. Darwin's voyage on the Beagle, which led to the theory of evolution, is another example. Such opportunities are sufficiently rare, and have been controversial enough, that they must be taken on with circumspection, for it would be inappropriate for a government to attempt the task of informing people what they should or should not believe about their origins and place in the universe in a religious sense. Nevertheless, not to enquire of nature---not to look at the evolution of galaxies and not to look for Earth-like planets around other stars---would be a perilous choice for people committed to truth, and for a society as committed to objective thinking and technological progress as is the United States of America. The design of our government was a singular product of the Enlightenment, which sought to establish the principle that all human endeavours can and should be informed by science. Today, the same democratic institutions that arose from that principle can decide whether or not to shed the light of reason on human origins in a cosmic context.