In the past few years, programmatic changes at NASA, issues raised by the NRC report, Connecting Quarks with the Cosmos: Eleven Science Questions for the New Century(CQC), and scientific and technological advances combined to prompt consideration of a reexamination of the overall science strategy set forth in Astronomy and Astrophysics in the New Millennium (AANM). Discussions followed between the Board on Physics and Astronomy and NASA and NSF that resulted in a request by the two agencies to prepare a short report addressing the points leading up to calls for the reexamination. The report was also to assess progress towards the vision set forth in the AANM and CQC studies. This letter report presents the result of that study. It reviews the context that led up to the request and the most exciting advances in astronomy and astrophysics and key technological developments since the AAMN report was published, and it provides an outlook for fulfilling the decadal vision of the two previous studies.

The 1991 NRC decadal survey for astronomy and astrophysics included a project called the Millimeter Array (MMA). This instrument would be an array of millimeter-wavelength telescopes intended to capture images of star-forming regions and distant star-burst galaxies. With the addition of contributions form Europe, the MMA evolved into the Atacama Large Millimeter Array (ALMA), a proposed array of 64, 12-meter antennas. The project is now part of the NSF Major Research Equipment and Facilities budget request. Increased costs, however, have forced the NSF to reconsider the number of antennas. To help with that review, NSF asked the NRC to assess the scientific consequences of reducing the number of active antennas from 60 to either 50 or 40. This report presents an assessment of the effect of downsizing on technical performance specifications, performance degradation, and the ability to perform transformational science, and of the minimum number of antennas needed.