development or operations costs. In this sense the ATD/NTOT will be like possible future missions under the aegis of NASA’s proposed New Millennium program.

  1. The ATD/NTOT’s astronomical promise is sufficient, even at this preliminary stage, that it is appropriate to plan for a mission phase devoted to astronomical observations. The resources devoted to planning an astronomical mission should be kept to a minimum until such time as the ATD/NTOT’s scientific and technological capabilities are better defined.

    If an extended mission occurs, the task group offers several additional recommendations regarding the way in which it should be managed. These recommendations reflect the philosophy that development costs for astronomical research programs should be kept to an absolute minimum because of the ATD/NTOT mission’s nature as a demonstration.

  2. An extended ATD/NTOT mission devoted to astronomical research should be carried out by a principal investigator and a science team, with rotating membership to involve people with different types of expertise during different phases of the mission. No provision should be made for a traditional guest observer program.

  3. An extended mission should concentrate on extensive surveys that repeatedly use the ATD/NTOT in a single mode. Pointed observations of specific targets suggested by guest observers should be carried out only if they can be done simply by adding fields to the survey program and provided that suitable guide stars are available in those fields.

  4. All scientific data collected during the ATD/NTOT mission should be delivered promptly to an existing public archive that is independent of and expected to outlive the mission. Such an archive might be that for the Hubble Space Telescope, the Planetary Data System, or the Infrared Processing and Analysis Center, with a specific choice to be made at a later date.

    Because DOD sponsorship of the ATD/NTOT is uncertain, the mission ’s exact specifications are not yet clear. As noted in this report, the task group has assumed a baseline performance predicated on the requirements necessary to perform a mission that BMDO has now deferred. Several of the potential enhancements outlined by the task group would have a significant impact on the ATD/NTOT’s astronomical capability relative to that baseline. Some of these enhancements may ultimately be required by, or at least be consistent with, a DOD mission if and when it is finally defined. All of the suggested improvements must be evaluated for their cost-effectiveness during the system engineering phases of the mission. The task group has discussed its suggested enhancements with representatives of Lockheed and Itek. In the case of improvements to the figure of the primary mirror, the costs are well defined and the performance benefits reasonably well determined. In other cases, neither the costs nor the actual improvement in performance are very well determined, but it is the sense of this task group that the enhancements are likely to be very cost- effective and important for the astronomical aspects of the mission. In particular:

  5. The figure of the ATD/NTOT’s primary mirror should be improved by roughly a factor two to reduce its surface error to ~17 nm, and, thus, the total system’s wavefront error to roughly 50 nm rms. This enhancement would allow both a better evaluation of the ATD/NTOT’s technology and significantly enhance its astronomical potential. The cost of this improvement is reasonably well determined at $100,000 according to representatives of Itek.

  6. A large-format, framing, optical CCD of astronomical quality should be included in the ATD/NTOT’s focal-plane package. This CCD should be optimized for performance in the far red (say, ~0.8 micron) and should be of normal astronomical quality with respect to dark current, readout noise, and other relevant parameters. Its inclusion would enhance astronomers’ ability to evaluate the technology and would lead to dramatic increases in the astronomical return from the mission. A less expensive but clearly less desirable option would be to replace the baseline line-transfer CCDs in the fine-tracking sensors with frame-transfer CCDs.

  7. The ATD/NTOT’s baseline InSb infrared array should be optimized for sensitivity by, for example, further cooling of the array itself and by minimizing the number of emitting surfaces in the optical path. The astronomical return would be significantly enhanced if the system ultimately reaches the sensitivity limit set by the zodiacal light.



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement