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NASA Advisory Council SSAC Origins Subcommittee Minutes 6-7 Mar 2001

Status Report From: NASA Advisory Council
Posted: Wednesday, March 7, 2001

Letter to SEC Director Dr. Anne Kinney from Dr. Alan Dressler, Chair of OS

Dear Dr. Kinney,

The Origins Subcommittee (OS) met at JPL on March 6 and at the Carnegie Observatories on March 7. We appreciated the briefing provided by you through Rick Howard on developments within Origins since our October meeting, and are grateful that Associate Administrator Ed Weiler was able to review the health of OSS missions in general. As at our last meeting, all three of you stressed the substantial progress and great enthusiasm for Origins missions tempered by the concerns of difficult schedules and budgets. In this connection we thought it particularly important to make time during our second day to review the Origins Theme architecture from the perspective of scientific directions, schedules, and budgets now that Origins is maturing. We append to this letter a summary of our thoughts on these broad-reaching concerns.

SIM - Space Interferometry Mission

The OS was apprised by Tom Fraschetti (SIM Project Manager) of how the SIM team plans to address the recent SIM replan imposed by the OSS. This replan entails a $930 M cost cap, the requirement that terrestrial planet detection be a key mission goal, and the requirement that SIM identify potential targets for TPF. Fraschetti summarized three design options, the Shared Baseline SIM, ParaSIM, and Sonata, that meet the new requirements. Shao and Fraschetti both advocated the Shared Baseline option over the other two as still cost-effective, while maintaining most of the original science capabilities of the SIM reference design. The OS commends the SIM team for its impressive efforts in redesigning SIM to meet the new requirements of OSS and for its continuing and steady technological progress towards meeting the current SIM metrology and astrometry goals.

The Shared Baseline SIM would still retain an unmatched single observation accuracy (~100 times better than FAME), and would be the only astrometry mission in the near-term that might detect large terrestrial planets. We note that the ability to make wide-angle astrometric measurements is essential if SIM is to find and characterize planets in Jupiter-like orbits, i.e., analogs to our own solar system. We are gratified that this same wide angle capability also enables a robust program of general astrophysics with strong community support, and note that it does not appear to impact significantly the cost of SIM.

The problems they are addressing are difficult, but the SIM team is making steady progress: the project is close to achieving the milestone of picometer metrology and has positive momentum. However, the OS believes that their charter should not be open-ended. We recommend that the SIM team be given approximately two years to develop the required component technology for picometer metrology (using the MAM-1 testbed) and then to integrate that technology into a systems-level testbed that validates SIM's error budget and performance at the level necessary to detect (large) terrestrial planets. These demonstrations should be prerequisites to initiating the Non-Advocate Review and entering into Implementation Phase. If at that time (early in Phase B) they are not able to demonstrate such performance, then a significant restructuring of the program or cancellation should be considered.

NGST - Next Generation Space Telescope

The OS was briefed by Project Manager Bernie Seery and Project Scientist John Mather on the project's proposed rescope, aimed at returning NGST to the intended budget and schedule and at eliminating the need for a full-up technology demonstration (the proposed Nexus). The plan calls for a reduced aperture, a warmer telescope (about 50K), and some reductions in focal plane instrumentation, in particular a proposal for a reduction in the number of pixels of the near-IR camera. The OS believes that even with any or all of the proposed changes the NGST would remain the immensely powerful facility that was given first rank by the McKee-Taylor Decadal Survey.

The OS was pleased to hear of the Project's progress on various fronts; there seems to be a steady march toward technology readiness in all phases so as to allow NGST to move into its next phase on schedule. The OS does, however, share the concern of the ISWG --- apparently also felt at Headquarters ---- about the complexity of proposed instrument collaborations among US, Canadian, and European instrument builders and their respective space agencies. We strongly favor agreements which place the responsibility of the near-IR camera wholly or primarily with US scientists and institutions, and similarly clean, workable interfaces for US participation with foreign partners in the other instruments, as appropriate. The OS agrees with the ISWG that the success of these negotiations can have a huge impact, positive or negative, on the future of NGST.

The OS discussed the priority of mid-IR capability on NGST. Mid-IR science was ranked highly by both the ASWG and ISWG, with three of the six identified core science topics requiring this waveband. The OS also wishes to stress the importance of mid-IR imaging and spectroscopic capability on NGST.

The mid-IR waveband is an important probe of galaxy formation and evolution at high redshift, NGST's core mission. Stellar populations older than ten million years have spectral energy distributions which peak at a rest wavelength of 1.6 microns, which is redshifted into the mid-IR for the likely first epoch of star formation. In addition, there is abundant evidence that dust plays a major role in the energy distributions of a substantial fraction of high-z galaxies, so coverage in the mid-IR could be crucial. This also could be relevant to the direct detection of the epoch of re-ionization, which might be more easily observed through observations of redshifted H-alpha than Lyman-alpha if the absorption of the latter by dust or neutral hydrogen is very important.

Circumstellar disks, another key component of the Origins program, are also a prime target for the mid-IR, and high-resolution imaging can detect small disks with gaps, rings, and warps, all of which may be dynamical signatures of the presence of planets. Mid-IR spectroscopy of these disks can measure the evolution from an active accretion disk to a planetary debris disk. In addition, there are spectroscopic signatures of both the chemical and physical mineralogy of the solid material in these disks, providing important diagnostics to the planet formation process.

The OS heard from Bernie Seery that mid-IR instrumentation is not driving the cost of NGST (a concern expressed in the HST & Beyond Report), for example, by requiring a lower telescope temperature. (Of course, we recognize that each additional instrument adds not just its own cost but also the expense of integrating it into the system, but this to us does not qualify as "driving the cost.") From the point of view of continuity within the Origins program, NGST with mid-IR capability would provide a powerful scientific descendant of SIRTF, with an improvement of a factor of 7.5 in angular resolution and two orders of magnitude in sensitivity, and also provide a technology precursor for the proposed nulling interferometer design for TPF. Putting it all together, the OS believes that mid-IR science is very important for NGST, a substantial increase in science for a modest increment in cost. We think it premature to consider giving up this capability before an in-depth investigation of possible tradeoffs at the instrument complement level and at the systems level. We were glad to learn that the Project could present to the ISWG a number of similar cost options that retain the mid-IR instrument, an approach we strongly endorse.

SIRTF - Space Infrared Telescope Facility

The OS thanks Mike Werner for an update on progress towards the launch of SIRTF in July, 2002. We learned of the cryostat over-pressure problem during testing and the progress toward recovery. Despite the regrettable cost implications, we look forward to a successful fix and the likelihood of the mission staying on schedule.

It was exciting and gratifying to have the SIRTF Legacy programs reviewed by Tom Soifer. The breadth and depth of these early programs re-emphasize the powerful scientific potential of SIRTF that we are all anticipating.

SOFIA - Stratospheric Observatory for Infrared Astronomy

We thank Cliff Imprescia and Eric Becklin for bringing us up to date on SOFIA. Although optimism was expressed about the state of technology development, the OS remains concerned that the Program can be brought to a successful conclusion with the available resources. This notwithstanding, we support your decision to attempt to accommodate the projected cost overruns within the SOFIA Program budget.

This committee has previously stressed the importance of ensuring that SOFIA data be easily and quickly available to the larger scientific community. While we understand the project's current concern with completing the observatory and initial suite of instruments, we encourage the project to continue to press forward its data handling development program as rapidly as possible. Particularly with the now-anticipated delay of order two years in the start of observatory operations, it is of great importance that the data processing, analysis tools, and archival access be available to the science community at the beginning of observatory operations, at least for facility instruments and preferably for PI instruments as well. We request, again, a detailed description of the plans for data processing and distribution from the SOFIA project at our next meeting.

The OS feels that it is very important that the difficulties SOFIA is encountering not adversely affect other Origins programs, which suggests regular updates until the program has demonstrated it is on the road to a successful implementation within the budget envelope. Accordingly, the OS requests a detailed briefing on the new budget, schedule, and management structure at our next meeting.

Starlight

The OS appreciated the opportunity to hear from Leslie Livesay about the progress of the Starlight technology demonstration mission (formerly known as ST-3) and to view the experimental testbed in the laboratory. We were impressed to see the progress made in proving the viability of the innovative design change that allows the mission to achieve its goals using only two spacecraft instead of the original three. The two technologies to be demonstrated, precision formation flying and separated spacecraft interferometry, are necessary for development of a multi-spacecraft architecture --- one possible option for Terrestrial Planet Finder (TPF) --- and are of importance for several other proposed Code S missions. However, given the uncertainty of the TPF technology path, the OS is concerned about the large and growing investment in this particular technology demonstration mission.

Kepler and Eclipse

Bill Borucki and John Trauger briefed the OS on the status of the proposed Kepler and Eclipse science missions, respectively. Both missions seek to answer important and complementary Origins questions regarding the statistics of habitable planets and solar system analogs. The results from these missions or missions like them would doubtless influence the design of TPF. Each received high marks for science in the recent Discovery AO process. Because the OS also strongly endorses their scientific goals, we are pleased that the Kepler program has been approved for Phase A study and that you have provided funding for technology development of the high contrast imaging required for a coronagraphic study of the nearest stars, as has been described in the Eclipse proposal. <B>Given the renewed interest in using coronagraphy in the TPF mission, and the potential for excellent and relatively rapid science return in a mission like Eclipse, the OS recommends that the Origins theme continue to invest in developing this and related technologies.

We append to this letter a summary of our discussion, made at your request, about the current state of the Origins program. We look forward to continuing the discussion on this and the items mentioned above at our next meeting at NASA HQ July 11-13.

Sincerely,

Alan Dressler, for the Origins Subcommittee

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