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Space Studies Board Board on Physics and Astronomy Division on Engineering and Physical Sciences September 24, 2001 Dr. Edward Weiler Associate Administrator for Space Science NASA Headquarters 300 E. Street, SW Washington, DC 20546-0001 Dear Dr. Weiler: As you requested in your letter of May 10, 2001, to Space Studies Board Chair John McElroy, the Committee on Astronomy and Astrophysics (CAA) has reviewed NASA’s plans for the Next Generation Space Telescope (NGST). NGST is the highest-priority new initiative for astronomy in the recently completed report of the National Research Council’s Astronomy and Astrophysics Survey Committee (AASC), Astronomy and Astrophysics in the New Millennium (National Academy Press, Washington, D.C., 2001). As described in the AASC’s report, NGST was to have been an 8-meter-class, infrared optimized telescope in space. Recently, due to budget and schedule constraints, your office began to consider modifications to the original mission concept and asked the CAA to assess the scientific merits of a descoped NGST with a 6-meter-class mirror. At its meeting on April 9-10, 2001, the CAA received presentations from the NGST project office; the AASC’s Panel on Ultraviolet, Optical, and Infrared Astronomy from Space; Alan Dressler, chair of NASA’s Origins subcommittee; and groups involved in large ground-based telescope programs that might have complementary near-infrared capabilities. The CAA notes that the proposed new baseline plan for the NGST project no longer includes the NEXUS precursor mission that was intended to test the technologies needed for the 8-meter NGST. The NGST project office testified that the plan for a descoped NGST would reduce the technical risk sufficiently that the NEXUS mission would no longer be necessary. The CAA was not asked to consider the engineering and technical risks involved in abandoning NEXUS and cannot offer an expert opinion on the matter. The scientific capabilities of the descoped NGST plan will not be affected by the loss of NEXUS. The proposed new baseline plan for NGST involves three changes that might have an impact on the scientific performance of the observatory. The first, and most significant, change is the replacement of the 8-meter mirror by a 6-meter mirror. This reduction in mirror size will result in a 25% loss in spatial resolution (λ/2D = 0.0344 arcseconds at 2 microns instead of 0.0258 arcseconds) and a ~44% loss in collecting power. As a result, the limiting point source brightness for a fixed observing time will be increased by a factor of ~1.8, while the observing time (~D4) required to reach a point source of a given brightness will increase by a factor of ~3. As a result, 2101 Constitution Avenue, NW, Washington, DC 20418 Telephone (202) 334 3520 Fax (202) 334 3701 nationalacademies.org/ bpa/caa

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the number of observations that the descoped NGST will be able to make to a given sensitivity limit during its lifetime will be reduced by a factor of ~3. The CAA regards this loss in observing capability as the most serious consequence of the proposed descope. The second change is the specification of a near-infrared camera detector with 48 megapixels rather than 64 megapixels as planned originally. This cost-saving change is appropriate given the loss of angular resolution inherent in the proposed reduced aperture of the primary mirror. Assuming that the camera will be designed to provide Nyquist sampling at a wavelength of 2 microns, the new detector will provide roughly the same field of view as the original baseline design (~4 arcminutes). The third change is the specification of a baseline operating temperature of 45 K for the telescope instead of 25 K. This change, according to the NGST project office, will reduce the level of technical risk by permitting active thermal control and improved dimensional stability of the telescope assembly. The increase in operating temperature will not affect the scientific performance of the observatory as specified in the original baseline design. The thermal background of the observatory will be greater than that of the zodiacal light only for wavelengths greater than about 12 microns, but this background is expected to be dominated by stray light from the sunshield rather than the thermal radiation from the telescope itself. The increased temperature proposed for the observatory would adversely affect the observatory’s scientific performance at the longer wavelengths only if the thermal background from the sunshield could be reduced by more than an order of magnitude, a reduction that the NGST project office does not regard as likely. The AASC report (p. 36) outlined five major science goals for NGST: (1) measure the light from the first epoch of star formation in the universe, (2) trace the evolution of galaxies from their birth to the present, (3) observe the birth of stars and planets in our own galaxy, (4) study Kuiper Belt objects in our own solar system, and (5) observe dust emission in galaxies out to redshifts of 3. The report emphasized that the NGST’s capability to address the latter three goals will depend substantially on whether its sensitivity in wavelength will extend to 27 microns. The CAA finds that all these major science goals can be met with the descoped option, despite the substantial loss in observing capability noted above. For detecting faint sources at wavelengths greater than 2.5 microns, the descoped NGST will still be 100 to 1,000 times more sensitive than the Space Infrared Telescope Facility (SIRTF), the most sensitive existing or planned facility for observing in this wavelength band (see the AASC report, Figure 3.2), and it will have nearly an order-of-magnitude better angular resolution than SIRTF. It will, for example, provide a unique capability to observe newborn star clusters at redshifts greater than 5. With the capabilities to achieve this goal and comparable milestones addressing the other major science goals listed above, the descoped NGST retains the priority recommended by the Astronomy and Astrophysics Survey Committee. In his March 15, 2001, letter to Origins Theme Director Anne Kinney, Alan Dressler, on behalf of NASA’s Origins subcommittee, stressed the importance of retaining the mid-infrared (5 to 27 microns) imaging and spectroscopy on NGST. The CAA concurs. The mid-infrared wavelength region offers the greatest potential improvement in sensitivity compared to the wavelength regions accessible to existing and planned telescopes on the ground and in space. At mid-infrared wavelengths, NGST will be able to study dust-enshrouded galaxies, newly forming stars, and planetary systems that may be invisible at shorter wavelengths. It will provide a unique capability for extending the process of discovery that will be initiated with SIRTF. NASA should 2

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make all possible efforts to preserve the mid-infrared capability and instrument package as described in the current project plan. In considering the scientific capability of the descoped NGST, the CAA regards the new baseline plan provided by the NGST project team as a sound approach. The CAA did not consider the possible trade-offs among scientific performance and technical capability that led to this plan. If further major adjustments in the baseline capability of NGST are required, however, it will be important to engage the scientific community in considering the necessary scientific and technical trade- offs. Sincerely, /s/ /s/ John H. McElroy, Chair John P. Huchra, Chair Space Studies Board Board on Physics and Astronomy Attachments: Letter of request from E. Weiler to J. McElroy Letter from A. Dressler to A. Kinney Presentation to CAA by NGST Project Office cc: Richard M. McCray, Co-chair, CAA Wendy L. Freedman, Co-chair, CAA Joel R. Parriott, Study Director, CAA Joseph K. Alexander, Director, Space Studies Board Donald C. Shapero, Director, Board on Physics and Astronomy 3

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March 15, 2001 Dr. Anne Kinney Origins Theme Director NASA Headquarters 300 E. Street, SW Washington, DC 20546-0001 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 it 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 1

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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. 2

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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 3

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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. 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 4

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Next Generation Space -- Outline -- Telescope (NGST) • NGST at a glance • Rescope process • Rescope summary A Presentation to the National Academy of • Instruments and Science Sciences Committee on Astronomy and • International partnership concepts Astrophysics • Schedules and major procurements Bernard D. Seery • NASA-funded technology development status update John C. Mather • Wrap up and discussion April 9, 2001 1 2 040901 CAA NGST Mather.ppt 040901 CAA NGST Mather.ppt NGST Concepts NGST at a Glance • 6-meter class primary mirror • 0.6-10+ µm wavelength range • 5 year mission life (10 year goal) • Passively cooled to <50K • L2 orbit - Logical - Logical successor successor to HST to HST - Key part of - Key part of the Origins the Origins Program Program Formulation Phase (A/B) Implementation Phase (C/D) 99 00 01 02 03 04 05 06 07 08 09 PDR NAR CDR Select Prime Launch 3 4 040901 CAA NGST Mather.ppt 040901 CAA NGST Mather.ppt NGST at L2 halo orbit Rescope Process L5 • Driven by procurement process and design to cost - must have resources consistent with the purchase plan • Initiated by Project Office last summer with detailed in-house L2 L3 L1 cost estimates of all parts of project, with schedules, PERT Earth charts, test plans, risk management plans, and budget and Sun schedule targets • Based on US-only cost analyses, but ESA and CSA have agreed L4 in the past that our methods were close enough to theirs • Single sunshield protects from Earth and Sun • Main technical changes were to meet the following objectives: • 8-16 hour visibility from single ground station – Risk reduction without Nexus flight demonstration • Simple operations compared to HST – Launch by 2009 • 0.01 AU away, but not serviceable by astronauts • Hold schedule • Halo orbit around L2 avoids Earth shadow • robustness – Compatible with more than one launch vehicle • Unstable orbit requires ~ 3 m/sec/year corrections – Stay with core instrument complement and ASWG priorities- preserve science program 6 040901 CAA NGST Mather.ppt

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Re-scoped NGST Reduces OTA Risk Rescope Process Flow Re-Scope Specific Impact Risk Assessment Systems Briefing to Flt Critical Item Contractor Briefing to Project Cost Projects PM Diameter: • Reduces total optics fab time • Reduces schedule risk Engineering Cost Studies Focused Cost Origins Theme Summit (Gov’t) re-optimization (Gov’t) Studies Directorate Director Nov 20 Nov 22 Nov 21-22 Jun-Oct 2000 Jul-Oct, 2000 Nov 30 8m class ➟ 6m class • Frees up mass & vol allocation, • Increased structural OTA can be applied to other critical rigidity, reduced 1G off- Cryocooler ➢ ➢ Sent Note to ISIM MIR accommodation ➢ ➢ elements loading complexity inform Int’l Dressler minimum - 4m WFC ➢ Partners Grnd System ➢ The Rescope Areal Density: OTA V&V • Reduces risk in PM segment • Reduces tech & Nov 23 ➢ development (segment design programmatic risk Contacted Key trade space less restricted) associated with most critical members of Sci NGST new technology kg/m2 kg/m2 15 ➟ >20 Community Nov 24 • Reduces 1G sag (more rigid • Reduces 1G off-loading backplane) complexity, reduces risk in system level WFS/C testing Hubble was 180 kg/m2 Status of Int’l Telecon Briefing to Briefing to Briefing to Briefing to ISWG • Enables OTA active thermal • More robust telescope OTA Temperature: Rescope w/ discussions of OSS Theme Administrator GPMC OSS AA Telecon AETD/STAAC control Rescope Director architecture Dec 18 (PM) Dec 13 Dec 18 (AM) Dec 21 Jan 3, 2001 Dec 7 Dec 15 30K/passive ➟ up to • Reduces dependence on • Reduces risk associated material properties and with opto-thermal stability 45K/active * GSFC Concurrence * HQs Concurrence environmental effects Presentation ISWG Rescope Reconcile Origins Formal direction • Increase bandwidth of sensing • Adds robustness & design WFS/C Update rescope req’s Science to Primes to ESA TIM To the Subcommittee AAS Mtg w/ POP conduct delta & control loops margin to OTA subsystems Impacts Jan 16-19 ISWG Pasadena guidelines Phase A Jan 7-8 2001 Mar 12-13 Jan 16, 2001 1 month ➟ 1 day Jan 15 3/7/01 1/24/01 • Reduces thermal & structural stability requirements • Enables system-level optical • Critical step in integrated 1-g Testability: SScAC Review Tripartite tests with "star-like" source Release Begin model validation and NAS BPA NAS CAA Contractor Release Draft Meeting Final RFP Wash, D.C. Phase 2 Selection Limited subaperture testing • Allows control system to see RFP Package observatory-level performance April 9 April 28, Apr 2-4, Mar 20-22, Jun 2001 Feb 2002 2001 2001 Jan 2002 April 2001 vs full aperture plane wave substantial portion of full confirmation 2001 2001 (TBR) aperture 7 8 040901 CAA NGST Mather.ppt 040901 CAA NGST Mather.ppt Rescoped NGST Eliminates Need for Nexus ASWG Prioritized Instrument Metrics Re-scope Nexus • Sensitivity Over Wide Fields of View Risk Mitigation Risk Mitigation – Discover faint new objects WFS/C performance in the space Increased WFS/C bandwidth & – Support General Observer science environment more robust design Wavelength Range Observatory long-term imaging Fully utilize discovery Raise operating temperature to stability in space space enable active thermal control Ensure widest possible Validation of integrated models redshift coverage and I &T approach Pre-launch system-level optical Spectral & Spatial Resolution testing (designed for 1-G for DRM Science testing) Establish cost curve and develop mirror fabrication & production • Surveying Efficiency processes for ultra-low mass Increase areal density & reduce segmented telescope – Spatially multiplexed spectroscopic capability mirror area, thereby reducing – Statistics of galaxies & lenses; guide stars cost & schedule uncertainty of primary mirror development – Accomplish DRM in 2.5 years 9 10 040901 CAA NGST Mather.ppt 040901 CAA NGST Mather.ppt 4th Instruments rec. by ASWG (not in plan) ASWG recommended Instrument Suite • 4´ x 4´NIR Camera • NIR R=3000-5000 psf-sampled spectrometer – " 0.1´´ angular resolution, ~2´´ x 2´´ FOV – Nyquist sampled at 2 µm, 0.6-5 µm, R~100 grism mode – 2d for single, extended object spectroscopy Flight Data System • 3´ x 3´ NIR R~1000 Multi-Object • 0.6 - 1 µm camera (sampling diffraction spike) H/W & S/W Spectrograph – ~0.01´´ angular resolution, 1´ x 1´ FOV NIRMOS – Simultaneous source spectra(" 100), 1-5 – (Note-- assumes NIRCAM has 0.6 µm capability) µm MIR – stellar pops/WD cooling curve, circumstellar disks, high z (incl. • 2´ x 2´ Mid IR Camera/R~1500 cooler) gal. Morphology Spectrograph • MIR R=3000-5000 psf-sampled spectrometer – Nyquist sampled at ~10 µm, 5-28 µm, NIRCam – " 0.3´´ angular resolution, " 2´´ x 2´´ FOV, 5-28.3 µm grisms & slit – Instead of R~1500 add-on spectrograph to MIR camera 11 12 040901 CAA NGST Mather.ppt 040901 CAA NGST Mather.ppt

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NGST & the Early Universe NGST Deep Imaging: 0.5–10 µm ASWG: Simon Lilly Depth: AB ~ 34 in 106 s 5000 galaxies to ASWG: Simon Lilly AB ~ 28, Redshifts: Lyman α to z = 40 (?) 4’x4’ 105 galaxies to deep 4000 Å to z = 10 AB ~ 34 • Early evolution of stars and galaxies: survey NGST will detect 1 M yr-1 for 106 yrs photometry, field ∆ρ/ρ to z ≥ 20 and 108 M at 1 Gyr to z ≥ 10 morphology & z's ~ 10-5 – What were the first sources of light in the (conservatively assuming Ω = 0.2) universe? – How were galaxies assembled? Galaxy – What is the history of star birth, heavy element assembly production, and the enrichment of the IGM? – How were giant black holes created and what is their role in the universe? Galaxies, stars, planets, life NGST & Extrasolar Planets Evolution of Planetary Systems ASWG: Marcia Rieke From Angel & Woolf 1998, in Science with the NGST, ASP, 133, 172 Vega Disk Detection 108 Fν (µJy) “Sun” Flux* Contrast λ Control of primary only: 106 • (µJy) Star/Disk (µm) – Jupiter at 10 < λ < 20 “Solar System" at 8 pc, µm 11µm 2.4 1.5x107 6m primary 104 22µm 400 2x104 Active wavefront correction 102 to 30 nm rms 33µm 1300 3x103 λdiff=1 µm Direct detection of Jupiter Jupiter Reflected & emitted λ > 0.4 µm 1 light detected with a 10σ Earth Not a baseline program, simple coronograph. but a natural upgrade 0.01 30nm issue for future missions NGST resolution at 24µm = 5 AU at Vega, > 10 pixels such as TPF or an 0.1 1 10 100 NNGST. across the inner hole *per Airy disk 16 040901 CAA NGST Mather.ppt Design Reference Mission 7 Core Programs Requirements • DRM contains the Dressler Report science • 1: 2 µm diffraction limited imaging, wide FOV, 8m sensitivity, 0.6-5 µm • DRM does not preempt proposal process • 2: 1-5 µm NIR multiplexed spectroscopy, R=100- • 23 large, critical science programs that could be 3000; 5-10 µm spectroscopy, R=3000 carried out in ~2.5 years • 3: Wide FOV; stable psf • 7 Core Programs • 4: Very sensitive NIR spectroscopy – 1: Form. & Evol. of Galaxies - Imaging R=100-300 – 2: Form. & Evol. of Galaxies - Spectroscopy – 3: Mapping Dark Matter • 5: Ability to follow fields over months – 4: Search for Reionization Epoch • 6: MIR (10-28+ µm) imaging/spectroscopy, – 5: Measuring cosmological parameters R=300 – 6: Form. & Evol. of Gals. - Obscured Stars & AGN • 7: MIR (10-28+ µm) imaging/spectroscopy, – 7: Physics of Star Formation: Protostars R=3000+ 17 18 040901 CAA NGST Mather.ppt 040901 CAA NGST Mather.ppt

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Yardstick Cameras vs. other observatories Observing Speed Scaling Laws (8m, 4´x4´, 64Mpixel NIRCAM, 35K OTA) • D2Npix for diffraction limited survey to given depth Primary: 8m • D4Nobj for multiobject spectrograph, detector limited FOV(arcmin): 4x4 • 1/(zodiacal light + stray light) for background limited detector sensitivity (R<50 in near IR) %DRM: 100% • 1/(physical pixel area) for dark current and cosmic Diff Lim(µm): 1.5 ray limited sensitivity - NGST has funded OTA Temp: 35K development of detectors with smaller pixels MIR: Yes • (exposure time)2/(read noise)2 for read noise limited EELV detectors - sets minimum useful exposure time for spectroscopy • (optical efficiency * QE * Strehl)2 for dark current or read noise limit; linear if background limited • Conclusion for NGST: Design Reference Mission takes about 2-3x as long for 6.5 m, 48 Mpix NIRCAM as for 8 m with 64 Mpix 19 20 040901 CAA NGST Mather.ppt 040901 CAA NGST Mather.ppt Rescoped Cameras vs. other observatories 25 m GSMT / 8 m NGST: spectroscopy (6.5m, 4´x4´ 48Mpixel NIRCam, 50K) Primary: 6.5m FOV (arcmin): 4x4 %DRM: 67% Diff Lim(µm): 2.0 OTA Temp: 50K MIR: Yes EELV Decade Survey Draft, p. 107 21 22 040901 CAA NGST Mather.ppt 040901 CAA NGST Mather.ppt What’s Changed since 1996? The outlook for NGST in the Near IR • Discovery of cosmic far IR background and its ASWG: Simon Lilly sources shows dust re-emits half the luminosity of It is reasonable to be pessimistic about ground- based observations for: the universe (COBE, SCUBA, ISO) (a) all deep observations at λ > 2.2 µm • Discovery of large numbers of high redshift AGN (b) systematic multi-line spectroscopy at 1 < λ < 2 µm (OH emission and H20 absorption) and dusty Chandra X-ray sources shows black holes (c) anything requiring diffraction limited imaging are significant part of total luminosity at λ < 1 µm or (wide-field) imaging at 1 < λ < 2 µm (c.f. AO) • Discovery of many unexpected planetary systems IR astronomy from the ground shows planetary formation is very important problem i.e. modest progress in programs involving: (d) the very highest redshifts • Theoretical predictions that first objects in the (e) systematic diagnostic spectroscopy universe were at redshift 20-30 ups the ante for (f) stellar (CO-bandhead) masses at high z sensitivity and wavelength range (g) the energy sources in all except the most luminous high z ULIRGs (c.f. SIRTF) • Multi-Conjugate Adaptive Optics and proposed 20- These are the central goals of NGST program 30 m ground based telescope complement NGST on the formation and evolution of galaxies, (like Keck and HST), and reduce NGST advantage which are therefore likely to remain current at λ < 2.5 µm, especially for spectroscopy 24 040901 CAA NGST Mather.ppt

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Scientists think Mid IR is worth the cost Engineers think the mid IR cost is reasonable • Telescope design not driven by mid IR • Dressler 1996 - yes: “Extension of this telescope’s wavelength range shortward to about 0.5 µm and longward to at least 20 µm – Shortest wavelength drives accuracy spec would greatly increase its versatility and productivity. The • Test program not driven by mid IR Committee strongly recommends this course, if it can be done – Telescope can be regulated at 50 K to stabilize it without a substantial increase in cost.” • Passive cooling design not driven by mid IR • ASWG (Ad Hoc Science Working Group): yes (unanimous vote on core instrument complement, and wavelength range was 2nd – Needed for InSb to run at 30 K priority after sensitivity) – Mid IR system gets its own sub-cooler • Decadal Survey: yes: “Extending NGST’s sensitivity deeper into • Detectors not major cost the infrared, from the 10 µm currently planned to 30 µm, would – SIRTF sensitivity already adequate, small number of chips substantially improve its ability to study Kuiper Belt Objects (KBOs) in our solar system, the formation of planets in our • Mid IR instruments not major consumers of services (data rate, Galaxy, and the dust emission from galaxies out to redshifts of 3.” mass, power) • ESA advisory system: yes (was basis for selection for F mission – All dominated by the Near IR camera funding) • ISWG (Interim Science Working Group): yes • Origins Subcommittee - yes: “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.” 25 26 040901 CAA NGST Mather.ppt 040901 CAA NGST Mather.ppt Could the First Objects be seen in the Mid IR? Origins of Planets - Primary Mid IR NGST Science • UV objects re-ionized the universe - but was most of • History of metal abundances as raw materials over the UV and Ly α absorbed by the IGM? Or by dust? age of Universe - when could life first form? Which came first? • Direct view of protoplanetary and planetary debris • Massive objects and AGN could form dust very disks rapidly (10 Myr) if the dust stays near the objects, so – Temperature, density, chemistry, orbital resonances with the first objects might almost immediately become planets MIR bright too – Relation to formation of binary stars – Organic chemistry - astrobiology • At z = 20, Ly α is 2.6 µm, but H α is 13.8 µm - we’d • First direct view of planetary-mass objects like to see it – Easy shot for objects separated from bright stars • To know something is primordial, we need to show – Scientific precursor for TPF it has NO metals or dust • Comparative planetology - Solar System objects – [O III] 5007 A is strongest metal line expected for z > 9, versus observed disks, “loose planets” falls beyond 5 µm for z > 9 27 28 040901 CAA NGST Mather.ppt 040901 CAA NGST Mather.ppt International Partnership Concept Instrument Partnership Concepts • ESA ~$200M (FY96) value of effort, gains 15% • Current favorite idea, from Tripartite meeting 4/4/01: observing time on HST and NGST; ESA has – NASA to provide shared instrument services (electronics, thermal, data system, …) and integration and test approved funding subject to successful detailed plan – NASA AO to provide NIRCAM • CSA ~$50M (FY96) value of effort, gains 5 – ESA to provide NIRSPEC, based on US detectors and observing time on NGST multiobject selector • Initial goal 50-50 split of instrument/non-instrument – NASA/ESA/member nations to develop detailed contributions partnership plan for Mid IR instrument, using Mid Infrared Steering Committee to define the concept and work • Exploring ESA contribution to spacecraft bus, based breakdown structure. US to provide detectors and their on Herschel (FIRST)/Planck bus contract to be electronics. announced shortly – CSA to provide separate fine guidance sensor, and • CSA contribution probably fine guidance sensor and contributions to NIRCAM contribution to near IR camera • CSA and ESA would fund staff at STScI 29 30 040901 CAA NGST Mather.ppt 040901 CAA NGST Mather.ppt

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NGST Phase A Products NGST Top Level Observatory Schedule FY 00 FY 01 FY 02 FY 03 FY 04 FY 05 FY 06 FY 07 FY 08 FY 09 34 1 23 41 234 1234123 4 123 4 1 23 4 1 23 4 1 234123 4 PDR NAR CDR MOR TRR ORR FRR 9/01 6/02 Independent 9/04 9/03 MDR Assessment 3/08 6/08 SRR 3/04 2/07 11/08 3/03 Prime PSR Down-Select 12/05 7/08 Mirror Fabrication 12/01 12/05 OTA Assembly/Integration 5/04 OTA I&T Complete SI Selections ISIM FSW 12/01 2/01 SI’s to GSFC12/06 3/07 9/07 ISIM Development 8/03 AO ISIM to Prime Prep ISIM FSW 8/03 Complete 2/02 CC & DH Development 11/01 7/08 Ground System Development Contract Award Final Build 9/07 Spacecraft Development 9/04 9/08 12/08 9/07 Observatory I&T / Launch Site Integration Begin Launch Site Integ Launch Timeframe STATUS AS OF: 03/09/01 31 32 040901 CAA NGST Mather.ppt 040901 CAA NGST Mather.ppt Cryo Testing of SBMD at MSFC Technology Development Progress Technology TRL in early 2000 TRL Currently Sunshield 4 5- WFS&C 3 4 Cryo Test Facility Layout SBMD (9.8 kg/m2) Mounted in Chamber Mirrors 3 4 Actuators 4 5 MEMS 3 4 Cryo DM 4 5 Cryo Figure Deployables 3 4 Detectors 3 4 Cryo Deformation Final Surface @ 35K Surface error: 34K - 288K (17 nm rms) Gravity Corrected (571 nm p-v; 63 nm rms) 33 34 040901 CAA NGST Mather.ppt 040901 CAA NGST Mather.ppt Validation of SBMD Cryo-Null Figuring NGST Mirror Technology Development (0.134 µm p-v; 0.016µm rms) (0.571 µm p-v; 0.083µm rms) High spatial frequency Shack-Hartmann test of Shack-Hartmann test of SBMD in Difference between cryo residual error left over SBMD in XRCF at 34K . Print- XRCF at ambient temperature in and ambient surface after subtracting best-fit through of the lightweighted vacuum. The anticipated figures. The cryomap to be 42 term Zernike web structure is clearly astigmatism comes from the self- applied to the existing Kodak Mirror polynomials from cryomap. visible as the mirror distorts weight deflection of the assembly surface is generated from at cryogenic temperatures. held with optical axis horizontal. this data. SBMD Mirror Ambient temperature measurement of At 38K, web print-through and center Final surface of SBMD at cryogenic COI Mirror SBMD with cryomap applied, ready for dimple are significantly reduced compared temperatures, with gravity effects final test. to cryo map at 34K prior to cryofiguring. removed by averaging of multiple rotations. NMSD Mirror Safely Deblocked 35 36 040901 CAA NGST Mather.ppt 040901 CAA NGST Mather.ppt

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WCT- 2 Segment Mirror Phasing Microdevice Test Arrays for NGST • Objective: Develop technology to defocus = 25 mm defocus = -25 mm defocus = 0.8 mm allow selection of >100 targets 20 50 40 per/FOV for NIR spectroscopy 100 60 150 80 200 100 • Pursuing both micromirror and 120 250 50 100 150 200 250 50 100 150 200 250 20 40 60 80 100 120 Typical images used for microslit selector technologies In-focus image and model image at 633 nm WF sensing and control Data Image Model Image 10 10 • Major focus for NRA 2 funding 20 20 Sandia National Lab 30 30 - Issue: Riskiest instrument technology, 40 40 (Both designs feature 100 µm 50 50 offramps to be pursued by ESA mirror elements) WF error = 44 nm RMS 60 60 x 10 4 x 10 4 Horizontal Slice 20Vertical Slice 20 40 60 40 60 18 16 15 14 12 Data is Model is 10 10 blue green 8 6 5 4 Double 2 Shutter Transport Mechanism 0 Retrieved WF 20 40 60 20 40 60 In-focus images prove excellent after control broad-band phasing Single Shutter GSFC 256x256 array 37 38 040901 CAA NGST Mather.ppt 040901 CAA NGST Mather.ppt JPL Phase Retrieval Camera Report Card for Last Year - Accomplishment Metrics Last Year’s Goals Status to Date Comments • System Studies - ISIM Delta formulation - Formulation and cost studies complete - Revisiting weight margin and investigating cryo-materials studies/cost estimates in October 2000 issues - OTA cost model - New, joint NASA/DoD telescope cost - Based on AMSD developments development curve developed in October 2000 - Cryocooler vs cryostat - Trade study by both primes complete - Project to proceed with cryostat trade in September 2000 due to near term cost pressures, and push cryocooler development off on LTSI - International - Agreements on the non-instrument - Agreement on the MIR TBD agreements and Phase components put on hold till after - Bilaterals in March/Tripartite in rescope; signed annexes to the Letters April A/B studies of Agreement in place • Pathfinder Flights - Cancelled due to shuttle manifest - Cost overruns projected to - ISIS delays of flight until 2002 continue on the ILC Dover shield contract - Cancelled due to budget shortfall in - Large-scale OTE testbed pulled - Nexus 2001-2002 and mirror delivery forward in the program - LTS may enable SIM STS schedules longer than originally launch strategy anticipated 39 40 040901 CAA NGST Mather.ppt 040901 CAA NGST Mather.ppt Cost Growth Since Pre A Studies Report Card for Last Year - Accomplishment Metrics Cost growth since the Pre A estimate: Last Year’s Goals Status to Date Comments • Nexus startup had been delayed twice in the last 2 years due to • Programmatic budget shortfalls - Original target of March 2001 - Phase 2 Downselect - SEB on track to release RFP in June delayed 3 months by rescope – Schedule delays precluded the original early risk mitigation intent - NRA 2 Instrument Tech - 6 awards made in January 2001 Awards – Flight test by mission CDR was deemed too late • Contributed to cost growth in early Phase C as higher fidelity testbeds • Technology - Phase 2 underway and hardware being - Traceability/manufacturing were required early - Advanced Mirror Systems Demonstrator developed process review held in January – New agency risk posture drove up verification costs in Phase D 2001 Phase 2 • Instrument module growth due to: - NGST Mirror Systems - COI hybrid glass mirror completed 2 of - Completion determined by XRCF testing schedule 3 cryo figuring cycles; U of A mirror Demonstrator Phase 2 – Increased requirements to improve performance above SIRTF actuator fab behind schedule and 2nd complete deblocking took longer than advertised – Need to develop key instrument technologies like MEMs – Desire to reduce development risk through a more conservative (more - Hardware scale-up continues with first - Technology downselect in June - Focal plane expensive) model philosophy SCA deliverables in July 2006 2003 development – Inability to achieve planned level of integration due to international - WCT 3 complete; PRC complete by - Gov’t will continue to further - Wavefront Control agreements May 2001 refine the testbed until NAR Testbed completion • International agreements have not yielded dollar-for-dollar savings • Science - First face-to-face meeting in - ISWG replaced ASWG in - Revitalize Science January 2001 November/December of 2000 Advocacy Group 41 42 040901 CAA NGST Mather.ppt 040901 CAA NGST Mather.ppt

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NGST Monograph Series Goals for Next Year (2002) NGST MONOGRAPH NO. 7 NGST Optical Quality Guidelines By NGST MONOGRAPH NO. 5 Pierre Bely, Richard Burg, Stefano Casertano, Harry Ferguson, John Krist, Knox Long, Dwight Moody, Maria Nieto-Santisteban, Peter Stockman and John Trauger NGST MONOGRAPH NO. 1 System Level Requirements, April 2000 • Programmatic Recommendations NGST and Guidelines “Yardstick Mission” By NGST MONOGRAPH NO. 3 John Mather, Bernard Seery, Peter Stockman, Pierre Bely, Richard Burg, Joseph Burt, Paul Geithner, – Phase 2 Contract Award By Matthew Greenhouse, John Isaacs, Implications of the Mid-Infrared Pierre Bely, Charles Perrygo and Richard Burg Harry Ferguson, Knox Long and Larry Petro Capability for NGST July 1999 May 2000 Next Generation Space Telescope Project Study Office By – ST ScI under separate NGST contract Goddard Space Flight Center Pierre Y. Bely, Richard Burg, Steve Castgles, Matt Greenhouse, D. Jacobson, K. Parrish, Larry Petro, Dave Redding November 1998 – International agreements in place and MOUs drafted NGST MONOGRAPH NO. 8 Next Generation Space Telescope Next Generation Space Telescope The Radiation Environment for the Project Study Office Project Study Office Goddard Space Flight Center • Technology Next Generation’s Space Telescope Goddard Space Flight Center By Janet L. Barth (NASA/Goddard Space Flight Center) and Next Generation Space Telescope John C. Isaacs (Space Telescope Science Institute) Project Study Office Goddard Space Flight Center December 1999 – Detector technology downselect NGST MONOGRAPH NO. 2 NGST MONOGRAPH NO. 6 Straylight Analysis of – AMSD cryotesting underway NGST NGST MONOGRAPH NO. 4 The Yardstick Mission Performance Analysis NGST Using Integrated Modeling By Next Generation Space Telescope Pierre Y. Bely, Matt Lallo, Larry Petro Integration and Testing – Wavefront algorithms demonstrated with PRC and both Project Study Office Keith Parrish, Kimberly Mehalick, Charles Perrygo By Goddard Space Flight Center Gary Peterson, Robert Breault Gary Mosier and Dave Redding Stawman Plan Richard Burg March 2000 July 1999 By high/low authority cryo mirrors Mike Menzel (Lockheed-Martin) July 1998 NGST MONOGRAPH NO. 9 NGST • Science Optical Component and System Testing Strawman Plan Next Generation Space Telescope Next Generation Space Telescope Project Study Office By Project Study Office Goddard Space Flight Center – ISWG review of the degree to which science program has The Optical Testing Study Team Goddard Space Flight Center Next Generation Space Telescope March 2000 Project Study Office Goddard Space Flight Center been preserved in rescope Next Generation Space Telescope Project Study Office Goddard Space Flight Center 44 43 44 030601_NGST_origins.ppt 040901 CAA NGST Mather.ppt 040901 CAA NGST Mather.ppt Biggest Worries • Cost growth in Phase B after teams are selected – Unknown unknowns – Would have to rescope again to meet budget • Bureaucratic obstacles – International collaboration difficulties – ITAR regulations • But: – NAS says this is top priority – Strong international desire to cooperate – Large Phase A technology investment by NASA – Adequate time to get ready for NAR 45 46 040901 CAA NGST Mather.ppt 040901 CAA NGST Mather.ppt Points to Remember • Rescope restores an affordable program while preserving most of science program • NGST still essential 5 years after start, but advantage shifts to longer wavelengths • Phase A Studies complete and cost estimates sufficiently mature to warrant commencing Phase B immediately after downselect 47 040901 CAA NGST Mather.ppt