Scientific Assessment of the Descoped Mission Concept for the Next Generation Space Telescope (NGST): Letter Report (2001)

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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 

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 

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 





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 

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 

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 

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 

Next Generation Space -- Outline -- Telescope (NGST) • NGST at a glance • Rescope process • Rescope summary A Presentation to the National Academy of Sciences Committee on Astronomy and • Instruments and Science Astrophysics • International partnership concepts • Schedules and major procurements Bernard D. Seery • NASA-funded technology development status update John C. Mather • Wrap up and discussion April 9, 2001 040901 CAA NGST Mather.ppt 1 040901 CAA NGST Mather.ppt 2 NGST at a Glance NGST Concepts • 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 Select Prime PDR NAR CDR Launch 040901 CAA NGST Mather.ppt 3 040901 CAA NGST Mather.ppt 4 NGST at L2 halo orbit L5 Rescope Process • Driven by procurement process and design to cost - must have resources consistent with the purchase plan L2 L1 L3 • Initiated by Project Office last summer with detailed in-house Earth cost estimates of all parts of project, with schedules, PERT Sun charts, test plans, risk management plans, and budget and schedule targets L4 • Based on US-only cost analyses, but ESA and CSA have agreed 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 • Unstable orbit requires ~ 3 m/sec/year corrections – Compatible with more than one launch vehicle – Stay with core instrument complement and ASWG priorities- preserve science program 040901 CAA NGST Mather.ppt 6 

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

NGST & the Early Universe NGST Deep Imaging: 0.5–10 µm ASWG: Simon Lilly 5000 galaxies to Depth: AB ~ 34 in 106 s ASWG: Simon Lilly AB ~ 28, 4’x4’ Redshifts: Lyman α to z = 40 (?) deep 105 galaxies to 4000 Å to z = 10 AB ~ 34 • Early evolution of stars and galaxies: survey photometry, NGST will detect 1 M yr-1 for 106 yrs ∆ρ/ρ field ~ 10-5 morphology & z's to z ≥ 20 and 108 M at 1 Gyr to z ≥ 10 – 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” λ Flux* Contrast (µm) (µJy) Star/Disk • Control of primary only: 106 – Jupiter at 10 < λ < 20 “Solar System" at 8 pc, µm 11µm 2.4 1.5x107 104 6m primary 22µm 400 2x104 Active wavefront correction to 30 nm rms 102 33µm 1300 3x103 Direct detection of Jupiter λdiff=1 µm Reflected & emitted λ > 0.4 µm Jupiter 1 light detected with a 10σ simple coronograph. Not a baseline program, Earth but a natural upgrade 0.01 issue for future missions 30nm NGST resolution at 24µm = 5 AU at Vega, > 10 pixels such as TPF or an 0.1 1 10 100 *per Airy disk across the inner hole NNGST. 040901 CAA NGST Mather.ppt 16 Design Reference Mission 7 Core Programs Requirements • DRM contains the Dressler Report science • 1: 2 µm diffraction limited imaging, wide FOV, 8m • DRM does not preempt proposal process sensitivity, 0.6-5 µm • 23 large, critical science programs that could be • 2: 1-5 µm NIR multiplexed spectroscopy, R=100- carried out in ~2.5 years 3000; 5-10 µm spectroscopy, R=3000 • 7 Core Programs • 3: Wide FOV; stable psf – 1: Form. & Evol. of Galaxies - Imaging • 4: Very sensitive NIR spectroscopy – 2: Form. & Evol. of Galaxies - Spectroscopy R=100-300 – 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+ 040901 CAA NGST Mather.ppt 17 040901 CAA NGST Mather.ppt 18 

Observing Speed Scaling Laws Yardstick Cameras vs. other observatories (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 040901 CAA NGST Mather.ppt 19 040901 CAA NGST Mather.ppt 20 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 040901 CAA NGST Mather.ppt 21 040901 CAA NGST Mather.ppt 22 The outlook for NGST in the Near IR What’s Changed since 1996? ASWG: Simon Lilly • Discovery of cosmic far IR background and its It is reasonable to be pessimistic about ground- sources shows dust re-emits half the luminosity of based observations for: (a) all deep observations at λ > 2.2 µm the universe (COBE, SCUBA, ISO) (b) systematic multi-line spectroscopy at 1 < λ < 2 • Discovery of large numbers of high redshift AGN µm (OH emission and H20 absorption) (c) anything requiring diffraction limited imaging and dusty Chandra X-ray sources shows black holes at λ < 1 µm or (wide-field) imaging at 1 < λ < 2 are significant part of total luminosity µm (c.f. AO) IR astronomy from the ground • Discovery of many unexpected planetary systems i.e. modest progress in programs involving: shows planetary formation is very important problem (d) the very highest redshifts (e) systematic diagnostic spectroscopy • Theoretical predictions that first objects in the (f) stellar (CO-bandhead) masses at high z universe were at redshift 20-30 ups the ante for (g) the energy sources in all except the most sensitivity and wavelength range 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, which are therefore likely to remain current (like Keck and HST), and reduce NGST advantage at λ < 2.5 µm, especially for spectroscopy 040901 CAA NGST Mather.ppt 24 

Scientists think Mid IR is worth the cost Engineers think the mid IR cost is reasonable • Dressler 1996 - yes: “Extension of this telescope’s wavelength • Telescope design not driven by mid IR 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 Committee strongly recommends this course, if it can be done • Test program not driven by mid IR without a substantial increase in cost.” – Telescope can be regulated at 50 K to stabilize it • ASWG (Ad Hoc Science Working Group): yes (unanimous vote on • Passive cooling design not driven by mid IR 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 the infrared, from the 10 µm currently planned to 30 µm, would • Detectors not major cost substantially improve its ability to study Kuiper Belt Objects – SIRTF sensitivity already adequate, small number of chips (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.” 040901 CAA NGST Mather.ppt 25 040901 CAA NGST Mather.ppt 26 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 • At z = 20, Ly α is 2.6 µm, but H α is 13.8 µm - we’d – Organic chemistry - astrobiology like to see it • First direct view of planetary-mass objects • To know something is primordial, we need to show – Easy shot for objects separated from bright stars it has NO metals or dust – Scientific precursor for TPF – [O III] 5007 A is strongest metal line expected for z > 9, • Comparative planetology - Solar System objects falls beyond 5 µm for z > 9 versus observed disks, “loose planets” 040901 CAA NGST Mather.ppt 27 040901 CAA NGST Mather.ppt 28 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, approved funding subject to successful detailed plan thermal, data system, …) and integration and test • CSA ~$50M (FY96) value of effort, gains 5 – NASA AO to provide NIRCAM observing time on NGST – ESA to provide NIRSPEC, based on US detectors and 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 • Exploring ESA contribution to spacecraft bus, based Steering Committee to define the concept and work 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 040901 CAA NGST Mather.ppt 29 040901 CAA NGST Mather.ppt 30 

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

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

Goals for Next Year (2002) NGST Monograph Series 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 NGST “Yardstick Mission” NGST MONOGRAPH NO. 3 Recommendations and Guidelines By John Mather, Bernard Seery, Peter Stockman, Pierre Bely, Richard Burg, Joseph Burt, Paul Geithner, – Phase 2 Contract Award By Matthew Greenhouse, John Isaacs, Pierre Bely, Charles Perrygo and Richard Burg Implications of the Mid-Infrared Harry Ferguson, Knox Long and Larry Petro July 1999 Capability for NGST May 2000 Next Generation Space Telescope By Project Study Office – ST ScI under separate NGST contract Pierre Y. Bely, Richard Burg, Steve Castgles, Matt Greenhouse, Goddard Space Flight Center D. Jacobson, K. Parrish, Larry Petro, Dave Redding November 1998 – International agreements in place and MOUs drafted Next Generation Space Telescope Next Generation Space Telescope NGST MONOGRAPH NO. 8 Project Study Office Goddard Space Flight Center Project Study Office The Radiation Environment for the • Technology Goddard Space Flight Center Next Generation’s Space Telescope By Next Generation Space Telescope Janet L. Barth (NASA/Goddard Space Flight Center) and 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 The Yardstick Mission NGST MONOGRAPH NO. 4 NGST NGST Performance Analysis By Pierre Y. Bely, Matt Lallo, Larry Petro Using Integrated Modeling Next Generation Space Telescope Integration and Testing – Wavefront algorithms demonstrated with PRC and both Keith Parrish, Kimberly Mehalick, Charles Perrygo By Project Study Office Gary Peterson, Robert Breault Gary Mosier and Dave Redding Goddard Space Flight Center Richard Burg Stawman Plan March 2000 July 1999 By high/low authority cryo mirrors Mike Menzel (Lockheed-Martin) July 1998 NGST MONOGRAPH NO. 9 NGST • Science Next Generation Space Telescope Next Generation Space Telescope Project Study Office Optical Component and System Testing Strawman Plan Project Study Office By Goddard Space Flight Center – ISWG review of the degree to which science program has Goddard Space Flight Center The Optical Testing Study Team Next Generation Space Telescope Project Study Office March 2000 Goddard Space Flight Center been preserved in rescope Next Generation Space Telescope Project Study Office Goddard Space Flight Center 040901 CAA NGST Mather.ppt 43 030601_NGST_origins.ppt 040901 CAA NGST Mather.ppt 44 44 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 040901 CAA NGST Mather.ppt 45 040901 CAA NGST Mather.ppt 46 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 040901 CAA NGST Mather.ppt 47