A Report of the SSB and BPA ad hoc Committee on the Review of Progress Toward the Decadal Survey Vision in New Worlds, New Horizons in Astronomy and Astrophysics
New Worlds, New Horizons in Astronomy and Astrophysics1 (NWNH), the report of the 2010 decadal survey of astronomy and astrophysics, put forward a vision for a decade of transformative exploration at the frontiers of astrophysics. This vision included mapping the first stars and galaxies as they emerge from the collapse of dark matter and cold clumps of hydrogen, finding new worlds in a startlingly diverse population of extrasolar planets, and exploiting the vastness and extreme conditions of the universe to reveal new information about the fundamental laws of nature. NWNH outlined a compelling program for understanding the cosmic order and for opening new fields of inquiry through the discovery areas of gravitational waves, time-domain astronomy, and habitable planets. Many of these discoveries are likely to be enabled by cyber-discovery and the power of mathematics, physics, and imagination. To help realize this vision, NWNH recommended a suite of innovative and powerful facilities, along with balanced, strong support for the scientific community engaged in theory, data analysis, technology development, and measurements with existing and new instrumentation. Already in the first half of the decade, scientists and teams of scientists working with these cutting-edge instruments and with new capabilities in data collection and analysis have made spectacular discoveries that advance the NWNH vision. This summary begins by presenting highlights at mid-decade of this remarkable scientific progress. The full report describes these key results in more detail, as well as a broad palette of other similarly exciting advancements in astronomy and astrophysics from the first half of this decade.
Following more than two decades of pioneering investment by the National Science Foundation (NSF) in high-risk, high-payoff technologies for precision measurement, the Advanced Laser Interferometry Gravitational-wave Observatory (LIGO) detected gravitational waves emitted by two distant black holes that collided and merged 1.3 billion years ago. This first direct detection of gravitational waves confirms Einstein’s prediction that gravitational waves exist and that they transport energy through a dynamic spacetime. The waveforms are consistent with general relativity and encode information about the warping of space and time near the event horizons of the black holes. The direct detection of gravitational waves enables new, stringent tests of general relativity and, as envisioned by NWNH, initiates the discovery area of gravitational wave astronomy for studying the most extreme events in the universe across cosmological distances.
The Kepler satellite has enabled the discovery of an extraordinary diversity of planets and planetary systems, and through a careful census of the demographics of these planets, we have learned that there must be billions of Earth-sized worlds throughout our galaxy. Determining the nature of these many planets is extremely challenging, but the combination of transit measurements and high-precision ground-based Doppler studies has identified seven that are similar in size and density to Earth. A ground-based survey has recently discovered an Earth-sized planet only 39 light years distant. The technology of coronagraphy has advanced, and it has already resulted in the direct images of massive planets around younger stars.
With the deepest surveys from the Hubble Space Telescope (HST), astronomers have discovered hundreds of galaxies from the first billion years of cosmic history, and radio experiments are approaching the whisper-like sensitivity needed to detect the primeval transition when ionization of hydrogen made the universe transparent to ultraviolet light. With these observations, scientists are beginning to probe the Cosmic Dawn of stars and galaxies. The combination of mid-infrared photometry from Spitzer and observations from HST has allowed identification of the very highest redshift galaxies whose emissions have shifted into the infrared wavelength range.
An important milestone was reached in 2015 with the completion of the Atacama Large Millimeter/submilli-
* NOTE: “Summary” reprinted from New Worlds, New Horizons: A Midterm Assessment, The National Academies Press, Washington, D.C., 2016, pp. 1-12.
1 National Research Council (NRC), 2010, New Worlds, New Horizons in Astronomy and Astrophysics, The National Academies Press, Washington, D.C.
meter Array (ALMA). ALMA has already enabled transformational results on planet formation in the observations of HL Tau and TW Hya, and has opened new windows on the study of the mass loss in evolved stars. ALMA has also yielded direct kinematic measurements of the masses of supermassive black holes in nearby galaxies, with a precision better than HST, among other major advances.
FINDING 2-4: The completion and successful operation of ALMA are a remarkable success and the culmination of significant investment by NSF through the Major Research Equipment and Facilities Construction (MREFC) program.
Similarly, the Daniel K. Inouye Solar Telescope (DKIST) has been fully funded by the MREFC program, and the community anticipates operation beginning in 2019, launching unprecedented capabilities for studying variability and magnetic phenomena in the Sun, with broad implications for plasma processes that underlie a wide variety of astrophysical phenomena throughout the universe.
The James Webb Space Telescope (JWST) is scheduled for launch in late 2018, now on track following a rebaselining in 2011, and it is expected to deliver the groundbreaking scientific capability that was envisioned when it received the highest ranking in the 2001 decadal survey.2 Its superb near-infrared sensitivity and angular resolution will allow detailed characterization of redshift z = 8-12 galaxies that are barely detectable with HST, as well as enable the discovery of the smallest of the universe’s first galaxies below the sensitivity limits of current telescopes. JWST will study in unprecedented detail the birth of stars and protoplanetary disks; may detect individual supernovae occurring in the first galaxies; will provide a huge leap in sensitivity for studies of relatively cool planets, including many targets identified by the Transiting Exoplanet Survey Satellite (TESS); and will provide radically new insights into the composition and structure of exoplanet atmospheres.
The above assessment of spectacular scientific productivity and progress in new instrumentation during the first half of the decade has to be tempered, however, by acknowledgment of budget realities and programmatic developments and the resultant limited progress toward the full program envisioned by NWNH.3
FINDING 2-1: The NSF Division of Astronomical Sciences (AST) budget through the first half of the decade has been approximately flat in real-year dollars. This budget reality is somewhat lower than that baselined by NSF for NWNH (approximately flat in inflation-adjusted dollars) and significantly lower than that assumed by NWNH (doubling in real-year dollars).
FINDING 2-2: For the NASA Astrophysics Division (APD), NWNH assumed a flat budget in inflation-adjusted dollars. The actual combined budget for NASA-APD and JWST has roughly tracked this assumption. However, the late-breaking schedule delay and associated budget increase of JWST have delayed the availability of funding for new initiatives by about 4 to 5 years.
FINDING 2-3: At the Department of Energy (DOE), support for astrophysics has been strong, and the budget reality has been close to the baseline plan presented in NWNH.
2 NRC, 2001, Astronomy and Astrophysics in the New Millennium, National Academy Press, Washington, D.C.
3 The survey provided some discussion of the priorities in scenarios in which less funding was available than was planned for. For NASA:
In the event that insufficient funds are available to carry out the recommended program, the first priority is to develop, launch, and operate WFIRST and to implement the Explorer program and core research program recommended augmentations. The second priority is to pursue the New Worlds Technology Development Program, as recommended, to mid-decade review by a decadal survey implementation advisory committee . . . to start LISA as soon as possible subject to . . . conditions . . . and to invest in IXO technology development. . . . The third priority is to pursue the CMB Technology Development Program . . . .
If the realized budget is truly flat in FY2010 dollars, the implication is that, given the obligation to provide operational costs for the forthcoming ALMA and ATST, there is no possibility of implementing any of the recommended program this decade—without achieving significant savings through enacting the recommendations of the first 2006 senior review process and/or implementing a second more drastic senior review before mid-decade. Because the termination of programs takes time to implement in practice, it will be difficult to accrue significant new savings before the end of the decade. Thus, in practice, very few new activities could be started within NSF-AST.
(See NRC, 2010, New Worlds, New Horizons.)
NWNH advocated a program of vigorous investment in research, new facilities, and human infrastructure. The highest-priority, new, large-scale ground-based facility—the Large Synoptic Survey Telescope (LSST)—is well along the path envisioned by NWNH for exploiting new technologies to address the most important astrophysics questions. LSST was awarded NSF MREFC funding in 2014 and, in combination with DOE construction of its 3.2-gigapixel camera, it is on schedule for first light in 2020 and a 10-year science survey commencing in 2022. LSST will survey the entire sky visible from its site in Chile more than 800 times in six colors. It will produce unprecedented catalogs of objects and of variable and transient events, exploring the NWNH discovery frontier of time-domain astronomy.
FINDING 3-1: LSST planning and construction have progressed well and are on schedule and within budget, successfully bringing together NSF funding, DOE funding, and private funding.
FINDING 3-2: Current projections for LSST performance and data products promise transformational scientific impact, as envisioned by NWNH. To realize the full scientific potential of this great new facility, funding that enables individual investigators and groups of investigators to deliver the scientific results will be critical.
The second-highest priority for the ground-based program, the Mid-Scale Innovations Program (MSIP), is a competed program intended to fund projects and activities that fall between the funding boundaries of the NSF Major Research Instrumentation program and the MREFC program. Midscale facilities had been funded in the past by NSF, but in an ad hoc manner, and NWNH recommended a program that would enable these activities to be regularly competed at an increased level of funding. NSF-AST created a funding stream for MSIP by combining several existing programs, including its previously unsolicited midscale program, the university radio observatories, and the optical telescope instrumentation program. With these funds, MSIP has supported an exciting set of highly ranked proposals in a heavily oversubscribed competition. The inability to fund the program at the level envisioned by NWNH, however, represents a significant loss of scientific opportunity.
FINDING 3-3: Implementation of the NWNH recommendation of MSIP has been possible only by subsuming previous programs into MSIP and by aggressive divestment from older facilities. The total NSF-AST funding for mid-scale initiatives has dropped by nearly a factor of two since the start of the decade, in stark contrast to the NWNH recommendation of MSIP as a new initiative that would expand opportunities for mid-scale projects.
FINDING 3-4: Despite limited resources for MSIP, NSF-AST has funded an exciting set of highly ranked proposals in a heavily oversubscribed competition. Some mid-scale programs recommended by NWNH have also moved forward with funding from DOE and from the NSF Physics and Polar Programs. The scientific promise of these projects confirms the NWNH expectation that a mid-scale program would enable major advances that respond nimbly to opportunities on a diverse range of science topics.
Participation in one of the U.S. Giant Segmented Mirror Telescope (GSMT) projects was the third-ranked large priority in ground-based astronomy. The highly constrained budget environment has prevented any significant involvement by NSF-AST in either of the two GSMT projects so far this decade. Both projects are proceeding with private funding and with support from international partners. Site preparation and initial construction activities have begun for the two projects, and both are working to engage the broader U.S. science community.
FINDING 3-5: The Giant Magellan Telescope (GMT) and Thirty Meter Telescope (TMT) projects have both made major progress since 2010, and both offer technically feasible routes to achieving the GSMT science goals set forth by NWNH. However, programmatic hurdles remain, and neither project has secured the funding needed to complete construction at its full intended scope. NSF budget constraints have prevented NSF’s implementation of the NWNH recommendation that NSF-AST select one partner and participate in GSMT construction.
An Atmospheric Cerenkov Telescope Array (ACTA) was ranked fourth in the ground-based, large-scale projects in NWNH. The leading ground-based teams in this field worldwide have joined to form the Cerenkov Telescope Array (now CTA). With support from NSF, progress has been made in technology development addressing new telescope concepts and in maturing the array design. If sufficient funding is secured, construction could proceed as early as 2016. The U.S. groups have developed a plan for participation in CTA, but at a lower level than that originally proposed at the time of NWNH.
FINDING 3-7: U.S. participation in CTA at budget levels below those recommended by NWNH would still have a significant positive impact on the scientific productivity of the observatory and would give U.S. scientists leadership roles in the CTA program. If the U.S. CTA proposal competes successfully in the MSIP and NSF-Physics mid-scale programs, the NWNH recommendation can be implemented, albeit at a level lower than anticipated in 2010.
NWNH had a single recommendation for a medium-scale, ground-based facility, the Cerro Chajnantor Atacama Telescope (CCAT, formerly the Cornell-Caltech Atacama Telescope), a submillimeter-wave survey telescope. The NSF Portfolio Review placed funding for MSIP at a higher priority than funding for the construction of CCAT. As a result, NSF-AST did not provide directed funding for CCAT. The CCAT consortium subsequently submitted a proposal to the MSIP competition, but this proposal was not funded. In the current budget climate, NSF will only contribute to CCAT through future MSIP competitions. The project is now being rebaselined, and a number of potential international partners have expressed interest, including the host country of Chile.
FINDING 3-8: In the current budget climate, NSF-AST has not been able to fund CCAT beyond an initial contribution to the design. This is because the NSF-AST budget increases anticipated by NWNH did not materialize, and NSF-AST, consistent with the Portfolio Review’s guidance, gave higher priority to funding the MSIP program within the constraints imposed by the budget.
While NWNH placed strong emphasis on expanding support for individual investigator grants, the core grants programs have declined in real-year dollars and dropped still further in purchasing power over the first half of the decade, following the trends of the overall NSF-AST budget. This reduction in funding has contributed to a substantial decline in grant funding rates, significantly impacting the scientific productivity of the community. NWNH also specifically recommended a number of small-scale activities for enhancing the scientific productivity of the ground-based astronomy program. One of these activities, augmented U.S. access to Gemini, occurred at no cost to NSF because the United Kingdom withdrew from the partnership. With the exceptions of the augmentation of U.S. participation in Gemini and 2 years of funding for Theory and Computation Networks, NSF-AST has been unable to achieve any of these recommendations, and all of these programs are now funded at a lower level than they were in 2011.
FINDING 3-9: Because the NSF-AST budget did not grow at the rate assumed by NWNH, NSF-AST has not implemented the majority of the NWNH recommendations for small-scale projects or for expanded support for individual investigator programs. Support for the individual investigator programs has decreased during the first half of the decade.
The shrinking of small- and mid-scale investment at NSF is symptomatic of a more general problem: in a flat NSF-AST budget, the operations costs of powerful new facilities are squeezing out funding for mid-scale and individual investigator programs. Recognizing the need to divest from older facilities to release funds for new ones, NWNH recommended that NSF conduct a senior review of all its existing facilities. NSF-AST responded with a full Portfolio Review and, thereby, received advice from the community on the prioritization of the existing facilities in the context of its overall program. NSF-AST is in the process of implementing a vigorous divestment program. However, divestment is a challenge, and even with the recommended divestment, the projected NSF-AST budgets are not sufficient to fund both the operations of the upcoming new facilities and their research programs.
The expected operations costs for ALMA, DKIST, and LSST by the beginning of the next decade will, in the presence of a flat NSF-AST budget, severely constrict the already squeezed mid-scale, small, and individual investigator programs and limit the community’s ability to sustain a robust ground-based astronomy and astro-
physics program. The remarkable scientific progress of the first half of the decade was made possible by capital investment in previous decades. Without funding for a balanced program that realizes the benefits of this decade’s capital investment, the visionary scientific program put forward by NWNH will not be realized.
FINDING 3-12: Even following the divestment recommended by the Portfolio Review, the operations costs of ALMA, DKIST, and LSST will compromise the ability of the U.S. community to reap the scientific return from its premier ground-based facilities. Moderate increases in the NSF-AST budget would have highly leveraged science impact as a consequence of these powerful new facilities.
RECOMMENDATION 3-1: NSF should proceed with divestment from ground-based facilities that have a lower scientific impact, implementing the recommendations of the NSF Portfolio Review, which is essential to sustaining the scientific vitality of the U.S. ground-based astronomy program as new facilities come into operation.
RECOMMENDATION 3-2: NSF and the National Science Board should consider actions that would preserve the ability of the astronomical community to fully exploit NSF’s capital investments in ALMA, DKIST, LSST, and other facilities. Without such action, the community will be unable to do so because at current budget levels the anticipated facilities operations costs are not consistent with the program balance that ensures scientific productivity.
The Wide-Field Infrared Survey Telescope (WFIRST) was NWNH’s highest-ranked large space initiative, with a science program that incorporated precision measurements of cosmic acceleration from large imaging, spectroscopic, and supernova monitoring surveys; statistical characterization of the demographics of exoplanet systems from a gravitational microlensing survey of the galactic bulge; a large area survey of the galactic plane; and a wide range of galactic and extragalactic investigations enabled by guest investigator studies of the survey data sets and by a Guest Observer (GO) program. Substantial progress has been made in the first half of the decade toward realizing WFIRST, although its scope, design, and launch date have changed since the original concept put forward by NWNH. Anticipating the successful completion of JWST, WFIRST entered Phase A in fiscal year (FY) 2016 and is moving toward launch in 2025. While the formal mission start was delayed 3 years beyond NWNH’s anticipated start in 2013 and 5 years beyond NWNH’s anticipated launch in 2020 as a result of the delayed completion of JWST, the extended pre-formulation phase allowed substantial technology development, most importantly the adoption of larger-format infrared detectors and the 2.4-meter telescope assembly that became available in 2012. A vigorous program in coronagraphy technology development, coupled with the 2.4-meter telescope assets, has extended WFIRST’s capabilities in the study of exoplanets to include the exciting prospect of direct detection of large planets orbiting nearby stars.
FINDING 4-1: The 2.4-meter telescope, larger infrared detectors, and addition of a coronagraph make the 2016 design of WFIRST an ambitious and powerful facility that will significantly advance the scientific program envisioned by NWNH, from the atmospheres of planets around nearby stars to the physics of the accelerating universe.
The WFIRST coronagraph responds to an opportunity that arose after NWNH—the availability of a 2.4-meter telescope, which enables a space-borne coronagraph to carry out an exciting exoplanet science program. It also demonstrates technology needed for future missions capable of imaging Earth-like planets around nearby stars and is therefore responsive to the NWNH recommendation of a New Worlds Technology Development Program. Given the remarkable developments in exoplanet discovery and the emphasis on this science area in NWNH, the committee agrees that the addition of the coronagraph represents an appropriate shift in emphasis for WFIRST’s science program. However, some of the wide-field survey capabilities envisioned by NWNH have been deemphasized and, as noted by Evaluation of the Implementation of WFIRST/AFTA in the Context of New Worlds, New Horizons in Astronomy and Astrophysics,4 with the larger mirror and the coronagraph, the risk for cost growth of the mission is now greater.
4 NRC, 2014, Evaluation of the Implementation of WFIRST/AFTA in the Context of New Worlds, New Horizons in Astronomy and Astrophys-
FINDING 4-5: Coronagraph technology has matured rapidly over the past 2 years, addressing one of the key recommendations of the 2014 report Evaluation of the Implementation of WFIRST/AFTA in the Context of New Worlds, New Horizons in Astronomy and Astrophysics. The coronagraph remains a schedule, cost, and technical risk for WFIRST.
An independent estimate of the 2015 WFIRST Design Reference Mission projected its cost at $2.3 billion to $2.5 billion (FY2015 dollars) and found that the cost growth since the NWNH estimate was fully attributable to the coronagraph, the GO program, and inflation. However, changes in the mission design leading up to Key Decision Point A led to an increase in the estimated mission cost of approximately 25 percent ($550 million).
FINDING 4-2: Because of the risk of cost growth, the concern raised in Evaluation of the Implementation of WFIRST/AFTA that WFIRST could distort the NASA program balance remains a concern. In addition, the delay in the implementation of WFIRST over the schedule anticipated in NWNH means that cost growth in WFIRST would limit options for the next decadal survey.
RECOMMENDATION 4-1: Prior to Key Decision Point B, NASA should commission an independent technical, management, and cost assessment of the Wide-Field Infrared Survey Telescope, including a quantitative assessment of the incremental cost of the coronagraph. If the mission cost estimate exceeds the point at which executing the mission would compromise the scientific priorities and the balanced astrophysics program recommended by the 2010 report New Worlds, New Horizons in Astronomy and Astrophysics, then NASA should descope the mission to restore the scientific priorities and program balance by reducing the mission cost.
NASA’s Explorer program has a distinguished history of high scientific impact through the deployment of relatively low-cost missions that can respond to opportunities on a short timescale. The Explorer missions also provide a strong connection between NASA and the university community, with benefits to intellectual cross-fertilization and the training of students and future mission Principal Investigators. NWNH recommended a significant augmentation of the Explorer program—doubling, or more than doubling, the number of mission selections per decade. Like the mid-scale program at NSF, limited budgets have had a very large impact on NASA’s Explorer program. The first Announcement of Opportunity for a Mission of Opportunity (MoO) was canceled before selection. The second round, including calls for both a Smaller Explorer (SMEX) and an MoO, has so far enabled three SMEX and two MoO Phase A studies to begin. The NASA-APD plan includes a total of four opportunities and selections of Explorers, each with an MoO, during this decade. The committee is concerned that growth in NASA-APD’s large programs may prevent even this reduced implementation of the Explorer program augmentation. Maintaining the budget profile is critical for this important program to succeed as envisioned by NWNH.
RECOMMENDATION 4-3: NASA’s Astrophysics Division should execute its current plan, as presented to the committee, of at least four Explorer Announcements of Opportunity during the 2012-2021 decade, each with a Mission of Opportunity call, and each followed by mission selection.
NASA-APD’s intent to execute four Explorer opportunities this decade, despite budgetary constraints, is commendable. If budgets increase, restoring the full Explorer augmentation would be consistent with the priorities of NWNH.
The third-ranked large-class space mission recommended in NWNH was the Laser Interferometer Space Antenna (LISA). Because of JWST’s cost increase and LISA’s ranking, it became clear early in the decade that NASA would not have the resources to begin a gravitational wave space mission in the 2010s. This led to the European Space Agency’s (ESA’s) decision to proceed without U.S. involvement, which in turn led to the loss of science and technology funding directed toward the mission in the United States. The ESA-led LISA Pathfinder (LPF), a mission intended to demonstrate certain technologies needed by a space-based gravitational wave detector, was launched in December 2015, several years behind schedule. NWNH’s ranking of LISA was based on the
ics, The National Academies Press, Washington, D.C.
expectation of an equal ESA-NASA partnership, and NWNH identified a decision point based on the outcome of LPF that would trigger a mid-decade assessment of whether to proceed with LISA.
The dramatic direct detection of gravitational waves by LIGO greatly strengthens the scientific case for a space-based mission by establishing gravitational wave astronomy as a revolutionary new probe of astrophysical phenomena. LISA would explore the source-rich millihertz band that is inaccessible from the ground, allowing for the detection of massive galactic black holes and intermediate-mass black holes throughout the universe, and providing unique insight into early black hole–galaxy coevolution. Relative to LIGO, typical LISA detections would have higher signal-to-noise ratios and execute many more cycles in band, allowing for more precise measurements and significantly stronger tests of general relativity. The early operation of LPF has been successful, and its results have demonstrated the feasibility of many of the key technologies needed by LISA.5 The committee believes that NASA and ESA together should rethink their strategy for LISA and take steps to reduce mission risk and to maximize its scientific return as recommended below.
RECOMMENDATION 4-4: NASA should restore support this decade for gravitational wave research that enables the U.S. community to be a strong technical and scientific partner in the European Space Agency (ESA)-led L3 mission, consistent with the Laser Interferometer Space Antenna’s high priority in the 2010 report New Worlds, New Horizons in Astronomy and Astrophysics (NWNH). One goal of U.S. participation should be the restoration of the full scientific capability of the mission as envisioned by NWNH.
The fourth-priority large-scale mission in NWNH was the International X-ray Observatory (IXO). Recognizing that it was unlikely that IXO could proceed in the 2010s, NWNH recommended a substantial technology development program in preparation for the next decade. However, if IXO were selected as ESA’s first large mission, then NWNH recommended that NASA accelerate the program with guidance from the community. Because of the budget constraints early in this decade in the United States, ESA is instead proceeding with Athena, an ESA-led X-ray mission that is reduced in scope but whose capabilities address many of the science goals of IXO, as its second large mission. The committee acknowledges that Athena enables a compelling subset of the science envisioned for IXO and that participation in Athena therefore addresses the high priority given to IXO science by NWNH.
RECOMMENDATION 4-5: NASA should proceed with its current plan to participate in Athena, with primary contributions directed toward enhancing the scientific capabilities of the mission.
In the category of space-based, medium-scale activities, NWNH recommended two technology development programs, the New Worlds Technology Development (NWTD) Program and an Inflation Probe Technology Development (IPTD) Program. Advancing the technology of starlight suppression was an important goal of NWTD, along with exploring options for a future mission for studying habitable exoplanets. NWNH recommended a mid-decade review and selection of appropriate starlight suppression technology for full development. Events played out differently than anticipated, and the WFIRST coronagraph is the main activity aimed at NWTD, satisfying some aspects of the broader program envisioned by NWNH. The WFIRST coronagraph, combined with other smaller programs still supported by NASA-APD, represents a decadal investment larger than that envisioned by NWNH. The committee believes that this is an appropriate response to the rapid advancements in exoplanet science but reiterates that WFIRST cost growth and its effect on scientific prioritization and program balance is a major concern.
Measuring the B-modes of the cosmic microwave background (CMB) polarization caused by gravitational waves created during inflation is the major long-term goal of IPTD, as well as neutrino mass, mapping large-scale structure with gravitational lensing, and reionization science. Measurements by Planck, ground-based instruments, and balloon-borne instruments continue to improve and to place increasingly stringent limits on the amplitude of the B-modes and therefore on the energy scale associated with inflation. Enormous progress has been made in the capabilities of detector systems and other technologies needed for improved sensitivity of polarization measure-
5 M. Armano, H. Audley, G. Auger, J.T. Baird, M. Bassan, P. Binetruy, M. Born, et al., 2016, Sub-femto-g free fall for space-based gravitational wave observatories: LISA pathfinder results, Physical Review Letters 116(23):231101-1-231101-10.
ments. The CMB community has recently defined a program, CMB-S4, to identify science goals and instrument requirements for the next generation of experiments, with potential support from NASA, NSF, and DOE. These activities are well aligned with the NWNH recommendation for IPTD, with all three agencies supporting technology development and precursor science on a path to a future space mission.
As for the ground-based program, NWNH recommended a slate of small space-based projects and activities, consistent with its emphasis on program balance. Despite the challenging budget environment, NASA has roughly maintained the funding level of its core and research programs, although the committee notes that this was preceded by a decline in overall funding for individual investigator grants at the end of the past decade. The greatest challenge to the maintenance of program balance is NASA-APD’s investment in its large missions, JWST and WFIRST, and the risk of growth in their cost.