Next Generation Great Observatories

• Next Generation Great Observatories are coordinated, multi-facility systems integrating third-generation gravitational-wave detectors, large-aperture UVOIR telescopes, and precision radio arrays.
• They employ innovative designs—such as the Einstein Telescope, Cosmic Explorer, and ATLAST—with order-of-magnitude sensitivity improvements to explore low-frequency and high-resolution regimes.
• Their systems-level approach emphasizes interoperability, robust calibration, advanced computing pipelines, and multimessenger coordination to enable transformative astrophysical discoveries.

Next Generation Great Observatories denotes a class of future flagship facilities and coordinated networks designed to extend astronomy into regimes inaccessible to current instruments. In the supplied literature, the term is used explicitly for third-generation ground-based gravitational-wave observatories and, more broadly, for future astrophysics flagships and major ground-based facilities whose scientific return depends on architecture, calibration, operations, and governance. Within that landscape, the Einstein Telescope and Cosmic Explorer define a worldwide 3G gravitational-wave network with roughly an order-of-magnitude improvement in strain sensitivity and access down to a few hertz, while ATLAST represents a family of 8–16.8 m UVOIR observatory concepts built around diffraction-limited performance at 500 nm. The same body of work also treats next-generation radio astrometric facilities, multimessenger follow-up systems, and cross-community operational requirements as integral parts of the broader observatory ecosystem (Reitze et al., 2021, 0904.0941, Rioja et al., 2019).

1. Defining characteristics and historical setting

The modern Next Generation Great Observatory concept is organized around a combination of sensitivity gains, broader spectral or messenger coverage, system-level stability, and interoperability with other facilities. For gravitational-wave astronomy, the GWIC 3G Subcommittee frames next-generation observatories as facilities that must extend the observational horizon “well beyond” current detectors, with conception-to-operations timescales of 15–20 years, a globally coordinated network, sustained R&D, and a commensurate revolution in computing and data analysis (Reitze et al., 2021). For UVOIR astronomy, ATLAST is described as a versatile flagship observatory concept with transformational sensitivity, stability, and versatility, designed to “far outlast the vision of current-day astronomers” through modular instruments, two simultaneous foci, and servicing-compatible architecture (0904.0941).

A recurring theme across the literature is that “great observatory” status is not defined solely by aperture or raw strain sensitivity. It also depends on whether a facility can function as a mature astronomical probe: wide field where required, stable calibration, rapid response, data products suitable for large communities, and interfaces to complementary observatories. In gravitational-wave astronomy this means non-colocated detectors with complementary geometries; in UVOIR astronomy it means diffraction-limited imaging, high-contrast imaging, and instrument modularity; in planetary and time-domain contexts it means moving-target support, high-cadence modes, and robust target-of-opportunity operations (Kalogera et al., 2021, Hammel et al., 2020).

The historical framing is also programmatic. The first direct detection of gravitational waves in 2015 motivated plans for facilities that can turn detection into precision, high-throughput astronomy, while the Hubble-to-JWST transition is used as a lesson in how early scientific engagement changes requirements and first-light capability. HST launched without moving-target tracking; JWST, after early and continuous involvement of Solar System scientists, incorporated moving-target tracking, ephemeris-driven operations, and bright-object strategies from the outset (Reitze et al., 2021, Hammel et al., 2020).

2. Third-generation gravitational-wave observatories as a great-observatory pillar

The 3G ground-based gravitational-wave program is anchored by two flagship efforts: the Einstein Telescope in Europe and Cosmic Explorer in the United States. ET is described as a triangular underground facility with 10 km sides and six V-shaped interferometers, implementing a “xylophone” concept in which co-located interferometers are band-optimized: a cryogenic low-frequency instrument to beat suspension/coating thermal and Newtonian gravity noise, and a room-temperature high-frequency instrument to push shot-noise-limited sensitivity at kilohertz frequencies. CE is described as one or two L-shaped overground interferometers with 40 km arms, using longer baselines, high circulating power, and frequency-dependent squeezing for broadband quantum-noise reduction (Kalogera et al., 2021).

The key design target is sensitivity from approximately $3$–$5$ Hz up to beyond $5$ kHz, with an order-of-magnitude improvement in amplitude spectral density relative to Advanced LIGO/Virgo/KAGRA across the band. ET’s underground siting is intended to mitigate seismic and Newtonian gravity noise, while CE’s longer arms reduce displacement-to-strain and high-frequency quantum shot noise. Together they realize complementary geometries that, in network, improve sky localization, polarization recovery, and parameter estimation (Kalogera et al., 2021).

The sensitivity–science connection is expressed through standard waveform relations. For a compact-binary inspiral, the leading-order frequency-domain amplitude scales as

$$|h(f)| \approx \frac{1}{d_L}\sqrt{\frac{5}{24}}\pi^{-2/3}\left(\frac{G\mathcal{M}_c}{c^3}\right)^{5/6} f^{-7/6},$$

with chirp mass

$\mathcal{M}_c=(m_1m_2)^{3/5}(m_1+m_2)^{-1/5},$

and matched-filter signal-to-noise ratio

$$\rho^2 = 4 \int_{f_{\rm low}}^{f_{\rm high}} \frac{|h(f)|^2}{S_n(f)}\,df.$$

Lowering $f_{\rm low}$ into the few-hertz regime increases $\rho$ and parameter precision, especially for binary neutron stars and other lower-mass systems that spend substantial time at low frequencies (Reitze et al., 2021).

The same framework governs neutron-star matter inference. The tidal deformability

$$\Lambda = \frac{2}{3}k_2\left(\frac{c^2R}{GM}\right)^5$$

enters the waveform phase, and the tidal contribution scales as

$$\psi_{\rm tidal}(f)\propto -\frac{39}{2}\Lambda(\pi M f)^{5/3},$$

so early low-frequency measurements and high-SNR inspirals are essential to equation-of-state studies (Reitze et al., 2021).

3. Quantitative science reach, discovery space, and astrophysical floors

The Science Book describes a network capable of accumulating catalogs of hundreds of thousands of binary black holes per year and millions of binary neutron stars across cosmic history, with stellar-mass BBH detections out to $5$0–$5$1 and BNS detections to $5$2–$5$3. Many loud events are expected to have network SNRs in the hundreds to thousands, enabling precision population inference, strong-field tests of gravity, and large standard-siren catalogs (Kalogera et al., 2021).

This reach changes compact-object astrophysics from source-by-source discovery to statistical cartography. Hierarchical modeling of mass, spin, and eccentricity distributions can trace formation channels and their redshift evolution, while low-frequency sensitivity opens the discovery space for intermediate-mass black holes. The Science Book states that low-frequency sensitivity to $5$4–$5$5 Hz is required to chart $5$6–$5$7 mergers, and that 3G can detect equal-mass $5$8 binaries at $5$9 in the inspiral regime (Kalogera et al., 2021).

At still higher redshift, higher-order multipoles become critical. For heavy stellar black-hole binaries with total source-frame mass $5$0–$5$1 at $5$2–$5$3, ET’s $5$4 Hz and CE’s $5$5 Hz materially affect detectability because the dominant $5$6 mode can fall below the low-frequency cutoff. Using IMRPhenomXPHM, the analysis finds that for systems of approximately $5$7 the network can confidently infer a minimum redshift of at least $5$8, and for systems of approximately $5$9 a minimum redshift of at least $$|h(f)| \approx \frac{1}{d_L}\sqrt{\frac{5}{24}}\pi^{-2/3}\left(\frac{G\mathcal{M}_c}{c^3}\right)^{5/6} f^{-7/6},$$0, provided higher-order modes contribute to the signal and parameter estimation (Fairhurst et al., 2023).

The cosmological program is comparably quantitative. For bright sirens, the Science Book states that $$|h(f)| \approx \frac{1}{d_L}\sqrt{\frac{5}{24}}\pi^{-2/3}\left(\frac{G\mathcal{M}_c}{c^3}\right)^{5/6} f^{-7/6},$$1 events can reach $$|h(f)| \approx \frac{1}{d_L}\sqrt{\frac{5}{24}}\pi^{-2/3}\left(\frac{G\mathcal{M}_c}{c^3}\right)^{5/6} f^{-7/6},$$2 on $$|h(f)| \approx \frac{1}{d_L}\sqrt{\frac{5}{24}}\pi^{-2/3}\left(\frac{G\mathcal{M}_c}{c^3}\right)^{5/6} f^{-7/6},$$3 and $$|h(f)| \approx \frac{1}{d_L}\sqrt{\frac{5}{24}}\pi^{-2/3}\left(\frac{G\mathcal{M}_c}{c^3}\right)^{5/6} f^{-7/6},$$4 events reach $$|h(f)| \approx \frac{1}{d_L}\sqrt{\frac{5}{24}}\pi^{-2/3}\left(\frac{G\mathcal{M}_c}{c^3}\right)^{5/6} f^{-7/6},$$5, while 3G networks will supply thousands of such events with improved inclination–distance de-degeneracy from precession and higher harmonics. On the dense-matter side, forecasts indicate neutron-star radii determined to $$|h(f)| \approx \frac{1}{d_L}\sqrt{\frac{5}{24}}\pi^{-2/3}\left(\frac{G\mathcal{M}_c}{c^3}\right)^{5/6} f^{-7/6},$$6–$$|h(f)| \approx \frac{1}{d_L}\sqrt{\frac{5}{24}}\pi^{-2/3}\left(\frac{G\mathcal{M}_c}{c^3}\right)^{5/6} f^{-7/6},$$7 km for multiple NSs in BNSs at $$|h(f)| \approx \frac{1}{d_L}\sqrt{\frac{5}{24}}\pi^{-2/3}\left(\frac{G\mathcal{M}_c}{c^3}\right)^{5/6} f^{-7/6},$$8 Mpc with $$|h(f)| \approx \frac{1}{d_L}\sqrt{\frac{5}{24}}\pi^{-2/3}\left(\frac{G\mathcal{M}_c}{c^3}\right)^{5/6} f^{-7/6},$$9–$\mathcal{M}_c=(m_1m_2)^{3/5}(m_1+m_2)^{-1/5},$0 per source, and the $\mathcal{M}_c=(m_1m_2)^{3/5}(m_1+m_2)^{-1/5},$1–$\mathcal{M}_c=(m_1m_2)^{3/5}(m_1+m_2)^{-1/5},$2 kHz band is identified as essential for post-merger spectral peaks and hot supranuclear matter (Kalogera et al., 2021).

Catalog-level inference extends into cosmic dawn. In a one-year CE+ET scenario restricted to $\mathcal{M}_c=(m_1m_2)^{3/5}(m_1+m_2)^{-1/5},$3, hierarchical Bayesian inference with a Bayesian deep-learning emulator separates Population III from Population I/II black-hole mergers and excludes a Population III merger rate of zero at nearly $\mathcal{M}_c=(m_1m_2)^{3/5}(m_1+m_2)^{-1/5},$4 credibility. In the same framework, the spectral index of the Pop III initial mass function is constrained to within roughly $\mathcal{M}_c=(m_1m_2)^{3/5}(m_1+m_2)^{-1/5},$5 of the true value, and the log of the star-formation-rate density to within $\mathcal{M}_c=(m_1m_2)^{3/5}(m_1+m_2)^{-1/5},$6 over redshifts $\mathcal{M}_c=(m_1m_2)^{3/5}(m_1+m_2)^{-1/5},$7 to $\mathcal{M}_c=(m_1m_2)^{3/5}(m_1+m_2)^{-1/5},$8 (Plunkett et al., 25 Apr 2025).

A central caveat is that improved detector sensitivity does not remove astrophysical foregrounds. For the stochastic background, the unresolvable CBC foreground is described as an astrophysical floor at $\mathcal{M}_c=(m_1m_2)^{3/5}(m_1+m_2)^{-1/5},$9–$$\rho^2 = 4 \int_{f_{\rm low}}^{f_{\rm high}} \frac{|h(f)|^2}{S_n(f)}\,df.$$0 at $$\rho^2 = 4 \int_{f_{\rm low}}^{f_{\rm high}} \frac{|h(f)|^2}{S_n(f)}\,df.$$1 Hz, with $$\rho^2 = 4 \int_{f_{\rm low}}^{f_{\rm high}} \frac{|h(f)|^2}{S_n(f)}\,df.$$2 dex uncertainty today, and remains detectable to $$\rho^2 = 4 \int_{f_{\rm low}}^{f_{\rm high}} \frac{|h(f)|^2}{S_n(f)}\,df.$$3 Hz for the combined BNS+NSBH population. Many cosmological SGWB models in the $$\rho^2 = 4 \int_{f_{\rm low}}^{f_{\rm high}} \frac{|h(f)|^2}{S_n(f)}\,df.$$4–$$\rho^2 = 4 \int_{f_{\rm low}}^{f_{\rm high}} \frac{|h(f)|^2}{S_n(f)}\,df.$$5 Hz band are therefore impeded unless their amplitudes exceed both the instrumental sensitivity and this CBC floor, or can be distinguished statistically through spectral or anisotropy information (Bellie et al., 2023).

4. Multimessenger networks, localization, and optical follow-up

The 3G program is conceived as part of a broader multimessenger system. The Science Book explicitly couples the 3G network to LISA, Vera C. Rubin Observatory, JWST/ELTs, SKA, Athena/Lynx, and next-generation neutrino detectors, emphasizing that robust localization, precise distance inference, and polarization recovery require a distributed network rather than a single observatory (Kalogera et al., 2021).

For binary neutron stars, the Rubin follow-up forecasts quantify the transition from detection to systematic optical discovery. With ET operating alone, Rubin is expected to detect about ten to a hundred kilonovae per year. In a network with current GW detectors, the joint optical yield improves by a factor of about $$\rho^2 = 4 \int_{f_{\rm low}}^{f_{\rm high}} \frac{|h(f)|^2}{S_n(f)}\,df.$$6. Under a fiducial $$\rho^2 = 4 \int_{f_{\rm low}}^{f_{\rm high}} \frac{|h(f)|^2}{S_n(f)}\,df.$$7, BLh EOS, Gaussian-mass population, and realistic target-of-opportunity strategy, ET-triangle alone yields $$\rho^2 = 4 \int_{f_{\rm low}}^{f_{\rm high}} \frac{|h(f)|^2}{S_n(f)}\,df.$$8 ten-year KN detections in the $$\rho^2 = 4 \int_{f_{\rm low}}^{f_{\rm high}} \frac{|h(f)|^2}{S_n(f)}\,df.$$9 criteria, ET-triangle+LVKI yields $f_{\rm low}$0, ET-triangle+1 CE yields $f_{\rm low}$1, and ET-triangle+2 CE yields $f_{\rm low}$2, although the last configuration can exceed Rubin’s time allocation unless localization cuts are tightened (Loffredo et al., 2024).

Sky localization is therefore an operational resource, not only a parameter-estimation metric. The same study shows that wide baselines dominate localization once CE enters the network: ET-triangle + 2 CE yields $f_{\rm low}$3 events localized to $f_{\rm low}$4 in ten years for a uniform-mass, $f_{\rm low}$5, BLh population, and the presence of CE dramatically increases the number of sources with relative distance errors below $f_{\rm low}$6, including several dozen with $f_{\rm low}$7 uncertainty (Loffredo et al., 2024).

The role of geometry is sharpened by the LIGO-India study. For BNS mergers out to $f_{\rm low}$8, replacing the 20 km CE detector in a CE+CE+ET network with LIGO-India at $f_{\rm low}$9 sensitivity yields nearly identical localization performance: over $\rho$0 events within $\rho$1, $\rho$2 within $\rho$3, and $\rho$4 events with luminosity-distance uncertainties under $\rho$5, including $\rho$6 under $\rho$7. Both CE4020ET and CE40I$\rho$8ET provide $\rho$9 early-warning detections up to $$\Lambda = \frac{2}{3}k_2\left(\frac{c^2R}{GM}\right)^5$$0 minutes before merger with localization areas $$\Lambda = \frac{2}{3}k_2\left(\frac{c^2R}{GM}\right)^5$$1. The paper identifies the reason directly: the factor-of-five shorter arms are offset by a fourfold increase in baseline relative to a second CE in the United States, preserving localization accuracy while sacrificing reach for some other science goals such as Population III BBHs at $$\Lambda = \frac{2}{3}k_2\left(\frac{c^2R}{GM}\right)^5$$2 and neutron-star mergers at $$\Lambda = \frac{2}{3}k_2\left(\frac{c^2R}{GM}\right)^5$$3 (Pandey et al., 2024).

These studies make clear that multimessenger performance depends on network geometry, cadence strategy, and follow-up time budgets as much as on single-detector strain sensitivity. A plausible implication is that the observatory concept is intrinsically systems-level: the scientific yield is set by how detection, localization, alerting, and external follow-up are coupled.

5. Large-aperture UVOIR space observatories: the ATLAST case

ATLAST is a family of UVOIR flagship observatory concepts with primary apertures in the $$\Lambda = \frac{2}{3}k_2\left(\frac{c^2R}{GM}\right)^5$$4–$$\Lambda = \frac{2}{3}k_2\left(\frac{c^2R}{GM}\right)^5$$5 m class, wavelength coverage from approximately $$\Lambda = \frac{2}{3}k_2\left(\frac{c^2R}{GM}\right)^5$$6 to $$\Lambda = \frac{2}{3}k_2\left(\frac{c^2R}{GM}\right)^5$$7 nm, diffraction-limited performance at $$\Lambda = \frac{2}{3}k_2\left(\frac{c^2R}{GM}\right)^5$$8 nm with system wavefront error of approximately $$\Lambda = \frac{2}{3}k_2\left(\frac{c^2R}{GM}\right)^5$$9 nm rms, and Sun–Earth L2 operation. Three point designs were developed: ATLAST-8m with a monolithic primary mirror, ATLAST-9.2m with a segmented primary sized for an EELV-class fairing, and ATLAST-16.8m with 36 large segments arranged in three rings (0904.0941).

The architecture is explicitly dual-tracked. The 8 m option uses a solid meniscus glass primary mirror launched as a single piece, a modified HST-style optical bench, and a thermal system in which a scarfed sunshield isolates the OTA while zonal heaters regulate it at $$\psi_{\rm tidal}(f)\propto -\frac{39}{2}\Lambda(\pi M f)^{5/3},$$0. The 9.2 m and 16.8 m concepts use segmented mirrors, continuous wavefront sensing and control, and, for the largest design, a laser-metrology “optical truss” derived from SIM-like distance gauges to measure each segment’s six degrees of freedom relative to the secondary mirror at up to kilohertz rates (0904.0941).

The scientific drivers are flagship-level. For exoEarth characterization, the white paper assumes an inner working angle of $$\psi_{\rm tidal}(f)\propto -\frac{39}{2}\Lambda(\pi M f)^{5/3},$$1 at $$\psi_{\rm tidal}(f)\propto -\frac{39}{2}\Lambda(\pi M f)^{5/3},$$2 nm, $$\psi_{\rm tidal}(f)\propto -\frac{39}{2}\Lambda(\pi M f)^{5/3},$$3, 3-zodi backgrounds, starlight suppression of at least $$\psi_{\rm tidal}(f)\propto -\frac{39}{2}\Lambda(\pi M f)^{5/3},$$4 mag ($$\psi_{\rm tidal}(f)\propto -\frac{39}{2}\Lambda(\pi M f)^{5/3},$$5), and counts stars for which an $$\psi_{\rm tidal}(f)\propto -\frac{39}{2}\Lambda(\pi M f)^{5/3},$$6 spectrum with SNR $$\psi_{\rm tidal}(f)\propto -\frac{39}{2}\Lambda(\pi M f)^{5/3},$$7 at the O$$\psi_{\rm tidal}(f)\propto -\frac{39}{2}\Lambda(\pi M f)^{5/3},$$8 A band can be acquired in $$\psi_{\rm tidal}(f)\propto -\frac{39}{2}\Lambda(\pi M f)^{5/3},$$9 ksec. Under these assumptions, ATLAST-8m with an internal coronagraph can survey about $5$00 different star systems, each visited three times over five years while consuming $5$01 of observatory time, and ATLAST-16m can reach up to about $5$02 stars under the same cadence (0904.0941).

The underlying optical scalings are standard: $5$03 At $5$04, the diffraction-limited angular resolution is approximately $5$05 mas for $5$06 m and approximately $5$07 mas for $5$08 m; at $5$09 nm with $5$10, the IWA is approximately $5$11 mas for $5$12 m and approximately $5$13 mas for $5$14 m (0904.0941).

ATLAST is equally a general-purpose astrophysics observatory. The concept includes a TMA channel for wide-field instruments, a Cassegrain channel for high-throughput UV and exoplanet imaging/spectroscopy, visible/NIR wide-field imagers of gigapixel scale, IFUs, UV spectrographs, and internal coronagraph or starshade operation. The galaxy-evolution program includes UV absorption-line spectroscopy of the cosmic web, IMF studies to $5$15 out to $5$16 Mpc, and resolved star-formation histories beyond the Local Group. The white paper states that an 8 m space telescope can reach approximately $5$17 galaxies for main-sequence-turnoff studies, while a 16 m extends to approximately $5$18 galaxies, and that HST UDF depth is reached $5$19 faster for 8 m and $5$20 faster for 16 m (0904.0941).

6. Operational design, planetary capability, and precision astrometry

A major theme in the broader Great Observatory literature is that capability must be designed in early, not appended after launch. The Solar System science paper treats HST and JWST as contrasting examples: HST launched without moving-target tracking, whereas JWST incorporated moving-target tracking, ephemeris-driven operations, bright-object strategies such as subarray readouts, and stray-light analyses because Solar System scientists were included on the Science Working Group from the earliest phases. The paper therefore recommends formal involvement of planetary scientists from pre-Phase A onward and translates that recommendation into concrete requirements: continuous non-sidereal tracking, native integration with JPL Horizons/SPICE, bright-object resilience, high-cadence timing, and moving-target-aware pipelines (Hammel et al., 2020).

The recommended performance envelope is explicit. For non-sidereal tracking, the paper gives a baseline of $5$21 arcsec/s continuous tracking and a stretch goal of $5$22 arcsec/s. Maximum allowable trailing during an exposure is framed by

$5$23

with typical $5$24. High-cadence requirements include frame rates up to tens–hundreds of Hz and absolute time-stamping better than $5$25 ms. The same paper links these capabilities to aurorae, plumes, rings, cometary outbursts, Titan weather, Mars context observations, and precursor reconnaissance for planetary missions (Hammel et al., 2020).

Precision astrometry extends this operational perspective into the radio domain. The astrometry review frames SKA and ngVLA as next-generation facilities that can further increase astrometric precision provided systematic errors are corrected. The core relations are

$5$26

At low frequencies, MultiView astrometry uses at least three surrounding calibrators and 2D interpolation to synthesize a virtual in-beam calibrator, and VLBA demonstrations at $5$27 GHz achieved an order-of-magnitude improvement relative to single-calibrator phase referencing, reaching the thermal noise limit. At millimeter wavelengths, SFPR and MFPR use simultaneous or rapid multi-frequency observing to remove non-dispersive tropospheric terms; the Korean VLBI Network demonstrated bona fide astrometric images at $5$28 GHz with calibrator separations of $5$29–$5$30 (Rioja et al., 2019).

These requirements and calibration modes are not peripheral. They define whether a future observatory can support Solar System science, cross-band reference frames, and radio–optical interoperability at first light. The literature therefore treats operations, calibration, and pipeline design as part of the scientific architecture rather than as downstream implementation details.

7. Computing, governance, and future extensions of the observatory landscape

The GWIC 3G program makes computing and governance explicit observatory components. Orders-of-magnitude increases in event rates and data volume require low-latency alerts and pipelines, GPU-accelerated matched filtering, reduced-order models, surrogate waveforms, efficient likelihood methods, scalable HPC solutions, cloud or industry partnerships, and sustained investment in open-source software and personnel. The same six-part effort argues for a centralized governance framework for a global network, with a central coordinating body that harmonizes standards, schedules, and funding interfaces while preserving regional autonomy for site-specific projects such as ET and CE (Reitze et al., 2021).

The governance question is tied to data-sharing and multimessenger science. The recommended model prioritizes rapid, open data products where feasible, staged releases, protections for commissioning periods, transparent membership structures, and shared R&D programs. In this formulation, a Next Generation Great Observatory is not only an instrument or a site; it is also a durable international organization capable of common standards, common software, and coordinated external interfaces (Reitze et al., 2021).

The observatory landscape is also likely to expand beyond the flagship classes already most developed. A 2025 study of tidal disruption events models full and repeated-partial TDEs using the full harmonic content of the gravitational-wave signal and concludes that full disruptions of stars will not be seen by LISA but will be important targets for deci-Hertz observatories, while repeated disruptions will not be individually detectable in the near future. For a deci-Hz mission represented by the DO-optimal curve, the forecasts are tens to hundreds of MS-fTDE detections over 10 years, tens to hundreds of WD-fTDE detections in dwarf galaxies with SNR up to $5$31, and a detectable WD-fTDE stochastic background with SNR $5$32, peaking near $5$33 Hz (Toscani et al., 28 May 2025).

This suggests that the Next Generation Great Observatories landscape is best understood as an evolving, multi-band system rather than a closed list of facilities. The mature form of that system, as represented in the supplied literature, combines 3G gravitational-wave observatories, large-aperture UVOIR space telescopes, precision radio astrometric arrays, and multimessenger follow-up infrastructures into a coordinated framework for precision surveys, rapid transients, strong-field gravity, exoplanet spectroscopy, Solar System dynamics, and cosmic structure across the observable Universe.