Astro2020 Ground-Based Technology Development
White Paper
Cosmic Explorer: The U.S. Contribution
to Gravitational-Wave Astronomy
beyond LIGO
Principal Author:
Name: David Reitze
Institution: LIGO Laboratory, California Institute of Technology
Email: dreitze@caltech.edu
Phone: +1–626–395–6274
Co-authors:
Rana X Adhikari,
a
Stefan Ballmer,
b
Barry Barish,
a
Lisa Barsotti,
c
GariLynn Billingsley,
a
Duncan A. Brown,
b
Yanbei Chen,
d
Dennis Coyne,
a
Robert Eisenstein,
c
Matthew Evans,
c
Peter Fritschel,
c
Evan D. Hall,
c
Albert Lazzarini,
a
Geoffrey Lovelace,
e
Jocelyn Read,
e
B. S. Sathyaprakash,
f
David Shoemaker,
c
Joshua Smith,
e
Calum Torrie,
a
Salvatore Vitale,
c
Rainer Weiss,
c
Christopher Wipf,
a
Michael Zucker
a
,
c
a
LIGO Laboratory, California Institute of Technology, Pasadena, California 91125, USA
b
Department of Physics, Syracuse University, Syracuse, NY 13244, USA
c
LIGO Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
d
Caltech CaRT, Pasadena, CA 91125, USA
e
California State University Fullerton, Fullerton, CA 92831, USA
f
The Pennsylvania State University, University Park, PA 16802, USA
1
Executive Summary
1
Executive Summary
Gravitational-wave astronomy is a completely new way to observe the universe. The breakthroughs
made by the National Science Foundation’s Advanced LIGO, and its partner observatory Advanced
Virgo,
1
,
2
are only the beginning of our exploration of the gravitational-wave sky.
3
–
7
This white paper
describes the research and development that will be needed over the next decade to realize “Cosmic
Explorer,” the U.S. component of a future third-generation detector network.
8
Cosmic Explorer,
together with a network of planned and proposed observatories spanning the gravitational-wave
spectrum, including LISA
9
,
10
and the Einstein Telescope,
11
will be able to determine the nature of
the densest matter in the universe; reveal the universe’s binary black hole population throughout
cosmic time; provide an independent probe of the history of the expanding universe; explore warped
spacetime with unprecedented fidelity; and expand our knowledge of how massive stars live, die,
and create the matter we see today.
This white paper presents a technology development program that will lead to a two-stage plan
for Cosmic Explorer, similar to the path successfully followed by the National Science Foundation’s
LIGO. The first stage (CE1) scales up Advanced LIGO technologies to create an L-shaped interfer-
ometric detector with arms that are closer to the wavelength of the gravitational waves targeted
by ground-based detectors. A facility with 40 km long arms is the baseline for achieving Cosmic
Explorer’s science goals. The second stage (CE2) upgrades the 40 km detector’s core optics using
cryogenic technologies and new mirror substrates to realize a full order of magnitude sensitivity
improvement beyond Advanced LIGO.
12
With its spectacular sensitivity, Cosmic Explorer will see gravitational-wave sources across the
history of the universe. Sources that are barely detectable by Advanced LIGO will be resolved
with incredible precision. The explosion in the number of detected sources — up to millions per
year — and the fidelity of observations will have wide-ranging impact in physics and astronomy. By
peering deep into the gravitational-wave sky, Cosmic Explorer will present a unique opportunity
for new and unexpected discoveries. Operating as part of a world-wide network with the Einstein
Telescope,
11
or other possible detectors, Cosmic Explorer will be able to precisely localize sources
on the sky,
13
,
14
coupling gravitational-wave astronomy to electromagnetic and particle astronomy.
After a review of Cosmic Explorer’s scientific potential (§
2
) and an overview of its design (§
3
),
we outline the engineering study that must be completed in order to design and construct Cosmic
Explorer (§
4.1
). This includes designing a vacuum system for two 40 km beam tubes and developing
the civil engineering program needed to prepare the facility site. We then describe a program of lab-
oratory research and prototyping to evolve existing LIGO-class detector components and concepts
to those needed for Cosmic Explorer (§
4.2
). We discuss a program of international collaboration
to coordinate the construction and operation of a unified third-generation network of gravitational-
wave detectors (§
5
). Finally, we summarize the schedule and cost of these activities (§
6
).
The new technologies needed to realize Cosmic Explorer (including cost-effective long ultra-
high-vacuum systems, civil engineering studies, new optical materials, and cryogenics) will require
a substantial investment in research and design, large-scale prototyping, and tabletop research. A
three-year “Horizon Study,” funded by the National Science Foundation (PHY–1836814), is under-
way to lay the groundwork for the activities described in this white paper. However, this is only
the first step: further investment at a level of $65.7M (cost category: medium scale ground-based)
early in the coming decade will be needed to ensure that CE1 can begin observing in the 2030s,
with CE2 to be operational in the 2040s.
2
Key Science Goals and Objectives
2
Key Science Goals and Objectives
10
100
1000
Frequency
/
Hz
10
−
25
10
−
24
10
−
23
Strain noise
/
Hz
−
1
/
2
CE2
CE1
A
+
Design
O3
Figure 1: Amplitude spectrum of the
detector noise as a function of fre-
quency for the two stages of Cosmic
Explorer (CE1, CE2) and the current
(O3), design, and upgraded (A+) sen-
sitivities of Advanced LIGO.
A series of 2020 Decadal Survey White Papers describes the
science case for a third-generation gravitational-wave detec-
tor network.
3
–
7
To achieve these science goals, Cosmic Ex-
plorer must push the low-frequency sensitivity limit of the
detector down by a factor of two, from 10 Hz to 5 Hz, and
push the detector sensitivity well beyond the limits of the
LIGO facilities
12
(Fig.
1
). The leap in sensitivity between
second- and third-generation detectors will take the scientific
community from first detections to seeing and characterizing
every stellar-mass black hole merger in the universe.
The broad and deep discovery aperture of Cosmic Ex-
plorer is a consequence of the wide range of sources in the
5–4000 Hz band of the gravitational-wave spectrum, the vast
number of objects that it will detect, and the precision with
which a third-generation network will map the gravitational-
wave sky. In this section, we highlight some of the key sci-
ence goals that will be possible once third-generation detec-
tors are observing the universe.
Determining the Nature of the Densest Matter in the Universe
Neutron stars are made of the densest matter in the universe and can have incredibly large magnetic
fields. Six decades after discovering neutron stars, we still do not understand how matter behaves at
the pressures and densities found in their interiors, or how neutron-star matter can generate magnetic
fields a million times stronger than the strongest fields ever created on Earth. Subtle signatures of
the star’s interior are encoded in the gravitational waves emitted when neutron stars spiral together
and merge. Cosmic Explorer will capture these mergers with the precision needed to understand the
cold, dense nuclear equation of state that governs neutron-rich matter. When neutron stars merge,
they create a hot, dense remnant which can emit both gravitational waves and light in a variety of
ways. Observation of the mergers and post-merger remnants of neutron stars can reveal unknown
physics in the state of matter at ultra-high densities.
Multimessenger Observations of Binary Systems
As part of a third-generation network, Cosmic Explorer will provide a unique opportunity to observe
thousands of neutron-star mergers in concert with electromagnetic telescopes. A large number
of such multimessenger observations is required to understand the dynamics of the collision, the
astrophysical processes that form jets, and the formation of heavy elements in the universe. A third-
generation network can localize binary neutron stars prior to their merger, allowing electromagnetic
facilities to capture the first moments of the collision that are critical to understanding jet physics,
kilonovae, and neutrino winds in remnant disks. Some black-hole binaries will also be seen by
LISA, allowing us to localize them before they enter the Cosmic Explorer band and look for signs
of matter in their circumbinary environment.
Seeing Black Holes Merge throughout Cosmic Time
Cosmic Explorer can detect merging stellar-mass black holes at redshifts of up to
z
20. This
immense reach will reveal for the first time the complete population of stellar-mass black holes,
3
Key Science Goals and Objectives
starting from an epoch when the universe was still assembling its first stars. Cosmic Explorer will
detect hundreds of thousands of black-hole mergers each year, measuring their masses and spins.
These observations will reveal the black-hole merger rate, the underlying star formation rate, how
both have changed throughout cosmic time, and how both are correlated with galaxy evolution.
Probing the Evolution of the Universe
Observations of gravitational waves from sources at cosmological distances will allow the third-
generation network to probe the geometry and expansion of the Universe independent of electro-
magnetic techniques. We can infer the sources’ luminosity distance without the need to calibrate
them with standard candles. For some of these sources, electromagnetic counterpart observations
will let us measure the source redshift. These observations will let us precisely measure cosmologi-
cal parameters, such as the Hubble parameter and the dark matter and dark energy densities, giving
a completely independent and complementary measurement of the history of the Universe.
Exploring the Nature of Gravity and Compact Objects
Gravitational waves emanate from spacetime regions of strong gravity and large curvature. The
emitted waves encode the nature of the gravitational field, characteristics of the sources, and the
physical environment in which they reside. The large number of detected merging black holes will
likely include uncommon mergers that are too rare for today’s detectors to observe; for example,
highly spinning black holes, the inspiral of a neutron star into an intermediate-mass black hole,
or a binary black hole with enough surrounding matter to produce an electromagnetic counterpart.
Measuring the properties of these rare mergers could revolutionize our understanding of the nature
of compact objects, as well as the fundamental nature of gravity. Cosmic Explorer will observe the
loudest gravitational-wave sources with an order of magnitude more sensitivity than today’s detec-
tors. These extremely high-fidelity observations will put general relativity to the most stringent tests
while revealing the nonlinear dynamics of strongly warped spacetime. A third-generation network
will have numerous opportunities to discover physics beyond general relativity, for example, in the
form of new particles and fields that violate the strong equivalence principle, Lorentz invariance
violations, or extra polarizations in addition to the two predicted by general relativity.
The Life and Death of Massive Stars
The evolution of massive stars, the detailed physics of supernovae, and the origin of pulsar glitches
are open problems in astrophysics. Every year, Cosmic Explorer will detect more neutron stars than
have been found in radio surveys of our galaxy over the last forty years. Together with a complete
census of the universe’s stellar-mass black-hole binaries, the properties of this vast population of
compact objects will help us understand the evolution of massive stars and the supernova engine
that creates the compact-object remnants. The core collapse of a massive star in the Milky Way
or Magellanic Clouds will generate gravitational waves that could be directly observed by Cos-
mic Explorer. Emissions from quakes in pulsars and glitches in magnetars in our galaxy could
be detected. Together with electromagnetic-wave and neutrino observations, observations of these
systems would revolutionize our understanding of the extreme astrophysics that powers them.
Sources at the Frontier of Observations
Beyond the known and guaranteed sources of gravitational waves, Cosmic Explorer might see other
spectacular sources, the detection of any one of which would be revolutionary. For example, third-
generation detectors might detect some forms of dark and exotic matter including axionic and other
dark matter fields around black holes or in the cores of neutron stars, the mergers of primordial black
holes formed in the early universe, or gravitational-wave emission from cosmic (super)strings.
4
Technology Overview
2024 2026 2028 2030 2032 2034 2036 2038 2040 2042 2044 2046
Cosmic Explorer Stage 1
2022
2020
seismic isolation
improvements
Cosmic Explorer Stage 2
Facility engineering design &
detector design
construction &
commissioning
observations &
operations
install &
commission
observations
& operations
stage 2 detector
fabrication
2018
CE
Horizon
study
squeezing
improvements
large test masses
& suspensions
coatings
for 2 μm
high-power laser
and high-QE diodes
interferometer prototype testing
(40 m, e.g.)
cryogenics
large silicon test
masses & coatings
Stage 2 R&D
Stage 1 R&D
Figure 2: A top-level timeline showing a phased approach to the Cosmic Explorer detector. A
detailed timeline for Cosmic Explorer technology development in the 2020s in given in Figure
3
.
3
Technology Overview
The LIGO and Virgo instruments have opened a new window on the universe, but they are, like
Galileo’s first telescope, just sensitive enough to observe the brightest sources. Today the Advanced
LIGO detectors now see signals roughly weekly; when the recently funded “A+” upgrade comes
online in 2024, it will deliver roughly ten detections per week. This may be the most sensitive
detector to be installed in the present LIGO infrastructure, and may exhaust the lifetime of the
LIGO vacuum systems. The above science goals are only achievable by making observations of
these bright sources with significantly higher fidelity and over a wider frequency band, as well as
by observing much more distant sources. This requires a new generation of observatories with an
order of magnitude greater sensitivity in the audio frequency band than current observatories allow.
We envision the U.S. contribution to the global third-generation ground-based gravitational-wave
detector network to be Cosmic Explorer, a 40 km L-shaped observatory designed to greatly deepen
and clarify humanity’s gravitational-wave view of the cosmos.
12
3.1
Design architecture
The Cosmic Explorer facility baseline requirements are two 40 km ultrahigh-vacuum beam tubes,
roughly 1 m in diameter, built in an L-shape on the surface of flat and seismically quiet land in
the United States. The longer arm length will increase the amplitude of the observed signals with
effectively no increase in the noise. Although there are areas of detector technology where improve-
ments would lead to incremental increases in the sensitivity and bandwidth of the instruments, the
dominant improvement will come from significantly increasing the arm length.
Cosmic Explorer will be realized in two phases. The initial phase, “Cosmic Explorer Stage 1,”
is expected to use the technology developed for the “A+” upgrade to Advanced LIGO, scaled up to
a 40 km detector with correspondingly better sensitivity. This provides a straightforward approach
to significant improvement, as seen in the last rows of Table
1
. The second stage, “Cosmic Explorer
Stage 2,” improves on the Stage 1 sensitivity with a new set of technologies to reduce the quantum
and thermal noises of the detector. The main parameters of both stages of Cosmic Explorer, and the
comparison with LIGO A+, are given in Table 1, along with a few key astrophysical performance
5
Technology Drivers
LIGO A+
CE Stage 1
CE Stage 2
Arm length
4 km
40 km
40 km
Test mass
40 kg fused silica 320 kg fused silica
320 kg silicon
Suspension
0.6 m silica fibers 1.2 m silica fibers 1.2 m silicon ribbons
Temperature
297 K
297 K
123 K
Laser wavelength
1 μm
1 μm
2 μm
Circulating power
0.8 MW
1.4 MW
2 MW
Squeezed light level
6 dB
6 dB
10 dB
BNS (BBH) horizon redshift
15
0.17 (2.6)
3.1 (26)
12 (37)
BNS SNR at
z
=
0
:
01
150
1700
3300
BNS early warning at
z
=
0
:
01
10 minutes
40 minutes
90 minutes
Table 1: Key design parameters and astrophysical performance measures for the LIGO A+ and
Cosmic Explorer detectors. The astrophysical performance measures assume a 1.4–1.4
M
⊙
binary-
neutron-star (BNS) system and a 30–30
M
⊙
binary-black-hole (BBH) system, both optimally ori-
ented. “Early warning” is the time before merger at which the event has accumulated a signal-to-
noise ratio (SNR) of 8.
measures. Figure
2
shows the top-level timeline for realizing Cosmic Explorer, with Stage 1 observ-
ing in the 2030s and Stage 2 observing in the 2040s. The current NSF-funded “Horizon Study”
(PHY–1836814) is further developing the science case for Cosmic Explorer and identifying prelim-
inary considerations for the siting, costing, R&D, and project organization required for Cosmic
Explorer to achieve its goals.
3.2
Key performance requirements
Achieving the mid- and high-frequency performance of Cosmic Explorer requires high-quality op-
tical materials, high-power lasers, and careful control of optical losses in the detector. Achieving
the low-frequency performance requires eliminating scattered laser light, mechanically isolating the
detector test masses from the environment using high-quality multi-stage suspensions and active
seismic isolation, and measuring and subtracting local gravity fluctuations induced by the ground
and atmosphere.
3.3
Technical, site, and infrastructure requirements
The Cosmic Explorer facility must be capable of holding the 40 km beam tubes under ultrahigh
vacuum for decades. The facility site and the civil infrastructure must provide as much as possible
a stable environment both to preserve the integrity of the beam tubes and to reduce environmental
fluctuations near the detector test masses.
4
Technology Drivers
Significant technology development is required to realize the Cosmic Explorer facility and detectors.
To ensure continuity of gravitational-wave astronomy, it is critical that this development take place
in the 2020s, while the current 4 km observatories are still operational.
The construction cost and robustness of the Cosmic Explorer beam tube vacuum system can
benefit from recent developments and new ideas in vacuum technology, including novel topologies,
materials, treatments, and procedures. Additionally, significant civil engineering is required to
6
Technology Drivers
prepare the facility site, with one of the main challenges being leveling the 30 m of sagitta attained
over 40 km due to the curvature of the Earth. In order to develop these technologies, in the first half
of the 2020s we will undertake an engineering study to develop a conceptual design and cost for
the vacuum beam tube and the associated civil engineering for an appropriate site; this is described
in §
4.1
.
For the Cosmic Explorer detectors, technology development is required to extend existing LIGO
technology to the scale required for Cosmic Explorer Stage 1, principally to develop larger mirrors
and to handle the longer arm lengths; most technologies remain unchanged. Parallel development
is required to realize the 2 μm cryogenic silicon technologies for Cosmic Explorer Stage 2 (Table
1
).
Therefore, throughout the 2020s we will undertake a series of laboratory upgrades for large sus-
pensions, cryogenic silicon, and tabletop prototypes as described in §
4.2
. This R&D effort will
identify the most promising approaches for Cosmic Explorer Stage 2, but will not provide a cost
estimate for the detector.
4.1
An engineering study for Cosmic Explorer
The Cosmic Explorer engineering study will focus on two central and costly aspects of the Cosmic
Explorer: (1) the design, fabrication, testing, and maintenance of the 80 km of ultrahigh-vacuum
beam tubes, and (2) the civil engineering required to prepare the site to support and lay out the
beam tubes.
4.1.1
Prerequisite work for the engineering study
Before embarking on the formal engineering study, we will develop a pre-conceptual beam tube
vacuum design and identify a plausible reference site for Cosmic Explorer. Together these will
serve as a starting point for the engineering study. The pre-conceptual design of the beam tube
vacuum system will be based on our experience with the current systems, augmented by recent
developments in vacuum technology and by research that we will pursue in the next two years into
materials, coatings, pumping strategies and new types of vacuum valves and system geometries.
The intent of these studies is to significantly reduce the costs per length of the beam tube vacuum
system relative to the initial costs of the 16 km of the present LIGO detectors. The research will
include laboratory prototyping of the more promising ideas for cost reduction. The pre-conceptual
design will also specify the vacuum pressures, beam tube diameter, and beam tube optical properties
to achieve the Cosmic Explorer sensitivity. It will also set operational requirements for pumpdown
times, mean time between failures, and allowable motion induced by the environment.
Simultaneously we will identify a plausible reference site in the United States for the 40 km,
L-shaped Cosmic Explorer facility. The primary challenge is to lay out a plane on the curved Earth
with minimum cost at an accessible location with benign environmental conditions (low probability
of earthquakes, floods,
etc.
). The plane will have height differences as large as 30 m compared to
the Earth geoid, and smaller differences if the site terrain is bowl-shaped. Critical cost factors will
be the differential elevation contours of the site and its geotechnical properties. We will carry out
preliminary geotechnical measurements and a preliminary survey at a promising site to establish
a concept for the layout of the system —
i.e.
, where the beam tube will be above, below and at the
surface. This site will serve as the reference site for the engineering design study. Several alternative
sites will be identified for comparison but will not be investigated in as much detail.
7
Technology Drivers
4.1.2
Description of the engineering study
With the pre-conceptual vacuum design and reference site in hand, the formal engineering design
study will proceed in two phases.
Phase 1
will analyze the pre-conceptual vacuum design and make modifications and iterations
as considered useful both from an engineering perspective and to reduce costs. In the beginning
of the study the new concepts being proposed — for fabrication, materials, coatings, pumping, and
configurations to reduce costs — will be reassessed and the ability to implement them with industry
will be determined. This phase of the study will develop a refined conceptual design with enough
detail to be able to construct a prototype beam tube vacuum system in the laboratory. The prototype
would establish the specialized construction techniques (welding, forming, cleaning), materials,
and components (valves and pumps) that would be used in the assembly and demonstrate that the
vacuum specifications can be achieved in the required pumping times.
Phase 1 will additionally confirm the properties of the reference site with a full topographic
survey and geotechnical investigation. It will then make a revised conceptual design of the beam
tube layout and structures at the site. This phase of the engineering design ends with a report on
the vacuum performance and the techniques used in making the prototype that will be applied to
the construction in the field. An assessment of the reference site and, if needed, a comparison with
the alternative sites will be made. It will also provide a first-order costing of the vacuum system,
the layout of the structures in the field, and the civil work.
Phase 2
will produce a full design with complete drawings of the vacuum system and the struc-
tures and layout at the site. This phase of the study will also provide a schedule and plan for the
logistics to acquire the vacuum components and tube manufacture as well as the civil construction
at the site. The second phase will also provide an authoritative cost estimate. More detail and a
specific list of tasks for both phases of the engineering study is provided online.
16
4.1.3
Schedule and cost of the engineering study
The preparatory work for the engineering study — namely, development of the pre-conceptual beam
tube vacuum design and the identification of a reference site — will be carried out in 2019–2022
and funded by a combination of the current NSF Cosmic Explorer “Horizon Study” grant and a
new funding request for lab studies of innovative vacuum system ideas. The vacuum studies will
be done in collaboration with vacuum engineers at CERN and Fermilab and other participants of
an NSF-sponsored workshop on vacuum technology which held its first meeting in January, 2019.
17
These activities will have been completed before the activities proposed in this white paper begin.
Phase 1 of the engineering study will take place in 2022–2023, with an estimated cost of $15M.
Phase 2 of the engineering study will take place in 2024–2025, and will deliver the full concep-
tual design, a schedule for construction, and the authoritative cost estimate for the vacuum system,
structures and civil work. The estimated cost for phase 2 of the study is $18M.
4.2
Laboratory research and prototypes
4.2.1
Cosmic Explorer prototype test mass chamber
Several LIGO detector technologies will need to be scaled up for Cosmic Explorer. Although the
concepts for these detector elements are the same or similar to those for Advanced LIGO, the in-
creased scale for Cosmic Explorer requires significant engineering development and testing. The
Cosmic Explorer test masses are scaled up by a factor of two in each dimension, and the test mass
suspension is twice as long as in Advanced LIGO. The active seismic isolation system must be
re-engineered for this larger payload, and outfitted with new sensors to improve the performance.
8
Technology Drivers
The larger test masses also present optical fabrication challenges (polishing and coating) that must
be proven on the larger scale. To develop and test these technologies, we will design and build a
prototype Cosmic Explorer Test Bed, consisting of a test mass chamber, complete with a seismic
isolation system, a full-sized test mass and its suspension, and associated hardware.
New engineering design is also required for the test mass vacuum chamber. In addition to
scaling up the size, new features are needed that are motivated by past experience and the future uses
of the test bed. These include design elements for scattered light baffling, in-situ particulate removal,
improved access for personnel, faster pump-down speed; design elements to support cryogenic
suspensions, and design of the interface to the seismic isolation system to minimize vibrations.
Initially this test bed will be used for prototyping Cosmic Explorer Stage 1 — the detector based
on room temperature, fused silica test masses and 1 μm lasers. Later, the test bed will prototype
Cosmic Explorer Stage 2, with cryogenic silicon masses and 2 μm light. In order to support the
preliminary and final designs of Cosmic Explorer, this test bed should be in operation in the 2022–
2023 time frame. We estimate the cost of the first phase of the test bed at approximately $20M.
4.2.2
Conversion of the LIGO 40m prototype
To demonstrate the 2 μm cryogenic silicon technology, envisioned for Stage 2 of Cosmic Explorer,
we will undertake a modest set of upgrades to the LIGO 40 m prototype interferometer located at
Caltech. An initial phase of upgrades is already planned in 2020–2021 to install cryogenic infras-
tructure, silicon test masses, and a 2 μm laser system. This configuration will establish the basic
feasibility of the 2 μm cryogenic silicon technology. A second phase of upgrades will demonstrate
the low-noise, high-power capabilities of this technology, including the use of monolithic silicon
test mass suspensions, the reduction of coating thermal noises, and the mitigation of scattered light.
Successful demonstration of a prototype 2 μm cryogenic silicon interferometer is an important
step for validating the Cosmic Explorer Stage 2 design, and will also set the stage for additional
validation by deploying 2 μm cryogenic silicon technology in an existing LIGO facility, if desired;
this option is termed the “Voyager” upgrade. The second phase of the 40 m upgrade effort will take
place during 2022–2024, with an estimated cost of $3M.
4.2.3
Large cryogenic suspension testing
To further develop the detector designs that employ cryogenic test masses, we will outfit the LIGO
test mass chamber in the existing LIGO Advanced Systems Test Interferometer facility located at
MIT with the largest cryogenic suspension compatible with the current Advanced LIGO infrastruc-
ture: a 200 kg silicon test mass, cooled to 123 K. There are three main elements of this project: the
test mass suspension, designed for much higher mass than the Advanced LIGO suspension (200 kg
vs 40 kg); the test mass cryogenic system; the silicon test mass, polished and coated for 2 μm laser
light. We expect that the existing seismic isolation system would accommodate the new payload,
perhaps with minor modifications.
The results of cryogenic suspension testing would feed into the second phase of the Cosmic
Explorer test bed described earlier. This prototyping would also be directly applicable for deploying
such technology in a “Voyager” upgrade of an existing LIGO 4 km facility. The time frame for this
R&D effort is expected to be 2022–2023, and we estimate its cost at $4M.
4.2.4
Tabletop research
Key proposed elements of both stages of Cosmic Explorer must be researched on tabletop before
being scaled up and integrated into a kilometer-scale detector. Of particular importance are the tech-
nologies to manufacture adequate test masses: low-loss mirror coatings, low-absorption and low-
9
Organization, Partnerships, and Current Status
Activity
Cost, M$ Time frame Estimated by
Engineering study phase 1 (§
4.1.2
) 15
2022–23
}
LIGO Laboratory and
vacuum consultants
Engineering study phase 2 (§
4.1.2
) 18
2024–25
Prototype CE chamber (§
4.2.1
) 20
2022–23
LIGO Laboratory
Caltech 40 m upgrade
(§
4.2.2
)
3
2022–24
LIGO Laboratory
MIT LASTI upgrade
(§
4.2.3
)
4
2023–24
LIGO Laboratory
Tabletop research
(§
4.2.4
)
3
2022–28
CE Horizon Study Team
CE project planning
(§
5.1
)
0.7
2022–24
LIGO Laboratory
Global governance
(§
5.2
)
2
2022–24
LIGO Laboratory
Total
65.7
Table 2: Summary of activities, schedules, and cost estimates. Estimates performed in June 2019.
scatter optics, as well as sensing and control of wavefront distortion induced by high-power laser
light. Cryogenic detectors additionally require efficient and low-vibration heat extraction from the
test masses, and mitigation of cold layer deposition on the coatings. Research is also required for im-
proved quantum noise reduction techniques and their extension to 2 μm laser wavelength, improved
inertial sensors for seismic isolation, and low-noise, high-power lasers. Some of these efforts are
already underway in the US and worldwide as part of a broader program to advance gravitational-
wave detector technology.
18
For tabletop efforts in the US throughout the 2020s directly related to
Cosmic Explorer, we anticipate an investment of $3M.
5
Organization, Partnerships, and Current Status
5.1
Project planning for Cosmic Explorer
To provide a complete picture of the path to an operating Cosmic Explorer observatory, in paral-
lel with the engineering study we will provide a refined timeline (a resource-loaded schedule) and
identification of critical paths showing the major deliverables and milestones (and possible diffi-
culties) that were identified in the study. In addition, we will examine the observing capabilities
and plans for LIGO and other second-generation detectors, and the R&D readiness. Phasing of the
construction project will be addressed. Possible management plans will be evaluated, exploring
the advantages of coordination between global gravitational-wave detectors. Estimates of operat-
ing costs for the Observatory will also be developed using LIGO experience as a guide and scaling
where appropriate. The costs of exploiting the science, and scoping computational resources and
community support, will be estimated. Approximately $700k will be needed for this planning.
5.2
Cosmic Explorer and the Global Gravitational-Wave Network
We anticipate that Cosmic Explorer will operate with other third-generation detectors, such as Ein-
stein Telescope, as part of a global network. For the network to operate effectively, it is critical
that there be a unified, coordinated worldwide effort to ensure that the science goals can be real-
ized and that investments in each observatory are leveraged by the development of the network.
The science requires coordinated development and observing programs, optimally with three third-
generation detectors distributed to localize sources on the sky, with the data analyzed as a network
to maximize the science return. The ground-based gravitational-wave community has recognized
10
Schedule and Cost Estimates
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
Half 1 Half 2 Half 1 Half 2 Half 1 Half 2 Half 1 Half 2 Half 1 Half 2 Half 1 Half 2 Half 1 Half 2
Half 1 Half 2 Half 1 Half 2 Half 1 Half 2 Half 1 Half 2
Vacuum/Site Pre-Conceptual Design
Eng. Study Phase 1:
Design evolution & Initial cost
Eng. Study Phase 2:
Conceptual Design & Cost
Final Design
CE Horizon Study
CE Project Planning and
Third-Generation Global Governance
Preliminary Design
CE prototype chamber
Test CE1 suspension
40 m Phase 1
Upgrade
40 m Phase 2 Upgrade
and Commissioning
Upgrade LASTI and install
cryogenic suspension
Test cryogenic suspension
Tabletop research
Figure 3: Schedule for Cosmic Explorer technology development in the 2020s. Activities in green
are within the scope of this white paper and contribute to the cost estimate (Table
2
). The broader
timeline for Cosmic Explorer, extending into the 2040s, is given in Figure
2
.
the imperative to form a globally coherent effort, and has made some progress toward that goal, but
we will significantly further the worldwide coordination in parallel with the engineering study.
Towards this end, a series of NSF-supported meetings
19
–
22
began in 2015 to plan for the future
of ground-based gravitational-wave astronomy. The Gravitational-Wave International Committee
(GWIC)
23
chartered a subcommittee to study detector astrophysical and instrumental science.
24
Einstein Telescope has formed a Consortium,
25
and core US participants in the Cosmic Explorer
effort are participating in the “Horizon Study” funded by the NSF. We will form an “umbrella
organization” for these current endeavors. This organization is starting to take form now, but needs
to evolve from a forum for discussion of a coordination of projects and sharing of effort (the current
state) to a single worldwide laboratory for gravitational-wave observation. We will develop and
realize an operating global governance through interactions with the international community and
funding agencies and work to put it in place.
’22
’23
’24
’25
’26
’27
’28
Year
0
5
10
15
20
Cost (M$)
Figure 4: Cost per year for the activ-
ities in Table
2
and Figure
3
.
To achieve this goal, we see a need for support for com-
munity meetings, technical workshops, participation in con-
ferences, extended working visits, organization of documen-
tation and facilitation/organization of design information,
and advocacy to and collaboration with the greater scientific
community. This effort will serve to continue to cultivate
the organization, and create personal relationships (“social-
ization”) between members of different efforts. The end goal
in the 2020s is a governance organization that is facilitating
the design and implementation of Cosmic Explorer and other
third-generation detectors, and that can grow to running the
worldwide third-generation observatory network. We esti-
mate $2M over three years is needed for this community development program.
6
Schedule and Cost Estimates
A summary of the technological development activities, along with costs and timeframe, is given
in Table
2
; the total cost for the activities is $65.7M. We intend primarily to solicit federal funding,
and possibly also private support. A schedule of these activities, along with other Cosmic Explorer
activities in the 2020s, is shown in Figure
3
and the cost breakdown per year is shown in Figure
4
.
11
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