Lynx X-ray Observatory

The Lynx X-ray Observatory
Names	Lynx X-ray Surveyor (previous name)
Mission type	Space telescope
Operator	NASA
Website	www.lynxobservatory.org
Start of mission
Launch date	2036 (proposed)
Orbital parameters
Reference system	Sun–Earth L2 orbit
Main
Type	Wolter telescope
Diameter	3 m (9.8 ft)
Focal length	10 m (33 ft)
Collecting area	2 m2 (22 sq ft) at 1keV
Wavelengths	X-ray
Resolution	0.5arcsec across the entire field of view
Instruments
Lynx X-ray Mirror Assembly (LMA) High Definition X-ray Imager (HDXI) Lynx X-ray Microcalorimeter (LXM) X-ray Grating Spectrometer (XGS)
The Lynx X-ray Observatory Wordmark Large strategic science missions

TheLynx X-ray Observatory (Lynx) is aNASA-fundedLarge Mission Concept Study commissioned as part of theNational Academy of Sciences 2020Astronomy and Astrophysics Decadal Survey. The concept study phase is complete as of August 2019, and theLynx final report^[1] has been submitted to the Decadal Survey for prioritization. If launched,Lynx would be the most powerfulX-ray astronomy observatory constructed to date, enabling order-of-magnitude advances in capability^[2] over the currentChandra X-ray Observatory andXMM-Newton space telescopes.

In 2016, following recommendations laid out in the so-calledAstrophysics Roadmap of 2013,NASA established fourspace telescope concept studies for futureLarge strategic science missions. In addition toLynx (originally called X-ray Surveyor in theRoadmap document), they are theHabitable Exoplanet Imaging Mission (HabEx), theLarge Ultraviolet Optical Infrared Surveyor (LUVOIR), and theOrigins Space Telescope (OST, originally called the Far-Infrared Surveyor). The four teamscompleted their final reports in August 2019, and turned them over to both NASA and theNational Academy of Sciences, whose independentDecadal Survey committee advises NASA on which mission should take top priority. If it receives top prioritization and therefore funding,Lynx would launch in approximately 2036. It would be placed into a halo orbit around thesecond Sun–Earth Lagrange point (L2), and would carry enoughpropellant for more than twenty years of operation without servicing.^[1][2]

TheLynx concept study involved more than 200 scientists and engineers acrossmultiple international academic institutions,aerospace, andengineering companies.^[3] TheLynx Science and Technology Definition Team (STDT) was co-chaired byAlexey Vikhlinin andFeryal Özel.Jessica Gaskin was the NASA Study Scientist, and theMarshall Space Flight Center managed theLynx Study Office jointly with theSmithsonian Astrophysical Observatory, which is part of theCenter for Astrophysics | Harvard & Smithsonian.

According to the concept study'sFinal Report, theLynx Design Reference Mission was intentionally optimized to enable major advances in the following three astrophysical discovery areas:

• The dawn ofblack holes (Chapter 1 of theLynx Report)
• The drivers ofgalaxy formation and evolution (Lynx Report, Chapter 2)
• The energetic properties ofstellar evolution and stellar ecosystems (Lynx Report, Chapter 3)

Collectively, these serve as three "science pillars" that set the baseline requirements for the observatory. Those requirements include greatly enhancedsensitivity, asub-arcsecondpoint spread function stable across the telescope'sfield of view, and very highspectral resolution for bothimaging and gratingsspectroscopy. These requirements, in turn, enable a broad science case with major contributions across theastrophysical landscape (as summarized in Chapter 4 of theLynx Report), includingmulti-messenger astronomy,black holeaccretion physics,large-scale structure,Solar System science, and evenexoplanets. TheLynx team markets the mission's science capabilities as "transformationally powerful, flexible, and long-lived", inspired by the spirit ofNASA'sGreat Observatories program.

As described in Chapters 6-10 of the concept study'sFinal Report,Lynx is designed as anX-ray observatory with agrazing incidenceX-ray telescope and detectors that record the position, energy, and arrival time of individual X-rayphotons. Post-facto aspect reconstruction leads to modest requirements on pointing precision and stability, while enabling accurate sky locations for detected photons. The design of theLynxspacecraft draws heavily on heritage from theChandra X-ray Observatory, with few moving parts and hightechnology readiness level elements.Lynx will operate in ahalo orbit aroundSun-Earth L2, enabling high observing efficiency in a stable environment. Its maneuvers and operational procedures on-orbit are nearly identical toChandra's, and similar design approaches promote longevity. Without in-space servicing,Lynx will carry enoughconsumables to enable continuous operation for at least twenty years. The spacecraft and payload elements are, however, designed to be serviceable, potentially enabling an even longer lifetime.

The major advances in sensitivity, spatial, and spectral resolution in theLynx Design Reference Mission are enabled by the spacecraft's payload, namely the mirror assembly and suite of three science instruments. TheLynx Report notes that each of the payload elements featuresstate-of-the-art technologies while also representing a natural evolution of existing instrumentation technology development over the last two decades. The key technologies are currently atTechnology Readiness Levels (TRL) 3 or 4. TheLynx Report notes that, with three years of targeted pre-phase A development in early 2020s, three of four key technologies will be matured to TRL 5 and one will reach TRL 4 by start of Phase A, achieving TRL 5 shortly thereafter. TheLynx payload consists of the following four major elements:

• TheLynx X-ray Mirror Assembly (LMA): The LMA is the central element of the observatory, enabling the major advances in sensitivity, spectroscopic throughput, survey speed, and greatly improved imaging relative toChandra due to greatly improvedoff-axis performance. TheLynx design reference mission baselines a new technology calledSilicon Metashell Optics (SMO), in which thousands of very thin, highly polished segments of nearly puresilicon are stacked intotightly packed concentric shells. Of the three mirror technologies considered forLynx, the SMO design is currently the most advanced in terms of demonstrated performance (already approaching what is required forLynx). The SMO's highly modular design lends itself to parallelized manufacturing and assembly, while also providing high fault tolerance: if some individual mirror segments or even modules are damaged, the impact to schedule and cost is minimal.
• TheHigh Definition X-ray Imager (HDXI): The HDXI is the mainimager forLynx, providing highspatial resolution over a widefield of view (FOV) and high sensitivity over the 0.2–10keVbandpass. Its 0.3arcsecond (0.3′′) pixels will adequately sample theLynx mirrorpoint spread function over a 22′ × 22′ FOV. The 21 individual sensors of the HDXI are laid out along the optimal focal surface to improve the off-axis PSF. TheLynx DRM usesComplementary Metal Oxide Semiconductor (CMOS) Active Pixel Sensor (APS) technology, which is projected to have the required capabilities (i.e., high readout rates, high broad-bandquantum efficiency, sufficientenergy resolution, minimal pixelcrosstalk, andradiation hardness). TheLynx team has identified three options with comparable TRL ratings (TRL 3) and sound TRL advancement roadmaps: the Monolithic CMOS, Hybrid CMOS, and DigitalCCDs with CMOS readout. All are currently funded for technology development.
• TheLynx X-ray Microcalorimeter (LXM): The LXM is animaging spectrometer that provides highresolving power (R ~ 2,000) in both thehard and soft X-ray bands, combined with high spatial resolution (down to 0.5′′ scales). To meet the diverse range ofLynx science requirements, the LXM focal plane includes three arrays that share the same readout technology. Each array is differentiated by its absorber pixel size and thickness, and by how the absorbers are connected to thermal readouts. The total number of pixels exceeds 100,000 — a major leap over past and currently planned X-ray microcalorimeters. This huge improvement does not entail a huge added cost: two of the LXM arrays feature a simple, already proven, "thermal" multiplexing approach where multiple absorbers are connected to a single temperature sensor. This design brings the number of sensors to read out (one of the main power and cost drivers for the X-ray microcalorimeters) to ~7,600. This is only a modest increase over what is planned for the X-IFU instrument on Athena. As of Spring 2019, prototypes of the focal plane have been made that include all three arrays at 2/3 full size. These prototypes demonstrate that arrays with the pixel form factor, size, and wiring density required by Lynx are readily achievable, with high yield. The energy resolution requirements of the different pixel types is also readily achievable. Although the LXM is technically still at TRL 3, there is a clear path for achieving TRL 4 by 2020 and TRL 5 by 2024.
• TheX-ray Grating Spectrometer (XGS): The XGS will provide even higher spectral resolution (R = 5,000 with a goal of 7,500) in the soft X-ray band forpoint sources. Compared to the current state of the art (Chandra), the XGS provides a factor of > 5 higher spectral resolution and a factor of several hundred higher throughput. These gains are enabled by recent advances in X-ray grating technologies. Two strong technology candidates are: critical angle transmission (used for theLynx DRM) and off-plane reflection gratings. Both are fully feasible, currently at TRL 4, and have demonstrated high efficiencies and resolving powers of ~ 10,000 in recent X-ray tests.

The Chandra X-ray Observatory experience provides the blueprint for developing the systems required to operate Lynx, leading to a significant cost reduction relative to starting from scratch. This starts with a singleprime contractor for the science and operations center, staffed by a seamless, integrated team of scientists, engineers, and programmers. Many of the system designs, procedures, processes, and algorithms developed for Chandra will be directly applicable for Lynx, although all will be recast in a software/hardware environment appropriate for the 2030s and beyond.

The science impact of Lynx will be maximized by subjecting all of its proposed observations to peer review, including those related to the three science pillars. Time pre-allocation can be considered only for a small number of multi-purpose key programs, such as surveys in pre-selected regions of the sky. Such an open General Observer (GO) program approach has been successfully employed by large missions such asHubble Space Telescope,Chandra X-ray Observatory, andSpitzer Space Telescope, and is planned forJames Webb Space Telescope andNancy Grace Roman Space Telescope. The Lynx GO program will have ample exposure time to achieve the objectives of its science pillars, make impacts across the astrophysical landscape, open new directions of inquiry, and produce as yet unimagined discoveries.

The cost of theLynx X-ray Observatory is estimated to be between US$4.8 billion to US$6.2 billion (inFY20dollars at 40% and 70%confidence levels, respectively). This estimated cost range includes thelaunch vehicle, cost reserves, and funding for five years of mission operations, while excluding potential foreign contributions (such as participation by theEuropean Space Agency (ESA)). As described in Section 8.5 of the concept study'sFinal Report, theLynx team commissioned five independentcost estimates, all of which arrived at similar estimates for the total mission lifecycle cost.

• Advanced Telescope for High Energy Astrophysics
• International X-ray Observatory
• Nuclear Spectroscopic Telescope Array (NuSTAR)
• List of proposed space observatories

• Lynx home page
• Lynx home page for scientists at NASA

• Space telescopes
• X-ray telescopes
• Proposed NASA space probes

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