The Large Synoptic Survey Telescope (LSST) is a large (8.4 meter), wide-field (3.5 degree) survey telescope, undergoing assembly on the summit of Cerro Pachón, in Chile<sup>1</sup> . In May 2015 EIE Ground Technologies Srl - Company of EIE GROUP with headquarters in Venice-Mestre, Italy – signed the contract with AURA Inc. The Design Phase of the rotating enclosure system (Dome) was completed in February 2016. All the structures, mechanisms, electronics, software, etc. are approaching completion. On-site activities started in the spring of 2017, and are scheduled to finish testing in early 2019, in time to begin the installation of the telescope. The Dome’s steel structure supports the two Slit Doors, a moving Permeable Windscreen, a Light Baffled Louver System, numerous platforms and the exterior cladding. The Dome structures are shielded by insulated sandwich panels which provide protection from the exterior environment. The Dome is equipped with a series of Louvers, with associated hinged light baffles, which simultaneously provide exceptional Dome flushing and stray light attenuation. The Windscreen also functions as a light screen, and helps define the optical aperture of the Telescope. The Dome’s azimuth rotation is enabled by trolleys acting on tracks, fixed to the cylindrical, concrete Dome Pier. The rotational torque is provided by the Azimuth Drives fixed directly on the Dome Pier. This simplifies the glycol/water cooling and eliminates the need for a utility cable wrap. During the day, internal temperature control is provided by an Air Duct System interfacing with the facility thermal control system. These ducts align when the Dome is in its parked position. Furthermore, the Dome is equipped with electrical systems, a safety and interlock System, and an overhead bridge crane. A series of ladders, stairs and platforms allow inspections, maintenance and repair of all of the Dome installations. In this paper, we present the status of the manufacturing activities, erection processes, and testing.
The LSST Coating Plant consists of a Coating Chamber for high reflective optical coatings deposition and a Cleaning and Stripping Station for the M1M3 and M2 mirrors. The Coating Chamber sputtering process will be capable of depositing bare and protected Silver/Aluminum coating recipes. The Cleaning and Stripping Station consists of a rotating washing/drying boom, perimeter platforms, and an effluent handling system within the M1/M3 mirror cell. This paper describes the status of the Coating Plant construction effort at the Von Ardenne and MAN facilities. Progress on factory testing, review of the design features and reflective/coating requirements, and results are presented.
The Large Synoptic Survey Telescope (LSST) primary/tertiary (M1M3) mirror cell is a 25-ton, 9-meter x 9-meter x 2- meter steel weldment that supports the 19-ton borosilicate M1M3 monolith mirror on the telescope and acts as the lower vessel of the coating chamber when optically coating the mirror surfaces. The M1M3 telescope mirror cell contract was awarded to CAID Industries, Inc., of Tucson, Arizona in October 2015. After the mirror cell final acceptance in October 2017, the integration of the mirror support system started. The M1M3 cell assembly with the surrogate mirror will take place in a dedicated controlled-environment area at CAID Industries. All components of the mirror support system that were developed and tested by the LSST Telescope and Site M1M3 team at the NOAO offices in Tucson have been moved to CAID premises and have been integrated into the cell by a team of LSST, CAID and Richard F. Caris Mirror lab personnel. After completion of the cell integration and its assembly with the surrogate, a test phase that includes zenith and offzenith testing for the mirror support system will be carried by the LSST team. These tests aim to verify that the active support system components, mirror control, and software are performing as expected and the mirror support system is safe for the next step, the M1M3 cell to borosilicate glass assembly and tests at the RFC Mirror Lab of the University of Arizona.
The Large Synoptic Survey Telescope (LSST) large field of view is achieved through a three-lens camera system and a three-mirror optical system comprised of a unique 8.4-meter diameter monolithic primary/tertiary mirror (M1M3) and a 3.4-meter diameter secondary mirror (M2)<sup>1</sup>. The M2 is a 100mm thick meniscus convex asphere. The M2 Assembly includes a welded steel cell and a support system comprised of 72 axial and 6 tangential electromechanical actuators to control the mirror figure. The M2 Assembly (including optical polishing and integrated optical testing) is being fabricated by Harris Corporation in Rochester, NY. The summary status of this system and results are presented.
The Large Synoptic Survey Telescope<sup>1</sup> (LSST) is an altitude-azimuth mounted three mirror telescope and camera. The primary (M1) and tertiary (M3) mirrors are integrated into a single, monolithic borosilicate substrate 8.42 m diameter. The annular secondary (M2) mirror is located above the M1M3 mirror and the camera is nested inside the M2. The M1M3 mirror is supported on a mirror cell by two independent systems: one system is for Active Mode and the other for Static Mode. <p> </p>During observing, or Active Mode<sup>2</sup>, the M1M3 mirror is supported by an array of 156 support and figure control actuators consisting of 268 pneumatic cylinders that react to gravity and inertial loads and provide figure error correction. Load cells on the actuators measure forces that are communicated to the M1M3 control system. However, the figure actuators do not define the mirror position. This is defined with six axially stiff linear actuators called hardpoints<sup>3</sup> arranged in a hexapod pattern to restrain rigid body motion of the mirror in a kinematic fashion. By adjusting the length of each hardpoint, the mirror can be adjusted in all six degrees of freedom with respect to the cell. Displacement sensors and load cells on the hardpoints communicate displacements and forces to the control system, which processes the telemetry and issues force corrections to the figure actuators to zero out any loads and moments on the hardpoints. <p> </p>In Static Mode, the M1M3 mirror is no longer supported by figure actuators and the position sensing of the hard point hexapod is inactive. A second support system consisting of 288 wire rope isolators called Static Supports come into play. The static supports mechanically capture the mirror whether in Active or Static Mode and in the event the mirror experiences motion beyond the active motion range in any direction. The static supports also safely support the mirror during seismic events for all elevation angles. In active mode, the static supports do not contact the mirror and thus, do not affect the mirror positioning or figure. <p> </p>This paper focuses on the detailed design, development, testing, integration, and current status of the M1M3 pneumatic figure actuators.
The Large Synoptic Survey Telescope (LSST) Project<sup>1</sup> received its construction authorization from the National Science Foundation in August 2014. The LSST Telescope and Site (T and S) group has achieved significant progress in the development and delivery of an integrated telescope system solution to meet the LSST science mission requirements. The summit facility construction has been completed on Cerro Pachón in Chile, construction of the base facility and data center continues in La Serena, and many major vendor subsystem integration and verification efforts are currently in progress. This paper summarizes the status of the T and S group, which is responsible to provide the summit and base facilities and infrastructure necessary to support the wide, fast, deep LSST survey mission. The major elements of the telescope system are well into factory assembly and testing, in anticipation of shipping, integration and final acceptance testing and verification on the summit. Progress continues on the dome system assembly atop the lower enclosure of the summit facility. The M1M3 primary/tertiary and M2 secondary mirror assembly systems are undergoing integrated system testing prior to shipment to Chile. Factory testing has been achieved on the telescope mount assembly, hexapod and rotator systems, coating plant, and the auxiliary calibration telescope. Other in-house efforts including software for observatory supervisory functions, scheduling of the survey, and active optics control has also advanced. The summary status of these subsystems and future integration and verification plans are presented.
Proc. SPIE. 9911, Modeling, Systems Engineering, and Project Management for Astronomy VI
KEYWORDS: Actuators, Telescopes, Mirrors, 3D modeling, Space telescopes, Finite element methods, Computer aided design, Large Synoptic Survey Telescope, Large Synoptic Survey Telescope, Systems modeling, Solid modeling
During this early stage of construction of the Large Synoptic Survey Telescope (LSST), modeling has become a crucial system engineering process to ensure that the final detailed design of all the sub-systems that compose the telescope meet requirements and interfaces. Modeling includes multiple tools and types of analyses that are performed to address specific technical issues. Three-dimensional (3D) Computeraided Design (CAD) modeling has become central for controlling interfaces between subsystems and identifying potential interferences. The LSST Telescope dynamic requirements are challenging because of the nature of the LSST survey which requires a high cadence of rapid slews and short settling times. The combination of finite element methods (FEM), coupled with control system dynamic analysis, provides a method to validate these specifications. An overview of these modeling activities is reported in this paper including specific cases that illustrate its impact.
This paper describes the status and details of the large synoptic survey telescope<sup>1,2,3</sup> mount assembly (TMA). On June 9<sup>th</sup>, 2014 the contract for the design and build of the large synoptic survey telescope mount assembly (TMA) was awarded to GHESA Ingeniería y Tecnología, S.A. and Asturfeito, S.A. The design successfully passed the preliminary design review on October 2, 2015 and the final design review January 29, 2016. This paper describes the detailed design by subsystem, analytical model results, preparations being taken to complete the fabrication, and the transportation and installation plans to install the mount on Cerro Pachón in Chile. This large project is the culmination of work by many people and the authors would like to thank everyone that has contributed to the success of this project.
The Large Synoptic Survey Telescope (LSST) is currently under construction and upon completion will perform precision photometry over the visible sky at a 3-day cadence. To meet the stringent relative photometry goals, LSST will employ multiple calibration systems to measure and compensate for systematic errors. This paper describes the design and development of these systems including: a dedicated calibration telescope and spectrograph to measure the atmospheric transmission function, a collimated beam projector to characterize the spatial dependence of the LSST transmission function and an at-field screen illumination system to measure the high-frequency variations in the global system response function.
At the core of the Large Synoptic Survey Telescope (LSST) three-mirror optical design is the primary/tertiary (M1M3) mirror that combines these two large mirrors onto one monolithic substrate. The M1M3 mirror was spin cast and polished at the Steward Observatory Mirror Lab at The University of Arizona (formerly SOML, now the Richard F. Caris Mirror Lab at the University of Arizona (RFCML)). Final acceptance of the mirror occurred during the year 2015 and the mirror is now in storage while the mirror cell assembly is being fabricated. The M1M3 mirror will be tested at RFCML after integration with its mirror cell before being shipped to Chile.
The Large Synoptic Survey Telescope (LSST) primary/tertiary (M1M3) mirror cell assembly supports both on-telescope operations and off-telescope mirror coating. This assembly consists of the cast borosilicate M1M3 monolith mirror, the mirror support systems, the thermal control system, a stray light baffle ring, a laser tracker interface and the supporting steel structure. During observing the M1M3 mirror is actively supported by pneumatic figure control actuators and positioned by a hexapod. When the active system is not operating the mirror is supported by a separate passive wire rope isolator system. The center of the mirror cell supports a laser tracker which measures the relative position of the camera and secondary mirror for alignment by their hexapods. The mirror cell structure height of 2 meters provides ample internal clearance for installation and maintenance of mirror support and thermal control systems. The mirror cell also functions as the bottom of the vacuum chamber during coating. The M1M3 mirror has been completed and is in storage. The mirror cell structure is presently under construction by CAID Industries. The figure control actuators, hexapod and thermal control system are under developed and will be integrated into the mirror cell assembly by LSST personnel. The entire integrated M1M3 mirror cell assembly will the tested at the Richard F Caris Mirror Lab in Tucson, AZ (formerly Steward Observatory Mirror Lab).
In the construction phase since 2014, the Large Synoptic Survey Telescope (LSST) is an 8.4 meter diameter wide-field (3.5 degrees) survey telescope located on the summit of Cerro Pachón in Chile. The reflective telescope uses an 8.4 m f/1.06 concave primary, an annular 3.4 m meniscus convex aspheric secondary and a 5.2 m concave tertiary. The primary and tertiary mirrors are aspheric surfaces figured from a monolithic substrate and referred to as the M1M3 mirror. This unique design offers significant advantages in the reduction of degrees of freedom, improved structural stiffness for the otherwise annular surfaces, and enables a very compact design. The three-mirror system feeds a threeelement refractive corrector to produce a 3.5 degree diameter field of view on a 64 cm diameter flat focal surface. This paper describes the current status of the mirror system components and provides an overview of the upcoming milestones including the mirror coating and the mirror system integrated tests prior to summit integration.
The Large Synoptic Survey Telescope (LSST) Project<sup>1</sup> received its construction authorization from the National Science Foundation in August 2014. The Telescope and Site (T and S) group has made considerable progress towards completion in subsystems required to support the scope of the LSST science mission. The LSST goal is to conduct a wide, fast, deep survey via a 3-mirror wide field of view optical design, a 3.2-Gpixel camera, and an automated data processing system. The summit facility is currently under construction on Cerro Pachón in Chile, with major vendor subsystem deliveries and integration planned over the next several years. This paper summarizes the status of the activities of the T and S group, tasked with design, analysis, and construction of the summit and base facilities and infrastructure necessary to control the survey, capture the light, and calibrate the data. All major telescope work package procurements have been awarded to vendors and are in varying stages of design and fabrication maturity and completion. The unique M1M3 primary/tertiary mirror polishing effort is completed and the mirror now resides in storage waiting future testing. Significant progress has been achieved on all the major telescope subsystems including the summit facility, telescope mount assembly, dome, hexapod and rotator systems, coating plant, base facility, and the calibration telescope. In parallel, in-house efforts including the software needed to control the observatory such as the scheduler and the active optics control, have also seen substantial advancement. The progress and status of these subsystems and future LSST plans during this construction phase are presented.
The Large Synoptic Survey Telescope (LSST) is a large (8.4 meter) wide-field (3.5 degree) survey telescope, which will be located on the Cerro Pachón summit in Chile. Both the Secondary Mirror (M2) Cell Assembly and Camera utilize hexapods to facilitate optical positioning relative to the Primary/Tertiary (M1M3) Mirror. A rotator resides between the Camera and its hexapod to facilitate tracking. The final design of the hexapods and rotator has been completed by Moog CSA, who are also providing the fabrication and integration and testing. Geometric considerations preclude the use of a conventional hexapod arrangement for the M2 Hexapod. To produce a more structurally efficient configuration the camera hexapod and camera rotator will be produced as a single unit. The requirements of the M2 Hexapod and Camera Hexapod are very similar; consequently to facilitate maintainability both hexapods will utilize identical actuators. The open loop operation of the optical system imposes strict requirements on allowable hysteresis. This requires that the hexapod actuators use flexures rather than more traditional end joints. Operation of the LSST requires high natural frequencies, consequently, to reduce the mass relative to the stiffness, a unique THK rail and carriage system is utilized rather than the more traditional slew bearing. This system utilizes two concentric tracks and 18 carriages.
The civil work, site infrastructure and buildings for the summit facility of the Large Synoptic Survey Telescope (LSST) are among the first major elements that need to be designed, bid and constructed to support the subsequent integration of the dome, telescope, optics, camera and supporting systems. As the contracts for those other major subsystems now move forward under the management of the LSST Telescope and Site (T and S) team, there has been inevitable and beneficial evolution in their designs, which has resulted in significant modifications to the facility and infrastructure. The earliest design requirements for the LSST summit facility were first documented in 2005, its contracted full design was initiated in 2010, and construction began in January, 2015. During that entire development period, and extending now roughly halfway through construction, there continue to be necessary modifications to the facility design resulting from the refinement of interfaces to other major elements of the LSST project and now, during construction, due to unanticipated field conditions. Changes from evolving interfaces have principally involved the telescope mount, the dome and mirror handling/coating facilities which have included significant variations in mass, dimensions, heat loads and anchorage conditions. Modifications related to field conditions have included specifying and testing alternative methods of excavation and contending with the lack of competent rock substrate where it was predicted to be. While these and other necessary changes are somewhat specific to the LSST project and site, they also exemplify inherent challenges related to the typical timeline for the design and construction of astronomical observatory support facilities relative to the overall development of the project.
The Large Synoptic Survey Telescope (LSST) has a 10 degrees square field of view which is achieved through a 3 mirror optical system comprised of an 8.4 meter primary, 3.5 meter secondary (M2) and a 5 meter tertiary mirror. The M2 is a 100mm thick meniscus convex asphere. The mirror surface is actively controlled by 72 axial electromechanical actuators (axial actuators). Transverse support is provided by 6 active tangential electromechanical actuators (tangent links). The final design has been completed by Harris Corporation. They are also providing the fabrication, integration and testing of the mirror cell assembly, as well as the figuring of the mirror. The final optical surface will be produced by ion figuring. All the actuators will experience 1 year of simulated life testing to ensure that they can withstand the rigorous demands produced by the LSST survey mission. Harris Corporation is providing optical surface metrology to demonstrate both the quality of the optical surface and the correctablility produced by the axial actuators.
The LSST M1/M3 combines an 8.4 m primary mirror and a 5.1 m tertiary mirror on one glass substrate. The combined mirror was completed at the Richard F. Caris Mirror Lab at the University of Arizona in October 2014. Interferometric measurements show that both mirrors have surface accuracy better than 20 nm rms over their clear apertures, in nearsimultaneous tests, and that both mirrors meet their stringent structure function specifications. Acceptance tests showed that the radii of curvature, conic constants, and alignment of the 2 optical axes are within the specified tolerances. The mirror figures are obtained by combining the lab measurements with a model of the telescope’s active optics system that uses the 156 support actuators to bend the glass substrate. This correction affects both mirror surfaces simultaneously. We showed that both mirrors have excellent figures and meet their specifications with a single bending of the substrate and correction forces that are well within the allowed magnitude. The interferometers do not resolve some small surface features with high slope errors. We used a new instrument based on deflectometry to measure many of these features with sub-millimeter spatial resolution, and nanometer accuracy for small features, over 12.5 cm apertures. Mirror Lab and LSST staff created synthetic models of both mirrors by combining the interferometric maps and the small highresolution maps, and used these to show the impact of the small features on images is acceptably small.
The Steward Observatory Mirror Lab is nearing completion of the combined primary and tertiary mirrors of the Large
Synoptic Survey Telescope. Fabrication of the combined mirror requires simulation of an active-optics correction that
affects both mirror surfaces in a coordinated way. As is common for large mirrors, the specification allows correction of
large-scale figure errors by a simulated bending of the substrate with the 156 mirror support actuators. Any bending
affects both mirrors, so this active-optics correction is constrained by the requirement of bending the substrate so both
mirrors meet their figure specifications simultaneously. The starting point of the simulated correction must be
measurements of both mirrors with the substrate in the same shape, i. e. the same state of mechanical and thermal stress.
Polishing was carried out using a 1.2 m stressed lap for smoothing and large-scale figuring, and a set of smaller passive
rigid-conformal laps on an orbital polisher for deterministic small-scale figuring. The primary mirror is accurate to about
25 nm rms surface after the active-optics correction, while work continues toward completion of the tertiary.
The Large Synoptic Survey Telescope (LSST) is a three-mirror wide-field survey telescope with the primary and tertiary
mirrors on one monolithic substrate<sup>1</sup>. This substrate is made of Ohara E6 borosilicate glass in a honeycomb sandwich,
spin cast at the Steward Observatory Mirror Lab at The University of Arizona<sup>2</sup>. Each surface is aspheric, with the
specification in terms of conic constant error, maximum active bending forces and finally a structure function
specification on the residual errors<sup>3</sup>. There are high-order deformation terms, but with no tolerance, any error is
considered as a surface error and is included in the structure function. The radii of curvature are very different, requiring
two independent test stations, each with instantaneous phase-shifting interferometers with null correctors. The primary
null corrector is a standard two-element Offner null lens. The tertiary null corrector is a phase-etched computer-generated
hologram (CGH). This paper details the two optical systems and their tolerances, showing that the uncertainty
in measuring the figure is a small fraction of the structure function specification. Additional metrology includes the radii
of curvature, optical axis locations, and relative surface tilts. The methods for measuring these will also be described
along with their tolerances.
The Large Synoptic Survey Telescope (LSST) is an 8.4 meter, 3.5 degree, wide-field survey telescope. The survey mission requires a short slew, settling time of 5 seconds for a 3.5 degree slew. Since it does not include a fast steering mirror, the telescope has stringent vibration limitations during observation. Meeting these requirements will be facilitated by a stiff compact Telescope Mount Assembly (TMA) riding on a robust pier and by added damping. The TMA must also be designed to facilitate maintenance. The design is an altitude over azimuth welded and bolted assembly fabricated from mild steel.
The Large Synoptic Survey Telescope (LSST) Telescope integration and test plan is phased to ensure that subsystems and services are available to support the integration flow. It begins with the summit facility construction and shows how the major subsystems feed into the activities through final testing. In order to minimize the amount of hardware mated for the first time during that period, the approach is to favor all hardware mated and pre-tested at vendors’ facilities with associated hardware and software prior to delivery onsite. The integration and test plan exploits the diffraction limited on-axis image quality of the three-mirror design. In addition, fiducials will be used during optical acceptance testing at vendors’ facilities to capture the optical axis geometry of each optical element. These fiducials will be used during the integration and tests sequence to facilitate the telescope optical alignment. In this paper, we describe the major steps of the LSST telescope integration and test sequence prior to the start of commissioning with the science camera.
The Large Synoptic Survey Telescope (LSST) is a large (8.4 meter) wide-field (3.5 degree) survey telescope, which will be located on the Cerro Pachón summit in Chile. As a result of the wide field of view, its optical system is unusually susceptible to stray light; consequently besides protecting the telescope from the environment the rotating enclosure (Dome) also provides indispensible light baffling. All dome vents are covered with light baffles which simultaneously provide both essential dome flushing and stray light attenuation. The wind screen also (and primarily) functions as a light screen providing only a minimum clear aperture. Since the dome must operate continuously, and the drives produce significant heat, they are located on the fixed lower enclosure to facilitate glycol water cooling. To accommodate day time thermal control, a duct system channels cooling air provided by the facility when the dome is in its parked position.
The Large Synoptic Survey Telescope (LSST) has recently completed its Final Design Review and the Project is preparing for a 2014 construction authorization. The telescope system design supports the LSST mission to conduct a wide, fast, deep survey via a 3-mirror wide field of view optical design, a 3.2-Gpixel camera, and an automated data processing system. The observatory will be constructed in Chile on the summit of Cerro Pachón. This paper summarizes the status of the Telescope and Site group. This group is tasked with design, analysis, and construction of the summit and base facilities and infrastructure necessary to control the survey, capture the light, and calibrate the data. Several early procurements of major telescope subsystems have been completed and awarded to vendors, including the mirror systems, telescope mount assembly, hexapod and rotator systems, and the summit facility. These early contracts provide for the final design of interfaces based upon vendor specific approaches and will enable swift transition into construction. The status of these subsystems and future LSST plans during construction are presented.
The Large Synoptic Survey Telescope (LSST) relies on a set of calibration systems to achieve the survey photometric performances over a wide range of observing conditions. Its purpose is to consistently and accurately measure the observatory instrumental response and the atmospheric transparency during LSST observing. The instrumental response calibration will be performed regularly to monitor any variation of the transmission during the duration of the survey. The atmospheric data will be acquired nightly and processed to atmospheric models. In this paper, we describe the calibration screen system that will be used to perform the instrumental response calibration and the atmospheric calibration system including the auxiliary telescope dedicated to the acquisition of spectral data to determine the atmospheric transmission.
The Large Synoptic Survey Telescope (LSST) is a large (8.4 meter) wide-field (3.5 degree) survey telescope, which will
be located on the Cerro Pachón summit in Chile. Both the Secondary Mirror (M2) Cell Assembly and Camera utilize
hexapods to facilitate optical positioning relative to the Primary/Tertiary (M1M3) Mirror. Geometric considerations
preclude the use of a conventional hexapod arrangement for the M2 Hexapod. A rotator resides between the Camera and
its hexapod to facilitate tracking. The requirements of the M2 Hexapod and Camera Hexapod are very similar;
consequently to facilitate maintainability both hexapods will utilize identical actuators.
The 3.5-meter diameter Large Synoptic Survey Telescope (LSST) secondary (M2) mirror utilizes a 100mm thick
meniscus ULE™ blank completed by Corning Incorporated in 2009. Sub-aperture interferometry will guide the
polishing process to meet mirror structure function requirements. The convex asphere is actively supported by 72
axial actuators and 6 tangential links. These tangent links utilize an embedded lever system to meet the
requirements. The axial actuators have force limiting devices. The control system utilizes a higher level "outer loop
controller" for monitoring and commanding the tangent links and axial actuators. Numerous sensors determine the
assembly status. To prevent thermally induced image degradation, the interior air of the M2 cell is conditioned.
The planned construction and completion of the Large Synoptic Survey Telescope (LSST) Project consists of phased
activities. The initial telescope construction period will transition to a multi-year commissioning phase, which will
conclude with final hand off to science operations. The initial telescope alignment will utilize laser tracker fiducials
and nodal aberration theory (NAT) to demonstrate Engineering First Light with a three-mirror optical system and
test camera, prior to the integration of the science camera. This plan exploits the diffraction limited on-axis image
quality of the three-mirror design. Commissioning consists of final integration of the three LSST subsystems
(Telescope, Camera, and Data Management), followed by on-sky science verification to show compliance with the
survey performance specifications.
As previously reported (at the SPIE Astronomical Instrumentation conference of 2010 in San Diego<sup>1</sup>), the Large
Synoptic Survey Telescope (LSST) utilizes a three-mirror design in which the primary (M1) and tertiary (M3) mirrors
are two concentric aspheric surfaces on one monolithic substrate. The substrate material is Ohara E6 borosilicate glass,
in a honeycomb sandwich configuration, currently in production at The University of Arizona’s Steward Observatory
Mirror Lab. We will provide an update to the status of the mirrors and metrology systems, which have advanced from
concepts to hardware in the past two years. In addition to the normal requirements for smooth surfaces of the appropriate
prescriptions, the alignment of the two surfaces must be accurately measured and controlled in the production lab,
reducing the degrees of freedom needed to be controlled in the telescope. The surface specification is described as a
structure function, related to seeing in excellent conditions. Both the pointing and centration of the two optical axes are
important parameters, in addition to the axial spacing of the two vertices. This paper details the manufacturing process
and metrology systems for each surface, including the alignment of the two surfaces. M1 is a hyperboloid and can utilize
a standard Offner null corrector, whereas M3 is an oblate ellipsoid, so it has positive spherical aberration. The null
corrector is a phase-etched computer-generated hologram (CGH) between the mirror surface and the center-of-curvature.
Laser trackers are relied upon to measure the alignment and spacing as well as rough-surface metrology during looseabrasive
The Large Synoptic Survey Telescope (LSST) utilizes a three-mirror design in which the primary (M1) and tertiary (M3)
mirrors are two concentric aspheric surfaces on one monolithic substrate. The substrate material is Ohara E6 borosilicate
glass, in a honeycomb sandwich configuration, currently in production at The University of Arizona's Steward
Observatory Mirror Lab. In addition to the normal requirements for smooth surfaces of the appropriate prescriptions, the
alignment of the two surfaces must be accurately measured and controlled in the production lab. Both the pointing and
centration of the two optical axes are important parameters, in addition to the axial spacing of the two vertices. This
paper describes the basic metrology systems for each surface, with particular attention to the alignment of the two
surfaces. These surfaces are aspheric enough to require null correctors for each wavefront. Both M1 and M3 are concave
surfaces with both non-zero conic constants and higher-order terms (6th order for M1 and both 6th and 8th orders for M3).
M1 is hyperboloidal and can utilize a standard Offner null corrector. M3 is an oblate ellipsoid, so has positive spherical
aberration. We have chosen to place a phase-etched computer-generated hologram (CGH) between the mirror surface
and the center-of-curvature (CoC), whereas the M1 null lens is beyond the CoC. One relatively new metrology tool is the
laser tracker, which is relied upon to measure the alignment and spacings. A separate laser tracker system will be used to
measure both surfaces during loose abrasive grinding and initial polishing.
The Large Synoptic Survey Telescope (LSST) flat-fields must repeatedly trace not only the spatial response variations,
but also the chromatic response through the entire optical system, with an accuracy driven by the photometric
requirements for the LSST survey data. This places challenging requirements on the LSST Calibration Dome Screen,
which must uniformly illuminate the 8.4-meter diameter telescope pupil over its 3.5-degree field of view at desired
monochromatic wavelengths in a way that allows the measurement of the total system throughput from entrance pupil to
the digitization of charge in the camera electronics. This includes the reflectivity of the mirrors, transmission of the
refractive optics and filters, the quantum efficiency of the sensors in the camera, and the gain and linearity of the sensor
read-out electronics. The baseline design uses a single tunable laser and includes an array of discrete projectors. The
projected flux of light produced by the screen must fill the entire telescope pupil and provide uniform illumination to 1%
at the focal plane and to within 0.25% over any optical trajectory within 0.5 degrees of each other. The wavelength of
light is tunable across the LSST bandpass from 320 nm to 1080 nm. The screen also includes a broad-band ("white")
light source with known Spectral Energy Density (SED) that spans the same range of wavelengths.
In this paper, conical foil x-ray telescope technology is reviewed and performance predictions of the Danish Space Research Institute XSPECT telescope design are conducted. Analysis includes discussion of geometrical aberrations, diffraction effects, assembly and alignment errors, and optical fabrication errors. NASA's Optical Surface Analysis Code and Encircled Energy for Grazing incidence optics computer codes are used to predict geometrical performance and model degradation effects of residual surface irregularities. Results are incorporated into a system error budget and parametric image quality predictions are performed. Finally, a summary of image quality predictions and an evaluation of conical foil telescope technology for space astronomy applications are presented.