This PDF file contains the front matter associated with SPIE Proceedings Volume 9906, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

Together with the ongoing major instrument upgrade of the Hobby-Eberly Telescope (HET) we present the planned upgrade of the HET Segment Control System (SCS) to SCS2. Because HET's primary mirror is segmented into 91 individual 1-meter hexagonal mirrors, the SCS is essential to maintain the mirror alignment throughout an entire night of observations. SCS2 will complete tip, tilt and piston corrections of each mirror segment at a significantly higher rate than the original SCS. The new motion control hardware will further increase the system's reliability. The initial optical measurements of this array are performed by the Mirror Alignment Recovery System (MARS) and the HET Extra Focal Instrument (HEFI). Once the segments are optically aligned, the inductive edge sensors give sub-micron precise feedback of each segment's positions relative to its adjacent segments. These sensors are part of the Segment Alignment Maintenance System (SAMS) and are responsible for providing information about positional changes due to external influences, such as steep temperature changes and mechanical stress, and for making compensatory calculations while tracking the telescope on sky. SCS2 will use the optical alignment systems and SAMS inputs to command corrections of every segment in a closed loop. The correction period will be roughly 30 seconds, mostly due to the measurement and averaging process of the SAMS algorithm. The segment actuators will be controlled by the custom developed HET Segment MOtion COntroller (SMOCO). It is a direct descendant of University Observatory Munich's embedded, CAN-based system and instrument control tool-kit. To preserve the existing HET hardware layout, each SMOCO will control two adjacent mirror segments. Unlike the original SCS motor controllers, SMOCO is able to drive all six axes of its two segments at the same time. SCS2 will continue to allow for sub-arcsecond precision in tip and tilt as well as sub-micro meter precision in piston. These estimations are based on the current performance of the segment support mechanics. SMOCO's smart motion control allows for on-the-y correction of the move targets. Since SMOCO uses state-of-the-art motion control electronics and embedded decentralized controllers, we expect reduction in thermal emission as well as less maintenance time.

The W. M. Keck Observatory Segment Repair Project is repairing stress-induced fractures near the support points in the primary mirror segments. The cracks are believed to result from deficiencies in the original design and implementation of the adhesive joints connecting the Invar support components to the ZERODUR mirror. Stresses caused by temperature cycling over 20 years of service drove cracks that developed at the glass-metal interfaces. Over the last few years the extent and cause of the cracks have been studied, and new supports have been designed. Repair of the damaged glass required development of specialized tools and procedures for: (1) transport of the segments; (2) pre-repair metrology to establish the initial condition; (3) removal of support hardware assemblies; (4) removal of the original supports; (5) grinding and re-surfacing the damaged glass areas; (6) etching to remove sub-surface damage; (7) bonding new supports; (8) re-installation of support assemblies; and (9) post-repair metrology. Repair of the first segment demonstrated the new tools and processes. On-sky measurements before and after repair verified compliance with the requirements. This paper summarizes the repair process, on-sky results, and transportation system, and also provides an update on the project status and schedule for repairing all 84 mirror segments. Strategies for maintaining quality and ensuring that repairs are done consistently are also presented.

The Canada-France-Hawaii-Telescope Corporation (CFHT) plans to repurpose its observatory on the summit of Maunakea and operate a (60 segment) 11.25m aperture wide field spectroscopic survey telescope, the Maunakea Spectroscopic Explorer (MSE). The prime focus telescope will be equipped with dedicated instrumentation to take advantage of one of the best sites in the northern hemisphere and offer its users the ability to perform large surveys. Central themes of the development plan are reusing and upgrading wherever possible. MSE will reuse the CFHT site and build upon the existing observatory infrastructure, using the same building and telescope pier as CFHT, while minimizing environmental impact on the summit. MSE will require structural support upgrades to the building to meet the latest building seismic code requirements and accommodate a new larger telescope and upgraded enclosure. It will be necessary to replace the current dome since a larger slit opening is needed for a larger telescope. MSE will use a thermal management system to remove heat generated by loads from the building, flush excess heat from lower levels, and maintain the observing environment temperature. This paper describes the design approach for redeveloping the CFHT facility for MSE. Once the project is completed the new facility will be almost indistinguishable on the outside from the current CFHT observatory. Past experience and lessons learned from CFHT staff and the astronomical community will be used to create a modern, optimized, and transformative scientific data collecting machine.

The Hobby-Eberly Telescope (HET) is an innovative large telescope, located in West Texas at the McDonald Observatory. The HET operates with a fixed segmented primary and has a tracker, which moves the four-mirror corrector and prime focus instrument package to track the sidereal and non-sidereal motions of objects. We have completed a major multi-year upgrade of the HET that has substantially increased the pupil size to 10 meters and the field of view to 22 arcminutes by replacing the corrector, tracker, and prime focus instrument package. The new wide field HET will feed the revolutionary integral field spectrograph called VIRUS, in support of the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX^§), a new low resolution spectrograph (LRS2), an upgraded high resolution spectrograph (HRS2), and later the Habitable Zone Planet Finder (HPF). The upgrade is being commissioned and this paper discusses the completion of the installation, the commissioning process and the performance of the new HET.

Chinese astronomical community has suggested to construct a high resolution precision and wide field survey of universal optical / infrared telescope, suitable for a wide range of cutting-edge scientific research subject. The telescope diameter is 12 meters, and it is composed of 84 pieces of hexagonal mirrors. After the completion, it could be a world's largest telescope. Its wide field survey function will be work together with the 30 meters telescope in the near future on the observation of complementary. The telescope optical system adopted innovative design ideas, its multiple focuses can achieve rapid switching; its atmospheric dispersion corrector lens-prism can correct aberration also, and with the advantage of simple structure; two layers of Nasmyth platform can be placed more scientific instruments. LAMOST, a Chinese large spectrum survey telescope has been built and put into operation many years, it has successfully developed the two segmented optical mirrors and one of them is with deformation of thin mirror active optical technology, as well as the batch grinding hexagonal off-axis mirror technology developed in recent years, for construction of the 12 meters telescope laid a good technical foundation.

Motivated by a desire to improve the KPNO Mayall 4m telescope’s pointing and tracking performance prior to the start of the DESI installation and by a need to improve the maintainability of its telescope control system (TCS), we recently completed a major modernization of that system based heavily on recent changes made at the CTIO Blanco 4m, as described by Warner et al (2012). We describe here the things we did differently from the Blanco upgrade. We also present results from the as-built performance of the new servo and pointing systems.

We present a new application of frame transfer Charge-Coupled Device (CCD) on measuring astronomical seeing. If a telescope is equipped with a shutterless, frame transfer CCD camera, a bright star will generate a trail during the frame transfer phase. Because the transfer is very fast, the trail is a series of short exposures (about 1 ms) of the target star. Therefore the centroid is jittery due to atmospheric turbulence, and the amplitude can be utilized to derive astronomical seeing. We present the preliminary results from STA1600FT CCD on the second Antarctic Survey Telescope (AST3) tested in China. The trail seeing moderately agrees with the simultaneous DIMM seeing.

During the last recent years, designs for several giant telescopes ranging from 20 to 40m in diameter are being developed: European Extremely Large Telescope Telescope (TMT). (E-ELT), Giant Magellan Telescope (GMT) and Thirty Meter It is evident that simple direct up-scaling of solutions that were more or less successful in the 8 to 10m class telescopes can not lead to viable designs for the future giant telescopes. New solutions are required to provide adequate load sharing, to cope with the large-scale derived deflections and to provide the required compliance, or to respond to structure-mechanism control interaction issues, among others. From IDOM experience in the development of the Dome and Main Structure of the European Extremely Large Telescope and our participation in some other giant telescopes, this paper reviews several design approaches for the main mechanisms and key structural parts of enclosures and mounts/main structures for giant telescopes, analyzing pros and cons of the different alternatives and outlining the preferred design schemes. The assessment is carried out mainly from a technical and performance-based angle but it also considers specific logistical issues for the assembly of these large telescopes in remote and space-limited areas, together with cost and schedule related issues.

The Canadian Hydrogen Intensity Mapping Experiment (CHIME) Pathfinder radio telescope is currently surveying the northern hemisphere between 400 and 800 MHz. By mapping the large scale structure of neutral hydrogen through its redshifted 21 cm line emission between z∼0.8-2.5 CHIME will contribute to our understanding of Dark Energy. Bright astrophysical foregrounds must be separated from the neutral hydrogen signal, a task which requires precise characterization of the polarized telescope beams. Using the DRAO John A. Galt 26 m telescope, we have developed a holography instrument and technique for mapping the CHIME Pathfinder beams. We report the status of the instrument and initial results of this effort.

The suspension and rotation systems (typically called bogies) for Extremely Large Telescope (ELT) enclosures will carry structures that are 2-3 times greater in diameter and much heavier than enclosures for the previous generation of 6-10m telescopes. Via on-site visits and/or engineering documentation, we have surveyed eleven optical, infrared, and submillimeter 3-15m telescope enclosures, and report on key design features of the suspension and rotation systems, including wheel and track geometry, the wheel/track interface, average load per wheel, rotation drive method, etc. We discuss key considerations for the development of future suspension and rotation systems for ELT enclosures.

Following a 7-year, multi-million dollar effort to fabricate a 730 kg, 4 element Wide Field Corrector (WFC) for the Hobby-Eberly Telescope (HET) Wide Field Upgrade (WFU), it needed to be transported 820 km to its destination at the McDonald Observatory in West Texas. The final system optical test for the assembly required repeatability in the +/- 2μm range. Due to the size, mass, and ultimate destination of the payload, the only option available for transport was via roadway on a flat-bed trailer. While the route was primarily interstate highway, it presented a great variety of vibrational inputs due to poor paving conditions, and mountain roadways. Consideration also had be given to avoiding high ambient temperatures. Early in the design of the corrector assembly it was assumed that cable isolators would be the key element to isolate the payload from vibrational inputs, however, few documented references were available to provide the assurances required for transporting a load so key to the success of the telescope program. Tests were designed to simulate the load conditions, and inputs and outputs to the test load were measured for verification of the isolator performance. This was followed up with monitoring of vibration throughput during the actual shipment of the WFC. Upon arrival at the destination, the alignment of the assembly was checked and found to have no appreciable change in the alignment. Data and lessons learned are presented on the performance of air-ride trailers as well as the performance of cable isolators.

Space debris is becoming a very important and urgent problem for present and future space activities. For that reason many public and private Institutions in the world are being involved in order to monitor and control the debris population increase and to understand which facilities can be used for improving the surveillance and tracking capabilities. In this framework in 2014 we performed some preliminary observations in a beam parking, CW mode and a bistatic configuration, with a transmitter of 4 kW of the Italian Air Force and the SRT (Sardinia Radio Telescope) a 64 meters radiotelescope used as a receiver. We performed the observations in P band at 410 MHz, receiving the signal diffused from some debris of different sizes and distances in LEO orbit, in order to understand the performances and capabilities of the system. In this article we will describe the results of this observations campaign, the simulation work done for preparing it, the RCS (radar cross section) observed, the level of the received signals, the Doppler measurements, and the work we are doing for developing a new and higher performing digital back end, able to process the data received.

In 2013 the process of developing an Orbital Debris and Satellite observation capability for the United Kingdom Infrared Telescope was initiated. This process involved the modification of various operational aspects of the observatory. After a year of implementing the modifications the observatory was capable of providing deep space observations of orbital debris and satellites in a queue based format. The telescope has been operating with this capability for the past 2.5 years and has generated terabytes of observational data on orbital debris and satellites that are in the GEO satellite belt distributed across the Pacific Ocean.

The Large Synoptic Survey Telescope (LSST) Project¹ 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.

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.

This paper describes the status and details of the large synoptic survey telescope^1,2,3 mount assembly (TMA). On June 9^th, 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 a large (8.4 meter) wide-field (3.5 degree) survey telescope, which will be located on the Cerro Pachón summit in Chile ¹. As a result of the Telescope wide field of view, the optical system is unusually susceptible to stray light ². In addition, balancing the effect of wind induced telescope vibrations with Dome seeing is crucial. The rotating enclosure system (Dome) includes a moving wind screen and light baffle system. All of the Dome vents include hinged light baffles, which provide exceptional Dome flushing, stray light attenuation, and allows for vent maintenance access from inside the Dome. The wind screen also functions as a light screen, and helps define a clear optical aperture for the Telescope. The Dome must operate continuously without rotational travel limits to accommodate the Telescope cadence and travel. Consequently, the Azimuth drives are located on the fixed lower enclosure to accommodate glycol water cooling without the need for a utility cable wrap. An air duct system aligns when the Dome is in its parked position, and this provides air cooling for temperature conditioning of the Dome during the daytime. A bridge crane and a series of ladders, stairs and platforms provide for the inspection, maintenance and repair of all of the Dome mechanical systems. The contract to build the Dome was awarded to European Industrial Engineering in Mestre, Italy in May 2015. In this paper, we present the final design of this telescope and site sub-system.

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.

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) 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).

The University of Tokyo Atacama Observatory Project is to construct a 6.5m infrared telescope at the summit of Co. Chajnantor (5640m altitude) in northern Chile, promoted by the University of Tokyo. Thanks to the dry climate (PWV~0.5mm) and the high altitude, it will achieve excellent performance in the NIR to MIR wavelengths. The telescope has two Nasmyth foci where the facility instruments are installed and two folded-Cassegrain foci for carry-in instruments. All these four foci can be switched by rotating a tertiary mirror. The final focal ratio is 12.2 and the telescope foci have large field-of-view of 25ʹ in diameter. We adopted the 6.5m light-weighted borosilicate honeycomb primary mirror and its support system that are developed by Steward Observatory Richard F. Caris Mirror Lab. The dome enclosure has the shape of carousel, and large ventilation windows with shutters control the wind to flush heat inside the dome. The operation building with control room, aluminizing chamber and maintenance facilities is located at the side of the dome. Two cameras, SWIMS for spectroscopy and imaging in the near-infrared and MIMIZUKU in the mid-infrared, are being developed as the first-generation facility instruments. The operation of the telescope will be remotely carried out from a base facility at San Pedro de Atacama, 50km away from the summit. The construction of the telescope is now underway. Fabrication of the telescope mount has almost finished, and the pre-assembly has been carried out in Japan. The primary, secondary, and tertiary mirrors and their cells have been also fabricated, as well as their cells and support systems. Fabrication of the enclosure is now underway, and their pre-assembly in Japan will be carried out in 2016. Construction of the base facility at San Pedro de Atacama has been already completed in 2014, and operated for the activities in Atacama. The telescope is now scheduled to see the first light at the beginning of 2018.

The Telescopio San Pedro Martir (TSPM) is a new ground-based optical telescope project, with a 6.5 meters honeycomb primary mirror, to be built in the Observatorio Astronomico Nacional on the Sierra San Pedro Martir (OAN-SPM) located in Baja California, Mexico. The OAN-SPM has an altitude of 2830 meters above sea level; it is among the best location for astronomical observation in the world. It is located 1830 m higher than the atmospheric inversion layer with 70% of photometric nights, 80% of spectroscopic nights and a sky brightness up to 22 mag/arcsec2.

The TSPM will be suitable for general science projects intended to improve the knowledge of the universe established on the Official Mexican Program for Science, Technology and Innovation 2014-2018. The telescope efforts are headed by two Mexican institutions in name of the Mexican astronomical community: the Universidad Nacional Autonoma de Mexico and the Instituto Nacional de Astrofisica, Optica y Electronica. The telescope has been financially supported mainly by the Consejo Nacional de Ciencia y Tecnologia (CONACYT). It is under development by Mexican scientists and engineers from the Center for Engineering and Industrial Development. This development is supported by a Mexican-American scientific cooperation, through a partnership with the University of Arizona (UA), and the Smithsonian Astrophysical Observatory (SAO). M3 Engineering and Technology Corporation in charge of enclosure and building design.

The TSPM will be designed to allow flexibility and possible upgrades in order to maximize resources. Its optical and mechanical designs are based upon those of the Magellan and MMT telescopes. The TSPM primary mirror and its cell will be provided by the INAOE and UA. The telescope will be optimized from the near ultraviolet to the near infrared wavelength range (0.35-2.5 m), but will allow observations up to 26μm. The TSPM will initially offer a f/5 Cassegrain focal station. Later, four folded Cassegrain and two Nasmyth focal stations are contemplated, nominally with focal ratios of f/5 and f/11. The concept will allow the use of existing instruments like MMIRS and MEGACAM. Available experience from currently working ground-based telescopes will be integrated with up-to-date technology specially for control and information management systems.

Its mount is the well-known azimuth-elevation configuration. The telescope total mass is estimated in about 245 metric tons, with a total azimuth load of 185 metric tons including around 110 metric tons as the total elevation load. A tracking error lower than 0.03 arcsec RMS is expected under steady wind up to 50 Km/h. An open-loop pointing accuracy between 10 and 2 arcsec is planned. The TSPM is in its design phase. It is the first large optical ground-based telescope to be designed and developed primarily by Mexican scientists and engineers. This endeavor will result in the improvement of the scientific and technical capabilities of Mexico including complex scientific instruments development, systems engineering and project management for large engineering projects. In this paper, which aims to gather the attention of the community for further discussions, we present the engineering preliminary design, the basic architecture and challenging technical endeavors of the TSPM project.

ALMA is now nearing the end of its third cycle of operations, and is transitioning from ‘early science’ to regular PI-driven observing. The array has been operated over the complete range of available baseline lengths, from <10m with the ACA out to the maximum of 16km in the long-baseline configuration. Typically 40 12m-diameter antennas are now used at any one time. In this paper, we summarise the advertised capabilities and how they have evolved in the first 5 years, the proposal pressure and ‘hot spots’, and describe some of the issues with the real measured system performance. We also outline the observing statistics, project completion rates, and papers from ALMA. Finally we highlight some of the new transformational science coming from this facility.

Since the ALMA North America Prototype Antenna was awarded to the Smithsonian Astrophysical Observatory (SAO), SAO and the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA) are working jointly to relocate the antenna to Greenland. This paper shows the status of the antenna retrofit and the work carried out after the recommissioning and subsequent disassembly of the antenna at the VLA has taken place. The next coming months will see the start of the antenna reassembly at Thule Air Base. These activities are expected to last until the fall of 2017 when commissioning should take place. In parallel, design, fabrication and testing of the last components are taking place in Taiwan.

The MMT Observatory, a joint venture of the Smithsonian Institution and the University of Arizona, operates the 6.5-m MMT telescope on the summit of Mount Hopkins approximately 45 miles south of Tucson, AZ. The upgraded telescope has been in routine operation for nearly fifteen years and, as such, is a very reliable and productive general purpose astronomical instrument. The telescope can be configured with one of three secondary mirrors that feed more than ten instruments at the Cassegrain focus. In this paper we provide an overview of the the telescope, its current capabilities, and its performance. We will review the existing suite of instruments and their different modes of operation. We will describe some of the general operations challenges and strategies for the Observatory. Finally, we will discuss plans for the near-term future including technical upgrades, new instrumentation and routine queue operation of MMIRS and Binospec.

ESO is now fully engaged in building the European Extremely Large Telescope (E-ELT), a 40-m class optical nearinfrared telescope to be installed on top of Cerro Armazones, Chile and become operational around 2025. The Programme was formally approved by ESO Council back in 2012. However the required funding level for starting construction was actually reached in 2014, leading to a Green Light to start large construction contracts in December of that year. Since then, the programme has entered a very busy phase leading to the signature of the first major industrial contracts as well as the agreements with scientific institutes in ESO Member States to design and built the first suite of science instruments. This paper summarizes the current status of the E-ELT Programme and presents some aspects related to scientific objectives, managerial organization, programmatic aspects and system engineering approach. It also outlines the procurement strategies put in place to achieve the goal of the Programme: building the 'world's biggest eye on the sky' within the next decade.

EELT AIV is the activity of assembly, integration and verification of EELT (European Extremely Large Telescope) subsystems to deliver a telescope capable of fulfilling its top-level requirements and ready to start science commissioning, leading to operations. The AIV (Assembly Integration Verification) phase covers all technical activities on Armazones and nearby Paranal Observatory from the moment the sub-systems and components are delivered or accepted on-site (from the responsible sub-system project manager). AIV includes final system tests of the completed telescope (known as “Technical Commissioning”) and the installation, alignment and telescope integration of the science instruments. The AIV phase ends with the handover of the completed telescope with installed instruments, to the start of Science Commissioning. Responsibility then passes to the Commissioning team, however the technical resources for debugging and tuning the telescope and instrument will come from a combination of the AIV team working together with the Paranal operations staff. AIV is one of the major technical challenge of E-ELT. The sheer scale and complexity of the telescope involves challenging logistics and scheduling i.e. 798 mirror segments with a staged delivery over four years, including 9,048 edge sensor and 2,394 position actuators. More than ten major sub-systems e.g. M2-3-4-5, PreFocal Station (PFS) and instruments will be integrated and tested in parallel. Finally, the technical commissioning phase will be a significant challenge. E-ELT is a highly complex active telescope system with a fully-integrated adaptive optics (AO) system. During early testing nothing will be straightforward and there will be many system-level problems to overcome. It will take a dedicated team of the “best of the best” people to troubleshoot, debug, tune, and hand over as an operational facility.

For the Thirty Meter Telescope (TMT) that aims high-resolution and high-sensitivity observations for optical-infrared astronomy, detailed design is underway for Telescope Structure System (STR) including the mount control system and the segment handling system. The technical requirements for the STR system are very challenging on its performance and interface condition with telescope-mounted optics and observation instruments. The major challenging technical requirements include low flexure of mirror support structure and low optical path length variation due to gravitational deformation, high seismic performance against large earthquake, very accurate mount drive control for high tracking and guiding performance, and fast, safe and labor-saving segment exchange. To meet these technical requirements, Mitsubishi Electric Corporation (MELCO) has made a detailed design and technology development. In this paper, overview of major key technologies is introduced that is adopted for the TMT telescope structure in the detailed design and technology development.

This paper describes the design of the surface metrology instrument used for manufacturing the 1.5m segmented telescope mirrors. It discusses challenges associated with the design of the instrument, tracking of segment surface data measured with the instrument and cross calibration of the instruments for use at multiple manufacturing sites. The instruments were evaluated for repeatability and reproducibility.

The Giant Magellan Telescope (GMT) will have a 25.4-meter diameter effective aperture, and is one the three currently planned next generation extremely large telescopes (ELTs). The GMT will be located at the summit of Cerro Campanas at the Las Campanas Observatory (LCO) in Chile, one the world’s best observing sites. This paper provides an overview of the site master plan comprising site infrastructure, enclosure, and facilities, and outlines the analysis of alternative trade studies that will lead to the final design. Also presented is an update of the site infrastructure development and preconstruction activities currently underway that will be completed prior to the beginning of enclosure construction near the end of 2016.

Future large telescopes, such as E-ELT and TMT, will need feedback control of the thousands of actuators underneath their segmented primary mirrors (M1). Differences in actuator dynamics and spatially and temporally changing disturbances make it extremely difficult to formulate classical controllers which are both sufficiently robust and highly performing. Therefore, TNO has developed and tested a control approach, in which the actual system response is quickly measured, disturbances are continuously estimated and the controller is adapted in real-time. The algorithm is tested on an actual M1-relevant setup, in which it converges to a sub-nm optimum within a few minutes, keeps track of changing disturbances and shows its reliability over multiple days.

The Giant Magellan Telescope Project is in the construction phase. Production of the primary mirror segments is underway with four of the seven required 8.4m mirrors at various stages of completion and materials purchased for segments five and six. Development of the infrastructure at the GMT site at Las Campanas is nearing completion. Power, water, and data connections sufficient to support the construction of the telescope and enclosure are in place and roads to the summit have been widened and graded to support transportation of large and heavy loads. Construction pads for the support buildings have been graded and the construction residence is being installed. A small number of issues need to be resolved before the final design of the telescope structure and enclosure can proceed and the GMT team is collecting the required inputs to the decision making process. Prototyping activities targeted at the active and adaptive optics systems are allowing us to finalize designs before large scale production of components begins. Our technically driven schedule calls for the telescope to be assembled on site in 2022 and to be ready to receive a subset of the primary and secondary mirror optics late in the year. The end date for the project is coupled to the delivery of the final primary mirror segments and the adaptive secondary mirrors that support adaptive optics operations.

The Giant Magellan Telescope (GMT)¹ is a 25 m telescope composed of seven 8.4 m “unit telescopes”, on a common mount. Each primary and conjugated secondary mirror segment will feed a common instrument interface, their focal planes co-aligned and co-phased. During telescope operation, the alignment of the optical components will deflect due to variations in thermal environment and gravity induced structural flexure of the mount. The ultimate co-alignment and co-phasing of the telescope is achieved by a combination of the Acquisition Guiding and Wavefront Sensing system and two segment edge-sensing systems². An analysis of the capture range of the wavefront sensing system indicates that it is unlikely that that system will operate efficiently or reliably with initial mirror positions provided by open-loop corrections alone³.

The project is developing a Telescope Metrology System (TMS) which incorporates a large number of absolute distance measuring interferometers. The system will align optical components of the telescope to the instrument interface to (well) within the capture range of the active optics wavefront sensing systems. The advantages offered by this technological approach to a TMS, over a network of laser trackers, are discussed. Initial investigations of the Etalon Absolute Multiline Technology™ by Etalon Ag⁴ show that a metrology network based on this product is capable of meeting requirements. A conceptual design of the system is presented and expected performance is discussed.

The Iranian National Observatory site is under construction at an altitude of 3600m at Mount Gargash in central Iran. It offers a promising site for optical and near-IR observations with a 0.7 arcsec median seeing and thus a number of observing facilities have been planned. The largest facility is a 3.4m Alt- Az reflecting Ritchey-Chretien optical telescope under development with an exit focal ratio of ~f/11 providing a generous 20 arcmin field of view at the main Cassegrain focus. This telescope will be equipped with high resolution medium-wide field imaging camera as well as medium and high resolution spectrographs. The telescope will benefit from an active support for the primary mirror. The primary mirror has been manufactured, polished and delivered. In this project overview, the design parameters for the 3.4m telescope and the current status of the project are presented.

Described is the M1 segment support, as designed by TNO in the period 2015-2016. The design has significantly changed and improved compared to the earlier designs. During the period 2009-2010 prototypes for the primary mirror support of the E-ELT have been developed. These have been extensively tested by ESO. Design improvement were found to be necessary, especially in the field of manufacturability and maintainability. Furthermore, the technical performance had to improve in specific areas as well. This has evolved into a new specifications which have resulted in a new design for the segment support structure. The design rules that have led to the prototype design have been maintained but the implementation has been much improved. Also considerable improvement has been obtained with respect to the dynamic behavior. Accessibility and visibility on all parts and subsystems has changed such that everything is now clearly visible. Despite the increased performance no mass increase has been recorded meaning that more efficient use has been made of the material.

The active means to influence the segment shape by use of the warping harness has been completely redesigned. A very important quality that has been achieved is simplicity. Hence a minimum amount of components is used. Reliability and safety are other aspects that have been greatly improved compared to the prototypes. The design for the M1 segment support provides a solution that not only performs to specification but one that can be operated in a telescope environment, all 798 of them.

ASTRI SST-2M is an end-to-end telescope prototype developed by the Italian National Institute of Astrophysics (INAF) in the framework of the Cherenkov Telescope Array (CTA). The CTA observatory, with a combination of large-, medium-, and small-sized telescopes (LST, MST and SST, respectively), will represent the next generation of imaging atmospheric Cherenkov telescopes. It will explore the very high-energy domain from a few tens of GeV up to few hundreds of TeV.

The ASTRI SST-2M telescope structure and mirrors have been installed at the INAF observing station at Serra La Nave, on Mt. Etna (Sicily, Italy) in September 2014. Its performance verification phase began in autumn 2015. Part of the scheduled activities foresees the study and characterization of the optical and opto-mechanical performance of the telescope prototype.

In this contribution we report the results achieved in terms of kinematic model analysis, mirrors reflectivity evolution, telescopes positioning, flexures and pointing model and the thermal behavior.

The First G-APD Cherenkov Telescope (FACT) is pioneering the usage of novel Geiger-mode operated Avalanche Photo Diodes (G-APD, nowadays usually called SiPM) for Cherenkov Telescopes. The camera consists of 1440 pixels with dedicated electronics operated at 2 GHz and is installed on a refurbished telescope with a mirror area of ≈ 9:5 m² at the Canary Island La Palma. The camera was installed in October 2011, and data are taken almost every night since then. The very stable and reliable operation allows to operate FACT from remote without the need of a data taking crew on-site. Over the years, operation became more and more automatic, and the next step will be to switch to fully automatic operation. This results in a very high data taking efficiency. The operation of FACT allows monitoring the long-term behavior of few variable extra-galactic very-high energy sources with unprecedented sampling density as well as testing the behavior of the sensors under harsh conditions. Despite operating also under strong moonlight conditions and therefore collecting far more signals than during dark nights, the G-APDs show no change in their performance or any indication for ageing. Understanding the behavior of the G-APDs under all the varying conditions allows to operate FACT without the need of any external calibration device. The properties of the sensors themselves allow for a high precision self-calibration of the camera.

We provide an update on the construction status of the Daniel K. Inouye Solar Telescope. This 4-m diameter facility is designed to enable detection and spatial/temporal resolution of the predicted, fundamental astrophysical processes driving solar magnetism at their intrinsic scales throughout the solar atmosphere. These data will drive key research on solar magnetism and its influence on solar winds, flares, coronal mass ejections and solar irradiance variability. The facility is developed to support a broad wavelength range (0.35 to 28 microns) and will employ state-of-the-art adaptive optics systems to provide diffraction limited imaging, resolving features approximately 20 km on the Sun. At the start of operations, there will be five instruments initially deployed: Visible Broadband Imager (VBI; National Solar Observatory), Visible SpectroPolarimeter (ViSP; NCAR High Altitude Observatory), Visible Tunable Filter (VTF (a Fabry-Perot tunable spectropolarimeter); Kiepenheuer Institute for Solarphysics), Diffraction Limited NIR Spectropolarimeter (DL-NIRSP; University of Hawaii, Institute for Astronomy) and the Cryogenic NIR Spectropolarimeter (Cryo-NIRSP; University of Hawaii, Institute for Astronomy).

As of mid-2016, the project construction is in its 4th year of site construction and 7th year overall. Major milestones in the off-site development include the conclusion of the polishing of the M1 mirror by University of Arizona, College of Optical Sciences, the delivery of the Top End Optical Assembly (L3), the acceptance of the Deformable Mirror System (Xinetics); all optical systems have been contracted and are either accepted or in fabrication. The Enclosure and Telescope Mount Assembly passed through their factory acceptance in 2014 and 2015, respectively. The enclosure site construction is currently concluding while the Telescope Mount Assembly site erection is underway. The facility buildings (Utility and Support and Operations) have been completed with ongoing work on the thermal systems to support the challenging imaging requirements needed for the solar research.

Finally, we present the construction phase performance (schedule, budget) with projections for the start of early operations.

The 1.8-m primary mirror of solar telescope is heated by the solar radiation and introduce harmful mirror seeing degrading the imaging quality. For the Chinese Large Solar Telescope (CLST), the thermal requirement based on the quantitative evaluation on mirror seeing effect shows that the temperature rise on mirror surface should be within 1 kelvin. To meet the requirement, an active thermal control system design for the CLST primary mirror is proposed, and realized on the subscale prototype of the CLST. The experimental results show that the temperature on the mirror surface is well controlled. The average and maximum thermal controlled error are less than 0.3 and 0.7 kelvins respectively, which completely meets the requirements.

The Daniel K. Inouye Solar Telescope (DKIST) was envisioned from an early stage to incorporate a functional safety system to ensure the safety of personnel and equipment within the facility. Early hazard analysis showed the need for a functional safety system. The design used a distributed approach in which each major subsystem contains a PLC-based safety controller. This PLC-based system complies with the latest international standards for functional safety. The use of a programmable controller also allows for flexibility to incorporate changes in the design of subsystems without adversely impacting safety. Various subsystems were built by different contractors and project partners but had to function as a piece of the overall control system. Using distributed controllers allows project contractors and partners to build components as standalone subsystems that then need to be integrated into the overall functional safety system. Recently factory testing was concluded on the major subsystems of the facility. Final integration of these subsystems is currently underway on the site. Building on lessons learned in early factory tests, changes to the interface between subsystems were made to improve the speed and ease of integration of the entire system. Because of the distributed design each subsystem can be brought online as it is delivered and assembled rather than waiting until the entire facility is finished. This enhances safety during the risky period of integration and testing. The DKIST has implemented a functional safety system that has allowed construction of subsystems in geographically diverse locations but that function cohesively once they are integrated into the facility currently under construction.

The Daniel K Inouye Solar Telescope (DKIST) will be the largest solar telescope in the world, and will be able to provide the sharpest views ever taken of the solar surface. The telescope has a 4m aperture primary mirror, however due to the off axis nature of the optical layout, the telescope Mount has proportions similar to an 8 metre class telescope. The Telescope Mount Assembly (TMA) includes both the telescope Mount and the 16m diameter laboratory table or Coudé Rotator. The Coudé Rotator supports the full instrument suite of up to 40 tonnes and has full rotation capabilities similar to the Mount azimuth axis. The TMA has been going through the design, fabrication and assembly process since 2009 with Ingersoll Machine Tool’s and this culminated with the Factory Acceptance Testing (FAT). The preparation for the FAT started not long after the Final Design Review was complete and planning continued through the assembly stages. The official Factory Acceptance testing of the Coudé Rotator was conducted during May/Jun 2014 and the Mount in Feb through Apr 2015. This paper provides an overview and discussion of the testing that was carried out. The depth and extent of testing will be described with discussion on what we would do differently next time. Also details of the preparation / process that lead into the testing will be presented. Most importantly the results will be summarized and lessons learned during the testing provided as well as discussion on how this influences the planned site assembly and extent of re-test post assembly.

Repairs to the W.M. Keck Observatory primary mirror segments are needed to stop the cracking at the bonded supports. The repairs include changes to the design of the axial and radial inserts and the way these are bonded to the mirror backsurface. In this paper, we present finite element analyses of a primary mirror segment including whiffletree and radial mirror support system to determine the effect of the modified supports on the mirror figure. Displacements of the front surface are calculated for a number of operational and assembly fit-up cases, and differential displacements between the old and new support system are found. Zernike coefficients are calculated for front surface displacements and differential displacements. Stresses on the glass surface at the radial pad bond locations are also determined. The results show that the residual deformations of the mirror front surface with the new supports are similar to those with the old supports, differing only in the immediate vicinity of the axial inserts and radial pads, and the impact on the image quality of the Keck telescopes is negligible.

On 15 October 2006, a large earthquake damaged both telescopes at W. M. Keck Observatory resulting in weeks of observing downtime. A significant portion of the downtime was attributed to recovery efforts repairing damage to telescope bearing journals, radial pad support structures, and encoder subsystems. To reduce the risk of damage and loss of observing time in future seismic events, we developed a conceptual design for the seismic upgrade of the twin Keck Telescopes. The paper covers the design requirements and constraints for the seismic upgrade, the evaluation method used to check the safety of sensitive components, and the trade-off study used to compare different options and to select the best design. Various design options such as base isolating the structure, strengthening seismic restraints, adding dampers, adding break-away mechanisms, and combinations of these design options are considered in this study. Nonlinear time history analyses are performed to evaluate the performance of the design concepts.

The Maunakea Spectroscopic Explorer (MSE) project is a collaboration designing the largest non-ELT optical/NIR astronomical telescope to date. MSE is unique as a major astronomical facility since it involves the redevelopment of an existing facility, that of the Canada France Hawai‘i Telescope (CFHT), with a newly expanded partnership. The project office is hosted at CFHT in Waimea HI, and includes new partners from Australia, China, India and Spain. The project is being developed by an international collaboration with design team membership distributed across four continents. In addition to a report on the progress and organization of design work, this paper describes the challenges of redeveloping a major astronomical site in Hawai‘i. We discuss the Project Office and engineering work from the aspects of meeting the Science Requirements while satisfying the unique conditions imposed by redevelopment on Maunakea.

The QUIJOTE Experiment (Q-U-I JOint TEnerife) is a combined operation of two telescopes and three instruments working in the microwave band to measure the polarization of the Cosmic Microwave Background (CMB) from the northern hemisphere, at medium and large angular scales. The experiment is located at the Teide Observatory in Tenerife, one of the seven Canary Islands (Spain). The project is a consortium maintained by several institutions: the Instituto de Astrofísica de Canarias (IAC), the Instituto de Física de Cantabria (IFCA), the Communications Engineering Department (DICOM) at Universidad de Cantabria, and the Universities of Manchester and Cambridge. The consortium is led by the IAC.

The Evryscope is a new type of telescope which covers the entire accessible sky in each exposure. Its 8000- square-degree field-of-view and 691 MPix telescope is sensitive to exoplanet transits and other short timescale events not discernible from existing large-sky-area astronomical surveys. The telescope, which places 24 separate individual telescopes into a common mount which tracks the entire accessible sky with only one moving part, is building 1%-precision, many-year-length, high-cadence light curves for every accessible object brighter than ~16th magnitude. The camera readout times are short enough to provide near-continuous observing, with a 97% survey time efficiency. The Evryscope has the largest survey grasp of any current ground-based survey, and for bright-object high-cadence observations is the only existing survey within an order of magnitude of LSST's etendue. We deployed the Evryscope, funded by NSF/ATI, at CTIO in May 2015. We here present the telescope design, performance, and project status.

The Magellan Telescopes are a set of twin 6.5 meter ground based optical/near-IR telescopes operated by the Carnegie Institution for Science at the Las Campanas Observatory (LCO) in Chile. The primary mirrors are f/1.25 paraboloids made of borosilicate glass and a honeycomb structure. The secondary mirror provides both f/11 and f/5 focal lengths with two Nasmyth, three auxiliary, and a Cassegrain port on the optical support structure (OSS). The telescopes have been in operation since 2000 and have experienced several small earthquakes with no damage. Measurement of in situ response of the telescopes to seismic events showed significant dynamic amplification, however, the response of the telescopes to a survival level earthquake, including component level forces, displacements, accelerations, and stresses were unknown. The telescopes are supported with hydrostatic bearings that can lift up under high seismic loading, thus causing a nonlinear response. For this reason, the typical response spectrum analysis performed to analyze a survival level seismic earthquake is not sufficient in determining the true response of the structure. Therefore, a nonlinear transient finite element analysis (FEA) of the telescope structure was performed to assess high risk areas and develop acceleration responses for future instrument design. Several configurations were considered combining different installed components and altitude pointing directions. A description of the models, methodology, and results are presented.

The Antarctic Survey Telescope-AST3 consists of three optical telescopes with 680mm primary mirror and 8 square degree field of view, mainly for observations of supernovas and extrasolar planets searching from Antarctic Dome A. The first two AST3 telescopes (AST3-1 and AST3-2) were successfully installed on Dome A by Chinese expedition team in Jan. 2012 and Jan. 2015 separately. Multi-anti-frost methods were designed for AST3-2 and the automatic observations are keeping on from March 2016. The best limited magnitude is 19.4m with exposure time 60s in G band. The third AST3 will have switchable interface for both optical camera and near infrared camera optimized for k dark band survey. Now the telescope is under development in NIAOT and the K-band camera is under development in AAO.

Dome A 5m Terahertz Explorer (DATE5) is a proposed telescope to be deployed at Dome A, Antarctica to explore the excellent terahertz observation condition unique to the site. One of the key challenges of the telescope is to realize and maintain the required 10 μm rms overall reflector surface accuracy under the extreme site conditions and unmanned operating mode. Aluminum panels on carbon fiber backup structures is one of the candidate options for the 5 meter main reflector. For aluminum panels, three major technical risks were identified: 1) the large CTE of aluminum causes significant panel deformation due to the large seasonal soak temperature change; 2) internal stress may cause additional surface deformation when operating under a cold environment; 3) reflector panels working at Dome A run high risks of icing (which degrades antenna efficiency and increases noise) and automatic active de-icing mechanisms has to be implemented on the panels. In order to verify the feasibility of the aluminum panels for DATE5 and identify possible technical risks, a prototype panel was fabricated and went through rigorous tests. The manufacture error at the room temperature is 3.2 μm rms, which meets the budget. The panel surface is then measured at various ambient temperatures down to -60°C in a climate chamber using photogrammetric techniques. The additional surface error at the low temperatures is found to be mainly contributed by defocusing error, and the dependence of the panel focal length on temperature is well predictable. No additional surface error caused by internal stress has been observed. Next, the icing condition of the panel is analyzed and a prototype de-icing system based on polyimide film heaters was installed on the panel. The performance of the de-icing system was tested in a climate chamber as well as in the field experiments to simulate a variety of operating environments. The experiments indicate that the power required for de-icing the entire main reflector is less than 1kW and the temperature field produced by the de-icing system has trivial effect on the surface accuracy of the panel. This study indicates that aluminum panels have the potential to meet the reflector surface error budget under the harsh environment of Dome A.

The Stratospheric Observatory For Infrared Astronomy (SOFIA) reached its full operational capability in 2014 and completed hundreds of observation flights. Since its installation in 2002, the Secondary Mirror Mechanism was subject to thousands of operating hours equivalent to millions of load cycles. During the aircraft heavy maintenance in fall 2014, a four month time window enabled the removal of the mechanism from the telescope structure for service and improvements. Next to visual corrosion- and crack-inspection of the flexures, critical electronic components (in particular the set of three eddy current position sensors that determine the mirror tilt) were replaced. Moreover, a detailed temperature dependent position calibration of the system was performed in a cold chamber to improve the pointing accuracy. Until then, a simple temperature independent linear gain was used to translate the sensor output voltage into a position. For accurate positioning across the whole temperature range, a temperature dependent correction function had to be developed. This calibration would have cost hours of observing time when performed in flight which made it an essential goal for completion during the maintenance period. An autocollimator was used as optical reference camera to measure the tip-tilt position of the secondary mirror in the cold chamber. Using this calibration setup, a pattern of many mirror positions in the tip-tilt domain was approached at several temperature points to provide a high resolution data set for the new multidimensional calibration function. Follow-up in-flight verification measurements confirmed a large improvement in pointing accuracy as soon as the temperature measurements were included into the position correction. Improvements of up to a factor of 10 were especially noticed in the lower temperature range. This contribution provides an insight into the work performed during the SOFIA - Secondary Mirror Mechanism maintenance with the focus on the temperature dependent position calibration.

The Stratospheric Observatory for Infrared Astronomy (SOFIA) has already successfully conducted over 300 flights. In its early science phase, SOFIA's pointing requirements and especially the image jitter requirements of less than 1 arcsec rms have driven the design of the control system. Since the first observation flights, the image jitter has been gradually reduced by various control mechanisms. During smooth flight conditions, the current pointing and control system allows us to achieve the standards set for early science on SOFIA. However, the increasing demands on the image size require an image jitter of less than 0.4 arcsec rms during light turbulence to reach SOFIA's scientific goals. The major portion of the remaining image motion is caused by deformation and excitation of the telescope structure in a wide range of frequencies due to aircraft motion and aerodynamic and aeroacoustic effects. Therefore the so-called Flexible Body Compensation system (FBC) is used, a set of fixed-gain filters to counteract the structural bending and deformation. Thorough testing of the current system under various flight conditions has revealed a variety of opportunities for further improvements. The currently applied filters have solely been developed based on a FEM analysis. By implementing the inflight measurements in a simulation and optimization, an improved fixed-gain compensation method was identified. This paper will discuss promising results from various jitter measurements recorded with sampling frequencies of up to 400 Hz using the fast imaging tracking camera.