Allen Farris

THE CONCEPTUAL DESIGN OF THE MAGDALENA RIDGE OBSERVATORY INTERFEROMETER

We describe the scientific motivation for and conceptual design of the Magdalena Ridge Observatory Interferometer, an imaging interferometer designed to operate at visible and near-infrared wavelengths. The rationale for the major technical decisions in the interferometer design is discussed, the success of the concept is appraised, and the implications of this analysis for the design of future arrays are drawn out.

Magdalena Ridge Observatory Interferometer automated alignment system

Here is presented the current outline and progress of MROIs automated alignment system design. Depending on the location of each of MROIs unit telescopes (UT), light can travel distances ranging from 460 to 660 meters via several reflections that redirect the beams path through the beam relay system (BRS), delay line system (DLS), beam compressing telescope (BCR), switchyards and finally to the beam combiners (BC). All of these sub-systems comprise three major optical axes of the MROI which must be coaligned on a nightly basis by the AAS. The AAS consists of four subsystems: the primary fiducial-for beam injection, the UT tilt and shear measurement components (TASM), the BC TASM components, and the secondary fiducial-for quick alignment checks. All of these subsystems contribute to the unique design of the AAS which will allow for simultaneous measurements from the visible to the near-IR wavelengths, full automation, the capability to perform optical path difference (OPD) alignment and spectral calibration, making it cost effective and saving on realty in the beam combining area (BCA). The AAS is nearing completion and assembly of the various subsystems is expected to commence soon. The latest results on all of the following are reviewed here.

Software architecture of the Magdalena Ridge Observatory Interferometer

Merging software from 36 independent work packages into a coherent, unified software system with a lifespan of twenty years is the challenge faced by the Magdalena Ridge Observatory Interferometer (MROI). We solve this problem by using standardized interface software automatically generated from simple highlevel descriptions of these systems, relying only on Linux, GNU, and POSIX without complex software such as CORBA. This approach, based on gigabit Ethernet with a TCP/IP protocol, provides the flexibility to integrate and manage diverse, independent systems using a centralized supervisory system that provides a database manager, data collectors, fault handling, and an operator interface.

The MROI fast tip-tilt correction and target acquisition system

The fast tip-tilt correction system for the Magdalena Ridge Observatory Interferometer (MROI) is being designed and fabricated by the University of Cambridge. The design of the system is currently at an advanced stage and the performance of its critical subsystems has been verified in the laboratory. The system has been designed to meet a demanding set of specifications including satisfying all performance requirements in ambient temperatures down to -5 °C, maintaining the stability of the tip-tilt fiducial over a 5 °C temperature change without recourse to an optical reference, and a target acquisition mode with a 60” field-of-view. We describe the important technical features of the system, which uses an Andor electron-multiplying CCD camera protected by a thermal enclosure, a transmissive optical system with mounts incorporating passive thermal compensation, and custom control software running under Xenomai real-time Linux. We also report results from laboratory tests that demonstrate (a) the high stability of the custom optic mounts and (b) the low readout and compute latencies that will allow us to achieve a 40 Hz closed-loop bandwidth on bright targets.

The Magdalena Ridge Observatory interferometer: first light and deployment of the first telescope on the array

The Magdalena Ridge Observatory Interferometer (MROI) has been under development for almost two decades. Initial funding for the facility started before the year 2000 under the Army and then Navy, and continues today through the Air Force Research Laboratory. With a projected total cost of substantially less than

The MROI fringe tracker: closing the loop on ICoNN

200M, it represents the least expensive way to produce sub-milliarcsecond optical/near-infrared images that the astronomical community could invest in during the modern era, as compared, for instance, to extremely large telescopes or space interferometers. The MROI, when completed, will be comprised of 10 x1.4m diameter telescopes distributed on a Y-shaped array such that it will have access to spatial scales ranging from about 40 milliarcseconds down to less than 0.5 milliarcseconds. While this type of resolution is not unprecedented in the astronomical community, the ability to track fringes on and produce images of complex targets approximately 5 magnitudes fainter than is done today represents a substantial step forward. All this will be accomplished using a variety of approaches detailed in several papers from our team over the years. Together, these two factors, multiple telescopes deployed over very long-baselines coupled with fainter limiting magnitudes, will allow MROI to conduct science on a wide range and statistically meaningful samples of targets. These include pulsating and rapidly rotating stars, mass-loss via accretion and mass-transfer in interacting systems, and the highly-active environments surrounding black holes at the centers of more than 100 external galaxies. This represents a subsample of what is sure to be a tremendous and serendipitous list of science cases as we move ahead into the era of new space telescopes and synoptic surveys. Additional investigations into imaging man-made objects will be undertaken, which are of particular interest to the defense and space-industry communities as more human endeavors are moved into the space environment. In 2016 the first MROI telescope was delivered and deployed at Magdalena Ridge in the maintenance facility. Having undergone initial check-out and fitting the system with optics and a fast tip-tilt system, we eagerly anticipate installing the telescope enclosure in 2018. The telescope and enclosure will be integrated at the facility and moved to the center of the interferometric array by late summer of 2018 with a demonstration of the performance of an entire beamline from telescope to beam combiner table shortly thereafter. At this point, deploying two more telescopes and demonstrating fringe-tracking, bootstrapping and limiting magnitudes for the facility will prove the full promise of MROI. A complete status update of all subsystems follows in the paper, as well as discussions of potential collaborative initiatives.

Implementing the Magdalena Ridge Observatory interferometer supervisory system

The characterization of ICoNN, the Magdalena Ridge Observatory Interferometers fringe tracker, through labor tory simulations is presented. The performance limits of an interferometer are set by its ability to keep the optical path difference between combination partners minimized. This is the job of the fringe tracker. Understanding the behavior and limits of the fringe tracker in a controlled environment is key to maximize the science output. This is being done with laboratory simulations of on-sky fringe tracking, termed the closed-loop fringe experi ment. The closed-loop fringe experiment includes synthesizing a white light source and atmospheric piston with estimation of the tracking error being fed back to mock delay lines in real-time. We report here on the progress of the closed-loop fringe experiment detailing its design, layout, controls and software.

Towards integration of the Unit Telescope for the Magdalena Ridge Observatory interferometer

The Magdalena Ridge Observatory Interferometer (MROI) software system contains distributed systems managed by a centralized Supervisory System. Interface software is generated from spreadsheets that describe commands, monitor points, and fault conditions for each subsystem. The Supervisory System consists of an Executive, Operator, Database Manager; one or more Supervisors plus Fault Manager, and Data Collectors. System-wide simulations are discussed: (1) a test framework is generated from the spreadsheets characterizing a subsystem; (2) a detailed simulation of the actual hardware in a subsystem; (3) a system-wide simulation of collecting astronomical data based on executing observing projects. The first two levels have been implemented.

A new path to first light for the Magdalena Ridge Observatory interferometer

The Unit Telescope (UT) for the Magdalena Ridge Observatory (MROI) is composed of four major hardware components: The Unit Telescope Mount (UTM), Enclosure, Optics and the Fast Tip Tilt System (FTTS). Integration of the UT started in 2016 when the UTM arrived and its Assembly, Integration and Verification activities began. Critical activities included: installation at the Maintenance Facility, integration and alignment of the Optics and Wave Front Sensor (WFS) and finally the complete optical alignment. End-to-end UTM Site Acceptance Tests (SAT) were performed. Subsequent activities included receiving and integrating the FTTS. With the arrival and assembly of the Enclosure, the last component of the UT was ready for integration on a dedicated concrete pier. Specialized equipment will be used for the final integration of the UT, and for transportation to its final location on the array where SAT for the UT will take place.

The performance of the MROI fast tip-tilt correction system

The Magdalena Ridge Observatory Interferometer (MROI) was the most ambitious infrared interferometric facility conceived of in 2003 when funding began. Today, despite having suffered some financial short-falls, it is still one of the most ambitious interferometric imaging facilities ever designed. With an innovative approach to attaining the original goal of fringe tracking to H = 14th magnitude via completely redesigned mobile telescopes, and a unique approach to the beam train and delay lines, the MROI will be able to image faint and complex objects with milliarcsecond resolutions for a fraction of the cost of giant telescopes or space-based facilities. The design goals of MROI have been optimized for studying stellar astrophysical processes such as mass loss and mass transfer, the formation and evolution of YSOs and their disks, and the environs of nearby AGN. The global needs for Space Situational Awareness (SSA) have moved to the forefront in many communities as Space becomes a more integral part of a national security portfolio. These needs drive imaging capabilities ultimately to a few tens of centimeter resolution at geosynchronous orbits. Any array capable of producing images on faint and complex geosynchronous objects in just a few hours will be outstanding not only as an astrophysical tool, but also for these types of SSA missions. With the recent infusion of new funding from the Air Force Research Lab (AFRL) in Albuquerque, NM, MROI will be able to attain first light, first fringes, and demonstrate bootstrapping with three telescopes by 2020. MROI’s current status along with a sketch of our activities over the coming 5 years will be presented, as well as clear opportunities to collaborate on various aspects of the facility as it comes online. Further funding is actively being sought to accelerate the capability of the array for interferometric imaging on a short time-scale so as to achieve the original goals of this ambitious facility