United States Naval Observatory Flagstaff Station

The United States Naval Observatory Flagstaff Station (NOFS), is an astronomical observatory near Flagstaff, Arizona, USA. It is the national dark-sky observing facility for the U.S. Department of Defense, under the United States Naval Observatory (USNO). NOFS and USNO combine as the Celestial Reference Frame manager for the U.S. Secretary of Defense.

General information
The USNO and NOFS are commands within the CNMOC claimancy, the latter which serves the U.S. Navy on meteorological and oceanographic matters in addition to overseeing astronomical ones. The Flagstaff Station is a command which was established by USNO (due to a century of eventually untenable light encroachment in Washington, D.C.) at a site five miles west of Flagstaff, Arizona in 1955, and has positions for primarily operational scientists (astronomers and astrophysicists), optical and mechanical engineers, and support staff. It is currently manned with a core of civil service personnel, supported by defense and astronomical contractors. Its principal mission is to provide the military and others extremely accurate, ground-based astrometry (defined as the positions of celestial and artificial space objects), Celestial mechanics (dynamical motions of celestial objects) and photometry (defined as brightness variations, often in terms of 'color') – in the form of extremely rigorous million-to-billion-star catalogs for a wide diversity of U.S. global (and spaceborne) position and navigation interests. NOFS specializes in extremely faint-magnitude, extremely accurate observations which cannot normally be obtained from space telescopes, and remains the most respected astrometric observatory in the world. NOFS remains the senior U.S. Navy facility/unit in the state of Arizona.

NOFS science supports every aspect of protection-oriented operations to some level, providing national support and beyond. Work at NOFS covers the gamut of astrometry and astrophysics  in order to facilitate its production of very accurate/precise astronomical catalogs, such as USNO-B,   NOMAD, UBAD (USNO Bright-Star Astrometric Database), UNAC (USNO NPOI Astrometric Catalog), ITAU (Infrared Two-Micron Astrometric Update), USNO-Zoetic, and others delivered by NOFS. Astrometry for such catalogs (producing a "celestial reference frame" (CRF), such as the ICRF is), requires handling terabytes of diverse data on a billion or more celestial objects, all the while accurately characterizing the centroids of the point spread functions (PSFs) of each object in that vast database, including pinning down positions of innumerable, diverse types of objects. Such diversity severely complicates how to dynamically determine where many of the large collections of celestial objects really 'are'. Complete catalogs require much study of binary/multiple, flare, oblate, starspot-laden stars, and astrometrically extended objects, in addition to the classically 'simple', spheroidally shaped single stars. Many of these types of "problem stars" (and their oddly shaped cousins) proliferate much of the night sky, so must have some accounting, in large major catalogs. Characterizing the astrophysical diversity, so as to know the objects' positions, helps to determine how up to a billion positions can be made accurate to perhaps to a few, critical milliarcseconds, to provide an accurate faint—or bright – "background", upon which users may reference their own critical work. Ultimately catalogs will have requirements for microarcsecond levels of accuracy (a microarcsecond is an angle smaller than the thickness of hair on a six foot man seen from Earth to be standing on the Moon). As well, users may need a large collection of just the brighter magnitude stars, or the much fainter ones (much more difficult to assess), or both. Users may also require a catalog suited to blue or red optical, near or far (or thermal) infrared, or millimeter/microwave/radio portions of the electromagnetic spectrum. This matches the user's need for a background similar to their observational interests. In astrometry, the PSFs of the stars' centroids vary significantly from one bandpass to another, so must be atoned for in catalog development. Faint star densities are almost exponentially more numerous in a given patch of sky, so faint catalogs will require much more effort to produce for the user.

Also, owing to the celestial dynamics (and relativistic effects ) of the huge number of such moving objects across their own treks through space, the time expanse required to pin down each set of celestial locations and motions for a perhaps billion-star catalog, can be quite long. Multiple observations of each object may themselves take weeks, months or years, by themselves. This, multiplied by the large number of cataloged objects that must then be reduced for use, and which must be analyzed after observation for a very careful statistical understanding of all catalog errors, forces the rigorous production of most extremely precise and faint astrometric catalogs to take many years, sometimes decades, to complete.

Because stars move, both due to their own wanderings (proper motions) throughout space, and due to the observer's Earth orientation movements (such as precession, nutation, parallax, geophysical and tidal variations), a catalog's accuracy slowly but progressively degrades in increased error over time, beginning the moment after the sky is imaged for cataloging. The degrading motions 'confuse' observations with motions which astrometrists are usually not able to completely constrain despite extensive scientific modeling and deliberation. So eventually a whole new catalog must be produced when a user's needs for given accuracies force a new, updated catalog, for some later epoch. One remedy to break such a daunting cycle is to maintain an ongoing input and updating process, which makes the common operational picture (COP) produced by such a dynamic catalog, a more efficient and timely means to delver such large quantities of changing data to the variety of users. NOFS has a key program (awaiting funding) called the Dynamic Astrometric Database (DyAD) which will operate under the near real-time ("on-the-fly") paradigm.

While principally responsible for the Navy/DoD faint-star astrometric reference frame (and components of its bright-star counterpart), NOFS scientists also externally develop an improved understanding of celestial goings-on, by participating on many science teams and in relevant collaborations. Institutions NOFS works with include DARPA, NASA, NRL, MIT (such as Lincoln Laboratory), Draper Laboratory, NRAO, Smithsonian, GEODSS, Los Alamos National Laboratory (LANL), AMOS, USNA, Air Force Space Command, Lowell Observatory, NOAO, AAS, IAU, and many other academic and DoD institutions. Staff Astronomers observe both on local telescopes and at other observatories around the globe—using both terrestrial, interferometric and spaceborne instrumentation.

The NOFS staff is organized into five divisions: (1) Optical/Infrared Astrometry, Remote Sensing & Analysis, (2) Engineering & Site Operations, (3) Digital Catalogs & Astrometric Methods, (4) Navy Precision Optical Interferometer(NPOI), and the (5) Computers and Information Assurance Divisions. Additional management staff members serve executive, fiscal, administrative, and facilities functions. NOFS also serves as the contingency facility ("back-up") for its Washington counterpart's Earth Orientation Parameters and Astronomical Applications production centers.

.

NOFS is the U.S. Navy's National Dark Sky Site, and is responsible for the bulk of the 'astrometric component' of the U.S. DoD and national Position-Navigation-Time (PNT) mission.

The United States Naval Observatory, Flagstaff Station celebrated its 50th anniversary of the move there from Washington, D.C. in late 2005. Each autumn, NOFS opens its doors annually to the public, during the Flagstaff Festival of Science. In 2009, visitor attendance topped 710.

Dr. John Hall, Director of the Naval Observatory's Equatorial Division from 1947, founded NOFS. Dr. Art Hoag became its first director in 1955 (until 1965); both later were to also become directors of nearby Lowell Observatory. Subsequent directors at NOFS include (in order): 2nd – Dr. Gerald Kron (1965–1973); 3rd – Dr. Harold Ables (1974–1995); 4th – Dr. Conard Dahn (1996–2003); 5th – Dr. Jeff Pier (2003–2008); and 6th – Dr. Paul Shankland (2008–present).

NOFS remains active in supporting regional dark skies, both to support its national protection mission,  and to promote and protect a national resource legacy for generations of humans to come.

Site description
NOFS is the U.S. Navy's highest-elevation facility, and is 'land-locked', adjacent to Northern Arizona's San Francisco Peaks, on the alpine Colorado Plateau and geographically above the Mogollon Rim. The U.S. Navy selected the Flagstaff location to conduct the DoD's astrometric mission, owing to good seeing and dark skies there. Flagstaff and Coconino County minimize northern Arizona light pollution through legislation of progressive code – which regulates local lighting. Indeed, despite a half-century-young history, NOFS has a rich heritage which is derived from its parent organization, USNO, the oldest scientific institution in the U.S. NOFS is located west of town from the other observatory in the region, Lowell Observatory, and in fact Lowell Observatory's encouragement facilitated the elder Naval Observatory's decision to move its dark sky operations to Flagstaff in the mid-twentieth century.

At an elevation of approximately 7700 feet, NOFS is home to a number of astronomical instruments (some also described in the worldwide list of optical telescopes); some additional instrumentation is on nearby Anderson Mesa:

Instruments
NOFS telescopes are completely run (usually in a fully automated manner) through the use of a 'commonized', Python-code-based telescope control system (TCS), which allows astronomers to remotely control and prioritize all telescope operations throughout the observatory's IA-compliant high-speed computer network LAN. Owing to the its susceptibility to lightning strikes atop the mountain, all telescopes and IT systems are also carefully lightning-protected, fully electrically isolated, grounded to an underground earthing network, and protected with lighting arrestors. All domes are of metal design and grounded, in order to provide Faraday cage-type lightning protection for the sensitive instrumentation within. While essential to protect from the severe effects caused by lightning, the Faraday caging only partially protects electronics from man-made EMI/RFI that causes CCD read noise. Dome/Slit 'focusing' of EMI requires distancing EMI sources from the observatory, as has been done at NOFS. As well, a locally designed, automated weather station can robotically close telescope domes using its TCS interface, if it detects inclement weather (or even the damaging smoke from possible wildfire   ), and protect NOFS telescopes.

Kaj Strand Telescope
Congressionally appropriated in 1961, the 61-inch Kaj Strand Telescope (or 1.55-m Kaj Strand Astrometric Reflector, KSAR) remains largest telescope operated by the U.S. Navy since it saw first light in 1964. This status will change when the NPOI four 1.8-meter telescopes see their own first light in the near future. KSAR rides in the arms of an equatorial fork mount. The telescope is used in both the visible spectrum, and in the near infrared (NIR), the latter using a sub-30-Kelvin, helium-refrigerated, InSb (Indium antimonide) camera, "Astrocam". In 1978, the 1.55-m telescope was used to discover the moon of dwarf planet Pluto, named Charon (Pluto itself was discovered in 1930, across town at Lowell Observatory). The Charon discovery led to mass calculations which ultimately revealed how tiny Pluto was, and eventually caused the IAU to reclassify Pluto as a dwarf (not a principle) planet. The 1.55-meter telescope was also used to observe and track NASA's Deep Impact Spacecraft, as it navigated to a successful inter-planetary impact with the celebrated Comet 9p/Tempel, in 2005. This telescope is particularly well-suited to perform stellar parallax studies, narrow-field astrometry supporting space navigation, and has also played a key role in discovering one of the coolest-ever known Brown Dwarf objects, in 2002. The 61" dome is centrally located on NOFS grounds, with support and office buildings attached to the dome structures. The large vacuum coating chamber facility is also located in this complex. The chamber can provide very accurate coatings and overcoatings of 100 (+/-2) Angstrom thickness (approximately 56 aluminium atoms thick), for small-to-multi-ton optics up to 72-inches (1.82 meters) in diameter, in a vacuum exceeding $7 Torr$, using a vertical-optic, 1500-ampere discharge system. A dielectric coating capability has also been demonstrated. Large optics and telescope components can be moved about NOFS using its suite of cranes, lifts, cargo elevators and specialized carts. The main complex also contains a controlled-environment, optical and electronics lab for laser, adaptive optics, optics development, collimation, mechanical, and micro-electronic control systems needed for NOFS and NPOI.

The KSAR Telescope's 60-foot diameter steel dome is quite large for the telescope's aperture, owing to its telescope's long f/9.8 focal ratio (favorable for very accurate optical collimation, or alignment, needed for astrometric observation). It uses a very wide 2-shutter, vertical slit. Development studies have taken place to successfully show that planned life-cycle replacement of this venerable instrument can be efficiently done within the original dome, for a future telescope with an aperture of up to 3.6-meters, by using fast, modern-day optics. However, the 61-inch telescope remains unique in its ability to operationally conduct both very high-accuracy relative astrometry to the microarcsecond level, and close-separation, PSF photometry. Several key programs take advantage of this capability to this day.

1.3 m telescope
The 1.3 m (51-inch) large-field R-C telescope was initially produced by DFM Engineering and then corrected and automated by NOFS staff. Corning Glass Works and Kodak made the primary mirror. The hyperbolic secondary has an advanced, computer-controlled collimation (alignment) system in order to permit very precise positions of stars and satellites (milliarcsecond astrometry) across its wide field of view. This system analyzes optical aberrations of the optical path, modeled by taking slope fits of the wavefront deviations revealed using a Hartmann mask. The telescope also now sports a state-of-the art, cryogenic wide-field mosaic CCD camera. It will also permit employment of the new "Microcam", an orthogonal transfer array (OTA), with Pan-STARRS heritage. Other advanced camera systems are also deployed for use on this telescope, such as the LANL-produced RULLI single photon counter, nCam. Using the telescope's special software controls, the telescope can track both stars and man-made satellites orbiting the Earth, while the camera images both. The 1.3 m dome itself is compact, owing to the fast overall optics at f/4. It is located near by and southwest of, the very large 61-inch dome. In addition to astrometric studies (such as for Space Situational Awareness, SDSS and SST), research on this telescope includes the study of blue and K-Giant stars, celestial mechanics and dynamics of multiple star systems, characterizations of artificial satellites, and the astrometry and transit photometry of exoplanets. Astrometrically, exoplanets also confuse centroid of a parent star's PSF—and there are many exoplanets—so the impact of their not-bland dynamics must be understood.

1.0 m telescope
The 40-inch (1-meter) "Ritchey Telescope" is also an equatorially driven, fork-mounted telescope. The Ritchey is the original Station telescope which was moved from USNO in Washington in 1955. It is also the first R-C telescope ever made from that famous optical prescription, and was coincidentally the last telescope built by George Ritchey himself. The telescope is still in operation after a half century of astronomy at NOFS. It performs key quasar-based reference frame operations, transit detections of exoplanets, Vilnius photometry, M-Dwarf star analysis, dynamical system analysis, reference support to orbiting space object information, horizontal parallax guide support to NPOI, and it performs photometric operations support to astrometric studies (along with its newer siblings). The 40-inch also can carry a number of liquid Nitrogen-cooled cameras, a coronagraph, and a nine-stellar magnitude neutral density spot focal plane array camera, through which star positions are cross-checked before use in fundamental NPOI reference frame astrometry. This telescope is also used to test internally developed optical adaptive optics (AO) systems, using tip-tilt and deformable mirror optics. The Shack-Hartmann AO system allows for corrections of the wavefront's aberrations caused by scintillation (degraded seeing), to higher Zernike polynomials. AO systems at NOFS will migrate to the 1.55m and 1.8m telescopes for future incorporation there.

The 40-inch dome is located at the summit and highest point of the modest mountain upon which NOFS is located. It is adjacent to a comprehensive instrumentation shop, which includes sophisticated, CAD-driven CNC fabrication machinery, and a broad array of design and support tooling.

0.2 m FASTT
A modern-day example of a fully robotic transit telescope is the small 0.2 m (8 in) Flagstaff Astrometric Scanning Transit Telescope (FASTT) located at the observatory. FASTT provides extremely precise positions of solar system objects for incorporation into the USNO Astronomical Almanac and Nautical Almanac. These ephemerides are also used by NASA in the deep space navigation of its planetary and extra-orbital spacecraft. Instrumental to the navigation of many NASA deep space probes, this telescope is responsible for NASA JPL's successful 2005 navigation-to-landing of the Huygens Lander on Titan, a major moon orbiting Saturn, and is currently providing navigational reference for NASA's New Horizons deep space mission to Pluto, slated to arrive at the edge of the Solar System in July 2015. FASTT has also been used help NASA's SOFIA Airborne Observatory correctly locate, track and image a rare Pluto occultation. FASTT is located 150 yards southwest of the primary complex. Attached to its large "hut" is the building housing NOFS' electronics and electrical engineering laboratories and clean rooms, where most of the advanced camera electronics, cryogenics and telescope control drives are developed and made.

Latest telescopes
NOFS has just added the USNO Robotic Astrometric Telescope (URAT) to its suite of instrumentation. URAT was devised in Washington, DC, from previous instrumentation (the NOFS Twin Astrograph), used the astrograph to produce the catalog, UCAC. URAT deployed to NOFS late 2011, and after several years in Arizona, will be transported to CTIO, for additional southern hemisphere coverage (so as to complete four pi-steradians sky coverage). The URAT system employs a very large, liquid-nitrogen-cooled, CCD chip (10K by 10K), to allow wide-field operations with its 111 megapixel camera (at a pixel size of 9 by 9 µm). URAT's dome is adjacent to the NOFS 40" Ritchey dome. Initial testing is completed, and operational fields are now being collected for catalog use. The focal plane itself is the largest single CCD ever made.

Navy Precision Optical Interferometer
NOFS operates the Navy Precision Optical Interferometer  (recently the "P" was modified to mean precision vice prototype) in collaboration with Lowell Observatory and the Naval Research Laboratory at Anderson Mesa, 15 miles south-east of Flagstaff. NOFS (the operational astrometric arm of USNO) funds all principle operations, and from this contracts Lowell Observatory to maintain the Anderson Mesa facility and make the observations necessary for NOFS to conduct the primary astrometric science. The Naval Research Laboratory (NRL) also provides additional funds to contract Lowell Observatory's and NRL's implementation of additional, long-baseline siderostat stations, facilitating NRL's primary scientific work, synthetic imaging (both celestial and of orbital satellites). The three institutions - USNO, NRL, and Lowell - each provide an executive to sit on an Operational Advisory Panel (OAP), which collectively guides the science and operations of the interferometer. The OAP commissioned the chief scientist and director of the NPOI to effect the science and operations for the Panel; this manager is a senior member of the NOFS staff and reports to the NOFS Director.

NPOI is a successful astronomical interferometer of the venerable and proven Michelson Interferometer design. As noted, the majority of interferometric science and operations are funded and managed by NOFS; however, Lowell Observatory and NRL join in the scientific efforts through their fractions of time to use the interferometer; 85% Navy (NOFS and NRL); and 15% Lowell. NPOI is one of the few major instruments globally which can conduct optical interferometry.<ref See an illustration of its layout, at bottom. NOFS has used NPOI to conduct a wide and diverse series of scientific studies, beyond just the study of absolute astrometric positions of stars,; additional NOFS science at NPOI includes the study of binary stars, Be Stars, Oblate stars, rapidly rotating stars, those with starspots, and the imaging of stellar disks (the first in history) and flare stars. In 2007–2008, NRL with NOFS used NPOI to obtain first-ever closure phase image precursors of satellites orbiting in geostationary orbit. In 2009 NOFS and USNO began efforts to finalize acceptance of four additional 1.8-meter telescopes into the NPOI array, which formerly were slated to be a part of the Keck Observatory interferometric array. Under Secretary of the Navy acceptance occurred in November 2010, and these four telescopes were assigned to NOFS. Installation plans were developed in 2010-2012 by the scientific and engineering staffs at NOFS, based on the funded science performed by NOFS and NRL. In 2012 NOFS, with support from USNO, CNMOC and the Chief of Naval Operations' Oceanographer staff, began developing funding and programming plans in order to install the array. NOFS endeavors to facilitate construction starts in the 2012-2015 timeframe.