Navy Optical Interferometer
Navy Precision Optical Interferometer
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| Alternative names | NPOI |
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| Location(s) | near Flagstaff, Arizona |
| Coordinates | 35°05′45″N 111°32′02″W / 35.0959°N 111.5339°WCoordinates: 35°05′45″N 111°32′02″W / 35.0959°N 111.5339°W |
| Organization | USNO, USNOFS, NRL, Lowell |
| Altitude | 2,163 meters (7,096 ft) |
| Wavelength | Optical/Near-infrared |
| Built | 1992 |
| First light | 1994 |
| Telescope style | Interferometer |
| Website | Navy Precision Optical Interferometer |
 Location of The Kenneth J. Johnston Navy Precision Optical Interferometer (NPOI)
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The Navy Precision Optical Interferometer (NPOI) is an American astronomical interferometer, with the world's largest baselines, operated by the Naval Observatory Flagstaff Station (NOFS) in collaboration with the Naval Research Laboratory (NRL) and Lowell Observatory. The NPOI primarily produces space imagery and astrometry, the latter a major component required for the safe position, navigation, and orienting of the world's orbiting satellites through upwards of more than 19,000 pieces of orbiting space debris. The facility is located at Lowell's Anderson Mesa Station on Anderson Mesa about 25 kilometers (16 mi) southeast of Flagstaff, Arizona (USA). Until November 2011, the facility was known as the Navy Prototype Optical Interferometer (NPOI). Subsequently the instrument was temporarily renamed the Navy Optical Interferometer, and now permanently, the Kenneth J. Johnston Navy Precision Optical Interferometer (NPOI) - reflecting both the operational maturity of the facility, and paying tribute to its principal driver and retired founder, Kenneth J. Johnston.
The NPOI project was initiated by the United States Naval Observatory (USNO) in 1987. Lowell joined the project the following year when the USNO decided to build the NPOI at Anderson Mesa. The first phase of construction was completed in 1994, which allowed the interferometer to see its first fringes, or light combined from multiple sources, that year. The Navy began regular science operations in 1997. The NPOI has been continuously upgraded and expanded since then, and has been operational for a decade. The workings of NPOI as a classic interferometer, are described at Scholarpedia, and at the NPOI site.
The NPOI is an astronomical interferometer laid out in a three-arm "Y" configuration, with each equally-spaced arm measuring 250 meters (820 ft) long. There are two types of stations that can be used in the NPOI. Astrometric stations, used to measure the positions of celestial objects very accurately, are fixed units placed 21 meters (69 ft) apart, with one on each arm and one at the center. Imaging stations can be moved to one of nine positions on each arm, and up to six can be used at one time to perform standard observing. Light from either type of station is first directed into the feed system, which consists of long pipes which have been evacuated of all air. They lead to a switchyard of mirrors, where the light is directed into the six Long Delay Lines, which is another set of long pipes that compensate for the different distances to each station. The light is then sent into the Beam Combining Facility, where it enters the Fast Delay Lines. This third set of evacuated pipes contains mechanisms that move mirrors back and forth with a very high degree of accuracy. These compensate for the movement of the mirrors as they track an object across the sky, and for other effects. Finally, the light leaves the pipes inside the BCF and goes to the Beam Combining Table, where the light is combined in a way that allows images to be formed.
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Wikipedia