Far Ultraviolet Spectroscopic Explorer
Encyclopedia
The Far Ultraviolet Spectroscopic Explorer (FUSE) is a space-based telescope
operated by the Johns Hopkins University
Applied Physics Laboratory
. FUSE was launched on a Delta II
rocket on June 24, 1999, as a part of NASA
's Origins program
. FUSE detected light in the far ultraviolet
portion of the electromagnetic spectrum, between 90.5-119.5 nanometre
s, which is mostly unobservable by other telescopes. Its primary mission was to characterize universal deuterium
in an effort to learn about the stellar processing times of deuterium left over from the Big Bang
.
FUSE resides in a low Earth orbit
, approximately 760 km (410 nmi
) in altitude, with an inclination of 25 degrees and just less than a 100 minute orbital period. Its Explorer
designation is Explorer 77.
On July 12, 2007, FUSEs final reaction wheel
, which is required for accurately pointing a spacecraft, failed and efforts to restart it were unsuccessful. An announcement was made on September 6 that because the fine control needed to perform its mission had been lost, the FUSE mission would be terminated.
-type grazing incidence telescope, the final design of the FUSE telescope comprises four individual mirrors. Each of the four mirrors is a 39-by-35 cm (15.4-by-13.8 in) off-axis parabola. Two mirror segments are coated with silicon carbide
for reflectivity at the shortest ultraviolet wavelengths, and two mirror segments are coated with lithium fluoride
over aluminum that reflects better at longer wavelengths. This optimizes performance over the entire spectral range.
Each mirror has a corresponding astigmatism
-corrected, holographically
-ruled diffraction grating
, each one on a curved substrate so as to produce four 1.65 m (5.4 ft) Rowland
circle spectrograph
s. The dispersed ultraviolet light is detected by two microchannel plate
intensified double delay-line detectors, whose surfaces are curved to match the curvature of the focal plane.
. Because of the large number of atomic absorption and emission lines in the far-ultraviolet, FUSE enabled many studies of galactic, extragalactic and intergalactic chemistry and chemical evolution.
Telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...
operated by the Johns Hopkins University
Johns Hopkins University
The Johns Hopkins University, commonly referred to as Johns Hopkins, JHU, or simply Hopkins, is a private research university based in Baltimore, Maryland, United States...
Applied Physics Laboratory
Applied Physics Laboratory
The Johns Hopkins University Applied Physics Laboratory , located in Howard County, Maryland near Laurel and Columbia, is a not-for-profit, university-affiliated research center employing 4,500 people. APL is primarily a defense contractor. It serves as a technical resource for the Department of...
. FUSE was launched on a Delta II
Delta II
Delta II was an American space launch system, originally designed and built by McDonnell Douglas. Delta II is part of the Delta rocket family and was in service from 1989 until November 1, 2011...
rocket on June 24, 1999, as a part of NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
's Origins program
Origins Program
NASA's Origins program is a decades-long study addressing the origins of the universe, various astronomical bodies, and life. The Origins program was started in the 1990s.So far, it consists of the following missions:* Hubble Space Telescope*...
. FUSE detected light in the far ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
portion of the electromagnetic spectrum, between 90.5-119.5 nanometre
Nanometre
A nanometre is a unit of length in the metric system, equal to one billionth of a metre. The name combines the SI prefix nano- with the parent unit name metre .The nanometre is often used to express dimensions on the atomic scale: the diameter...
s, which is mostly unobservable by other telescopes. Its primary mission was to characterize universal deuterium
Deuterium
Deuterium, also called heavy hydrogen, is one of two stable isotopes of hydrogen. It has a natural abundance in Earth's oceans of about one atom in of hydrogen . Deuterium accounts for approximately 0.0156% of all naturally occurring hydrogen in Earth's oceans, while the most common isotope ...
in an effort to learn about the stellar processing times of deuterium left over from the Big Bang
Big Bang
The Big Bang theory is the prevailing cosmological model that explains the early development of the Universe. According to the Big Bang theory, the Universe was once in an extremely hot and dense state which expanded rapidly. This rapid expansion caused the young Universe to cool and resulted in...
.
FUSE resides in a low Earth orbit
Low Earth orbit
A low Earth orbit is generally defined as an orbit within the locus extending from the Earth’s surface up to an altitude of 2,000 km...
, approximately 760 km (410 nmi
Nautical mile
The nautical mile is a unit of length that is about one minute of arc of latitude along any meridian, but is approximately one minute of arc of longitude only at the equator...
) in altitude, with an inclination of 25 degrees and just less than a 100 minute orbital period. Its Explorer
Explorer program
The Explorer program is a United States space exploration program that provides flight opportunities for physics, heliophysics, and astrophysics investigations from space. Over 90 space missions have been launched from 1958 to 2011, and it is still active...
designation is Explorer 77.
On July 12, 2007, FUSEs final reaction wheel
Momentum wheel
A reaction wheel is a type of flywheel used primarily by spacecraft for attitude control without using fuel for rockets or other reaction devices....
, which is required for accurately pointing a spacecraft, failed and efforts to restart it were unsuccessful. An announcement was made on September 6 that because the fine control needed to perform its mission had been lost, the FUSE mission would be terminated.
Optical design
Although the original specification was to have a WolterWolter telescope
A Wolter telescope is a telescope for X-rays using only grazing incidence optics. Visible light telescopes are built with lenses or parabolic mirrors at nearly normal incidence. Neither works well for X-rays. Lenses for visible light are made of a transparent material with an index of refraction...
-type grazing incidence telescope, the final design of the FUSE telescope comprises four individual mirrors. Each of the four mirrors is a 39-by-35 cm (15.4-by-13.8 in) off-axis parabola. Two mirror segments are coated with silicon carbide
Silicon carbide
Silicon carbide , also known as carborundum, is a compound of silicon and carbon with chemical formula SiC. It occurs in nature as the extremely rare mineral moissanite. Silicon carbide powder has been mass-produced since 1893 for use as an abrasive...
for reflectivity at the shortest ultraviolet wavelengths, and two mirror segments are coated with lithium fluoride
Lithium fluoride
Lithium fluoride is an inorganic compound with the formula LiF. It is the lithium salt of hydrofluoric acid. This white solid is a simple ionic compound. Its structure is analogous to that of sodium chloride, but it is much less soluble in water. It is mainly used as a component of molten...
over aluminum that reflects better at longer wavelengths. This optimizes performance over the entire spectral range.
Each mirror has a corresponding astigmatism
Astigmatism
An optical system with astigmatism is one where rays that propagate in two perpendicular planes have different foci. If an optical system with astigmatism is used to form an image of a cross, the vertical and horizontal lines will be in sharp focus at two different distances...
-corrected, holographically
Holography
Holography is a technique that allows the light scattered from an object to be recorded and later reconstructed so that when an imaging system is placed in the reconstructed beam, an image of the object will be seen even when the object is no longer present...
-ruled diffraction grating
Diffraction grating
In optics, a diffraction grating is an optical component with a periodic structure, which splits and diffracts light into several beams travelling in different directions. The directions of these beams depend on the spacing of the grating and the wavelength of the light so that the grating acts as...
, each one on a curved substrate so as to produce four 1.65 m (5.4 ft) Rowland
Henry Augustus Rowland
Henry Augustus Rowland was a U.S. physicist. Between 1899 and 1901 he served as the first president of the American Physical Society...
circle spectrograph
Spectrograph
A spectrograph is an instrument that separates an incoming wave into a frequency spectrum. There are several kinds of machines referred to as spectrographs, depending on the precise nature of the waves...
s. The dispersed ultraviolet light is detected by two microchannel plate
Microchannel plate detector
A micro-channel plate is a planar component used for detection of particles and impinging radiation . It is closely related to an electron multiplier, as both intensify single particles or photons by the multiplication of electrons via secondary emission...
intensified double delay-line detectors, whose surfaces are curved to match the curvature of the focal plane.
Science results
Over 400 scientific papers have been written using data from FUSE, with subjects ranging from cool stars to the intergalactic medium. One of the primary science goals of FUSE was to study the abundance of deuterium, an isotope of hydrogenHydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
. Because of the large number of atomic absorption and emission lines in the far-ultraviolet, FUSE enabled many studies of galactic, extragalactic and intergalactic chemistry and chemical evolution.
External links
- FUSE website at Johns Hopkins University
- FUSE website at Institut d'Astrophysique de Paris
- FUSE archive at Multimission Archive at STScI (MAST)