The
Stratospheric Observatory for Infrared Astronomy (SOFIA) is a joint project of
NASAThe National Aeronautics and Space Administration is an agency of the United States government, responsible for the nation's public space program. NASA was established by the National Aeronautics and Space Act on July 29, 1958, replacing its predecessor, the National Advisory Committee for...
and the
German Aerospace CenterThe German Aerospace Center is the national centre for aerospace, energy and transportation research of the Federal Republic of Germany. It has multiple locations throughout Germany. Its headquarters are located in Cologne. It is engaged in a wide range of research and development projects in...
(DLR) for the construction and maintenance of an
airborne telescopeAn airborne observatory is a airplane or balloon with an astronomical telescope. By carrying the telescope high, the telescope can avoid cloud cover, pollution, and carry out observations in the infrared spectrum, above water vapor in the atmosphere which absorbs infrared radiation.Examples of...
.
Universities Space Research AssociationThe Universities Space Research Association was incorporated on March 12, 1969 in the District of Columbia as a private, nonprofit corporation under the auspices of the National Academy of Sciences . Institutional membership in the Association has grown from 49 colleges and universities when it was...
(USRA) was awarded the contract by NASA in 1996 for development, operation of the observatory and management of the American part while the DSI (Deutsches SOFIA Institut) manages the German part (mainly science and telescope related).
Facility
SOFIA is based on a
Boeing 747SPThe Boeing 747SP is a widebody commercial airliner. It is a highly modified version of its predecessor, the Boeing 747-100 with SP standing for "special performance"...
wide-body aircraftA wide-body aircraft is a large airliner with two passenger aisles, also known as a twin-aisle aircraft. The typical fuselage diameter is . In the typical widebody economy cabin, passengers are seated seven to ten abreast, allowing a total capacity of 200 to 600 passengers...
. The aircraft has been modified to carry a 2.5 meter diameter
reflecting telescopeA reflecting telescope is an optical telescope which uses a single or combination of curved mirrors that reflect light and form an image. The reflecting telescope was invented in the 17th century as an alternative to the refracting telescope which, at that time, was a design that suffered from...
in the aft section of the fuselage. This telescope is designed for
infrared astronomyInfrared astronomy is the branch of astronomy and astrophysics which deals with objects visible in infrared radiation. Visible radiation ranges from 380 nm to 750 nm...
observations at altitudes of about 41,000 feet (about 12 km) in the
stratosphereThe stratosphere is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. It is stratified in temperature, with warmer layers higher up and cooler layers farther down. This is in contrast to the troposphere near the Earth's surface, which is cooler...
. The
water vaporWater vapor or water vapour , also aqueous vapor, is the gas phase of water. Water vapor is one state of the water cycle within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from the sublimation of ice...
in the Earth's atmosphere blocks some infrared wavelengths from reaching the ground, but SOFIA's flight capability allows it to rise above almost all of the water vapor in the Earth's atmosphere. At the aircraft's cruising altitude, 85% of the full infrared range will be available. The aircraft can also travel to almost any point on the Earth's surface, allowing observation from the northern and southern hemispheres.
Once ready for use, the expectation is for observing flights to be flown 3 or 4 nights a week for the next 20 years. SOFIA is now based at NASA's Dryden Aircraft Operations Facility at
LA/Palmdale Regional AirportLA/Palmdale Regional Airport , also United States Air Force Plant 42, is an airport in the city of Palmdale in Los Angeles County, California, United States....
, California, while staff at
NASA Ames Research CenterNASA Ames Research Center located at Moffett Field, California, was founded Dec. 20, 1939 as the second National Advisory Committee for Aeronautics laboratory. The center was named after Joseph Sweetman Ames, a founding member and longtime chairman of the NACA...
, in Mountain View, California, operate the SOFIA Science Center where astronomical observation missions are planned for the flying observatory.
The telescope
SOFIA uses a 2.5-meter reflector telescope, which has an oversized, 2.7 meter diameter primary mirror, as is common with most large infra-red telescopes. The optical system uses a
Cassegrain reflectorThe Cassegrain reflector is a combination of a primary concave mirror and a secondary convex mirror, often used in optical telescopes and radio antennas.In a symmetrical Cassegrain...
design with a parabolic primary mirror and a remotely configurable hyperbolic secondary. In order for the telescope to fit into the fuselage, the primary is shaped to an
f-numberIn optics, the f-number of an optical system expresses the diameter of the entrance pupil in terms of the focal length of the lens; in simpler terms, the f-number is the focal length divided by the "effective" aperture diameter...
as low as 1.3. However, the resulting optical layout has an f-number of 19.7. A flat, tertiary,
dichroic mirrorDichroism has two related but distinct meanings in optics. A dichroic material is either one which causes visible light to be split up into distinct beams of different wavelengths , or one in which light rays having different polarizations are absorbed by different amounts...
is used to deflect the infrared part of the beam to the
Nasmyth focusThe Nasmyth telescope is a reflecting telescope developed by James Nasmyth. It is a modified form of a Cassegrain telescope, mounted on an alt-azimuth mount....
where it can be analyzed. An optical mirror located behind the tertiary mirror is used for a camera guidance system.
The telescope looks out of a large door in the side of the
fuselageThe fuselage is an aircraft's main body section that holds crew and passengers or cargo. In single-engine aircraft it will usually contain an engine, although in some amphibious aircraft the single engine is mounted on a pylon attached to the fuselage which in turn is used as a floating hull...
near the airplane's tail, and will initially carry nine instruments for
infrared astronomyInfrared astronomy is the branch of astronomy and astrophysics which deals with objects visible in infrared radiation. Visible radiation ranges from 380 nm to 750 nm...
at
wavelengthIn physics, the wavelength of a sinusoidal wave is the spatial period of the wave – the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
s from 1–655
micrometreA micrometre or micron is one millionth of a metre,or equivalently one thousandth of a millimetre....
s and high-speed optical astronomy at
wavelengthIn physics, the wavelength of a sinusoidal wave is the spatial period of the wave – the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
s from 0.3–1.1 micrometres. The main instruments are the FLITECAM, a near infrared camera covering 1–5 micrometres; FORCAST, covering the mid-infrared range of 5–40 micrometres, and HAWC, which spans the far infrared in the range 40–300 micrometres. The other five infrared instruments are
spectrometerA spectrometer is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify materials. The variable measured is most often the light's intensity but could also, for instance, be the polarization...
s with various overlapping spectral ranges. SOFIA’s telescope is by far the largest ever to be placed in an aircraft, although there are a number of larger ground-based research observatories. For each mission one interchangeable science instrument will be attached to the telescope. Two groups of general purpose instruments are available. In addition an investigator can also design and build a special purpose instrument.
The open cavity housing the telescope will be exposed to high-speed turbulent winds. In addition, the vibrations and motions of the aircraft introduce observing difficulties. The telescope was designed to be very light-weight, and the mount includes a system to isolate the instrument from vibration. The telescope cabin must be pre-cooled prior to aircraft takeoff so that the telescope matches the external temperature (thus avoiding thermally induced shape changes). Prior to landing the compartment is flooded with nitrogen gas in order to avoid condensation of moisture on the chilled instrument.
DLR is responsible for the entire telescope assembly and design, whereas NASA is responsible for the plane only. The manufacturing of the telescope was subcontracted to European industry. The telescope is German, the mirror is French-made and the secondary mirror mechanism is Swiss-made. The consortium has a mirror coating facility in
Moffett FieldMoffett Federal Airfield , also known as Moffett Field, is a joint civil-military airport located 3 miles north of downtown Mountain View, in Sunnyvale, California, USA. The airport is near the south end of San Francisco Bay, north of San Jose...
, allowing a fast recoating of the primary mirror.
The aircraft
The SOFIA aircraft is a
widebodyA wide-body aircraft is a large airliner with two passenger aisles, also known as a twin-aisle aircraft. The typical fuselage diameter is . In the typical widebody economy cabin, passengers are seated seven to ten abreast, allowing a total capacity of 200 to 600 passengers...
Boeing 747SP (manufacturers serial number 21441) with a distinguished history. It was originally acquired by
Pan American World AirwaysPan American World Airways, commonly known as Pan Am, was the "flagship" international airline of the United States from the 1930s until its collapse on December 4, 1991...
and was delivered on May 6, 1977. The "SP" (Special Performance) designates that this is a special short-body version of the 747, designed for longer flights than the basic model.
United AirlinesUnited Air Lines, Inc., trading as United Airlines , is a major airline of the United States. It is a subsidiary of UAL Corporation with corporate offices in Chicago at 77 West Wacker Drive in the Chicago Loop. United's largest hub is O'Hare International Airport, where it has more than 550 daily...
purchased the plane in February 1986, and removed it from active service in December 1995. Two years later, NASA purchased it from United for use by the SOFIA project. A series of "baseline" flight tests were conducted in 1997 prior to heavy modification of the aircraft by
L-3 CommunicationsL-3 Communications Holdings, Inc. is a company that supplies command, control, communications, intelligence, surveillance and reconnaissance systems and products, avionics and ocean products, training devices and services, instrumentation, space and navigation products. Its customers include the...
Integrated Systems of
Waco, TexasWaco is a city in and the county seat of McLennan County, Texas. The city has a 2008 estimated total population of 124,009. It is the 21st largest city by population in Texas, and 194th in the US...
, for its new role as a flying astronomical observatory. A dismantled section from another 747SP (N141UA) was used as a full-size mock-up to ensure proper modification.
Pan Am had named this aircraft
Clipper Lindbergh in honor of the famous aviator
Charles LindberghCharles Augustus Lindbergh was an American aviator, author, inventor and explorer.On May 20–21, 1927, Lindbergh, then a 25-year old U.S...
. The aircraft was personally christened by Lindbergh's widow,
Anne Morrow LindberghAnne Morrow Lindbergh, born Anne Spencer Morrow was a pioneering American aviator, author, and the spouse of fellow aviator Charles Lindbergh.-Early life:...
, on the occasion of the 50th anniversary of her husband's historic flight from New York to Paris in 1927, although the aircraft had been officially placed into service on May 6, 1977. Similarly, Lindbergh's grandson, Erik Lindbergh, re-christened the aircraft
Clipper Lindbergh on May 21, 2007 at L-3's Waco facilities.
The telescope is mounted in the aft part of the aircraft behind a pressurized bulkhead. The telecope's
focal pointA focal point may mean:* Focus , the point at which initially collimated rays of light meet after passing through a convex lens, or reflecting from a concave mirror....
is located at a science instruments suite in the pressurized section. In the center of the aircraft is the mission control and science operations section, while the forward section hosts the education and public outreach area.
Project development
The first use of an aircraft for performing infrared observations occurred in 1965 when Gerard P. Kuiper used the NASA Convair 990 to study Venus. Three years later, Frank Low used the Ames Learjet to perform observations of Jupiter and nebulae. In 1969, planning began
for mounting a telescope on an airborne platform. The goal of this instrument was to perform astronomy from the
stratosphereThe stratosphere is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. It is stratified in temperature, with warmer layers higher up and cooler layers farther down. This is in contrast to the troposphere near the Earth's surface, which is cooler...
, where there was a much lower
optical depthOptical depth, or optical thickness is a measure of transparency, and is defined as the negative logarithm of the fraction of radiation...
from water vapor absorbing
infraredInfrared radiation is electromagnetic radiation whose wavelength is longer than that of visible light , but shorter than that of terahertz radiation and microwaves...
radiation. This project was named the
Kuiper Airborne ObservatoryThe Gerard P. Kuiper Airborne Observatory was a national facility operated by NASA to support research in infrared astronomy. The observation platform was a highly modified C-141A jet transport aircraft with a range of 6,000 nautical miles, capable of conducting research operations up to 45,000...
, and it was dedicated on May 21, 1975. The telescope became instrumental in numerous scientific studies, including the discovery of the ring system around the planet Uranus.
The proposal for a larger aircraft-mounted telescope was officially presented in 1984, which called for a
Boeing 747The Boeing 747 is a widebody commercial airliner, often referred to by the nickname "Jumbo Jet". It is among the world's most recognizable aircraft, and was the first widebody ever produced...
to carry a three-meter telescope. The preliminary system concept was published in 1987 in the
Red Book. It was agreed that Germany would contribute 20% of the total cost, and they would provide the telescope. However, the reunification of Germany and budget cuts at NASA led to a five-year slide in the project. NASA then contracted the work out to the Universities Space Research Association (USRA), and in 1996, NASA and DLR (the German Space Agency or
Deutsches Zentrum fur Luft- und Raumfahrt) signed a memorandum of understanding for the building and operation of SOFIA.
The SOFIA telescope's primary mirror was manufactured out of
ZerodurZerodur is a glass-ceramic made by Schott AG. It has both an amorphous component and a crystalline component. The most important properties of Zerodur are:...
, a glass-ceramic composite produced by Schott AG that has almost zero
thermal expansionWhen the temperature of a substance changes, the energy that is stored in the intermolecular bonds between atoms changes. When the stored energy increases, so does the length of the molecular bonds...
. REOSC, the optical department of the
SAGEMSAGEM was a major French company involved in defence electronics, consumer electronics and communication systems.In 2005, Sagem merged with SNECMA to form SAFRAN...
Group in France, performed weight reduction by milling honeycomb-shaped pockets out of the back. They finished polishing the mirror on December 14, 1999, achieving an accuracy of 8.5 nm over the optical surface. The hyperbolic-shaped secondary mirror was made out of
silicon carbideSilicon carbide , also known as carborundum, is a compound of silicon and carbon with a 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...
,
with polishing completed by May 2000.
During 2002, the main components of the telescope were assembled in
AugsburgAugsburg is a city in the south-west of Bavaria in Germany. It is a College town and home of the Regierungsbezirk Schwaben and the Bezirk Schwaben. Augsburg is an urban district and home to the institutions of the Landkreis Augsburg. It is, as of 2008, the third-largest city in Bavaria with a...
, Germany. These consisted of the primary mirror assembly, the main optical support and the suspension assembly. After successful integration tests were made to check the system, the components were shipped to
Waco, TexasWaco is a city in and the county seat of McLennan County, Texas. The city has a 2008 estimated total population of 124,009. It is the 21st largest city by population in Texas, and 194th in the US...
on board an
Airbus BelugaThe Airbus A300-600ST or Beluga is a version of the standard A300-600 wide-body airliner modified to carry aircraft parts and over-sized or awkward cargo...
aircraft. They arrived on September 4, 2002. SOFIA completed its first ground-based "on-sky" test on August 18-19, 2004 by taking an image of the star
PolarisPolaris is the brightest star in the constellation Ursa Minor. It is very close to the north celestial pole , making it the current northern pole star.Polaris is about 430 light-years from Earth...
.
In February 2006, following delays, and costs which increased from US$185 million to $330 million,
NASA placed the project "under review" and suspended funding. On June 15, 2006, SOFIA passed the review when NASA concluded that there were no insurmountable technical or programmatic challenges to the continued development of SOFIA.
The maiden flight of SOFIA took place on April 26, 2007 at the L-3 Integrated Systems' (L-3 IS) Waco, Texas facility. After a brief test program was conducted in Waco to partially expand the flight envelope and perform post-maintenance checks, the aircraft was moved to
Edwards Air Force BaseEdwards Air Force Base is a United States Air Force base located on the border of Kern County, Los Angeles County, and San Bernardino County, California, in the Antelope Valley. It is southwest of the central business district of North Edwards, California and due east of Rosamond. It is named in...
on May 31, 2007. The first phase of loads and flight testing was used to check the aircraft characteristics with the external telescope cavity door closed. This phase was successfully completed by January,
2008 at NASA-Dryden F.R.C.
In mid-2009, the aircraft will undergo flight tests at high altitude cruising speed with the telescope door open. This test phase is scheduled to run through the end of 2009, after which SOFIA will begin limited science observation flights. Normal science observation flights should begin in 2011 and the observatory is slated for full capability by 2014.
Scientific research
The primary science objectives of SOFIA are to study the composition of
planetA planet , is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...
ary
atmosphereAn atmosphere is a layer of gases that may surround a material body of sufficient mass, by the gravity of the body, and are retained for a longer duration if gravity is high and the atmosphere's temperature is low...
s and surfaces; to investigate the structure, evolution and composition of
cometA comet is a Small Solar System Body that has coma and is bigger than a meteoroid. When close enough to the Sun, a comet exhibits a visible coma , and sometimes a tail, both because of the effects of solar radiation upon the comet's nucleus...
s; to determine the
physicsPhysics is a natural science; it is the study of matter and its motion through spacetime and all that derives from these, such as energy and force...
and
chemistryChemistry is the science concerned with the composition, behavior, structure, and properties of matter, as well as the changes it undergoes during chemical reactions...
of the
interstellar mediumIn astronomy, the interstellar medium is the gas and dust that pervade interstellar space: the matter that exists between the star systems within a galaxy. It fills interstellar space and blends smoothly into the surrounding intergalactic space...
; and to explore the formation of
starA star is a massive, luminous ball of plasma that is held together by gravity. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth. Other stars are visible in the night sky, when they are not outshone by the Sun...
s and other stellar objects. While SOFIA aircraft operations are managed by NASA Dryden, NASA Ames Research Center in Mountain View, California, is home to the SOFIA Science Center.
External links
- SOFIA Science Center, USRA
The Universities Space Research Association was incorporated on March 12, 1969 in the District of Columbia as a private, nonprofit corporation under the auspices of the National Academy of Sciences . Institutional membership in the Association has grown from 49 colleges and universities when it was...
& DSIDSI is an initialism for the following companies:*Nintendo DSi, Nintendo's third iteration of the Nintendo DS handheld*Delphine Software International, a now bankrupt software company*Destination Software, Inc., a video game company...
- SOFIA mission, NASA
The National Aeronautics and Space Administration is an agency of the United States government, responsible for the nation's public space program. NASA was established by the National Aeronautics and Space Act on July 29, 1958, replacing its predecessor, the National Advisory Committee for...
- SOFIA Mission Profile by Solar System Exploration at NASA
The National Aeronautics and Space Administration is an agency of the United States government, responsible for the nation's public space program. NASA was established by the National Aeronautics and Space Act on July 29, 1958, replacing its predecessor, the National Advisory Committee for...
- SOFIA Website des DLR (de)
- SOFIA on Astronomy Picture of the Day
- Stratospheric Observatory For Infrared Astronomy (SOFIA), Department of Astronomy and Astrophysics at University of Chicago
The University of Chicago is a private, coeducational research university in Chicago, Illinois, USA. It was founded by oil magnate and benefactor John D...
- SOFIA: Stratospheric Observatory For Infrared Astronomy, Moonfest 2009 by NASA
The National Aeronautics and Space Administration is an agency of the United States government, responsible for the nation's public space program. NASA was established by the National Aeronautics and Space Act on July 29, 1958, replacing its predecessor, the National Advisory Committee for...
Contractors
Multimedia
- SOFIA Photo Collection, Dryden Flight Research Center
The Dryden Flight Research Center , located inside Edwards Air Force Base, is an aeronautical research center operated by NASA. On March 26, 1976 it was named in honor of the late Hugh L. Dryden, a prominent aeronautical engineer who at the time of his death in 1965 was NASA's deputy administrator...
- SOFIA Movie Collection, Dryden Flight Research Center
The Dryden Flight Research Center , located inside Edwards Air Force Base, is an aeronautical research center operated by NASA. On March 26, 1976 it was named in honor of the late Hugh L. Dryden, a prominent aeronautical engineer who at the time of his death in 1965 was NASA's deputy administrator...