Submillimeter Wave Astronomy Satellite (SWAS, also Explorer 74 and SMEX-3) is a
NASA
The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research.
NASA was established in 1958, succeeding t ...
submillimetre astronomy
Submillimetre astronomy or submillimeter astronomy (see spelling differences) is the branch of observational astronomy that is conducted at submillimetre wavelengths (i.e., terahertz radiation) of the electromagnetic spectrum. Astronomers plac ...
satellite, and is the fourth spacecraft in the Small Explorer program (SMEX). It was launched on 6 December 1998, at 00:57:54
UTC, from
Vandenberg Air Force Base Vandenberg may refer to:
* Vandenberg (surname), including a list of people with the name
* USS General Harry Taylor (AP-145), USNS ''General Hoyt S. Vandenberg'' (T-AGM-10), transport ship in the United States Navy, sank as an artificial reef in K ...
aboard a
Pegasus XL
Pegasus is an air-launched launch vehicle developed by Orbital Sciences Corporation (OSC) and now built and launched by Northrop Grumman. Capable of carrying small payloads of up to into low Earth orbit, Pegasus first flew in 1990 and remai ...
launch vehicle.
The telescope was designed by the
Smithsonian Astrophysical Observatory
The Smithsonian Astrophysical Observatory (SAO) is a research institute of the Smithsonian Institution, concentrating on astrophysical studies including galactic and extragalactic astronomy, cosmology, solar, earth and planetary sciences, the ...
(SAO) and integrated by
Ball Aerospace
Ball Aerospace & Technologies Corp. is an American manufacturer of spacecraft, components and instruments for national defense, civil space and commercial space applications. The company is a wholly owned subsidiary of Ball Corporation (NYSE: BAL ...
, while the spacecraft was built by NASA's
Goddard Space Flight Center
The Goddard Space Flight Center (GSFC) is a major NASA space research laboratory located approximately northeast of Washington, D.C. in Greenbelt, Maryland, United States. Established on May 1, 1959 as NASA's first space flight center, GSFC empl ...
(GSFC).
The mission's
principal investigator
In many countries, the term principal investigator (PI) refers to the holder of an independent grant and the lead researcher for the grant project, usually in the sciences, such as a laboratory study or a clinical trial. The phrase is also often us ...
is Gary J. Melnick.
[ ]
History
The Submillimeter Wave Astronomy Satellite mission was approved on 1 April 1989. The project began with the Mission Definition Phase, officially starting on 29 September 1989, and running through 31 January 1992. During this time, the mission underwent a
conceptual design Conceptual design is an early phase of the design process, in which the broad outlines of function and form of something are articulated. It includes the design of interactions, experiences, processes, and strategies. It involves an understanding of ...
review
A review is an evaluation of a publication, product, service, or company or a critical take on current affairs in literature, politics or culture. In addition to a critical evaluation, the review's author may assign the work a content rating, ...
on 8 June 1990, and a demonstration of the Schottky receivers and acousto-optical spectrometer concept was performed on 8 November 1991.
Development
The mission's Development Phase ran from February 1992, through May 1996. The Submillimeter Wave Telescope underwent a
preliminary design review
In the United States military integrated acquisition lifecycle the Technical section has multiple acquisition "Technical Reviews". Technical reviews and audits assist the acquisition and the number and types are tailored to the acquisition. Over ...
on 13 May 1992, and a
critical design review
In the United States military integrated acquisition lifecycle the Technical section has multiple acquisition "Technical Reviews". Technical reviews and audits assist the acquisition and the number and types are tailored to the acquisition. Over ...
(CDR) on 23 February 1993.
Ball Aerospace
Ball Aerospace & Technologies Corp. is an American manufacturer of spacecraft, components and instruments for national defense, civil space and commercial space applications. The company is a wholly owned subsidiary of Ball Corporation (NYSE: BAL ...
was responsible for the construction of and integration of components into the telescope. The
University of Cologne
The University of Cologne (german: Universität zu Köln) is a university in Cologne, Germany. It was established in the year 1388 and is one of the most prestigious and research intensive universities in Germany. It was the sixth university to ...
delivered the acousto-optical spectrometer to Ball for integration into the telescope on 2 December 1993, while
Millitech Corporation
Proxim Wireless Corporation is a San Jose, California-based company that builds scalable broadband wireless networking systems for communities, enterprises, governments, and service providers. It offers wireless LAN, point-to-multipoint and point- ...
delivered the Schottky receivers to Ball on 20 June 1994. Ball delivered the finished telescope to Goddard Space Flight Center on 20 December 1994. GSFC, which was responsible for construction of the spacecraft bus, conducted integration of spacecraft and instrument from January through March 1995. Spacecraft qualification and testing took place between 1 April 1995, and 15 December 1995. After this, SWAS was placed into storage until 1 September 1998, when launch preparation was begun.
Mission
SWAS was designed to study the chemical composition, energy balance and structure of
interstellar cloud
An interstellar cloud is generally an accumulation of gas, plasma, and dust in our and other galaxies. Put differently, an interstellar cloud is a denser-than-average region of the interstellar medium, the matter and radiation that exists in t ...
s, both galactic and extragalactic, and investigate the processes of
stellar and planetary formation.
Its sole instrument is a telescope operating in the submillimeter wavelengths of
far infrared
Far infrared (FIR) is a region in the infrared spectrum of electromagnetic radiation. Far infrared is often defined as any radiation with a wavelength of 15 micrometers (μm) to 1 mm (corresponding to a range of about 20 THz to ...
and
microwave
Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ran ...
radiation. The telescope is composed of three main components: a elliptical off-axis
Cassegrain reflector
The Cassegrain reflector is a combination of a primary concave mirror and a secondary convex mirror, often used in optical telescopes and radio antennas, the main characteristic being that the optical path folds back onto itself, relative to th ...
with a beam width of 4 arcminutes at operating frequencies,
two
Schottky diode
The Schottky diode (named after the German physicist Walter H. Schottky), also known as Schottky barrier diode or hot-carrier diode, is a semiconductor diode formed by the junction of a semiconductor with a metal. It has a low forward voltage ...
receivers, and an
acousto-optical spectrometer
An acousto-optical spectrometer (AOS) is based on the diffraction of light by ultrasonic waves. A piezoelectric transducer, driven by the RF signal (from the receiver), generates an acoustic wave in a crystal (the so-called Bragg-cell). This a ...
.
The system is sensitive to frequencies between 487–557
GHz
The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that one he ...
(538–616
μm), which allows it to focus on the
spectral line
A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to iden ...
s of molecular
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
(O
2) at 487.249 GHz; neutral
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent
In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...
() at 492.161 GHz; isotopic
water
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...
(H
218O) at 548.676 GHz; isotopic
carbon monoxide
Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
(
13CO) at 550.927 GHz; and water (H
2O) at 556.936 GHz.
Detailed 1° x 1° maps of giant molecular and dark cloud cores are generated from a grid of measurements taken at 3.7
arcminutes spacings. SWAS's submillimeter radiometers are a pair of passively cooled subharmonic
Schottky diode
The Schottky diode (named after the German physicist Walter H. Schottky), also known as Schottky barrier diode or hot-carrier diode, is a semiconductor diode formed by the junction of a semiconductor with a metal. It has a low forward voltage ...
receivers, with receiver noise figures of 2500-3000 K. An
acousto-optical spectrometer
An acousto-optical spectrometer (AOS) is based on the diffraction of light by ultrasonic waves. A piezoelectric transducer, driven by the RF signal (from the receiver), generates an acoustic wave in a crystal (the so-called Bragg-cell). This a ...
(AOS) was provided by the
University of Cologne
The University of Cologne (german: Universität zu Köln) is a university in Cologne, Germany. It was established in the year 1388 and is one of the most prestigious and research intensive universities in Germany. It was the sixth university to ...
, in
Germany
Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
. Outputs of the two SWAS receivers are combined to form a final intermediate frequency, which extends from 1.4 to 2.8 GHz and is dispersed into 1400 1-MHz channels by the AOS. SWAS is designed to make pointed observations stabilized on three axes, with a position accuracy of about 38 arcseconds, and jitter of about 24 arcseconds. Attitude information is obtained from gyroscopes whose drift is corrected via a star tracker. Momentum wheels are used to maneuver the spacecraft.
Experiment
Submillimeter Wave Telescope
![SWAS OBSERVES SOURCES THROUGHOUT THE GALAXY](https://upload.wikimedia.org/wikipedia/commons/1/1a/SWAS_OBSERVES_SOURCES_THROUGHOUT_THE_GALAXY.jpg)
The SWAS instrument is a submillimeter wave telescope that incorporates dual heterodyne radiometers and an acousto-optical spectrometer. SWAS will measure water, molecular oxygen, atomic carbon, and isotopic
carbon monoxide
Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
spectral line emissions from galactic interstellar clouds in the wavelength range 540-616 micrometres. Such submillimetre wave radiation cannot be detected from the ground because of atmospheric attenuation. The SWAS measurements will provide new information about the physical conditions (density and temperature) and chemistry in star-forming molecular clouds.
[ ]
Launch
The spacecraft was delivered to
Orbital Sciences Corporation
Orbital Sciences Corporation (commonly referred to as Orbital) was an American company specializing in the design, manufacture, and launch of small- and medium- class space and launch vehicle systems for commercial, military and other governmen ...
at Vandenberg Air Force Base on 2 November 1998, for integration onto their
Pegasus XL
Pegasus is an air-launched launch vehicle developed by Orbital Sciences Corporation (OSC) and now built and launched by Northrop Grumman. Capable of carrying small payloads of up to into low Earth orbit, Pegasus first flew in 1990 and remai ...
launch vehicle.
Launch occurred on 6 December 1998, at 00:57:54 UTC, from Orbital Sciences' ''
Stargazer''
L-1011 TriStar
The Lockheed L-1011 TriStar, also known as the L-1011 (pronounced "El-ten-eleven") and TriStar, is an American medium-to-long-range, wide-body trijet airliner built by the Lockheed Corporation. It was the third wide-body airliner to enter comme ...
mothership.
Its initial orbit was a near-circular with an
inclination
Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a Plane of reference, reference plane and the orbital plane or Axis of rotation, axis of direction of the orbiting object ...
of 69.90°.
[ ]
SWAS was originally scheduled to launch in June 1995, but was delayed due to back-to-back launch failures of the Pegasus XL launch vehicle in June 1994 and June 1995. A launch opportunity in January 1997 was again canceled due to a Pegasus XL launch failure in November 1996.
The commissioning phase of the mission lasted until 19 December 1998, when the telescope began producing useful science data.
The SWAS mission had a planned duration of two years and a cost estimate of US$60 million,
but mission extensions allowed for five and a half years of continuous science operations. During this time, data was taken on more than 200 astronomical objects.
The decision was made to end science and spacecraft operations on 21 July 2004, at which time the spacecraft was placed into hibernation.
Deep Impact mission
To support the ''
Deep Impact'' mission at comet
9P/Tempel
Tempel 1 (official designation: 9P/Tempel) is a periodic Jupiter-family comet discovered by Wilhelm Tempel in 1867. It completes an orbit of the Sun every 5.5 years. Tempel 1 was the target of the ''Deep Impact'' space mission, which photogra ...
, SWAS was brought out of hibernation on 1 June 2005. Vehicle check-out was completed on 5 June 2005 with no discernible degradation of equipment found. SWAS observations of the comet focused on isotopic water output both before and after the ''Deep Impact'' impactor struck the comet's nucleus on 4 July 2005. While water output was found to naturally vary by more than a factor of three during the observation campaign, SWAS data showed that there was no excessive release of water due to the impact event. After three months of observation, SWAS was once again placed into hibernation on 1 September 2005.
, SWAS remains in Earth orbit on stand-by.
See also
*
Explorer program
The Explorers program is a NASA exploration program that provides flight opportunities for physics, geophysics, heliophysics, and astrophysics investigations from space. Launched in 1958, Explorer 1 was the first spacecraft of the United Stat ...
References
Further reading
*
*
External links
SWAS websiteby the
Center for Astrophysics Harvard & Smithsonian
SWAS data archiveby NASA's Legacy Archive for Microwave Background Data Analysis
by the NASA/IPAC Infrared Science Archive
SWAS website(archive) by NASA's Goddard Space Flight Center
{{Orbital launches in 1998
Satellites orbiting Earth
Explorers Program
Space telescopes
Spacecraft launched in 1998
Submillimetre telescopes
Spacecraft launched by Pegasus rockets