SCISAT-1
Encyclopedia
SCISAT-1 is a Canadian satellite
Satellite
In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....

 designed to make observations of the Earth's atmosphere
Earth's atmosphere
The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...

. Its most important instrument is an optical Fourier transform infrared spectrometer
Spectrometer
A 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...

, the ACE-FTS Instrument. This device records the spectrum of the Sun, as sunlight passes through the Earth's atmosphere, and makes an analysis of the chemical elements of the atmosphere possible.

SCISAT is a relatively small satellite weighing 150 kg (~330 pounds). It is partly drum shaped with a diameter of about five feet and a depth of about five feet. The Canadian Space Agency coordinated its design, launch and use. The main contractors were Bristol Aerospace
Bristol Aerospace
Bristol Aerospace is a Canadian aerospace firm located in Winnipeg, Manitoba and is an operating division of Magellan Aerospace.-History:Bristol Aerospace began in 1930 as the MacDonald Brothers Aircraft Company. Brothers Jim and Grant MacDonald moved to Winnipeg from Nova Scotia in 1904 to start a...

 of Winnipeg, Manitoba and ABB Bomem inc. of Quebec City, Quebec.

SCISAT passes through the Earth's shadow 15 times per day, profiting from the occultation
Occultation
An occultation is an event that occurs when one object is hidden by another object that passes between it and the observer. The word is used in astronomy . It can also refer to any situation wherein an object in the foreground blocks from view an object in the background...

 of the Sun to make a spectrographic analysis of the structure and chemistry of those parts of the upper atmosphere that are too high to be reached by balloons and airplanes and too low to be visited by orbiting satellites. This kind of analysis can help understand the depletion of the ozone layer
Ozone layer
The ozone layer is a layer in Earth's atmosphere which contains relatively high concentrations of ozone . This layer absorbs 97–99% of the Sun's high frequency ultraviolet light, which is potentially damaging to the life forms on Earth...

 and other upper atmosphere phenomena.

SCISAT was placed in 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...

, or LEO, by a Pegasus rocket
Pegasus rocket
The Pegasus rocket is a winged space launch vehicle capable of carrying small, unmanned payloads into low Earth orbit. It is air-launched, as part of an expendable launch system developed by Orbital Sciences Corporation . Three main stages burning solid propellant provide the thrust...

 launched from a 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...

 Lockheed L-1011
Lockheed L-1011
The Lockheed L-1011 TriStar, commonly referred to as the L-1011 or TriStar, is a medium-to-long range, widebody passenger trijet airliner. It was the third widebody airliner to enter commercial operations, following the Boeing 747 and the McDonnell Douglas DC-10. Between 1968 and 1984, Lockheed...

 carrier aircraft on August 12, 2003 from Vandenberg Air Force Base
Vandenberg Air Force Base
Vandenberg Air Force Base is a United States Air Force Base, located approximately northwest of Lompoc, California. It is under the jurisdiction of the 30th Space Wing, Air Force Space Command ....

. It is expected to operate for two to five years.

The University of Waterloo
University of Waterloo
The University of Waterloo is a comprehensive public university in the city of Waterloo, Ontario, Canada. The school was founded in 1957 by Drs. Gerry Hagey and Ira G. Needles, and has since grown to an institution of more than 30,000 students, faculty, and staff...

, York University
York University
York University is a public research university in Toronto, Ontario, Canada. It is Canada's third-largest university, Ontario's second-largest graduate school, and Canada's leading interdisciplinary university....

, the University of Toronto
University of Toronto
The University of Toronto is a public research university in Toronto, Ontario, Canada, situated on the grounds that surround Queen's Park. It was founded by royal charter in 1827 as King's College, the first institution of higher learning in Upper Canada...

, and several other Canadian universities collaborated in the design of the experiments, and in several aspects of the testing of the satellite.

ACE-FTS

The ACE-FTS instrument is the main payload of the SCISAT-1 spacecraft. The primary scientific goal of the Atmospheric Chemistry Experiment (ACE) is to measure and understand the chemical and dynamical processes that control the distribution of ozone in the upper troposphere and stratosphere. The principle of ACE measurement is the solar occultation technique. A high inclination (74 degrees), low earth orbit (650 km/400 miles) will provide ACE coverage of tropical, mid-latitudes and polar regions.

The spectrometer is an adapted version of the classical Michelson interferometer using an optimized optical layout. Its highly folded double-pass optical design results in a very high performance instrument with a compact size. A signal-to-noise ratio (SNR) better than 100 is achieved, with a field-of-view (FOV) of 1.25 mrad and an aperture diameter of 100 mm (4"). A semiconductor
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...

 laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...

is used as the metrology source of the interferometer sub-system.

The auxiliary Visible/Near-infrared Imager (VNI) monitors aerosols based on the extinction of solar radiation using two filtered detectors at 0.525 and 1.02 micrometres. The instrument also includes a suntracker mechanism providing fine pointing toward the radiometric center of the sun with stability better than 3 μrad. The ACE-FTS instrument was launched on August 12, 2003.

ABB was the prime contractor for the design and manufacturing of the ACE-FTS instrument.
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