The SPARTAN 201 instruments

Each of the SPARTAN 201 telescopes will study the extremely hot corona and its expansion into the solar wind, but in different and complementary ways. The Ultraviolet Coronal Spectrometer (UVCS) will use ultraviolet emissions from neutral hydrogen and ions in the corona to determine the velocities of the coronal plasma within the solar wind source region, and the temperature and density distributions of protons. The White Light Coronagraph (WLC) will measure visible light to determine the density distribution of coronal electrons within the same regions. Because the Earth's atmosphere interferes with emissions at these wavelengths, the measurements have to be made from space, rather than from the ground. The coordinated results will provide new insight into the unknown source of energy that heats the solar corona and accelerates the solar wind particles. No previous missions have focused specifically on these fundamental questions. The answers will have tremendous importance for our current scientific understanding of the winds that carry away mass and momentum from stars other than the Sun, and might help explain why the Sun's rotation has slowed down to its current rotation rate of once every 27 days. These answers will also have important practical implications for studies of how the variations in radiation and particle outputs of the Sun affect terrestrial magnetism, and ultimately, climate and weather.

There are two coronagraphs --- telescopes that images the Sun's tenuous, outer atmosphere, the corona, by creating an artificial eclipse --- on board SPARTAN 201. They are:

The Ultraviolet Coronal Spectrometer (UVCS)

Visit the SPARTAN UVCS Web pages at the Harvard-Smithsonian Center for Astrophysics

The primary targets for the SPARTAN 201-3 flight of the Ultraviolet Coronal Spectrometer aboard SPARTAN 201 will be the north coronal hole and the boundary regions between coronal holes and streamers. Coronal holes are regions in the solar corona of exceptionally low density and temperature. Streamers are bright regions that are formed where the particles are trapped by the Sun's magnetic field. Temperature, density and velocity models for these regions will be determined using measurements of the atomic (neutral) hydrogen Lyman-alpha (H I 1216 Å) line profiles and the intensities of the ionized oxygen (O VI 1032/1037 Å) lines. They will provide an identification of solar wind source regions, while also mapping the sources of solar-wind streams detected by distant in situ measurements with the Smithsonian Astrophysical Observatory (SAO) in Cambridge, Massachusetts. The SPARTAN system was developed as a program in the Special Payloads Division of NASA Goddard Space Flight Center's Engineering Directorate.

The White Light Coronagraph (WLC)

What is a coronagraph?

The SPARTAN 201 coronagraph is the third in a series of externally occulted coronagraph designs produced by the

SPARTAN 201 White Light Coronagraph Parameters

Length:          		2.63 m

Mass:            		Telescope: 47 kg
                 		Electronics:  44 kg

Objective Lens:  		SMM backup achromatic coronagraph lens
                 		with a 3.1 cm diameter and a 223 mm
                 		focal length.

Central Operating Wavelength:	5200 Å

Filter Bandwidth		500 Å

Detector:			RCA 256 x 320 pixel CCD

Image Scale:     		22.5 arc seconds per pixel

Field of View:   		Offset field of view.  Maximum height
                 		limit is 6.0 solar radii, inner occulting
                 		disk diameter of 1.25 solar radii.

Data rate:       		19.2 kbit/sec

Exposure Times:  		1 - 15 seconds

Calibration:     		External path injects filtered solar disk
                 		light for calibration.

Polarimeter:     		Rotating half wave plate using a single
                 		polarizer for minimizing instrumental
                 		uncertainty.

Effective Data Rate:  		Approximately 30 images/55 minute orbit
                 		or about 900 images/mission (including
                 		calibration.

Well, what have we learned from this (so far)?

Some processed data from the first flight of SPARTAN 201 (on board STS-56) in 1993 April:

Narrow coronal plumes evidently have a different temperature structure from the rest of the corona.
A coronal mass ejection, measured by differencing White Light Coronagraph images taken at two different times

Text provided by Dr. Richard Fisher, NASA Goddard Space Flight Center; and Dr. Leonard Strachan, Smithsonian Astrophysical Observatory.

This is the access to this page since July 10, 1995.

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