SAMPEX: DETECTING PARTICLES FROM THE SUN AND THE COSMOS SAMPEX SCIENCE

Scientists know that space, far from being empty, is full of matter and energy.
Streams of electrically charged particles from the Milky Way galaxy and from
the Sun constantly bombard the magnetic field that surrounds the Earth. Near
the equator these particles are repelled by the strength and geometry of the
Earth's magnetic field, but at the north and south poles the particles, known
as galactic cosmic rays and solar energetic particles, are able to enter our
atmosphere.  The Solar Anomalous and Magnetospheric Particle Explorer (SAMPEX)
mission has been investigating the composition and energy of both these types
of particles in order to answer questions regarding their origin and effect on
the Earth, including a possible link to atmospheric ozone production and
depletion.

One of the newest areas of scientific investigation under study by SAMPEX is
the composition of "anomalous" cosmic rays.  Anomalous cosmic rays are thought
to be atoms of the local interstellar gas that enter the solar system, become
electrically charged by losing one or more electrons (ionized), and then are
accelerated to cosmic ray energy levels as they encounter the boundary between
the solar system and interstellar space.  If the current theory of anomalous
cosmic rays is correct, anomalous cosmic rays should be only partially ionized
and therefore be able to penetrate the Earth's magnetic field at much lower
latitudes than fully ionized particles.  The opportunity to measure the
composition of a sample of local interstellar matter from beyond the solar
system directly will help to answer many questions concerning the evolution of
the Milky Way galaxy and the formation and evolution of our own solar system.

It has long been known that the Sun undergoes periodic cycles in the amount and
intensity of solar activity.  SAMPEX will monitor large and small solar flares
during the decline in activity following the peak of the solar cycle in 1990
and 1991.  By measuring particles from these events, we will gain new
understanding of the Sun's composition and of the mechanisms which cause
flares, including such basic information as changes in the temperature of the
area of the Sun's surface from which the particles originate.

Another SAMPEX investigation measures and maps the way electrons and protons
from the Sun travel along the Earth's magnetic field and enter our atmosphere
during such activity, as the major flare that occurred in November 1992.  A
particularly timely question is that of the production of hydrogen and nitrogen
molecules in the Earth's middle atmosphere as a result of energetic particle
precipitations.  It is not yet known whether this electron activity affects
ozone depletion in our atmosphere.  SAMPEX will help determine whether a link
exists between solar activity and fluctuations in the size and density of the
"ozone hole" above the south pole.

THE COOPERATIVE SATELLITE LEARNING PROJECT

The SAMPEX program is participating in the first Cooperative Satellite Learning
Project (CSLP).  CSLP is a unique educational partnership among Laurel High
School in Laurel, Maryland, Bendix Field Engineering Corporation, Falcon
Microsystems, and Goddard Space Flight Center that involves high school
students in developing and operating SAMPEX. Additional schools will be
included in the next couple of years.  A CSLP at Berkeley, California (in
cooperation with the University of California at Berkeley) is being planned,
with more CSLP's being discussed for schools in Boulder, Colorado, and Boston,
Massachusetts.

This pilot program trains students in the overall end-to-end system used to
support SAMPEX investigations, demonstrating the way in which NASA develops and
implements science missions.  It also demonstrates the application of
technology in a satellite mission, focusing on physics, computer science, and
electronics.

High-school students have already completed a detailed study of the spacecraft
subsystems such as communications, guidance, and thermal control, and
procedures for satellite data processing and analysis, and are being trained to
operate the satellite for a day from the Goddard Space Flight Center control
room.  Students have produced a newsletter, science exhibits, a career video,
and a production for local cable television, for local schools from K~12.

THE SAMPEX SPACECRAFT AND MISSION OPERATIONS

SAMPEX is part of NASA's Small Explorer (SMEX) program.  The SMEX program
allows universities and other research institutions to develop specific
investigations in a timely manner and to fly experimental equipment on smaller
and relatively low-cost launch vehicles such as Scout and Pegasus rockets.
Payloads are limited to a weight of 250 kilograms and have a correspondingly
short development period of two to three years.

The SAMPEX spacecraft is custom-designed to accommodate the existing science
instruments, all of which were originally developed for other missions, within
the Scout rocket payload volume.  The SAMPEX spacecraft uses an internal
momentum wheel for stabilization and pointing (rather than reaction jets), and
keeps its gallium-arsenide solar panels always pointing toward the Sun in order
to achieve the required power.  With a mission design life of 3 years or more,
the only spacecraft expendable resource is a 36-month supply of isobutane gas
for the HILT sensor.

The onboard data processing unit collects data for storage in an onboard 26
megabyte solid state memory.  Every 12 hours, the memory is dumped to the NASA
Wallops Island Flight Facility or to another available Deep Space Network
facility and relayed to the Goddard Space Flight Center.

Spacecraft and instrument operations are supported 12 hours a day by teams at
the Goddard Space Flight Center and at the University of Maryland. The same
flight operations team will also support new Small Explorer missions in the
future, including the Fast Auroral Snapshot Explorer (FAST) and the
Submillimeter Wave Astrophysical Satellite (SWAS), both of which are now in
development.

SCIENCE INSTRUMENTS

The SAMPEX satellite carries four science instruments.  Their overlapping
energy ranges provide a continuous observing spectrum of particles associated
with solar flares, and anomalous and galactic cosmic rays.

LOW ENERGY ION COMPOSITION ANALYZER (LEICA)-

LEICA is a mass spectrometer that identifies the mass and energy of particles
by simultaneously measuring the time of flight and residual kinetic energy of
these particles as they penetrate the telescope and are deflected onto one of
four solid- state detectors by a series of electrostatic mirrors.  Like all the
SAMPEX instruments, LEICA detects elemental particles of hydrogen, helium,
carbon, silicon, and iron in specific energy ranges. (University of Maryland in
College Park, Maryland).

HEAVY ION LARGE TELESCOPE (HILT)-

HILT measures the direction, energy, and atomic charge of anomalous cosmic rays
and solar energetic particles in the region of the Earth's magnetic poles.
HILT uses a proportion counter, drift chamber, and solid-state detectors to
determine particle mass, atomic charge, velocity, and arrival direction. (Max
Plank Institute for Extraterrestrial Physics of Garching, Germany).

MASS SPECTROMETER TELESCOPE (MAST)-

MAST determines the direction, energy, element, and isotope of all elements
from lithium to nickel entering the instrument with velocities about one-tenth
to three-quarters the speed of light.  It uses stacked layers of solid-state
detectors to determine particle trajectories and energy. (California Institute
of Technology in Pasadena, California, and the NASA Goddard Space Flight Center
in Greenbelt, Maryland).

PROTON/ELECTRON TELESCOPE (PET)-

PET is similar to MAST and complements MAST measurements by including energy
ranges for electrons, protons, and helium nuclei.  The electrons measured by
PET will be moving very close to the speed of light and may have a significant
effect on the destruction of ozone high in the Earth's atmosphere. (California
Institute of Technology in Pasadena, California).

SAMPEX MISSION OVERVIEW

LAUNCHED:	July 3, 1992
VEHICLE:	4-stage Scout rocket
LAUNCH SITE:	Vandenberg Air Force Base, California
ORBIT:		Polar elliptical, non-Sun-synchronous;
		inclination 82 degrees; 545 km by 645 km
DEVELOPMENT
CENTER:		NASA Goddard Space Flight Center, Maryland
SCIENTIFIC
INSTRUMENTS:	Low-Energy Ion Composition Analyzer (LEICA), 
		Heavy Ion Large Telescope (HILT),
		Mass Spectrometer Telescope (MAST), and 
		Proton/Electron Telescope (PET)

WHAT ARE COSMIC RAYS AND WHERE DO THEY COME FROM?

Despite their name, cosmic rays are not electromagnetic energy like x rays and
gamma rays; rather they are atomic particles of matter that have been
accelerated to extremely high energy levels and velocities by various processes
in space.  These particles are generally divided into three categories:
galactic cosmic rays, anomalous cosmic rays, and solar energetic particles,
depending on where they come from and what they are made of.

Galactic cosmic ray particles are atomic nuclei from which most or all of the
surrounding electrons have been stripped away.  The electrons are lost as the
result of violent supernova explosions in distant parts of our galaxy (which
also accelerate the remaining particles) and subsequent collisions with gas and
dust as the particles travel at extremely high speed through space.  The
simplest galactic cosmic rays are protons, the nuclei of hydrogen atoms, and
carry a single positive electrical charge.  However, SAMPEX will also be able
to detect the nuclei of heavier elements, such as oxygen, helium, silicon, and
iron.  The study of the abundance and energy of these elements and their
isotopes provides us with the only direct sample of matter from regions of the
galaxy far beyond our own solar system.

Anomalous cosmic rays are believed to consist largely of atoms that have lost
only one of their outer electrons, rather than most or all of them, and have
come from just beyond our solar system.  These atoms are not thought to have
experienced such violent processes as their galactic cousins, and they have a
correspondingly lower velocity and energy.  As our solar system moves through
clouds of local interstellar gases at about 20 kilometers per second, some of
the surrounding gas atoms are pulled in by the Sun and undergo single
ionization (the loss of one electron) as a result of an interaction with solar
ultraviolet radiation.  These anomalous cosmic rays provide a direct sample of
the interstellar medium around our solar system.

A third type of cosmic ray is a solar energetic particle.  These are atoms
which originate in the Sun and undergo a wide range of ionization and
acceleration processes in the various levels of the Sun's atmosphere as they
escape into interplanetary space.  The number, direction, and energy of solar
energetic particles can frequently be associated with solar flares, and their
study by SAMPEX provides information about the composition of the Sun and about
the mechanisms that created them.
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