Probing the Universe
Asteroids are small celestial bodies ranging in size from
a mile or two in diameter to almost 500 miles. They orbit the
Sun in the same direction as the principal planets, although
their orbits, as a rule, are far more eccentric; most revolve
about the Sun in a cosmic zone between the orbits of Mars and
Jupiter.
This February 1996 launch from Kennedy Space Center sent the
Near Earth Asteroid Rendezvous (NEAR) spacecraft off on a three-year
flight to a rendezvous with a 25-mile-long asteroid known as
433 Eros.
Asteroids have on occasions in the distant past collided with
Earth and left evidence of great devastation; one theory holds
that an asteroid impact with Earth caused the demise of the dinosaurs.
These mysterious cosmic objects clearly have potential for influencing
the evolution of the atmosphere and life on Earth. They also
offer clues to the nature of the early solar system processes
and conditions, which have long been erased by evolution on Earth
and other large bodies, but which are preserved in various forms
on these small bodies that do not have sufficient gravitational
power to retain an atmosphere.
All of which makes asteroids prime targets for comprehensive
scientific investigation. Such an investigation is under way;
before the century ends, scientists will know a great deal more
about asteroids than they do today.
The investigation formally began on February 17, 1996 with
the launch of the Near Earth Asteroid Rendezvous (NEAR) spacecraft
on a three-year odyssey toward a rendezvous with a 25-mile-long
asteroid known as 433 Eros. In February 1999, a firing of NEAR's
main thruster will put the spacecraft into an orbit around the
asteroid-the first spacecraft ever to accomplish such a feat-to
circle Eros for a year, coming at times as close as 10 miles
from its surface.
An international project conducted in cooperation with Germany
and France, NEAR is designed to image the asteroid and measure
its size, shape, volume, mass, gravity field and spin; its elemental
and mineral composition; its mass distribution and magnetic field.
Built by Johns Hopkins University's Applied Physics Laboratory
(APL), the spacecraft measures approximately nine feet in length,
five feet in diameter and weighs some 1,800 pounds. APL is NASA's
manager for the project.
NEAR is an exciting and important project in its own right, but
it takes on added significance by virtue of its status as the
prototype, or pathfinder, of a relatively new NASA program known
as Discovery, an ongoing effort to foster development of low
cost spacecraft that will enable frequent solar system exploration
missions. As the first flight project of that program, NEAR bears
the responsibility for demonstrating that the concept of low-cost
planetary exploration is valid.
NEAR was built under a ceiling of $150 million, a fraction
of the cost of some interplanetary missions, and it was completed
in only two years under a new streamlined management approach.
Although cost was a primary consideration throughout the development
period, NASA and APL did not compromise capability in the search
for economies. NEAR has a full complement of five sophisticated
instruments and multiple redundancies in its operating systems.
NEAR exemplifies one aspect-solar system exploration-of NASA's
broad space science program, whose primary missions and goals
embrace these general areas of investigation:
- Examining the content, structure, origin and evolution of
the galaxy and the universe;
- Defining the relationships among the Sun, Earth and the heliosphere;
- Seeking greater understanding of the origin and evolution
of planetary systems;
- Pursuing greater understanding of the origin and distribution
of life in the universe;
- Observing Earth's air, land, water and life resources toward
greater understanding of the complex mechanisms that control
Earth's behavior.
Selected examples of ongoing and upcoming programs in these
areas are contained in the following pages.
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