SOLAR SYSTEM EXPLORATION

SOLAR SYSTEM EXPLORATION1995

Pictured above is a sequential concept of a Mars Pathfinder landing which is discussed in the following article.

The historic Ulysses spacecraft, which in 1994 became the first space exploration vehicle to reach a polar region of the Sun, continued its history- making odyssey in 1995 as it passed its perihelion, its closest approach to the Sun.

The spacecraft, built by the European Space Agency (ESA) for the joint ESA/NASA mission to study the solar polar areas, passed over the vicinity of the south pole in June 1994 after a four- year journey from Earth. Then, traveling at a velocity of about 73,000 miles per hour with respect to the Sun, Ulysses moved northward to collect data on the Sun's equatorial region, where it reached perihelion on March 12,1995. At that point the spacecraft was within 124 million miles of the Sun.

In April 1995, the spacecraft crossed into the northern hemisphere of the heliosphere (the region of space dominated by the forces of the solar wind) and in June reached a point 70 degrees north of the Sun's equator. That marked the start of a new phase of the

Ulysses mission, a four- month observation of the north polar region. Upon completion of the north polar reconnaissance, Ulysses concluded its primary mission; depending on available funding, it could continue to collect data through part or all of an 11-year solar cycle. The Ulysses program is managed for NASA's Office of Space Science by Jet Propulsion Laboratory (JPL).

In July 1995, the Galileo spacecraft began the "final approach" - a 50-million-mile approach - of its six-year roundabout journey to Jupiter, after releasing an instrumented probe that was to proceed independently to Jupiter and descend into the Jovian atmosphere. The probe was targeted for arrival at Jupiter on December 7,1995, at which time it would make the most difficult planetary entry ever attempted. Flying at a speed of 106,000 miles per hour, the probe was expected to encounter deceleration forces up to 350G (350 times Earth's gravity) on its descent some 400 miles into the planet's complex atmosphere, making the first direct measurements of Jupiter's clouds, lightning, winds and other features. The probe was to radio its data to the main Galileo spacecraft for later transmission to Earth.

Arriving at the planet at about the same time as the probe, the main spacecraft will pass 133,000 miles above Jupiter's cloud tops, then swing into orbit around the planet. Galileo will then begin two years of observation of Jupiter, its moons and its powerful magnetosphere. Galileo is a cooperative U.S./Germany project managed for NASA by JPL, which designed and built the main spacecraft. Ames Research Center has management responsibility for the probe, which was built by Hughes Aircraft.

Ulysses and Galileo were two of six NASA deep space projects active during 1995. The others were three veteran spacecraft‹Pioneer 10, Voyagers 1 and 2‹operating billions of miles from Earth and conducting scientifically important research, looking for the boundary between the solar system and interstellar space.

Another major planetary exploration project advanced in 1995 as static testing began on components of the Cassini spacecraft. Cassini is a joint project of NASA, ESA and the Italian Space Agency, managed for NASA by JPL. To be launched in 1997, the Cassini spacecraft, consisting of an orbiter and a probe, will conduct an extensive survey of Saturn and its principal moon Titan, beginning in 2004.

The large (750-pound) ESA-built instrumented probe - named Huygens - will descend into the atmosphere of Titan, which is believed to be chemically similar to the atmosphere of early Earth and is therefore of immense scientific interest.

The 24-ton Cassini main spacecraft will conduct a four-year orbital survey of Saturn, during which time it will orbit the planet about 60 times and encounter Titan 30 times; the spacecraft will provide data and imagery on the planet, its moons, rings and magnetosphere. NASA's Discovery program is an ongoing effort to foster development of low cost spacecraft that will enable frequent solar system exploration missions. The flight program will get under way early in 1996 with the launch of the Near Earth Asteroid Rendezvous (NEAR). The NEAR spacecraft will rendezvous with the largest of the near-Earth asteroids - 433 Eros - and orbit the asteroid for at least a year, beginning in 1999. It will collect a wealth of data on these little known celestial bodies.

Later in 1996, the second of the Discovery spacecraft, Mars Pathfinder, will be boosted into a trajectory toward the Red Planet. Pathfinder is designed to demonstrate the technology, systems and mission elements involved in landing a series of small surface stations and rovers on Mars. Pathfinder will land on Mars in mid 1997 and dispatch a "minirover," a small, inexpensive vehicle designed to roam the Martian surface and send back to Earth three- dimensional images of the Marscape.

Above is a sequential concept of a Pathfinder landing. The "balloons" are air bags to cushion the landing. In the final sequence, the spacecraft has landed and is unfolding its petals to expose its solar panels and release the rover.

In February 1995, NASA added a third Discovery developmental project, the Lunar Prospector. Scheduled for launch in June 1997, Lunar Prospector will map the chemical composition of the lunar surface and the Moon's magnetic and gravitational fields at a level greater than that achieved by any previous lunar mission. The mission will also seek to locate any significant quantities of water that might exist in shadowed craters near the lunar poles, a factor of importance in planning further human exploration of the Moon.

INTERNATIONAL SPACE STATION 1995

The Lunar Prospector (above) is being built by Lockheed Martin Missiles and Space Company and it will be launched by the company's new Lockheed Launch Vehicle. Ames Research Center is responsible for technical support and for one of the spacecraft's instruments.

In 1996, NASA will resume the comprehensive exploration of Mars that began with the Viking orbiters/landers of the late 1970s. The Mars Surveyor program, managed by Jet Propulsion Laboratory (JPL), consists of an initial mission by an orbiter known as the Mars Global Surveyor, followed by a series of orbiter/lander pairs to take advantage of launch opportunities that occur about every two years as Mars comes into alignment with Earth. Scheduled for launch in November 1996, the Mars Global Surveyor will carry five science instruments to conduct a systematic mapping of the planet from polar orbit. The mission is intended to provide most of the science data that would have been supplied by the Mars Observer spacecraft lost in 1993; the instrument complement is comprised largely of spare parts from the Mars Observer. Compared with previous planetary explorers, Global Surveyor is small at one ton liftoff weight. The spacecraft is being built by Lockheed Martin Astronautics.

In March 1995, NASA selected the second set of spacecraft in the Mars Surveyor program. They are two small complementary spacecraft known as Mars Surveyor 1998 Orbiter/Lander. The label pretty much describes the project: the pair will be launched in the Mars opportunity that spans two months beginning in December 1998. The orbiter will be launched in December 1998 and go into orbit around the planet in September 1999. The lander will be launched in January 1999, enter the Martian atmosphere in October of that year, descend by parachute and land softly with the help of rocket thrusters. The two craft will team in a study of the planet's climate and a search for water in the Martian soil.

Lockheed Martin Astronautics is building both vehicles of the Mars Surveyor 1998 mission. The project exemplifies the trend toward smaller, less expensive NASA spacecraft. Both will be built within a funding level previously allocated for a single mission. The 1996 orbiter will weigh only half as much as the 1996 Mars Global Surveyor; the lander will weigh only half as much as the 1996 Mars Pathfinder, the smallest planetary lander yet constructed. The low weight of the craft will allow them to be launched on a new vehicle, now in development, called Med-Lite, which is roughly half the size of the Delta II launch vehicles that will boost the 1996 Global Surveyor and Pathfinder missions.


SPINOFF 1995 TABLE OF CONTENTS


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