The United States and Russia return to Mars this fall with the launch of three missions destined to explore Earth's planetary neighbor in greater detail than has ever before been accomplished.
NASA's Mars Global Surveyor and Mars Pathfinder and Russia's Mars '96 mission are scheduled for three separate launches in November and December 1996. Mars Global Surveyor, an orbiter carrying six scientific instruments to study the atmosphere, surface and interior of Mars, will be launched Nov. 6. It will be followed by Russia's Mars '96, an orbiter carrying 12 instruments plus two small landers and two penetrators, which will lift off Nov. 16. Mars Pathfinder will carry a lander and small rover robot when it is lofted into space Dec. 2.
Launch of the NASA spacecraft marks the beginning of a new era in Mars exploration and an ambitious new initiative by the United States to send pairs of spacecraft to the red planet every 26 months through the year 2005.
NASA's new decade-long program of robotic exploration known as the Mars Surveyor program takes the next step in expanding scientists' knowledge of Mars. The program is focused on three major areas of investigation: the search for evidence of past life on Mars; understanding the Martian climate and its lessons for the past and future of Earth's climate; and understanding the geology and resources that could be used to support future human missions to Mars.
The unifying theme of the Mars exploration program is the search for water, which is a key requirement for life, a driver of climate and a vital resource. Early missions will thus focus partially on finding and understanding the past and present state of water on Mars. Mars Global Surveyor and Mars Pathfinder will be the forerunners in this quest, becoming the precursors to a series of missions that may culminate in the first few years of the next century with robotic return of a Martian soil sample to Earth, followed by eventual human exploration.
Continuing Exploration Program
NASA's 1996 missions to Mars further the global explorations of the planet begun in 1965 with the Mariner 4 mission to Mars and continued in the mid-'70s by the Viking lander missions.
From earlier investigations, scientists have compiled a portrait of Mars full of stark contrasts. Mars' surface features range from ancient, cratered terrain like Earth's Moon to immense volcanoes that would dwarf Mt. Everest and a canyon that would stretch across the United States.
Mars' atmosphere is less than 1 percent as thick as Earth's, but there are permanent polar caps with reservoirs of water ice. Closeup shots of Mars' terrain resemble that of an Earthly desert, with surface features that look like river channels carved long ago by flowing water.
The next step in Mars exploration, according to scientists, is to obtain an overview of the entire planet and to verify remote observations with measurements taken from the ground. Mars Global Surveyor is designed to study the atmosphere, surface and interior systematically over a full Martian year. The Russian Mars '96 orbiter has similar objectives, but will also characterize the uppermost atmosphere and its interactions with the solar wind.
To obtain "ground truth" -- observations on the surface verifying those made from space -- the Russian Mars '96 spacecraft will deploy two landers that will touch down in the northern hemisphere in a region called Amazonis Planitia and two penetrators that will impact and lodge themselves anywhere from 1 to 6 meters (3 to 20 feet) underground. These probes will furnish details of the atmosphere and surface at the specific locations in which they land. NASA is contributing two experiments to Mars '96: the Mars Oxidation Experiment, which will measure the oxidation rate of the Martian environment, and the Tissue- Equivalent Proportional Counter, which will study the radiation environment in interplanetary space and near Mars.
Mars Pathfinder will deploy a mobile rover that will characterize rocks and soil in a landing area over hundreds of square meters (yards) on Mars. Pathfinder's instruments and mobile rover are designed to provide an in-depth portrait of Martian rocks and surface materials over a relatively large landing area, thereby giving scientists an immediate look at the crustal materials that make up the red planet.
Pathfinder Arrival in July 1997
Although the last to leave Earth, Mars Pathfinder takes a shorter flight path and will be the first of the three spacecraft to arrive at Mars, touching down in Ares Vallis on July 4, 1997.
Pathfinder is designed to demonstrate an innovative approach to landing a spacecraft and rover on the surface of Mars. Pathfinder will dive through the upper atmosphere of Mars on a parachute, then inflate a huge cocoon of airbags to cushion its impact. The spacecraft will collect engineering and atmospheric science data along its descent to the ground.
The primary objective of the mission is to test this low- cost method of delivering a spacecraft, science payload and free- ranging rover to the surface of the red planet. Landers and rovers of the future will share the heritage of spacecraft designs and technologies that evolve from this pathfinding mission.
Once on the surface, the lander's first task will be to transmit engineering and science data collected during descent through the thin atmosphere of Mars. Then its camera will take a panoramic image of its surroundings and begin transmitting the data directly to Earth at a few thousand bits per second. Much of Pathfinder's mission after this will be focused on collecting atmospheric and surface composition data, and supporting the rover by storing and transmitting images captured by its cameras. Pathfinder's nominal mission lifetime is approximately 30 "sols," or Martian days (about the same number of Earth days).
Pathfinder's rover, Sojourner, will be carried to Mars in a stowed configuration with its chassis and wheels folded up like an accordion. Once its solar cells are exposed to the Sun, the rover will power up and stand to its full height before leaving the lander. Driving off onto the floor of an ancient flood plain believed to contain a wide variety of rocks, Sojourner will explore the surface independently, relying on the lander primarily for communications with Earth.
Mars Global Surveyor and Mars '96
Two months later, NASA's Mars Global Surveyor and Russia's Mars '96 orbiter will arrive at Mars on September 11 and 12, 1997, respectively.
At first, Mars Global Surveyor will be in a highly elliptical orbit and spend four months dipping lower and lower into Mars' upper atmosphere using a technique called aerobraking to bring it into a low-altitude, nearly circular mapping orbit over the poles. By March 1998, Surveyor will be ready to begin data collection, compiling a systematic database as it surveys the Martian landscape and photographs unique features, such as the polar caps and Mars' network of sinuous, intertwining river channels.
Mars '96 carries a dozen instruments and a dozen smaller devices designed to study the evolution of the Martian atmosphere, surface and interior. In addition to meteorological and seismic instruments, the spacecraft carries instruments to image the Martian surface, explore the chemistry and water content of rocks and attempt to detect and measure the Martian magnetic field.
The Jet Propulsion Laboratory manages the Mars Pathfinder and Mars Global Surveyor missions for NASA's Office of Space Science, Washington, DC. Lockheed Martin Astronautics Inc., Denver, CO, is NASA's industrial partner for development and operation of the Mars Global Surveyor spacecraft. Russia's Mars '96 is managed by the Russian Space Agency. The Russian Academy of Sciences, Moscow, Russia, is responsible for the Mars '96 science payload.
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