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Mars Global Surveyor is the first in a series of spacecraft to be sent to Mars over the next ten years under the Mars Surveyor Program. It carries five of the seven experiments that were aboard the lost Mars Observer, including the Thermal Emission Spectrometer (TES) controlled by operators at Arizona State University.
Contact with NASA's Mars Observer was lost on August 21, 1993. Since that time, the Mars science community has been working toward establishing a new program to recover the lost science for a fraction of the original cost of Mars Observer. The new program is Mars Surveyor. Mars Surveyor is an aggressive but tightly cost-constrained approach to exploring Mars over the decade from 1995 through 2005. A series of small orbiters and landers built by industry will be sent at each Mars launch opportunity (26 months apart) over the next decade. Total annual costs for this program are capped at $100 million (Mars Observer cost about $900 million between 1984 and 1993). Besides Mars Global Surveyor, additional orbiters and landers are planned to launch in 1998, 2001, 2003, and 2005. These missions will likely involve international cooperation with Russia, Japan, Germany, France, Italy, and others.
The Mars Global Surveyor mission will study the geology, geophysics, and climate of the Red Planet. The primary objectives are to:
The interdisciplinary investigations of the mission will combine data from more than one instrument to explore questions that cross boundaries between scientific disciplines and individual investigations. The six interdisciplinary investigations are:
The mission is expected to provide a major increase in the amount of scientific data available for Mars while at the same time recovering more than half the original objectives of Mars Observer. Orbiters launched in 1998 and 2001 will attempt to make up the difference by flying at least one of the remaining experiments that were on Mars Observer (Pressure Modulator Infrared Radiometer [PMIRR] in 1998, Gamma Ray Spectrometer [GRS] in 2001).
The TES will measure infrared thermal radiation emitted by the martian atmosphere and surface. The thermal properties of the surface materials and their mineral content may be determined from these measurements. When viewing the surface beneath the spacecraft, the spectrometer has six fields of view, each covering an area of 3 by 3 kilometers (1.9 by 1.9 miles). The TES has three sets of these 6 fields of view: the Spectrometer (143 spectral bands), the Bolometer (1 broad thermal infrared band), and the Reflectance or Albedo channel (1 broad visible/near-infrared band). The spectrometer will determine the composition of surface rocks and ice and map their distribution on the martian surface. Other capabilities of the instrument will investigate the advance and retreat of the polar ice caps, as well as the amount of radiation absorbed, reflected, and emitted by these caps. The distribution of atmospheric dust and clouds will also be examined over the 4 seasons of a martian year.
The MOC will photograph the martian surface with very high resolution (1.5 meters; 4.6 ft). Resolution is a measure of the smallest object that can be seen in an image. Low-resolution global images of Mars-- a daily "weather map"-- will also be acquired each day using two wide-angle cameras operated at 7.5 kilometer (4.7 miles) resolution per picture element (pixel). These same cameras will acquire moderate-resolution photographs at 240 meters (787 feet) per pixel. The low-resolution camera system will capture global views of the martian atmosphere and surface so that scientists may study the martian weather and related surface changes on a daily basis. Moderate-resolution images will monitor changes in the surface and atmosphere over hours, days, weeks, months, and years. The high-resolution camera will be used selectively because of the high data volume required for each image.
The MOLA uses a very short pulse of laser light to measure the distance from the spacecraft to the surface with a precision of several meters. These measurements of the topography of Mars will provide a better understanding of the relationship among the martian gravity field, the surface topography, and the forces responsible for shaping the large-scale features of the planet's crust.
The radio science investigation will use the spacecraft's telecommunication system and the giant parabolic (dish) antennas of NASA's Deep Space Network to probe the martian gravity field and atmosphere.
Gravity. During a part of the orbit when the spacecraft is in view of the Earth, precise measurements of the frequency of the signal received at the ground tracking stations will be made to determine the velocity change (using the Doppler effect) of the spacecraft in its orbit around Mars. These Doppler measurements, along with measurements of the distance from the Earth to the spacecraft, will be used to navigate the spacecraft and to study the planet's gravitational field. Gravitational field models of Mars will be used along with topographic measurements to study the martian crust and upper mantle.
Mars is now the only planet in the Solar System, except Pluto, for which a planetary magnetic field has not yet been detected. In addition to searching for a martian planetary magnetic field, this instrument also will scan the surface material for remnants of a magnetic field that may have existed in the distant past. The magnetic field generated by the interaction of the solar wind with the upper atmosphere of Mars will also be studied. Unlike Mars Observer, the magnetometer on Mars Global Surveyor will not be at the end of a boom but instead will be fixed to the spacecraft.
The spacecraft will carry a radio system supplied by the French Centre National d'Etudes Spatiales (CNES, the French space agency) to support the Russian Mars 96 mission. Mars 96 consists of an orbiter, two small landers and 2 penetrators (amounting to four landed spacecraft). This Russian mission was formerly scheduled to launch in October 1994 but will now wait until 1996 for launch. The landers will carry instruments to directly sample both the atmosphere and surface. The landers will send data to Earth via the Mars 96 orbiter, using the relay antenna as a back-up. As of this writing (July 1995), whether Mars 96 will be launched remains uncertain, because of funding problems in Russia.
Mars Global Surveyor is scheduled for launch on November 3, 1996, aboard a McDonnell Douglas Delta II rocket from the Kennedy Space Center in Florida. The spacecraft will reach Mars in September 1997. Systematic mapping of Mars will begin in January 1998. From this point, the mission is expected to last at least 687 days, thus taking the primary mission into the year 2000.
Upon arrival, Mars Global Surveyor will be inserted into a very elliptical capture orbit. Over the next four months, a combination of aerobraking maneuvers and rocket firings will slow the spacecraft and adjust its orbit. The goal is an orbit that closely matches the one originally planned for Mars Observer-- a polar orbit crossing the equator around 2 p.m. on the day side and 2 a.m. on the night side.
Aerobraking is a technique which uses atmospheric drag to slow the spacecraft. The method requires the spacecraft to dip low enough to encounter the atmosphere, but the approach must be controlled carefully so that the spacecraft does not burn up. Aerobraking will save the amount of fuel needed for the mission. This method was not to be done on Mars Observer, and has only been attempted at another planet once: Magellan did it (with success) at Venus in 1993.
The Mars Global Surveyor mission operations at the Jet Propulsion Laboratory (JPL) will be supported by NASA's Deep Space Network (DSN) and the JPL Advanced Multimission Operations System. The DSN antennas and facilities are located in Pasadena and Goldstone, California; Canberra, Australia; and Madrid, Spain. Three such facilities scattered around the Earth ensure continuous coverage of the sky. The instrument scientists remain at their home institutions, from which they can access Mars Global Surveyor data using workstations and electronic communications links. During the mapping phase, the instrument investigations will return processed science data products to the database at JPL for access by the interdisciplinary scientists and other investigation teams.