PDS_VERSION_ID = PDS3 LABEL_REVISION_NOTE = "R. SIMPSON, 1997-09-12; S. SLAVNEY, 1998-10-07" RECORD_TYPE = STREAM OBJECT = MISSION MISSION_NAME = "MARS GLOBAL SURVEYOR" OBJECT = MISSION_INFORMATION MISSION_START_DATE = 1994-10-12 MISSION_STOP_DATE = UNK MISSION_ALIAS_NAME = "N/A" MISSION_DESC = " Mission Overview ================ The Mars Global Surveyor (MGS) spacecraft was launched from the Cape Canaveral Air Station in Florida on 7 November 1996 aboard a Delta-2/7925 rocket. The 1062-kilogram spacecraft, built by Lockheed Martin Astronautics, traveled nearly 750 million kilometers over the course of a 300-day cruise to reach Mars on 11 September 1997 [JPLD-12088]. Upon reaching Mars, MGS fired its main rocket engine for a 25-minute Mars orbit insertion (MOI) burn. This maneuver slowed the spacecraft and allowed the planet's gravity to capture it into orbit. Initially, MGS whirled around the red planet in a highly elliptical orbit that took 48 hours to complete. After orbit insertion, MGS performed a series of orbit changes to drop the low point of its orbit into the upper fringes of the Martian atmosphere at an altitude of about 110 kilometers. During every atmospheric pass, the spacecraft slowed by a small amount because of air resistance. This slowing caused the spacecraft to lose altitude on its next pass through the orbit's high point. MGS was to use this aerobraking technique over a period of four months to lower the high point of its orbit from 56,000 km to near 400 km in altitude. However, at the low point of orbit 15, on October 8, 1997, the spacecraft experienced difficulties later diagnosed as due to excess vibrations of one of the solar panels. The problem was associated with a fracture of a panel damper arm [ALBEEETAL1998]. While an evaluation of the solar array problem was underway, periapsis was raised to about 172 km on October 13, 1997 and remained near that altitude until November 7, 1997 (orbits 19 through 36). During this 26-day period the spacecraft instrument panel was pointed towards Mars during close approaches (i.e., near periapsis) and the first extensive set of science observations from MGS was collected. Orbits 19 through 36 are known as the assessment orbits, and the time period is known as the Assessment Subphase of the Orbit Insertion Phase. The science observations were acquired during the descending leg of each orbit; that is, as the spacecraft moved from north to south. Aerobraking was restarted on November 8, 1997 (orbit 37), but with a periapsis approximately 10 km higher than that previously used. Aerobraking was then conducted at about 1/3 the rate originally planned, placing the spacecraft in a 2 AM Sun-synchronous mapping orbit in March 1999 rather than the planned 2 PM mapping orbit in March 1998. (The 2 PM orbit meant that the spacecraft would have crossed the equator in the descending leg of the orbit -- north to south -- at 2 PM, a desirable time for data collection for some instruments. This orbit could not be achieved given the new orbital characteristics. However, a 2 AM orbit was satisfactory because if the descending leg of the orbit crossed the equator at 2 AM, it meant that the ascending leg, south to north, crossed the equator at the desired time of 2 PM.) Another aerobraking hiatus began on April 21, 1998, and extended through September 11, 1998. This period, termed the Science Phasing Orbits of the mission, was necessary to ensure that the final two hour circular orbit would have an equatorial crossing time of 2 AM. After a final period of aerobraking beginning in September, 1998, the spacecraft is scheduled to enter mapping mode on April 1, 1999. During mapping operations, the spacecraft will orbit Mars with a period of 118 minutes, at an average altitude of 400 km. The mapping phase of the mission lasts for one Mars year, or 687 days. The spacecraft was three-axis stabilized and powered by solar cells. It was built of lightweight composite materials and divided into four sub-assemblies: the equipment module, the propulsion module, the solar array support structure, and the high-gain antenna support structure. Most science instruments were bolted to a nadir equipment deck. Mars Global Surveyor carried four on-board science instruments. The Mars Orbiter Camera (MOC) had both a wide-angle mode for global coverage and a narrow-angle mode with resolution of 1.4 meters [MALINETAL1992]. The Thermal Emission Spectrometer (TES) measured infrared radiation. TES was used to determine the general mineral composition of patches of ground as small as 9.0 square kilometers; in addition, TES also scanned the Martian atmosphere to provide data for the study of the clouds and weather [CHRISTENSENETAL1992]. The Magnetometer and Electron Reflectometer (MAG/ER) was used to measure the global magnetic properties of Mars, which provided insight on internal structure [ACUNAETAL1992]. The Mars Orbiting Laser Altimeter (MOLA) gathered data that allowed calculation of surface feature heights to accuracies of 30 meters [ZUBERETAL1992]. An ultra-stable oscillator (USO) in conjunction with the on-board telecommunications equipment and ground equipment at stations of the NASA Deep Space Network (DSN) made up the Radio Science Subsystem (RSS). RSS measurements included radio tracking of the spacecraft to improve the gravity field model of Mars and radio occultation observations to study the structure of the atmosphere [TYLERETAL1992]. A sixth 'instrument' was the Mars Relay -- a cylindrically shaped antenna used to collect data transmitted to Surveyor from landers on the Martian surface. These landers were carried to Mars by later spacecraft and operated after completion of the MGS primary mission (late January 2000). A seventh instrument is the Accelerometer which measures the deceleration of the spacecraft as it passes through the atmosphere. These quantities can then be reduced to atmospheric density. Knowing the density and the altitude, pressures and temperatures can be derived for the Martian atmosphere. Mission Phases ============== Six mission phases were defined for significant spacecraft activity periods. These included Pre-Launch, Launch, Cruise, Orbit Insertion, Mapping, and Relay Phases. The Cruise Phase included both Inner and Outer Cruise components. Once every seven Martian days during the Mapping Phase, the spacecraft approximately retraced its ground track; these 88-orbit intervals were known as 'repeat cycles.' PRELAUNCH --------- The Prelaunch Phase extended from beginning of the MGS mission until the start of the launch countdown at the Kennedy Space Center. Spacecraft Id : MGS Target Name : MARS Mission Phase Start Time : 1994-10-12 Mission Phase Stop Time : 1996-11-06 Spacecraft Operations Type : ORBITER LAUNCH ------ The Launch Phase extended from the start of launch countdown until completion of the injection into the Earth-Mars trajectory. Spacecraft Id : MGS Target Name : MARS Mission Phase Start Time : 1996-11-06 Mission Phase Stop Time : 1996-11-07 Spacecraft Operations Type : ORBITER CRUISE ------ The Cruise Phase extended from injection into the Earth-Mars trajectory until 10 days before Mars orbit insertion. During the Inner Cruise sub-phase, MGS aimed its solar panels toward the Sun and communicated through its low-gain antenna; during the Outer Cruise sub-phase, the high-gain antenna could be used while the solar panels generated acceptable levels of power. The transition occurred on 1997-01-09. Spacecraft Id : MGS Target Name : MARS Mission Phase Start Time : 1996-11-07 Mission Phase Stop Time : 1997-09-02 Spacecraft Operations Type : ORBITER ORBIT INSERTION --------------- The Mars Orbit Insertion Phase extended from 10 days before Mars orbit insertion until the spacecraft reached the final mapping orbit and was declared ready for collection of science data. It was during this phase that the problem with the solar panel was discovered, and aerobraking was halted while the problem was assessed. Sub-phases of the Orbit Insertion Phase are listed below. Spacecraft Id : MGS Target Name : MARS Mission Phase Start Time : 1997-09-02 Mission Phase Stop Time : 1999-04-01 Spacecraft Operations Type : ORBITER Aerobraking Phase I Subphase : 1997-09-17 to 1997-10-11 Assessment Subphase : 1997-10-13 to 1997-11-07 Aerobraking Phase I continued : 1997-11-08 to 1998-04-21 Science Phasing Orbits 1 (SPO-1) : 1998-04-21 to 1998-05-01 Solar conjunction : 1998-05-01 to 1998-05-25 Science Phasing Orbits 2 (SPO-2) : 1998-05-26 to 1998-09-11 Aerobraking Phase II Subphase : 1998-09-12 to 1999-02-08 MAPPING ------- The Mapping Phase was the period of concentrated science data acquisition. It lasted for one Martian year (687 days). Spacecraft Id : MGS Target Name : MARS Mission Phase Start Time : 1999-04-01 Mission Phase Stop Time : 2001-02-16 Spacecraft Operations Type : ORBITER RADIO RELAY ----------- The Radio Relay Phase began at the end of the Mapping Phase and continued for the remainder of the spacecraft on-orbit lifetime. Nominal end of mission was 1 January 2003. Spacecraft Id : MGS Target Name : MARS Mission Phase Start Time : 2001-02-16 Mission Phase Stop Time : 2003-01-01 Spacecraft Operations Type : ORBITER" MISSION_OBJECTIVES_SUMMARY = " One of the most intriguing, unanswered scientific questions is why do Earth and Mars appear different today? At the time of their formation several billion years ago, Mars and Earth shared similar conditions. Both planets harbored vast quantities of surface water, thick atmospheres, and climates warmer than at present. Today, Earth is a lush world filled with a countless number of animal and plant species. In contrast, data gathered from Mars prior to MGS showed that the planet was trapped in conditions reminiscent of a global ice age. The dry and seemingly lifeless Martian surface makes the Sahara look like an ocean in comparison, and average daily temperatures made Antarctica seen balmy. Comparing the history and evolution of the two planets yielded clues into Earth's past and possibly its future. Science objectives for the failed Mars Observer Mission [ALBEEETAL1992] were essentially identical to those for Mars Global Surveyor. Basic Measurements and Data Collection ====================================== Although several spacecraft preceded MGS to Mars, fundamental measurements remained to be made. No topographic model of the planet existed at the 100 meter level (and many areas were uncertain by kilometers); MOLA provided one with typical accuracies of 30 m. Preliminary measurements on the magnetic field had been carried out by early spacecraft; but MGS MAG/ER was the first instrument to carry out a systematic mapping effort. Gravity models had been compiled from Mariner 9 and Viking data, but MGS RSS provided an order of magnitude improvement in these -- leading to improved understanding of the planet's interior. Atmospheric Processes ===================== Despite its forbidding climate, surface temperatures on Mars resemble the Earth's more than any other planet. These similarities in temperature result in part from the fact that Mars orbits the Sun only slightly farther out than the Earth as compared to other planets. For example, the ground at some locations near Mars' equator may warm up to as high as 25C at noontime. However, daytime temperatures still average well below freezing, and night temperatures dip much lower. Martian temperatures may seem almost inviting to the seasoned outdoors explorer, but the composition of the atmosphere leaves much to be desired from a human perspective. Most of the martian air consists of carbon dioxide (CO2), similar to conditions on Venus. If breathing carbon dioxide seems uninviting, the density of the air will appear worse. Average barometric pressures on Mars are lower than that found at Earth's sea level by a factor of more than 125. In other words, the air at the surface of Mars is thinner than that found on Earth at an altitude 19 times higher than Denver, Colorado. The extremely thin Martian air directly impacts the mystery of potential life on Mars, either in the past or present. The reason is that almost all of the water lies trapped in the Martian polar ice caps or frozen beneath the surface. Liquid water cannot exist on the surface because the thin atmosphere will cause melting ice to evaporate directly into water vapor. Despite the hostile composition, density, and temperature by today's standards on Earth, the atmosphere of Mars is both interesting and dynamic. MGS objectives in this area included recording global daily images of the planet so that cloud patterns could be followed and the growth of dust storms could be monitored over a full martian year. TES and RSS were both able to measure vertical structure within the atmosphere, another key to understanding transport of material within the atmosphere -- including precipitation of CO2 itself on the winter polar cap. Surface Processes ================= Geologically, Mars is one of the most interesting planets in the Solar System. Although only half the diameter of Earth, Mars maintains large water and CO2 ice caps at the poles, a canyon much deeper than the Grand Canyon and longer than the contiguous 48 United States are wide, crater valleys as large as the western United States, and a handful of monstrous volcanoes that make Mount Everest appear tiny in comparison. A study of Martian geology is crucial toward revealing clues into the history of the Earth. Mars is the only planet in the solar system that both has an atmosphere, and contains surface features that cover almost the entire range of history. On Earth, pristine rocks and other surface features from the first billion years of our planet's existence do not exist because geological events, weather, and life have caused drastic alterations. Because Earth and Mars shared similar conditions near the time of their formation, the MGS exploration of Mars allowed us to take a peek into Earth's past in a way not possible by studying the Earth by itself. Although liquid water on Mars will quickly evaporate, photographs transmitted back to Earth by NASA missions prior to MGS revealed giant flood channels, dry river beds, and flood plains on the surface. This evidence of past water on Mars led some scientists to consider Mars as the prime location in the Solar System to search for extraterrestrial life. The speculation was that because Mars once possessed a thicker atmosphere and vast quantities of surface water billions of years ago, then the planet may have harbored conditions favorable to the formation of life despite its present forbidding climate. Viking and Mars Pathfinder returned information on elemental composition of some Mars surface materials at specific landing sites. But regional and global information is needed to understand both the current state and history of rocky surfaces. MOC provided high-resolution image data; TES acquired spectral signatures of rock units so that thermal inertia, surface rock distributions, and composition could be inferred. Search for Life =============== Sensors aboard various NASA spacecraft launched to Mars over the 30 years prior to MGS showed that advanced life forms almost certainly do not exist on the planet today. However, many felt that the planet might hide bacterial forms of life or their fossil remains. Although Mars Global Surveyor did not conduct a search for life on Mars, it gathered detailed data that will help in understanding the mystery of the missing water. This type of study provided important background data that helped scientists in their search for Martian life on future missions." END_OBJECT = MISSION_INFORMATION OBJECT = MISSION_HOST INSTRUMENT_HOST_ID = "MGS" OBJECT = MISSION_TARGET TARGET_NAME = "MARS" END_OBJECT = MISSION_TARGET END_OBJECT = MISSION_HOST OBJECT = MISSION_REFERENCE_INFORMATION REFERENCE_KEY_ID = "ACUNAETAL1992" END_OBJECT = MISSION_REFERENCE_INFORMATION OBJECT = MISSION_REFERENCE_INFORMATION REFERENCE_KEY_ID = "ALBEEETAL1992" END_OBJECT = MISSION_REFERENCE_INFORMATION OBJECT = MISSION_REFERENCE_INFORMATION REFERENCE_KEY_ID = "ALBEEETAL1998" END_OBJECT = MISSION_REFERENCE_INFORMATION OBJECT = MISSION_REFERENCE_INFORMATION REFERENCE_KEY_ID = "CHRISTENSENETAL1992" END_OBJECT = MISSION_REFERENCE_INFORMATION OBJECT = MISSION_REFERENCE_INFORMATION REFERENCE_KEY_ID = "JPLD-12088" END_OBJECT = MISSION_REFERENCE_INFORMATION OBJECT = MISSION_REFERENCE_INFORMATION REFERENCE_KEY_ID = "MALINETAL1992" END_OBJECT = MISSION_REFERENCE_INFORMATION OBJECT = MISSION_REFERENCE_INFORMATION REFERENCE_KEY_ID = "TYLERETAL1992" END_OBJECT = MISSION_REFERENCE_INFORMATION OBJECT = MISSION_REFERENCE_INFORMATION REFERENCE_KEY_ID = "ZUBERETAL1992" END_OBJECT = MISSION_REFERENCE_INFORMATION END_OBJECT = MISSION END