PDS_VERSION_ID = PDS3 LABEL_REVISION_NOTE = "R. SIMPSON, 1997-09-12; S. SLAVNEY, 1998-10-07; S. SLAVNEY, 1999-02-11; S. SLAVNEY, 1999-03-10; M. CAPLINGER, 2000-04-04; R. SIMPSON, 2000-11-03; S. SLAVNEY, 2001-01-25; S. SLAVNEY, 2001-01-30; S. SLAVNEY, 2001-04-06; M. CAPLINGER, 2002-03-12" 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 12 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 45 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, resulting in a nearly circular orbit for mapping. 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 or the Aerobraking Hiatus. 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 by 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.) Aerobraking was halted again on March 27, 1998, and resumed on September 24, 1998. The period from March 27 through April 28 is known as Science Phasing Orbit 1 (SPO-1, orbits 202 through 268). Solar conjunction occurred between April 29 and May 27, followed by Science Phasing Orbit 2 (SPO-2, orbits 329-573) from May 28 through September 23. This second aerobraking hiatus was necessary to ensure that the final two-hour circular orbit would have an equatorial crossing time of 2 AM. A final period of aerobraking began September 24, 1998, and ended February 4, 1999. The spacecraft then began mapping on March 9, 1999. During mapping operations, the spacecraft orbited Mars with a period of about 118 minutes, at an average altitude of 400 km. The mapping phase of the mission lasted for approximately one Mars year, ending January 31, 2001. This date marks the end of the MGS primary mission. An extended mission will run from February 1, 2001, through April 22, 2002. Mapping operations will continue during the extended mission in much the same way as they were conducted during the primary mission, with ongoing data acquisition from all science instruments and the radio science experiment. The spacecraft is three-axis stabilized and powered by solar cells. It is 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 carries four on-board science instruments. The Mars Orbiter Camera (MOC) has 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) measures infrared radiation. TES is used to determine the general mineral composition of patches of ground as small as 9.0 square kilometers; in addition, TES also scans the Martian atmosphere to provide data for the study of the clouds and weather [CHRISTENSENETAL1992]. The Magnetometer and Electron Reflectometer (MAG/ER) are used to measure the global magnetic properties of Mars, which provided insight on internal structure [ACUNAETAL1992]. The Mars Orbiting Laser Altimeter (MOLA) gathers data that allow 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) make up the Radio Science Subsystem (RSS). RSS measurements include 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' is the Mars Relay, a cylindrically shaped antenna that will be used to collect data transmitted to Surveyor from landers on the Martian surface. These landers will be carried to Mars by later spacecraft and operated after completion of the MGS primary mission (late January 2001). 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 originally defined for significant spacecraft activity periods. These were the 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 are known as 'repeat cycles.' The final mission phase, Relay, was intended to support the 1998 Mars Polar Lander and possibly the Mars 2001 Lander. It was planned to run from February 1, 2001, through January 1, 2003. Since the Mars Polar Lander was lost and the 2001 mission was reconfigured without a lander, MGS is no longer needed for relay. Instead, the Extended and Extended-Extended (E2) Mission Phases replace Relay. Relay support for the Mars Exploration Rovers is planned for 2004. PRELAUNCH --------- The Prelaunch Phase extended from beginning of the MGS mission until the start of the launch countdown at the Kennedy Space Center. Mission Phase Start Time : 1994-10-12 Mission Phase Stop Time : 1996-11-06 LAUNCH ------ The Launch Phase extended from the start of launch countdown until completion of the injection into the Earth-Mars trajectory. Mission Phase Start Time : 1996-11-06 Mission Phase Stop Time : 1996-11-07 CRUISE ------ The Cruise Phase extended from injection into the Earth-Mars trajectory until 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. Mission Phase Start Time : 1996-11-07 Mission Phase Stop Time : 1997-09-12 ORBIT INSERTION --------------- The Mars Orbit Insertion Phase began on 1997-09-12. It was during this phase that the problem with the solar panel was discovered, as described above, and aerobraking was halted while the problem was assessed. The original schedule for aerobraking was then revised to proceed more slowly than planned, in order to put less stress on the solar panel arm. Aerobraking ended in early February 1999 and was followed by a Gravity Calibration Orbit, various other calibration activities, and trajectory adjustments to put the spacecraft into the mapping orbit. Mission Phase Start Time : 1997-09-12 Mission Phase Stop Time : 1999-03-09 Subphases Dates Orbits --------- ----- ------ Aerobraking Phase 1A 1997-09-12 to 1997-10-12 1-18 Aerobraking Hiatus 1997-10-13 to 1997-11-07 19-36 Aerobraking Phase 1B 1997-11-08 to 1998-03-27 37-201 Science Phasing Orbit 1 1998-03-27 to 1998-04-28 202-268 (SPO-1) Solar conjunction 1998-04-29 to 1998-05-27 269-328 Science Phasing Orbit 2 1998-05-28 to 1998-09-23 329-573 (SPO-2) Aerobraking Phase 2 1998-09-24 to 1999-02-04 574-1284 Transition to Mapping 1999-02-04 to 1999-03-09 1285-1683 MAPPING ------- The Mapping Phase is the period of concentrated science data acquisition. At the beginning of this phase, orbit numbering was restarted at 1. The Mapping Phase is planned to last for 695 days, a little more than one Martian year. As a risk reduction measure against possible problems with the deployment of the High-Gain Antenna, the first 20 days of the Mapping Phase were operated in so-called 'Fixed High-Gain Antenna' or FHGA mode. In this mode, the undeployed HGA was pointed at Earth for four to five orbits out of every twelve to transmit data. During data transmission, the science instruments were not pointed at Mars. The HGA was deployed on 1999-03-29, and the first day of full mapping was 1999-04-03. Soon after the antenna was deployed (1999-04-16) its azimuth gimbal jammed, causing an entry into contingency mode and interruption in the acquisition of science data. This interruption lasted until 1999-04-29, and then data were acquired in a modified FHGA mode (HGA deployed, but boresight fixed in the spacecraft +x direction) until 1999-05-06, when normal mapping resumed. It was determined that the restricted range of travel on the azimuth gimbal would allow normal mapping operations until early 2000. So-called 'beta supplement mode' operations, in which the antenna was reoriented to allow Earth tracking during data acquisition, were begun on 2000-02-07. But beta supplement mode required that the antenna be 'rewound' while the spacecraft was being tracked and precluded collection of egress (exit) radio occultations. Approximately three days of FHGA operation were inserted into the schedule (2000-03-05 to 2000-03-07) to mitigate impact on radio science. Unexpected heating of MOLA resulted, and further FHGA operation was suspended pending resolution of the thermal problems. Mission Phase Start Time : 1999-03-09 Mission Phase Stop Time : 2001-01-31 EXTENDED MISSION ---------------- The Extended Mission Phase will begin at the end of the Mapping Phase, 1 February 2001, and continue through 22 April 2002. Mapping operations will continue in much the same way as operations during the Mapping Phase, with data acquisition expected to continue as before for all science experiments. A new type of spacecraft maneuver has been designed for targeted science observations during the extended mission: the Roll Only Targeted Observation (ROTO). The maneuver is constrained to occur primarily in the roll axis and cannot exceed +/- 30 degrees off nadir. The spacecraft will be rolled during selected orbits to acquire off-nadir contiguous MOC, MOLA, and TES data, which will be used primarily to support landing site certification for future missions. Starting on 16 August 2001, the spacecraft was put into the 'Relay 16' or R16 attitude, in which it was pitched back along the velocity vector by 16 degrees. This reduced gravity-gradient torques, slowing momentum buildup in the spacecraft's reaction wheels, and hence minimized fuel consumption. Mission Phase Start Time : 2001-02-01 Mission Phase Stop Time : 2002-04-22 EXTENDED-EXTENDED (E2) MISSION ------------------------------ The E2 Mission Phase will begin at the end of the Extended Mission Phase, 23 April 2002, and nominally continue through the end of fiscal year 2003. Mapping operations will be similar to those in the Extended Mission. ROTOs and the R16 attitude will be continued. Beginning in early 2004, MGS will be used to support telemetry return from the Mars Exploration Rover missions, using the Mars Relay UHF system. Mission Phase Start Time : 2002-04-23 Mission Phase Stop Time : 2004-09-26" 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 make Antarctica seen balmy. Comparing the history and evolution of the two planets yields 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 remain to be made. No topographic model of the planet exists at the 100 meter level (and many areas were uncertain by kilometers); MOLA will provide one with typical accuracies of 30 m. Preliminary measurements on the magnetic field have been carried out by early spacecraft; but MGS MAG/ER is the first instrument to carry out a systematic mapping effort. Gravity models have been compiled from Mariner 9 and Viking data, but MGS RSS provides 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 include recording global daily images of the planet so that cloud patterns can be followed and the growth of dust storms can be monitored over a full martian year. TES and RSS are 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 allows 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 will provide high-resolution image data; TES will acquire 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 will not conduct a search for life on Mars, it will gather detailed data that will help in understanding the mystery of the missing water. This type of study will provide important background data to help scientists in their search for Martian life on future missions. Other Studies ============= In addition to studying Mars, the spacecraft could also be used for experiments of opportunity, such as searching for gravitational waves during cruise [ESTABROOKETAL1995] and probing the Sun's corona during solar conjunction [WOO1993]." END_OBJECT = MISSION_INFORMATION OBJECT = MISSION_HOST INSTRUMENT_HOST_ID = "MGS" OBJECT = MISSION_TARGET TARGET_NAME = "MARS" END_OBJECT = MISSION_TARGET OBJECT = MISSION_TARGET TARGET_NAME = "PHOBOS" END_OBJECT = MISSION_TARGET OBJECT = MISSION_TARGET TARGET_NAME = "SUN" 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 = "ESTABROOKETAL1995" 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 = "WOO1993" END_OBJECT = MISSION_REFERENCE_INFORMATION OBJECT = MISSION_REFERENCE_INFORMATION REFERENCE_KEY_ID = "ZUBERETAL1992" END_OBJECT = MISSION_REFERENCE_INFORMATION END_OBJECT = MISSION END