Mars Global Surveyor

Template:Infobox Spacecraft The Mars Global Surveyor (MGS) was a US spacecraft developed by NASA's Jet Propulsion Laboratory and launched November 1996. It began the United States's return to Mars after a 10-year absence. It completed its primary mission in January 2001 and was in its third extended mission phase when, on 2 November 2006, the spacecraft failed to respond to messages and commands. A faint signal was detected three days later which indicated that the craft had gone into safe mode. All attempts to recontact the Mars Global Surveyor and resolve the problem failed. In January 2007 NASA officially ended the mission.

Specifications

The Surveyor spacecraft, fabricated at the Lockheed Martin Astronautics plant in Denver, is a rectangular-shaped box with wing-like projections (solar panels) extending from opposite sides. When fully loaded with propellant at the time of launch, the spacecraft weighed 1,060 kg (2,337 lb). Most of Surveyor's mass lies in the box-shaped module occupying the center portion of the spacecraft. This center module is made of two smaller rectangular modules stacked on top of each other, one of which is called the equipment module and holds the spacecraft's electronics, science instruments, and the 1750A mission computer. The other module, called the propulsion module, houses Surveyor's rocket engines and propellant tanks.

Scientific instruments

Five scientific instruments fly onboard Mars Global Surveyor:

• MOC - the Mars Orbiter Camera, operated by Malin Space Science Systems
• MOLA - the Mars Orbiter Laser Altimeter
• TES - the Thermal Emission Spectrometer
• MAG/ER - a Magnetometer and electron reflectometer
• USO/RS Ultrastable Oscillator for Doppler measurements
• MR Mars Relay - Signal receiver

The Mars Orbiter Camera (MOC) science investigation used 3 instruments: a narrow angle camera that took (black-and-white) high resolution images (usually 1.5 to 12 m per pixel) and red and blue wide angle pictures for context (240 m per pixel) and daily global imaging (7.5 km per pixel). MOC returned more than 240,000 images spanning portions of 4.8 Martian years, from September 1997 and November 2006. A high resolution image from MOC is either 1.5 or 3.1 Km wide. So any image from this camera is at most 3.1 Km wide. Often, a picture will be smaller than this because it has been cut to just show a certain feature. These high resolution images may be 3 to 10 Km long. When a high resolution image is taken, a context image is taken as well. The context image shows the image footprint of the high resolution picture. Context images are typically 115.2 Km square with 240 m/pixel resolution.

Launch and orbit insertion

The Surveyor spacecraft was launched from the Cape Canaveral Air Station in Florida on November 7, 1996 aboard a Delta II rocket. The spacecraft traveled nearly 750 million kilometers (466 million miles) over the course of a 300-day cruise to reach Mars on September 11, 1997.

Upon reaching Mars, Surveyor fired its main rocket engine for the 22-minute Mars orbit insertion (MOI) burn. This maneuver slowed the spacecraft and allowed the planet's gravity to capture it into orbit. Initially, Surveyor entered a highly elliptical orbit that took 45 hours to complete. The orbit had a periapsis of 262 km (163 mi) above the northern hemisphere, and an apoapsis of 54,026 km (33,570 mi) above the southern hemisphere.

Aerobraking

After orbit insertion, Surveyor performed a series of orbit changes to lower the periapsis of its orbit into the upper fringes of the Martian atmosphere at an altitude of about 110 km (68 mi). During every atmospheric pass, the spacecraft slowed down by a slight amount because of atmospheric resistance. The density of the Martian atmosphere at such altitudes is comparatively low, allowing this procedure to be performed without damage to the spacecraft. This slowing caused the spacecraft to lose altitude on its next pass through the orbit's apoapsis. Surveyor used this aerobraking technique over a period of four months to lower the high point of its orbit from 54,000 km (33,554 mi) to altitudes near 450 km (280 mi).

On October 11, the flight team performed a maneuver to raise the periapsis out of the atmosphere. This suspension of aerobraking was performed because air pressure from the atmosphere caused one of Surveyor's two solar panels to bend backward by a slight amount. The panel in question was slightly damaged shortly after launch in November 1996. Aerobraking was resumed on November 7 after flight team members concluded that aerobraking was safe, provided that it occurs at a more gentle pace than proposed by the original mission plan.

This image taken by Mars Global Surveyor spans a region about 1,500 m (4,921 ft) across, showing gullies on the walls of Newton Basin in Sirenum Terra. Similar channels on Earth are formed by flowing water, but on Mars the temperature is normally too cold and the atmosphere too thin to sustain liquid water. Nevertheless, many scientists hypothesize that liquid groundwater can sometimes surface on Mars, erode gullies and channels, and pool at the bottom before freezing and evaporating.

Under the new mission plan, aerobraking occurred with the low point of the orbit at an average altitude of 120 km (75 mi), as opposed to the original altitude of 110 km (68 mi). This slightly higher altitude resulted in a decrease of 66 percent in terms of air resistance pressure experienced by the spacecraft. During these six months, aerobraking reduced the orbit period to between 12 and 6 hours.

From May to November 1998, aerobraking was temporarily suspended to allow the orbit to drift into the proper position with respect to the Sun. Without this hiatus, 'Surveyor' would complete aerobraking with its orbit in the wrong solar orientation. In order to maximize the efficiency of the mission, these six months were devoted to collecting as much science data as possible. Data was collected between two to four times per day, at the low point of each orbit.

Finally, from November 1998 to March 1999, aerobraking continued and shrank the high point of the orbit down to 450 km (280 mi). At this altitude, Surveyor circled Mars once every two hours. Aerobraking was scheduled to terminate at the same time the orbit drifted into its proper position with respect to the Sun. In the desired orientation for mapping operations, the spacecraft always crossed the day-side equator at 14:00 (local Mars time) moving from south to north. This geometry was selected to enhance the total quality of the science return.

Mapping

The spacecraft circled Mars once every 117.65 minutes at an average altitude of 378 kilometers (235 miles). It is in a near polar orbit (inclination = 93°) which is almost perfectly circular, moving from being over the south pole to being over the north pole in just under an hour. The altitude was chosen to make the orbit sun-synchronous, so that all images that were taken by the spacecraft of the same surface features on different dates were taken under identical lighting conditions. After each orbit, the spacecraft viewed the planet 28.62° to the west because Mars had rotated underneath it. In effect, it was always 14:00 for Mars Global Surveyor as it moved from one time zone to the next exactly as fast as the Sun. After seven sols and 88 orbits, the spacecraft would approximately retrace its previous path, with an offset of 59 km to the east. This ensured eventual full coverage of the entire surface.

In its extended mission, MGS did much more than study the planet directly beneath it. It commonly performed rolls and pitches to acquire images off of its nadir track. The roll maneuvers, called ROTOs (Roll Only Targeting Opportunities), rolled the spacecraft left or right from its ground track to shoot images as much as 30° from nadir. It was possible for a pitch maneuver to be added to compensate for the relative motion between the spacecraft and the planet. This was called a CPROTO (Compensation Pitch Roll Targeting Opportunity), and allowed for some very high resolution imaging by the on board MOC (Mars Orbiting Camera).

The Phobos monolith (right of center) as taken by the Mars Global Surveyor (MOC Image 55103) in 1998.

In addition to this, MGS could shoot pictures of other orbiting bodies, such as other spacecraft and the moons of Mars. In 1998 it imaged what was later called the Phobos monolith, found in MOC Image 55103.

Primary Mission Results

Results from the Mars Global Surveyor primary mission (1996-2001) were published in the Journal of Geophysical Research by M. Malin and K. Edgett. Some of these discoveries are:

-The planet was found to have a layered crust to depths of 10 km or more. To produce the layers, large amounts of material had to be weathered, transported and deposited.

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  Layers in an old crater in Arabia, as seen by Mars Global Surveyor (MGS)Mars Global Surveyor Layers may form from volcanoes, the wind, or by deposition under water. The craters on the left are pedestal craters.
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  Layers in crater found within the Schiaparelli crater basin as seen by Mars Global Surveyor. Image from the Sinus Sabaeus quadrangle.
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  Layers in Monument Valley. These are accepted as being formed, at least in part, by water deposition. Since Mars contains similar layers, water remains as a major cause of layering on Mars.
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  Buttes and layers in Aeolis quadrangle, as seen by Mars Global Surveyor.

-The northern hemisphere is probably just as createred as the southern hemisphere, but the craters are mostly buried.

-Many features, like impact craters, were buried, then recently exhumed.

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  Crater that was buried in another age and is now being exposed by erosion, as seen by the Mars Global Surveyor. Image is located in the Noachis quadrangle.
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  Lava flows were once covered over, now these platy flows are being exposed.
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  Crater was buried, now it is being exhumed by erosion. Image located in Ismenius Lacus quadrangle.
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  The northern hemisphere appears smooth, but the craters are covered over. Here, a group of craters are patially exposed. Image located in Cebrenia quadrangle.

-Hundreds of gullies were discovered that were formed from liquid water, possible in recent times.

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  Group of gullies on north wall of crater that lies west of the crater Newton (41.3047 degrees south latitude, 192.89 east longitide). Image taken with Mars Global Surveyor. Image is located in the Phaethontis quadrangle.
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  Gullies in a crater in Eridania quadrangle, north of the large crater Kepler. Also, features that may be remains of old glaciers are present. One, to the right, has the shape of a tongue.
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  Gullies on one wall of Kaiser Crater. Gullies usually are found in only one wall of a crater.
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  Full color image of gullies on wall of Gorgonum Chaos. Image is located in the Phaethontis quadrangle.

-Large areas of Mars are covered by a mantle that coats all, but the very steepest slopes. The mantle is sometimes smooth, sometimes pitted. Some believe the pits are due to the escape of water through sublimation (ice changing directly to a vapor) of buried ice.

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  Close up image of Phaethontis surface taken with Mars Global Surveyor. Pits are thought to be caused by buried ice turning into a gas.
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  The mantle drapes most of the area. Note the absence of boulders on the cliff face. An area that shows the edges of the mantle is circled. Image located in Ismenius Lacus quadrangle.
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  Mantle material, as seen by MGS.
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  Steep Cliff in Ismenius Lacus quadrangle with smooth mantle covering its face.

-Some areas are covered by hematite-rich material. The hematite could have been put in place by liquid water in the past.

-Dark streaks were found to be caused by giant dust devils. Dust Devil Tracks were observed to frequently change; some changed in just one month.

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  Pattern of large and small tracks made by giant dust devils as seen by Mars Global Surveyor. Image is located in Eridania quadrangle.
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  Kepler (Martian crater) showing dust devil tracks, as seen by Mars Global Surveyor. Kepler is a large crater in the Eridania quadrangle.
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  Dust Devil, as seen by MGS.
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  Dust Devil in action showing shadow to the right. Image located in Cebrenia quadrangle.

-The south pole's residual cap was observed to look like swiss cheese. The holes are generally a few meters deep. The holes get bigger each year, so Mars may be warming.

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  Changes in South Pole from 1999 to 2001, as seen by Mars Global Surveyor. Notice how swiss-cheese type holes have grown in the two years.
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  Swiss Cheese Terrain, as seen by MGS. Largest mesa in image is 4 meters high.
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  Layers in Swiss Cheese Terrain. There is a bright upper layer and a darker lower layer.
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  Close-up view of Swiss Cheese Terrain. Polygonal pattern was probably formed by shallow troughs.

-The Thermal Emission Spectrometer found that just about all of the surface of Mars is covered with volcanic rock.

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  Ceraunius Tholus, one of many volcanoes found on Mars.
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  Lava flows in the Tharsis quadrangle.
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  Image shows both young and old lava flows from the base of Olympus Mons. The flat plain is the younger flow. The older flow has channels with levees along their edges. The presence of levees is quite common in many lava flows.
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  Small Volcano in Phoenicis Lacus quadrangle. Image is 1.9 miles wide.

-Hundreds of house-sized boulders were found in some areas. This indicates that some materials are strong enough to hold together, even when moving downslope. Most of the boulders appeared in volcanic regions so they were probably from weathered from lava flows.

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  House-sized boulders are scattered throughout this image.
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  These boulders are near Ascraeus Mons, a Martian volcano. Volcanoes on Mars probably form hard boulders made up of basalt that is resistant to erosion in the current environment of Mars.

-Thousands of Dark Slope Streaks were observed. Most sciencetists believe they result from the avalanching of dust. However, some researchers think that water may be involved.

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  Dark streaks were discovered with the sensitive camera of the MGS.
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  Many streaks underwent changes during the many years that MGS functioned.
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  Tikonravev Crater Floor, as seen by Mars Global Surveyor. Click on image to see dark slope streaks and layers. Tikonravev Crater is in the Arabia quadrangle.
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  Dark streaks in Diacria quadrangle, as seen by Mars Global Surveyor.

MER communications subsystem

Mars Global Surveyor functioned as a communications satellite relaying data back to Earth from the MER surface landers. Portions of MGS had been scheduled to remain active until at least September 2008 to support MER.

Loss of contact

On 2 November 2006, NASA lost contact with the spacecraft after commanding it to adjust its solar panels.

Several days later a faint signal was received indicating that the spacecraft had entered safe mode, and was awaiting further instructions from Earth.

On November 20, the Mars Reconnaissance Orbiter spacecraft attempted to take a picture of Mars Global Surveyor in order to check the craft's orientation towards the Sun and Earth to help diagnose the problem. The effort was unsuccessful.

On November 21–November 22 MGS failed to relay communications to the Opportunity rover on the surface of Mars.

After this failed effort, Mars Exploration Program manager Fuk Li said, "Realistically, we have run through the most likely possibilities for re-establishing communication, and we are facing the likelihood that the amazing flow of scientific observations from Mars Global Surveyor is over."

On 10 January 2007, NASA announced that the loss of the spacecraft might have been caused by a flaw in a parameter update to the spacecraft's system in June, 2006. In this update, two memory addresses were incorrect. Consequently the solar arrays were driven until a hard stop and the spacecraft subsequently went into safe mode. One of the consequences of the parameter flaw was that the spacecraft incorrectly diagnosed a failure of a gimbal motor. In special logic built into MGS' flight software, this meant that the spacecraft was rotated to point the "stuck" solar array at the Sun. But in this geometry, the radiator that should cool down the spacecraft's last surviving battery was also pointed at the sun, resulting in an overheating of (and subsequent failure of) the battery. NASA said this scenario should be treated as preliminary. But ultimately, the fate of the spacecraft may never be known for certain.

On 13 April 2007, NASA reported that the likely cause of the spacecraft's demise was "battery failure caused by a complex sequence of events involving the onboard computer memory and ground commands."

Originally, the spacecraft was to observe Mars for 1 Mars year, roughly 2 Earth years. Based on the valuable science data, the National Aeronautics and Space Administration extended its mission three times.

MGS and general relativity: the Lense-Thirring test

Main article: frame-dragging

Data from MGS have also been used to perform a test of the general relativistic Lense-Thirring effect which consists of a small precession of the orbital plane of a test particle moving around a central, rotating mass such as a planet. The interpretation of the out-of-plane Root-Mean-Square (RMS) time series of MGS in terms of such a relativistic feature of motion by L. Iorio was criticized by K. Krogh; however, L. Iorio supported his thesis with new arguments.

Discovery of water on Mars

Main article: Water on Mars

On 6 December 2006 NASA released photos of two craters called Terra Sirenum and Centauri Montes which appear to show the presence of water on Mars at some point between 1999 and 2001. The pictures were produced by the Mars Global Surveyor and are quite possibly the spacecraft's final contribution to our knowledge of Mars and the question of whether life or water exists on the planet.

Hundreds of gullies were discovered that were formed from liquid water, possible in recent times. These gullies occur on steep slopes and mostly in certain bands of latitude.

A few channels on Mars displayed inner channels that suggest sustained fluid flows. The most well-known is the one in Nanedi Valles. Another was found in Nirgal Vallis.

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  Inner channel on floor of Nanedi Valles that suggests that water flowed for a fairly long period. Image from Lunae Palus quadrangle.

Mission timeline

• 7 November 1996: Launch from Cape Canaveral.
• 11 September 1997: Arrival at Mars, began orbit insertion.
• 1 April 1999: Primary mapping phase began.
• 1 February 2001: First extended mission phase began.
• 1 February 2002: Second extended mission phase began.
• 1 January 2003: Relay mission began.
• 30 March 2004: Surveyor photographed the Mars Exploration Rover Spirit along with its wheel tracks showing its first 85 sols of travel.
• 1 December 2004: Science and Support mission began.
• April, 2005: MGS became the first spacecraft to photograph another spacecraft in orbit around a planet other than Earth when it captured two images of the Mars Odyssey spacecraft and one image of the Mars Express spacecraft.
• 1 October 2006: Extended mission phase began for another two years.
• 2 November 2006: Spacecraft suffers an error while attempting to reorient a solar panel and communication was lost.
• 5 November 2006: Weak signals were detected, indicating the spacecraft was awaiting instructions. The signal cut out later that day.
• 21 November 2006: NASA announces the spacecraft has likely finished its operating career.
• 6 December 2006: NASA releases imagery taken by MGS of a newly found gully deposit, suggesting that water still flows on Mars.
• 13 April 2007: NASA releases its Preliminary Report on the cause(s) of MGS' loss of contact. (See External Links for document)

Other pictures

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  Surface of Mars taken by the Mars Global Surveyor and released on October 16, 2000.
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  Surface of Mars taken by the Mars Global Surveyor.
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  Surface of Mars taken by the Mars Global Surveyor.
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  Surface of Mars taken by the Mars Global Surveyor on August 10, 1999.
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  Surface of Mars taken by the Mars Global Surveyor on August 10, 1999.
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  The Mars Rover Spirit's landing site and tracks taken by Mars Global Surveyor.
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  The Mars Express spacecraft image taken by Mars Global Surveyor.
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  The Mars Odyssey spacecraft image taken by Mars Global Surveyor.
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  Group of gullies on north wall of crater that lies west of the crater Newton (41.3047 degrees south latitude, 192.89 east longitide). Image taken with Mars Global Surveyor.
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  Layers in an old crater in Arabia, as seen by Mars Global Surveyor (MGS)Mars Global Surveyor Layers may form from volcanoes, the wind, or by deposition under water. The craters on the left are pedestal craters.
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  Layers in the canyon wall in Coprates quadrangle, as seen by Mars Global Surveyor.
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  Banded or taffy-pull terrain in Hellas, as seen by Mars Global Surveyor. Origin is unknown at present.
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  Lava flow in Elysium. There are many lava flows in the Elysium quadrangle. In this one, the lava flowed toward the upper right. Image taken by Mars Global Surveyor.
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  Bright rays caused by impact throwing out a bright lower layer. Some bright layers contain hydrated minerals. Picture taken with Mars Global Surveyor. Location is Memnonia quadrangle.
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  Mars Global Surveyor orbiter's photograph of Opportunty Rover's landing site showing "hole in one."
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  Inverted Channels in Aeolis quadrangle. It is believed that stream channels became raised features after coarse materials were deposited and cemented.
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  Picture probably is of a delta that formed in a huge lake. The area is of great interest to geologists. Evidence of life may be found in this location.
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  Pavonis Mons, located on the equator in Tharsis quadrangle.

See also

• Exploration of Mars
• Space exploration
• Unmanned space mission
• Nickel hydrogen battery

References

• "MOC Imaging Phases, Subphases, and Image Identification Numbers". Retrieved 28 May 2006.

Further reading

• Mars Global Surveyor

External links

• NASA JPL Mars Link
• NASA mission overview
• Mars Global Surveyor Mission Profile by NASA's Solar System Exploration
• Global Surveyor Mission plan
• Malin Space Science Systems (complete image gallery)
• Preliminary Report: MGS Loss of Contact (Released April 13, 2007)
• 04/13/07: Mars Global Surveyor: Report Reveals Reasons for Loss.
• New Scientist article on the general relativistic test
• 04/13/07: Nasa confirmes first speculations about the reason for the loss of the spacecraft
• MGS Photograph