The Mars Global Surveyor (MGS) was a US spacecraft developed by NASA and the Jet Propulsion Laboratory and launched November 1996. It began the United States's return to Mars after a 20-year absence. It completed its primary mission in January 2001 and was in its third extended mission phase when it lost contact with NASA in November 2006.

On November 2, 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, used to convert sunlight into electricity) extending from opposite sides. When fully loaded with propellant at the time of launch, the spacecraft weighed 1,060 kilograms (2,342 pounds). 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 Surveyors rocket engines and propellant tanks.

Scientific instruments

Five scientific instruments fly onboard Mars Global Surveyor:^[1]

• MOC - the Mars Orbiter Camera, operated by Malin Space Science Systems http://www.msss.com/mars/observer/camera/papers/moc_ijist/moc_ijist.html
• 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

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 above the northern hemisphere, and an apoapsis of 54,026 km 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 kilometers (68 miles). 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 kilometers to altitudes near 450 kilometers.

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 Surveyors 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 1500 meters 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.

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).

In addition to this, MGS could shoot pictures of other orbiting bodies, such as other spacecraft and the moons of Mars.

MOC images

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.^[2]

Loss of contact

On November 2, 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.^[3] The effort was unsuccessful.

On 21 November-22 November 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."^[4]

On January 10, 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.^[5]

On April 13, 2007, NASA reported that the likely cause of the spacecraft was "battery failure caused by a complex sequence of events involving the onboard computer memory and ground commands."^[6]

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.

Discovery of water on Mars

On December 6, 2006 NASA released photos of two craters called Terra Sirenum and Centauri Montes which appear to show the presence of water on Mars within just the past 5 to 7 years (from 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.^[7][8]

Mission timeline

• November 7, 1996: Launch from Cape Canaveral.
• September 11, 1997: Arrival at Mars, began orbit insertion.
• April 1, 1999: Primary mapping phase began.
• February 1, 2001: First extended mission phase began.
• February 1, 2002: Second extended mission phase began.
• January 1, 2003: Relay mission began.
• March 30, 2004: Surveyor photographed the Mars Exploration Rover Spirit along with its wheel tracks showing its first 85 sols of travel.
• December 1, 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.^[9]
• October 1, 2006: Extended mission phase began for another two years.^[10]
• November 2, 2006: Spacecraft suffers an error while attempting to reorient a solar panel and communication was lost.
• November 5: Weak signals were detected, indicating the spacecraft was awaiting instructions. The signal cut out later that day.^[11]
• November 21: NASA announces the spacecraft has likely finished its operating career.
• December 6, 2006: NASA releases imagery taken by MGS of a newly found gully deposit, suggesting that water still flows on Mars.
• April 13, 2007: NASA releases its Preliminary Report on the cause(s) of MGS' loss of contact. (See External Links for document)

Other pictures

See also

• Exploration of Mars
• Space exploration
• Unmanned space mission

References

Notes

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 13th, 2007)
• 04/13/07: Mars Global Surveyor: Report Reveals Reasons for Loss.
• 04/13/07: Nasa confirmes first speculations about the reason for the loss of the spacecraft

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