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Mars Global Surveyor


(CNN) -- If Pathfinder is the hare in the race to Mars, then Mars Global Surveyor is the tortoise. Weighing in at 2,342 pounds (about as heavy as a Dodge Neon), Surveyor is bigger, slower, and not nearly as nimble as Pathfinder. It won't land on the planet surface; it won't be able to find definitive evidence of life there; and it won't accomplish its mission until the beginning of the next century. Even so, Surveyor could prove to be every bit as valuable as Pathfinder, if not quite so dramatic.

Surveyor successfully entered the Martian orbit September 11, 1997 to begin its two-year mission: to map the entire planet by taking high-resolution pictures of the Martian surface. These observations will lay the foundation for a 10-year NASA program that will send pairs of Surveyor-like orbiters and Pathfinder-like landers to Mars every 26 months.

A mapping configuration of Mars Surveyor

3-D model of the Mars Surveyor

Surveyor will "return more data than all the planetary missions to Mars in the past have ever returned," according to Glenn Cunningham, the manager of the Global Surveyor project at the Jet Propulsion Laboratory.

Redemption for the Observer failure

Surveyor's success entering the Martian orbit has special significance for NASA scientists. The satellite is the successor to the ill-fated Mars Observer, which disappeared in August 1993, just days before it was supposed to reach the red planet. NASA scientists still aren't sure what happened, but they think a propulsion system failure might have sent Observer hurtling past Mars into an orbit around the sun.

In the wake of that fiasco, NASA built Surveyor on a budget: it cost only $135 million, a fraction of Observer's nearly $1 billion price tag. Surveyor carries the same scientific equipment as Observer and many of the earlier craft's spare parts.

Launched from Cape Canaveral, Florida, on November 7, 1996, Surveyor successfully reached Mars after a journey of 466 million miles in just 308 days.

How it works

Before it could begin its task, it was necessary for Surveyor to reshape its orbit above Mars. The spacecraft slowed itself down using a technique called "aerobraking," in which it used its wing-like solar panels to provide atmospheric drag. Nearly six months of aerobraking maneuvers lowered Surveyor from 56,000 kilometers (34,800 miles) to altitudes near 400 kilometers (250 miles) above Mars. In late March 1998 the spacecraft began intensive scientific data collection.

Then, for one Martian year (687 Earth days), the spacecraft will be high overhead the red planet using a battery of cameras to photograph the entire Martian globe. The photos will create a portrait of the planet's topography and mineral composition as Surveyor's on-board sensors gather information about the planet's magnetic and atmospheric properties -- including the possible presence of water.

Once the scientific mission has been completed, Surveyor will remain in the Martian orbit as a communications satellite, relaying signals from other landers and probes for three more years.

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