Michael Braukus
Headquarters, Washington, D.C.                                                
January 15, 1992
(Phone:  202/453-1549)

Jim Doyle
Jet Propulsion Laboratory, Pasadena, Calif.
(Phone:  818/354-5011)


RELEASE: 92-8

NASA'S MAGELLAN SPACECRAFT TO RESUME VENUS MAPPING MISSION


     The Magellan spacecraft will use its backup transmitter to 
resume mapping the surface of Venus with imaging radar on Jan. 24, 
following a week of routine battery recharging, project officials 
at NASA's Jet Propulsion Laboratory, Pasadena, Calif., said today.

     The primary transmitter failed Jan. 4, an official said.  The 
backup transmitter had been turned off since last March because of 
a noise problem which interfered with the mapping data.

     Mission Director Doug Griffith said tests over the past 
several days, however, have confirmed that mapping data can be 
received very well by the backup transmitter using a lower rate to 
transmit the data back to Earth.

     "One small uncertainty remains with respect to some noise in 
the downlink mapping signal," he said.  "To account for this, the 
signal is being reduced to 115 thousand bits per second, 43 
percent of the normal rate.  Despite this uncertainty, we're 
confident that Magellan will be operating in a routine mapping 
mode by the 24th of January."

      Project Scientist Steve Saunders said his team was anxious 
to resume mapping and planned to gather images from a northern 
latitudes area missed during the spacecraft's first cycle because 
of superior conjunction, when Earth and Venus were on opposite 
sides of the sun and mapping was interrupted.

     Magellan's primary mission, to map 70 percent of the planet, 
was completed before the end of the first cycle on May 15, 1991.  
To date it has mapped more than 95 percent of Venus.  The next 
major target will be Maxwell Montes, the highest mountain range on 
Venus.

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     Magellan today began its third 243-day mapping cycle which 
will emphasize stereoscopic mapping.  Each mapping cycle 
represents one Venus day or 243 Earth days, while the planet 
rotates beneath Magellan's orbit.  Images taken earlier in the 
mission can be viewed along with new images to reveal stereo views 
of high resolution topography, Saunders said.

     Features can be imaged in stereo by looking at them twice at 
angles at least 15 degrees apart.  Magellan's imaging radar looks 
to the side on each orbit to see the surface.  "Stereo imaging, 
which produces a three-dimensional picture, increases our ability 
to interpret the images many fold," Saunders said.

     Magellan is managed by the Jet Propulsion Laboratory for 
NASA's Office of Space Science and Applications, Washington, D.C.

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