THE MAGELLAN SPACECRAFT ENDS HIS VENUS MISSION

Today, The Grandma has continued enjoying time with her friend Joseph de Ca'th Lon. They have been talking about the Magellan spacecraft, the robotic space probe, that burnt up in the atmosphere of Venus on a day like today in 1994.

The Magellan spacecraft was a 1,035-kilogram robotic space probe launched by NASA on May 4, 1989. Its mission objectives were to map the surface of Venus by using synthetic-aperture radar and to measure the planetary gravitational field.

The Magellan probe was the first interplanetary mission to be launched from the Space Shuttle, the first one to use the Inertial Upper Stage booster, and the first spacecraft to test aerobraking as a method for circularizing its orbit. Magellan was the fifth successful NASA mission to Venus, and it ended an eleven-year gap in U.S. interplanetary probe launches.

Beginning in the late 1970s, scientists advocated for a radar mapping mission to Venus. They first sought to construct a spacecraft named the Venus Orbiting Imaging Radar (VOIR), but it became clear that the mission would be beyond the budget constraints during the ensuing years. The VOIR mission was canceled in 1982.

A simplified radar mission proposal was recommended by the Solar System Exploration Committee, and this one was submitted and accepted as the Venus Radar Mapper program in 1983. The proposal included a limited focus and a single primary scientific instrument. In 1985, the mission was renamed Magellan, in honor of the sixteenth-century Portuguese explorer Ferdinand Magellan, known for his exploration, mapping, and circumnavigation of the Earth.

The objectives of the mission included:

-Obtain near-global radar images of the Venusian surface with a resolution equivalent to optical imaging of 1.0 kilometre per line pair.

-Obtain a near-global topographic map with 50 kilometres spatial and 100 metres vertical resolution.

-Obtain near-global gravity field data with 700 kilometres resolution and two to three milligals of accuracy.

-Develop an understanding of the geological structure of the planet, including its density distribution and dynamics.

Magellan returned data to perform three so called experiments:

-Synthetic Aperture Radar (SAR), already covered above while discussion the RDRS instrument;

-Gravimetry, consisting on detailed measurements of the Venus gravitational field, with the principal investigator being Georges Balmino from Centre National d'Etudes Spatiales;

-Magellan Radio Science Occultation Experiment (ROCC), consisting on measurements of the atmospheric density and radio occultation data on the atmospheric profile. The principal investigator was Jon M. Jenkins from NASA Ames Research Center.

Magellan was launched on May 4, 1989, at 18:46:59 UTC by the National Aeronautics and Space Administration from KSC Launch Complex 39B at the Kennedy Space Center in Florida, aboard Space Shuttle Atlantis during mission STS-30. Once in orbit, the Magellan and its attached Inertial Upper Stage booster were deployed from Atlantis and launched on May 5, 1989 01:06:00 UTC, sending the spacecraft into a Type IV heliocentric orbit where it would circle the Sun 1.5 times, before reaching Venus 15 months later on August 10, 1990.

On September 9, 1994, a press release outlined the termination of the Magellan mission. Due to the degradation of the power output from the solar arrays and onboard components, and having completed all objectives successfully, the mission was to end in mid-October. The termination sequence began in late August 1994, with a series of orbital trim maneuvers which lowered the spacecraft into the outermost layers of the Venusian atmosphere to allow the Windmill experiment to begin on September 6, 1994. The experiment lasted for two weeks and was followed by subsequent orbital trim maneuvers, further lowering the altitude of the spacecraft for the final termination phase.

On October 11, 1994, moving at a velocity of 7 kilometers/second, the final orbital trim maneuver was performed, placing the spacecraft 139.7 kilometers above the surface, well within the atmosphere. At this altitude the spacecraft encountered sufficient ram pressure to raise temperatures on the solar arrays to 126 °C.

On October 13, 1994 at 10:05:00 UTC, communication was lost when the spacecraft entered radio occultation behind Venus. The team continued to listen for another signal from the spacecraft until 18:00:00 UTC, when the mission was determined to have concluded. Although much of Magellan was expected to vaporize due to atmospheric stresses, some amount of wreckage is thought have hit the surface by 20:00:00 UTC.

More information: NASA

Venus and Mars are our next of kin: 
they are the two most Earth-like planets 
that we know about. 
They're the only two other very Earth-like planets 
in our solar system, 
meaning they orbit close to the sun; 
they have rocky surfaces and thin atmospheres.

David Grinspoon