NASA will reposition two spacecraft in Mars' orbit and send another spacecraft to study Comet C/2013 A1 Siding Spring that will fly by Mars on October 19.

Rich Zuker, Chief Scientist for the Mars Exploration Program, said three expert teams have modeled the comet for NASA and provided forecasts on its flight plan.

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He said that the danger to the spacecraft won't come from an impact with the comet's nucleus, which will miss Mars by about 82,000 miles, but from the trail of debris emitted by the comet.

Zuker added that Mars will be right at the edge of the debris cloud and may or may not encounter particles from the comet.

The distance between the comet's nucleus and Mars will be less than one-tenth the distance of any known comets that fly by Earth.

NASA said the most dangerous period of the comet's contact with the spacecraft will start 90 minutes after the comet enters Martian orbit and will last for 20 minutes.

The Mars Reconnaissance Orbiter (MRO) was maneuvered into orbit last July 2 as part of preparations for the upcoming comet.

NASA plans to move the MRO again on August 27 to give ground personnel a clearer view of the comet.

Meanwhile, the NASA Mars Odyssey Orbiter will be maneuvered on August 5 to place it on the right track to observethe comet.

The Mars Atmosphere and Volatile Evolution, or MAVEN, is already on its way to Mars. It will enter Mars' orbit on September 21, a month before the comet flies by.