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It's Done With Math
Columnist: Dr. James Green

It's Done With Math
14 April 2011

At the Stardust NExT press conference in February, Dr. Ed Weiler, Associate Administrator for NASA's Science, had a message for school kids curious about how we navigate our spacecraft. How were we able to reposition Stardust NExT -- a spacecraft that had been in space for 12 years -- to intercept a rotating comet travelling 24700 mph in the other direction. His answer? "It's done with math!"

With math as our primary tool, we not only rendezvous with comets and visit planets and asteroids, we're also headed into interstellar space via the twin Voyager spacecraft. An event will be held April 28th at NASA Headquarters to celebrate the accomplishments of these amazing space probes.

The Voyagers were launched in 1977* and for the past 33 years have been on an incredible journey, making discoveries that have had a profound influence on our world of planetary science. They are the longest operating, continuously functioning mechanisms (space probes) ever sent into space by humankind -- a fabulous accomplishment considering the astronomical expanses traveled and the distances over which control commands are sent. Most certainly, it's math!

Having left the "planetary" domain behind many years ago, the Voyagers are now exploring the heliosphere -- the enormous bubble of gas blown by the solar wind and enveloping our solar system. Voyager-1 is almost 117 AU (astronomical units) from our sun, and Voyager-2 is not far behind, about 95 AU from the sun. (To put that in perspective, 1 AU is the distance from the Earth to the sun, or about 149 million km, or 93 million miles. Do the math!)** The spacecraft are heading for the boundary of the heliosheath, the outer layer of the heliosphere.

The sun controls the environment within this bubble, and once the spacecraft cross over into interstellar space, we'll have data never before available. What's it like out where the sun is no longer really influencing you? Will things be different there, where you're sort of drifting through space? It will be incredibly interesting to find out.

The Voyagers have already given us an entirely new perspective of our place in the solar system and the universe. When Voyager-1 reached a point, over twenty years ago, beyond the outermost planet in our solar system, the spacecraft's camera rotated inward to capture some final photographs of our family of planets. These images were pieced together to create the first group portrait. The MESSENGER spacecraft, before getting into orbit around Mercury, completed a second group picture of our solar system. It is the view that our sun would have.

In each of these "portraits" we see Earth as a blue speck of light within the vast expanse of our solar system -- which is itself only a small portion of a tremendous galaxy in a universe abundant with galaxies.

Not only have the Voyager spacecraft given us new perspective, they've greatly expanded our knowledge. Among their many discoveries are Jupiter's tumultuous atmosphere featuring hurricane-like storm systems; new moons -- new worlds in and of themselves, with volcanoes, methane lakes, erupting geysers and the like -- orbiting many of our solar system's planets; and the termination shock, the inner boundary between the heliosphere and the rest of interstellar space.

And we continue to progress. Since the Voyagers launched in the 1970's we've learned to do more than fly by the worlds we want to study. Advances in spacecraft are enabling us to explore many of our planets and other bodies within this solar system by orbiting, landing or roving on them. In the decades since the Voyagers launched, researchers have also discovered more than a thousand Kuiper Belt objects beyond Pluto and found close to 1,500 exoplanet candidates.

Space missions are daunting endeavors -- the distances traveled are vast and the challenges, including budget challenges, are tremendous. How are we able to continually meet these challenges and take the human race to new vistas? Just remember ... it's done with math!


  • Voyager 2 was launched first, on August 20, 1977, while Voyager I, on a faster, shorter trajectory, left Earth on September 5.
  • As of April 12, 2011, Voyager I was almost 17.446 billion km (116.62 AU) from the sun, and Voyager 2 was about 14.204 billion km (94.954 AU) from the sun.

Read More by Dr. James Green

About: Dr. James Green
Photo of Dr. James Green
Dr. Green is the Director of Planetary Science at NASA Headquarters. He views his job as the keeper of NASA's planetary program and the top advocate for that program to flourish and grow.
Read More by Dr. James Green
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