# How Does NASA Change a Spacecraft’s Orbit? Easy as Pi.

It’s “Pi Day” (March 14… 3.14… get it?) and, based on how we write the date in the U.S. anyway, all those of a sufficiently geeky nature take a moment to honor the universal usefulness of pi, the glorious Greek letter used to represent the mathematical ratio of a circle’s circumference to its diameter.

The basics of pi were known to the Babylonians over 4,000 years ago, and a method to determine pi to any degree of accuracy needed was developed by Archimedes in the third century BCE. Now, the value of pi has been calculated to many trillions of decimal places and its practical uses have extended far beyond the surface of our planet, helping engineers plot the orbits of planetary spacecraft and even measure the sizes of planets outside our solar system!

In fact NASA uses pi all the time in various extraterrestrial applications… read more:

How big are craters? What are asteroids made of? How to reorient a spacecraft’s orbit? All these questions become easy as pie with pi! (Well, maybe not *easy* but knowing how to calculate the circumference of a circle sure helps!)

Check out the infographic below:

In 2007, the Cassini spacecraft engineers used a method called a “pi transfer” (aka 180-degree transfer) to bring down the spacecraft’s inclination to get different perspectives on Saturn and, in that instance, thereby image its rings.

During a pi transfer, Cassini flies by Titan at opposite sides of its orbit about Saturn (i.e., Titan’s orbital position differs by pi radians between the two flybys) and uses Titan’s gravity to change its orbital perspective on the ringed planet.* (Source)*

You can find a brief history of pi here, OR if you’d rather get your geometry lesson today from published mathematician, educator (and ex-*Wonder Years* cutie) Danica McKellar, watch the video below:

(I won’t blame you for choosing the video. 🙂 )

Also, in related news, Pi Day just happens to be Albert Einstein’s birthday! The famed physicist would have been 135 years old today — watch a video on his achievements narrated by William Hurt here.

Posted on March 14, 2014, in Features, Saturn, Saturn's Moons and tagged 2014, Archimedes, Danica McKellar, Einstein, geometry, infographic, pi, pi day. Bookmark the permalink. Comments Off on How Does NASA Change a Spacecraft’s Orbit? Easy as Pi..