Dan Matutina

After a 4.3 billion-mile nonstop flight, Rosetta is about to reach its destination. The European Space Agency vehicle has spent a decade circling our solar system in pursuit of comet 67P/Churyumov-Gerasimenko. And to prepare for the trip, ESA tested and equipped the vessel for any cosmic curveballs it might encounter on the way.

Consider the temperature, for example. The area where Rosetta and 67P will rendezvous, out beyond the asteroid belt, receives only 4 percent as much sunlight as we get here on Earth—it's frigid and dark. So before launch, engineers exposed the ship to conditions near -300 degrees Fahrenheit. They also invented new solar technology—called low-intensity, low-temperature cells—to help the sun-powered craft utilize every last photon.

Even then, saving power was a top priority. For many of those billions of miles, Rosetta hibernated in what mission planners dubbed “rotisserie mode,” spinning around its main axis to maintain its stability and course.

And while cosmic dust particles are tiny, colliding with a cloud of them can spell disaster. Engineers prepared for the worst, wrapping Rosetta in thermal foil shielding and tucking away fuel lines safely in the interior. Now the easy part: landing a smaller onboard probe on a speeding ice-and-rock comet for the first time ever.