Roughly two-thirds of all missions to Mars have met a bad end. Some have burned up in Earth's atmosphere on launch, while others simply died along the way to their destination planet.

While the Russians, Japanese, and British have all suffered from the so-called "Mars Curse," most of NASA's missions have been successful. However, some big-ticket orbiters with billion-dollar price tags have failed for the U.S. agency, most notably the Mars Observer orbiter in 1993 and the Mars Climate Observer in 1999, both of which fell mysteriously silent just before or on arrival at Mars.

Here are five of the biggest challenges facing the intrepid MAVEN mission in the coming weeks and months:

Launching and leaving Earth's orbit only marks