As NASA's MAVEN spacecraft gets under way on its long journey to the red planet, the stakes are high for mission success.
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:
1. Long Cruise to the Red Planet
Launching and leaving Earth's orbit only marks the start of a lengthy 400-million-mile journey that will put MAVEN in orbit around Mars on September 22, 2014.
It will take the robotic probe about six weeks longer to reach the red planet than it took NASA's last mission, the Curiosity rover back in 2012.
The cruise phase may sound like an easy, laid-back part of the mission, but in fact it is an extremely busy time for mission controllers back on Earth. It's when all systems on the spacecraft are checked out to make sure they are working properly.
Outside threats like solar and cosmic radiation, which could knock out any number of scientific or flight instruments, must be monitored at all times.
The navigation team must make final calculations so that the spacecraft arrives on target. Course corrections, done by nudging the spacecraft using small retro-rockets, have to be extremely precise to ensure that the probe arrives in the right place at the right time by keeping its moving target, Mars, in its cross-hairs.
2. Communications Delay
Because of the enormous interplanetary distance between Earth and Mars, as MAVEN moves toward the red planet, mission controllers will encounter communication delays of up to 20 minutes one way. The actual time delay will depend on the positions of Earth and Mars in their orbits.
This ultimately means that there can be up to 40 nerve-wracking minutes when no one back on Earth knows what exactly is happening with the Mars probe.
3. Orbit Capture
As the spacecraft approaches Mars, NASA controllers will command MAVEN to reduce its velocity so that it can be captured by the planet's gravity and enter orbit. Otherwise, if it doesn't slow down enough, it would just fly past Mars and out toward the asteroid belt.
Once it's in a large elliptical orbit, MAVEN will use a daring technique called aerobraking, in which the probe will use the drag from Mars' thin atmosphere to enter a lower orbit that will allow it to collect the data it needs.
4. Dangerous Dips
Upon arrival, MAVEN will settle into a stable elliptical orbit around the planet that brings it as close as 93 miles (150 kilometers) and as far away as 3,728 miles (6,000 kilometers).
MAVEN will make periodic "deep dips" into the upper atmosphere—at least five over the course of its year-long prime mission—so that the onboard instruments can sample the atmosphere directly.
Expectations are that MAVEN will be able to dive down possibly within 77 miles (124 kilometers) of the surface, so that it can taste and smell the Martian air before being raised back up to higher altitudes.
5. Solving the Long-Standing Martian Climate Change Riddle
Scientists believe that at one point in Mars' ancient past, billions of years ago, the planet was habitable, with a thick atmosphere and liquid water flowing on its surface. What went wrong?
Something drastic happened that changed the planet from being Earth-like to being a cold, desert world that has only the thin remnant atmosphere we see today.
MAVEN mission scientists will not only get a chance to directly analyze the composition of today's Martian atmosphere for the first time, but also hope to get a better understanding of why Mars has lost most of its atmosphere into space.