Getting a spacecraft to Mars is one challenge, says Johnston, but making one stay there is quite another. Imagine driving at 100 miles per hour, slamming on your brakes and maneuvering perfectly into a tiny parallel parking spot. That roughly compares to the difficulty of delivering a spacecraft to Mars with a trajectory, orbit insertion maneuver and aerobraking scheme that places it in the particular orbit needed for scientific observations.

"We can get to Mars, but these circular, low-altitude science orbits are tremendously difficult to reach," Johnston says. "It's very difficult to achieve a low-altitude orbit propulsively because of the tremendous burden of carrying the propellant. To supplement the onboard propulsive capability, the Reconnaissance Orbiter mission plans to use aerobraking. If we did not use aerobraking we would need even more propellant and a much larger launch vehicle to initiate the journey to Mars."

If the science team was content to stay in the original highly elliptical orbit in which the spacecraft was captured, that would be difficult enough, says Johnston. But the task will be even tougher for the Mars Reconnaissance Orbiter flight team because of the mission requirement for a low, circular orbit.

The actual execution of that task will be another story. But the initial parameters to accomplish it were foretold in a porkchop.