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Roller Coaster to Mars

"The porkchop plots for the 2005 Mars opportunity show that for our launch vehicles, this is one of the most challenging opportunities to get to Mars in this decade," says Johnston. The interplanetary doorway to Mars open at that time requires the spacecraft to be delivered to a spot above Earth's higher latitudes. This high-latitudinal orbit requires more launch energy - a bigger rocket - than most launches.

In terms of physics, the price paid for poising a spacecraft at that jumping-off point can be compared to that paid for a bigger, steeper roller coaster ride, says Johnston: "The cars have to be pulled up a longer hill to get to the highest point before the roller coaster's first plunge," he says. "In effect, we need a steeper plunge to get onto our flight path in 2005. We've got to push ourselves up higher to get onto the Mars trajectory for this opportunity."

Nearly half the Reconnaissance Orbiter's entire 1,800 kilogram mass (3,968 pounds) is propellant that will be used to brake the spacecraft's speed when it reaches Mars, allowing it to be captured into orbit. The spacecraft also carries a heftier science package with about twice the mass of the instruments carried by its recent predecessors. All these factors mean that a rocket the size of an Atlas 3 or a Delta 3 will be required to send the Reconnaissance Orbiter on its way. (By comparison, its sibling spacecraft Mars Odyssey, at about half the mass, was lofted on its voyage by a Delta 2.)

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Porkchop Plot
    "Porkchop" is the First Menu Item on a Trip to Mars
    The Revolving Door to Mars
    Roller Coaster to Mars
    Save Your Baggage Allowance for Science
    Extreme Parallel Parking

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