21.   Starting in a week, the spacecraft will use the upper fringes of the Martian atmosphere to lower and circularize its orbit through a technique called aerobraking.

22.   Surrounded by a clamshell-shaped protective cover of high-tech plastic, Pathfinder is to pierce the thin Martian atmosphere.

23.   The automated production plant would combine its stored hydrogen with the carbon dioxide that laces the Martian atmosphere.

24.   The braking is to be accomplished by friction of the protective heatshield against the Martian atmosphere.

25.   The looping elliptical orbits will expose the spacecraft to the drag of the Martian atmosphere.

26.   The lander was engineered to make a direct, high velocity descent into the Martian atmosphere.

27.   The landing will be slowed in the thin Martian atmosphere by a heat shield, a parachute and retro-firing jets.

28.   The Martian atmosphere is thin, as Lowell had guessed, but not calm.

29.   The microprobes were designed to separate several minutes before the Polar Lander begins its plunge into the Martian atmosphere.

30.   The low point will dip the spacecraft into the thin Martian atmosphere.