The Apollo lunar lander had just entered orbit at an altitude of 120 miles above the surface of the moon, when its computer decided to fail catastrophically. You take manual control of the capsule, and your job (as in most Lunar Lander games) is to land it safely on the surface. In this case, your only control is over the fuel burn rate, which determines the upward thrust necessary to counter gravity and to help the capsule land in one piece. Burn rate must be carefully adjusted in real time, while keeping an eye on current altitude, velocity, weight and remaining fuel. The physics are recalculated once per second, and the lander's final impact velocity determines your success: 1.2 MPH or less is a perfect landing; more than 60 MPH will blast a new lunar crater (and get you deservedly chewed out for killing the crew).