Flying the LM

Basic Flight

The LM while in powered descent is a cross between a helicopter and a spacecraft.  Of course a helicopter always has aerodynamic forces acting on it so it has some very different behaviors then the vacuum flying LM.

Pitch and Roll are the primary mechanism for guiding the LM.  Pitching or rolling causes the engine thrust to be 'vectored' away from the direction of pitch or roll.  If you want to fly left you roll left.  A component of the engine thrust will begin to propel you to the left.  In order to stop moving left you must roll into a right bank to vector the engine the other way.  The same goes for pitch.  If you are flying with automatic throttle the computer will automatically calculate the additional thrust necessary to maintain you desired descent rate. Remember, as you roll or pitch the 'component' of thrust in the vertical and horizontal directions will change.  This can lead to some interesting effects.  For example: If you suddenly command a high descent rate and simultaneously roll into a steep bank to move left you will notice that despite the roll (and corresponding high horizontal thrust vector) you are not accelerating to the left like you would think.  That is because while the 'component' of thrust in the horizontal direction is high, the magnitude is very low because the computer has decreased engine thrust to descend more rapidly.


As mentioned in the previous paragraph, the engine is primarily controlled by the computer.  All of the Apollo landings were done with automatic throttle.  The astronaut could 'toggle' a requested descent or ascent rate and the computer would honor it along with the corresponding thrust vectors associated with pitch and roll.  However, landings were practiced using manual throttle.  If you select this more challenging mode, you will get bonus points added to your score.

Landing Approach

Your goal is to pick a flat spot and arrive at zero horizontal velocity 100' directly overhead.  You can then descend at 3-4fps (with a little flare perhaps to 1-2fps before touchdown) keeping the horizontal rates nulled.  You can use the instruments to help you.  The two primary ones are the X-pointer at the top and the FDAI (Flight Director Attitude Indicator) ball.  Of course make sure you are on low scale for the X-pointer as you reach that 100' hover point.  As you descend there will be an increasing amount of dust so make sure you don't rely too much on outside references when you are really low.  Armstrong was a bit confused because of the moving dust and he danced the LM around a bit too much in the final seconds.

Note: F3 will show the original landing site.  It is marked on the ground with the outline of the LM.


Practice, practice, practice.  You will get it.