Lunar Lander

Landing on the Moon

The Eagle, the Apollo 11 Lunar module, just after undocking from the Lunar Orbiter.
Photo courtesy of NASA. This and other photos from the Apollo 11
mission can be found at:
http://history/nasa.gov/ap11ann/kippsphotos/apollo.html

One of the most exciting achievements of the space program was landing a person on the moon--the first time that a human set foot on an object in the universe other than the earth. This occured on July 20, 1969, when Buzz Aldrin piloted the Apollo 11 Lunar Lander module, called the Eagle, to a safe landing on the moon.

Many technological feats had to be accomplished to do this. Among these was designing a module that could be landed safely on the surface of the moon, which has no atmosphere. The lack of an atmosphere means that the landing module could not use wings to fly in to a landing, or a parachute to let it dow gently. The only choice is to use rocket engines with just enough thrust to decelerate the velocity of the landing module to zero just as it reaches the surface of the moon.

This page is an interdisciplinary learning module created by geologists, chemists, physicists, and mathematicians. The module will help students and teachers learn more about kinematics and dynamics by using different tools and methods of these disciplines.

Buzz Aldrin, pilot of the Apollo 11 Lunar Lander
Photo courtesy of NASA

You are piloting a Lunar landing module approaching the surface of the moon at a speed of 1000 m/s. You are currently 50,000 meters above the surface of the moon, and have received a message from command control that it is time to turn on the thrusters that will slow your descent to the surface. The mass of your landing module is 20,000 kg. It is your task to determine the proper thrust such that the speed of the landing module will be zero when it reaches the surface of the moon.
Your Handbook for Lunar Pilots contains the information that the acceleration of gravity on the moon is 1.633m/s², and several kinematic equations:

Calculate the required value for the thrust, and enter in to the text box on the right. Then click on the button to initiate the landing sequence.

Enter the thrust, in Newtons:

This interactive problem makes use of the
Physlet Animator4. This and other
Physlets can be found at
webphysics.davidson.edu

Earthrise
The earth seen rising above the horizon
from the Eagle as it approached the surface of the moon on July 20, 1969.
Photo courtesy of NASA

Recommendation for Instructors

This module could be used in either of two ways. Either way would lend itself to student working in pairs, and discussing how to approach the problem with each other.

1. Students can use the animation to find the right amount of thrust by trial and error. I have built enough tolerance into the program so that students will not have to be too exact in the answer. Once the students have found the correct thrus, they should be asked to compare it with the weight of the lander on the moon (why the weight on the moon?). Is the thrust larger or smaller than this weight. Then have the students write out an explanation, which will need to take into account the correct direction of the acceleration of the lander as it is slowing down.

2. Students can be asked to determine the correct thrust, using the kinematic formulas and Newton's Second Law (recognizing that there are two forces acting on the lander). They can then check their calculations using the animation.

Another use of the animation is to illustrates the deceleration of the lander. Let the students watch the animation witrh the correct value for the thrust, and stop the animation when the lander is about half way down--ask the students if they think the lander will crash. The lander is still going pretty fast at that point, much faster than half the initial velocity.

Links for educators and others.

© 2003 The NASA/UNCF Project at Northeastern Illinois University. Last updated December 16, 2003.
Participating departments: Chemistry Earth Science Mathematics Physics