Apollo 13 Propulsion Activity

Jerry Woodfill - Apollo13 Warning System Engineer

Testimony:  After the explosion, there was concern over which engine should be used to speed the trip back to Earth,  the lander’s small descent engine at the lower left (the DPS or Descent Propulsion System) or the command ship’s much more powerful service module propulsion system (SPS)  at the right.  The larger  SPS was  designed to put Apollo 13 in lunar orbit and rocket Apollo 13 back to Earth.   The activity below deals with this facet of the rescue.

1.      Print the  picture below and have  the  children color  their copy.  Let them see a color picture of Apollo 13 with the NASA logo and American flag to copy.  

2.      Have the children cut out their  picture.

3.      Paste the picture  of Apollo 13 length-wise on a lunch sack.  After threading the string through a straw as pictured below, tape the straw length-wise along the top of the lunch sack as pictured below and parallel to  their picture of Apollo 13

4.      Place a balloon in the lunch sack.  Have one child  paste his picture with the lunar lander’s engine pointed toward the open end.  Have another child point the service module’s engine toward the sack’s open end. One represents the SPS, the other the DPS.  Blow the SPS balloon up much more than the DPS balloon corresponding to the much larger thrust of the SPS than the DPS.  

5.      Assign  four children to holding  the four ends of two 10 foot long strings.  Assign each child as a moon holder or Earth holder.  Explain that the 10 feet represents 240,000 miles between the Earth and the Moon. 

6.      After blowing up each balloon, use a paper clip holder (or clothes pin clip) to keep air from escaping from the balloon as pictured below. 

7.      The string's direction and position controls the trajectory and linear orbit of the Apollo 13 craft between the make believe Earth and Moon. (Round pieces of cardboard with photo-copies of the Earth and Moon pasted on them could be used to anchor the ends of the string by threading the string through a center hole in both the Earth and Moon cardboards. Have students hold the ends of the string which was threaded through the Earth and the Moon.)

8.      To “blast off” quickly release the clip on the SPS sack first.  Watch the speed and distance the Apollo 13 lunch sack  ship goes.   Do the same with the Apollo 13 sack propelled by the lunar lander’s engine.  Compare the speeds. 

9.      Repeat the process after blowing up the SPS balloon especially hard.   Explain that this would be to speed the journey back to Earth before the crew ran out of oxygen, water, and electrical power.  Attached the clip to the balloon nozzel.   Have the clip jaws closed with your fingers on the release metal tabs.  Conceal in your other hand a pin.  Have the children count down from ten to similate NASA’ countdown clock.  At the count of zero, prick the balloon with the pin so that it explodes.  Explain to the children that this might have been the case because the SPS might have been damaged by the oxygen tank explosion.  The wiser and safer decision was to use the lander’s engine. This made the trip back to Earth slower but safer.

Materials:

drinking straw, string (kite string), balloon  (long rather than round), tape, 2 chairs  (or students), paper lunch sack, scissor, paper holder clip, crayons


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