Problem Graphic

Delta 2 Rocket (US)

Mu-3SII Rocket (Japan)


The lead engineer on the new Starfinder rocket must determine the force in each member of the inter-stage truss structure. If the load is too high, the first-stage thrust will buckle the truss members.

What is known:

  • The base ring radius is 1 m.
  • The top ring radius is 0.75 m.
  • The base and top ring are 1 m apart.
  • The total thrust of the first-stage main engine is 2,400 kN (300 kN per joint).


Dimension Diagram


Space Shuttle (US)

What is the force in each of the truss members of the truss structure between the second- and third-stage rockets when the first-stage main engine is firing?


  • Sum all forces at a joint (method of joints).

         ΣF = 0

  • Find the 3D unit vectors for all forces at the joint. Find the unknown magnitudes of the member forces.
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