The pedagogical aim of the present paper, thought for an undergraduate audience, is to help students
to appreciate how the development of elementary models based on physics first principles is a
fundamental and necessary preliminary step for the behaviour of complex real systems to be grasped
with minimal amounts of math. In some particularly fortunate cases, such models also show reasonably
good results when are compared to reality. The speed behaviour of the Space Shuttle during its first
two minutes of flight from liftoff is here analysed from such a didactical point of view. Only the
momentum conservation law is employed to develop the model, which is eventually applied to
quantitatively interpret the telemetry of the 2011 last launches of Shuttle Discovery and Shuttle
Endeavour .