Aerospace Engineering on the Back of an Envelope

Engineers need to acquire “Back-of-the-Envelope” survival skills to obtain rough quantitative answers to real-world problems, particularly when working on projects with enormous complexity and very limited resources.

In this talk, the principals for developing first-cut solutions to difficult engineering problems are presented. Initial engineering estimates are carried out using both a “Quick-Fire” Back-of-the-Envelope technique and a more detailed, but still approximate, physics-based engineering modeling approach. These methods have been utilized to obtain quantitative estimates for key geometric, performance, and design dimensions associated with two very important engineering projects: the Space Shuttle and the Hubble Space Telescope.

For this presentation, our case study is the Columbia Space Shuttle accident. Back-of-the-Envelope techniques are used to model the impact of a piece of foam, separated from the Shuttle external fuel tank, with the Orbiter wing. Back-of-the-Envelope engineering criteria are developed to assess potential damage to the wing based on estimates of the collision velocity, impact angle, and the maximum impact stress.