Mass Properties Engineering

Mass Properties Engineers do pretty much what the job title implies -- they estimate how much the sundry parts of a spacecraft will weigh and add up the numbers. This requires having an intimate knowledge of spacecraft manufacturing techniques as well as the types of materials used and the properties of each material. It's a little bit science, a little bit geometry, and a lot of statistical analysis.

It's a little bit science, a little bit geometry, and a lot of statistical analysis.

Mass Properties Engineers also calculate the sundry moments of inertia and location of the center of gravity of the spacecraft. That's important for controlling the spacecraft and writing the software that controls the maneuvering rockets.

For instance, suppose Daniel Designer wants to design a liquid oxygen tank that will be used to refuel a translunar passenger ship. Based on the mission, initial estimates of the mass Daniel can calculate the volume of the tank. Armed with that information, he goes to Mary Massprop, who can look up previous detailed analyses of LOX tanks, estimate the mass of the support structure and bracketry required, estimate the mass of the insulation and meteoroid protection, calculate the moments of inertia and center of mass of the tank system and then fit those numbers into the same calculations for the vehicle as a whole. Daniel and Mary will feed their data to Sam Structures, who runs a detailed analysis of the structural performance of the system based on the structural loads and vibration environment.

Now Daniel has some more accurate numbers to fit into his equations for the overall configuration. He plugs in the numbers and the whole cycle iterates. If the initial estimates are close the mark, then it won't take too many iterations to close in on a point design. If the initial estimates are way off, it will take longer, or the spacecraft design might even diverge so that there's no solution. (I've seen this divergence happen in both aircraft and spacecraft design. When that happens, we figure out what's causing the divergence and change the basic design to fix the problem. It's all part of engineering.)

. . . the body of knowledge required to perform well in all engineering disciplines exceeds the capacity of a single human mind.

You might be wondering why Daniel Designer couldn't just do his own Mass Properties engineering, and everything else. For conceptual design, he probably can; however when you get to final design, the body of knowledge required to perform well in all engineering disciplines exceeds the capacity of a single human mind. Daniel would spend all this time keeping up and learning, leaving no time to actually design something, and still he would never be able to get his arms around all the disciplines.

Alternatively, we might try programming all the mass properties knowledge into a big data base, and write computer programs to do all the analysis. Of course we do these things, but without Mary Massprop's human presence in the process, we have no route to new innovation and no way to cope with continuing research in material science.

Human innovation in engineering makes progress. We might be thankful that the colleagues of the Wright Brothers did not have computers to design all those early airplanes. If they had, today we might be building ever-more-elegant airplanes from wood and canvas, and spacecraft would still be a mad dream.