Weightless, but Not Without Mass

NASA Mission Specialist Ryan Stone—unnerved, immobile, gasping for oxygen—spins in the zero gravity, her suit and accessories weightlessly bumping against the walls of the International Space Station.

In this instantly-iconic scene from blockbuster film Gravity, the audience is given a rare moment of respite to take in the film's infamous authenticity: velcroed scissor handles, tethered clipboards, netted toolboxes. And there's an equally-accurate absence: No microgravity scale that can mass objects between one and five kilograms.

Undergraduate engineering students in the Mechanical Design class are the first to create such a scale, with the ultimate goal of pitching their product to NASA for use on future space missions.

But building and testing a scale designed for zero gravity without actually sending it into space—that's tough. "This challenge appeals to the whole team," team member Matt O'Donoghue ('14) points out, "and we have had fun tackling it."

The scales most people have at home rely on the earth's gravitational constant to determine weight and ultimately calculate mass. In space, where the effect of gravity is far diminished, the students' scale will instead use a stepper motor to oscillate the desired object side to side, then measure the required force and resulting acceleration—an elegant use of the Newtonian laws students learn in elementary physics.

In that regard, the class is a culmination of the team's engineering studies. "It has combined electronics with programming and machining, giving us a hands-on feel for the design process," O'Donoghue says. "When we turned the motor on for our prototype and we saw [the scale] move for the first time, it was a huge reward for the time we had put in."

A reward that will propel them to the end of the semester—and beyond.