The Zero Gravity Mass Measurement Device

The Zero Gravity Mass Measurement Device (ZGMMD) provides the ability to quantify the mass of objects, including live animal specimens, in a microgravity environment. There are currently no mass measurement devices available on the International Space Station (ISS) that can accurately measure objects with a relatively low mass. The fundamental principle behind the ZGMMD is Newton’s second law, which states that the acceleration of an object is proportional to the resultant force acting on it and inversely proportional to its mass. With the assumption that mass does not change with respect to time (which is reasonable when considering the timeframe in which measurement of the mass is occurring) by utilizing Newton’s second law, the mass of an object can be derived by quantifying both the acceleration and the forces acting upon it (m = F/a). In the ZGMMD the mass (m) is derived from the force (F) measured by load cells, and the acceleration (a), which is a known entity exerted by an actuator. The ZGMMD Phase I prototype was used to investigate measurement accuracy and precision and to demonstrate the basic feasibility of using mass acceleration to determine the mass of samples less than 1kg. Prototype testing demonstrated that a range of masses from a few grams to 1kg could be readily determined with acceptable accuracy and precision. The initial ZGMMD prototype demonstrated the ability to provide an accuracy of +/- 0.1 grams for masses less than 20 grams and 1.0% of sample mass for masses greater than 20 grams, and a repeatability of +/ 0.1 grams. The prototype was also used to test specimen mounting and ease of use. Results from Phase I testing are being used to further improve accuracy and precision in addition to refining a flight compatible design.