Small mass measurement instrument for measuring weight under weightless conditions

A small mass measurement instrument (SMMI), developed for NASA experiments conducted in the near zero environment is described. The SMMI is based on the principle of an oscillating spring-mass system, for which a period of oscillation is a function of the system's mass. It has the capacity of weighing specimens in the weight range of below 1 g to over 10,000 g, with an accuracy of 0.05 percent. The instrument has a keyboard, liquid crystal display, and microprocessor, which provide capabilities for entering and deleting data, display of messages, prompts, and specimen weight values, memory, and self-calibration features. The SMMI is scheduled for use beginning with Spacelab 4. Included in the description are the SMMI block diagram, detailed descriptions of the principles involved in the construction of the assemblies of the instrument, and photographs of its various parts.