The bone loss associated with extended space missions in astronaut represents a serious health threat, both over the flight period and upon returning to gravitational fields. Continuously monitoring bone qualities during prolonged space missions will lead to a better understanding of the progressive adaptation of bone loss in astronauts subject to both microgravity and aging, and the ensuing musculoskeletal complications such as osteoporosis. In this proposal, Boston Applied Technologies Incorporated (BATi), collaborated with University of Florida, proposes a portable and noninvasive ultrasound measurement apparatus for rapid assessment of human bone densities. With our unique approach and algorithm, the proposed device will have greater measurement accuracy and sensitivity than those of other noninvasive techniques. In addition, the self-calibration feature of the instrument will assure the diagnostic methodology to be accurate, fast, and simple.