How Do Astronauts Weigh Themselves In Space?
How Do Astronauts Weigh Themselves In Space?
Many of us take for granted the morning ritual of stepping on the scales after a shower, still wet, to assess the damage caused by indulging in Aunt Leslie's pecan pie during a late-night snack. After grimacing, we start the day.
However, for astronauts floating high above Earth, determining whether last night's meal of thermostabilized turkey and freeze-dried cornbread dressing has caused a bit of a belly is far from simple. The first obstacle is that their weight in the microgravity of space is essentially zero all the time. Nevertheless, astronauts still have mass, which they can measure to determine their weight on Earth and allow medical researchers to track changes in body mass due to deconditioning in orbit.
At present, crew members aboard the space station utilize two instruments to determine their weight. The first is NASA's Space Linear Acceleration Mass Measurement Device (SLAMMD), which employs Newton's Second Law of Motion. As explained by astronauts Michael Barrett and Koichi Wakata in a video, the astronaut experiences a force generated by two springs mounted on an extension arm. Since the force is a known quantity, the resulting acceleration (remember F=ma?) is used to determine the crew member's mass. The SLAMMD is precise to 0.5 pounds.
The other device is Russia's Body Mass Measurement Device (BMMD), as demonstrated by Reid Wiseman in a Vine he posted last October. The astronaut bounces on the BMMD like a pogo stick, and the spring oscillation measures mass.
While both devices work, they consume a lot of power, a scarce resource on the already confined space station. This has led a group of European researchers to suggest a weight-measuring system based on Kinect technology familiar to gamers. The name "Kinect" refers to a type of motion-sensing input device, not only a platform for clumsy dancing to One Direction songs on "Just Dance 4" after a few too many adult beverages. The Kinect system uses camera inputs to construct a 3D model of the astronaut, which is then matched against a statistical model of almost 30,000 people to predict the astronaut's weight. The proposed device is small, lightweight, and energy-efficient, with 97% accuracy.
The Kinect system would estimate body volume, distinct from SLAMMD and BMMD, which measure mass. One potential issue is the displacement of water inside an astronaut's body in microgravity, which may influence the precision of the measurements. Paolo Ariano, a researcher at the Fondazione Istituto Italiano di Tecnologia's Center for Space/Human Robotics, says the team is working on a new prototype of their Kinect-based device and seeking additional funding to conduct space trials.
