robison@rocke.electro.swri.edu (Bob Robison) (06/17/91)
In article <1991Jun14.174759.9041@pmafire.inel.gov> alan@pmafire.inel.gov (Alan Herbst) writes: >>How are body mass measurements made aboard the shuttle in the weight- >>lessness of space? Is it the mirco-gravity at 180 miles up? >> >A good answer was received from: > >-- Ken Jenks, NASA/JSC/GM2, Space Shuttle Program Office > <kjenks@gothamcity.jsc.nasa.gov> >"There are various devices used, including spring-based mechanisms which >"bounce" the crew member off a spring and calculate body mass through >f=ma, a "shaker" mechanism which moved crew members around and >calculated their mass by measuring inertia, and several others. I once >took a class from Dr. Thornton, a former astronaut (STS-51C) and >researcher of human physiology in space. Fascinating stuff. The main >problem with all zero-G mass measurement systems for humans has been >that people are flexible and mostly fluid. When measuring a flexible, >fluid-filled body by bouncing or shaking, that body tends to wiggle and >slosh, which throws off the mass measurements." > Sorry I'm lating responding to this -- I was out last week and am just now reading my news... Southwest Research Institute designed and built the Body Mass Measurement Device (BMMD) and the Small Mass Measuring Instrument (SMMI) that were aboard the Columbia on this past mission. Both of these devices work by supporting the mass to be measured on stiff springs. The mass is then deflected to one side and released which causes the mass to oscillate as the springs deflect one way and then the other (This is a side to side type of motion). The period of oscillation is measured very accurately and the mass is calculated from that period. As mentioned in the above post, the "sloshing" of one's internal organs is one of the problems with getting accurate measurements. On the BMMD, the subject sits in the device in a sort of "cannonball" position with knees pulled up close to the chest and is asked to tighten his/her muscles during the measurement. This minimizes the "sloshing" and provides better mass measurements. One thing I found interesting when we were researching how the Soviets did this, is that their version of the BMMD looked like a column with a plunger in it that moved up and down. The subject bent over the column with the (presumably) padded plunger pressed up against the subjects abdomen. The plunger then oscillated up and down -- doesn't sound like a fun way to be 'weighed' to me. BTW, the SMMI is used to measure masses in the range of about 1 gram to 1 kilogram, and is used for measuring chemicals, rodents, etc. The earlier version of the SMMI was called the SMMD. Both the SMMD and the BMMD were aboard SKYLAB. The SMMD required a connection to a TI calculator that ran the mass calculation. The SMMI is more automated and uses a built in computer to do the calculation and drive a dedicated display. This was the first flight for the SMMI, which I first worked on in 1979. Yes, it uses a state-of-the-art 6502 processor! Well, didn't mean to carry on so much -- but that is the background. And Dr. Thornton worked very closely with SwRI on the development of these mass measurement techniques. I believe work began on that in the late 60's. bob -- Bob Robison - Southwest Research Institute, Electromagnetics Div. brobison@swri.edu {sun!texsun, gatech!petro, uunet!cs.utexas.edu}!swrinde!dfsun1!robison