In order to validate the experiments, scientists first had to overcome the task of accurately measuring mass in a microgravity environment. The Body Mass Measurement Device (BMMD) was designed to meet this objective. Since the instrument was a prototype, several functional objectives were outlined in addition to the primary objective of obtaining accurate body mass measurements of the crew. The objectives of the Body Mass Measurement experiments were (1) to demonstrate mass measurement without gravity, (2) to verify the operation of the BMMD, and (3) to support the nutrition and energy metabolism experiments.
The data from the 28 day Skylab 2 mission showed a consistent pattern of weight loss for each of the three crewmembers. Weight loss began with the initiation of the flight diet which was started 30 days preflight. The inflight loss pattern was characterized by a moderate decrease during the first few days of flight and an accelerated rate of loss during the remainder of the mission. Immediately postflight, there was a transient increase in weight followed by a plateau. Preflight and inflight weight loss amounts (lbs.) for the Commander, Pilot, and Scientist Pilot were 2.2, 3.6; 3.7, 8.3; and 2.7, 6.6, respectively. These data demonstrate a loss pattern that is consistent with a simple metabolic deficit.
Food intake and exercise were increased for the 59 day Skylab 3 mission and, therefore, a different pattern of weight loss was shown by these data. This pattern was characterized by a relatively stable preflight period during which only minimal weight loss was noted. The inflight data for the Commander and the Pilot show a sharp loss during the immediate inflight period and another loss near the end of the mission. The data for the Scientist Pilot also show a sharp immediate loss, however, a gradual loss was noted for the remainder of the mission. Upon recovery, all three crewmembers experienced an increase in weight followed by a plateau. Preflight and inflight weight losses (lbs.) for the Commander, Pilot, and Scientist Pilot were 1.8, 8.7; 1.4, 9.7; and 2.7, 8.2, respectively. The patterns observed on the Skylab 3 mission indicate that fluid shifts may be involved in body mass losses.
Further increases in food intake and exercise were implemented on the 84 day Skylab 4 mission and as a result, one crewmember, the Commander, did not show a loss in body mass. His data profile shows a preflight gain, a small initial inflight loss followed by a gradual increase, and a postflight gain. The other two crewmembers had loss patterns similar to the patterns observed for the Skylab 3 crew, however, the overall losses were smaller. The Commander had a preflight gain of 2 lbs. which stayed relatively constant throughout the mission. The preflight losses (lbs.) for the Scientist Pilot and the Pilot were 1.0 and 0.2, respectively. The Scientist Pilot and the Pilot had inflight losses of 3.0 lbs.