NASA's extended duration orbiter medical program
The physiological issues involved in safely extending Shuttle flights from 10 to 16 days have been viewed by some as academic. After all, they reasoned, humans already have lived and worked in space for periods exceeding even 28 days in the United States Skylab Program and onboard the Russian space stations. The difference in the Shuttle program is in the physical position of the astronauts as they reenter the Earth's atmosphere. Crewmembers in the earlier Apollo, Skylab, and Russian programs were returned to Earth in the supine position. Space Shuttle crewmembers, in contrast, are seated upright during reentry and landing; reexperiencing the Earth's g forces in this position has far more pronounced effects on the crewmember's physiological functions. The goal of the Extended Duration Orbiter (EDO) Medical Project (EDOMP) has been to ensure that crewmembers maintain physiological reserves sufficient to perform entry, landing, and egress safely. Early in the Shuttle Program, it became clear that physiological deconditioning during space flight could produce significant symptoms upon return to Earth. The signs and symptoms observed during the entry, landing, and egress after Shuttle missions have included very high heart rates and low blood pressures upon standing. Dizziness, 'graying out,' and fainting have occurred on ambulation or shortly thereafter. Other symptoms at landing have included headache, light-headedness, nausea and vomitting, leg cramping, inability to stand for several minutes after wheel-stop, and unsteadiness of gait.