THE FEASIBILITY OF DOPPLER MONITORING DURING EVA

During extravehicular activities (EVA) outside the spacecraft, astrona uts have to work under reduced pressure in a space suit. This pressure reduction induces the risk of decompression sickness (DCS) by the for mation of gas bubbles from excess nitrogen dissolved in the organism b y breathing air at normal pressure. Under laboratory conditions the ga s bubbles moving in the blood stream can be detected by the non-invasi ve ultrasonic Doppler method. By early detection of excessive bubble f ormation the development of DCS symptoms may be prevented by early app lication of preventative measures. The method could also be useful whe n applied in the space suit in order to compare the results of laborat ory tests with operational results, because there is a discrepancy acc ording to the DCS risk of laboratory experiments and actual EVA missio ns, where no symptoms have been reported yet. A prototype Doppler sens or has been developed and implemented in the Russian Orlan suit. To in vestigate the feasibility of this method under simulated space conditi ons, the equipment has been used in a series of 12 thermovacuum chambe r tests with suited subjects, where intravenous bubble formation was c ompared to unsuited control experiments. In more than 50% of the suite d tests good Doppler recordings could be achieved. In some cases with unsatisfying results the signal could be improved by breathholding. Al though the results do not yet allow any conclusion about a possible di fference between suited and unsuited subjects due to the small number of tests performed, the method proved its feasibility for use in EVA s uits and should be further developed to enhance the safety of EVA proc edures.