Suited for Spacewalking pdf - Virtual Astronaut

On the opposite side of the other steel plate is as e c ond chamber through which water from the liquidtra n s p o rt circuit passes. The liquid tra n s p o rt circuitis a closed-loop system that is connected to theplastic tubing of the LC VG . Water in this circ u i t ,d ri ven by a pump, a b s o rbs body heat. As the heatedwater passes to the heat exchanger and sublimator,heat is tra n s fe r red through the aluminum wall to thechamber with the porous wall .The ice formed in thep o res of that wall is sublimated by the heat dire c t lyinto gas, p e rmitting it to tra vel through the pore sinto space. In this manner, water in the tra n s p o rtc i rcuit is cooled and re t u rned to the LC VG . T h ecooling rate of the sublimator is determined by thew o rkload of the astron a u t . With a greater work l o a d ,m o re heat is released into the water loop, causing iceto be sublimated more ra p i dly and more heat to beeliminated by the sys t e m .The last group of components in the PrimaryLife-Support System is the primary oxygen circuit.Its two tanks contain a total of 0.54 kilograms ofoxygen at a pressure of 5,860.5 kilopascals, enoughfor a normal seven-hour EVA. The oxygen of thiscircuit is used for suit pressurization and breathing.Two regulators in the circuit step the pressure downto usable levels of 103.4 kilopascals and 29.6 kilopa s ca l s . Oxygen coming from the 103.4-kilopascalregulator pre s s u ri zes the water tanks, and ox y-gen from the 29.6-kilopascal regulator goes to theventilating circ u i t .To insure the safe ty of astronauts on EVA s , aSe c on d a ry Oxygen Pa ck (SOP) is added to the bottom of the PLSS. The two small tanks in this sys t e mc ontain 1.2 kilograms of oxygen at a pre s s u re of41,368.5 kilopasca l s . The Se c on d a ry Oxygen Pa ckcan be used in an open-loop mode by activating apurge valve or as a backup supply should the pri m a rys ystem fall to 23.79 kilopasca l s .The supply autom a t-i ca lly comes on line whenever the oxygen pre s s u reinside the suit drops to less than 23.79 kilopasca l s .If the Displays and Control Module (DCM)purge valve (discussed below) is opened, used-oxygencontaminants and collected moisture dumpdirectly out of the suit into space.Because oxygen isnot conserved and recycled in this mode, the largequantity of oxygen contained in the SOP is consumedin only 30 minutes.This half-hour still givesthe crew member enough time to return to theo rb i t e r’s airl o ck . If ca rb on dioxide con t rol isrequired, the helmet purge valve may be openedinstead of the DCM purge valve. That valve has alower flow rate than the DCM valve.Displays and Control ModuleThe PLSS is mounted directly on the back ofthe Hard Upper Torso, and the controls to run it aremounted on the front. A small, irregularly-shapedbox, the Displays and Control Module (DCM),houses a variety of switches, valves, and displays.Along the DCM top are four switches for power,feedwater, communications mode selection, andcaution and warning. A suit-pressure purge valveprojects from the top at the left. It is used fordepressurizing the suit at the end of an EVA andcan be used in an emergency to remove heat andSuited for Spacewalking An Activity Guide for Technology Education, Mathematics, and Science, EG-1998-03-112-HQ • 2 9