Suited for Spacewalking pdf - Virtual Astronaut

digital display on the chest-mounted control moduleis read. To assist in reading the display, anoptional Fresnel lens inside the space helmet maybe used to magnify the numbers. Some leakage ofspacesuit pressure is normal. The maximum allowablerate of leakage of the Shuttle EMU is 1.38kilopascals per minute, and this is checked beforethe suit is brought back down to air lock pressure.As the suit pre s s u re is elev a t e d ,c rew members maye x p e rience discom f o rt in their ears and sinus ca v i t i e s .T h ey compensate for the pre s s u re change by swall owin g, y a w n i n g, or pressing their noses on an option a ls p onge mounted to the left on the inside of the helmetri n g. Attempting to blow air through the nose whenp ressing the nose on the sponge forces air inside the earsand sinus cavities to equalize the pre s s u re .During the next several minutes the two spacesuitsare purged of any oxygen/nitrogen atmosphereremaining from the cabin;this is replaced with pureoxygen. Additional suit checks are made while thefinal oxygen prebreathe takes place.The inner door of the air lock is sealed,and theair lock pre s s u re bleed-down begins. A smalldepressurization valve in the air lock latch is openedto outside space, permitting the air lock atmosphereto escape. While this is taking place the EMU automaticallydrops its own pressure to 66.9 kilopascalsand leak checks are conducted. Failure of the leaktest would require repressurizing the air lock, permittingthe EVA crew to reexamine the seals oftheir suits.Final depressurization is begun by opening theair lock depressurization valve. The outer air lockhatch is then opened and the suited astronauts prepareto pull themselves out into the payload bay. Asa safety measure, they tether themselves to theorbiter to prevent floating away as they move fromplace to place by hand holds. It is at this point thatthey disconnect the orbiter Service and CoolingUmbilical from the EMU. The PLSS begins usingits own supply of oxygen, cooling water, and electricity.The astronauts pull themselves through theouter air lock hatch, and the EVA begins.The Primary and SecondaryLife-Support SystemsA s t ronauts experienced their first real fre e d omwhile wearing spacesuits during the Ap o ll oM o onwalk EVA s , b e cause of a portable life - s u p-p o rt system worn on their back s . A ll other EVA sup to that time were tied to the spacecra ft by theu m b i l i cal-tether line that supplied oxygen and keptc rew members from dri fting away. In one sense, t h etether was a leash, b e cause it limited move m e n t sa w ay from the spacecra ft to the length of the tether. On the Moon , h ow eve r, a s t ronauts were noth a m p e red by a tether and, in the later mission s ,w e re permitted to dri ve their lunar rovers up to 10k i l ometers away from the lander. (That distancelimit was imposed as a safe ty measure . It was determinedthat 10 kilometers was the maximum distancean astronaut could walk back to the lander ifa lunar rover ever broke dow n . )Space Shuttle astronauts have even gre a t e rf re e d om than the Ap o llo lunar astronauts beca u s etheir EVAs take place in the micro g ra v i ty env i ronmentof space. T h ey do employ tethers when EVA scenter in and about the Sh u t t l e’s payload bay, b u tthose tethers act on ly as safe ty lines and do notp rovide life support . Fu rt h e rm o re, the tethers ca nbe moved from one loca t i on to another on theo rbiter along a slide wire, p e rmitting even gre a t e rdistances to be cove re d .The fre e d om of movement afforded toShuttle astronauts on EVAs is due to the Pri m a ryL i fe - Su p p o rt System (PLSS) ca r ried on theirb a ck s . The PLSS, an advanced ve r s i on of theAp o llo sys t e m , p rovides life support , voice commun i ca t i on s , and biom e d i cal telemetry for EVA slasting as long as seven hours. Within its dimensi ons of 80 by 58.4 by 17.5 centimeters, the PLSSc ontains five major groups of com p onents for lifes u p p o rt . Those are the ox y g e n - ve n t i l a t i n g, c onde n s a t e, fe e d w a t e r, liquid tra n s p o rt , and pri m a ryoxygen circ u i t s .2 6 • Suited for Spacewalking An Activity Guide for Technology Education, Mathematics, and Science, EG- 1 9 9 8 - 0 3 - 1 1 2 - H Q