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Biological Effects of Simulated Micrometeoroid Penetration of a Sealed Chamber Containing Animal Specimens

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Biological Effects of Simulated Micrometeoroid Penetration of a Sealed Chamber Containing Animal Specimens Biological Effects of Simulated Micrometeoroid Penetration of a Sealed Chamber Containing Animal Specimens CHARLES F. GELL, M.D., D.Sc., ALLEN B. THOMPSON, M.S.A.E. and VERNE STEMBRIDCEr M.D. CHANCE Vought Cortx~ation, in its in- density has varied from 0.05 grams/cubic cen- house research, has been firing aluminum pel- timeter dust balls to 8.00 grams/cubic centimeter lets at hypervelocities into a small chamber nickel-iron fragments.3. 5 It is probably safe to containing rat specimens. This Chamber was assume that the average frequency of occurrence located inside a large vacuum tank and the lies somewhere between these values--probably projectiles fired through a vacuum attained approximately 1000 tons per day. Likewise, velocities of "~3,000 fps or approximately 17,000 it has been accepted practice by several in- mph. Evidence of oxidative explosion within vestigators to separate space debris into two the chamber was secured by photography. Ani- categories--the stony and ferrous type mete- mal experiments demonstrated the pathological orites varying in density from 2.8 grams/cubic effect of these explosions on incarcerated rats centimeter to 8.0 grams/cubic centimeter and as ranging from mild to lethal, depending on the dust particle masses of cometary origin certain physical factors and the internal en- having a density of approximately 0.05 to 0.3 vironment of the animal chamber. grams/cubic centimeter.Z,s, ~ Meteoritic debris is generally concentrated in the plane of the REVIEW OF THE LITERATURE ecliptic in the form of streams along the orbits Extraterrestrial material in space poses a of comets and within the belt of the asteroids. 5 potential hazard to .the crews of space vehicles, In the near vicinity of the earth, satellite particularly on long voyages where the proba- sampling results have indicated millions of bility of receiving a damaging metem'ite hit is micrometeorites of up to pinhead size, in earth enhanced by the long flight time. There is more orbits from 100 miles altitude to several thou- individual energy in meteoroids than any other sand miles. These particles probably have a type of incident space radiation. Due to their density of approximately 2.8 grams/cubic centi- relatively low velocity (11 to 72 km/sec) as meter, that of stone when taken individually~. compared to high energy corpuscular radiation, They are trapped by the gravitation field into meteoroid~ penetrate only a small distance on elongated orbits about the earth, eventually impact and release all their energy in this dis- burning up in the atmosphere only to be replac- ed by other incoming particles. tance. TM Hence the immediate direct effects are much greater than those of cosmic radiation. Of interest, from the standpoint of manned The estimated frequency of occurrence of space travel, are the frequency of occurrence micrometeorites and meteorites entering the and the probability of penetra.tion of the vehicle earth's atmosphere has varied from 10 tons to on impact with this debris, the effects of pene- I million tons per day 3,~ and estimates of their tration into pressurized crew compartmentsr and methods of protection from meteoroid damage. From Vought Astronautics and Southwestern Medical Based on calculated data by Thompson, using School of the University of Texas, Dallas, Texas. Whipple's distribution and Bjork's penetration Presented at the Aerospace Medical Association meeting in Chicago, Illinois, April 26, 1961. relationship, it has been estimated that an aver- 156 AIM~OSPACB MEDICINE MICROMETEOROID PENETRATION--GELL ET AL age size space vehicle of 1000 square meter sur- may determine compartment size and the need face area will be penetrated once in 24 hours if for compartmentation due to rate of decom- it has a .070-inch thick aluminum skin, and pression considerations. Fig. 1. Hypervelocity impact test facility for simulated meteoroid penetration investigations. once in 120 hours if its skin is 0.1-inch thick. METHOD AND RESULTS. Clearly, the meteoroid risk must be considered To determine the more unique effects of for orbiting manned space stations or vehicles hypervelocity impact into pressurized crew enroute to the moon or planets. compartments, a series of tests were conducted As penetration of the space vehicle by by Vought Astronautics in a hypervelocity test meteoroids is a distinct possibility, it is of prime facility shown in Figure 1. By means of a importance to assess the effect of hypervelocity special shaped double-density explosive charge, impact into pressurized compartments contain- particles were accelerated to hypervelocities in ing various gas mixtures simulating crew area a vacumrt and impacted into a number of small atmospheres. Undoubtedly, there will be decom- vessels containing various atmospheric mixtures. pression, the rate of which will be dependent The penetration wall used was .070-inch thick upon the hole size and internal pressure. In aluminum and the impacting particles were 2S some designs, the hole size vs. cabin volume aluminum, varying in diameter from around 10 FEBRUARY, 1962 157 MICROMETEOROID PENETRATION--GELL ET AL microns to approximately 2 millimeters. Veloci- the pressures propose& for typical space vehicle ties obtained were in the order of 8 km/sec. systems. The peak flash intensity varies from for the larger particles and 20 km/sec, for the a low of about 3 million lumens for a standard very small particles. atmospheric composition at sea level pressure Fig. 2. Oxidative flash occurring in test cell from hypervelocity pellet penetra- tion.--(a) Sea level atmosphere. (,b) 1/'a atmospheric pressure with sea level pp Oz. (c) 1/3 atmospheric pressure with 100 per cent 02. (d) 100 per cent O~ with animal specimen. (All exposures through approximately 0.1 per cent trans- missibility filter). When the particles with their very high to approximately 20 million lumens for a pure kinetic energy strike the target surface, the oxygen atmosphere at 5 psia. As a comparison, impact produces a very high heat which melts a standard General Electric Number 5 flashbulb and/or vaporizes the impacting particle and a reaches a peak intensity of only 1.2 million significantly large volume of the target ma- lumens. Temperature measurements taken in terial producing craters or holes. free air at a distance of 1 inch from the flash If the crater is deep enough to completely indicate temperatures in excess of 1500 .0 F. penetrate the vehicle wall, the remains of the The results of the foregoing experiments particle and melted or vaporized target material demonstrated a potentially dangerous situation enter the atmosphere, anda very rapid, almost to man in space should his space craft be explosive~ oxidation occurs. An intense flash of penetrated by a meteoroid and an oxidative light is evidenced for a period of .8 to t.2 explosion occur. Generally, it has been assumed milliseconds. Open shutter photographs ~were that small meteoroid punctures in a space ship taken of the flash in the test chamber through would be accompanied by relatively slow leak- an aluminum coated Mylar filter having a trans- age. It was presumed that the crewz protected missibility of approximately 0.1 per cent. Figure by full pressure suits could conduct damage 2 (a, b, and c) shows the flash occurring in control and repair the damage. The possibility various atmospheres of oxygen and nitrogen at of intense heat, light and blast introduced a 158 AEROSPACE Mlal)ICINE MICROMETEOROID PENETRATION--GELL ET AL dire possibility. In view of the above informa- involved second and third degree burns of the tion, it was considered highly desirable to con- skin and extensive lung damage. duct some animal studies to assess this danger. A series of tests were conducted wherein single, DISCUSSION 300 gram white rats were placed inside the The significance of these experiments indicate chamber and exposed to the oxidative explosion the necessity for further study in the effects of following penetration by the ultra-high velocity oxidative explosion relative to potential pene- Fig. B. Various minor injuries sustained by specimen due to hypervelocity pellet penetration of test cell wall. (a), (b), (c) Shrapnel damage to bead, tail and leg from spalled wall and pellet materials. (d) Blast damage to back. pellet. Six rats were thus exposed. Figure 2-d trafion of space vehicles by meteoroids. If man shows a rat in the chamber at the time of the is to have a fair modicum of safety in space explosion due to penetration. In the first five flight, we must understand fully the factors that rat tests~ the atmosphere in the chamber was promote the internal explosion accompanying of near normal atmospheric pressure and com- the oxidative effect and attempt to alter them position. All of these rats demonstrated hair in his favor. Under sea level atmospheric con- and skin burns of varying degrees and extent ditions, the animals survived the flash and heat ('Fig. 3--a, b, c, and d). Minor injuries were of the explosion, but suffered various superficial demonstrated and in most cases subjective sym- injuries, burns, and possible diminution in visual ptoms of shock were present. In two cases, acuity. They also demonstrated evidence of there were fractured backs with total paralysis shock and had they been human, their per- of the lower extremities. None of these animals formance capabilities undoubtedly would have succumbed in the test, but postmortem studies been severely reduced during and for an un- were made. In the final test, a rat was exposed determined time after the exposure. At the to oxidative explosion in 100 per cent oxygen. other extreme, with 100 per cent oxygen at The result was catastrophic with instant death sea level pressure, the animal died instantly to the rat (Fig.-4---a, b, c, and d).
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