Using NASA and the Space Program to Help High School and college Students Learn Chemistry Part 1. The Shuttle and Our Living Earth Paul 6. KeRer University of Wisconsin-Oshkosh. Oshkosh. WI 54901 William E. Snyder Poland Seminary High School, Poland, OH 44514 Constance S. Buchar Mail Stop 6-1, NASAlLewis Research Center, Cleveland, OH 44135
In this age of rapidly changing video images, MTV, and fast-moving commercials, both the high school and college educator, as never before, require tools that capture attention. instill curiositv. arouse auestiouine. and eenerate new challenges for studeits. ~ e a c h e r swh;have incorporated ideas from NASA and the mace nroeram into their chemistry lessons have noted that studenis enjoy learning about material reaardina, for example, the chemistrv of the space shuttle. ~ i & s i o n of the prop&ion system &I the s h k t l e not onlv raises technical auestions but also, if the discussion is propkr~ydirected, ties chemistry to many social and economic issues. We will show, for example, how the reactions that describe the comhustion of the shuttle's solid rocket fuel teach students about stoichiometrv. thermodvnamics. and acid-base chemistry and force them-to address host ofenvironmental concerns. It should be uointed out that there are excellent classroom reference materials which deal with the relatiouship between science and society (1-4). In this two-part article we discuss some of the chemical concepts that the space program illustrates which can be used to excite high school and college students to learn chemistry and its relationship to our world. I t is not feasible to cover every possible topic in detail in such a limited space; however, we have added additional areas of investigation a t the end of each section. If more detailed information about the subject of a section is desired, the references in that section will nrovide excellent information. We also outline ways of gett;ug handouts, books, slides, speakers, and other information from the appropriate NASA educational office.
a
Areas of Interest It is important to understand that virtually every single area of chemistry relates to the aeronautics and space research that NASA does. However, it is possible to classify NASA's work into six areas that should relate well to most chemistry curricula. The areas are
Enuironmental Chemistry: We analyze the shuttle's rocket booster comhustion products. Biochemistry; We discuss the chemistry of life support systems and the level of pollutants and radiation on board the shuttle. Spectroscopy: We outline some modern detectors and techniques that help elucidate the nature of our universe. Materials Processing: This covers the realm of polymer, ceramics, and metal alloy research on earth and in space. Electrochemistry: Power systems for local space flight and new types of batteries are chief interests. Analysis: NASA uses modern instrumentation as well as traditional wet chemistry in analysis procedures. An analysisoutline for combustion products as performed at Lewis Research Center will be presented. 60
Journal of Chemical Education
Environmental chemistry and biochemistry will be discussed in this essay. The remaining topics will be examined next month. The topics that we have chosen to deal with are by no means a complete listing nor even the best ones for your classes. They have been found to be very interesting to students. Bv adding discussion of these examples to vour lectures, yo& students will have the most up-tordate knowledge of some important parts of the space program and will a new interest in modern chemistry &d its scope Examples and Classroom Appllcatlons EnvironmentalChemistry Both liquid and solid propellants are used to get the space shuttle into its orbit several hundred miles above the earth. Over 1,440,000L of liquid hydrogen a t 70 K and 541,000 L of liquid oxygen a t 90 K are available for combustion in the space shuttle main engines (SSME) (5).Some of the hydrogen is used to cool the SSME nozzles during combustion and liftoff. If the propellants are mixed stoichiometrically at room temperature, then
At comhustion temperatures (several thousand kelvins), small amounts of free radicals such as H. and OH. are present (6). Even though the heat comhustion per mole of fuel is anuroximatelv halved.. hieher .. - soecific . imoulse (thrust produced/(mass ofbrope~lantexpelled per unit time)) is eained bv makine the combustion mixture fuel rich.. eivine (at comhustion temperature):
.
2H,(g) + 1/20,
-
-
0.99H,O
-
+ 0.985H2(g)+ 0.03H + 0.0150H.
Energetic students may then he able to calculate AHaom as Table 1. Solid Rocket Booster Statistics ( 6 ) ThwstatLi#-off = 11,790 kN (2.650.000 lb) Propeiiant Atomized aluminum powder (fuel) Ammonium perchiorate (oxidizer) Iron oxide powder (catalyst) Polybutadiene acrylic acid acrylonihile (binder) Epoxy curing agem
16% 69.83% 0.17% (varies) 12% 2%
Mass EmpV Propellant Gross
87.550 kg 502.125 kg 589.675 kg
well as A S and AG for the above reaction. From the products of the liquid propellant reaction, it is apparent that pollution is not a problem here. I n addition, the specific impulse of liquid propellants tends to he higher than for solids. However, the demands of keeping liquid propellants so cold (70 K for Hz, 90 K for 0 2 ) make them impractical as the sole shuttle fuel. Solid propellants, because of their transportability and storage potential, provide most of the thrust necessary to put the shuttle into orbit. These solid rocket boosters (SRBs) also are the cause for environmental concerns. The vital statistics for each SRB are -aiven in Tahle 1 (7). The combustion reaction can be written as NH,ClO,(s)
FelO3lrat1 + Al(4 + hinder +
1/2AI,O,(s)
+ HCl(g) + Cl,(g) + CO(g) + NO,(g) + others
Annual Emissions from 40 Launches 16)
Emissions
kilograms
He@) Od9) Volatile organic compounds PaRiculateS (largelyA1 related) Ha@) cO(g) HCI(9)
NO&) Hydrocarbons Cld9) SOA) NH,. N,Hn, monomethylhydrarine and dimethylhydrazine
(3)
Tahle 2 lists the total expected shuttle emissions, assuming 40 launches in a year, from Kennedy Space Center. There room to auestion the long-term impact - - ~ is ~certainlv - ~ of both shuttle launches and conventional au&mohile emissions on the land and aouatic life around the cape. NASA studies (7) seem to conilude that there is no &ere longterm daneer. assumine care is taken regarding launch times, prevailing w'inds, andhumidity level; However, questions must he raised with students regarding the potential for acid rain damage, lowering of the of the water table in the surrounding region, particulate release, and the effect of SRB emissions on nearby flora and fauna. Further student activities in environmental chemistry: ~
Table 2.
Fresh canisters are put in place almost every day. An exothermic reaction of interest is
~
p~
Determine the percent composition of the solid propellants. Investigate the equations for the reactions of other solid and liquid rocket propellants. Calculate AH, AG and AS for these reactions. Determine the fate of CO and NO, from the SRB's combustion (with equations). Investigate how combustion products are determined at the cape. Have students set up a "mini-combustion chamber" and test for products, and water pH, in a nearby "mini-lake." Bv literaturesearch or actual emerimentation find out which plants -, are moqt affected hv ehanses in water DH.
Though LiOH is not as readily available as sodium or potassium hydroxide, its theoretical COs capacity per gram (0.92 g C02lg LiOH) is substantially higher than with NaOH or KOH, (0.55 and 0.39 g COdg absorbent, respectively). In addition, LiOH is not nearly as hygroscopic as other ahsorbents, so it is easier to store and handle (with proper safety measures). An i m ~ o r t a nstudent t exercise is to calculate the theoretical C0z absorption capacities for a variety of group I and I1 oxides and hydroxides and compare them to that of LiOH. There are two primary methods of producing potable water on board the space shuttle. The reaction outlined above is a major source. Another important water source is as the product of the H2102 fuel cell reaction. Oxygen and nitrogen are supplied on the shuttle from crvoeenic storaee . " tanks. so on these short flights reeenera" tion is not a problem. A variety of methods have been investieated for oxveen reeeneration on loneer flights. A mod one fo; classroomdiscuss~onis the ~ a h a t i e F ~ r o c &(9). . T h e first step in the urocess is the hvdrogenation of CO? over a nickel
-
Discuss risk vs. henefit of the shuttle launches. Biochemistry
The examination of how humans live for long periods of time in space while in a closed system such as the shuttle or the uncomine-mace . station will have students probing many areasAofgeneral chemistry and biochemistry: A surprising number of stoichiometric calculations can also he brought into this discussion. Ask your students to list those things that are necessary for survival in a spacecraft. Their list might include air, water, and food. A bit of discussion will extend the list to include waste disposal, electricity, and comrnuniration etluipment.nmony other items. A major point to bring ncn,si td your students is the idea of regeneration of necessities. Since only so much air and water can be brought on hoard, these necessities must he produced on the craft by chemical processes. The control system shown in the figure is presented as an example of oxygen and water generation as well as carhon dioxide control. The four methods for carhon dioxide removal that have been investigated (8) are reaction with lithium hydroxide, reaction with solid amines, inclusion in hydrogen-depolarized cells, and passage through molecular sieves. The lithium hydroxide method is used on the space shuttle. Air is circulated by fans through a charcoal filter for odor control and then through canisters which contain lithium hydroxide. ~
The reaction is more than 99% complete under stoichiometric conditions, although the reaction seems to have an optimum reaction rate a t a molar H2:C02 ratio of 4.31. The
~
Atmosphere control system for space vehicle application
Volume 64
Number 1 January 1987
61
Table 3.
methane produced can be pyrolyzed and the hydrogen product can be recovered and recycled:
Malor Toxic Substances Aboard the Shuttle TLV
Substance
The water produced from eq 5 can be electrolyzed to give additional hydrogen and the desired product, oxygen: There are a number of other oxygen recovery processes which are discussed in references 6 and 8. Other life-suooort .. processes, not directly related to chemistry, such as temperature control, are discussed in reference 5. Protection from toxic hazards has played an important role in the space since the Apollo missions. Toxic - orogram . substances can come from leaks or spil& from storage tanks, metabolic waste products of the crew, particulate or food pollutants that do not settle out in microgravity, leaks from environmental or flight control systems, thermal reaction ~ r o d u c t from s a varietv of sources. and outeassine " " of cabin construction materials (insulation, paints, adhesives, etc.) (10). Table 3 lists the maior toxic fluids and eases aboard the space shuttle, their purpose, and effects. An ongoing toxicological test program exists on the shuttle. It has been determined through gas sample monitoring that the shuttle is a safe place to be for a week or two, the typical shuttle mission length. An interesting student exercise is to determine. throueh literature searches,. . phone calls, etc., what the safe level of each contaminant is. Once this is done, they can try to determine the biochemistry of why some contaminants are more hazardous than others and how safe levels of contaminants are maintained in the industrial and academic workplace. Radiation exposure has always been a major concern in the space program. On Earth we get about 0.1 rem over a year a t sea level. In space, astronauts do not have the protection provided by the Earth's atmosphere so other types of shielding must he found and levels of exposure must be monitored. The career dosage level limit for soacefliaht crewmembers has been established a t 400 rem. his is double the level that is considered a risk for contractine leukemia. Radiation exposure levels have been published for most American spaceflights (10). The levels vary from a low of 0.010 rem (Gemini 8) to a high of 7.810 rem (Skylab 4). Most astronauts have had career doses of between 1and 10 rem, so rzrliation exposure is not a severe hazard to spaceflight crewmembers, although radiation can be a hazard to equipment such as on-board computers. Students can compare the levels of radiation on spacecraft with those obtained from living in maior cities such as New York a t sea levelor Denver a t one mile above sea level. They can also make comparisons with diaenostic tools such as a chest X-rav or a barium enema. ~ u i s t i o n scan then be raised regarding the safety of spaceflieht from the standooint of radiation exposure versus what a &pica1 person a t sea level might be exposed to. Ancillary questions such as types of radiation exposure and risk versus benefit in chemotherapy can also he raised. Other areas of biochemistry that relate well to the space program are the effects of microgravity on body chemistry and the possibility of life on other worlds. Further student activities in biochemistry: If the human body emits about 924 g of Codday, calculate how muehLiOH must be carried on hoard theshuttle for 5people for 7 days. lnvestieatewhv lithium hydroxide is a favored reactant with carbon dio& on t i e shuttle (;how calculations). List other methods of carbon dioxide removal. Discuss the advantages and disadvantages of each. Find out what some methods of oxygen recycling are on the shuttle.
62
Journal of Chemical Education
Use
(PP~)
Ammonia
25
Liquid axygen
None (6h)
Freon
