Using NASA and the Space Program To Help H i ~ h School and College Students Learn Chemistry Part II. The Current State of Chemistry in the Space Program Paul B. Kener Science Outreach, University of Wisconsin-Oshkosh, Oshkosh, WI 54901 William E. Snyder Poland Seminary High School, Poland. OH 44514 Constance S. Buchar Mail Stop 6-1, NASAILewis Research Center, Cleveland, OH 44135
In Part I of this article, the effects of the shuttle on the ecosystem in general, and humans in particular, were emphasized. We discussed the chemistry of the solid rocket boosters and the external tankas wellas life support systems on the shuttle. The potential for excess radiation exposure in space was also dealt with. In this essay, we discuss the current state of space-related research and manufacturing techniques. The focus is on the areas of spectroscopy, materials processing, electrochemistry, and analysis. The discussion is by no means complete. The references and other information a t the end of the essay should enable the interested teacher to obtain virtually all of the available information on a given topic. Examples and Classroom Applications Spectroscopy
It must be made clear t o chemistry students that nothing can be learned ahout the chemistry of objects in our universe (except the earth) without the ability to gather electromagnetic radiation. Although Copernicus theorized that the sun was the center of the universe (such as it was known ca. 1500) he had no convincing proof. Based on the best light detector I
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then known (the eye) his predictions of planetary positions proved to he no better than those of Ptolemy 2000 years earlier. The measurements of Tycho Brahe (1546-1610) were more exact but still inconclusive. Only when Galileo built his first telescope in 1608 and pointed it toward the heavens did we truly begin to learn about the nature of our universe. Within the next four years, using only the visible region of the spectrum, he was able to determine among other things, that the moon has very high mountains, that Jupiter has four satellites, that the Milky Way is filled with stars, and that sun spots are in fact spots on the sun rather than small planets ( I ) . For 250 years after Galileo made his 20-power telescope, visible observations helped tell the story of what was out there, from comets to newly discovered planets to nebulas. However, until about the mid-1800's, we did not know what these objects were made of. The first spectroscopic observations of a comet were made in 1864 by Giovanni Donati on comet Tempe1 (2). Other scientists soon acquired faint cometary emission spectra. The bands from these early spectra were eventually identified to be from Cz, (CN)s Ca, and CH. We now know that a t least a dozen elements, two dozen molecules, and a dozen ions exist in the various parts of a comet. (References 3 a n d 4
.
Draw a picture, divide it into 100 pixels, and code each pixel into a 6-hit binary number (let 0 = black, 63 = white, 32 = gray). Give the code to a classmate to deconvolute and draw your picture. Discuss the cost vs. benefits of deep space spectroscopy probes.
Atmospheric filtering of electromagneticradiation
aive a eood overview of the chemistrv of comets. Reference 5 gives an overview of the chemistry 0; space.) Our knowledge has become so detailed that we can senarate cometarv tails into Type I (ion) and Type I1 (molechar dust) t a i l s . " ~ o s t comets contain both. The study of comets is important to our understanding of our chemical solar system because comets ere perhaps t h e smallest bodies that have been essentially unchanged since the solar system's formation. However, the earthbound study of the chemistry of comets as well as planets and stars is limited to the visible and radio regions of the spectrum because of the filtering effect of the earth's atmosphere (see figure). It was, therefore, critical in the 1960's to heein sendi n i instruments on rockets outside the bulk of th'k earth's atmosphere. Sending spectrometers outside the earth's atmosphere was certainly a most significant breakthrough in our ability to determine extraterrestrial chemistry. The other development that needs to be stressed to chemistry students is the array detector. References 6 and 7 are classic papers on the vidicon detector and its use in chemistry. The vidicon is being used on the Voyager probes to the outer planets and the newer Landsat satellites. The lovely pictures of Jupiter, Saturn, and Uranus that we saw during 1979-1986 were the products of 640,000 pixels (picture elements) in a detector arras about 1cm2. Each element gets a small chunk of the radiation from the planet. When the chunks are converted to binary numbers, transmitted to earth, and deconvoluted, a picture emerges. Students enjoy the exercise of acting as transmitters and receivers of comouterized arrav detector data. The most modern detector used in the space program is the Charge-Coupled Device (CCD). I t is an array detector like the vidicon, hut, whereas the vidicon is generally sensitive in the 400-800 nm region, CCD's can go from 100 to 900 nm, thus obtaining data in a good deal of the ultraviolet and Also. a t 500.000 miles from Juoisome infrared reeions (8). ter, where vidicons can resolve featurks about 1 km apart, CCD's are expected to he able to resolve features about 10 m apart. CCD'I are on the upcoming Galileo mission tar Jupiter as well as the Space 'l'elesrooe misdion (9.IOI. Further student activities-in spectroscopy:' List the regions of the electromagnetic spectrum as well as their wavelength, frequency, and energy relationships. Discuss what we have learned about the nature of our universe from studies in each spectral region. Try to predict why each of the planets has the atmosphere that it does U I ) .
What does this tell us about the mechanism of solar system formation?
Materials Processing Materials processing represents some of the most exciting and diverse work going on at NASA. Projects range from the manufacture of graphite-epoxy polymers for use around the outside of the space telescope t o new ceramic materials that can withstand high combustion temperatures in turbine engines. Other important examples include the manufacture of polystyrene spheres in orbit on the shuttle's mid-deck area, which are now the official 10-pm standard of measure, and Lockheed shuttle tiles. which reoresent a maior steu forward in thermal protection for astronauts. Even the tiles are slowly being replaced by a synthetic blanket. This section will focus on materials processing experiments that have been done in soace on the Skvlah. - . Aoollo-Sovuz. . . . and Shuttle missions. In order to understand whv materials orocessine is useful and important in space, students must be made aware of the key difference between being in mace and on earth. While i t is nor technicidly correct ti sny ;hat there is no gravity on orhiting spacecraft, it is n close approximation. T h e g forces depending on a vary from approximately lW1 to 10." number uf factors including poaitim within the shuttle and the rmition of theshuttlr. "l4icrogravitv"can have an effect on processing intended for zero gravity, but it will he nealected in this discussion. Ask your students what is the implication of zerog on how water boils or how oil and water mix. If they can understand that heat-related shifts in density or inherent liquid density differences do not cause conuectiue flow in zero c. then thev have all the tools that they need to grasp materials Processing in soace. The ;illwater experiment was done on Skylah in 1974. In this ex~eriment(12) three cvlinders were filled with varvine .* percentages of oil and wate;, 25%,50%,and 75% oil, respectivelv. When the cvlinders were shaken on the Earth's surface;all three mixtures separated within 10 s, though the mixture that was 75%oil took thelonaest because the viscosityof the oil generally slows down themotion in the cylinder. When the experiment was performed in Skylah all three mixtures showed no tendency 1 0 separate even after 10 h. C'rystals grown in a zero-g environment arc of a hetter quality than those grown on earth. If the dynamics of the process are examined, it can he shown that as the solvent deposits solute a t the crystal surface i t goes from a higher solute concentration (more dense) to a lower solute concentration (less dense). Concentration-gradient-induced convection occurs readily here, causing imperfect crystal growth. Non-surface-tension-driven convection is not a problem in a zero-g environment, so better crystals should result. Other roadblocks to oerfect crvstal erowth from aqueous solution involve the container. ite ern ate nucleation sites often occur. Also, as the crystal is forming, radial heat hands often occur in the container, thus leading to increased convection. A zero-g environment presents an alternative to this. Containerless processing has been in the testing phase for over 10 years. Liquids do not require containers in a true zero-g environment. However, the shuttle is not at true zerog, because it is not in a true free-fall situation, and the instruments are not a t the shuttle's center of eravitv. " Therefore, a tremendous amount of energy is required to keep a liquid suspended at a fixed place. In spite of this problem, containerless processing has been attempted with solids and liquids on Skvlab, Aoollo-Sowz. and the shuttle (12). . . Crystals fo; detectors wer;gr;wn in a semi-containerless mode on Spacelab 3 in 1985. The first of these was mercuric iodide (HgI2).The crystal is of interest as a gamma radiation detector. It is not as good as some other currently available
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combinations, such as Ge:Li, but such detectors must be operated at cryogenic temperatures, whereas HgI2 can he used at ambient temperatures. Because tetragonal HgIz crystals are very soft, they tend to distort under their own weight when grown to the desired size (-1 cm2)on Earth due to the force of mavitv. I t was hoped that growine more perfect tetragonil ~~f~crystals in space can iead t;better nuclear monitoring outside the lahoratorv. In addition, this was a gas phase tosolid phase depositionso it was an excellent test system (13). The semi-containerless site for crystal growth is called a sting. I t is made from a metal of which the temperature can be programmed. A seed crystal is "glued" t o the tip of the sting and crystal growth is initiated by slowly lowering the sting temoerature. rather than the solution temoerature (though this can hk modified too). This greater control of crystal growth rate. Remember, convection isnot a problem in zero g. References 12 and I 3 give very detailed information on the apparatus used on Spacelab. A final useful example of materials processing in space can he introduced to students hv raising the auestion of how welding and brazing can be d i n e in space. For example, the ~ r o p o s e dspace station, t o be operational hv 1992, will be iaunched id parts from the shuttle over aperiod of two years. Putting some parts tngether may require repeating a procedure that was first done experimentally on Skylah. On that mission, four set3 of sleeves were to be brazed to their resoective tubes. Two sets had oure nickel sleeves and tubes and two were stainless steel. he hraze alloy was 72% silver. 28% comer. and 0.2% lithium bv weieht (12). The heat sourck for th:bra;e was the classic bt&& reaction (shown here for iron and aluminum): Fe209+ 2AI
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2Fe + Al20,
AH = -849 kJ
(1)
which is hiehlv exothermic. Note the similaritv between the reactants (ere and those in the following eqiation for the combustion reaction of the SRB's. which we discussed last month.
sions on both electrochemistry and the design difficulties that confront NASA researchers and engineers. On the shuttle, the following needs for electric pow& must he met: lifesupport systems, microgravity experiments, communications systems, and the myriad of instrumentation such as computers, propulsion control, clocks, environmental regulators, and telemetry devices. With regard to these energy needs, one must consider the usable power output in W-h/ kg, the ability to undergo several discbargelcharge cycles, temperature extremes, and the cost of components and performance. When snch needs are outlined i t is evident that spacecraft must be serviced by either a combination of solar/electrochemical resources or extremely dependahle electrochemical cells. During a geosynchronous orbit (GEO) the day-to-night ratio is such that there exists a heavy dependence on solar cells for both immediate electrical needs and recharging the secondary elertrochemiral cells; however, in low ~ a n &bit h (LEO) the daylnight ~. ratio is such that a greater rapacity . of electrical energy may be supplied by storage batteries and fuel cells. Hence, the low Earth orbit spacecraft, including the proposed space station, must employ batteries that complete 5000-6000 charge-recharge cycleslyear which is 50-60 times more than in high orbit snacecraft (16). An additional challenge centers around the effects of tempirature on electrochemical cell behavior especially in reference to planetary and solar probes such as the upcoming International Solar Polar Mission. It is limiting factors snch as these that stndents should understand as genuine problems, or challenges, that must be met and resolved for continued cost-efficient progress in the space program. Good examples of "current" use of electrochemistry lie with fuel cells and storage batteries. Without solar cells as part of its electrical structure, the space shuttle orbiter draws electricity from two fuel cells with a third designed for Spacelab activities. Using cryogenic Oz and Hz as reactants, fuel cells have been used successfullv in US. manned snacecraft, initially with Apollo missionsin the late 1960's (i7). The redox reactions for this simple fuel cell are as follows:
--
Anode: H,(g) + 20H2H,O + 2e(3) Cathode: O,(g) + 2H,O + 4eC 40H(4) yielding a net reaction as given in the following equation: Iron(II1) oxide is a much less powerful oxidant than ammonium perchlorate and as such serves as a catalyst in eq 2. The hraze worked far better in Earth's orbit (zero g) than on the Earth's surface (one g)because in orbit there is no gravity to act in opposition to capillary flow of the braze alloy. Classroom demonstration of the thermite reaction (see reference 14 for instructions) will give a vivid presentation of the energy released as iron forms. Further student activities in materials processing: Discuss why it is important to have nearly perfect crystals for electronic materials. Discuss the advantages of microgravity processing of items such as metals, glasses, and ceramics (15). List all the synthetic materials you are now wearing. Do the same with materials around your house. Investigate what environmental problems arise due to the manufacture of synthetics. Information is readily available regarding the manufacture of shuttle tiles. Have the students find out ahout the tiles and describe why they are so effective yet fragile. Have students synthesize nylon.'
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Electrochemistry
The unique challenges of providing power for use in the space environment will have students involved in discus-
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Send $3.00 to Paul Kelter for a set of 50 chemical demonstrations that we w e in class often.Nylon synkhesis is one such demonstration. 230
Journal of Chemical Education
Additional information pertaining to design and function of fuel cells in space can he obtained from reference 18. Currently, most fuel cells are designed for Hz102 use because (1) half-cells of these gases have been extensively researched and improved. (2) hydrogen and hydroxide ions are more mobile than other ions so that larger current densities can be obtained, and (3) the product, water, is stored or regenerated into the initial reactants. The hydrogen-bromine fuel cell, currently being developed at NASA Lewis Research Center's (LRC) Space Power Technology Division, has "potential" for high energy density and high round-trip efficiency. Main concerns when developing this cell include storage system design, working with highly toxic gaseous bromine, bromine and hydrogen electrode modifications, weight reduction, and membrane screening (19). Electrochemical storage for space operations such as Explorer, Gemini, Mariner, and Ranger satellites was in the form of silver-cadmium or nickel-cadmium batteries, with the Ni-Cd system as the most efficient to date. The halfreactions for the latter are as follows:
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CdD CdZ++ 2eNilC+ 2e-
Ei, = + 0.40 V vs. NHE at 25 'C (6)
Ni"
EL, = -0.25 V m. NHE at 25 OC
(7)
A nickel-hydrogen battery offers encouraging improvements such as lighter weight, longer life, and deeper depth of discharge. This state-of-the-art energy storage system was employed recently in Intelsat VI. LRC currently supports a program to improve nickel-hydrogen technology by developing a bipolar system with, among other advantages, high discharge-current capability and significant weight reduction. Yet another battery, nickel-zinc, has been demonstrated on a small scale. Perhaps this technology could be transferred to electrically powered vehicles. While the nickel-zinc hnt,terv is not new.~the - ~~-~ ,~~~~ .~ Lewis nickel-zinc batterv has solved basic life and reliability problems by improving the separan smedicine and m i n i n- ~are tor 1201. , . Additional a ~ ~ l i c a t i u in powered prosthetic devices and mine emergency evacuation vehicles. Further student activities in electrochemistry: Use as a lead-in to corrosion studies with redox nrincinles. Caleulnte Eo for eachofthe cells liktcd in thrr sectilbn. Write and hnlmce redox equations for thespare stmire battrrics. Apply rhe effects of ronrentra~ionon voltaxe wing the Nrrnst equation. Discuss effects of weight, required voltage, operating temperature, efficiency, and maintenance. Construct a high-temperaturecell, a low-temperature cell, and a fuel cell (18). ~
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~
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A.
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The following example will serve t o show the laboratory work that occurs on a dav-to-day basis at LRC, one of nine NASA regional centers.- he center is involved in engine propulsion and combustion research. As such, fuels and oils . . charattrrization is very important. A number of different analyses can he performed to rharncterize a fuel. For examnle. measurement of the eross heat of combustion allows the researcher to determine the thermal efficiency of an engine and the available energy in a fuel. The measurement instrument is a bomb calorimeter. As the fuel sample is burned in the bomh portion of the instrument, heat is generated and absorbed by a surrounding water bath. The moss heat of combustion is eaual to the rise in temperature of the water bath multiplied by the effective heat capacitv of the calorimeter svstem. h he net heat of combustion of afuel can be determined by measuring the amount of hydrogen in that fuel. The net heat of combustion is the gross heat of combustion minus the heat of condensation of water vapor formed by the combustion of hvdroeen in the fuel. Thevalue of the net heat of combustion is needed to calculate the thermal efficiency of an engine operating without a condenser. The amount of hydrogen in a fuel is measured hy Nuclear Magnetic Resonance Spectrosc o w (NMR). The nuclei of hvdroeen atoms and all other " odd-nimbered mass nuclei are magnetic and can be aligned in a maenetic field. NMR measures the enerev to -.required . change the alignment of the hydrogen nuclei in a magnetic field and so measures the amount of hvdrogen . . .present in a fuel. The amount of sulfur oxides that form during combustion of the fuel can be measured by sulfur determination. Sulfur oxides can cause corrosion by combining with water to form acids. The amount of sulfur in a fuel can he measured bv combusting the sample in the bomh calorimeter to convert the sulfur to sulfate. This sulfate solution can then he analyzed by using ion chromatography. The sample is injected into the separator column of the ion chromatograph where the sulfate ions, as well as any other anions, are segregated. These anions then elute through a suppressor column where they are converted to their respective acids (e.g., sulfuric acid). These acids then pass through a conductivity cell where they are quantified. Oils as well as fuels, must be analyzed t o insure the proper functioning of engine systems. Engine oils must be routinely A
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analyzed for wear by measuring metals build-up. This is done by mixing a portion of the oil with acid and a solvent and then aspirating i t into an atomic absorption spectrophotometer. Any metal in the oil absorbs a portion of light given off by a hollow cathode lamp specific t o that metal. This absorption is detected and measured. If the amount of metal increases from one analysis to another, engine maintenance is suggested. Though this section has covered the specific areas of fuels and oils analyses, many other types of analyses are performed in the laboratory. The analyses vary and with each change comes the opportunity to develop new techniques of anslvsis " ~-~and to exnlore the limits of the instrumentation. Further student activities in analysis: ~~
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~
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Perform an entire fuel analy~is.~ Determine structuresfrom sample NMR's. Grmh the relationshin between temperature of engine operation and eneine effieiencv. (hmparr atumlc alrsorption spertn,phorornetry and ion rhnmarography with regard tuspcrifirity, lwrr limit of detection. rnnge uf iubitanrrs determined, and cost. ~~~
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Conclusion We have presented just a few of the many examples of the relationship between chemistry and the space program. I t would certainly be possible to devote years of class time to the suhject. The authors are happy t o answer any questions regarding any NASA-related information. NASA publications can he obtained from: Don Zylstra, Head Publications Division Code N NASA Headquarters Washington, DC 20546 Slides can be obtained from any one of the nine NASA center educational offices for a nominal fee. For a list of centers and contacts and to request NASA speakers, write to: Larry Bilbrough Code LEE NASA Headquarters Washington,DC 20546 Acknowledgment The authors wish to thank Barbara James for her assistance in the preparation of this manuscript.
Literature Clted 1.
Drake. S. The Dircoueries and Ooinions
of
Galileo: Doubledsv: Garden City, NY,
No. NAS1-19:127. Carbo,R.:Ginebrda.A. Clin. Chem. 197d,20,1028. 7, Santini, R. E.; Milano, M . J.;Pardue,H.L.Anol.Cham, 1913,45,915A. 8. Krirtisn.J.:Blouk.M. Sci. Am. 1982.247(41,67. 5. J. Chom. Edur. 1985,62,832. 6. Pardue, H. L.;Hewift,T.E.:Milano,M. J.
9. Johnson, T. V.; Yeafos. C. M. Sky Telescope 1983,6612). 90. 10. B ~ a t t yJ. , K. Sky Telescope 1383,66131,189. 11. For example, Shu, F. H. The Physical Uniuerm. An Introduction to Astronomy; University Science: Mill valley, CA, 1982; pp 459483: or any other boginning
~
1982: 439-444.
Space; Elsevier: New York. pp 11. Shakheahiri.B. 2. C h ~ m i c d D e m o n s l m f i o Uniu. ~ : Wisconsin:
Madison. 1983: Vol. 1,
19. Hsmerty. J. J. SpinoN 1985, NASA: Wsshington, DC. 1985;p 86. 20. NASAINi-Zn Rorlery Technology: NASA: Washington, DC, 1980. Write to Constance Buchar for a fuel analysis procedure. Volume 64
Number 3 March 1967
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