REPORT FOR ANALYTICAL
CHEMISTS
Analytical Chemistry a n d the Satellite The earth satellite program has been d r a w i n g on the result of years of research by analytical chemists. In addition to the more obvious analytical problems presented by rocket fuels or propellants and materials of construction, there are a host of others. Long before the first satellites were made, for example, rockets were used to study characteristics of the upper atmosphere, to determine ion densities, and to collect dust from outer space. Semiconductor technology and corrosion problems are further examples. This Month's Report for Analytical Chemists presents a panorama of analytical possibilities of the satellite p r o g r a m . E N one thinks of an earth, satelW Hlite and the possible contributions of the analytical chemist to its design and destiny, the first impulse is to regard such devices as being out of his field, if not out of his world. On further reflection, the rocket fuels or propellants suggest some analytical problems, and, of course, the materials of construction fall in line for rather thorough analytical surveys. However, close inspection, of the m a n y requirements of a project as large and far reaching as the N a v y ' s Vanguard Satellite program reveals m a n y features and facets attributable to the accomplishments of the analytical chemists. M u c h of the analytical research t h a t provided a vast reservoir of usable information for satellite planning was accomplished before the advent of a formal satellite program, and without particular attention to space flight. Other pertinent facets of the analyst's work were keyed into the development of individual components t h a t were later to become p a r t of the fascinating p a t t e r n of the conquest of space. And, although there is no formal organizational role of the analytical chemist in the Vanguard Project, there is constant
call for his services in all aspects of its development. This report will consider a number of fields of research and development that are relevant to satellite technology and in which the analytical chemist has had a helping hand. I t is not intended to be exhaustive or limited to the work performed at the TJ. S. Naval Research Laboratory. R a t h e r it is m e a n t to be representative of the range and variety of the contributions of the chemist to the satellite program. I n some instances reference will be m a d e to instruments t h a t are the common tools of the analytical laboratory, b u t in the satellite program were used by physicists or astronomers. C o n t r a r y to good satellite procedure, this discussion will be launched in outer space and descend to more earthly considerations. Some attention will be given first to experiments performed in determining characteristics of u p p e r atmospheres and ion densities at various altitudes, the collection and analysis of dust from outer space, and emissivity and absorptivity requirements of surfaces subjected to the radiations in these far reaches. Semiconductor technology, corrosion problems, and pro-
pellant chemistry will be discussed briefly, and finally some construction details of a satellite and its launching vehicle will be given in order to display the panorama of analytical possibilities rather t h a n describe particular analytical problems. THE SKY IS NOT THE LIMIT
M a n ' s insatiable curiosity about the sky and the outer fringes of his little world has not only been a major factor contributing to the impetus for launching an earth satellite b u t has provided much background information necessary for design of satellite experiments. Early estimates of the character of the earth's atmospheric envelope were made from observations of the behavior of meteorites entering the earth's gravitational field, b u t more accurate data have been gained from analytical instruments rocketed into space. I n s t r u ments in the field of spectroscopy have been used in every conceivable manner for atmospheric studies, b u t perhaps the most fruitful application of spectroscopy in terms of data pertinent to man-made satellites was the use of rocket-borne Bennett radio-frequency
Dean I. Walter, 37-year-old head of the Analytical Chemistry Branch of the Naval Research Laboratory, is a native of Pennsylvania with a bachelor's degree in chemistry from Juniata College (1940). With the exception of a brief period with General Chemical Company, and two years of military service his 1 8 professional years have been spent as an analytical chemist for the Navy. He is best known for his work in high vacuum methods of analysis, particularly the " W a l t e r Method" for the determination of oxygen in titanium, for which he has received various awards and commendations. Recently, he received a cash award and a certificate for outstanding performance in the organization and conduct of the analytical laboratory (See Laboratory of the Month, this issue). Walter also serves as pastor of a central Pennsylvania church, to which he has commuted weekly for 1 3 years, and is in demand as a speaker on humanizing the sciences. His publications are largely in the field of high vacuum analysis, poetry, and Biblical exegesis. He is a member of the AMERICAN CHEMICAL SOCIETY. VOL. 3 0 , N O . 4 , APRIL 1958
·
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mass spectrometers to measure the rela tive abundance and the composition of positive and negative ions between mass numbers 54 and 6, at altitudes above 50 miles. These experiments, con ducted by Rocket Sonde scientists of the U. S. Naval Research Laboratory, provided information on total gas den sities, the ratios of gases over wide altitude ranges, and the degassing char acteristics of rocket components at high altitudes. The density of the earth's atmosphere at given altitudes is not the only den sity problem of critical significance to the designers of satellite experiments, however. Meteorite dust constitutes a threat of rather startling proportions to all man-made space devices. Esti mates vary on the possible penetrating power of fast-moving microscopic par ticles into the skin material of satel lites, but there is unanimous agreement that particles even of submicron size will have an abrading effect on all ex posed surfaces. Although this may not be of too great significance in terms of destroying a satellite skin, it may result in greatly impaired efficiency of optical equipment and solar cells used to energize transmitting equipment. Chemical examinations have been performed on the exposed surfaces of rocket nose-cones that have been re covered after successfully launching to high altitudes. This type of experi ment gave indication of meteorite dust encounter but could not establish quan tities or densities. Attempts to pro vide more quantitative measurements were made by flying plastic cones equipped with photomultipliers and re corders. These experiments provided not only an electronic means of meas uring encounters but a surface medium that would indicate more pronounced physical evidence of collision and pos sibly retain the colliding particle. These surfaces were examined microscopically and spectrochemically for iron and nickel contamination. An even more fascinating experiment for capturing dust in outer space in volved an ingeniously devised rocketborne meteorite trap, the inner walls of which were coated with carefully analyzed silicone grease to provide a medium for retaining the captured par ticles. In flight, this trap opened at burn-out altitude and scooped up all solid particles in its path until the rocket reached its peak altitude, at which time the trap closed, and fell with the rocket nose-cone to earth. Upon recovery of the trap, the par ticles were remo\^ed from the silicone grease by centrifuging and magnetic extraction. Microscopic examination identified spherical particles that ap
peared to be meteoritic in origin. This preliminary identification was further verified by spectrochemical means. Further examination of these particles is in progress with the electron probe, an x-ray spectrograph designed to scan areas as small as a few square microns. While spectrochemical tech niques can identify the metallic constit uents of these microscopic particles, the electron probe can provide cross-sec tion analyses and suggest something of the particle's history and origin. THE SURFACE OF THE N E W
MOON
In order to provide the most efficient choice of material for use in fabricat ing the outer skin of the satellite, a large number of metals and coated metal surfaces were studied under con ditions approximating those of outer space. A satellite circling the earth every 100 minutes is in direct sunlight for at least 60 minutes and in darkness for no more than 40 minutes. Under various conditions the time in sunlight may be much greater. This set of extremes, without the moderating in fluence of an atmosphere, suggests the need for a surface that will absorb a minimum amount of energy during the satellite's day and radiate a maximum during its night. Scientists of the NRL Optics Division designed experiments in which a spherical radiator was coated with the particular metal or film and suspended within a large evacuated sphere, the inner walls of which had been treated for maximum absorptive properties. The sphere was cooled to dry ice temperatures and the emissivity characteristics of the surfaces meas ured over a wide range of tempera tures. The analyst's contribution to these experiments lies in the area of metal and metal film analysis, the establish ment of vacuum degassing conditions for vacuum-tight castings, and the preparation of oxide surfaces of definite composition and absorptive properties. SEMICONDUCTORS BECOME SPACE SENTINELS
Fundamental to most satellite con siderations, of course, is the develop ment of electronics and circuitry for gathering and transmitting data to the ground stations. When the whole panorama of satellite activities is seen in proper perspective, the data gath ering is by far the most significant part of the program and really the only part of the achievement keyed to IGY considerations. Obviously, these nerve centers of the various satellites must possess a delicacy and a sensitivity for specific types of data perception; they must have ruggedness and stability of
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Heat radiation tests, simulating those existing in outer space, are conducted at the Naval Research Laboratory on the 6.4 inch Vanguard test sphere. Launching is accomplished by a three-stage, 72-foot rocket. The six rectangular objects on the surface of the aluminum sphere are solar batteries which power one of the two radio transmitters. Plans call for the launching of 20-inch instrumental satellites construction at minimum mass; and they must have a high degree of o p erational efficiency. These require ments could scarcely have been m e t before the advent of transistor or semi conductor technology; and this tech nological development has leaned heav ily upon the a r m of the analyst. The level of m a n y significant impuri ties in semiconductor materials falls into the elusive p a r t s per billion area. This is well below the p a r t s per million working range of colorimetry and spec trochemistry. For the determination of impurity levels of this magnitude, several radioactivation techniques have been developed to identify the elements and measure their induced radiation. G a m m a scintillation spectroscopy has the advantage of being able to detect and determine a fair number of ele ments in silicon and germanium with a minimum of preliminary chemical separation or concentration; however, it is not applicable in analyses where the desired element is a beta emitter, and is not as sensitive as methods t h a t utilize the beta radiation for identifica tion and measurement. T h e beta method requires rather extensive radio chemical separation work in order to isolate the element sought from all
other possible interfering radioactive products b u t achieves phenomenal sen sitivity. A dozen or more elements whose presence m a y affect the electrical properties of semiconductors have been determined by this method in amounts as small as a fraction of a p a r t per billion. Details appear in the table. Results of Activation Anc lysis o n Silicon (7) Analysis, Element Isotope P.P.M. Determined Measured ρ 32 0.01 Phosphorus Fe 5 w9 0.1 Iron Cu 0.002 Copper 8 Zn" 0.007 Zinc As™ 0.00002 Arsenic 110 Ag 0.001 Silver 113 Cd 0.0002 Cadmium 122 Sb 0.0003 Antimony CORROSION CAN BE COSTLY
P e r h a p s the last thing one might ex pect to be significant in m a t t e r s relat ing to satellites is corrosion. While it is true t h a t the satellite itself travels in near vacuo, save for an occasional cloud of stellar dust, and has about it the protective aura of the celestial, all other materials associated with its launching and tracking are terrestial
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and fall under t h e inevitable trending of "ashes to ashes a n d dust t o dust." Corrosion of metals, or to be more general, t h e reversion of materials to their original or most stable t h e r m o dynamic state, has constituted one of the most troublesome a n d most expen sive problems in every construction project since t h e dawn of civilization. How m a n y rocket misfirings or ineffi cient blast-offs m a y be a t t r i b u t a b l e t o corrosion-initiated difficulties may never be fully discernible. W h e n one considers t h e complexity of functions, electronic and mechanical, required for the successful launching of a compli cated rocket a n d a t t h e same time con siders the variety of subtle corrosive influences t h a t might affect t h e opera tion of a relay, a valve, or t h e efficiency of an oxidant, t h e possibilities of fail ure are staggering arid almost frus trating. F r o m t h e time of Solomon, who h a d the wisdom a n d wealth t o use gold overlay for protecting surfaces, to mod ern m a n , who has a wide choice of plastics, paints, a n d inhibitors, t h e m a jor effort directed a t t h e prevention of corrosion has been of a protective coat ing n a t u r e . However, if materials of construction are t o keep pace with· a satellite-minded society, every possi bility of corrosion prevention m u s t be probed a n d t h e diagnosticians m u s t come from t h e r a n k s of t h e analytical a n d physical chemists. P e r h a p s t h e most fruitful possibilities lie in t h e study of high p u r i t y materials a n d t h e formation of self-induced protective coatings. M u c h work of this n a t u r e is already being done b y corrosion spe cialists a t N R L a n d in other laborato ries a r o u n d t h e world in a n a t t e m p t t o u n d e r s t a n d more fully t h e mechanism of corrosion, t h e influence of certain trace impurities in establishing gal vanic-type cell action within t h e m a t r i x metal a n d t h e actual chemistry of t h e corrosion resistance contributed b y cer tain alloying elements. T h e electron probe, already d e scribed, has been of assistance in iden tifying components of corrosion p r o d ucts a n d localized impurities so small as t o b e virtually beyond t h e reach of even microchemical analysis. FUELING FOR INFINITY
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REPORT
ANALYTICAL CHEMISTRY
T h e rocketry for t h e V a n g u a r d satel lite is of three-stage design a n d em ploys three different sets of fuels or propellants. T h e first stage is powered b y liquid oxygen a n d kerosine a n d pro vides about 6 5 % of t h e energy t o raise the remaining stages t o orbital altitude and about 15% of t h e orbital velocity. T h e second stage, which contains t h e complete guidance and control system
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for the entire launching vehicle, is powered by white fuming nitric acid and unsymmetrical dimethylhydrazine. It provides the energy to raise the last two stages to orbital altitudes and con tributes also to orbital velocity. With in the nose of this second stage is housed the third-stage rocket and the satellite itself. The cone protects the delicate satellite sphere from aerody namic heating during ascent through the earth's atmosphere. Since there is no steering mechanism in the third stage, flight stability is provided by spinning it around its longitudinal axis before separation from the second stage. This takes place at the Orbital height of about 300 miles, at which point the solid propellant third-stage rocket is activated to provide the final 50% of the required orbital velocity of 18,000 miles per hour. The primary role of the analytical chemist in the field of rocket fuels in volves the determination of impurities that affect the stability of the fuel in storage and the burning characteristics of the fuel mixtures. Of the fuels used in Vanguard rocketry, only the white fuming nitric acid poses any particular problems of consequence. The composition of fuming nitric acid can be affected either by too high storage temperature or reaction with the walls of the storage container. The later action contributes metal salts to the mixture, which may form trouble some solids and also catalyze the fur ther decomposition of the mixture. The need for field analysis has been mini mized considerably by the addition of 0.5% by weight of hydrofluoric acid, which tends to form a protective layer of fluorides on the container walls, thus greatly reducing the decomposition of the nitric acid as well as the container. Usually, the composition of the fum ing nitric acid is determined by wet chemical analysis at the manufacturing plant prior to storage, and sampling of the stored liquid thereafter is kept to a minimum. The wet analysis pro cedures are entirely too lengthy for field use, and conductometric tests have been devised that appear to be satis factory to determine whether or not the acid falls within acceptable limits. One of the weaknesses in the usual wet chemical analysis is that water is de termined by difference, and since the water concentration dilutes the oxidiz ing power of the acid and thereby cuts the burning efficiency when used as a rocket fuel component, slight inherent errors can be costly. This difficulty has been largely overcome by recent devel opments in spectrophotometry that utilize the strong optical absorbance of water in near-infrared (1.4 microns).
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If it is true, as the adage affirms, that it takes all kinds of people to make a world, it is equally true that it takes all kinds of men to make a moon. For as one surveys the magnitude of the construction problems involved in a man-made satellite and its associated launching equipment and tracking devices, it suggests a cross-section sampling of all skills and sciences. A cursory inspection of these items is sufficient for the chemist in the field of materials analysis to identify his contribution. T h e satellite, a 20-inch-diameter sphere, weighing 21.5 pounds complete with instrumentation, is fabricated largely from magnesium and magnesium alloys. The choice of magnesium is particularly understandable when one considers that for every pound of satellite, a half-ton of rocket and propellants is required. The shell consists of two hemispheres of AZ31B magnesium alloy (96% Mg, 3% Al, and 1% Zn), fabricated by the metalworking operation known as "spinning," and held together by hundreds of stainless steel, jeweler-type screws. The AZ31B alloy has a very low calcium content and was chosen for its excellent weldability, and good working characteristics. The internal structure and support framework is magnesium tubing, except the antenna mounts, which are machined from solid magnesium stock. After stress relief of the welded framework, it is placed inside the hemispheres, which are then joined, machined, and polished to mirror brightness, and plated with successive layers of copper, silver, and gold. This basic structural portion of the satellite is produced by contract and is furnished to NRL for instrumentation and final application of the surface layers of temperature-regulating materials. Adjacent to the polished gold-plate is added a plate of chromium metal, then a coating of silicon monoxide, a vaporized film of aluminum, and a final coating of silicon monoxide. Although the first satellite cannot possibly contain all the devices that inquiring scientific minds would like to incorporate in a "space laboratory," it does contain a remarkable number, thanks to miniaturization and semicon-
ductor technology. Included in or on the satellite are two ionization chambers, a solar aspect cell, erosion gages, a cadmium sulfide cell for erosion studies, micrometer microphones, thermistors, a Minitrack radio transmitter, a telemetry system, and ultraviolet radiation (Lyman alpha) memory storage units. Eight pounds of chemical batteries are required. The launching vehicle or rocket mechanism is a conglomeration of construction compromises that is required to do a job of exacting specifications under intolerably difficult circumstances. The wide temperature range to which the materials of construction are subjected, the stresses and strains created by the development of energy at the rate of a quarter million horsepower, the corrosive and temperamental behavior of the propellants, and the relentless demands for minimum weight impose a set of restrictions and limitations upon the project that call for the closest of working relationships between chemist, metallurgist, and construction engineer. Minimum weight considerations along with advances in the state of the rocket art have removed the stabilizing fins from the first-stage rocket and eliminated structural reinforcements to the point that propellant tanks also form the walls of the rocket. All of which means that the rocket tanks must be loaded while the rocket is in a vertical position in the servicing gantry, for the loaded rocket cannot support its own weight in the horizontal position. The first-stage rocket operates for nearly 2.5 minutes, and generates temperatures many times in excess of the melting point of the combustion chamber materials. In addition, it must help to impart guidance to the entire structure by the direction of its thrust. To do this the gimbal rocket motor must move through as much as five degrees, with the necessary attendant flexibility of fuel lines. A steam turbine is required to operate the fuel pumps at the enormous capacity specified. It in turn is driven by the steam generated by the decomposition of carefully analyzed hydrogen peroxide. As the propellants are pumped from the tanks, helium from stainless steel reservoirs floods the volumes to maintain pressure and provide rigidity. Valving arrangements permit part of the helium and steam to be diverted to the external roll jets that assist in stabilizing flight. Thrust for the second stage is provided by the reaction between white fuming nitric acid and unsymmetrical dimethylhydrazine ; and an ingenious rocket motor makes use of the nitric
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acid for cooling purposes. The acid circulates through the combustion chamber of the motor. Controlling all of the activities from launching to orbiting time is the auto matic guidance system located in the second stage. This system, in itself an analyst's delight, actuates the valves, relays, jets, turbines, motors, pumps, ignitors, and spinning and discard mechanisms that control over 11 tons of materials required to throw a 20inch research laboratory into its place in space. The launching vehicle and portions of the satellite are produced under several major contracts, which in turn are the summation of many minor con tracts. There is a basic pride among the people who knowingly contribute to the satellite program that carries some thing of a new spirit of pioneering and calls forth their best, whether it be running a lathe or running an analysis. It generates a thoroughness and an attention to detail that demands that each component be evaluated and every analysis be accurate. REPORT FROM T O M O R R O W
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After the satellite has been hurled into orbit and the first two stages of the vehicle have fallen into the sea, 10 electronic laboratories, known as Minitrack stations, will start searching the great abyss for a 20-mw. voice, the report of our sentinel from space. As this tiny reporter signals its location and begins to transmit its periodic sum maries of conditions on the new fron tier, a restless world that is chafing under impatience with one-planet ex istence will begin to interpret and ponder the new data and plan new conquests. There will be little respite for those whose hands and minds have shaped the new technology; there will be more reconnaissance, more refinement, more research. The analytical chemist will not be last or least on the new fron tier. As his work was the nucleating center around which the atomic age crystallized, so his work has been vital in developments for the space age. He has contributed to surveys of upper atmosphere, the development of elec tronic technology, the synthesis of ce ramics and plastics, the production and refinement of fuels, and research and development of pure metals and new alloys. He has proved himself, his tools, and his techniques. He has estab lished his reputation among his peers. If there are yet new worlds to conquer, he will go in with the landing party. (1) Kant, Arthur, Cali, J. P., Thompson, H. D., ANAL. CHEM. 28, 1870 (1956).
