R E R O R T F O R A N A L Y T I C A L C H E M I S T S

Probing the Upper Atmosphere Thousands of rockets costing millions of dollars have been

launched during the past 20 years for both military and scien­tific purposes. The military rocket is an investment in the security and freedom of the United States. The return from the scientific rocket program includes new understanding of our surroundings and thus helps man to exercise greater control over his environment. This month's Report for Analytical Chemists describes rocket investigations of the upper atmos­phere as a modern scientific discipline. The bulk of this re­search, carried out quietly by NRL over the past decade, is now of great public interest as man seeks to conquer space.

Τ Ή Ε ATMOSPHERE, which protects -*- and nourishes our various forms of

life as well as having determined their chemistry, maintains some of the most interesting and complex physical and chemical activity with which the sci­entific profession is concerned. The atmosphere provides the air we breathe, waters our crops, makes possible audio and radio communication, provides a medium for high speed travel, produces such phenomena as aurorae by shield­ing us from extra-terrestrial radiation, and which, by maintaining its delicate chemical balance, assures us of a cli­mate tha t is neither intolerably hot nor cold. Yet this vast " laboratory" of physical phenomena has only recently enjoyed the accessibility tha t is ac­corded classical investigations. I t s many processes, of which we have only second hand or macroscopic knowledge, are now being subject to direct meas­urement by balloon- and rocket-carried instruments. The advent of the rocket vehicle has allowed us to enter and penetrate the upper atmosphere and thus begin a new series of investigations

which will give us insight into these elusive terrestrial and solar phenomena.

Prior to the existence of the sounding rocket, some measurements concerning atmospheric properties were made with ground-based and balloon-borne instru­ments. Balloons were utilized as they are today for low altitude studies of wind, pressure, and temperature. These studies provide the weather forecaster with up-to-date information for short range predictions and aid meteorologists in their a t t empt to syn­thesize a lower atmosphere whose be­havior will be predictable over long periods.

Balloons, for example, have enabled physicists to study such other high alti­tude phenomena as primary cosmic rays without the filter action of the dense lower atmosphere. Balloons have also provided information about the chemis­t ry of the atmosphere to about 20 miles. Such work has inevitably led to specu­lation about the higher altitudes where physical phenomena are perhaps gov­erned by solar influence more than terrestrial.

Today, the high altitude sounding rocket reaches farther and farther out, providing a look at the solar atmos­phere with less and less intervening earth contamination. Studying the na­ture of the corpuscular radiation falling on the outer reaches of our atmosphere yields information concerning the physics of fields and plasmas. Certain chemical reactions which take place in the upper atmosphere are very difficult to reproduce on the ground where the dimensions of appara tus are small com­pared with those of particle trajectories in .the high vacuums of our high atmosphere.

Many classical and modern theories of atmospheric and ionospheric behav­ior may now be studied experimentally. The question of what sort of mat te r populates the upper atmosphere has long challenged scientists. Dalton, early in the 19th century, was con-corned to the extent of making a sample measurement of the atmospheric com­position near sea level and another on a mountain top. His conclusion was that the ratio of heavy-to-light gases

Julian C . Holmes (r ight) and Charles Y. Johnson are members of the Rocket Sonde Branch of the Naval Research Laboratory. Johnson, 38-year-old native of the District of Columbia, graduated from the University of Virginia (1942) with a bachelor's degree in electrical engineering. He joined the Navy and worked on radar and radar beacons. Since 1946, which marked the beginning of the NRL upper atmosphere research program, his work has been with cosmic rays and ion composition of the ionosphere. He is a member of the American Geophysical Union, American Physical Society, and Institute of Radio Engineers.

Holmes, a 27-year-old physicist from Maine, received a bachelor's degree in physics from Bowdoin Col lege ( 1952). He is presently doing part-t ime gradu­ate work in physics at the University of Maryland. Since he joined the NRL staff in 1952, his work has been in the fields of electronic counter measures and ion composition of the ionosphere. The authors, standing in f ront of the spectrometer electronics of the Aerobee-Hi, are each holding Bennett radio-frequency ion mass spectrometers.

Figure I . Properties of the upper atmosphere investigated with probing techniques by NRL include ion composition and electron density of the ionosphere, diffusive separation of the atmosphere, auroral particles, cosmic rays, solar energy, atmospheric pressure, temperature and density, and alt i tude of night glow

was lower a t the higher altitude. His experimental evidence was probably unsound, but his s tudy of gravitational diffusive separation is being carried out today with considerable interest and new tools. The winds in the lower atmosphere keep the gases well mixed. Investigations as to the effectiveness of such mixing mechanisms have been carried out to altitudes of over 150 km.

Atmospheric diffusive separation is only one of the mechanisms responsible for the variations of composition with

altitude. Explorations of the atmos­phere between 85 and 250 km. show tha t impinging solar energy produces chemical reactions which are directly responsible for the changing composi­tion. The electrically active region, the ionosphere, owes its existence to solar radiation, both electromagnetic and corpuscular. Many of its proper­ties can be inferred from classical ground-based studies of this region. However, recent rocket-borne iono­sphere probes have changed some of

these concepts and added new ones which are the basis for our current understanding. Radio blackouts are being correlated with ionospheric changes. Accurate world-wide predic­tions for communication may some day result from this study.

Aurorae. A form of ionospheric activity, the aurorae, has for centuries captured man's imagination. Spectros-copists, while they have identified in the aurorae spectra of atomic oxygen, neutral and ionized molecular nitrogen,

R O C K E T C H A R A C T E R I S T I C S

Rocket Diameter,

Inches Length, Inches

Payload, Lb.

Altitude, Miles Propellant

Rockoon (Deacon)

6V2 150 30-40 60 Solid

Nike-Cajun

Aerobee-Hi Aerobee-Hi

l6V 2 -N ike 63 /4-Cajun 15 15

309

303 303

40

120 200

100 2 stage Solid

165 Liquid 122 Liquid

Launching Method

Rocket suspended below balloon, launched at 70-80,000 f t .

Nike launching stand (Zero length launcher) Tower, boosted for 2.5 sec. Tower, boosted for 2.5 sec.

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REPORT FOR ANALYTICAL CHEMISTS

and ionized hydrogen, have not been able to explain the mechanism of exci­tation. The fine detailed, vertically curtained aurora with its "drapes" par­allel to the earth 's magnetic field lines suggests the excitation of atmospheric gases by incoming extra-terrestrial charged particles. The high luminosity of auroral pa t te rns throughout an alti­tude range of hundreds of kilometers is harder to explain, as are the other types of aurorae having no visible vertical s t ructure at all.

M a g n e t i c S t o r m s . Closely con­nected with the aurorae are the so-called magnetic storms, the association having been made as early as the mid 18th century. Small variations in the ground level direction and intensity of the measured earth field are evidence of upper atmosphere fields which in tu rn indicate some sort of current flow in the ionized regions. Sheets or streams of ionospheric particles at high altitudes have been postulated in many forms by as many people. Others say tha t the magnetic variations can be ex­plained by the effects of charged solar particle streams impinging on the earth 's magnetic field.

One reason for the present intense interest in these solar emissions is the high energy with which they apparently enter our atmosphere. Rocket probes of the auroral sky have recorded charged particle activity in the million-electron-volt region, thus indicating a very high energy for the pr imary auroral particles. The current aggre­gate of evidence favors the sun as their initial source. However, if they leave the sun with solar thermal energy, then an accelerating mechanism of million-el cctron-volt or billion-electron-volt proportions between the sun and earth must be postulated.

One suggestion of interest postulates particle acceleration from radiation pressure in the vicinity of the sun; another theory suggests explosive-type emission from the sun which would im­par t equal velocities to heavy and light particles so tha t the heavy ones would have sufficient initial energy to penetrate our atmosphere to auroral levels. Other theories utilize Fermi and betatron mechanisms, and still an­other postulates magnetic separation of particles of unlike charge with the resulting electric field becoming the source of acceleration. Satellite-borne instrumentation is being built to in­vestigate such phenomena by mapping the magnetic field of the earth at very high altitudes.

Sun Spots . Last, but of t remen­dous importance, is the optical s tudy of solar flares, sun spots, and their corre­lation with the appearance of high

REPORT FOR ANALYTICAL CHEMISTS

IGY composition experiment prior to a test in the preparation area at Fort Churchi l l . A f te r the test the rocket is taken to the launching tower through the tunnel in the background

energy ultraviolet and x-radiation in our upper atmosphere. Special empha­sis will be placed on this program dur­ing the maximum of the 11-year sun-spot activity cycle in 1958.

Upper Atmosphere Tools

One can readily see how closely con­nected are these many lines of endeavor. Yet, the variety of tools used for these investigations gives little evidence of the common goal, t ha t of finding out what goes on both inside and outside the atmosphere. Many of these tools are adaptations of appara tus familiar to most scientific people; others are developed specifically for use in this newly acquired "laboratory." Some of the more recent information ac­quired by these instruments is summa­rized in Figure 1.

In the far right are shown, at typical peak-of-fiight altitudes, the rocket vehicles most often used for this re­search work. The solid-fueled Rockoon is light and manageable enough to be carried by balloon to about 15 miles, where it is fired. By balloon-lifting the rocket through most of the earth's atmosphere prior to firing, the amount of rocket performance lost through atmospheric friction is minimized. The Nike-Cajun comprises a solid fuel Cajun rocket and a Nike solid fuel booster. This medium-high altitude combination is easy to handle and requires a mini­mum in the way of launching facilities compared to the Aerobee-Hi which is a liquid-fueled, boosted rocket travel­ing 50 miles higher than the Nike-Cajun. Satellites are now making measurements at higher altitudes where the atmospheric drag is low enough to allow many complete orbits of data gathering before satellite destruction in the lower atmosphere.

In the center of Figure 1 is the dominant source of activity, the sun. To the right of center is seen a tempera­ture graph, pressure (in atmospheres) , and mean free pa th figures, all of

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which are plotted against altitude, with miles on the right and kilometers on the left. These parameters to 200 km. were measured with pressure gages flown in Aerobee-Hi rockets. The nov­elty of this particular experiment lies not only in the instrumentation, but in the method of its use.

Mechanical and Ionization Gages. Two types of instruments are flown: mechanical pressure gages, some of which have a sensitivity to pressure changes of less than 10~5 mm. of mer­cury, and ordinary Philips ionization gages to read absolute pressures from 10~4 to 10~e mm. of mercury and pres­sure changes of 10~8 mm. of mercury. The mechanical gages gather data from 20 to 150 km., while the Philips gages perform best at altitudes above 100 km. Whereas these gages are cali­brated before flight to measure only one parameter (pressure), the proper placement of gages on the side of the rocket enables a determination of the density and temperature vs. altitude as well as that of the pressure.

During powered flight the rocket is intentionally spun about its long axis. Because most rockets precess in free flight so that the long axis rarely lies along the trajectory, the side mounted gages will enounter pressures which are dependent on the instantaneous atti­tude of the rocket. In particular, the measured pressure is spin-modulated, and above 100 km., the atmospheric density is a simple function of the rocket attitude, rocket velocity, the pressure gage temperature, and the peak-to-peak value of the spin pres­sure modulation.

Density (P) = j-^ (attitude, velocity, Τ gage, AP) The absolute pressure

Ρ = f2 (attitude, Tgage, velocity,

Τ ambient) where Γ ambient is equal to the ambient atmospheric tempera­ture. The gas law relation is

P = p(k/m) (Tambient) where k is Boltzmann's constant and m is the average mass of the gas particles (measured by other rocket experi­ments) .

In the above equations, gage pres­sure changes and gage temperatures are directly measured quantities. Radar plots the rocket velocity and altitude; magnetic and optical aspect devices measure the rocket attitude at all times. The three equations with the three unknowns are sufficient to de­duce temperature and density from pressure measurements. The mean free path numbers are computed di­rectly from the density and pressure figures.

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Data on atmospheric temperature and density above 250 km. are being provided by observations of the effect of atmospheric drag on the orbits of earth satellites.

Cosmic Ray Instruments. Directly under and to the right of the tempera­ture plot in Figure 1 is shown the region under 70 km. where meteor trails are visible and where primary and secondary cosmic ray investiga­tions are carried out by balloons and rockets. Primary cosmic rays, which must have energies in the BEV region to penetrate the earth's magnetic field at low latitudes, almost completely interact with our atmosphere leaving only secondary products to reach ground level. Balloons are a most appropriate vehicle for carrying cosmic ray instruments because the transition region between primary and secondary cosmic ray phenomena lies within bal­loon altitudes. Much of the existing knowledge of cosmic ray particles and energies has been gathered by balloon-and rocket-carried nuclear emulsions, a device not unlike a photographic plate. High energy particles travers­ing a stack of such emulsions leave distinctive tracks which enable particle identification to be made after develop­ment of the plates.

An instrument which avoids tedious plate examination is known as the cos­mic ray telescope and consists of a multilayered sandwich of Geiger coun­ters, proportional counters, and lead plates. The thickness of lead that a particle can traverse before being ab­sorbed is a measure of its energy. Alternate layers of lead plates and Geiger counters placed in a beam of particles serve as an. energy "filter" with the high energy particles passing through more plates and activating more counters than the low energy ones. By proper placement of the Geiger counters in the sandwich in con­junction with the appropriate elec­tronic coincidence circuitry, only those particles which enter nearly perpen­dicular to the surface of the sandwich (parallel to the telescope axis) are counted. Proportional counters placed ahead of the absorbers measure the specific ionization of each incoming par­ticle before it is analyzed by the lead plate filters. The penetration depth of the particle, the amplitude of the pro­portional counter signal, and a plot of the specific ionizations and stopping power of lead for the particles that one expects to encounter are sufficient data to identify both the particle and its energy range in many cases. Such equipment has been balloon-borne to altitudes of about 32 km.

The reduced camera-recorded data has identified primary cosmic radiation

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as composed mainly of protons and alpha particles in a ratio of 6 to 1, having a total intensity of about 0.3 particles per sq. cm. per second. Other measurements have found that the particle energies range from 109

to 1017 electron volts with a resultant total incident energy about equal to that of starlight.

Experiments of a similar principle have been flown in auroral zones in Aerobee-Hi rockets to measure particle composition and flux. Two types of particles have been found in the auroral sky: energetic [thousands of electron-volts (KEV)] hydrogen or helium ions and electrons of similar high energies. On an aurora-intercepting flight the electron flux increased when the rocket entered a visible display and diminished when it left. The ion flux, which re­mained constant above 140 km., was unaffected by the presence or non-presence of aurorae. However, upon entering the aurora, the electron flux energy (Figure 1) increased to a value of 30 to 100 times that of the ions. Distribution of both the ion and elec­tron fluxes was very nearly isotropic over the upper hemisphere while the rocket was above 140 km. No high energy electrons were detected on flights which failed to intercept aurorae, and no low energy electrons between 3 EV and 1 KEV were detected on either auroral or nonauroral flights.

Recently, U. S. satellites instru­mented with Geiger counters have de­tected high intensity radiation at 1000 km. altitudes. Current interpretation identifies the radiation as Bremsstrah-lung produced by energetic electrons having many KEV of energy striking the satellite skin.

Proton Precessional Magnetom­eter. Another instrument which is beginning to play an important role in the probing of aurorae is the proton precessional magnetometer, a device which is capable of measuring magnetic field strengths to an accuracy of 10~5

gauss. These instruments have been flown in each of the rockets which car­ried auroral particle detectors. Sharp discontinuities in the earth's field at auroral altitudes were detected on each flight, and are believed to be the result of high altitude patterns of electric current flow. Such phenomena are rather exciting and will be the object of much future investigation with both rocket- and satellite-borne equipment.

Solar Radiation. Solar radiation (Figure l) 'has been observed by rocket-borne optical instruments which have established the solar constant to be 2 calories per sq. cm. per minute, now the generally accepted value. Some of this energy is in x-radiation (about 0.1 erg

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per sq. cm. per second). Evidence is being collected that point to these solar x-rays as the mechanism responsible for producing the increased ionization in the lower ionosphere (D region) which in turn prevents long distance radio communication. Optical observations of solar flares have been correlated with radio blackouts, but it was not until a series of Rockoons, fired during such an event, discovered hard x-rays in the lowest part of the ionosphere that the connection was understood. Normal solar coronal x-rays are generally re­stricted to wave lengths greater than 10 Α., whereas those detected during flares are apparently much shorter.

The x-ray detector itself is a gas filled Geiger counter with a special window for admitting the radiation. The range of spectral sensitivity is determined at the short wave length end by the gas in the counter and at the long wave length end by the cutoff characteristic of the window. Various combinations of window material and fill gases have resulted in a number of sensitive narrow band detectors for both the x-ray and ultraviolet spectrum.

Such rocket-borne detectors have measured not only the intensity of the solar ultra\dolet (hydrogen Lyman a, 1216 A.) radiation but have dis­covered distinct celestial sources (about 1300 A.) from which we receive energy at the rate of about 10 4 erg per sq. cm. per second.

By making intensity versus altitude profiles of ultraviolet radiation, the amount of absorption per unit altitude is computed. In this way, the density of ultraviolet absorbers such as water vapor and molecular oxygen have been determined at high altitudes. Other types of photometers have measured the altitude distribution of the night glow emissions of sodium, OH, and atomic oxygen.

Ionospheric Electron Density. The left side of Figure 1 is concerned with ionospheric parameters. The graph of electrons per cubic cm. vs. altitude has been obtained with rocket-borne equipment. Until recently, all our elec­trical knowledge of the ionosphere was gathered by bouncing radio signals off the ionosphere from below and examin­ing the reflections. From the maximum frequency which sustains reflection, and from the time delays between trans­mission and receipt of the return signal, the heights and electronic densities of the reflecting ionized "layers" were in­ferred. The connotations E, F 1 ; and F 2 were given to these layers.

A rocket experiment has changed a number of these concepts. The appara­tus consists of a radio transmitter which radiates simultaneously two har-

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Figure 2. Internal structure of a 3-stage Bennett radio frequency ion mass spectrometer for measuring the ion composition of the ionosphere. This tube is made up of circular grids of tungsten mesh, knit on a stocking machine, and separated by ground glass spacers. The two cylinders are shields for the dr i f t spaces between the r.f. t r ip let -gr id analyzer stages. Ions enter the tube at the bot tom. Retarding potential grids, a t r ip let , and collector assembly are at the top

monically related continuous unmodu­lated signals, the relative phase of which is continuously recorded at a ground receiving station as the rocket travels through the ionosphere. This phase is determined by the velocity of each signal which would be the same except for the presence of free elec­trons in the intervening portion of the ionosphere. The electrons change the velocity of the low frequency signal but not the high. The phase shift record when compared with the rocket trajectory enables direct computation of the electron concentration vs. alti­tude. Results are as follows:

1. There is no longer a justification for considering the ionosphere as being made up of distinct layers. The ionos­phere is more nearly a continuum of electron density (Figure 1) where the "layers" are now known as regions.

2. By conducting conventional ground-based soundings simultaneously

with rocket firings, it has been possible to establish a technique for properly analyzing the conventional records to obtain correct electron densities.

3. During a radio blackout, the measured ionization in the D region between 60 and 85 km. is greatly enhanced.

Ion Composit ion and Dif fusive Separation Determinations

Measurement of two parameters, the ionosphere's ion composition and the diffusive separation of the atmosphere, illustrates the manner in which upper atmosphere studies are made.

R.f. Mass Spectrometer. To meas­ure these two parameters the Bennett radio frequency (r.f.) mass spectrom­eter was chosen as the sensor to deter­mine the atomic masses present and their abundance. The choice, in 1950, of the Bennett tube for use in the rocket was based on its weight, adapt-

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REPORT

32 A · For further Information, circle number 32 A on Readers'

ANALYTICAL CHEMISTRY

Akron 9, Ohio Service Card, page 101 A

ability to a rocket installation, and elec­tronic and mechanical simplicity. Fig­ure 2 shows the internal construction of a three-stage ion spectrometer, for which no magnet is required.

Mass separation is based on the prin­ciple that additional energy is imparted to an ion by a radio frequency field if the ion passes through the field with the proper phase and velocity. Each stage of the analyzer section, separated from the preceding by a drift space, consists of three grids, the center one being connected to a common r.f. source. In addition, a sawtooth sweep poten­tial is applied to the analyzer which accelerates incoming ions to velocities depending on their masses. For a given instantaneous sweep voltage, ions of a given mass will have the proper veloc­ity consistent with grid and stage spac­ing to traverse the analyzer and gain maximum energy from the r.f. field in each stage. Ions with other velocities cannot gain this maximum energy. Ions gaining maximum energy are then separated from the others by a poten­tial barrier through which only the energetic ones can penetrate. Those which reach the collector are detected by a vacuum tube electrometer.

For the Aerobee-Hi rocket installa­tion, the spectrometer (see photo of authors) is enclosed in a stainless steel envelope, and mounted perpendicular to the rocket axis in a nose cone exten­sion section (Figure 3). When the rocket is in flight, positive ions from the ionosphere are drawn directly into the tube and analyzed. On the opposite side of the rocket is an identical tube for analyzing negative ions.

At the top of this instrumentation is a third spectrometer. Its function is to analyze the neutral gas present in the upper atmosphere. Internally it resembles the ion spectrometer, but because increased mass resolution (one part in 40 instead of one part in 25) is required, it has four analyzer stages. Ions for this tube are created by elec­tron bombardment of the neutral gas at the forward end of the tube. The gas spectrometer is enclosed in a glass envelope. Prior to flight it is cali­brated, evacuated, and sealed off. A cut away view of the break off and nose tip ejection system which opens this tube when the Aerobee-Hi rocket has attained sufficient altitude is shown in Figure 4. The scheme is to attach the nose tip with a flexible cable to the rocket via the glass tubulation at the top of the spectrometer. A hammer operated by a pyrotechnic squib breaks the glass tubulation upon electrical com­mand. Energy in the compressed spring then separates the tip from the rocket and the spectrometer starts its

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3 4 A · ANALYTICAL CHEMISTRY

REPORT FOR ANALYTICAL CHEMISTS

analysis of the upper atmosphere. Al­though differential vacuum pumping is not used with these spectrometers, mass analysis begins at pressures as high as 10~3 mm. of mercury in the ion tubes and 10-4 mm. of mercury in the gas tube. The large inlet area ensures that ambient conditions exist inside the spectrometer.

The necessary instrumentation to operate the three spectrometers is labeled in Figure 3. The telemeter radioes all the data gathered to ground stations. A radar beacon is used for trajectory determination; a cutoff sys­tem is installed to terminate rocket propulsion in case the rocket turns out of the safe area.

An essential feature of the Aerobee-Hi's design is the use of vacuum seals to prevent contamination of the upper atmosphere by gas carried within the rocket. Vacuum sealing is accom­plished by the extensive use of " 0 " ring gaskets at all joints and openings in the rocket skin. Placement of a few " 0 " rings around the nose tip is shown in Figure 4. Similarly, the rocket's tail section is sealed with " 0 " rings. Finally, pyrotechnic shut-off valves installed in the propellant lines close the propellant tanks after burn­out.

Gas spectrometer data, in which the argon to molecular nitrogen ratio ob­tained during flight is compared to the ground ratio at the same pressure within the spectrometer, show that dif­fusive separation begins between 100 and 120 km. The significance here is that below this region turbulence and winds overcome gravitational forces and keep the atmosphere mixed, but above it, gravitational forces predominate and separation of the neutral gases accord­ing to their weights exists. This result is indicated by the wavy line in the center of Figure 1.

On the left side of Figure 1 are the results of the ion composition measure­ments, with the positive ions listed in the order of their relative abundance at the indicated altitudes. I t is not surprising to see that oxygen and oxides of nitrogen are the ions present in the ionosphere. However, the predomi­nance of the nitric oxide (NO) ion in the ionosphere was unexpected since its neutral abundance may be only a few parts per million. No accurate meas­urements have been made of its neutral abundance. Its appearance as an ion is certainly related to its low ionization potential (9.5 volts compared to 12.5 volts for 0 2 and 15.5 volts for N2) and to charge exchange reactions.

Future Explorations

In the future, the hydrogen, helium,

Figure 4 . Nose t ip ejection system •for protect ing the gas spectrometer during powered f l ight, and when ejected at 100 km. opens the sealed spectrometer

and low mass constituents of the at­mosphere as well as the dissociation of the molecular gases will be studied from 100 km. up. Atmospheric densities, neutral, ionic, and electronic, will be measured at higher altitudes as new rocket and satellite vehicles become available. Solar radiation and auroral particles will be under more intense observation; and satellite and rocket measurements of interplanetary mag­netic fields, at present an area open only to speculation, may produce evi­dence for the auroral particle accelerat­ing mechanisms.

What the next few years may bring is, of course, speculation; but when appropriate vehicles are available, the moon and solar atmosphere are the next logical areas of interest.

Acknowledgments The Upper Atmosphere Research

Program has been realized through the financial backing of the Department of Defense, with a portion of the IGY program being supported by the United States National Committee for the IGY. The IGY rocket flights at Fort Church­ill were made possible by generous coop­eration of the Canadian government.

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