Summary Session, 19 February 1957
Environment and Measurements Panel
Participants and Their Topics
Fred L. Whipple (Panel Leader), Director, Smithsonian Astrophysical Observatory; Professor of Astronomy, Harvard College Observatory
Spencer, Research Engineer, Engineering Research Institute, University
"Possibilities for Measuring Gas Composition at Very High Altitudes"
Institute of Geophysics, University of California at Los Angeles
"Recent Studies of the Atmosphere and Ionosphere Between 90 and 300 km."
Roberts, Director; High Altitude Observatory, University of Colorado
"Effects of Abnormal Solar Activity"
Friedman, Head, Electron Optics Branch, Naval Research Laboratory
"Solar X-rays and the Ionosphere"
Hinteregger, Chief, Physical Measurements Unit, USAF Cambridge Research
"Interaction of Extreme UV Radiation with Matter"
John E. Naugle,
Senior Staff Scientist, Convair Scientific Research Laboratory
"The Temperature Balance"
H. Victor Neher,
Professor of Physics, California Institute of Technology, Pasadena,
"Cosmic Rays in Space"
Ralph J. Havens,
Head, Experimental Physics Dept., Aeronutronic Systems, Inc., Glendale,
"Magnetic Field, Cosmic Ray and Ion Density Measurements in Interplanetary Space"
Head, Research Department, Litton Industries, Beverly Hills, Calif.
"The Concept of an Inhabited Space Simulated Laboratory"
I should like to preface this report by a very short statement concerning the progress of the last decade, particularly in our knowledge of the environment to limited altitudes as reckoned by this group, but also to considerable altitudes as measured from the ground. I would say that, as a result of investigations conducted by the rocket research program, by other geophysical research, and by astronomical research, we now have good knowledge of atmospheric temperature, pressure, density and electron content to an altitude of some 200 kilometers. To a somewhat lesser altitude of about 120 km we have a good knowledge of atmospheric composition and some certainty in regard to certain ions, to winds, cosmic rays, and a bit on magnetic fields. Again, at great distances, we have a fair information on the solar radiation field and on the meteors, the latter unfortunately in a range of little interest to space travel because of the infrequency of larger meteors.
We still need more information on the extremes of x-ray and ultraviolet radiation from the sun, on ions, electrons and motions of the gas in the higher atmosphere, on meteors, particularly among the smaller dust particles and on primary cosmic rays. Many of these data we need in terms of variations with solar activity with seasonal effects and even with tidal effects. So our panel on environment has taken up various aspects of these problems from the viewpoint of needs and how we might conduct experiments to get the information. We have, to some extent weighed the importance of the information on eventual space travel.
We start with a report by Mr. Nelson W. Spencer of the University of Michigan, who discussed methods of measuring the gas composition. The desired result, to conduct spectrometer-type composition experiments to altitudes within the range of instruments that are postulated, is seen feasible to the order of 10–11 milobars (10–14 atmospheres) which is not much above the altitudes that I discussed before. We need and can get more information at the 200 to 300 kilometer level. Above that, most of the methods now look rather unfeasible. He discussed various problems and various detailed techniques that might be utilized in making these measurements. In the discussion it came out that we do have a bit of information by induced radiation up to an altitude as high as 1,000 km via the sunlit aurora measures. It may be possible that we can obtain more information by exciting large masses of the gas.
Then, on the ionospheric side, Dr. Hilde K. Kallmann of the Institute of Geophysics at U. C. L. A. discussed what I think is the first successful effort to reconstruct theoretically the ionospheric electron content. As a basis she used rocket data for the incoming solar radiation equilibrium conditions' in the high atmosphere, including various methods for removing the electrons. She has now developed a theoretical ionosphere good to nearly 300 km, consistent with the observations as we know them. The most striking result of these rocket experiments on the ionosphere has been to give a quite different picture of it than the ionospheric physicist gave us. They visualized rather discreet layers, D, E and two F layers, which coalesce or disappear and vary in altitude. The measurements do not indicate strikingly distinct layers, but only slight variations in the electron content as a function of altitude, i.e., rather small perturbations on the generally smooth ionospheric gradient. Dr. Kallmam finds the "layers" to be considerably lower than earlier measures suggested.
Then we go to the trinity of papers on solar activity, the resultant x-rays and ultraviolet radiation and their effects on matter. The first of these, by Dr. Walter 0. Roberts of the High Altitude Observatory in Colorado, concerns two types of solar activity which result in changes in the environment in planetary atmospheres and all through the solar system. The first of these so-called abnormal activities is the solar flare, in which you have essentially a very high velocity jet radiating out from the surface of the sun and producing temperature effects up to about a million degrees Kelvin. The flares, which generally last for rather short times, minutes to hours, can produce explosive rises in ultraviolet and soft x-ray emission. There is also evidence for increased particle emission, corpuscular radiation, which consists mostly of hydrogen ions moving at high velocities and, occasionally, cosmic ray activity. The other type of abnormal solar activity is less spectacular but perhaps more significant in certain respects. This is the type of activity that appears as an irregularity in the solar corona. Lasting for days to weeks, these hot regions around the sun can reach temperatures of the order of several million degrees with marked increase in radiation in the unobservable region between 100 angstroms and 900 angstroms. More observations are needed of these phenomena, particularly the latter from above the atmosphere, to darify what is occurring on the sun, and as a result, also in the high atmosphere and in space.
In the second paper of this group, Dr. Herbert Friedman, of the Naval Research Laboratory, discussed the effects of the solar x-rays on the ionosphere. He comes to the conclusion, based upon the rocket research of the Naval Research Laboratory, that the E region is largely formed by the x-rays of wavelengths from 10 to 100 angstrom units and that the energy distribution seems to resemble a gray body at a temperature of something of the order of 700,000 degrees. The maximum is at 30–40 A, giving a flux of about 0.1 erg/cm2/sec at the ionosphere. The short wavelength end of this soft x-radiation, 10 to 20 angstroms, is highly variable and he confirms the statement that during a Class-1 flare, emission was observed down to 3 angstroms, which is verging on the region of hard x-rays. These x-rays penetrated to an altitude of 75 kilometers, which is lower than we expected a few years ago, and were s d a e n t to double the D-region electron density. He feels rather strongly that these x-rays play an important part in the production of the D-region ionization.
The third paper on the subject, by Dr. Hans E. Hinteregger of the Air Force Cambridge Research Center, concerned the effects of the extreme ultraviolet radiation on matter. He stressed heavily the various problems that need to be studied in the laboratory, particularly with radiation below 900A. He has been responsible in the past for great advances in knowledge of the photo-electric effect; the efficiency goes up from the order of 10–3 for visible radiation to a moderate fraction of unity, even 0.2 for radiation in this far-ultraviolet region. He does not know and would like to know, as would all of us, the possibilities and the hazards, concerning the photoelectric sputtering removal of actual atoms from solid surfaces by ultraviolet and x-radiation. And there are other related problems of great astronautical interest. Dr. Hinteregger discussed to a considerable extent the type of laboratory research and also rocket and satellite research that is needed in the extreme ultraviolet to find out the interaction with matter. I'm glad that he is investigating these problems and doubt that it will be long before we may expect some very significant answers from him on this matter.
Then, on an entirely different subject, Dr. John E. Naugle of Convair, discussed what off-hand seems Like one of the simpler problems – the energy balance of a body out of space. It receives radiation primarily in the visual region from the sun, in the far infrared from the earth, and, of course, radiates in the far infrared heat spectrum. We might think it is a relatively simple matter to find surfaces with the proper emission and absorption coefficients to maintain the desired temperatures for vehicles in space. This does not prove to be the case. It is difficult to find the proper surfaces with these proper characteristics of emission and absorption in the two extreme regions of the spectrum to maintain this temperature balance. Particularly this is true in the case of a near earth satellite where the satellite is moving from the shadow of the earth into the sunshine and back again in relatively short periods. The problem is complicated by uncertainties that must be resolved before we can hope to have this problem entirely solved, namely, the deterioration that may occur on these surfaces after we put them into space. A suitable surface material subjected to x-rays, ultraviolet radiation, corpuscular radiation, high energy ions and meteoric bombardment in space may or may not maintain its delicately selected characteristics of emission and absorption so essential to the maintenance of proper temperature in a space vehicle. Of course, if we are elaborate enough in the vehicle, we can put curtains, windows, shutters or what not, to vary the circumstances as the surface varies with time; nevertheless, it would be desirable to have one that would maintain the proper temperature without such complicated arrangements.
Next I presented some discussion of the situation with regard to meteors, or meteorites, in space and the possibility that they may be a hazard. There are two aspects to this problem; one concerns the larger particles that can actually puncture the skin of a vessel to do serious damage and, the other, the lower extreme of the particle size distribution where most of the mass is contained, dust particles that erode away the surface producing small pits and general deterioration of the surface. A number of years ago, about ten years ago, and again about five years ago, (in the Physics and Medicine of the Upper Atmosphere) I presented tables of the best guesses on this subject. Since that time, we have learned quite a bit about meteors. It now looks as though the numbers are probably higher. I point out that we are extrapolating by a factor of several hundred times to get to the puncturing size; on the other hand, we've discovered that we are not dealing in the ordinary meteors with typical museum meteorites, stones or irons, but with cometary fragments which have very low density. The consequence is to increase the derived masses of meteors. So these tables have changed markedly in the direction of more hazards from meteorites in space. The masses increase by about 20 times, the energies about 10 times and the frequencies or numbers about a factor of seven from those earlier estimates. As a concrete result suppose we have a half-millimeter aluminum skin on the satellite vehicles, the IGY satellites. The chance of puncturing according to this still very crude estimate is the order of one fourth per day, or, on the average, one puncture in four days.
Some extremely valuable work has been done recently on micrometeorites by Berg and Meredith, through certain experiments in rockets above the lower atmosphere between 80 and 100 kilometers. They confirm the rough order of magnitude of the total mass of this fine material that we expected to find in space. Calculations on that basis indicate that if we are to deteriorate a surface, etching away the order of visible wavelength of light divided by 2 pi (which I would consider not very serious in terms of optical characteristics) the amount of time invo1;ed would be the order of a year. So it doesn't look as though deterioration of surfaces optically would be very serious in a time less than a year, but I emphasize the need for more observations to confirm these calculations.
Dr. H. Victor Neher, of the California Institute of Technology, discussed the observations of cosmic rays. Some rather remarkable results have come out in the last few years with regard to the distribution of particle masses in the cosmic rays. As you know, a cosmic ray is merely a high-velocity atomic nucleus, usually hydrogen, frequently helium and sometimes heavier. Compared to ordinary cosmic abundances the fraction of the heavier elements is extremely small and there is, in the rest of the universe, practically no lithium, beryllium and boron. However, in cosmic rays it turns out there's about a half a percent of lithium, beryllium and boron, about the same abundances of these elements as for carbon nitrogen and oxygen. Relative to ordinary stellar cosmic abundances there are more of the heavier nuclei. This presents a theoretical problem and, in terms of space travel, we are very interested in these heavy nuclei with high energies, which can do a great deal of damage.
Dr. Neher pointed out that during maxima of solar (sunspot) activity the cosmic-ray influx on the earth decreases from the solar minimal activity. He concludes, therefore, that the sun does not produce cosmic rays. If it did there should be more cosmic rays produced by the much increased activity of the solar surface layers. Dr. Roberts, on the other hand, contested this deduction on the grounds that: (a) solar activity does, indeed, produce cosmic rays but (b) it also produces stronger magnetic fields that (c) in some fashion, possibly by greater extent, reduce the cosmic-ray flux at the earth. This fundamental difference needs badly to be resolved. Perhaps the IGY research will answer the question.
Now, we go on to a paper by Dr. Ralph J. Havens of Aeroneutronic Systems, on magnetic field, cosmic ray, and ion density measurements. He has calculated the weights required to send up to 106 miles experiments to answer some of the basic questions with regard to these three unknowns, magnetic fields, cosmic rays, and ion density. Dependent upon the efficiency of the rocketry system used, he finds for each pound of payload the need is somewhere between 1,000 and 60,000 pounds of initial rocket weight. Rockets with general efficiency of those that have been utilized in upper-atmospheric rocket research belong to the high-ratio class. It doesn't take much more power to go from a million miles on indefinitely. Dr. Havens says that the size of this ratio will decrease from a higher to a lower value in the next few years, as the rocket performances increase. He visualizes half pound equipment for cosmic rays, 1/4 pound for magnetic fields (to 10–5 gauss accuracy), a half a pound for ion densities (to 1/cm3). He combines all these together with a half pound of batteries and a miniaturized telemetering system for a total of only 4 pounds to provide the total combined experiment. It is very dear that we need this information. The 4pound experiment for all three would give us about 100,000 bits of information. I am told that it takes 5 bits for one letter, 25 for a word. That gives about 4,000 words, which is quite a bit of information, the length of this report.
Now we come to an entirely different concept, a paper by Dr. Richard A. Roche, head of the Research Department of the Litton Industries, about an inhabited space simulation laboratory. The time has come when such a laboratory is absolutely essential for an understanding of the operation of equipment in space and the building, construction and testing of equipment to go there. He has particularly in mind the desire to test electron tubes that are to operate in space where the charge may be variable, and problems of temperature equilibrium and surface phenomena. In this vacuum laboratory he has been investigating the difficulties of inserting a man. They find that it is indeed difficult to keep a man alive in a vacuum! Some of the problems that seemed rather simple off-hand, such as the ability to bend one's arm and flex one's fingers, turned out to be extremely difficult under the high pressure conditions in a space suit. Also difficult are the problems of cooling, of protecting the vacuum against the gases from the suit itself, of dealing with evaporation within the suit and combating the particular hazard of possible breakage in the equipment, i.e., instant decompression. By a show of hands, eleven people definitely have experiments that need this type of laboratory equipment very badly. It is interesting to see how such a laboratory simulation of space is required in the development of equipment to go into space, not necessarily for manned vehicles but equipment for sounding rockets, satellite vehicles and other space vehicles.
I think it must be clear that we were able in the course of one afternoon only to discuss a few of the major problems of the environment that require basic research as necessary requirements before scientists can go out of this world.
In this audience there are many experts in this field who could have made major contributions. I regret that there was no time for them to join in the presentations. I wish to thank all of the members on the panel for their cooperation and effort. Thank you.
Thank you very kindly, Dr. Whipple, for the very interesting presentation. We hope that the experts who did not come to words will use these last opportunities.