STRATOSPHERE EXPLORATION AN ADDRESS BY CAPTAIN ALBERT W. STEVENS, AIR CORPS, U.S.A.
Thursday, February 27, 1936
The President, Mr. J. H. Brace, in the Chair.
PRESIDENT: Gentlemen, in our modern life, preceding the known design of any particular device, we find years of work carried on by scientists, by physicists, by research engineers. There is a small group of scientists who for some few years have been making studies of the stratosphere. As far as I know, the only time the stratosphere has been used, really, for transportation was during the course of the big war when shells from big Berthas landed on French sail some thirty miles distant. There is now, however, hope that at least in the sub-stratosphere use can be made for the transportation of passengers and express over distances now far apart and at a speed such as we at present do not visualize. Among this group of scientists we find our guest speaker of today, Captain Stevens, who has been associated with three flights, the last of which occurred on November 11, 1935, when he and his assistants rose to an altitude of 13.7 miles, the highest altitude yet attained by man. (Applause) As the result of that work and the scientific data which they were able to collect, Captain Stevens has received from Washington the Gardner Green Medal. His flight was carried on under the auspices of the War Department and of the National Geographic Society in Washington and I presume many of you have seen something of that, particularly if you have had an opportunity to read last January's copy of the National Geographic.
I think it is most timely to have this address of Captain Stevens's succeeding by one or two weeks the very marked lecture that we had from Air-Marshal Bishop, as I think there is a definite association between the thoughts of the two men and the work that they are carrying on in this particular field. I have much pleas ure, indeed, in presenting to you Captain Stevens. (Applause.)
CAPTAIN ALBERT W. STEVENS: Last year, and the year before, the National Geographic Society and the United States Army co-operated to put into the air two great stratosphere balloons-by far the largest ever constructed. Because of previously unknown factors in the design of such enormous balloons, the first one ripped in flight and finally exploded; we, in the gondola, had to jump for our lives. Another balloon was built, and it burst while still on the ground. Fortunately, our spon sors still had faith in us. We discovered the weak places in design, repaired the balloon, and finally flew it last Armistice Day to an elevation of 72,395 feet. This flight was entirely successful, and we returned to earth with many films and other records of performance of instruments at very high altitude.
The advantage to be gained with such very large balloons is that one may carry standard size, comparatively heavy, instruments into the stratosphere. Our load of instruments was over a ton. Balloon, gondola, instruments and ballast weighed 7 1/2 tons at the time of takeoff. The balloon envelope, or bag, weighed over three tons, and when it filled out it was nearly 200 feet in diameter, with a volume of 3,700,000 cubic feet. At sea level this enormous balloon would have lifted much more than a hundred tons, had it been filled. But we filled it less than seven per cent full, and this comparatively small quantity of gas swelled and swelled as we rose, until it filled the bag and then overflowed through openings in the bottom of the bag. When we stopped rising, we were in the air only 1/25th the density of air at sea level.
We remained at this elevation for nearly an hour and a half; our instruments, which had been operating automatically from the time we left the ground, continued to function, and many of our best records were obtained in the time spent at the very top of the flight.
At this elevation each of us in the gondola weighed a pound and a half less than when we were on the ground four hours earlier. Of course, we were not conscious of this change of less than one per cent in weight, but it was theoretically there, and one of the instruments we carried indicated this small change. We were nearly 14 miles from the earth. To reduce our weight to one half, we would need to go nearly two, thousand miles away from the earth's surface, which is, of course, impossible. That introduces the question that is sometimes asked us-"Some day aeronauts will go so high that they will start going the other way. Is there any probability of this?" There is no such probability, for it is calculated that an object must be shot out from the earth's surface at a truly tremendous speed - over seven miles per second - before it can escape the gravitational force of the earth. Such a speed has never been attained, or even approached, by our very largest guns, and it is not likely that guns will ever give this great speed to a projectile. With rockets it is doubtful, even theoretically, that this speed may be attained. Certainly, practically, there is no hope, for no certain means has been found to guide rockets on a straight course upward, and no material is known that will stand the terrific heat of the rocket flames for the time necessary to pass through the earth's atmosphere.
Airplanes have attained 47,000 feet, and are not likely to go much higher, except for a few possible thousands of feet, at increasingly prohibitive cost. The practical limit for high altitude flying, commercially, seems to be 30,000 feet. It is quite likely that the next year or two will see airplanes, built with air-tight cabins, flying at 30,000 feet for distances of six hundred to a thousand miles. At this elevation they escape storms, and are above most clouds. To go higher is unnecessary and costs too much in fuel and time. The pressure in the cabins of such airplanes will not be sea level pressure, but will be adjusted to a reduced pressure that a cabin will stand, and still permit the passengers to be comfortable.
That is exactly what we did in the gondola of our balloon, the Explorer II: We had an air pressure corresponding to that of a mountain 13,000 feet high. We were able to work in comfort. Actually, we only knew that we were surrounded by air extremely cold and 1/25th normal density, by our instruments.
At sea level scientists calculate that 30 cosmic rays per second pass through our bodies. At our elevation there were thousands per second passing through our bodies. The instruments we carried registered the number and the direction of these rays. If it were possible for a person to live for weeks at this great altitude, it is possible that the effect of this increased radiation might be harmful. On the other hand, at sea level, they may be beneficial or even necessary, to human life. No one knows at present. The total energy from them is not as great as popularly supposed, and at present scientists are more concerned in discovering what they are, and what causes them, rather than how they may be used.
The purpose in flying in the stratosphere is not primarily to get as far away from the earth as one can. It is rather to get up to an elevation where there is as little air above you as possible. There is a considerable difference between the two purposes. In other words, we wanted most of all to get to an elevation where radiation from space is coming in without being checked by a great mass of air.
Stratosphere flying, for many scientists, is to obtain data on cosmic radiation and on the amount of ozone present at high elevations. Stratosphere flying, from the view point of the Bureau of Standards and the United States Army Air Corps, is for the purpose of getting additional data on the temperature of the air, and the pressure at elevations reached as compared with measurements of the same elevation by means of aerial cameras.
In making the flight it was best not to concentrate on one line of work entirely, and so we decided to take all the apparatus that could be furnished by leading scientific institutions of the United States and to do as many things of scientific interest as possible.
For instance, we obtained samples of the air during the time of our highest elevation. Each of the two samples consisted of nearly six gallons. When six gallons of this very rare air, under only 1/25th of an atmosphere of pressure, is brought down to earth, it amounts to less than one quart under our normal pressure. These two samples represent the only sizable samples of air that have ever been captured at such a height above sea level. Their analysis has been completed by the National Bureau of Standards, by G. N. Shepherd. The studies indicate that the composition of the stratosphere air is almost the same as that of air at ground level. Very slight differences have been found, but their significance has not yet been established.
With the cosmic ray apparatus furnished by the Bartel Research Foundation of The Franklin Institute it was found that the intensity of radiation increased steadily up to 57,000 feet where it became 55 times as strong, from the vertical, as at sea level. At the maximum elevation of over 72,000 feet, the vertical intensity decreased to 42 times. The extraordinary thing was that it was found that at the highest elevation almost as much radiation came in horizontally as vertically. At the earth's surface practically all of cosmic radiation comes in vertically.
The study of the amount of ozone that is present in the atmosphere is tremendously interesting. Up to a few years ago it was thought that ozone existed largely at very high elevations, beginning at 25 miles or more above the earth's surface. But now, from the investigations of Professor Regener and others it is believed that ozone exists at much lower elevations. Two spectrographs were taken along on our last flight; one on the outside of the gondola and one on the inside. These instruments were designed and built by the Bausch & Lomb Optical Company and fitted with cameras made by the Folmer Graflex Corporation.
The atmosphere not only holds back cosmic rays but holds back a certain amount of sunlight. The shorter waves of sunlight apparently are responsible for the formation of ozone in the atmosphere. The changes in the spectrum of the sun as these instruments rose higher and ' higher were recorded photographically on ultra-violet sensitive film, especially coated for the flight by the Eastman Kodak Research Laboratory. The cameras of both instruments automatically made photographs of the spectra and at the University of Rochester and at the Bureau of Standards measurements are still being made showing the extension of the short wave end of the spectrum as the altitude increased. Dr. Brian O'Brien and Dr. F. L. Mohler point out that the balance of ozone in our atmosphere has a tremendous influence on life as we know it. If ozone were rare, we would be sunburned by a few minutes exposure to the sun. If ozone were more, then we would probably 'die for lack of essential vitamins. Also, it is likely that there would be an enormous increase in bacterial growth on the earth's surface which might be fatal to human life. It is evident that the small amount of ozone in the atmosphere is a very important regulator of life on the earth's surface. At the altitude reached by our balloon 20 per cent of the total ozone of the atmosphere lay beneath the balloon.
An apparatus made by the Department of Terrestrial Magnetism of the Carnegie Institution of Washington, D.C., measured the change in the electrical conductivity of air from the time the balloon left the ground until it attained its highest elevation. Ionization of the atmosphere grows greater as one rises above the earth to a region of greater cosmic radiation. The more the air is ionized, the more easily it conducts electricity. From the measurements of Dr. O. H. Gish and K. Sherman it appears that the conductivity of the air became 81 times sea level value at 61,000 feet and at 72,000 feet the recorded value was 50 times the sea level value.
The apparatus of the National Broadcasting Company functioned perfectly through the flight and the signals from the 8 watt transmitter in our gondola were received all over the United States. Above 60,000 feet the signal strength decreased somewhat and so far there has not been any satisfactory explanation for the phenomena. Not only were our outgoing signals well received, but we heard perfectly the conversation from the National Broadcasting Company ground station. Had it not been for the noise of the many instruments operated in the gondola, and for small difficulties caused by audio feedback in the confined limits of the gondola, we could have talked as easily as over an ordinary telephone.
At the top of the flight, the sky became very dark. Our instruments showed that the intensity of sky light was only 10 per cent of that at the earth's surface. To the eye the sky was almost black with a touch of very dark blue. It has been difficult to describe exactly the appearance of the sky. The nearest I can come to it is to compare it with the appearance of dark blue cloth under the rays of a quartz mercury vapor lamp.
The light that comes from many substances, on which ultra-violet light is shining, gives such substances a somewhat different appearance than when viewed under normal conditions. For instance, on the flight of the Explorer I, we noticed that the ropes which went up to the balloon had an unusual phosphorescent glow, and at times these ropes appeared larger than normal. Possibly water vapor was coming out of the ropes under the reduced pressures of our higher elevation. What we saw perhaps was the sun's light on minute quantities of vapor. At times clouds of smoke appeared to roll by the windows of they gondola. This, too, may have been vapor coming from ballast sacks, battery boxes, ropes, or parachute bags.
We received a letter from Mr. E. A. Klarup of Burke, South Dakota, who stated that he, and several other residents of Burke were watching the balloon through field glasses. While they were watching there suddenly appeared what seemed like quite a heavy smoke around the balloon. Several of the party saw this and some even remarked that the balloon might be on fire. This was at approximately 12.05 Central Standard Time when the balloon was almost due west of Burke, perhaps a trifle north of due west. It is estimated that the balloon was then approximately 100 miles west of Burke. The field glases used were eight power. The sky was very, clear with not a cloud in sight. Since several persons saw the same phenomenon, it is likely that there must have been something unusual. From our view point inside the gondola we were not aware of this general effect. Looking up through the upper window of the gondola we could see only the rigging and the lower surfaces of the balloon. We photographed with a National Graflex Camera loaded with DuFay color film, the balloon and the sky beyond it. These color films, when developed, showed that the sky was darker than the dark blue field of a large flag of the United States that hung in the rigging.
Our coldest temperature was at the very top of the flight, but it was not very much colder than it had been at 35,000 feet. On the day of the flight of the Explorer II the base of the stratosphere was apparently at 37,000 feet, for it was here that our instruments recorded an inversion of temperature. The temperature had been dropping from ground level until it reached -57 degrees C.
Then it rose to -55 degrees C. Then, as we rose higher, it dropped very slowly indeed to -62 degrees C. It will be seen that the great drop in temperature occurs in the first 35,000 feet. The next 35,000 feet gives very little difference in temperature. This region, the stratosphere, has been called the iso-thermal region, or the region of nearly constant temperature. It is probable that if we could ascend several miles more that the temperature will get slowly warmer, and if we could go another fifty or one hundred miles, it is then likely that the air, at least in the daytime, would prove to be very hot. Some scientists have estimated the temperature of the air at extremely high elevation as being hotter than boiling water and some have estimated that it is at the temperature of melting brass. Because of the extreme thinness of the air at these elevations, and its consequent lack of mass, it is not likely that water will boil, or brass melt, in the period of a half day at these elevations. However, a thermometer of very small mass would perhaps record such great temperatures if we could only send such an instrument to very high elevations and leave it there for several hours. There seems no way to do this, so the matter will probably remain one of speculation. Even if we could shoot rockets very high, some of the instruments carried would not record because it takes a certain length of time for them to register. Barometric readings would also be difficult because of the pressures generated by the travel of the rocket itself. Furthermore, since instruments are rather delicate it is doubtful whether any of them would survive the shock of the start of the rocket.
The frequency of the outgoing signals from the balloon was 13,050 kilocycles. The incoming signals were received on a frequently slightly over 6,000 kilocycles from a 200-watt transmitter located by the National Broadcasting Company at Rapid City. During the flight we talked to the giant China Clipper, an airplane flying over the Pacific between San Diego and San Francisco. We conversed with Captain Edwin C. Musick and with William Burke Miller aboard the airliner.
Miller arranged for us to talk to a newspaper in London and we were still talking to the newspaper man in London at the time we were forced to open the portholes at about 13,000 feet. We were descending at the maximum speed we dared to drop and had to open the portholes at a time when the outside pressure of the air exactly balanced the pressure inside the gondola.
Captain Anderson did a great amount of valving from 75,000 feet until the balloon got about 40,000 feet. Since the sun was shirting on the bag, the balloon tended to absorb heat faster than it radiated heat. Consequently, unless gas was valved it refused to fall.
But once we got to 40,000 feet conditions changed. At this elevation the air was still as cold as it had been higher up, but the air now began to have appreciable mass and, consequently, as the balloon fell through this air of greater density, still -57 degrees C, it served to cool the sides of the balloon as the balloon descended. Now the gas inside the balloon began to cool and shrink and very quickly we began to pick up speed of 'descent. Captain Anderson no longer had to use the valve, but instead began to drop ballast. This was easily accomplished with our electric device for discharging ballast on the outside of the gondola. We also discharged some fine lead shot through a trap inside the gondola. Later, we dropped batteries on parachutes by pulling steel pins on the inside of the gondola that released the batteries hanging on the outside. When we got the portholes open, we cast out on parachutes our air conditioning apparatus, which we no longer needed, and our supplies of liquid and compressed oxygen. The problem of Captain Anderson was to keep the descent below a velocity that would cause air currents to whip the bottom of the bag to a point where tearing might occur. He was very skillful in doing this, and at no time did the fabric whip to an alarming degree. Our later descent was about 600 feet per minute at a maximum.
When we were quite near the ground, we could see the lanes of dust caused by the automobiles of many people who were trying to follow the balloon. Some of these people were within a few hundred feet of the balloon as it landed. We shouted to the motorists to drive ahead, jump out and catch hold of the drag rope and thereby stop the balloon. Could we have induced twenty or more people to grasp the rope, the balloon could have been brought to a stop, in which case the helium could have been released gradually through the valves in the top of the balloon. In that event we would not have needed to rip the top of the bag in landing. But either through misunderstanding or because they were fearful of the great mass and pulling force of the balloon, the motorists refused to grasp the rope.
Consequently, we looked ahead for a clear field. Ballast was thrown out in small quantities to keep the balloon from settling to the ground until we were approaching a good field. Then the balloon was allowed to settle slowly to the ground. We were drifting at about ten miles per hour. We donned the football helmets loaned us by the Rapid City School, stretched a safety belt across the gondola, and then as the gondola nearly touched the ground, we pulled together on the ripcord. The top of the bag instantly opened. It deflated so quickly that the gondola turned over on its side. Hanging to the safety rope we swung to the centre of the car, while objects of all descriptions that had been on the floor, hurtled by us. We groped around with our feet and found that we were standing on some of our instruments. It was a matter of seconds to get outside and find that the balloon itself had fallen in the direction of the wind, laying itself out as perfectly as one could wish for. The balloon was not injured except for the opening at the very top. It could have been repaired and could have flown again, but the National Geographic Society and the Army Air Corps decided that it was best not to use the same bag for another flight, but rather to cut it up. The previous plans had been to fly the Explorer II in July with helium and to fly it again in September with hydrogen. Due to the failure caused by the rip panel in July, 1935, the flight with helium fell in November, leaving no further opportunity for a flight with hydrogen the same year.
If another flight ever is made by us, we would still choose the Rapid City location because of the natural protection against wind furnished by the Stratobowl. We would use hydrogen on another occasion as the recent flight shows that this gas can be used successfully under the conditions of the last flight. We would like some day to go up again to a much greater altitude. It seems possible, according to computations by the Bureau of Standards for a balloon carrying men to fly as high as 95,000 feet. Of course, if we carry as much apparatus as we did on the last flight we must be satisfied with a few thousand feet less. It seems better to be content with somewhat lower altitudes and bring back a quantity of scientific data, rather than to make a flight just to see how high men may be carried. We could have achieved a higher elevation on the last flight had we gone lightly loaded, but we are better satisfied that the flight carried so many instruments that have added to the store of information of scientists. (Applause.)
PRESIDENT BRACE: There are a number of men in this audience that go up in the air with lots of less preparation than Captain Stevens found necessary, but I think if, like Captain Stevens, you are going up over 13 miles in the air you will require considerable preparation as well. I know we have all listened enthusiastically to the remarkable address and we have enjoyed immensely the pictures that Captain Stevens has brought with him to show us more clearly just what was done and what was necessary in order to carry out this flight.
To Captain Stevens on your behalf, I am extending our very heartiest thanks for a most interesting address. (Applause)