MEASUREMENTS OF PRESSURE AND TEMPERATURE IN THE UPPER LAYERS OF THE ATMOSPHERE

In 1946–1947, at the White Sands proving ground, located at 33° north latitude and 105° west longitude in a desert region of the state of New Mexico (USA), a series of flights of German V-2 rockets was carried out, specially equipped for conducting scientific investigations at high altitudes. The published data are extremely scanty and amount to a few notes of a preliminary character.

Pressure measurements were made during two flights: October 10, 1946,^1 and March 7, 1947.^2 For this purpose manometers were installed on the rockets, whose readings were transmitted by radio to a self-recording station located on the ground.

The pressure at low altitudes was measured by manometers located in the tail section of the rocket, consisting of a sylphon bellows, whose displacement was transmitted to a potentiometer. The manometers were calcu-

were calibrated for a pressure interval from 760 to 10 mm of mercury. In the flight of 10 October the manometer failed at a pressure of 120 mm Hg (about 12 km altitude), probably as a result of resonance with the vibrations of the rocket.

As the authors indicate, German measurements made in an aerodynamic tube showed that at speeds of the order of 1.5 km/sec (a speed close to that of the rocket) a manometer located in the tail section of the rocket should indicate a pressure approximately 10% lower than the pressure of the surrounding medium. The pressure measurements at low altitudes were compared with data obtained on the basis of radiosonde measurements, and proved to be in good agreement with them. A discrepancy occurred only for altitudes of about 4–5 km, which corresponds to the moment when the rocket reaches the speed of sound (Mach number = 1). This agreement serves as direct proof of the possibility and accuracy of measuring pressure in the indicated manner.

For measuring pressures at great altitudes—from 2 to \(10^{-3}\) mm Hg—Pirani manometers with platinum and tungsten wire were used. The latter were ordinary incandescent signal lamps (6 watt, 110 volt), in the bulbs of which holes had been made for communication with the external atmosphere. These manometers were placed in the tail section of the rocket, and it was assumed that the rocking of the rocket (amounting to about \(15^\circ\) at an altitude of 110 km) and its rotation (with a period of about 40 sec) did not affect the readings of the manometers.

In the flight of 10 October another group of Pirani manometers was placed in a compartment inside a cone with an angle of \(13^\circ\) at the apex, forming the nose of the rocket. This compartment communicated with the external atmosphere through a group of holes concentrically encircling the surface of the cone. Calculations based on the theory and experimental investigations of Taylor and Maccoll showed that the pressure on the side of such a cone at speeds of the order of 1.5 km/sec should be approximately 1.8 times higher than the ambient pressure. In reality, however, the readings of both groups of manometers (both on the nose of the rocket and in its tail section) almost coincided, which remains inexplicable or at least, according to the authors, “most surprising,” since the expected discrepancy (by a factor of 1.8) considerably exceeds, in the authors’ estimates, both the errors of calculation and the errors of measurement.

The data obtained on 10 October 1946 are shown in Fig. 1. For comparison, curves corresponding to the standard mean atmosphere are given, as it is represented according to indirect-method data. The good agreement of the curves shows how successful the indirect methods of investigation prove to be.

In the flight of 7 March 1947, along with the Pirani manometers, a Phillips manometer was used, designed for the pressure interval \(10^{-3}\)—\(10^{-5}\) mm of mercury (altitude interval 100–120 km) and installed on the conical nose of the rocket at an angle of \(15^\circ\) at the apex. Its readings were reduced to ambient pressure on the basis of the Taylor and Maccoll theory, and it was established that at an altitude of 110 km the rocket was in conditions for which this theory is valid.

The results of the measurements of 7 March are given in Fig. 2. A curve of total pressure is also given there. The authors note that after all corrections to the inertia of the Pirani manometers, amounting to about 1.5 seconds (which corresponds to an altitude interval of about 2 km), had been introduced, the data of 10 October coincided with the data of 7 March for an altitude of 60 km, but for an altitude of 80 km turned out to be somewhat higher. The authors suppose that this may be a seasonal effect.

It should be noted that the data obtained in the manner described, in addition to the rather considerable errors connected with inaccurate allowance for aerodynamic factors, may also contain errors connected with the sensitivity of the manometers used to temperature changes, as

itself of the manometer, and of the air being measured, as well as their sensitivity to changes in the composition of the air (for example, dissociation). Which of these factors were taken into account, and how sound the data are that underlie such accounting, the authors do not report. It may be thought that the need

Fig. 1. Pressure measurements on October 10, 1946.
A — at low altitudes, by means of a siphon manometer (lower and left scales). B — at high altitudes, by means of a platinum Pirani manometer (upper and right scales).

for introducing such corrections is one of the weakest points of the measurements described.

The temperature data for the upper layers of the atmosphere according to the data of March 7, 1947 are shown in Fig. 3. They were obtained in two ways. First, directly from the pressure gradient (using the barometric formula and the equation of state) and, second, from the speed of sound. The speed of sound, in turn, was determined from the velocity of the rocket, calculated on the basis of radar measurements, and the Mach number, determined from the relation between the external pressure and the impact pressure. The results of direct measurements of the air temperature—such measurements, apparently, were made—are not given. The authors estimate the error in determining the temperature as follows: ±15° in the altitude interval 50–60 km, ±15°

in the altitude interval 65–70 km, ± 20° at an altitude of 72.5 km, and ± 40° above 100 km. For altitudes between 10 and 20 km the temperature determined in this way proved to be 5–20° lower than the actual temperature (determined from radiosonde observations), which the authors explain by the paucity of radar data for this altitude interval. Let us note that temperature data obtained by various

Fig. 2. External and stagnation pressure as a function of altitude according to measurements of March 7, 1947.

methods are presented for various altitudes (see Fig. 3), which shows, obviously, that there is no unintentional selection. The data for October 10 differ quite appreciably from the data for March 7, which the authors regard as a seasonal effect.

The general outlines of the temperature–altitude curve are determined quite clearly from the rocket data and, just as in the case of the pressure–altitude curve, agree fairly well with those representations which have developed on the basis of indirect measurements (the solid curve in Fig. 3 co-

corresponds to the mean standard atmosphere, and was constructed on the basis of indirect measurements).

Thus, the full published data of the rocket investigations generally confirm the picture of the structure of the upper layers of the atmosphere which has been revealed in recent years by means of indirect methods of investigation (and which differs so radically from that assumed

Fig. 3. Temperature as a function of altitude (March 7, 1947).
Crosses denote data computed directly from the pressure gradient; black circles denote data computed on the basis of measurements of total pressure; triangles denote data of balloon-sonde measurements.

earlier) and have not introduced anything essentially new into it. Individual refinements still remain insufficiently reliable, all the more since rocket measurements are still by no means impeccable. Undoubtedly, however, rockets, making it possible to raise research instruments (even if, it is true, only for a very short time) to previously unattainable altitudes, are becoming an important means of investigating the high layers of the atmosphere and make it possible to obtain a number of characteristics inaccessible to indirect methods.

Naturally, the question arises: what new contribution does the appearance of so powerful a means of direct investigation of the high layers of the atmosphere make to our attitude toward indirect methods? Does the need for their development and improvement disappear? Of course, indirect methods cannot everywhere compete with direct measurements. However, the range of questions accessible to investigation by means of rockets, launched from time to time to great altitudes, is significantly narrower than the range of questions accessible to investigation by indirect methods, especially if one takes into account the high cost of rocket investigations, which gives them the character of being unique. It is enough to point, for example, to questions of seasonal or diurnal variations of particular parameters. On the contrary, direct measurements can serve as an excellent check on the validity of those hypotheses which are laid down

into the basis of indirect methods, thereby completely removing some of the uncertainty inherent in indirect methods in the absence of such control. Thus, rocket investigations create a firm foundation for the development of indirect methods, at the same time considerably expanding their possibilities. It should be noted that Soviet scientists play an outstanding role—and, in a number of questions, a priority role—in the development of indirect methods for investigating the high layers of the atmosphere.

G. Rozenberg

CITED LITERATURE

1. N. R. Best, E. Durand, D. Gale and R. J. Havens, Phys. Rev., 70, 985 (1946).
2. N. Best, R. Havens and H. LaGow, Phys. Rev., 71, 915 (1947).