Abstract
The use of a container makes it possible to significantly reduce the disturbing effect of the body on the medium (gas release, disturbance of the ambient air temperature, etc.). This paper describes the instrumentation and the results of pressure measurements in the upper layers of the atmosphere (50–100 km) using an unstabilized container.
Full Text
MEASUREMENT OF PRESSURE IN THE UPPER ATMOSPHERE
V. V. Mikhnevich
In rocket experiments carried out in the United States, the rocket serves not only as a lifting device, but also as an instrument that performs measurements in the atmosphere, since various kinds of sensors are placed on the rocket itself.
In the USSR, at the Institute of Applied Geophysics of the Academy of Sciences of the USSR, in studying the structural parameters of the upper atmosphere, the rocket is used only to lift the apparatus upward. The measurements themselves are carried out away from the rocket, on a container. The container is raised in the rocket’s mortar to a certain altitude. At a specified altitude it is fired out of the mortar and continues its motion by inertia. At the moment the container separates from the rocket, the measuring apparatus on it is switched on and measurements in the atmosphere begin. During descent a parachute opens, and the container, preserving all the apparatus, lands.
The use of a container makes it possible to reduce to a considerable extent the disturbing action of the body on the medium (release of gases, disturbance of the temperature of the surrounding air, etc.).
The present paper describes the apparatus and the results of measurements of pressure in the upper layers of the atmosphere (50–100 km) by means of an unstabilized container.
APPARATUS
As is known, investigations carried out with rockets constitute a difficult experimental task.
The rocket moves at an enormous supersonic speed, traversing a distance of 200–500 km in several minutes. In the powered part of the flight, while vibrating strongly, the rocket moves with large accelerations; at the same time the vibration frequency varies over a wide range. The weight and dimensions of the scientific apparatus carried by the rocket are severely limited.
For this reason, apparatus used for measuring pressure and carried on a rocket must have low inertia, possess great strength, and have small weight and dimensions; moreover, the absence of a person during the experiments requires that the apparatus operate automatically. These requirements greatly limit the possibility of using complex and highly sensitive instruments.
On the basis of the stated requirements imposed on the apparatus, two types of manometers were chosen by us for measuring pressure:
1) magnetic electric-discharge manometer,
2) thermal manometer.
These manometers are widely used in laboratory investigations, and therefore we shall not describe them.
With magnetic electric-discharge manometers, the pressure was measured in the range \(5 \cdot 10^{-2}\)—\(1 \cdot 10^{-5}\) mm Hg.
With heat manometers, the pressure was measured in the range \(8 \cdot 10^{-1}\)—\(5 \cdot 10^{-2}\) mm Hg.
Labels in the figure: lower compartment; upper compartment; location of the manometric compartment.
Fig. 1. Container.
In the upper, openwork compartment of the container (Fig. 1) the manometer sensors are placed. The intake openings of the manometers are located in places where, as blow-down tests showed, the deviation of the local pressure from the static pressure is no more than \(\pm 30\%\) for angles of attack not exceeding \(20^\circ\) and Mach number not greater than 2.7.
In the lower compartment of the container are placed the measuring instruments, a photographic recorder, a clock, automation equipment, and electrical power supply. The compartment is hermetically sealed. In it, as in the sealed pipeline through which the high-voltage wires pass to the upper compartment, normal atmospheric pressure is maintained throughout the entire experiment. The electrical wires pass from the lower compartment to the upper one through special vacuum connectors.
The recording of pressures is carried out by photographing the readings of the measuring instruments mounted on the panel. Photographs are taken every 1.3–1.5 sec. The automation system and the manometers are switched on by means of special keys at the moment the container separates from the rocket.
The manometers are raised from the ground sealed, with a definite fixed pressure inside. At a specified altitude a special blow-off device (Fig. 2), located at the end of the manometer, is broken, and the manometer, having become connected with the atmosphere, begins to measure the pressure in the surrounding atmosphere.
Fig. 2. View of the blow-off device at the end of the manometer and the hammer.
RESULTS
Pressure. Let us consider the results of two series of pressure measurements carried out in the Central European part of the USSR (July, August, September).
Series I. The launches of the instrument containers were made at dawn. On each container two thermal and two magnetic electro-discharge manometers were installed. Fig. 3 shows the results of pressure measurements on various containers. Each of the curves is constructed from pressure-measurement data obtained simultaneously by two manometers during ascent and descent. As is seen from the graph, the results of pressure measurements on different containers differ from one another by no more than a factor of two, and from the mean curve by approximately 50%.
Series II. Measurements were carried out in the morning. The apparatus was installed both in the container and on the rocket. Only thermal manometers were placed in the rocket head (3–5 units), which measured pressures at altitudes of 50–70 km. Within the limits of measurement errors, the results of pressure measurements on the container coincided with the pressure data obtained on the rocket.
The mean pressure value determined from the measurements of Series I and the mean pressure value from the measurements of Series II agree with each other (Fig. 4).
From the results of all reliable measurements of Series I and II, a mean curve was constructed, presented in Fig. 4.
The root-mean-square error in determining the mean pressure from the smoothed curve from all measurements of Series I and II is of the order of 10%.
For altitudes of 50–67 km and 90–105 km the magnitude of the measurement error is greater than for altitudes of 70–90 km. The smoothed curves in Fig. 4 were constructed by the method of least squares, taking into account the weights of the points.
Table I and Figs. 5 and 6 present the results of pressure determinations by various researchers in the United States of America from rocket measurements.
Analysis of the data shows that up to an altitude of 85 km the pressure values determined on the container agree, within the limits of measurement errors,
Fig. 3. Change of pressure with height according to measurements on different containers.
3/x, 5/x, 6/x, 7/x, 8/x—the container norm.
Fig. 4. Change of mean pressure with height.
Fig. 5. Atmospheric pressure according to data from various researchers.
Labels in the figure:
- Vertical axis: Height (km)
- Horizontal axis: Pressure (mm Hg)
- Legend:
- Mean IPG
- Nazarek
- NRL
- Sicinski
Fig. 6. Pressure as a function of height. Standard American curve determined from indirect measurements.
Labels in the figure:
- Vertical axis: Height (km)
- Horizontal axis: Pressure (mm Hg)
- Legend:
- IPG
- Panel Rocket
- NACA
Table 1
Pressure, mm Hg
| Height, m | USSR (IIP AS), Series I | USSR (IIP AS), Series II | USSR (IIP AS), average | USA, Nazarek¹ | USA, NRL² | USA, Sicinski³ | USA, Rocket Committee⁴ |
|---|---|---|---|---|---|---|---|
| 50 000 | \(6.8\cdot10^{-1}\) | \(6.6\cdot10^{-1}\) | \(6.7\cdot10^{-1}\) | \(5.41\cdot10^{-1}\) | \(7.5\cdot10^{-1}\) | \(9\cdot10^{-1}\) | \(6.7\cdot10^{-1}\) |
| 60 000 | \(2.3\cdot10^{-1}\) | \(2.5\cdot10^{-1}\) | \(2.4\cdot10^{-1}\) | \(1.83\cdot10^{-1}\) | \(2.1\cdot10^{-1}\) | \(2.5\cdot10^{-1}\) | \(1.8\cdot10^{-1}\) |
| 70 000 | \(5.8\cdot10^{-2}\) | \(6.5\cdot10^{-2}\) | \(6.1\cdot10^{-2}\) | \(5.01\cdot10^{-2}\) | \(5.4\cdot10^{-2}\) | \(4.5\cdot10^{-2}\) | \(4.5\cdot10^{-2}\) |
| 80 000 | \(1.1\cdot10^{-2}\) | \(8.9\cdot10^{-3}\) | \(1.0\cdot10^{-2}\) | \(1.00\cdot10^{-2}\) | \(1.0\cdot10^{-2}\) | — | \(9.3\cdot10^{-3}\) |
| 90 000 | \(1.3\cdot10^{-3}\) | \(1.1\cdot10^{-3}\) | \(1.2\cdot10^{-3}\) | \(1.59\cdot10^{-3}\) | \(1.9\cdot10^{-3}\) | — | \(1.9\cdot10^{-3}\) |
| 100 000 | — | \(1.8\cdot10^{-4}\) | \(1.8\cdot10^{-4}\) | \(3.94\cdot10^{-4}\) | \(4.2\cdot10^{-4}\) | — | \(4.4\cdot10^{-4}\) |
with the pressure values obtained from measurements on rockets; above 85 km the value of the pressure measured on the container is less than that on the rocket. The higher pressure values obtained in measurements on rockets are explained by the drag of the rocket itself.
Temperature. In our experiments we did not measure temperature directly. The temperature of the atmosphere was calculated
Fig. 7. Change of temperature with altitude.
from the pressure determined by us in the rocket investigations; for this purpose the barometric formula was used
\[ T=\frac{h-h_0}{\ln\frac{p_0}{p}}\cdot\frac{g}{R}, \]
where \(p_0\) and \(p\) are the pressure at heights \(h_0\) and \(h\), respectively, \(g\) is the acceleration of gravity, varying with height, \(T\) is the mean temperature of the layer, and \(R\) is the gas constant for dry air.
The calculation was carried out under the assumption that the composition of the air up to an altitude of 100 km is unchanged, that the air is dry, and that the molecular weight is 29.
Figure 7 gives the temperature values calculated from the mean pressure of the first series of measurements, the second series of measurements, and from the mean pressure determined from all measurements of the first and second series.
Consideration of the temperature data makes it possible to establish that at an altitude of 80–85 km there is a temperature minimum, and at an altitude of about 55 km a temperature maximum. This corresponds to the results of observations by other investigators (Fig. 8). According to the data of the Rocket Committee,
Fig. 8. Atmospheric temperature. IAP, Academy of Sciences of the USSR — temperature calculated from the mean pressure.
committee, Koiper\(^5\), and others, the temperature minimum is located at an altitude of 80–85 km. However, the value of the temperature in the minimum obtained by us \((154^\circ K \pm 30^\circ K)\) differs substantially from the corresponding mean value of the U.S. Rocket Committee \((200^\circ K)\) and is equal, within the limits of measurement error, to the value of the temperature in the minimum according to Koiper, who obtained the temperature distribution from indirect measurements (mainly spectroscopic).
In our opinion, at the present time neither in the USA nor in our country is there a sufficient number of measurements for determining the structure
atmosphere at altitudes above 80 km, so that preference can be given to one or another set of results.
Table II gives the pressure values determined from a smoothed curve drawn by the method of least squares through points that are the arithmetic-mean pressure values from all measurements, and the corresponding temperature values of the upper atmosphere (rounded values are given in the table). The root-mean-square error of the temperature values presented is about 20%.
Table II
| Altitude, m | $p$, mm Hg | $T^\circ$ K | Altitude, m | $p$, mm Hg | $T^\circ$ K |
|---|---|---|---|---|---|
| 100 000 | $1.81 \cdot 10^{-4}$ | 208 | 77 500 | $1.69 \cdot 10^{-2}$ | 172 |
| 97 500 | $2.77 \cdot 10^{-4}$ | 192 | 75 000 | $2.69 \cdot 10^{-2}$ | 187 |
| 95 000 | $4.30 \cdot 10^{-4}$ | 181 | 72 500 | $4.14 \cdot 10^{-2}$ | 204 |
| 92 500 | $6.90 \cdot 10^{-4}$ | 173 | 70 000 | $6.05 \cdot 10^{-2}$ | 221 |
| 90 000 | $1.15 \cdot 10^{-3}$ | 163 | 67 500 | $8.75 \cdot 10^{-2}$ | 237 |
| 87 500 | $1.93 \cdot 10^{-3}$ | 156 | 65 000 | $1.23 \cdot 10^{-1}$ | 245 |
| 85 000 | $3.35 \cdot 10^{-3}$ | 154 | 62 500 | $1.71 \cdot 10^{-1}$ | 263 |
| 82 500 | $5.90 \cdot 10^{-3}$ | 154 | 60 000 | $2.39 \cdot 10^{-1}$ | 282 |
| 80 000 | $1.01 \cdot 10^{-2}$ | 161 | 57 500 | $3.15 \cdot 10^{-1}$ | 303 |
References
- Nazarek, Bull. Amer. Met. Soc. 31, No. 2, 44 (1950).
- R. L. Havens, P. T. Kole, H. E. Lagow, J. Geophys. Res. 57, No. 1 (1952).
- H. S. Sicinski, N. W. Spencer, W. G. Dow, J. Appl. Phys. 25, No. 2, 164 (1954).
- Panel Rocket, Phys. Rev. 88, No. 5 (1952).
- Kuiper, The Atmospheres of the Earth and Planets, Chicago, 1952; p. 417.