Atmospheric temperature, pressure, and density of Venus according to measurements obtained by AIS Venera-

Avduyevskiy, V. S.

Borodin, N. F.

Kuznetsov, V. V.

Marov, M. YA.

English

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National Aeronautics and Apace Administration
Goddard Space Flight Center
Contract No.NAS-5-12487
ST-- LPS-- PA-- 10708
TEMPERATURE, PRESSURE AND DENSITY OF VENUS' ATMOSPHERE
ACCORDING TO MEASUREMENT DATA OF THE AIS "VENERA-4"
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ff 653 July 65
by
V. S. Avduyevskiy
N. F. Borodin
V. V. Kuznetsov
M. Ya. Marov
... AT AL ...
(NASA CR OR TMX OR AD NUMBER)
(THRU)
(CATEGORY)
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8 MAY 1968
https://ntrs.nasa.gov/search.jsp?R=19680016114 2020-03-12T10:25:25+00:00Z
ST --LPS --PA--10708 '
TEMPERATURE_ PRESSURE AND DENSITY OF VENUS' ATMOSPHERE
ACCORDING TO MEASUREMENT DATA OF THE AIS _/ENERA-4
Doklady A.N. SSSR, Astronomiya
Tom 179, No.2, 310 - 313,
Izdatel'stvo "NAUKA" 1968
(*)
by V. S. Avduyevskiy, N. F.
Borodin, V. V. Kuznetsov, M. Ya.
Marov, ... ET AL(**)
SUMMARY
This paper is a preliminary communication relative to the results of
measurements obtained on AIS VENERA-4, relative to temperature, pressure and
density of Venus' atmosphere. As such, this paper seems to be superseded by
the more extensive communication verbally presented at the Second Arizona
Conference on Planetary Atmospheres in March 1968.(ST'LPS-PA-10704 of 19 April).
Since the mode of discussion, as well as some of the results differ
from the above paper, cover-to-cover translation of this paper is presented.
f
The Soviet automatic interplanetary station "WENERA-4" reached Planet
Venus on 18 October 1967. The main problem of station's descending probe
was the measurement of Venus' atmosphere parameters, i. e. pressure, tempera-
ture, density and composition.
Various hypotheses lay at the foundations of representations relative
to Venus' atmosphere; they were based upon ground observations in optical and
radiowave bands and certain theoretical estimates. They resulted in a great
uncertainty when attempting to create the planet's model atmosphere. The as-
sumed values of pressure at the surface lied in the interval from i to i00 atm,
while the temperature range was from 300 to 650°K.The projection of scientific
apparatus was• done for a Venus' model atmosphere with the respective values of
pressure and temperature at the surface of about i0 atm. and 700°K.
Two thermometers were installed to measure temperature. Hermetic resist-
ance thermometers were used for sensors, capable to operate in dense gaseous
and liquid media in the presence of chemically aggressive substances.
(*) TEMPERATURA, DAVLENIYE I PLOTNOST' ATMOSFERY VENERY PO DANNYM IZMERENIY
AVTOMATICHESMOY MEZHPLANETNOY STANTSII "VENERA-4"
(**) There are altogether eight authors.
2The sensitive part of the sensor was a platinum wire respectively with 36.8
and 16 ohmresistance at 20°C. The sensors were switched onto balanced bridge
circuits. The unbalanced voltage was amplified by highly-stable semiconductor
amplifiers. The range of measurementsof the first sensor was 270 - 600°K,
and that of the second 210 - 7300K. The root-mean-square error of temperature
measurement_T by the first sensor did not exceed ±4° , and that by the second
±7 ° .
In order to determine the density a special dens±meter was used, whose sen-
sor was a ionization chamber. The principle of dens±meter's operation was based
upon the dependence of the magnitude of the registered current on gas density.
The chamber constituted a hollow cylinder made of stainless steel of 14 mm in
diameter and 25 mm in length with wall thickness of 0,3 mm. A thin layer of
E-active strontium-90, with total activity of about i mill±curie was spread
over the internal surface of the cylinder. The measurement range of the den-
simeter was 5 "10 -4 - 1.5 "10 -2 g/cm 3 for the air, C02, N2, 02 and the mixture
of the indicated gases. The root-mean-square error of dens±meter readings,
constituted ± 0.18 "10 -3 g/cm 3 at the origin of measurements range and ±3 .10 -3
g/cm 3 at the end of it.
Pressure was measured by an aneroid-type manometer. The range of measure-
ments of the device was i00 - 5200 mm. Hg. The root-mean-square error of mea-
surements Op = ±150 mm Hg.
The transmission of measurement data of Venus' atmosphere parameters began
after the opening of the main parachute, when the transmitter of the descend-
ing probe was switched on. The velocity of apparatus' descent by parachute
varied by about I0 to 3 m/sec and, consequently, could not exert any aerodyna-
mic effect on the results of measurements.
The sensor interrogation by the telemetric commutator began at 07 h. 40 m.
52 sec Moscow time and was conducted with a frequency of once in 48 sec. The
variation of temperature T, density P and density p as a function of time
is shown in Fig.l. The measurement of temperature was conducted during the
entire experiment up until radiocommunication with the descending probe has
ceased at 09 h. 13 min.57 sec. The pressure and density were measured until
the devices went off-scale, respectively at 08 h. 30 min. 31 sec and 08 h. 50
min. 00 sec. These moments of time are marked on graphs Pvar(T) and Pvar(T)
in Fig.l. The limits of measured parameters' deviations, corresponding to the
indictaed root-mean-square errors OT, _p and _p.
In the subsequent time intervals the values of P and p are obtained by way
of extrapolation at a known temperature T variation and in the assumption that
the atmosphere consists of C02. Shown on the entropy=pressure diagram of Fig.2
are the curves of gas state variation over the measurement segments computed
according to T, P-ar (curve i) and T, Pvar (curve 2). The curves are prolonged
V O
to the isotherm T = 544 K, corresponding to the last measured temperature and
with inclination determined by terminal rectilinear portions of the curves.
The condition AS _ 0 at temperature increase constitutes the atmosphere's'sta-
bility condition. The dashed horizontal lines in Fig.2 correspond to the
-3
limit of extrapolation by the adiabat AS = 0. The values of pressure obtained
at the intersection of curves 1 and 2 with the isotherm T = 544°K are respect-
ively equal to 19.5 and 20.75 atm. The extrapolated portions of curves Pvar
and Pvar areplotted in the graphs of Fig.l by dashes.
|
•s0
J
K/"
-_00-_
! I
-_00-IQI
Ffg.i.
, z _####/
j
#
I I I I I
Results of measurements of
T, 0, P
kj Ik_ dee
0.1 OZ 0,3 O,V O# 0,,6 0,7 0,8 -0,9 t,0 1,1 I,Z t,3 f,_
Fig.2. Diagram "entropy - pressure"
From the consideration of Figures 1 and 2 it follows that the course of the
curves obtained with the aid of the manometer and densimeter is different up
to the time T = 08 h. 30 min. and T = 440°K. Compiled in Table 1 are the
values of the molecular weight _ counted by measured P, p and T and the
Clapeyron acceleration. Near 0830 hours
the values of _ approach 44, which
corresponds to CO atmosphere and
agrees well with the direct measure-
ment of the composition. The quan-
tity P = 44 is also preserved over
the portions of extrapolation. In
the preceding interval the overra-
ting of H is linked with the cha-
racter of the measured course of
the densi y curve and also with a
greater relative error of devices
at the beginning of measurements.
56,6
52,0
50,3
50,6
49,5
5i,7
56,7
OSCOW
time
i5 57,5
25 46,7
30 44,9 9h. OOM
35 45,2 O5
4O 44,7 tO
•7h. 40 ._z.
45
50
55
8h. OOM
05
iO
8h.
__._AL
45,0
44,7
45,5
44,7
45,2
44,7
The density inerease, registered approximately from 0803 to 0830 hours
may be explained by the influence of Venus' atmosphere components on densi-
meter readings, which do not affect the readings of temperature and pressure
sensors. Among one of the assumptions, it is possible to admit the hitting
of densimeter's measurementchamberof moisture.
From the examination of Fig.2 it follows that the densimeter readings
approach to of the manometer directly behind the curve of phase transition
water - vapor (curve 3). The possible influence of water and also of some
other components is presently investigated for the respective temperatures
and pressures.
In order to obtain the distribution of atmosphere parameters in height,
it is necessary to determine the alritude variation at: probe descent by parac
chute which was computed by two methods.
In the first case we utilized the equation of motion for a quasi-uniform
descent:
z-/(T)= V _ I °-_:'(O d_, (1)
where Cx is the aerodynamic drag coefficient; S is the characteristic area;
is the mass of the descending probe.
In the second case we utilized the hydrostatic equilibrium relation
P,
H CT)= T
,&"I
(2)
(g = 880 cm/sec ). The computations were conducted by gas parameters corres-
ponding to the state curves 1 and 2 of the entropy diagram (Fig.2).
The curves of altitude variation in time, obtained by independent methods,
(Fig.3), responding to the magnitude of the path covered by the descending
probe in the atmosphere of Venus, as an average agree satisfactorily among
themselves. The total height coincides with the readings of the radioaltime-
ter (26 ±1.3 km) with a precision to i0 percent.
Eqs. (i) and (2) could have been used for independent extrapolation of
initial values of pressures by the formula
I' p".= p[.+ _'I,1/m,,._c,.o,__... .."",('0-'"_' (3)
where R is a gas constant.
However, the character of atmosphere parameter variation is then unstable
(AS > 0). For constant values of coefficients condition (3) is not satisfied
over the segment, where measurementswere conducted either. This may be ex-
plained by the fact that local vertical flows exist in the atmosphere. Thus,
for example, calculation by formula (3) agrees well with the curve 1 of Fig.2
for a value of descending flow velocity of gas near the surface _ 0.4 m/sec.
The maximumdivergence in the determination of altitude by different methods
including that by radioaltimeter, is evidently determined by errors of measure-
ments of Cx, of atmosphere parameters and also by the presence of vertical flows
and influence of the local relief during a possible probe drift by the wind.
I
Fig.3. Altitude intervals.
I) according to Pvar, barometric
formula; 2) according to Pvar,
parachute; 3) according to Pvar_
parachute
I0 p__ 20 _r/cMzi
0 20 Z/cM7
L , P/03--_
0 t00 200 "G
Fig. 4
Model atmosphere
The cross-section of Venus'atmo-
sphere in height is shown in Fig.4.
In order to tie up the atmosphere para-
meters to altitude, we choose the curve
of Fig.3 with nominal altitude H = 27.3 km.
The character of processes of gas state variation in the atmosphere of
Venus to the altitudes of i0 - 15 km is close to adiabatic. The mean tempe,
rature gradient constituted about 8.5 to 8.7 degrees/km, which differs little
from the adiabatic gradient for C02 at corresponding values of temperature
and pressure. This is evidence of the fact that there exist in the lower layers
of the atmosphere the conditions of convective equilibrium with intense mixing,
and that the lower limit of the cloud layer lies above 27 km (or nted at the
altitude of 29 - 33 km).
Thus, pressure on Venus' surface near the morning terminator on the night
side constitutes 20 ± 3 atm, the density is 19" 10 -3 g/cm 3 ±15% and the tempe-
rature is 544 ±10°K.
The height of the uniform atmosphere at Venus' surface is found to be
about 12 km, while the total mass of gas is about 102° tons.
The authors extend their thanks to all technicians, constructors, engineers
and scientists having participated in the preparation, conducting and process-
ing of material relative to the experiment described.
**** T H E E N D
Manuscript received
on 1 December1967
CONTRACTNo.NAS-5-12487
VOLTTECHNICALCORPORATION
1145 - 19th St. NW
WASHINGTOND.C. 20036.
Telephones: 223-6700 (Ext.36. 37)
Translated by ANDREL. BRICHANT
on 7 - 8 May 1968


Temperature, pressure and density of Venus' atmosphere according to measurement data of the AIS Venera-4

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