Report on Contract NAGW 248

of the National Aeronautics and Space Administration

for a

DESIGN STUDY OF AN ENTRY PROBE SPECTRO-REFLECTOMETER

September 1982 - September 1983

by

Godfrey T. Sill

Uwe Fink

' Lunar and Planetary Laboratory

University of Arizona

Tucson, AZ 85721

(NASA-CR-177278) DEISGN STUDY OF AN ENTBY N86-27616

PEOBE SPECTRO-REFIECTCHETER Final Report,

Sep. .1982 - Sep. 1983 (Arizona Univ.,

Tucson.} 11 .p HC A02/MF. A01 CSCL 14B Unclas

G3/35 43224
Final Report on the "Design Study of an Entry-Probe Spectro-Reflectometer"

A renewal of proposal for this project was submitted 1n September 1983

to NASA for continued funding and this was approved. In the Renewal Request,

we Included a progress report on the work completed the previous year, which

dealt mainly with the design on fabrication of the "Jupiter Wind Tunnel."

This 1s reproduced below, and should serve as a final report for the first

proposal. The actual renewal obtained for 1984 was given a new funding

number, PR #10-31491.
[ 1

I. Introduction

The Entry Probe Spectro-Refleetometer 1s an Instrument which 1s suitable

for measuring the condensable minor species of a planetary atmosphere, as

well as the aerosols 1n a planetary cloud deck. The condensable minor

gaseous species are frozen out on a cold finger and Identified by their t

Infra-red reflection spectrum. The aerosols are simply collected by an

ambient surface, such as a filter, and may be Identified by Infrared reflection

spectroscopy.

The probe 1s particularly useful 1n reducing atmospheres since the major

components of these atmospheres (H~ and He in the case of giant planets; or

N2 in the case of Titan) are not condensable at the temperatures of typical

cold fingers (70-80K). This allows the minor components to be concentrated

on the surface of the cold finger. One immediately achieves a thousand to

one concentration effect. The minor gases, if condensable, are easily diagnosed by their characteristic IR reflection spectrum. Few condensed species

interact with each other, with the exception of NH-j-HJ) and NH--H2$; these

two form the hydrate NH.-HgO or the sulfide NH.HS. Other components are

condensed as simple mixtures. The components which are detectable by cryogenic freezing are: H20, NHj, H2$» PHj, S02, and C02. CH4 and CO are frozen

only at lower temperatures.

Aerosol particles 1n a planetary atmosphere can be collected by impingement on a flat surface or by being trapped on a filter network. Since

aerosols are likely to be complex polymers of carbon and/or other elements,

the composition of the aerosol 1s not so uniquely identified, but rather the

types of chemical bonds that exist 1n the aerosols may be evident in the IR

reflection spectrum, and a qualitative analysis of the particles should be

possible.
A more detailed description of the principles of operation of the entry

probe spectro-reflectometer was presented 1n the first proposal. We add the

section entitled: Principles of spectro-reflectometer operation as Appendix I,

and the section: Comparison and advantages of the frost spectro-reflectometer

as Appendix II. The reader Interested 1n further details of the method can

find them 1n these two sections.

It was realized when the original proposal was submitted, that the proposed studies could not be carried out within one year but would necessarily

extend over a longer period. We therefore first give a review of the progress

to data 1n section II, and then discuss the proposed Investigation for the

coming year in section III.
I

II. Progress To Date

Since we have had considerable experience 1n preparing frosts of volatile

substances and recorded many spectra of typical frozen gases, such as listed

1n the Introduction, we felt that the primary function of the first year of

the grant was to construct a facility which would serve as a simulator for

an entry probe spectrometer. Not only must the cryogenic cold finger sample

the ambient gases of a planet's atmosphere, It must do so 1n a high velocity

air flow. Therefore we concentrated on constructing a "Jupiter wind tunnel."

The wind tunnel has been built and tested and satisfies our demands to a very

high degree.

The "Jupiter wind tunnel" 1s a rough torus or oval 8 feet long, 4 feet

high, and about one foot wide, with a one horsepower fan, turning vanes and

carefully designed air path. A diagram of the wind tunnel is given in Fig. 1.

Several Polaroid pictures are shown in Fig. 2. The design was by Mike Williams,

engineering designer at LPL and the construction by Mr. Williams and Ron James.

Much of the heavy construction was performed by a metal fabricator in Tucson.

The specifications for the wind tunnel were such that it should operate at

pressures from 0.1 atmosphere to 4-5 atmospheres, comparable to those that a

probe experiences in traveling through a Jovian type atmosphere. The wind

tunnel has been tested with water and gas pressures to 45-50 lbs/1n . There

2

are a few small leaks, which are being sealed. At 45 Ibs/in the tunnel loses

about 5 Ibs of pressure In 12 hours. After the leaks near one flange are

corrected, the leak rate should be minimal. The thick walls of the tunnel

readily tolerate the high pressure as well as sub-atmospheric pressure. The

air 1s circulated in the tunnel by a blower which 1s driven by a shaft through

the wall of the tunnel. The shaft Is sealed by a pressure-vacuum bearing.

The bearing In our tests 1s gas tight, even at full power on the blower.
ORIGINAL

OF. POOR QUALITY

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Fig. 2 Two views of the completed frost deposition test facility (wind tunnel)

1n the machine shop of the Lunar and Planetary Laboratory.
The blower speed 1s controlled through a SCR motor speed control. Full

power at one atmosphere of pressure gives a velocity of 45 meters/sec

(•v 100 m.p.h.). This compares very well with the velocity of a probe In a

Jovian-type atmosphere. The Galileo probe for Its 56 minute proposed lifetime has an average velocity of 50 m/s, with pressures ranging from 0.1 bar to

19 bar. We can simulate velocities from zero to 45 m/s and pressures from

0.1 bar to 4 bar. While the atmospheric temperature of Jupiter over the range

of the Galileo probe varies from 130 K to 400 K as the probe drops from 0.1 bar

to 19 bar, our device 1s limited to room temperature (300 K). This should not

be a disadvantage in our simulation tests; one should be able to correct for

the heat excess or deficit 1n our simulation runs.

The wind tunnel has one section (the deposition chamber) where the condensation simulation experiments will be performed. The air flow velocity

across the diameter of the deposition chamber is quite uniform as is shown by

the measurements given In Table I. This device can be run with various

mixtures of gases from H2-He mixtures through N2 and ordinary air. It is and

will be available for any experimenters who wish to test devices in the airflow surrounding an entry probe. M. Tomasko, who has proposed an IR spectrometer for analyzing the ambient gas around the probe over a few meter pathway

plans to test his device in the turbulent flow by utilizing the wind tunnel.

Temperature and pressure probes, as well as other devices could well utilize

the versatility of this simulation device.

We have made preliminary Investigations of the feasibility of quantifying

the amound of precipitated volatile. The depth of an absorption band can

often be used to determine the optical path, and hence the thickness of a

frost deposit. But since the depth of an absorption band Is dependent on

other parameters of the frost beside thickness, we decided to investigate

whether the frost substrate Itself could serve as a thickness monitor. We
8

Table I

Determination of Air Flow Velocity Across Deposition Chamber

Dynamic Pressure

Distance from Edge

(Inches)

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

-Static Pressure

(Inches H20)

4.30

5.07

5.30

5.40

5.40

5.50

5.60

5.60

5.75

5.90

6.10

6.30

Velocity

(miles/hour)

94

102

105

106

106

107

108

108

109

110

112

114

Velocity

(m/sec)

42.0

45.6

46.9

47.4

47.4

47.8

48.3

48.3

48.7

49.2

50.1

51.0
I

purchased a Kronos QM-301 Thickness Monitor and designed a special cell to

hold the quartz-crystal oscillator. These oscillators typically are used

to monitor the thickness of thin film deposits for optical purposes, such

as beam splitters and Interference filters. They usually operate near room

temperature. We have succeeded 1n operating them at 200 K, and successfully

measured the deposition of ambient humidity as a thin 1ce coating on the

crystal. However, the quartz oscillators can easily be overloaded by the

1ce or frost deposit. Masking the area of the crystal detector by an

opaque shield seems to be one way to prolong the measurement process, i.e.

to measure greater thicknesses.
FINAL REPORT //!/-

NAGW-561

July 15. 1986

A wind tunnel was built to simulate the rapid movement of

an entry probe through the Jupiter atmosphere. The wind tunnel

could develop wind speeds from 1 to 50 meters per second In a

closed system. The wind tunnel had a viewing section 6 Inches

In diameter In which one could place wind velocity and temperature

probes as well as cryogenlcally cooled cold "finger".

The initial testing of the wind tunnel involved running

sectional profiles through the observation port of air currents

of 1/10 of an atmosphere to 3 atmospheres and the velocity profile

was very uniform throughout the cross section of the experimental

port, with the exception of wall effects. The deposition of

cooled volattles using the wind tunnel was not performed due to

termination of the grant. However, under ambient conditions,

namely room temperature and pressure, we did make measurements

of the deposition of H£0 ice on a cryogenlcally cooled thickness

modulator. This device was able to measure ice deposition at

thicknesses of about a half a millimeter and produced frost whose

reflectivity could easily be measured by reflectance FTS spectroscopy.