Thermal control of planetary probes during the descent phase of a mission is examined. Emphasis was placed on the problems of atmospheric uncertainties to be encountered by the probes, insulation performance, and equipment temperature limits

Mcmordie, R.

English

NASA Technical Reports Server

•:/i_i_"!
THERMALCONTROLFOR PLANETARYPROBES
Dr. Robert McMordie w --P
Martin Marietta Corporation _ 7
 0411
DR. MCMORDIE: Now, the area that I want to focus in on is
the thermal control of the probes, and particularly the descent
phase of the mission.
Notice that I will not be addressing the entry problem, rather
strictly the descent problem.
Now, if you ask ten thermal control engineers to devise a
chart describing the technique for the development of a thermal
control subsystem, you would probably get ten different graphs,
or charts. Figure 9-38 illustrates one of these approaches, and
I think it is fairly representative. You are given temperature
limits; equipment limits; constraints such as power, volume, weight;
and the environments that your equipment must survive in. Then you
perform analyses, starting with studies on your conceived design,
and often you will need to perform some development tests to sup-
port your trade studies.
For a probe mission you might conceive of a design that has
insulation on the exterior of a pressure vessel, or the interior
of a pressure vessel, or a vented design. In the case where you
have the exterior insulation, or a vented design, you need to know
how the insulation performs in the environment. In the case of
the planetary-probe mission, you need to know how the insulation
performs when subjected to hydrogen/helium atmosphere.
Also, it appears there are some problems in defining the
environments and, particularly, the wide variation in the temper-
atures that you might encounter.
In Figure 9-39 the nominal environments for a nominal descent ....
into three planetary atmospheres are shown. The important point
here is the wide variation in temperatures between the Jupiter and
Uranus missions. This is not an overwhelming problem, but it
certainly has to be considered by the thermal control designer.
IX-79
https://ntrs.nasa.gov/search.jsp?R=19750012339 2020-03-19T21:11:17+00:00Z
_i_._i_'_.i_
_i__,.%,_":,!'_•
(_9
Z
m-"
Z
m
CD
Z
C)
Z
<D
<.)
-I-
u,1
.4--'
r-
K.-
U9
t-
O
l
r- i
El
r- i
O I
K.. !
•m •
> I
_- U
''' I
I
I
I
I
I
-I
(D
C3.
r-
I
I i
I
L
J
_D
,-%
IX-80
f
r-
(D
m .ram
C3_
(D
<,
L
I
_J
0o
u
t9
_-!i,,.¸."1%_._
_ 3, k'. _,
u
!_i_
0
C_
13-
ry"
i,I
O-
l.l_J
I--
Z
C__
ILl
rY"
I---
I.i..J
z
5
I_1_
0
Z
0
0-
0
..C:
t I
()1 saaJ6ac])a._n_._adLuala!Jaqds0LuTv
CD
(--.
Jm
E
I.---
C
(..) t,,,-i
I
i-.i
IX-81
L .
,[.;. •
Figure 9-40 shows temperature vs. time plots for Uranus
descents. Here the temperature difference between a cold and
warm model atmosphere is as large (approximately 200°C) as it is
between the Jupiter and Uranus nominal descents.
Figure 9-41 shows data for a Venus descent probe. The test
article was a solid sphere that was insulated with a fibrous,
porous insulation. The test article was placed in a chamber that
was controlled to match the pressure and temperature versus time
for a Venus descent. The analysis, with and without mass transfer
considered, did not match the test data even though experimental
valves of the insulation conductivity was used.
The thing that we discovered was that there were two reasons
why our analytical model, using steady-state test data, did not
allow us to predict the performance. One was that free convection
actually took place within the insulation. This is something
that you would never expect, or at least I would never have ex-
pected to take place. In an earth environment, with the type of
insulation we are using, you would never have any free convection
or actual mass movement within the insulation.
The second thing that occurred that we feel accounts for
some of the differences is that during a descent, when the CO 2 is
moving into the insulation, you get an absorption effect which
represents an energy release that caused the difference between
the tests and the analyses.
The whole point here, then, is that for a new environment,
such as the hydrogen/helium that we will encounter in the outer
planets, I think transient tests of candidate insulations should
be performed. Then we can perform the trade studies, trading
interior, exterior or vented designs and determine the optimum
design.
Figure 9-42 is a logic diagram for a generalized descent
probe program. This program can be used for any planetary descent
IX-82
L'L_.,_:_._.,_i'_:_
: . _:.y)
L:'_::_>i
] =.. .
,C:.%1-<-_
, -..:!
ii:,_'!!i
1.2'-i._J2".!i_.i
<'i< ,:i
= • c:-iU ._,
' :"_:i :i::i:!i,_ki_:_:,
o')
Z
<
<<
._/
M
0
Z
0
I-1.1
CD
CD
"0
oo
_0
I
_D
I I I .I
0 _D _
'a. n)IJaduJal a!. aqds0Lu v
I I
_D
0 0
0 ¢,4
,---,I I
I
'aJnl JaduJal O!.mLIds0wlV
IX-83
J ..... _
o _
I
o
o
!
e-
,m
E
,m
e-
0
I
0'%
I--I
;;LSJL:¢.,q
.. :'4
- " a :
¢
.-
. ,7.,;: i
, ,_- o i_ !, J
• [ "-i
::>:t?i::i
" .:.:.if-.i
• _ .!,.,
Z ¸
0
<
ill
0
U
Z
0
!
<
D
!
Z
Ill
U
ill
ii
Z
Z
0
>-
I!
! I
_u'3
I
w
I ! I I _1
o 8 o g _o o
:to ':l_tl'l.l.Y_t]dW].l. _INIS IV]N
0
_q
I
i
0
I
H
IX-84
k.i._i:_i':_
I!
l&
L_
II
111
MI
D
W'
Z
c
I.-
I--
4_
r,,
i
0
d
KI
r--,==.-
H
o
va
.ff
-I
"4
-4
,q
,4!
!
J
.4
L
m
o
I--I
Cn
r._
ll_ IrA
T
H
:.:;., v _ -::"-]]
ORIGINAL PAGE IS.
OF.Poor Qu_
IX-85
r
OF POOR QUALITY
("4
I
c_
b-q
_T÷_ _ _'<-_
and couples the structural and thermal aspects of the problem.
At the same time, it performs weight calculations and analyzes
the need for phase-change material, if needed. Aerodynamic equa-
tions are also used to compute the time-temperature and time-pres-
sure profiles which would, in turn, define the environment for
the probe.
In summary, this program provides a powerful tool to per-
form trade studies for planetary probes.
Figure 9-43 shows diagram of a test fixture that has been
used to test an almost full-scale Pioneer-Venus large probe. The
diameter of the test article was twenty-two inches. This facil-
ity was used to perform a test matching the Venus descent profile,
both pressure and temperature in a CO 2 environment.
The problem areas relative to the thermal control of an
outer planet descent probe are given in Figure 9-44. Relative
to insulation performance, I would suggest that we perform tran-
sient tests on the candidate insulations in a helium/hydrogen
atmosphere so that we can, in turn, perform trade studies, look-
ing at various probe designs.
MR. TOMS: I think Bob McMordie made an important point about
the atmospheric uncertainties. Particularly with the Uranus probe,
the atmosphere definition needs to be refined if we are going to
get a design we can live with.
If there are no more questions, I want to thank the speak-
ers for being so well prepared and for giving us a good session
this morning.
_-'!;i. i_'_;_i•
, ,T i
i_:,I'__;;_;!
-_ _,_ i •
U
_5
IX-87
• . .-,
._. _ ._i -_ ,{_
• • "_: _ • .4
i!:i:i
Z
0
U')
I..ul
0
cu
>-
I..i.I
Z
,,<
,,_,1
ID_
0
I.I_
i.-.
,,<
i--,-
__.1
0
I--.
0
.,-i
,,<
rw-
1,1
I
i---
,.Z
,,<
,,<
I.ul
0
:.w,
r_
a.)
°_
',,4--'
0 0
t-
O 0
c-_ t_D
EE
0 0
!
LD
SESSION X
MISSION COST _STIMATION
Chairman: N. Voj vodich
NASA Ames Research Center
MR. VOJVODICH: I would like to welcome you to the last ses-
sion which is, in many respects, probably one of the most impor-
tant sessions because it deals with the question of cost. It is
not necessary for me to remind you that because of NASA's con-
strained fiscal situation, technical feasibility, which has been
discussed for the past two and a half days, is certainly necessary
but, unfortunately, not a sufficient condition for us to undertake
these missions. More than ever before we are going to have to do
them in a cost-effective manner if they are going to be, in fact,
accomplished.
Now, as many of you know, the art of cost estimation has evolved
over the years to become a relatively sophisticated combination of
analytical capability and what I call black art, or a certain am-
ount of magician's quality to it.
We have three distinguished practioners here. Unfortunately,
one of the practitioners, Steve Duscai of Martin Marietta, could
not make it because he is home in Denver costing out a new pro-
posal, actually working a problem from the standpoint of a cost
estimator.
We have changed the order of speakers around. Instead of
having Bill Ruhland of JPL speak third, he will speak second, and
Fred Bradley from McDonnell-Douglas will speak third.
The first speaker that we have on the agenda is eminently quali-
fied to address the question. He is John Niehoff, Senior Engineer
with the responsibility of planetary program manager with Science
Applications, Inc. He is in the process of working parametric
cost estimates for many of the outer-planet mission options under
contract to Dan Herman at NASA Headquarters.
X-I


Thermal control for planetary probes

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server