Outer planetary probe designs consider mission characteristics, structural configuration, delivery mode, scientific payload, environmental extremes, mass properties, and the launch vehicle and spacecraft interface

Cowan, W.

English

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PROBE DESIGN
W. Cowan
McDonnell-Douglas Astronautics Company
MR. W. COW,N: We have been wrestling now for some months
with ARC on the problem of outer planet probe designs. And we
have come to some feelings and convictions, as we have gone
through this process about these outer planet probes. One of
these is that the technology today will support these early mis-
sions (c.f. Figure 4-31).
i
We also feel that there is a high degree of commonality
across these missions. This doesn't necessarily mean the common-
ality of absolute identicality, but a commonality which really
leads to the cost-reduction we have been seeking; one which allows
you to take the technology that you have and apply it. This kind
of commonality keeps the cost down because you minimize the money
spent on new developments.
EARTH
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-SUN-
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CORRECT 1
JUPITER RETARGET
DEFLECT
DEFLECT
I SATURN
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URANUS
NEPTUNE
Figure 4-31. Mission Characteristics
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And, more recently, because of the confidence that has come
from the Pioneer i0 data, we are getting a conviction that an
early mission to Jupiter is feasible with what we know today and
the materials that we have available.
I would like to take just a few minutes to identify the high-
lights of this design £hat has been studied for almost two years.
It is a probe design that started out being studied for Saturn-
Uranus application; the probe is 35 inches in diameter; it varies
in weight from 200 pounds to 350 pounds, depending on the size of
the heat shield that is on it, the planet to which it is going and
whether it does or does not have planetary quarantine. Basically,
it is the same probe used across the several missions that we have
looked at for Saturn, Uranus, and/or Jupiter.
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Figure 4-32 presents the features of the design. The aft end
of the probe has a hemispherical yeat shield after body and pro-
ceeding forward we have the equipment cover with its microstrip
flat plate antenna, the 66 degree antenna that was described
earlier and will be discussed some more tomorrow. The principal
feature of the probe design is that everything is packaged far
forward. So the CG is far forward, and the probe is then inherently
stable, and does not require a parachute or any other separating
parts and pieces. This feature supports the goal of achieving the
maximum reliability, minimizing complexity, and cost.
The probe was designed as a ten bar probe, however, this
vehicle is capable of reaching the 30 bar level or below for
Jupiter. I would like to show you one other central feature of
this design which Howard Myers talked about this morning and that
is the mass spectrometer, which is a central element in the whole
probe. The mass spectrometer was designed for a 500 cubic inch
volume analyzer section, either quadropole or magnetic deflection
and it has an extendable inlet mechanism. The data handling
portions of the mass spectrometer are located within it.
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ENTRY SHIELD AND
PRIMARYSTRUCTURE
RADIOISOTOPEHEATERUNIT (4)
BOOTSTRAPBATTERIES
BATTERY
HANDLING D = 0.89M _ I
(35 IN.)1
;ELEROMETERS
PHELOMETER
UIPMENT COVER
LTEMPERATURE PROBE
PRESSURE
TEMPERATURESENSOR
RELAY
TRANSMITTER
MASS
SPECTROMETER
ANTENNA_'L, "
• 600 HALF CONEFOREBODY- 0.25 D NOSERADIUS
• HEMISPHERICALAFTERBODY
• HONEYCOMB- RING STIFFENED STRUCTURE
• TAILORED EQUIPMENTPACKAGING
• EXTERNAL INSULATION
ABLATIVE
COVER
MULTILAY ER BLANKET
Figure 4-32. Probe Configuration
The probe has an aluminum ring frame structure, a fiberglass
honeycomb, a carbon phenolic heat shield, and were all designed
around the mass spectrometer as a central structural element.
You will notice the accelerometer is mounted inside the mass spec-
trometer instrument package; placing it on the CG. The batteries
are toroidal, trapezoidal batteries. These data handling segments
are shown. Throughout the entire flight profile, the CG remains
forward.
You will see some pictures in Bill Kessler's presentation
tomorrow of the vehicle flying in the ballistics range here at
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Ames, and he will have some other data on that and can answer
other questions.
The usefulness of this probe, the value benefit of this probe,
is related to its ability to do missions at planets; can it be
carried by spacecraft that exist or are about to exist? The probe
has been designed to be compatible in general either with Pioneer
or with Mariner. As was pointed out earlier today, the delivery
mode is one in which the spacecraft points the probe at the aim
point and then deflects itself and continues with the mission• It
also is a relay communication system. The spacecraft maintains
Earth lock throughout the entire active portion of the mission
and relays the data back• (cf. Figure 4-33)
We have options of swingby and retargeting, and the three
principal planets we have looked at are shown on Figure 4-31. We
have also taken a cursory look at several of the satellites, and
have a small a_ount of data on Titan.
SUN " -IOHR_, .
EARTH ." /
.." /
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--_--6 HR--- "/
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SPACECRAFT._........._ ./
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ENT!Y.1HR _
Figure 4- 33. Planetary Arrival
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TEMPERATURESENSOF
TOTAL TEMPERATURE
PROFILE IN HIGH
DYNAMICPRESSURE
REGION
PRESSURE SENSOR
(3RANGES)
PRESSURE PROFILE
NEPHELOMETER
.
CLOUD LOCATION_-----_ .... _
AND
PRESSURE
SAMPLERS
MASSSPECTROMETER
ATMOSPHERICCOMPOSITION
RELATIVE ABUNDANCES
MEANMOLECULARWEIGHT
CLOUDCOMPOSITION
ACCELEROMETERS (3 RAN GES)
_1 DENSITY PROFILE
MAGNET
HOUSING
Figure 4- 34. Science Payload
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The instruments we have identified are shown on Figure 4-34.
It is perhaps slightly more than a minimum package. A minimum
package might be just the first three instruments, accelerometer,
temperature, and pressure measurements; but as a basic package,
if you add the mass spectrometer, the nephelometer and perhaps
some other candidates, such as the IR radiometer or the gas
chromatograph. There is some capability to put some other instru-
ments on board, depending on the weight constraints that you would
have. Shown on the figure is the basic package that was looked
at. These instruments, either exist or are expected to exist,
ready to go, without a lot of new development, by the time an
outer planets probe is launched.
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The active life for the probe is very short. It is passive
throughout most of the mission. Carried on the spacecraft for
most of the mission total time, it is released from three to
seven weeks before planetary encounter depending to which planet
you are going. It coasts along on its own; has a multilayer insul-
ation blanket around it as shown on the exploded view. Shortly
before it enters the sensible, high altitude atmosphere, it is
activated, it then has an active period during the entry that
could extend up to about an hour. As you saw from the phasing
curves this morning, in an attempt to maximize the certainty of
communications you try to maximize the relationship of the flyover
geometrys, the choice of frequencies; and in terms of the con-
straints of the electronics. As Carl said this morning we are
working with a 40-watt solid state transmitter. We did this de-
liberately because that represents a threshold in knowledge.
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Now what else affects design? Certainly, the kind of en-
vironment that a probe is going to find itself in is a principal
driving force.• I have reflected this on Figure 4-35 in decel-
eration terms, i have reflected it principally for the three
planets. These general comments also relate to the heating en-
vironment as well. The kind of variation you see on the figure
is reflected in the heat shield thickness. Tomorrow there is
going to be further discussion on the specific sizing of the
heat shields, although I will show you a weight statement in just
a few minutes. But notice that as the angles get steeper, as the
atmospheres go from Warm to more dense, and the boundaries shown
represent the extremes of the NASA SP defined atmospheres, the
extremes of the potential design conditions go up. The probe was
designed originally for 800 G's, with a thousand G ultimate, for
the Saturn-Uranus application. It was designed at a time when it
was thought that the Uranus, and this was for a Pioneer case at
that time, entry angle uncertainty might be as much as 15 degrees.
Therefore, if you were to aim at a box in this area, you would
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100
JUPITER
0 J
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SATURN
/
URANUS
ENTRY CONDITIONS
M/ICDA= 12.176gm/cm2
_NERTIAL vELOCITY
(km/sec)
3 _ABOUT NOMINAL AIM
0.54 8.04
POINT (DEG)
"RADIO + OPTICAL
• AIM POINT
JUPITERJSATURN
59.89 36.76
URANUS[ TITAN
24.95 14.28
15.86 0.002"
TITAN
_1 J i i I ,, | I
-20 -30 -40 -50 -60 -70 -80 -90
INERTIAL FLIGHT PATH ANGLE, DEG
=.;,.
i .....
Figure 4-35. Entry Deceleration Envelopes
be just within the bands. There is always some dilemma here in
terms of selection of design criteria so that you don't make them
so overly conservative that you drive your design off scale and
run your costs up, in a situation which implies a non-feasibility
to do the task that can really be done.
So what we are seeing here is that as you are able to re-
solve your uncertainties in either atmosphere and/or the angle
to which you can aim, then you can resolve uncertainties and your
design margins can go up. This particular probe, is designed
to the 800G level, and you see on the figure, from a G standpoint
for flat entry angles near grazing at Jupiter, the G load problem
essentially goes away.
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Figure 4-36.
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Mass Properties
SUBSYSTEM
STRUCTURE
HEAT SHIELDS
HEATERS & INSULATION
COMMUNICATIONS & DATA HANDLING
ELECTRICAL POWER
PYROTECHNICS
SCIENCE PAYLOAD
INSTRUMENTATION
PLANETARY QUARANTINE
WEIGHT MARGIN (I0°_)
SATURN/URANUS
WEIGHT
(LB)
28.9
81.6
15.3
21.1
20.0
8.2
24.2
l.B
16.3
213
PROBE WEIGHT 238.9
LESS: BIOSHIELD -11.6
INTERFACE WIRING -2.3
EXTERNAL INSULATION -5.9
AT ENTRY 219.1
LESS:ABLATED MATERIAL -19.0
END OF MISSION 200.1
C.G.& INERTIAS AT ENTRY
X AXISC.G.(IN.)
IX (ROLL) (SLUG- FT2)
Iy(PITCH)(SLUG- FT2)
Iz (YAW) (SLUG- FT2)
8.62
5.61
3.63
3.52
JUPITER
WEIGHT
(LB)
28.8
182.0
15.3
21.1
20.4
8.2
24.2
1.6 35
16.3 t
32.0
349.9
-11.6
-2.3
-5.9
330.1
-123.3
206.8
7.96
9.82
5.97
5.8B
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X= 15.08
= 2.03
Figure 4-36 presents the weight story for Saturn-Uranus broken
down by subsystem, leading to a total weight of around 250::pounds.
And for a Jupiter prole at seven and a half degree entry, around
350 pounds. Both of these are With planetary quaran£ine.
The essential difference between these two is in the heat
shield weight. As Sam will show you tomorrow, the carbon pheno-
lic heat shield thickness varies from approximately two inches
for the Saturn-Uranus ease to three inches for the Jupiter case.
As far as the probe is concerned for the Jupiter mission,
there is no other change except a slight rounding of the aluminum
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structure to provide for the extra carbon phenolic material as it
rounds the corner. The probe itself is at the same external
diameter. There are perhaps one or two small scale changes on the
instruments. Fundamentally, the design is one that is common and
almost has identicality in most aspects and, therefore, costs and
development and all can be minimized for this set of instruments.
Figure 4-37. Launch Vehicle and Spacecraft Interface
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PIONEERSPACECRAFT
INTERSTAGEADAPTERS
PROBE
STANDARD A_APTER
TITAN IIIE/
CENTAURD-IT/
TE-364-4
We have shown on Figure 4-37for illustrative purposes the
probe on a Pioneer spacecraft. I would like to reiterate that
these early missions, although we see them going on Titan IIIE
Centaur, it is anticipated, as time goes on, the shuttle will
become available and that there may be applicability of these
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probes on these and similar spacecraft for those kinds of missions.
But for the present, we are planning for the Titan launch vehicle
and either the Mariner or the Pioneer spacecraft. Because the
probe is essentially an autonomous, passive device, except for
minimal transfer of electrical power during the coast phase and
minimal attachment and heat interface support, it should then be
compatible with either of the two spacecraft.
MR. CANNING: There was a question on spinning, and the
answer was that the system is spinning at five RPM.
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