NOTE TO STAN FROM HAUS

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP80M00165A001700090005-3
• Release Decision: RIFPUB
• Original Classification: K
• Document Page Count: 7
• Document Creation Date: December 15, 2016
• Document Release Date: April 13, 2004
• Sequence Number: 5
• Publication Date: November 13, 1977
• Content Type: NOTES

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The. journey to upiter
Charles F. Hall, Hans Mark, and John H. Wolfe
Jupiter has always had a special fascination for mankind. It is very brilliant and it is steady in the
sky, being one of the slower moving planets. This circumstance is probably why it was named after
the king of the gods in the Roman Pantheon. Jupiter has also had a truly remarkable place in the
history of modern science for almost four centuries. The two Pioneer spacecraft missions described
here have now greatly advanced our knowledge of Jupiter, its satellites and interplanetary space.
In the year i 6 i o Galileo Galilei first turned a primitive
telescope on Jupiter. In doing so he discovered the four
brilliant `Galilean' satellites of the planet. The discovery
of the satellites of Jupiter was an extremely important
scientific event bui its cultural impact was even greater.
For the first time man saw a `quasi-solar system' from
the outside. It is likely that Galileo's observation was the
decisive factor in providing the framework for the
eventual acceptance of the Copernican model of the solar
system in preference to the earlier Ptolemaic or geo-
centric version.
A second important discovery was made by the Danish
astronomer Ole Romer working in Paris in 1676.
Romer used the occultation of the satellite lo by Jupiter
to make the first determination of the speed of light.
He noticed that the period of occultation varied slightly
? depending on whether the Earth was moving away from
or toward the planet. He correctly interpreted this
phenomenon as the result of the finite propagation
velocity of light and obtained a remarkably accurate
measurement of that velocity by making the appropriate
calculations.
Much information has been gained about Jupiter
since then. Improved telescopes led to the discovery of
the spectacular bands on the surface of the planet and
the mysterious red spot in the i 7th century. More
recently, radio wave emissions have been observed
arising from the complex electromagnetic interactions
occurring in the planet's magnetosphere and upper
atmosphere. Finally, spectroscopic measurements using
modern instruments have yielded important information
on the composition and the behaviour of Jupiter's upper
atmosphere.
The observations and measurements outlined here set
the stage for the next great step in the exploration of
Jupiter-an actual visit to the planet by an instrumented
space probe.
The Pioneer 10 and 11 spacecraft
The Pioneer exploration of Jupiter with an unmanned
spacecraft began in 1968 when, on the recommendation
of the U.S. National Academy of Sciences Space Science
Hans Mark, B.S.,Ph.D.
Was born in 1929 and studied at the University of California and the Massa-
chusetts Institute of Technology. He has done research in nuclear physics
and astrophysics and served as a member ofthefacultyatthe Massachusetts
Institute of Technology and at the University of California for a number of
years. Since 1969 he has been the Director of the NASA, Ames Research
Center.
Charles F. Hall, B.S.
Was born in 1920 and studied at the University of California at Berkeley.
He has conducted aeronautical research on the performance of wings,
stability and control, and propulsion. He joined NASA, Ames Research
Center in 1942 and became Manager of the Pioneer Project in late 1962.
John H. Wolfe, Ph.D.
Was born in 1933 and studied at the University of Illinois. He has carried out
research on gamma-ray spectroscopy and the measurement of the inter-
planetary solar wind and its interactions with planetary bodies. He joined
NASA, Ames Research Center in 1960 and is Chief of the Space Physics
Branch, Space Science .pivision. He JJs Iso the chief SciRry~i t fp{.the
Pioneer interplanetary aA~lp ii@ 6, o lease LUu4/U5/U5
Board, it was decided to undertake a project to send two
spacecraft to Jupiter. The stated scientific purposes of the
mission were: (i) The exploration of interplanetary
phenomena. (2) The study of the asteroid belt. (3) The
`in situ' measurement of the environment of Jupiter.
The two Pioneer spacecraft are almost identical, each
one carrying twelve instruments as listed in Table i. In
addition to the twelve instruments the S-band tele-
communication system signal was used to perform
measurements on Jupiter's ionosphere when the space-
craft were occulted by the planet. The S-band tracking
was also employed to get a more accurate measurement
of the gravitational field of the planet and the masses of
the Galilean satellites. There was a minor change in the
payload of Pioneer i 1 as compared to Pioneer i o in that
a fluxgate magnetometer was added for the second flight.
The Pioneer i o and i i spacecraft are relatively small
and simple spin-stabilized vehicles weighing approxi-
mately 258 kg. The total science payload weight is
about 30.4 kg and the payload uses 25 W of electrical
power provided by four radioisotope thermo-electric
generators. These operate on the heat produced by the
radioactive decay of a quantity of plutonium 238. The
S-band communications system requires a 2.74 in
diameter high-gain antenna reflector. The bit rate
capacity of the system at maximum is 2048 bits s-1. The
antenna is rigidly mounted on the spacecraft in such a
way that the spacecraft can always be pointed toward the
Earth. The spin axis of the spacecraft is in the plane of
the ecliptic and the spin axis is precessed occasionally
with small gas jets to keep the antenna dish properly
oriented. The spin rate normally is approximately
4.8 rev/min.
Figure i is a line drawing of the spacecraft depicting
the locations of the various instruments carried by the
spacecraft. The power supplies are located on the two
booms, as shown, to prevent radiation produced by the
decay of the 238Pu from seriously affecting the radiation
detection instruments mounted on the spacecraft. The
magnetometer experiment also must be mounted on a
long boom so that the very sensitive helium vector
magnetometer is removed from the spacecraft to prevent
stray magnetic fields produced by the electronic equip-
ment in the spacecraft from disturbing the readings.
Pioneer io was launched on 3 March 1972 and en-
countered Jupiter on 4 December 1973. The spacecraft
was launched using an Atlas Centaur launch vehicle
with a third stage solid-fuel motor from the NASA
Launch Complex at Cape Canaveral. Pioneer to's
Jupiter encounter trajectory was such that the space-
craft gained speed as a result of the encounter. In fact,
Pioneer io gained enough speed to become the first
man-made object to leave the solar system. Pioneer i i
was launched on 6 April 1973, also using an Atlas Centaur
launch vehicle with a third stage. It reached Jupiter on
3 December 1974. The trajectory in this case came
closer to the Jupiter cloud tops than did Pioneer 1 o, at
a distance of 43 00o km compared with 131 00o km for
Pioneer lo. After the encounter the Pioneer ii space-
Gi B0nQQ165 l@A 7 i O9A OiO5tri lake a close
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Magnetometer
(JPL)
(UCSD)
Plasma analyzer
High-gain antenna
feed assembly
Imaging
photopolarimeter diffuser
Nutation damper -
Magnetometer boom support
~V/precession thruster assembly
(U. of Arizona)
Spin/despin
thruster assembly
assembly
--Sun sensor
spacecraft the windows were twice as
thick, the sensitivity limit then being
10-8 g.
The results of the micrometeorite
experiment are shown in figure 4
in which the number of `hits' are
plotted as a function of the time of
flight for both spacecraft. The most
striking feature of the curve is that
there is no increase in the `hit' rate
in the region of the asteroid belt be-
tween the orbits of Mars and Jupiter.
Thus, there are no small particles
accompanying the larger objects that
are known to populate the asteroid
belt. The other interesting feature of
the curve is that there is an increase
in the counting rate during the en-
counter with Jupiter. This increase
is probably caused by small gravita-
tionally focused particles close to the
planet itself.
Plasma and magnetic field experiments.
The object of these measurements
Stellar reference assembly
light shield
A steroid- meteoroid
(OMNI) Thermal control
RTG'S antenna louver assembly
Figure 1 The Pioneer 11 Spacecraft. (Figures 1-4 and 7 appeared in Science, N.Y., 188,
445-79, 1975 and are reproduced by permission of the publishers and respective authors.)
(Copyright 1975 by the American Association for the Advancement of Science)
flyby of the planet Saturn late in 1979. Figure 2 shows
the trajectory geometry of the two spacecraft looking
down from above the plane of the ecliptic. Figure 3
shows the trajectories roughly edge-on to the plane of the
ecliptic. Pioneer 11 is the first man-made object sub-
stantially to leave the ecliptic plane. Its orbit now has
an inclination of about 15.9 degrees with the plane of
the ecliptic. At its maximum Pioneer 11 will be about
1.1 A.U. out of the ecliptic. The two trajectories allowed
a very thorough exploration of Jupiter's environment.
Experimental results
Micrometeorite experiment. The object of this experiment
was to measure the micrometeorite particle flux in the
interplanetary medium. The detector consisted of 234
pressurized cells mounted on the back of the parabolic
reflector dish. The detectors are covered with thin sheets
of stainless steel that would be pierced by small high-
velocity particles striking the spacecraft. An electric
field is maintained across each cell as long as the cell is at
atmospheric pressure. When the window is pierced by a
micrometeorite, the gas leaks out and at a certain
pressure a discharge is observed. The discharge gives
rise to a pulse which is counted by an appropriate
electronic circuit. On Pioneer 1 o the thickness of the
stainless steel windows was 25 pm making the detector
sensitive to particles as small as io-9 g. On the Pioneer 11
Table I
Instrumentation on Pioneer 11
was twofold. One was to look at the behaviour of the
interplanetary plasma and magnetic fields between the
Earth and Jupiter. The other was to observe the very
complex interactions between the solar plasma, that is
the solar wind, and the magnetosphere of Jupiter. Both
aims were achieved.
In the case of the interplanetary plasma, the Pioneer r. o
and 1 i spacecraft joined the earlier Pioneers (6 to 9) in
monitoring the solar plasma or the solar wind on a
continuing basis. Pioneers 6 to 9 were a series of solar
orbiting spacecraft launched in the late i g6os with the
primary purpose of monitoring the solar plasma. These
spacecraft are all in orbits having radii of approximately
i astronomic unit (A. U.). Pioneers so and i s are very
much further from the Sun. In several instances,
disturbances first observed by one of the earlier Pioneers
at i A.U. were later measured by Pioneers so or 11, thus
enabling us to obtain a more accurate dynamic map of
the plasma field created by the Sun.
In the vicinity of Jupiter, the plasma probe was most
important in mapping the interaction of the solar wind
with Jupiter's magnetosphere. In each flight a shock
wave created by the impingement of the solar wind on
Jupiter's magnetosphere was observed at a distance of
about i oo Jupiter radii (7 x i os km) from the planet.
A turbulent plasma layer exists behind the shock which
was also observed in detail and this region, the 'magneto-
Principal
Investigator
Helium vector magnetometer Jet Propulsion Laboratory (JPL) E. J. Smith
Flux-gate magnetometer Goddard Space Flight Center (GSFC) M. Acuna
Plasma analyser Ames Research Center (ARC) J. H. Wolfe
Charged-particle detector University of Chicago J. A. Simpson
Geiger-tube telescope University of Iowa J. A. Van Allen
Cosmic-ray telescope Goddard Space Flight Center (GSFC) F. B. McDonald
Trapped radiation detector University of California, San Diego R. W. Fillius
(UCSD)
Ultraviolet photometer University of Southern California D. L. Judge
(USC)
Imaging photopolarimeter University of Arizona T. Gehrels
Infrared radiometer California Institute of Technology G. Munch
Asteroid-meteoroid detector General Electric Company (G.E.) R. K. Soberman
sheath', is then followed by the mag-
netic field of the planet itself. The
magnetic axis of Jupiter is tilted with
respect to its axis of rotation at an
angle of approximately i o 8?. Since
Jupiter's rotation-time. around its axis
is very short-ten hours-and since
the dipole field is essentially fixed to
the magnetic axis, this leads to a
rapidly fluctuating set of measure-
ments when observed from a plat-
form in a hyperbolic orbit around
the planet. These rapid fluctuations
will become particularly apparent in
the discussion of the charged particle
measurements in Jupiter's vicinity.
The magnetosphere in its outer
regions is relatively `soft' as evidenced
by the observation that the position
of the shock structure changes in time
Meteoroid detector
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Figure 2 The Pioneer 10 and 11 trajectories as projected on
the plane of the ecliptic.
on it by the solar wind. The picture that emerges from
the plasma and the magnetic measurements is shown in
figures 5 and 6. The bow shock, the magnetosheath, the
magnetosphere, and the dipole field are all shown.
Measurements made by Pioneer i o and i i indicate that
the magnetic field at the surface of Jupiter is 10-14 gauss.
This is about 20 times larger than the value of the Earth's
magnetic field at its surface.
Charged particle experiments. The Pioneer i o and i i space-
craft carried a full complement of charged-particle
detectors. These devices were sensitive to electrons,
protons, and heavier charged particles over a wide range
of incident particle energies. As was the case for the
plasma and the magnetic field experiments, there were
two purposes in performing charged-particle measure-
ments. The first was to measure the charged-particle
species and energy distribution in interplanetary space,
and the second was to perform similar measurements
in the vicinity of Jupiter.
The charged-particle detectors differ from the plasma
probe in that they are sensitive to particles having
energies much higher than the `thermal' energies en-
countered in the case of plasma measurements. The
cosmic-ray background measurements revealed that the
high-energy cosmic ray flux stays roughly constant as the
spacecraft moves from the vicinity of the orbit of Earth
Heliocentric distance (A.U.)
1 2 3 4 5
Figure 3 The Pioneer 10 and 11 trajectories as seen roughly
from a point in the plane of the ecliptic.
to the orbit of Jupiter, 5 A.U. away. This result is to be
expected in view of the galactic origin of the cosmic rays.
Near Jupiter very complex patterns of charged
particles are observed. These arise because the dipole-
shaped magnetic field of Jupiter acts in such a manner
that energetic charged particles can execute long-lived,
stable orbits in the field. Such particles are usually said
to be trapped in the magnetic field. Both Pioneers i o and
I I flew by the planet in such a way that really detailed
measurements of the charged particles trapped in
Jupiter's magnetic field were possible for the first time.
Figure 7 shows the results of one of these charged-particle
experiments. Its important features are:
(t) Large fluctuations in the observed counting rate are
Magnetosheath
T
Jupiter encounter
B
Z3
0 100 200
300 400 500 600 700 800
Time from launch (days)
Figure 4 The number of 'hits' on the micro-meteoroid detectors
on Pioneers 10 and 11 is shown in this figure as a function of
time from launch.
Axis of rotation
Magnetic axis CID
Figure 6
shown.
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1.6 possess a sufficiently strong gravita-
130 R, 110 90 70 50 30 10 10 30 50 70 90 R, tional field to retain the hydrogen
10'
and helium and these light elements
104 The University of Chicago 10 hours were quickly lost early in the for-
Pioneer 11 M r i mation of these planets. Jupiter, on
10' B M M B B M M M B B the other hand, is so massive (approxi-
10 (b) mately 318 times the mass of the
Earth) that its elemental composition
10' (a) must be, today, essentially the same
Protons as the original solar nebula. The
10? 0.5-1.8 MeV study of the helium/hydrogen ratio is,
10 + + therefore, important for our under-
.S t a + t t t standing of the formation of our solar
o 10' system. The helium/hydrogen ratio
" 10o is also important as an engineering
10 _} Electrons parameter in designing the heat shield
&30 MeV _ for an entry probe that will even-
10 Core region tually be flown on a future mission to
Jupiter.
10 ' 328 It had already been determined
(24 Nov) 330 332 Day of 334 year, 1974 U U 3T (G.R.T.) 340 342 from ground-based measurements
that Jupiter apparently radiates more
Figure 7 This figure shows the counting rates of the detectors sensitive to 0.5 to energy-by about a factor of two-
1.8 MeV protons and 6 to 30 MeV electrons. Crossings of the bow shock are labelled than it receives from the Sun. The
(B) and magnetopause crossings are labelled (M), word `apparently' is used deliberately
here to highlight the fact that only the
`bright' side of the planet is visible
seen, these being due to the rapid rotation of the planet from the Earth. It is possible, but unlikely, primarily
and its associated dipole field. because of the rapid rotation rate of the planet, that the
(2) Higher counting rates are observed near the planet. energy radiated from the planet's dark side is substan-
This result is expected and is similar to that observed tially different from that observed from the vantage
in the case of charged particles trapped in the Earth's point of the Earth. Since the spacecraft, during the flyby,
magnetic field. viewed the dark side of the planet as well as the light,
(3) Reductions in the counting rates are observed when this matter could be settled once and for all. It was found
the spacecraft passes over the orbits of the large satellites during the flyby that the temperature of the planet is
of the planet. This is caused by the fact that the charged roughly uniform, irrespective of whether the dark or the
particles trapped in the magnetic field strike the satellites light side is observed. The surface temperature is approxi-
and are thus lost from those regions of the magneto- mately 125 ? 2 K which is somewhat lower than the
sphere traversed by the satellites. temperature estimated from observations made from
(4) There is an asymmetry between the measurements the surface of the Earth (134 K). This measurement
made on the incoming and the outgoing portions of the shows that the energy radiated by Jupiter is about
orbits for both spacecraft. This observation results from 1-9 ? 0.2 times the energy the planet receives from the
the asymmetry of the magnetic environment of the planet Sun. Since Jupiter is not large enough to burn in the
illustrated in figure 5. thermonuclear sense (that is, the planet is not a star) the
The charged particle measurements in the vicinity of excess energy must either come from radioactive decay
the planet yielded a great deal of new information. of heavy material in the core or, more probably, from
However, a complete understanding of the magnetic and residual heat left over from the initial gravitational col-
the charged particle environment must await the placing lapse associated with Jupiter's original formation.
of an orbiting spacecraft around Jupiter that will enable The pictures produced from the data provided by the
many repeated measurements to be made of the particle imaging photo-polarimeter also yielded some extremely
fluxes and the magnetic fields in the vicinity of the planet. important scientific results. The most significant are:
Spectroscopy and photometry. Several spectrometers were (i) The white bands on the planet's surface are at some-
carried aboard the Pioneer to and i i spacecraft to view what higher levels in the planet's atmosphere than the
the planet and its satellites. An ultraviolet photometer neighbouring dark bands. This was established by
was set to detect lines characteristic of hydrogen and observing the terminator that marks the boundary
helium which are the important constituents of Jupiter's between the sunlit and dark regions of the planet.
atmosphere. An infrared radiometer was used to make a (2) The `red spot' on the planet's surface seems to be
complete thermal map of the planet. Finally, an imaging above the surrounding white belt in which it is located.
photop larimeter was mounted on both spacecraft. This is consistent with the red spot being-a cloud deck
This instrument produced the spectacular pictures taken caused by-a more or less permanent vortex in the planet's
of Jupiter during the flybys of Pioneers i o and i i. These atmosphere. The red colour probably results from the
pictures are by far the most detailed images ever obtained material lifted from the lower layers of Jupiter's atmo-
of the planet. sphere above the uppermost cloud deck by the vortex.
The most important result of the ultraviolet photo- (3) There are a great many smaller vortex-like distur-
metry is an estimate of the helium to hydrogen ratio in bances of a non-permanent nature on the planet's
the upper atmosphere of Jupiter. The result is that surface.
He/Hz is approximately o? i 8, which is reasonable when (4) Jupiter's polar region has a mottled appearance
compared with the solar helium to hydrogen ratio. The rather than the characteristic stripes that are the major
solar nebula, from which the Sun and planets were features of the equatorial region of the planet.
formed some 5 x io9 years ago, was composed mostly Figures 8 and 9 are pictures of the planet taken with
of hydrogen and helium. The terrestrial planets the imaging photo-polarimeter that illustrate some of the
(Mercury, Venus, Earth, and Mars), however, did not points made in this section. It should be pointed out that
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Figure 8 (above) This remarkable picture of Jupiter was taken
by Pioneer 11 looking down on Jupiter from 50? north latitude.
The north pole of Jupiter itself is roughly on the terminator line
at the top of the picture. The Great Red Spot is shown, greatly
foreshortened because of the location of the spacecraft, at the
lower right. The polar regions of Jupiter cannot be observed
from the Earth. (Figures 8, 9 and 10 are NASA/University of
Arizona photographs).
Figure 9 (right) This close-up of Jupiter's Great Red Spot was
taken from a distance of 545 000 km. Details visible within the
spot seem to show a counter-clockwise spiral. The white oval
below the right end of the Red Spot is one of three such spots
about 120? apart around Jupiter.
the camera used was a spin-scan instrument and that
the pictures themselves are computer constructs of the
bit streams obtained from the spin-scan camera. The
colours are obtained by superposing two images taken
through a red and a blue filter in such a way as roughly
to reproduce the colours of Jupiter when it is observed
through a good optical telescope.
Figure io shows the satellite Ganymede taken with
the same camera system. It is the first picture ever to
show distinct surface features on one of the satellites
of an outer planet in our solar system.
The atmosphere of Jupiter. Both Pioneer i o and i i per-
formed radio wave absorption experiments when the
spacecraft was occulted by the planet. An interpretation
of the S-band occultation measurements yields an
atmospheric temperature of about 400 K at the 5 X 104 Pa
pressure level in the atmosphere. This result is in serious
disagreement with that obtained using the infrared
radiometer. At the present time there is no generally
accepted explanation for the observed discrepancy.
Table II
Jupiter gravity harmonics from an analysis of Doppler data from
Pioneer 10 (2) and Pioneer 11. Values are based on an assumed
equatorial radius of 71 398 km.
Coefficient
(x 10?)
14 720?40 14750+50 Figure 10 A picture of Ganymede taken from a distance of