Recommendations for a 1979 Mariner Jupiter-Uranus mission are discussed with the possibility of launching the first outer planet atmospheric entry probe. Measurement categories considered for the mission include conducting imaging experiments, observations in both the IR and UV spectral range, experiments associated with magnetic fields, plasma, charged particles, and S- and X-band occultation measurements

Moore, J.

English

NASA Technical Reports Server

URANUSSCIENCE PLANNING
Jesse Moore
Jet Propulsion Laboratory
MR. JESSE MOORE: As John Lewis said earlier, Uranus is some-
what of a unique planet in our solar system. I will talk about
science planning as related to a mission to Uranus (Figure 2-33).
Specifically, I will talk about the possibility of a 1979
Mariner Jupiter-Uranus mission with the possibility of launching
the first outer planet atmospheric entry probe. What I will
cover initially, to give you background information, are mission
recommendations that have been developed by recent Science ad-
visory groups concerned with the type of missions that make sense
scientifically, to plan for the outer planets. Then, I will fo-
cus on what I call the MJU Science Advisory Committee and talk
specifically about the charter, some of the objectives that this
group has and some of the outputs that are now emerging. I also
will give you a brief summary of where we think we are going
from here.
Figure 2-34 presents some of the past advisory groups, and
studies that have considered plans for the outer planets over
the past couple of years. These certainly are not all; they
don't address all the specific things like the Titan Workshop
or the Saturn Rings Workshop that have been held. One of the
earliest planning groups which existed over a fairly long period
of time, was the OPSAG. OPSAG looked at defining a broad pro-
gram of outer-planet exploration. A Mariner mission to Uranus
in 1979 was recommended by OPSAG. Its output was published in
the Space Science Reviews in 1973 and it existed for approxi-
mately fifteen months. Also, shortly after the OPSAG was ini-
tiated, the Space Science Board conducted a Summer Study and
in the report of the Space Science Board there was considerable
interest expressed in going to Uranus. The Summer Study publi-
cation came out in June, 1971.
11-86
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Following the OPSAG was an Outer Planet Science Working Group
(OPSWG) which looked at the work that had gone on previously and
recommended various modifications to the programs of exploration.
In December of last year, the Mariner Jupiter-Uranus Science
Advisory Committee (MJUSAC) was initiated. Let me now spend a
few minutes giving you some of the strategies that came out of
these groups and, also, identify the members who participated.
My intent here is to illustrate the point of commonality of
membership as well as commonality of identifying the Mariner
Jupiter Uranus mission as an important mission.
Figure 2-35 presents the membership of the OPSAG group, divi-
ded into various disciplines. As you can see, it represented
a fairly broad spectrum of the scientific community.
Figure 2-36 shows the recommendations that came from the
OPSAG. With regard to the 1979 Mariner Jupiter-Uranus mission
two launches were recommended as a logical program to follow the
1977 MJS mission which is currently approved and on-going.
You will also note there was a Pioneer-Uranus entry probe
mission planned in 1980, via Saturn. Dan Herman, earlier this
morning, mentioned how NASA's plans have changed. Now, the
Uranus entry probe is being considered as an integral part of
the 1979 MJU flyby. You wall be hearing more during the course
of the workshop concerning the mission design and spacecraft
design associated with this particular mission.
Figure 2-37 contains the membership list for the OPSWG. I
think you can recognize the commonality of membership with the
OPSAG. The recommendations from this group came out in two
strategies. Strategy A (Figure 2-38) recognized the 1979 Mar-
iner Jupiter-Uranus mission. It also added the Pioneer Jupiter-
Uranus mission in 1980 with the Uranus probe.
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Strategy B (Figure 2-39) was very similar. It however, recom-
mended the 1979 MJU mission with the addition of a Uranus probe
on the flybys. It also recommended two launches following the
MJS 1977 program.
The remainder of my discussion will be specifically about the
MJU mission and the MJUSACactivities. The MJUSAC (Figure 2-40)
was asked to develop detail science objectives, rationale and
requirements; to quantitatively evaluate payload options and
various instrumentation requirements; and to determine the sci-
ence instruments currently available to meet these requirements.
The final outputs were to develop an advisory committee po-
sition on this mission, indicating the scientific value of the
addition of the Uranus probe, and to recommend any SR&T develop-
ments for the science instrumentation.
Figure 2-41 presents the membership of MJUSAC. It is chaired
by Dr. Van Allen with Dr. A1 Cameron as Vice-Chairman. Space-
craft and probe inputs for the scientists to consider are being
developed while the science objectives, rationale, and payload
are evolving. I wouid like to point out that the spacecraft in-
puts to this particular group are coming from Ron Toms of JPL
and the probe inputs for consideration are being supplied by
Ben Padrick and Howard Matthews of Ames. I would like, also,
to recognize that Dr. Lewis is a member of MJUSAC.
For the engineers here who may not be familiar with Uranus, I
will describe several properties of Uranus (Figure 2-42). It has
a very long orbital period, as most of the outer planets do,
making the billiard'ball or the gravity-assist technique occur
in fairly rare opportunities: 1979 is a rare opportunity. The
energies and planet alignments are favorable to get a good swing-
by of Jupiter to go to Uranus in a reasonable flight time. The
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distance of Uranus from the Sun is 19.2 AU. Uranus is about
twice as far out in the solar system as Saturn, the second plane-
tary target of the 197.7 MJS mission. The Pioneer ii mission also
is currently targetted to Saturn as well. One of the unique
characteristics of Uranus is its inclination. The equator of
Uranus is inclined by 98 ° which means that as you approach Uranus
and its near equatorial satellites, the system appears as a bull's-
eye w:ith Uranus at the center. The period of rotation is about ten
hours. It is a fairly large planet with a mass about fifteen times
that of the Earth. There are five satellites, all within a very
compact range. They range from about 4.8 Ru (radius of Uranus)
out to about 21.6 Ru. Miranda is closest to Uranus. The satel-
lite radii range from about 140 to 1200 kilometers.
I will now discuss the science rationale (Figure 2-43) and I
will summarize very briefly the work that the MJUSAC has accom-
plished to date. The case for a Mariner Jupiter-Uranus mission
can be based primarily on the uniqueness of Uranus; the axial
orientation of Uranus; the cosmogonical considerations relating
to its origin within the solar system; the unique atmospheric
circulation which is likely to result from its axial orientation;
and, if it has a dipole field, the characteristics as would be
measured by approaching the planet from a head-on position look-
ing at a "pole-on" magnetosphere. Further, the dipole axis would
be pointed closest to the Sun at about the time the MJU space-
craft gets to Uranus in 1986.
As John Lewis pointed out, Uranus has a low atmospheric tur-
bulence level, which leads to the conclusion that it apparently
lacks an internal heat source, although there is certainly some
question on that. One of the other key points of rationale for
this mission is that previous groups have stated that the pair of
outer planets, Jupiter and Saturn, and the pair Uranus and Nep-
tune form very contrasting bodies. We now have missions that are
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planned or enroute to explore Jupiter and Saturn and a mission to
Uranus would certainly give us some data on the other pair of outer
planets to compare with the Jupiter and Saturn pair.
Finally, and certainly not of least importance, is the satel-
lite system of Uranus. The satellites are compact. They form a
very regular system, and there is considerable speculation that
their composition is quite different from the satellites around
Jupiter and Saturn.
Figure 2-44 is a generalization of the science objectives
that are being formulated in the MJUSAC. From these kinds of
objectives, the MJUSAC is formulating the measurement require-
ments and the payload to meet these particular requirements.
The first objective is pointed toward the physical properties of
Uranus. Secondly, as John Lewis pointed out, atmospheric charac-
teristics are extremely important with composition probably being
the most important. Because of the "pole-on" effect, Uranus may
have an exciting magnetosphere and you would like to get very good
measurements of its character; you would like to measure the solar
wind interaction; and, also, make measurements within the ionos-
phere. For the satellites, their masses, radii, topography, and
rotational period are extremely important determinations. Be-
cause of the distance of Uranus, understanding the satellite pro-
perties is difficult to do from Earth-based observations. Finally,
you would like to measure the interstellar/interplanetary media.
This mission will go out to about 20 AU, possibly beyond, and
certainly data in that region would add to the base of knowledge
we expect to acquire over the next several years from Pioneer i0
and ii and MJS77.
Figure 2_5 presents the measurement categories that the MJUSAC
is developing. On the flyby science we are talking about conduc-
ting imaging experiments; experiments both in IR and UV spectral
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ranges; experiments associated with the magnetic field; plasma
experiments; charged-particle experiments; and S- and X-Band
occultation measurements as the spacecraft encounters Uranus.
In the probe arena I think you have heard earlier about the
particular measurements listed here. I think it is very impor-
tant as Dan Herman pointed out that NASA is planning to formulate
a specific science group to address the Uranus atmospheric ques-
tion in-depth and, subsequently, define in more detail the probe
payload. The data generated by this group will be used to plan
a Phase B probe activity beginning in July 1975.
To develop a scientifically viable MJU mission, it is manda-
tory that flyby and probe science measurements be complimentary
in nature. Data from the probe and flyby spacecraft science in-
strumentation should be designed to contribute Uniquely to the
total integrated science return.
My final figure (Figure 2-46) describes the current activi-
ties and future plans of MJUSAC. We are in the process of getting
more specific input s on the payload options and the instrument
requirements, and in the process of developing final MJUSAC rec-
ommendations. I will comment that the MJUSAC has strongly en-
dorsed the 1979 Mariner Jupiter-Uranus mission with an atmospheric
entry probe of Uranus. I think the outputs of this technology
workshop will certainly serve as valuable input to the planning
and further development of the 1979 mission possibility. As far
as our future plans are concerned, the scientists under the direc-
tion of Dr. Cameron, are planning a publication in the fall of this
year in Icarus on detail science rationale, objectives and re-
quirements; the MJUSAC is preparing a final report which will
appear in draft form in early August. This report will inte-
grate both the science work as well as the mission, spacecraft
and probe design work.
II-104
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Again, I wish to say that I think the _probe workshop will
provide some very valuable inputs to the MJUSAC and we are
looking forward to seeing the outputs.
II-106


Uranus science planning

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