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Future in situ balloon exploration of Titan's atmosphere and surface 

A. Coustenis (LESIA, Paris-Meudon Observatory, 5, place Jules Janssen, 92195 
Meudon Cedex, France; Athena .coustenis @ obspm .fr ; +33145077720) and 

J. Lunine (LPL), D. Matson (JPL), K. Reh (JPL), P. Beauchamp (JPL), J.-M. 
Charbonnier (CNES, Toulouse), L. Bruzzone (Univ. Trento), M.-T. Capria (lASF, 
Rome), A. Coates (MSSL, Univ. College London), C. Hansen (JPL), R. Jaumann 
(DLR, Berlin), J.-P. Lebreton (ESA/ESTEC), R. Lopes (JPL), R. Lorenz (APL), 1. 
Mueller-Wodarg (Imp. College, London), F. Raulin (Univ. Paris 12), E. Sittler 
(NASA/GSFC), J. Soderblom (LPL), F. Sohl (DLR, Berlin), C. Sotin (JPL), T. Spilker 
(JPL), N. Strange (JPL), T. Tokano (Univ. Koln), E. Turtle (APL), H. Waite (SWRI), 
L. Gurvits (JIVE), C. Nixon (Univ. Maryland), T. Livengood (NASA/GSFC), J. 
Blamont (CNES, Paris), R. Achterberg (NASA/GSFC), M. Allen (JPL), C. Anderson 
(NASA/GSFC), D. Atkinson (Univ. Idaho), T. Balint (JPL), G. Bampasidis (Univ. 
Athens), D. Banfield (Cornell), A. Bar-Nun (Tel-Aviv Univ., Israel), J. Barnes (Univ. 
Idaho), R. Beebe (New Mexico State Univ.), E. Bierhaus (Lockheed Martin), G. 
Bjoraker (NASA/GSFC), D. Burr (Univ. Tennessee), F. Crary (SWRI), J. Cui (Imp. 
College, London), J. Elliott (JPL), M. Flasar (NASA/GSFC), A. Friedson (JPL), M. 
Galand (Imp. College, London), D. Gautier (Paris-Meudon Observ.), M. Gurwell 
(CFA, Harvard), J. Head (Raytheon), M. Hirtzig (Paris Observ.), T. Hurford 
(NASA/GSFC), T. Johnson (JPL), K. Klaus (Boeing), W. Kurth (Univ. Iowa), E. 
Lellouch (Paris-Meudon Observ.), J. Martin-Torres (Caltech), K. Mitchell (JPL), X. 
Moussas (Univ. Athens), M. Munk (NASA/LRS), C. Neish (APL), L. Norman (UCL), 
B. Noyelles (Univ. Namur), G. Orton (JPL), A. Pankine (JPL), D. Pascu (US Naval 
Obs.), E. Pencil (NASA/GRC), S. Rafkin (SWRI), T. Ray (JPL), F. Rocard (CNES, 
Paris), S. Rodriguez (AIM, Univ. Paris 7), A. Solomonidou (Univ. Athens), L. Spilker 
(JPL), R. West (JPL), D. Williams (ASU, SESE), E. Wilson (JPL and Univ. 
Michigan), M. Wright (NASA/AMES), V. Zivkovic (Univ. North Dakota). 

Additional material and the full list of the 79 co-authors with complete affiliations 
and e-mails can be found at the OP AG Titan Working Group Web site, Documents 

Section, Password: TWG_2009 at: 
http://www.lesia.obspm.fr/cosmicvision/tssm/tssm-public/?cat=25 




Abstract: Many of the questions remaining to be addressed after the Cassini-Huygens mission 
require both remote and in situ elements to achieve the desired science return. Our understanding of 
the lower atmosphere, surface and interior (subsurface ocean) of Titan will benefit greatly from 
detailed investigations at a variety of locations, a demanding requirement anywhere else, but one 
that is uniquely possible at Titan using a hot-air balloon (montgolfiere). 

1) Scientific motivation for a montgolfiere on Titan 

A wide range of high priority scientific investigations at Titan remains to be addressed after the 
Cassini-Huygens mission (cf. the 2008 joint NASA-ESA Titan Saturn System Mission study final 
report). Recent findings from Cassini Huygens answered some questions but also raised many 
more. Cassini will not be able to comprehensively address many of these questions because of 
inherent limitations in the instrument suite and because both remote and in situ elements are 
required to achieve much of the desired science return. Whereas a spacecraft in orbit around Titan 
could allow for a thorough investigation of Titan's upper atmosphere, there are questions that can 
only be answered by extending the measurements into Titan's lower atmosphere and down to the 
surface. Key steps toward the synthesis of prebiotic molecules that may have been present on the 
early Earth as precursors to life might be occurring high in the atmosphere; the products then 
descending towards the surface where they might replicate. In situ chemical analysis of gases, 
liquids, and solids, both in the atmosphere and on the surface, would enable the identification of 
chemical species that are present and how far such putative reactions have advanced. The rich 
inventory of complex organic molecules that are known or suspected to be present in the lower 
atmosphere and at the surface gives Titan a strong astrobiological potential (Pilcher, C, for the NAI 
Executive Council, "Titan is in the List of Highest Priority Astrobiological Targets in the Solar 
System", 22 September 2008). 

Our understanding of the forces that shape Titan's diverse landscape (dunes, cryovolcanoes, 
rivers, etc) and interior (subsurface ocean) will benefit greatly from detailed investigations relying 
on very high-spatial-resolution remote sensing at a variety of locations, a demanding requirement 
anywhere else, but one that is uniquely possible at Titan using a hot-air balloon (montgolfiere). 
Indeed, Titan's thick cold atmosphere and low gravity make the deployment of in situ elements 
using parachutes (as demonstrated by the Cassini-Huygens probe) and balloons vastly easier than 
for any other solar system body. A montgolfiere floating across the Titan landscape for long periods 
of time (Earth months or even years), with an adapted payload, would offer the mobility required to 
explore the diversity of Titan in a way that cannot be achieved with any other platform. 

In situ elements would also enable powerful techniques such as subsurface sounding and 
potentially seismic measurements, to examine and better understand Titan's crustal structure. 

Indeed, for the following reasons. Titan is the best place in the solar system for scientific 
ballooning: 

1. Its atmosphere is cold and dense: 5 kg/m^ at the surface compared to 1 kg/m^ on Earth. 
Therefore the effect of differential molecular mass between the buoyant gas and the ambient 
air is maximized. 

2. The low value of solar radiation (10^ of radiation at Earth) creates, in all practicality, no 
diurnal variation of the external energy source and opens the possibility of long duration 
flights - less stress on balloon materials and cyclic impact on buoyancy. 

3. Because of the scale height of Titan's atmosphere, inflation during descent occurs over a 
long period; for example, it can be initiated at a vertical velocity of 5 m/s' around 30 km of 
altitude (20 mbar pressure) and completed over a number of hours (compared to 30 m/s' 
initial velocity). 

A montgolfiere balloon has been identified in years of previous science driven mission studies as 
a necessary element in a comprehensive Titan exploration program. The most recent studies 
include the 2003 Vision Missions study, 2006 Titan Pre-biotic Explorer Study (TiPEx), 2007 Titan 
Explorer Flagship study, and the 2008 joint NASA/ESA Titan Saturn System Mission (TSSM) 
study. As a result of the 2008 TSSM study, the science panels and review boards confirmed that an 
orbiter and in situ elements are needed for a credible flagship mission to Titan. 

While other elements identified in Titan mission architectures (notably landers/surface elements) 
appear to have significant flight heritage, a balloon has not been flown at Titan before and will 
require further development. The 2008 TSSM NASA and ESA technical review boards confirmed 
the feasibility of implementing a montgolfiere balloon at Titan and identified the following risks 
that should be addressed to demonstrate flight readiness. 

Balloon deployment and inflation upon arrival at Titan 
Balloon packaging inside the aeroshell with RPS thermal management 
Interface complexity between balloon, RPS, and aeroshell 
- Late integration of the NASA provided MMRT 



To ensure readiness for launch of a flagship mission to Titan, JPL and CNES are entering into a 
joint risk reduction effort directed at maturing the flight readiness of the Titan montgolfiere. This 
activity would be co-funded by NASA and CNES over a multi-year period with the objective of 
achieving TRL 5-6 by 2015. The effort would leverage the complementary planetary flight system 
experience and balloon design and operational capabilities of JPL and CNES. 

While a wide range of balloon architectures are viable at Titan (Lorenz, 2008), the reasons 
outlined here, as well as the science objective to achieve at least one circumnavigation of Titan (> 6 
months lifetime), favor the choice of a montgolfiere. It should be noted that since the montgolfiere 
uses Titan's atmosphere and the thermal heat from its radioisotope power system to maintain 
buoyancy, it does not include the complexity, mass, and limited life of a lighter-than-air gas supply 
(e.g., hydrogen) and inflation system. 

Ever since its discovery by the Montgolfier brothers, the montgolfiere balloon has attracted 
significant attention in Earth's exploration and more recently for planetary missions. Balloons offer 
the only possibility today of conducting a long-duration voyage in the atmospheres of Venus, Mars, 
and Titan. To date, only in Venus' atmosphere have balloons ever been deployed. A montgolfiere is 
an open balloon with an aperture equal to approximately one tenth of the maximum diameter of the 
balloon envelope. During descent and inflation, the balloon fills with ambient Titan gas which is 
heated by the radioisotope power system heat to achieve neutral buoyancy. There is a large body of 
US, European, and Russian experience in flying Earth-based montgolfieres, as well as limited 
experience with planetary balloons (Venus). Since 1979, CNES has flown on average 2 to 5 long- 
duration infrared- heated montgolfieres per year. Also, JPL has conducted high altitude drop tests on 
Earth that have demonstrated the deployment and inflation of montgolfiere balloons similar to what 
would be flown on Titan. 

A montgolfiere as envisioned in previous 
mission studies, is capable of circumnavigating 
Titan every 3 to 6 months. Carried by 1-3 m/s 
winds, a Titan montgolfiere could explore the 
Titan environment with a host of highly 
capable instruments, including high-resolution 
cameras, chemical analyzers and subsurface- 
probing radar. There are no obvious life- 
limiting factors, and so its flight could 
continue for many months, perhaps even years 
and could provide global coverage from a 
nominal altitude of about 10 km (Fig. 1). 
Furthermore, the capability of performing 
surface sampling from the balloon has been 
investigated and development of this capability 
would further increase the science value of 
such a mobile platform. 

The combination of orbiting and in situ 
elements would provide a comprehensive and, 
for Titan (indeed, for the outer solar system!), 
unprecedented opportunity for synergistic 
investigations. The balloon platform alone, 
with a carefully selected instrumentation suite, 
is a powerful pathway to understanding this 
profoundly complex body. The montgolfiere 
is Titan's "Rover", albeit with the advantage of 
an extended range. 




2) Science return with the in situ balloon 

Titan is a very complex world (Fig. 2). It is the only one we know of today, beyond our own 
planet, not only to possess a thick nitrogen-based atmosphere, but also a geologically complex 
active surface with lakes and organic deposits and quite likely a sub-surface ocean. The physical 
processes within this world beg for further investigation in order to better understand these 
processes, not only on Titan, but also on Earth. If we are to focus on the Earth and its climate (cf. 
Nixon et al. Decadal White Paper on "Titan's greenhouse effect and climate"), as well as on its 
organic chemistry, we need in the future to concentrate on Titan, which sustains an active 
hydrologic cycle with surface liquids, meteorology, and climate change as established by Cassini 
Huygens. 



2.1) Scientific objectives for a montgolfiere on Titan 

A montgolfiere on Titan would open the possibility to address the following science objectives: 

• Perform chemical analyses in the atmosphere and the surface (options for in situ 
sampling of the surface, such as via a tether or via end-of-mission slow descent onto the 
surface, can be explored), the latter to determine the kinds of chemical species that accumulate 
on the surface (Fig. 2), to describe how far complex reactions have advanced, and define the 
rich inventory of complex organic molecules that are known or suspected to be present at the 
surface. New astrobiological insights will be inevitable from the possible combination of 
orbiter, montgolfiere, and lander (or surface in situ sampling via a montgolfiere) investigations. 

• Analyze the regional geology and composition of the surface, in particular any liquid 
or dune material and in context, the ice content in the surrounding areas by hyper- spectral 
imaging. 

• Study the forces that shape Titan's diverse landscape. This objective benefits from 
detailed investigation at a range of locations; the atmospheric conditions present at Titan make 
this relatively straightforward with a montgolfiere equipped with high-resolution cameras and 
subsurface-probing radar. 




Figure 2. Schematic of Titan's methane cycle and of the atmosphere-surface interactions that could be 
investigated by a montgolfiere (re-drafted from Lunine and Atreya, 2008). 

Thus, a long-lived in situ balloon, could contribute to or achieve the following investigations: 

• Determine the composition and transport of volatiles and condensates in the atmosphere and 
at the surface, including hydrocarbons and nitriles, on both regional and global scales, in 
order to understand the hydrocarbon cycle. Determine the climatological and meteorological 
variations of temperature , clouds, and winds. 

• Characterize and assess the relative importance, both past and present, of Titan 's geologic, 
marine, and geomorphologic processes (e.g., cryovolcanic, aeolian, tectonic, fluvial, 
hydraulic, impact, and erosion) . 

• Determine the chemical pathways leading to formation of complex organics in Titan's 
troposphere and their modification and deposition on the surface with particular emphasis on 
ascertaining the extent of organic chemical that has evolved on Titan. 

• Determine geochemical constraints on bulk composition, the delivery of nitrogen and 
methane, and exchange of surface materials with the interior. 

• Determine chemical modification of organics on surface (e.g., hydrolysis via impact melt). 



2.2) Titan investigation "Firsts" achievable with a montgolfiere balloon 

Depending on where the balloon might be placed (equator, north pole, etc.), a significant part of 
the lower atmosphere of Titan, still largely unknown today, will be thoroughly explored around the 
altitudes of the balloon's trajectory. Important information will be gained on the lower atmosphere 
and its interactions with the surface. Similarly, detailed images of thousands of kilometers of 
Titan's varied terrain, with image quality equal to or better than that of the Huygens probe during its 
descent, will reveal the extent of fluvial erosion on Titan, well matched to the scales mapped 
globally by the orbiter. This mobile capability will enable several significant scientific "firsts": 

1 . First analysis of the detailed sedimentary record of organic deposits and crustal ice geology 
on Titan, including the search for porous environments ("caverns measureless to man") 
hinted at by Cassini on Xanadu. 

2. Direct test through in situ meteorological measurements of whether the large lakes and seas 
control the global methane humidity, which is key to the methane cycle. 

3. First in situ sampling of the winter polar environment on Titan, a region expected to be 
vastly different from the equatorial atmosphere explored by Huygens. 

4. Compositional mapping of the surface at scales sufficient to identify materials deposited by 
fluvial, aeolian, tectonic, impact, and/or cryovolcanic processes. 

5. First search for a permanent magnetic field unimpeded by Titan's ionosphere. 

6. First direct search for the subsurface water ocean suggested by Cassini. 

7. First direct, prolonged exploration of Titan's complex lower-atmosphere winds. 

8. Exploration of the complex organic chemistry in the lower atmosphere and surface liquid 
reservoirs discovered at high latitudes by Cassini. Furthermore, astrobiological exploration 
by a non-destructive method (TBD after lab/modeling work) of non-terrestrial lifeforms 
within the surface and sub-surface reservoirs 



3) A possible scenario for the delivery and deployment of the montgolfiere 

The 2008 TSSM study developed a possible scenario for the delivery and deployment of a hot- 
air balloon in Titan's atmosphere and a scheme for conducting science operations. In brief, the 

montgolfiere would be released 
on approach to the first Titan 
flyby for a ballistic entry into 
Titan (Fig. 3). At its deployment 
latitude of ~20°N (where the 
most desirable zonal winds are 
expected), analysis based on 
Cassini-Huygens results 

indicates that the montgolfiere 
should circumnavigate Titan at 
least once over a 6-month 
period. 

The 2.6-m diameter entry 
vehicle and its encapsulated 
montogolfiere would have a 
mass of ~600 kg. The balloon 
itself could be ~10.5 m in 
diameter with its entrained gas 
heated by a multi mission 
radioisotope thermoelectric 

generator power system 
(MMRTG). The gondola, as 
defined by the TSSM studies, 
would weigh 144 kg, including 
22 kg of science instruments. 
The electrical power would be 
provided through the MMRTG 
(-100 W). 

With these parameters, and a 
wind speed of about 1 m/s, a nominal lifetime of 6 months is expected to meet the science 
requirement of achieving at least one circumnavigation of Titan. The montgolfiere entry, descent 
and inflation scenario is shown in Fig. 4. 




Figure 3 The release of the montgolfiere from the TSSM orbiter 
(TSSM report, 2008). 



Montgolfier 

Entry Profile 




Figure 4: Montgolfiere entry, descent and inflation (EDI) scenario (ESA TSSM assessment report, 2008). 



Stowed 
balloon 



Gondola 




Moitar & cbgiie 
paiacliute 

Main parachute 



Labyimtli 
sealing 



The TSSM balloon concept would 
be deployed at ~40 km in altitude. 
The airflow from the descent would 
fill the balloon envelope while it is 
simultaneously being heated beyond 
the local ambient air by the MMRTG. 
After ~13 hours, a stable altitude will 
be reached. The montgolfiere 
configuration is shown in Fig. 5. 

Communications would be 
achieved through an orbiter-to- 
balloon relay. The orbiter tracks the 
montgolfiere and closes the 
communications link during each 
flyby and throughout its orbit in the 
Saturnian system. A beacon signal is 
used to support establishment of the 
relay link. The direction to the Earth 
will be determined through the aid of 
sun sensors. 

Other options that could be 
investigated for this montogolfiere include an altitude-control system and/or the release of small- 
sized balloons at regular time intervals which could perform additional in situ measurements of the 
atmosphere operating like meteorological stations during their descent phage of their flight. Other 
balloon concepts (e.g. smaller hydrogen balloon) should be investigated. 



Platfomi 



MMRTG 



Figure 5 : montgolfiere configuration (ESA TSSM 
assessment report). 



4) Key measurements aboard the montgolfiere 

Key instruments would be placed aboard the gondola of the balloon to secure and optimize the 
science return. Some of them are described hereafter including their related measurements. 

4.1) Chemical analysis of the atmosphere with the montgolfiere: 

This mission would allow us to determine the methane and ethane mole fractions; to measure the 
noble gas concentration to 10s of ppb to detect and characterize molecules at concentrations above 
ppm levels, and to determine the concentration of aerosol particles as well as the bulk composition 
of individual particles. 

4.2) Hyperspectral imaging with the montgolfiere 

Near-infrared spectroscopy of the surface from the montgolfiere will provide high-resolution 
views of the surface composition from reflectance spectroscopy across the organic (or organic- 
coated) dunes, outwash plains and channels, impact craters and cryovolcanic features, and the 
enigmatic circular features of the low latitudes at regional and local scale with a spectral sampling 
of 10 nm. 




Figure 6: Imaging system on a Titan balloon. R. Jaumann. 



A unique feature of the montgolfiere will be its ability to circumnavigate the globe at low 
altitudes (10 km and lower) enabling very-high-resolution imaging of a broad sweep of terrains. 
The montgolfiere camera will perform stereo panoramic and high-resolution geomorphological 
studies at resolutions of better than 10 m per pixel, and select areas at 1 m per pixel with a narrow 
angle camera (Fig. 6). Several thousand images at least will be returned to the orbiter for relay to 

the Earth, over hundreds of thousands 
of square kilometers, a non-negligible 
fraction of Titan's surface area. Since 
resolutions among the three cameras 
(the orbiter, and the montgolfiere wide- 
and narrow-angle cameras) vary by an 
order of magnitude or less, the suite of 
cameras are almost ideally matched to 
provide scene context from the orbiter 
camera to the montgolfiere wide-angle 
camera, and from the montgolfiere 
wide- to the narrow-angle camera. 

The list of applications of such 
images includes fluvial erosion, 
transport, and sedimentation. From 
Cassini Orbiter Titan Radar images, 
broad valleys are seen at 300-500 m 
resolution (Jaumann et al., 2008, 
2009) , but there is no information as to 
the density of smaller- scale fluvial features. Is there higher order branching of the broad valleys into 
dense networks of fluvial features? The TSSM orbiter with the montgolfiere imaging systems will 
trace fluvial drainage systems from the largest channels down to Huygens scale features, providing 
the first possibility to determine processes of origin and calculate how much methane has flowed 
across various parts of Titan's surface. These data will also afford a detailed crustal stratigraphic 
profiling of a number of types of terrains that have been identified on Titan, from possible 
cryovolcanic flows, to plains, to mountains, thus enhancing our understanding of the geologic 
evolution of Titan. 

4.3) Atmospheric structure and meteorology instrument (ASI/MET) 

In situ measurements are essential for the investigation of the atmospheric structure, dynamics 
and meteorology. The estimation of the temperature lapse rate can be used to identify the presence 
of condensation and eventually clouds, and to distinguish between saturated and unsaturated and 
stable and conditionally stable regions. The variations in the density, pressure and temperature 
profiles provide information on the atmospheric stability and stratification and on the presence of 
winds, thermal tides, waves and turbulence in the atmosphere. 

ASI/MET will monitor environmental physical properties (density and mean molecular weight) 
of the atmosphere from the aerobot. ASI/MET data will also contribute to the analysis of the 
atmospheric composition. It will provide unique direct measurements of pressure and temperature 
through sensors having access to the atmospheric flow. 

4.4) Radar sounding 

This instrument is useful for reconstructing the geological history of Titan, characterizing and 
assessing the present day sedimentary environments and geomorphological features and identifying 
the stratigraphic relationships of ancient sedimentary units. More generally, it will allow us to detect 
sub-surface profiles and possible interfaces due to the presence of liquid or other structures (e.g., of 
tectonic or cryovolcanic origin). 

4.5) Magnetometry 

The magnetometer will measure the magnetic field in the spacecraft vicinity in the bandwidth 
DC to 64Hz, depending on science requirements and available telemetry. Also gradiometry 
measurements will be performed. Magnetometry aboard the montgolfiere and lake lander allow for 
sensitive field measurements beneath Titan's screening ionosphere. Crustal magnetism will also be 
searched for. 



4.6) Radio science: 

The radio science suite of the Titan montgolfiere could address the following scientific areas: 
o Diagnostics of the wind profiles and dynamics by means of Doppler and Very Long 

Base Interferometry (VLBI) tracking; 



o Diagnostics of the radio propagation media (Titan atmosphere and ionosphere, 

interplanetary medium) by means of radio signal monitoring; 

o Radio navigation support of in situ experiments and measurements (such as 

attributing specific topo coordinates to various in situ measurements); 

o Diagnostics of the dynamics of motion of the gondola. 

o Sounding of Titan's interior using S-band emission to the ground 

The set of on-board devices able to address the above tasks would be a straightforward and 
affordable addition to the service radio system. In combination with the Earth-based network of 
radio telescopes and deep-space communication stations, the montgolfiere's radio system would 
enable the Planetary Radio Interferometry and Doppler Experiment (PRIDE-TM) to work. While 
specific characteristics of PRIDE-TM should be assessed in conjunction with the overall 
architecture and design parameters of the montgolfiere system, it is safe to assume that the lateral 
positional accuracy can reach values better than 100 m over 10 s integration (X-band operations). 
Further enhancement of the radio science experiments could be achieved by combining PRIDE-TM 
with multi- spacecraft radio measurements involving the balloon, orbiter, and Earth-based antennas. 
With altimetry capabilities we shall be able to map out topography (i.e., reconnaissance phase) for 
safe navigation down to the surface. 

4.7) Direct-to-Earth (DtE) data transmission 

The nominal TSSM mission scenario assumes transmission of the science and housekeeping data 
from the Titan in situ elements via relay by the orbiter. Indeed, the amount of data produced by the 
Titan montgolfiere (e.g. images) and/or surface elements will require a high-capacity radio relay 
system. However, as an efficient backup for critical mission operations and experiments, a low 
data-rate link can be achieved with the nominal transmission from the montgolfiere and received by 
large Earth-based radio telescopes. The most attractive option of DtE would involve the Square 
Kilometer Array (SKA) as the Earth-based facility operating at S band (2.3 GHz) frequencies. This 
facility is expected to be fully operational in 2020. As shown by preliminary assessment estimates 
(Fridman et al. 2008), SKA will be able to receive data streams from the TSSM mission through 
their low-gain transmission at the rate of 30—100 bps. 

5) Summary and recommendations 

Previous studies have identified the montgolfiere balloon as a key element in a comprehensive 
Titan exploration strategy with very high science value. The most recent 2008 joint NASA/ESA 
Titan Saturn System Mission (TSSM) study provided a compelling concept for implementation of a 
montgolfiere at Titan. While orbiter and lander elements appear to have significant flight heritage, a 
balloon has not yet been flown at Titan and will require a focused study. For planetary protection 
purposes, we also recognize here the need for a pre-launch bioburden reduction. 

Based upon the high priority of Titan science, results from many years of mission studies, and 
current state of technology readiness, the co-authors recommend the following be pursued: 

Conduct focused studies of Titan balloon mission options , leveraging from previous work, 
to concentrate on selection of architecture(s) that best enable the achievement of highest priority 
decadal science (the sweet spot) . 

Initiate substantial sustained investment in risk reduction efforts needed to mature the Titan 
balloon concept for flight readiness. 

Early and sustained investment at reasonable levels would result in the demonstration of 
technical readiness acceptable for launch of a Titan balloon mission in the coming 10—15 years. 

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