Microsoft Word - JPL Pub 08-1 Assess Alternatives Europa 080131

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Table of Contents

Executive

Summary

................................................................................................................ 1

Background

............................................................................................................................. 2

Summary of Historical Europa Mission Concept Studies ...................................................... 2

3.1

Europa Orbiter (1996) ..................................................................................................... 4

3.2

Europa Orbiter; Pluto S/C Option Study (1996) ............................................................. 4

3.3

Europa Sample Return (1996) ........................................................................................ 4

3.4

Europa Orbiter, All Solar (1997) .................................................................................... 4

3.5

Europa Orbiter, All Solar (1998 IOM) ........................................................................... 4

3.6

Europa Orbiter (2001) ..................................................................................................... 5

3.7

Europa Orbiter Alternative Missions Study (2001) ........................................................ 5

3.8

Europa Orbiter Competitive (2002) ................................................................................ 5

3.9

Jupiter Icy Moons Tour (JIMT) Studies (2002) .............................................................. 5

3.9.1 Reactor

Options

......................................................................................................

3.9.2 Non-Reactor

Option

................................................................................................

3.10  Jupiter Icy Moons Orbiter (JIMO) .................................................................................. 7
3.11  Europa Geophysical Explorer (2005) ............................................................................. 7
3.12  Europa Explorer (2006) .................................................................................................. 8
3.13  Enhanced Europa Geophysical Explorer (2006) ............................................................. 8
3.14  Europa Explorer Solar Array Feasibility Study (2006) .................................................. 8
3.15  Europa Explorer Flagship Study (2007) ......................................................................... 8
3.16  Solar-Powered Europa Orbiter Design Study (2007) ..................................................... 9
3.17  Europa Lander Studies .................................................................................................... 9
3.18  Science Goals and Objectives ......................................................................................... 9

Assessment of Alternative Europa Mission Architectures ................................................... 11

4.1

Moon Orbiter, Plus Lander or “Dumb” Impactor ......................................................... 13

4.2 Multiple

Moon-Orbiting Platforms ............................................................................... 14

4.3 Multiple

Flybys

............................................................................................................. 14

4.4 Single

Flyby

.................................................................................................................. 15

4.5 Stand-Alone

Lander

......................................................................................................

4.6 Sample

Return

............................................................................................................... 16

4.7

Most Appropriate Architecture ..................................................................................... 16

Conclusions

........................................................................................................................... 17

References

............................................................................................................................. 18

Glossary

................................................................................................................................ 20

Europa Quick-Look Statistics ............................................................................................... 21

Executive Summary

The purpose of this study was to assess the science merit, technical risk and qualitative
assessment of relative cost of alternative architectural implementations as applied to a first
dedicated mission to Europa. The objective was accomplished through an examination of
mission concepts resulting from previous and ongoing studies. Key architectural elements that
were considered include moon orbiters, flybys (single flybys like New Horizons and multiple
flybys similar to the ongoing Jupiter System Observer study), sample return and

in situ

landers

and penetrators.
Science merit was assessed relative to the 2007 Europa Explorer (EE) Science Definition Team
(SDT) science objectives, which focus on global characterization. An orbital remote observation
type of mission is a natural fit to global characterization rather than the single location of a
lander or limited coverage of a few, even many, flybys. The most recent 2007 EE Flagship study
concluded that a dedicated moon orbiter would be the lowest cost and risk architecture that
would fully achieve all of the science objectives identified by the SDT. This is consistent with
the conclusions of previous studies.
An examination of multiple and single flyby missions indicates poor science value when
compared to a dedicated moon orbiter. A single flyby mission would yield very little in terms of
Priority 1 science objectives. A spacecraft in orbit around Jupiter that makes multiple flybys past
Europa, similar to the recently defined Jupiter System Observer mission with more than 6 low-
altitude (100–200 km) flybys of Europa, would provide significant science for some of the key
objectives; however, it falls short of achieving most top-priority science objectives. Because
flyby missions would not be in orbit around Europa and thus spend much less time in the near
vicinity of Europa, even the most favorable implementation would accomplish less than 50% of
the Priority 1 science objectives.
While landers have the potential to return significant new science from Europa’s surface, the
science results would be limited to only a single site. As a result, a lander-only mission falls far
short of achieving Priority 1 science objectives. In addition, due to the uncertainties in today’s
limited understanding of Europa’s surface features, a first dedicated mission at Europa consisting
only of a single lander would be characterized as having high risk. Data from a predecessor
Europa orbiter would greatly reduce the risk for subsequent implementation of an

in situ

mission.

The combination of a dedicated moon orbiter and a lander would clearly provide more science
return than an orbiter alone, but it would require more resources (fiscal and possibly technical)
than are currently anticipated to be practical in the near future.
The study concludes that a dedicated moon orbiter would provide the greatest science value at
lowest risk and cost for a first dedicated mission to Europa. This conclusion is consistent with
the conclusions of previous studies.

Background

Over the last decade there have been a number of mission and system studies that have defined
science objectives, mission architectures and implementation approaches applicable to a
dedicated mission at Europa. Over that period of time, variations in the programmatic and
technical environments have significantly influenced the results. For example, the Europa
Orbiter (EO) study of 2001 had a severe pressure on cost and flight time. This resulted in a
~$1.2B mission with less than 30 kg of science instrumentation delivered by a direct Earth-to-
Jupiter trajectory into Europa orbit. This was followed in the 2002–2005 timeframe with a focus
on breakthrough capability for solar system exploration (i.e., nuclear electric propulsion and
power) and expanded goals for Jupiter system science (multiple destinations: Ganymede,
Callisto, Europa). This resulted in the Phase A conceptual design of a nuclear electric Jupiter Icy
Moons Orbiter (JIMO) mission that was estimated to cost greater than $10B. In the current era,
following the success of Cassini/Huygens, serious consideration is being given to preparing for
the next outer planet flagship mission in a fiscally constrained environment. Current Flagship
Mission studies have targeted a total mission cost in the $2–3B range. This assessment of
alternative architecture options was undertaken to ensure that the science value of a Europa
flagship mission would be maximized relative to the currently defined science objectives at an
acceptable level of risk.
The approach to assessing alternatives has been to review what has been learned to date from
past studies and evaluate those results in context of the currently evolved science objectives and
programmatic/technical constraints. The 2007 EE science objectives resulted from over a decade
of community input and debate. The resulting objectives focus on understanding the global
aspects of Europa.
The balance of this report provides an historical summary of previous studies as well as an
assessment of alternative Europa mission architectures. A summary of conclusions is provided at
the end of this document.

Summary of Historical Europa Mission Concept Studies

In the last decade (spanning from April 1996 to present) more than a dozen Europa Mission
concepts have been studied at JPL to varying degrees. They are listed in chronological order in
Table 1. Brief highlights and references from those studies are included. This section provides a
summary of the studies in this table.

Table 1: Historical Europa Mission Studies

Study Name

Power
Source

Key Features

Ref

Europa Orbiter
(1996)

RPS, Solar

Series of studies by Team X of simple, low-cost
Europa orbiter mission. Looked at solar and RTG
options

Europa Orbiter;
Pluto S/C Option
Study (1996)

RPS, Solar

Study to look at adopting new technologies being
used on then-current Pluto mission study. Included
RTG, AMTEC and solar options

Europa Sample
Return (1996)

Solar

Study for potential Discovery proposal to fly
Stardust-type capture and return of sample
blasted from Europa surface by small impactor.

Study Name

Power
Source

Key Features

Ref

Europa Orbiter, All
Solar (1997)

Solar

Delta-V Earth Gravity Assist trajectory, Titan IV
(SRMU)/Centaur, payload 42 kg

Europa Orbiter, All
Solar (1998 IOM)

Solar

Revisit of 1997 All Solar study. Venus-Earth-Earth
Gravity Assist (VEEGA) trajectory, STS/IUS,
payload 20 kg, mass margin

−

15 kg, solar array

235 kg

Europa Orbiter
(2001)

RPS

Direct trajectory, science payload 27 kg

Europa Orbiter
Alternative
Missions Study
(2001)

RPS

Various trajectories, many options

Europa Orbiter
Competitive (2002)

RPS

Look at low cost Europa orbiter mission for
potential New Frontiers proposal

Jupiter Icy Moons
Tour (2002)

Reactor

Flagship Mission, science payload 490 kg

Non-Fission Icy
Moons Tour (2002)

RPS

Two S/C mission to all Galilean satellites, science
payload 273 kg, plus two landers (Callisto and
Ganymede)

Jupiter Icy Moons
Orbiter (2005)

Reactor

Flagship Mission, science payload 1,500 kg

Europa
Geophysical
Explorer (2005)

RPS

VEEGA trajectory, science payload 153 kg plus
additional margin 853 kg (additional 853 kg
probably too optimistic, ~340 kg is a more likely
figure)

Europa Explorer
(2006)

RPS

VEEGA trajectory, science payload 180 kg plus
unallocated margin of 340 kg

Europa Explorer
Solar Array
Feasibility Study
(2006)

Solar

Attempt at an all-solar implementation of Europa
Explorer science mission; found to be not
practical.

Enhanced Europa
Geophysical
Explorer (2006)

RPS

Broad architectural assessment for single orbiter.
VEEGA trajectory, science payload 150 kg plus
additional margin 340 to 1200 kg (additional
margin due to advanced RPS, larger LV and later
launch dates)

2007 Europa
Explorer Flagship
Study

RPS NASA-funded

flagship study. Numerous

architectures considered with focus on single
orbiter. VEEGA trajectory, ~205 kg science
payload (includes contingency), mass margins 982
kg including 185 kg “unallocated” margin

2007 Solar Europa
Feasibility Study

Solar

Investigation of an all-solar implementation of
Europa Explorer science mission; focused on
achieving floor science objectives of 2007 EE
Study.

3.1

Europa Orbiter (1996)

This represents the first study performed by Team X to investigate a mission to Europa. The
initial study was performed in April of 1996 aimed at developing a very simple, single
instrument (radar) mission to orbit Europa. Options explored included solar power and use of
one half of a General Purpose Heat Source Radioisotope Thermoelectric Generator (GPHS RTG)
to meet low power requirements (less than 150W). A series of updates to the original study were
performed through May of 1996, ending up with design using one full GPHS RTG and
incorporating technologies assumed for a concurrent Pluto mission study. Further options were
investigated including benefits of Solar Electric Propulsion (SEP) (not found to be of significant
value).

3.2

Europa Orbiter; Pluto S/C Option Study (1996)

The purpose of this study was to further develop the Europa mission concept using the then-
current Pluto spacecraft hardware design, taking full advantage of the advanced technologies
being considered for that mission. Three design options were investigated: one using a single
GPHS RTG, one using the Alkalai Metal Thermoelectric Converter (AMTEC) RPS then in
development, and a solar option.

3.3

Europa Sample Return (1996)

This study evaluated a possible candidate for a Discovery-class mission that would use the
Stardust spacecraft architecture to capture and return a surface sample from Europa. The concept
would have delivered a projectile to the surface of Europa to eject a plume through which the
spacecraft would fly at ~ 50 km altitude, capturing plume particles in aerogel for return to Earth.
Mission duration was estimated to be ~10 years. The mission was envisioned to be solar
powered, using a “hibernation” mode to conserve power at large sun ranges.

3.4

Europa Orbiter, All Solar (1997)

This study was performed by Team X in 1997 to develop a point design for an all-solar mission
to Europa. The study looked at a launch in late 2004 on a Titan IV launch vehicle followed by a
4.6-year flight to Jupiter using an Earth gravity assist. Wet mass for this concept was 3530 kg,
leaving a margin of 1952 kg for launch on the Titan IV. Payload mass was 42 kg (including a
15-kg surface package). Solar arrays were estimated at 159 kg.

3.5

Europa Orbiter, All Solar (1998 IOM)

This IOM reassessed the feasibility of designing an all-solar mission to Europa. The work
revisited the previous study performed by Team X in June 1997 by reexamining some spacecraft
assumptions and by considering the possible use of a Shuttle with an Inertial Upper Stage. The
combination of these two assumptions with the Team X study conclusions resulted in some
increased performance as compared to the Team X conclusion but not nearly enough to change
the ultimate conclusion that a Titan IVB launch vehicle would be required to attempt the mission
without using an RPS for a power source. Launch date for this reanalysis was October 2005.
Launch mass was decreased to 2925 kg and payload allocation was reduced to 20 kg. Solar array
mass was sized to accommodate 135 W of extra heater power to avoid the need for Radioisotope
Heater Units (RHUs). Even with the reduced capability and lower flight system wet mass, the
study was not able to achieve a positive margin for launch on the Shuttle.

Figure 1. 2001 Europa Orbiter Flight System.

3.6

Europa Orbiter (2001)

This was the first rigorously developed point
design for a Europa mission. The development
effort spanned several years and resulted in a
Radioisotope Power System (RPS)-based flight
system design (Figure 1) constrained to a direct
Earth-Jupiter trajectory. The science mission
duration of 30 days in Europa orbit was determined
by the SDT to be the minimum time required to
meet the science objectives. This concept
accommodated a modest science payload of 27 kg.
Wet mass of this design was~1790 kg and power
was to have been provided by two GPHS RTGs.
Driving science requirements included the category
1A objectives defined by the SDT:

•

Determine the presence or absence of a subsurface ocean

•

Characterize the 3D distribution of any subsurface liquid water and its overlying ice layers

•

Understand the formation of surface features, including sites of recent or current activity, and

identify candidate sites for future lander missions

The work performed in this study provided insights into the issues associated with
implementation of Europa missions, including a full assessment of the radiation environment and
technologies for accommodating operations in that environment.

3.7

Europa Orbiter Alternative Missions Study (2001)

This report assessed alternative approaches to the EO mission in an effort to investigate lower
cost options. Primary trades investigated included; an assessment of trajectory options including
both direct and indirect trajectories, flight system trades between the EO baseline and minimum
mass implementations, and endgame science mission options at Europa including an assessment
of orbiters and flyby missions. Mission architectures were developed that addressed subsets of
the full EO science objectives based on temporal or spatial observations. Alternative
architectures resulted in some cost savings, but at the expense of full science.

3.8

Europa Orbiter Competitive (2002)

This study investigated the possibility of developing a simple, low-cost (less than $1B) mission
to Europa that could potentially be developed as a New Frontiers proposal. The mission was
envisioned to use a single GPHS RTG for power and had a limited payload of six instruments: a
radar and a five-element Europa Integrated Science package totaling ~17 kg. Mission length was
30 days in orbit.

3.9

Jupiter Icy Moons Tour (JIMT) Studies (2002)

Three mission concepts were studied by independent teams: A reactor-powered mission
employing a single launch vehicle to deliver the flight system to space, a second reactor-powered
option employing multiple launches to low-Earth orbit (LEO) and using on-orbit assembly

techniques to construct the final flight system, and a third non-reactor–powered option consisting
of one or more flight systems to meet the same science objectives. All mission studies were
completed as directed.

3.9.1

Reactor Options

The reactor options fall into a unique category. They would utilize nuclear fission power systems
and advanced ion propulsion to enable exploration of multiple targets in a single mission. These
studies also offered greatly enhanced science payload mass and power. The single launch option
of the JIMT study had a science payload allocation of 490 kg and a total flight system launch
mass of 21,000 kg. It would have been delivered to LEO by a single Delta-IVH launch vehicle,
from which point it would have activated its nuclear electric propulsion (NEP) system to spiral

out to its Jupiter trajectory. The on-orbit
assembly option was similar to the single
launch option, but would have launched the
fuel tank and science module first on a heavy
Evolved Expendable Launch Vehicle (EELV),
to be followed by a shuttle launch of the
power and propulsion module which would
have been mated to the previously launched
elements in LEO. Large solar arrays were to
be used to provide solar-electric propulsion
for the initial spiral-out from LEO. Total
launch mass of this option would be about
23,000 kg with a payload allocation of 500 kg.

3.9.2

Non-Reactor Option

The non-reactor JIMT team was asked to create a mission concept that (a) would achieve, as a
minimum, the Europa Orbiter Level 1 science objectives at Europa, Ganymede and Callisto,
(b) could be implemented for launch by the end of the decade, (c) would cost not more than
$4.5B, and (d) could be implemented without use of fission power. A large number of possible
mission architectures was quickly reduced to five options for further study:
1.

Jupiter orbital flotilla consisting of three identical spacecraft in orbit around Jupiter with

multiple flybys of the three ice moons.

Icy moon flotilla consisting of a dedicated
orbiter to each of the three icy moons.

Single large cruiser that would sequentially
orbit each of the three icy moons for several
weeks before moving on to the next.

Dual identical cruisers that would sequentially
orbit each of two of the moons.

SEP/Radioisotope Electric Propulsion (REP)
mother ship that would deliver a dedicated
orbiter to each of the icy moons.

The fourth option was chosen for development in
the study. Dual, identical twin spacecraft (Fig. 3)

Figure 2. JIMT Single Launch Option.

Figure 3. Non-Fission Option Orbital

Configuration.

would be deployed to the Jovian system to provide full redundancy for Europa. Cruiser 1 would
be deployed to Callisto first, for 12 weeks of detailed mapping and deployment of a small lander.
It would then be flown into orbit around Europa for Europa science and end of mission. Cruiser 2
would be deployed to Ganymede into a 10-week mapping orbit, then into orbit around Io for its
end of mission. Redundancy for Europa would be provided by phasing Cruiser 2 flight time to
allow diversion to Europa in event of problems with Cruiser 1.
The flight system design took advantage of existing and a few high-value new technologies to
lower mission risk and cost. A 100-kW SEP system (beginning of life power) with NASA
Evolutionary Xenon Thrusters and Square Rigger Photovoltaic solar arrays was baselined. The
Science Mission Module would use radiation-hard avionics and three 250-W advanced RPSs. A
sixteen-instrument, 273-kg payload was accommodated on each spacecraft. One 132-kg lander
was also carried on each spacecraft for delivery to Callisto and Ganymede. Landers each carried
six instruments.

3.10

Jupiter Icy Moons Orbiter (JIMO)

The JIMO project mission and flight system designs evolved directly from the single launch
option of the JIMT study. Requirements expanded over the course of this study and both the
flight system and payload allocation grew. The payload allocation for JIMO (Fig. 4) was
1,500 kg and the total launch mass was more than 36,000 kg. While the capabilities of the JIMO
flight system would have
revolutionized the approach to outer
planets science missions, the estimated
cost of developing the project was
deemed too large; the programmatic
priorities changed at Headquarters,
and, after successfully completing
Phase A, further effort was
indefinitely deferred. For this reason
the Jupiter Icy Moons studies will not
be included in further assessments
contained in this report.

3.11

Europa Geophysical
Explorer (2005)

The Europa Geophysical Explorer
(EGE) study, funded by NASA’s Planetary Program Support task and the NASA RPS Mission
Systems Engineering Office, returned to the concepts of inner solar system gravity assists and
conventional chemical propulsion for a mission to Europa, using radioisotope power in the form
of the newly developed RPSs. This study made use of a Venus-Earth-Earth Gravity Assist
(VEEGA) trajectory to increase delivered mass over previous studies, resulting in a launch mass
capability of ~7230 kg using a Delta IVH launch vehicle. A payload allocation of 150 kg was
baselined. The payload was sufficient to meet all newly defined science objectives in a Europa
orbital mission phase of 30 days.

Electric Propulsion
Thruster Pods

High Gain Antenna

High Power
Electronics
Radiator

Bus Radiator

Heat Rejection
Subystem radiator
panels

Shunt Radiator panels

Reactor

Brayton Power
Conversion

Main Boom
Assembly

Xenon Tank Structure

Bus Compartment

Radiation
Shield

Boom Hinge (3)

Spacecraft Docking Adapter

Stowed Spaceship

Figure 4. JIMO Configuration.

3.12

Europa Explorer (2006)

The EE study, which was internally funded by JPL, involved a detailed analysis of a Europa
orbital mission. It took advantage of recent technology developments and additional knowledge
gained from past studies to develop a highly capable mission aimed at meeting current science
objectives for Europa. This study developed a flight system (Fig. 5) with a wet mass of 6988 kg.
Science payload allocation was ~180 kg, with an additional 340 kg “unallocated mass”
potentially available for a lander or other science payload. The orbital phase of the mission was
extended to 90 days in collaboration with the
science team. The improvements over past study
results were made achievable by significant
advances in radiation-hardened component
technologies, now-proven larger launch
capabilities and well-established gravity assist
trajectory options, and better characterized
radiation environment around Europa. The
concept relies on traditional chemical
propulsion system (similar to Cassini and
Galileo), Multi-Mission Radioisotope
Thermoelectric Generators (MMRTGs - as are
to be employed by Mars Science Laboratory)
and a real-time continuous data downlink.

3.13

Enhanced Europa Geophysical Explorer (2006)

The Enhanced Europa Geophysical Explorer (EEGE) study was performed in 2006 to update the
original EGE concept and assess the mass impacts associated with using different existing and
advanced radioisotope power systems. Also studied were the mass implications associated with
choosing different launch dates, interplanetary trajectories, and launch vehicles. The output was
a detailed trade space analysis that could be used to assess the enabling and potentially cost-
saving capabilities of using advanced RPS systems for a Europa mission. As expected, mass and
power gains were realized when using the most advanced RPSs and most capable launch
vehicles. EEGE was funded by NASA’s RPS office.

3.14

Europa Explorer Solar Array Feasibility Study (2006)

This study, which was internally funded by JPL, evaluated the potential for replicating the EE
2006 science mission using solar power instead of RPSs. The study looked at the issues involved
with the use of solar arrays in the Europa environment, considering radiation degradation and
low solar intensity. The very large size of the arrays needed to accommodate Europa eclipses and
the large gimbals and reaction wheels needed for this implementation led to the conclusion that
this approach was not practical within the EE mission orbital constraints.

3.15

Europa Explorer Flagship Study (2007)

The NASA-commissioned 2007 EE Flagship Study has recently been completed. For this study
NASA appointed an SDT to develop science objectives in light of the advances in understanding
made by the JIMO SDT and refined by subsequent studies and science advisory groups. A
further development of the mission and flight system developed in the EE 2006 study, it

Figure 5. EE Orbital Configuration.

accommodated 205 kg of science payload (maintaining 185 kg of unallocated margin) while
refining the design (lower telecom power and sequencing of instruments) to allow reduction in
the number of MMRTGs from eight to six. This study looked at a baseline implementation,
achieving all of the objectives of the Europa SDT, and a floor mission that would achieve many
of the SDT objectives at a lower total mission cost. Results were thoroughly reviewed by NASA-
appointed independent science and technical, management and cost panels.

3.16

Solar-Powered Europa Orbiter Design Study (2007)

In parallel with the 2007 EE Study, a
solar-powered Europa Orbiter Design
Study, which was internally funded by
JPL, was carried out to take another
look at the possibility of using solar
arrays to provide power to a Europa
mission (Fig. 6). This fairly high-level
study directly addressed the issues
raised by the 2006 EE solar study by
changing the science orbit at Europa
to one with continuous illumination,
thus greatly reducing the excess solar
array area needed to accommodate
frequent eclipses and enabling a
configuration with fixed solar arrays. A single-session Team X study was performed to evaluate
the feasibility of such a mission that could accommodate the floor science objectives as defined
by the 2007 EE SDT. Preliminary results indicate that such a mission might be viable and
warrants further study.

3.17

Europa Lander Studies

In addition to the orbital missions studied over the last decade a number of studies have been
carried out to investigate designs for Europa landers. These studies have looked at a wide range
of capabilities ranging from simple penetrators to very capable landers with cryobots and
submarine vehicles capable of exploring the Europan ocean. A summary of the design
parameters for some of these past studies is presented in Table 2.
None of the Europa mission studies ended up baselining a lander vehicle as part of their mission
architecture. Each mission study concluded that the accommodation of a Europa landed package
of some form would provide significant science above that required to meet the science
objectives. The reluctance to baseline such a package has come from a combination of the
estimated cost and risk impact that such an auxiliary element would have on the overall mission.

3.18

Science Goals and Objectives

The mission and spacecraft conceptual designs for exploration of Europa have significantly
progressed over the years in detail and maturity. In parallel, the Europa science goals and
objectives have evolved into a more comprehensive set of Priority 1 Objectives. Over the last
decade several key advisory groups have considered and recommended sets of science objectives

Figure 6. Solar Powered Europa Concept.

Table 2. Past Europa Lander Studies (ref. 18).

Study title

Wet

Dry

Propellant

Landing

Power

Europa Lander (Baseline,
1997)

886 kg

338 kg

549 kg

Soft

AMTEC RPS

Europa Lander (Microtech,
1997)

828 kg

279 kg

549 kg

Soft

AMTEC RPS

Europa Path

nder (2001)

221 kg

Solid Propulsion

Airbag

Battery + RHU

Europa Lander (1999)

487 kg

228 kg

259 kg

Soft

AMTEC RPS

Europa Lander + Cyobot+
Submarine (1998)

1502 kg

646 kg

856 kg

Soft

AMTEC RPS

Scout Lander (2000)

3451 kg

1502.1 kg

2340.2 kg

Multi

AMTEC ARPS

Europa Impactor (2000)

7kg

N/A N/A

Impactor

Battery

Cadmus (Ga Tech, 2004)

558 kg

248 kg

310 kg

Soft

MMRTG

EGReSS (Ga Tech, 2004)

1575 kg

440 kg

1135 kg

Soft

MMRTG

JuIcy (Ga Tech, 2004)

1211 kg

511 kg

700 kg

Soft

Undefined RTG

Europa Surface Science
Package (2004)

379 kg

44 kg

143 kg

Soft

Modified RTG

Jupiter Icy Moons Lander
(2006)

390 kg

362 kg

22 kg

Soft

Battery

for the exploration of Europa (Table 3). The lineage of Europa science objectives traces back to
the EO SDT, whose “Group 1” (highest priority) and “Group 2” (second priority) objectives
were subsequently endorsed by the NASA Campaign Science Working Group on Prebiotic
Chemistry in the Solar System, and then by the National Research Council’s Solar System
Exploration Survey (“Planetary Science Decadal Survey”). The Decadal Survey explicitly stated
that a flagship-class mission should address both the Europa Orbiter Group 1 and Group 2
objectives, in addition to Jupiter system science during its Jupiter orbiting phase.
Subsequent to the recommendations of the Decadal Survey, the JIMO SDT expanded the scope
of Europa objectives and included additional objectives relevant to the whole Jupiter system.
Following NASA’s indefinite postponement of the ambitious JIMO mission, the Outer Planets
Assessment Group honed the objectives for Europa exploration. These objectives were iterated
by the Europa Focus Group of the NASA Astrobiology Institute, and then codified by OPAG
[2006] in its Scientific Goals and Pathways document. This codification was subsequently
reflected in the 2006 Solar System Exploration Roadmap for NASA’s Science Mission
Directorate. The EE 2007 SDT reviewed and updated the 2006 objectives and relative priorities
for use in their study. It is these Europa objectives that form the basis of the latest EE mission
studies.

Table 3. Heritage of Europa Science Objectives.

Committee

Report Title

Ref.

Europa Orbiter Science Definition
Team

Europa Orbiter Mission and Project Description

Committee on Planetary and Lunar
Exploration (COMPLEX)

A Science Strategy for the Exploration of Europa

NASA Campaign Science Working
Group on Prebiotic Chemistry in the
Solar System

Europa and Titan: Preliminary Recommendations
of the Campaign Science Working Group on
Prebiotic Chemistry in the Outer Solar System

Solar System Exploration
(“Planetary Science Decadal”)
Survey

New Frontiers in the Solar System: An Integrated
Exploration Strategy

Jupiter Icy Moons Orbiter (JIMO)
Science Definition Team

Report of the NASA Science Definition Team for
the Jupiter Icy Moons Orbiter (JIMO)

Europa Focus Group of the NASA
Astrobiology Institute

Europa Science Objectives

Outer Planets Assessment Group
(OPAG)

Scientific Goals and Pathways for Exploration of
the Outer Solar System

NASA Solar System Exploration
Strategic Roadmap Committee

2006 Solar System Exploration Roadmap for
NASA’s Science Mission Directorate

Europa Explorer 2007 Science
Definition Team

2007 Europa Explorer Mission Study: Final Report

Assessment of Alternative Europa Mission Architectures

In the course of studying concepts for missions to Europa a number of candidate architectures
have been considered, as shown in Figure 7. These include both single-element and multiple-
element types. Single-element missions might consist of an orbiter around Europa, a Jupiter
orbiter that makes multiple close passes by Europa during its mission, or a single flyby
spacecraft, as in the Voyager and New Horizons missions. Architectures involving a single
capable lander-only mission delivered by a simple cruise stage and communicating directly to
Earth have not been studied yet in detail, for reasons given later in this section. Multiple-element
missions might add a lander to an orbiter or flyby spacecraft, with the lander design ranging from
a fully instrumented soft lander, to a more limited hard lander, to a simple impactor; multiple
orbiting platforms might also be possible, maybe even sample return missions, but they have not
been studied in detail, again for reasons given later in this section. One platform type, an aerial
vehicle (e.g., a balloon), is rejected after only cursory consideration. The Europan atmosphere is
so tenuous it is difficult even to

detect

with all but the most sensitive of instruments. Its mass

density is orders of magnitude too small to cause detectable aerodynamic drag on orbiting
spacecraft or impactors, let alone support any kind of aerial vehicle, so it need not be considered.

Europa Miss

Moon Orbiter

with or without

in-situ element

Jupiter Orbiter

Single Flyby

In-situ Only

Europa orbiter + Lander

Europa orbiter only

Jupiter orbiter multiple Europa flybys

Single Europa Flyby

Europa Lander

Architectural Options

Option Selection Rationale

Relative to 2007 EE SDT Science Objectives

Provides enhanced science return, however likely high cost and risk

Meets all science objectives, and has been the focus of majority of studies

Cannot meet most of key Europa science objectives

Unlikely to yield sufficient new information in any Priority 1 science cat.

Cannot provide global characterization, high cost and risk

Europa orbiter + dumb impactor

Investigation indicates the impactor may decrease overall science value

Preferred Mission Architecture

Sample Return

Landed Sample Return

Cannot provide global characterization, high cost and risk

Impactor with Sample Return

Cannot meet most key science objectives. High risk

Figure 7. Architecture Options.

Note: risk refers to Cost, Schedule and Mission Success

Previous studies have examined all these applicable options, with varying science objectives and
in greatly varying levels of detail. Reviewing the implications of these architectures in light of
current Europa science objectives, as summarized in Table 4 [16], and considering technological
readiness, cost and risk, the choice of optimal mission architecture quickly narrows to a
dedicated Europa orbiter mission. The EE mission concept, such a dedicated orbiter mission,
fully addresses all of the science objectives defined by the 2007 EE SDT and has been the focus
of most of the recent studies for Europa exploration. The remainder of this section addresses the
characteristics of the multiple-element architectures, and then the alternative single-element
architectures, that make them less attractive than the single-orbiter-only option for a first
dedicated mission to Europa. Further assessment would need to be done to address the impact of
planetary protection requirements on mission cost, design, mass, and schedule for landers and
sample return missions, as this study does not address planetary protection considerations.

Table 4. Architectures considered and rated against the Priority 1 Europa

Science Objectives.

(after Pappalardo et al., 2007)

Ocean

Ice

Chemistry

Geology

E. External

Environment

Europa Explorer

Europa Explorer +
Simple Lander

Europa Multiple
Fly-bys

Capable Lander (No
Orbiter)

4.1

Moon Orbiter, Plus Lander or “Dumb” Impactor

The addition of a simple instrumented lander to a Europa orbiter mission would provide even
greater science return, exceeding the EE SDT’s science objectives in all but one category [16]
(see Table 4, row 2). Such a mission architecture would enable global remote sensing with
ground truth for at least one site on the surface, and science measurements not possible from an
orbiter. Given the likelihood of significant Europan tidal flexing, levels of seismic activity
should be of sufficient magnitude that

in situ

measurements would provide unique geophysical

insight into the subsurface and interior. Although costs have not been accurately modeled for any
landed systems, the EE study determined that the cost for an orbiter with even a simple soft
lander would likely exceed the expected resources available [16]. Moreover, the inferred low

NOTES:

• Multiple fly-bys means a dedicated Europa fly-by

mission.

• Orbiter + lander implies a simple lander, carrying a

seismometer, imager, composition experiment.

• Capable Lander is stand-alone (no orbiter), modeled

after the Europa Astrobiology Lander.

Exceeds science objectives.

Fully addresses all science objectives.

Addresses most science objectives.

Addresses some science objectives.

May address partial science objectives.

Touches on science objectives.

Does not address science objectives.

technology readiness of a simple hard lander, especially one landing on a surface whose
topography is not well characterized, suggests a high risk to schedule and cost.
Multiple design teams have concluded that the only practical means of reducing the risk of safe
landing on Europa, in a time frame consistent with implementation of the lander, is high-
resolution imaging characterization of the surface, especially potential landing sites, from a
precursor orbiter mission. Imaging of the candidate landing sites from an orbiter that delivers the
lander is not useful, since the new information is not available for the design of the lander, and
there is no guarantee that an orbiter with a lander designed for specific surface characteristics
will find any scientifically interesting area, or any area at all, with those characteristics. It is an
appropriate role for an orbiter mission to provide the information that enables subsequent lander
missions with acceptable levels of risk.
A simple “dumb” impactor added to a Europa orbiter or flyby mission could allow remote
measurement of elemental composition from the impact flash, and would excavate material from
the shallow subsurface that might not have been radiolytically processed, for remote analysis
later. However, a preliminary assessment by the EE team of the impact energies for reasonable
masses and velocities suggest that the crater formed would be too small to yield significant
compositional measurements, and might be too small to locate [16]. Instruments optimized for
the Europa Priority 1 science objectives are different from the specialized instrumentation
needed to observe an impact flash and plume, implying additional cost and/or the loss of other
science.

4.2

Multiple Moon-Orbiting Platforms

Multiple orbiting platforms, in the form of an orbiting subsatellite deployed from a primary
orbiting spacecraft, have several avenues for augmenting the science from a single orbiter, but
would have significant impact on the resources available for the primary orbiter. At Europa, as
elsewhere, simultaneous measurements from multiple spacecraft improve magnetospheric
investigations. But according to the EE SDT, the greatest science gain would stem from
formation-flying gravity measurements [16] as done by the GRACE mission at Earth [27]. Such
investigations would primarily target the high-degree and -order (short spatial scale) gravity field
components. But the measurable tidal signal of an internal Europan ocean is low-order
(degree 2), and the most likely sources of non-isostatically–compensated gravity field anomalies
are sufficiently deep, below the icy shell and ocean, that the higher-order signal levels would be
quite feeble at orbital altitudes. Thus, the science gain from such a subsatellite would be limited.
But the impact on resources for the primary orbiter would be substantial: the subsatellite would
have to duplicate many of the subsystems of the primary orbiter, such as power, attitude
determination and control, communications, command and control, etc., in addition to the
subsatellite’s payload. Resources devoted to the subsatellite, especially mass and cost, would
subtract from those available to the primary orbiter and its payload. The EE SDT determined that
a subsatellite’s science did not justify the added cost and complexity [16].

4.3

Multiple Flybys

A Jupiter orbiter with multiple close flybys of Europa could provide significant science return to
address some of the key science objectives for Europa. However, important measurements
related to the ocean and other objectives cannot be achieved except from orbit. A flyby mission
cannot provide 1) gravity and altimetry data of the requisite accuracy measured at appropriate

phases of the tidal cycle, addressing the ocean objective; 2) significant areal coverage by an ice-
penetrating radar for the ice shell objective; 3) global and targeted spectral imaging coverage at
high resolution for the chemistry and geology objectives; and 4) sufficient temporal and spatial
coverage for the external environment objective [16]. The Jupiter System Observer (JSO)
flagship mission concept, studied by another team in parallel with the 2007 EE study, would do
Europa science in the multiple-flyby fashion, with a many-flyby tour of the Galilean satellites
that would include 6 or more Europa flybys. The 2007 EE SDT reviewed the JSO approach’s
performance in achieving its Europa science objectives and concluded that JSO would do a
“poor” job, addressing less than 50% of the high-priority objectives.
Some have wondered if a Juno-like spacecraft and mission could perform Europa flyby science.
But the JSO mission would provide far better science than would a Juno-like mission. To provide
the best science possible by keeping encounter velocities low, the JSO mission concept’s orbit
would be fairly narrowly constrained to Jupiter’s equatorial plane, with only small excursions to
adjust flyby geometries. Of the many JSO flybys, the best for science occur in low-eccentricity
orbits with low flyby V-infinities. The Juno mission’s highly eccentric polar orbit [28] will be
much less amenable to satellite science. It is such an orbit that will keep Juno’s radiation dose
relatively low for the first 20 (or so) orbits, despite a perijove within about 1.1 Jovian radii. Near
perijove, that orbit will thread an axially aligned, roughly cylindrical “clear zone” between the
planet and the inside edge of the main radiation belts, then recross the equatorial plane well
outside the roughly toroidal (“doughnut-shaped”) radiation belts. Jupiter’s oblateness, notably
the large J

component of its gravity field, will cause the eccentric polar orbit’s line of apsides to

rotate with each perijove pass, such that eventually the “long sides” of the ellipse will pass
briefly near each of the Galilean satellites. But the flyby V-infinities for such an approach to
Europa will be far greater than would be for JSO, more than 20 km/s compared to JSO’s less
than 10 km/s. Attempting to decrease the flyby velocities by rotating the Juno orbit into the
equatorial plane would thwart the “threading” approach and result in radiation fluxes even
greater than JSO would receive during its orbit insertion maneuver, just inside Io’s orbit. The
Juno spacecraft is not designed to survive this increased radiation level. For multiple reasons, the
Juno approach is not suitable for a Europa mission.

4.4

Single Flyby

The single-flyby option was dismissed from further consideration because it is unlikely to yield
significant new information in

any

of the highest-priority Europa science objective categories.

This conclusion is consistent with a similar conclusion by the “Billion Dollar Box” study [29] of
potential missions to Saturnian icy satellites Titan and Enceladus. The general conclusion that it
is difficult to justify a single-flyby mission at a satellite already visited multiple times by a well-
instrumented spacecraft orbiting the satellite’s primary would not be a surprise. In the case of
Europa, multiple Galileo flybys “raise the bar” for significant science there.

4.5

Stand-Alone Lander

A large stand-alone lander carrying a full suite of instruments for surface science could provide
significant new results for Europa, especially if it were long-lived (more than 5 eurosols or 18
days). While the science return from a capable surface lander could be high, a lander would
characterize only one location on Europa, which would not necessarily be representative of the
satellite as a whole. At the current stage of Europa exploration, science priorities focus on global

characterization, which would not be provided by a lander at a single location. Thus, a capable
lander without a supporting orbiter does not address the Europa Explorer SDT’s science
objectives well. Moreover, the technology readiness of such a lander is quite low, and the surface
topography of Europa is unknown at scales of concern to landers, posing significant problems for
a safe landing. A capable lander is anticipated to have a high risk and cost.

4.6

Sample Return

Planetary scientists have emphasized for decades the benefits of bringing samples of extra-
terrestrial materials to Earth, where the full power and flexibility of huge ground-based
laboratories can be brought to bear on the analyses of the samples. The role of the Apollo
samples in unraveling the origin of Earth’s moon is a prime example. But despite the potential
paradigm-altering science return, sample return missions to outer solar system destinations must
contend with three significant hurdles: long mission durations for a round-trip to a distant
location; risk that the required samples might not be collected or delivered to a useful location
such as a curation facility on Earth; and high cost. Note that these are common challenges, and a
specific mission could also face other challenges.
The proposed Europa Ice Clipper [30] mission is a sample return mission concept based on an
interesting variation on the single flyby spacecraft. In this architecture a flyby spacecraft would
release an impactor on approach to Europa. The impactor would create a crater and plume of
debris through which the spacecraft would fly, collecting debris samples as it passes through.
The samples would then be returned to Earth. While such a mission has the potential for
returning unique results, it has problems with both science value and technical risk: it can
address only a limited number of Europa science objectives at a single impact site, and is
generally considered high risk for a number of reasons, including a low probability of obtaining
an acceptable sample coupled with extremely demanding navigation requirements. The closer to
Europa’s surface the sample collecting spacecraft flies in an effort to increase the (small) chance
of acquiring a usable sample, the tighter are the navigation requirements to prevent a catastrophic
impact of the spacecraft on Europa’s surface.
A more “conventional” landed sample return mission, one that places a soft-lander on the surface
to collect and document samples, suffers greatly from the mission duration and cost problems.
Compared to the Ice Clipper architecture, the landed sample return mission involves much more
delta-V and thus more mass, time, and cost, and a much more complex flight system that is far
more costly. A previous study by Woodcock [31], and preliminary results of a current study by
some of this study’s authors [32], of the utility of the proposed Ares launch vehicles for solar
system exploration indicate that launching a landed outer solar system sample return mission
appears to be a job for an Ares V launch vehicle, with an anticipated unit cost over $1B. It is
clear that this type of sample return mission would far exceed the fiscal resources expected to be
available for a flagship mission in the relatively near future.

4.7

Most Appropriate Architecture

A single Europa orbiter with no lander, impactor, or subsatellite is the architecture of choice for a
first dedicated mission to Europa, since it fully addresses the science objectives at the lowest risk
and cost, and since it provides the information needed to enable a future Europa lander with
acceptable risk.

Conclusions

The objective of this study,

to assess the science merit, technical risk and qualitative assessment

of relative cost of alternative architectural implementations as applied to a first dedicated
mission to Europa,

was accomplished by 1) reviewing results from previous and current studies

and 2) examining alternative architectural options relative to the science objectives defined by
the 2007 EE SDT. This report summarizes a number of Europa mission and system concepts
studied over the last decade as well as the results from assessing alternative architectural options
in light of current science requirements. Based on this work, the study arrived at the following
conclusions:
1.

A dedicated orbiter mission to Europa provides the greatest science value (as measured by
the 2007 EE SDT science objectives) at lowest risk. This conclusion is consistent with the
conclusions of previous studies.

Varying programmatic constraints and evolving prioritization of science objectives affected
the details of studies over the last decade but not the high-level conclusions.

References

[1]

“Europa Orbiter”, Team X Final Report, July 12, 1996. (JPL internal document)

[2]

“Europa Orbiter, Pluto Spacecraft Option”, Team X Final Report, July 12, 1996. (JPL
internal document)

[3]

“Europa Sample Return”, Team X Final Report, June 25, 1996. (JPL internal document)

[4]

"Europa Orbiter, All Solar," Advanced Projects Design Team (Team X), Final Report, 2
June 1997. (JPL internal document)

[5]

Europa All-Solar Revisit, JPL IOM 311.1/98-5, May 29, 1998NS. (JPL internal
document)

[6]

Europa Orbiter Overview 7-9-01 (ppt). (JPL internal document)

[7]

Europa Orbiter Alternative Missions Study, JPL Advanced Mission Studies
Office, 8-15-01. (JPL internal document)

[8]

“Europa Orbiter Competitive”, Team X Final Report, October, 2002. (JPL
internal document)

[9]

Jovian Icy Moons Tour Mission Studies, Final Report, February 28, 2003. (JPL
internal document)

[10] Nuclear Systems Initiative (NSI) Jovian Icy Moon Tour Mission Study Non-

Fission Dual Cruisers to the Jovian Moons Flight System, January 27, 2003.

[11] Prometheus Project Final Report, Doc No. 982-R120461, October 1, 2005. (JPL

internal document)

[12] (a) Europa Geophysical Explorer Mission Concept Study, JPL internal document

D-32355, September 30, 2005 (b)Europa Explorer Design Team Report, JPL
internal document D-34109, April 27, 2006.

[13] Europa Explorer Study Report, JPL internal document D-34054, March 10, 2006.

[14] Europa Explorer Solar Array Feasibility Report, August 30, 2006. (JPL internal

document)

[15] Enhanced Europa Geophysical Explorer Study (EEGE) utilizing Advanced

Radioisotope Power System, October 2006. (JPL internal document)

[16] 2007 Europa Explorer Mission Study: Final Report, JPL internal document

D-41283, 1 November, 2007. Cleared for external release.

[17] Solar-Powered Europa Orbiter Design Study (2007), JPL internal document

D-40344, September 28, 2007. Cleared for external release as JPL Pub 08-2,
January 2008.

[18] Europa Surface Science Package Feasibility Assessment, JPL internal document

D-30050, September, 2004.

[19] NASA AO: 99-OSS-04, Europa Orbiter Mission and Project Description, 1999.

[20] COMPLEX,

Committee

on Planetary and Lunar Exploration (1999), National

Research Council,

A Science Strategy for the Exploration of Europa

, National

Academy Press, Washington, DC.

[21] Chyba, C. F., W. B. McKinnon, A. Coustenis, R. E. Johnson, R. L. Kovach, K.

Khurana, R. Lorenz, T. B. McCord, G. D. McDonald, R. T. Pappalardo, M. Race,
and R. Thomson (1999), Europa and Titan: Preliminary recommendations of the
Campaign Science Working Group on Prebiotic Chemistry in the Outer Solar
System.

Lunar Planet. Sci. Conf

XXX

, abstract #1537, Lunar and Planetary

Institute, Houston (CD-ROM), 1999.

[22] SSES, Solar System Exploration Survey (2003), Space Studies Board, National

Research Council, New Frontiers in the Solar System: An Integrated Exploration
Strategy, National Academy Press, Washington, D.C.

[23] JIMO SDT, Report of the NASA Science Definition Team for the Jupiter Icy

Moons Orbiter (JIMO) (2004), NASA, Washington, D.C., 2004.
<

http://www.lpi.usra.edu/opag/resources.html

[24] Pappalardo, R. (2006), Europa Science Objectives, NAI Europa Focus Group

(Report to OPAG),
<

http://www.lpi.usra.edu/opag/may_06_meeting/agenda.html

[25] OPAG, Outer Planets Assessment Group (2006), Scientific Goals and Pathways

for Exploration of the Outer Solar System, <

http://www.lpi.usra.edu/opag

[26] SSER, Solar System Exploration Roadmap (2006), NASA Science Mission

Directorate.
<http://solarsystem.nasa.gov/multimedia/downloads/SSE_RoadMap_2006_Repor
t_FC-A_med.pdf>

[27] NASA, “Gravity Recovery and Climate Experiment”, Science@NASA website,

<http://science.hq.nasa.gov/missions/satellite_19.htm>

[28] Matousek, Steve, “The Juno New Frontiers Mission”,

Acta Astronautica

Volume 61, Issue 10, November 2007, Pages 932–939.

[29] Reh, K. R. et al., Titan and Enceladus $1B Mission Feasibility Study, Prepared

for NASA’s Planetary Sciences Division, Performed at JPL, Final Report JPL
D-37401B posted on the OPAG website:
<http://www.lpi.usra.edu/opag/announcements.html> as “$1B Box Studies”,
January 30 (2007).

[30] “Europa Ice Clipper Summary”, excerpt from 1997 Discovery Proposal, posted on

the Astrobiology Web site:
<http://www.astrobiology.com/europa/clipper/index.html>

[31] Woodcock, G., Ares Report, Prepared for David B. Smith (Boeing Company),

PowerPoint presentation, December 13 (2007).

[32] “Ares V: Application to Solar System Scientific Exploration”, JPL D-41883,

December 12, 2007. Cleared for external release as JPL Pub 08-3.

Glossary

AMTEC

Alkali Metal Thermal to Electric Converter

ARPS

Advanced

Radioisotope

Power

Systems

BOL

Beginning

Life

COMPLEX

Committee on Planetary and Lunar Exploration

Delta IVH

Delta IV Heavy

Delta-V Delta

Velocity

EDL

Entry, Descent and Landing

Europa

Explorer

EEGE

Enhanced Europa Geophysical Explorer

EGE

Europa

Geophysical

Explorer

EIS

Europa Integrated Science package

Europa

Orbiter

GPHS

General Purpose Heat Source

GRACE

Gravity Recovery and Climate Experiment

IUS

Inertial

Upper

Stage

JIMO

Jupiter

Icy

Moons

Orbiter

JIMT

Jupiter

Icy

Moons

Tour

JSO

Jupiter

System

Observer

LEO

Low

Earth

Orbit

Launch

Vehicle

MMRTG Multi-Mission

Radioisotope Thermoelectric Generator

NEP

Nuclear

Electric

Propulsion

NASA Evolutionary Xenon Thruster

NSI

Nuclear

Systems

Initiative

OPAG

Outer Planets Assessment Group

REP

Radioisotope

Electric

Propulsion

RHU

Radioisotope

Heater

Unit

RPS

Radioisotope

Power

System

RTG

Radioisotope

Thermoelectric

Generator

S/C

Spacecraft

SDT

Science

Definition

Team

SEP

Solar

Electric

Propulsion

SMM

Science

Mission

Module

SRMU

Solid Rocket Motor Upgrade

STS

Space Transportation System (Space Shuttle)

Team X

JPL’s Advanced Projects Design Team (concurrent engineering)

VEEGA

Venus Earth Earth Gravity Assist

Europa Quick-Look Statistics

Discovery

Jan 7, 1610 by Galileo Galilei

Diameter (km)

3,138

Mass (kg)

4.8e22 kg

Mass (Earth = 1)

0.0083021

Surface Gravity (Earth = 1)

0.135

Mean Distance from Jupiter (km)

670,900

Mean Distance From Jupiter (Rj)

9.5

Mean Distance from Sun (AU)

5.203

Orbital period (days)

3.551181

Rotational period (days)

3.551181

Density (gm/cm³)

3.01

Orbit Eccentricity

0.009

Orbit Inclination (degrees)

0.470

Orbit Speed (km/s):

13.74

Escape velocity (km/s)

2.02

Visual Albedo

0.64

Surface Composition

Water Ice

http://www2.jpl.nasa.gov/galileo/europa/