This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

Robert Dean Abelson, Ph.D,

James H. Shirley, Ph.D.

NASA Jet Propulsion Laboratory

Robert Dean Abelson, Ph.D,

James H. Shirley, Ph.D.

NASA Jet Propulsion Laboratory

Small RPS-Enabled Europa Lander Mission

Space Technologies and Applications International Forum

(STAIF 2005)

13 February 2005

Albuquerque, NM

Small RPS-Enabled Europa Lander Mission

Space Technologies and Applications International Forum

(STAIF 2005)

13 February 2005

Albuquerque, NM

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

This is a conceptual mission study intended to demonstrate the

range of possible missions and applications that could be enabled

were a new generation of Small Radioisotope Power Systems to be

developed by NASA and DOE. While such systems are currently
being considered by NASA and DOE, they do not currently exist.

This study is one of several small RPS-enabled mission concepts

that were studied and presented in the NASA/JPL document

“Enabling Exploration with Small Radioisotope Power Systems”

available at:

http://solarsystem.nasa.gov/multimedia/download-detail.cfm?DL_ID=82

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

ELM Team Members and Acknowledgements

Science

•

Ellis Miner

•

Jim Shirley

•

Tom Spilker

RPS Systems

•

Bob Carpenter

•

Bill Nesmith

Mission Design

•

Erik Nilsen

Batteries

•

Rao Surampudi

Radiation Environment

•

Insoo Jun

JIMO Information

•

John Elliott

Europa Pathfinder (EPF) Team

•

Jacklyn R. Green

•

Wayne Zimmerman

•

Eric Archer

•

Alok Chatterjee

•

Savio Chau

•

Mona Delitsky

•

Wai Chi Fang

•

Jeff Hall

•

Ron Hall

•

Don Hunter

•

Lonne Lane

•

Bill Nesmith

•

Jagdish Patel/Elizabeth Kolawa

•

Adam Steltzner

•

Brian Sullivan

•

Leslie Tamppari

•

Ben Thoma

•

Marcus Traylor

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

Why Europa?

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

Europa is the single

highest-priority target

for future flagship-class

missions to the

outer solar system.

Solar System Exploration

Decadal Survey

(National Research Council)

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

Why Land on

Europa?

Because

life

may

exist within Europa’s

icy crust or in a

subsurface ocean.

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

Requirements for sustaining life as we know it:

An energy source

: Geothermal, geochemical, and gravitational

heating caused by other Jovian moons

Biologically significant

chemicals

(E.g., C, H, O, N, P, K,..)

Water

Europa satisfies these requirements

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

Potential Scientific Objectives for ELM

– To search for signatures of

biological activity

– To assess the

chemical and physical habitability

– To measure Europa's seismicity ("icequakes") to help

understand the interior structure and crustal dynamics

– To provide

"ground truth"

for remote measurements of surface

composition, radiation levels, and temperatures.

– To obtain

close-up images

of Europa surface features and

geology.

Source: From discussions at the JIMO Forum, Lunar and Planetary Institute, 2003

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

Proposed Mission Objectives for ELM

– To land on Europa to

take in-situ measurements

for a

minimum of

30 Earth days

(8.5 Europa days) that

meet the

science objectives

– Measurements include

surface imagery, spectroscopy,

seismometry, radiation

and

temperature trending

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

Europa Orbital and Physical Parameters

– Orbital Period about Jupiter: 3.55 Earth days

(85.2 Earth hours)

– Eclipse Period: 1.78 Earth days

(42.6 Earth hours)

– Semi Major Axis: 671,000 km
– Orbital Eccentricity: 0.0101
– Orbital Velocity: 13.74 km/sec
– Orbital Inclination: 0.464 deg. To Jupiter’s equator

– Diameter (Mean): 3,121 km
– Mass: 4.8E22 kg (0.8035% of Earth mass)

– Gravitational Acceleration at Surface: 1.315 m/s

(13.4% of Earth)

– Escape Velocity: 2.026 km/s (at surface)

– Sun Insolation at Surface relative to Earth: 3.7%

– Daytime Temperature of Surface: 124K
– Nighttime Temperature of Surface: 85K

– Average Temperature of Surface (Avg over one day): 103K
– Radiation Environment on Surface: ~14 kRad per Earth Day

•

Assumes 100 mils of aluminum shielding

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

Mission Architecture Overview

– The Europa Lander Mission (ELM) is derived from the Europa Pathfinder

(EPF) study and

takes advantage of RPS technology

to enable a 30 day

surface mission (EPF baseline was battery-limited at 3.5 days).

– ELM is assumed to ride as payload on the proposed

Jupiter Icy Moons

Orbiter (JIMO)

and arrive at Europa per the nominal JIMO timeline.

– JIMO acts as the

communication

relay

between ELM and Earth.

– The ELM landing site would be

selected to

maximize science

returns

and

minimize landing risk

– The

landing site could be

updated in-flight

if JIMO identified

higher-priority landing areas
during Europa approach.

Conceptual Only

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

ELM Mounting to Mother Spacecraft

Europa Lander

(ELM)

Europa Lander

(ELM)

Mother Spacecraft

ELM to Mother S/C

Communication

System

ELM to Mother S/C

Communication

System

ELM to Mother S/C

Mounting Adapter

ELM to Mother S/C

Mounting Adapter

Mother S/C to Earth

Communication

System

Mother S/C to Earth

Communication

System

Conceptual Only

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

Mission Architecture Overview (Continued)

– The baseline JIMO science orbit around Europa is assumed to be

100 km (circular) at 45 degrees inclination for 30 days.

– Once in orbit, ELM would separate from the JIMO bus and spin-stabilize

in preparation for two separate entry burns.

The burns are used to

perform a “stop and drop” maneuver

– The first entry burn (22 m/s) changes the lander orbit from 100km

elevation to

100 km x 1.5 km (elliptical)

using a Star 5 engine.

– The second entry burn (1458 m/s) is performed at periapse (1.5km

elevation) using a Star 17 engine.

This stops all forward motion,

causing the lander to “fall” into Europa

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

Burn#2: 1458 m/s Delta-V

Burn#1: 22 m/s Delta-V

Spin vector

After release from JIMO,
solid motors spin up the
Lander/EDL system.

Impact velocity: 63 m/s
Drop Time: 48 sec

Orbit altitude at periapse
burn ~1.5 km

Orbit altitude at
apoapse burn ~100 km

Conceptual Only

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

Mission Architecture Overview (Continued)

– Aeroshells and parachutes are ineffective

on Europa due to its

negligible atmosphere. Must use other methods for landing.

– A low periapse orbit (1.5km) is selected to reduce the impact velocity to

63 m/s

while maintaining enough elevation margin to handle insertion-

errors (i.e., Isp, rocket burn times, angle errors, etc.)

– Airbags

are used to reduce impact accelerations to

<600g

– After landing, the

pressurized air bags are separated and bounce away

from the lander

. This allows the lander to drop to the surface and

make

direct contact with Europa

– The surface mission starts following lander contact with the surface.

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

Conceptual Only

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

ELM External Configuration

Omni Antenna

Instrument port

Radiator Panels

Ortho View

Top View

Side View

Conceptual Only

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

Technology Applicability Trade Studies

– A trade study was conducted for

three different power systems

for ELM

(2 conventional and 1 RPS).

The conclusions are summarized below.

Option 1: Solar Power

Option 2: Primary Batteries

Option 3: RPS

Not F

easib

Not F

easib

Enab

ling

Enab

ling

Not F

easib

Not F

easib

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

Option #1 – Solar Power

Trade Study

Facts:

– Europa is ~5 AU distant from the sun;

receives 3.7% of the Earth insolation

– At high latitudes (~45 degrees), the solar flux received by a lander with fixed solar

arrays

peaks at 34 W/m2

. (Does not consider blockage of sun by Jupiter)

– Europa’s rotational period has

42.6 hours (1.775 days) of shadow per Europa Day

– Natural radiation over JIMO’s

13 year mission

significantly

degrades solar cells

– Lander needs to

operate right-

side up or upside-down

– Europa is cold

–nighttime

surface temp ~ 85K.

– Significant thermal power is

required to

maintain operating

temperatures

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

Option #1 - Solar Power Trade Study (Cont’d)

Results:

– Required

Solar Array (SA) size is drastically larger

(order of

magnitude) than the size of the entire lander.

• Would need extensible/deployable arrays that add additional

mass and complexity.

–

Mass of SA and battery is significantly heavier

than an

equivalent RPS system (is heavier than entire lander).

– Need

additional power source

to operate lander and keep it

warm

during 13 year cruise phase

Size

d M

ass

Pro

hib

itive

Size

d M

ass

Pro

hib

itive

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

Option #2 - Batteries Trade Study

Results:

–

Heater power

required to keep the

large batteries at

operating temperature

(>-40C) in the

frigid Europan

environment

(as low as -188C)

is prohibitive.

–

Mass and volume of battery is significantly larger

than an

equivalent RPS system.

–

Need additional power source

to operate lander and keep it

warm

during 13 year cruise phase

(i.e., for health, status

and comm. checks).

Pro

hibi

tive

Pro

hibi

tive

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

Option #3 - RPS Analysis (Continued)

Results:

–

RPS has the lightest mass

of all three options.

–

RPS is drastically smaller than the solar+battery option

, and

measurably smaller than the battery-only option.

–

The RPS option produces extra heat that can be used to keep
electronics, batteries and critical systems warm

during the entire 13

year cruise and 30 day surface missions.

–

The RPS is a self-contained system

, requiring no external recharging

or alternate power connectivity with the JIMO spacecraft during cruise.

RPS is an Enabling Power Technology for the

ELM Mission

RPS is an Enabling Power Technology for the

ELM Mission

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

RPS Characteristics and Assumptions

–

One GPHS module

using a

5% efficient thermoelectric (TE) converter

assumed to provide 250 Wt (thermal) /12.5 We (electric) at BOM.

•

Conversion efficiency numbers are conservative. May be able to achieve >7.5% efficiency with
segmented PbTe-TAGS/BiTe thermoelectrics (more with CPA designs) per DOE/OSC analyses.

•

Small RPS configuration based on work of DOE/OSC/Analytix

– Assume

Pu283 decay

decreases thermal power output by

0.8%/year

– Assume

TE decay

decreases electrical power by another

0.8%/year

– The

End-of-Mission

power output after

13 years

calculated at

225 Wt / 10.1 We

– Medium temperature TEs (e.g., PbTe/TAGS) are

assumed in baseline design for conservatism.

•

Cold shoe temp. ~155

– The RPS is assumed capable of surviving high

acceleration loads

(max of 600 g)

associated with

the ELM landing system.

– The RPS is packaging is a

short cylinder

with the

TEs arranged radially

(i.e., TE cold shoes / heat

rejection is via the sides).

Conceptual Only

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

RPS Installation and Orientation within ELM

GPHS Module (Grey)

Thermoelectric
Converters (Red)

Thermal Insulation /
RPS Canister (Green)

Conceptual Only

Note: Radiator panels, antennas and internal subsystems (other than RPS) not shown.

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

Mission Design and Constraints*

– Mission Dates

•

Earliest Availability:

Assumed 2015 via JIMO

; Earlier using Delta/Atlas (requires Europa Orbiter).

– Delivery Vehicle

•

Planned delivery vehicle: JIMO Spacecraft (

1500 kg total science payload capability)

– Lifetime

•

Transit duration:

TBD – Assumed 13 years total

for power system sizing.

–

9 years to Jupiter system, 4 more years to Europa

•

Active measurement duration:

30 days on Europa surface

•

Total: ~

13 years

(Assumed for power system sizing)

– Delta-V Requirements (Independent of Delivery Vehicle)

•

Delta-V:

1480 m/s

for ELM Stop and Drop maneuver.

– Constraints

•

JIMO would stay in orbit around Europa for 30 days and

provide the communications link between the

Lander and Earth.

•

Orbital Parameters:

JIMO is in a circular 100 km altitude orbit

during the 30 day lander mission.

•

Operational Constraints:

JIMO would need to be oriented

such that the JIMO-to-Lander comm. system

can

point towards the lander

during each comm. period to receive the omni-directional signal.

* JIMO information has not been finalized by the JIMO program office – Indicated values are study assumptions only.

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

ELM Communications Architecture

Conceptual Only

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

ELM Communication Architecture

– The

frequency and duration

of communication periods from ELM to

JIMO

drives the communications architecture

– The

frequency and duration

of communication events is

highly

dependent upon the latitude

of the ELM landing site.

Lander latitude

17 Comm. Cycles (Total mission)

5 Comm. Periods / Cycle (83 total)
710 min. of Comm. (Total)
~43 min. of Comm. / Cycle (Avg)
43 hours of eclipse / Cycle

Lander latitude

17 Comm. Cycles (Total mission)

5 Comm. Periods / Cycle (83 total)

710 min. of Comm. (Total)
~43 min. of Comm. / Cycle (Avg)

43 hours of eclipse / Cycle

Lander latitude

8 Cycles (Total mission)

14 Comm. periods / Cycle (111 Total)
1050 min. of Comm. (Total)
130 min. of Comm / Cycle (Avg)
84 hours of Eclipse / Cycle

Lander latitude

8 Cycles (Total mission)

14 Comm. periods / Cycle (111 Total)
1050 min. of Comm. (Total)
130 min. of Comm / Cycle (Avg)

84 hours of Eclipse / Cycle

– The ELM bandwidth requirement is driven by the short communication

duration (42.7 min/cycle) of the 0

latitude case.

– The ELM data storage requirement is driven by the long eclipse period

(84 hours/cycle) of the 45

latitude case.

– The ELM

bandwidth requirement

is driven by the short communication

duration (42.7 min/cycle) of the

latitude case

– The ELM

data storage requirement

is driven by the long eclipse period

(84 hours/cycle) of the

latitude case

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

LOS Periods at 45 deg Latitude

(14 Comm. Periods per Cycle)

LOS Periods at 0 deg Latitude

(5 Comm. Periods per Cycle)

5 degree Minimum LOS for Communications Event

Europa Day #1

Europa Day #2

Elevation Line-of-Site (LOS) Angle from Lander to JIMO Over

Two Europa Days (~7 Earth days)

LOS Angle (Degrees)

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

Baseline Instrumentation Suite

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

Instruments

Data Rate

(kbits / msmt)

# of

Instruments

#Measuremts

per Europa

Day

Measuremt

Frequency

(# / Earth Hr)

Accumulated Data

Volume per Europa

Day (kbits)

Accumulated

Data Volume per

Europa Day

(Mbits)

Imager

2600

219762

220

Microseismometer

304286

3600

912858

913

Raman Spectrometer

845

0.85

LIBS

423

0.42

Temperature Sensors

0.016

169

0.04

Radiation Sensors

0.016

304286

3600

19474

Engineering Data

0.100

5071

507

0.51

1154

3407

0.47

1.40

195%

1154

1385

Margin in Uplink Capability (Also Have 3dB margin)

Data Storage Reqt Based on Longest Eclipse (Mbits)

Total Accumulated Data Volume / Euro Day (Mbits)

Uplink Capability / Euro Day (Mbits)

Req'd Uplink Rate (Mbit/s)

Available Uplink Rate (Mbit/s)

Design Data Storage w/ 20% Margin (Mbits)

Data Requirements

•

Data uplink requirement is 1.4 Mbit/s – Draws 6 We Peak Power.

– Comm. design has uplink margin of ~200%

•

Data storage requirement is 1.4 Gb – Draws 3 We Peak Power.

•

Data uplink requirement is 1.4 Mbit/s –

Draws 6 We Peak Power.

– Comm. design has uplink margin of ~200%

•

Data storage requirement is 1.4 Gb –

Draws 3 We Peak Power.

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

Data Taking Schedule

Measurements Stop During All Comm. Events

Imager (8 ports)

(1 meas./hour)

Microseismometer

(Continuous)

Raman (8 ports)

(1 meas./hour)

LIBS (8 ports)

(1 meas./hour – days)

Temp. sensors

(1 meas./30 min)

Radiation sensors

(Continuous)

Engineering Data

(1 meas./min)

Day (~42.6 hrs)

Night (~42.6 hrs)

Day (~42.6 hrs)

Daytime #1

Nighttime #1

Daytime #2

Time

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

ELM Duty Cycles and Subsystem Power Levels

Qty

Power Draw

(W / unit)

Power Draw All

Units (W)

Duty Cycle

Avg Power Draw per

Europa Day (W)

Operating Time
per Europa Day

(Hrs)

Command Data and Handeling

System Flight Computer

2.60

0.30

0.78

85.20

Peripheral Subsystem Intf (PSI)

1.00

0.30

85.20

Power Distribution

DC/DC Converter Card

3.00

0.30

0.90

85.20

Power Distribution Slice

2.20

0.30

0.66

85.20

Science Instruments

Imager

0.20

1.00

0.20

0.23

Microseismometer

0.14

0.42

1.00

0.42

84.52

Raman Spectrometer

5.00

1.00

5.00

2.82

LIBS

5.00

1.00

5.00

2.82

Temperature Sensors

0.10

1.60

1.00

1.60

0.47

Radiation Sensors

0.10

0.40

1.00

0.40

84.52

Comm. Subsystem (JIMO Link)

Transceiver (2W RF Output, 33%
Efficient)

6.00

1.00

6.00

0.68

Data Storage

Data Storage (SSR)

3.00

0.30

0.90

85.20

System

ELM Operating Modes and Durations are selected to Maximize

Science Return while Meeting the Power Budget.

ELM Operating Modes and Durations are selected to Maximize

Science Return while Meeting the Power Budget.

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

Battery Requirements

ELM Operating Modes and Power Requirements

Maximum Power Draw: 17.8 W

Avg Power Draw: 4.5 W

RPS Power Output (EOM): 10.1 W

Req’d Battery Size: 63.1 W-Hr

Req’d Battery Mass: 0.53 kg

Maximum Power Draw:

17.8 W

Avg Power Draw:

4.5 W

RPS Power Output (EOM): 10.1 W

Req’d Battery Size:

63.1 W-Hr

Req’d Battery Mass: 0.53 kg

Additional Peak NRG Req'd (W-Hr)

12.49

Battery Depth of Discharge (%)

33%

Battery Charging Efficiency (%)

90%

Battery Energy Density (W-Hr/kg)

120

Battery Energy Volume (W-Hr/liter)

200

Min. Reqd Batt. (W-Hr)

42.05

Batt w/ 50% Margin (W-Hr)

63.08

Batt Mass (kg)

0.526

Batt Volume (Liters)

0.315

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

Power Levels for Each Operating Mode

Standby Mode

Basic Measmt Mode

Raman Mode

LIBS Mode

Comm. Mode

Operating Mode

Power Draw (W)

Average
Peak

Standby Mode

Basic Measmt Mode

Raman Mode

LIBS Mode

Comm. Mode

Operating Mode

Power Draw (W)

Average
Peak

GPHS Power Output 10.14W (EOM)

17.8 W

17.3 W

12.3 W

11.8 W

7.5 W

9.1 W

4.1 W

1.5 W

Average Power Usage 4.5 W (EOM)

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

ELM Mass Requirements

Lander Mass: 38.7kg

Total S/C Mass: 232.7kg

Lander Mass: 38.7kg

Total S/C Mass: 232.7kg

Item

Qty

CBE (kg)

Uncertainty

(kg)

Total CBE

(kg)

Lander Payload

38.7

Command Data and handling

1.84

System Flight Computer

0.50

0.08

0.58

Peripheral Subsystem Intf (PSI)

0.10

0.02

0.12

Bus

1.00

0.15

1.15

Power Distribution

1.64

Power Distribution Slice

0.49

0.05

0.54

DC/DC Converter Card

1.00

0.10

1.10

Power

11.16

GPHS RPS

5.00

10.00

Batteries

0.33

0.17

0.50

Packaging

0.63

0.03

0.66

Pyro and Valve Control

0.87

Battery Charge Control

0.30

0.03

0.33

Prop Drive

0.49

0.05

0.54

Science Instruments

9.30

Seismometer

0.05

0.01

0.18

Imagers

0.20

0.04

3.84

Raman Spectrometer

2.00

0.40

2.40

LIBS

2.00

0.40

2.40

Radiation Sensor

0.10

0.02

0.48

Temp sensors

0.01

0.00

0.17

Telecom - S-Band Subsystem

3.30

Transceiver

0.30

0.03

0.33

S-Band Antenna

0.25

0.03

1.65

Packaging

0.30

0.03

0.33

Coax Cables to antennas

0.15

0.02

0.99

G & C Sensors

0.21

Accelerometers

0.05

0.00

0.16

3 axis gyro

0.05

0.00

0.05

Thermal

1.26

Heater Elements

0.02

0.00

0.21

Insulation

1.00

0.05

1.05

Mechanical Systems

10.00

Structure

3.60

0.36

3.96

Covers

0.10

0.01

0.66

Misc (fasteners)

0.72

0.03

0.75

Cabling

0.60

0.03

0.63

Radiation Shielding

2.00

4.00

Net Lander

38.7

Item

Qty

CBE (kg)

Uncertainty

(kg)

Total CBE

(kg)

Propulsion

111.4

Upper Desent Stage

13.7

Support and Separation Mechanism

1.00

0.05

3.15

Support structure

2.54

0.25

2.79

ARC Solid KS40B Thrusters (spin-up)

0.38

0.02

0.80

ARC Solid PAC-3 Thrusters (spin-down)

0.16

0.01

0.34

Hydrazine trim system

1.80

0.09

1.89

Star 5 rocket motor

4.50

0.23

4.73

Lower Desent Stage

97.7

Support and Separation Mechanism

1.00

0.05

3.15

Support Structure

5.70

0.57

6.27

Star 17 Motor

84.10

4.21

88.31

Thermal

2.2

Thermal Blankets

1.00

0.05

1.05

Temp sensors

0.01

0.00

0.11

Misc

1.00

0.05

1.05

Mechanical Systems

13.9

JIMO Attachment System

5.00

3.00

8.00

Ballest

5.00

0.50

5.50

Fasteners

0.40

0.01

0.41

Landing System

61.0

NSI - Gas Generator

1.00

0.05

3.15

Airbags

16.06

3.21

57.82

JIMO-Based Comm.system

5.5

Antenna

3.00

1.00

4.00

Gimbal

1.00

0.50

1.50

Net Spacecraft (EPF)

232.7

38.7

111.4

2.2

13.9
61.0

5.5

232.7

Lander Mass (Total)

Thermal Mass (Total)
Mechanical Systems Mass (Total)

S/C subtotal

Landing System Mass (Total)
JIMO-Based Comm. System

Propulsion Mass (Total)

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

ELM Thermal Requirements

•

Assumptions

– GPHS Thermal Power: 250 We (BOM) /

225 We (EOM @ 13yrs)

– Thermoelectric Cold-Leg Temp.

155

•

Thermal Control is Accomplished via Multiple Approaches:

–

Conduction straps

and

thermal switches

keep critical electronics, batteries and

subsystems warm.

– Thermal radiation to space is performed through variable-emissivity

radiators

mounted on

both surfaces of the lander

• The

emissivity

can be actively varied between

~0.3 and 0.7

to maintain the

desired lander temperature profile (Beasley, Kislov, Biter STAIF 2004).

– Heat rejection to the Europan surface is made via

contact conduction

between

the surface and lander structure. Thermal switches control heat flow.

•

The RPS Waste Heat is Used to Keep Critical
Electronics and Subsystems Warm.

•

Variable emissivity radiators permit active thermal
control using minimal power and no moving parts.

•

The

RPS Waste Heat

is Used to Keep

Critical

Electronics and Subsystems Warm

•

Variable emissivity radiators

permit

active thermal

control

using minimal power and no moving parts.

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

Radiation Environment

–

Externally Generated Radiation

•

ELM receives an external dose of

~420 kRad during the 30 day surface mission

•

The total received

lifetime (13 year) dose is ~6 MRad

•

Potential

mitigation strategies

include housing ELM in a

JIMO-mounted radiation

shelter

, using

spot shielding

around critical components, and employing

rad-hard

electronics

with >1 MRad tolerance.

–

Shelter and shielding could potentially reduce lifetime ELM external dose to <1 MRad.

•

ELM will capitalize off the JIMO radiation studies and technology

currently being

studied, and will utilize similar or identical mitigation schemes.

–

Internally Generated Radiation

•

Internally-generated radiation is produced by the

GPHS module

•

Intensity of

radiation falls of quickly with distance

from the GPHS due to spatial and

structural attenuation through the RPS and ELM structure.

•

GPHS

-generated radiation is

significantly lower

than the

natural radiation

dose (Can

be made <100 kRad with proper design).

•

Judicious placement of electronic and lander structure can keep the

total GPHS-

emitted dose to levels tolerable with existing technology

* Calculations extrapolated from those provided by Insoo Jun (JPL) and assume 100 mil aluminum shielding.

Radiation can be mitigated using a JIMO-mounted radiation

shelter, spot shielding, and rad-hard parts.

Radiation can be mitigated using a JIMO-mounted radiation

shelter, spot shielding, and rad-hard parts.

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

Radiation Environment (Continued)*

*Radiation Data provided by Insoo Jun (JPL).

Total Radiation Dose vs. Distance from Center of GPHS

Module for 13 year Duration

0.00

0.10

0.20

0.30

Unshielded Distance from GPHS Module Center, (cm)

Total Radiation Dose, (MRad)

Total Z-Axis Radiation for 13
years (MRads)
Total Y-Axis Radiation for 13
years (MRads)

4-pi spherical total dose depth curves

Breakdown by mission segments

1.0E+02

1.0E+03

1.0E+04

1.0E+05

1.0E+06

1.0E+07

1.0E+08

100

1000

10000

aluminum spherical shell thickness, mils

rad

(Si)

TOTAL

301 days at Ganymede

120 days from Ganymede to Europa

113.5 days at Europa

Reactor dose

Earth Spiral-out from 1000km

4-pi spherical DDD depth curves based on GIRE model

Breakdown by mission segments

1.0E+05

1.0E+06

1.0E+07

1.0E+08

1.0E+09

1.0E+10

1.0E+11

1.0E+12

1.0E+13

1.0E+14

1.0E+15

100

1000

10000

aluminum spherical shell thickness, mils

1 M

utro

/cm

TOTAL

301 days at Ganymede

120 days from Ganymede to Europa

113.5 days at Europa

Reactor neutron

Earth spiral-out from 1000km

GPHS Module

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

Alternate Power System Concepts

– Current ELM design uses one GPHS/TE RPS and a small battery to

meet all power requirements.

•

Battery needed to supply peak power demands

during LIBS, Raman and Communication

events (

max. of 17.8 Watts

– Could

eliminate the need for a battery

using alternate power system

architecture, including:

• Use

Two GPHS RPSs

with baseline 5% TE Conversion Efficiency

– Capable of generating 20.2W (EOL) –

meets all power modes

– Requires larger, more massive spacecraft –

redesign necessary

– Heat rejection

becomes a significant issue.

• Use

Higher-Efficiency

Power Converters

– A

9% efficient

TE converter could generate

>17.8 W (EOM)

using one GPHS

module.

– A small

20% efficient Stirling

engine could generate >17.8 W (EOM) using just

two

GPHS Fuel Pellets

Stirling needs to be sufficiently vibration-free to prevent interference with
microseismometer measurements.

Not r

ecom

men

ded

Not r

ecom

men

ded

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

Summary and Conclusions

– The Europa Lander Mission (

ELM

) is designed to search for signatures

biological activity

and measure the

chemical and physical properties

of Europa.

– ELM would ride

“piggyback”

on the proposed

JIMO S/C

during the ~13

year cruise phase, and would land on Europa to perform its

30 day

science mission

– The ELM Mission is

enabled

by the

RPS

power system.

• A single

GPHS/TE RPS

powers ELM and provides

126% energy margin

• A small

63 W-Hr Li-Ion battery

is used to carry the

peak loads

• The

excess heat

is used to

warm critical electronics, batteries and

subsystems

in the frigid Europan environment.

– Higher-efficiency power converters

could further optimize the system:

• Could

eliminate

the need for the

Li-Ion battery.

• Could

reduce

the req’d amount of

Pu238 fuel

. (Use 2 pellets vs. current 4)

This information is pre-decisional and for discussion purposes only.

Europa Lander Mission

Additional RPS-Enabled Missions

– The

ELM configuration

can be used for missions on

Callisto and

Ganymede

with

minimal modification

• The ELM RPS configuration would be adequate for a

60 day Callisto

surface mission

, and a

120 day Ganymede mission

– Durations are based on a preliminary JIMO mission timeline.

– Additional small RPS-enabled Lander mission could include:

• Small landers for

outer solar system solid bodies

– Includes moons, Pluto, asteroids and comets.

•

Lunar human-precursor missions

– RPS enables operation through the

14 day eclipse

, at

poles

and in the

shadows

canyons and mountains

•

Mars Network

Scout Class

and

Human Precursor Landers

– RPS permits

continuous, long term missions

polar regions

and other

low-insolation areas

Document Outline