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Plasma in the solar system: science and missions

Stas BarabashSwedish Institute of Space Physics (IRF)

Kiruna, Sweden

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Swedish Institute of Space Physics

• Established 1957• A governmental research institute under the

auspice of Ministry of Education. Annual budget ~ 9 M€

• Basic research in the area of space physics, space technology/instrumentation, atmospheric physics, and long-term observations (geophysical observatory)

• Division of Space engineering of Luleå Technical University and EU Erasmus Mundus SpaceMaster program

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PI missions since 1978

Experiment Mission Launch, Org/Country TargetPROMICS-1 Prognoz-7 1978, USSR Earth's magnetospherePROMICS-2 Prognoz-8 1980, USSR Earth's magnetosphereV3 Viking 1986, Sweden Earth's magnetosphereASPERA Phobos-1/2 1988, USSR Mars / PhobosTICS/MATE Freja 1992, Sweden Earth's magnetospherePROMICS-3 Interball-1/2 1995/96, Russia Earth's magnetospherePIPPI/EMIL/MIO Astrid-1 1995, Sweden Earth's magnetosphereASPERA-C Mars-96 1996, Russia MarsIMI Nozomi 1998, Japan MarsMEDUSA, PIA Astrid-2 1999, Sweden Earth's magnetosphereMEDUSA, DINA Munin 2000, Sweden Earth's magnetosphereASPERA-3 Mars Express 2003, ESA MarsNUADU (Co-PI) Double Star 2004, China Earth's magnetosphereICA Rosetta 2004, ESA Comet Churyumov-GerasimenkoASPERA-4 Venus Express 2005, ESA VenusSARA Chandrayaan-1 2007, ISRO MoonPRIMA PRISMA 2010, Sweden Technol.YPP Yinghuo 2011, China MarsDIM Phobos-Grunt 2011, Russia MarsMINA Mars 2013 2013, China MarsLINA Luna-Globe 2014, Russia Moon (lander)MIPA BC MPO 2014, ESA MercuryENA BC MMO 2014, ESA Mercury

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Swedish missions

Magnetospheric physics: Viking, Freja, Astrid-1/2, Munin

Technology demonstrator: PRISMA

Atmospheric physics / Astronomy: Odin

Viking, 1986

Freja, 1992

Astrid-1, 1995

Munin, 2000

Astrid-2, 1999

PRISMA, 2008

Odin 2001

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QuickTime™ and aSorenson Video decompressorare needed to see this picture.

Solar wind

• Solar wind is a plasma flow blowing away from the Sun.

• The complicated wave - particle interaction near the photoshere (“Sun surface”), which is not well - understood, results in the heating of the solar corona plasma from 6·103 K to 106 K.

• The thermal expansion of the solar corona in the presence of the gravitation field converts the thermal energy to the direction flow (“gravitational nozzle”).

• Solar wind is a supersound flow of plasma (95% p+, 5-particles) with a velocity of 450 km/s and density about 70 cm-3 (Mercury) to 3 cm-3 at Mars

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What defines the type of the solar wind interaction

• Charge particles of the solar wind can be only affected by a magnetic field at an obstacle

• The magnetic field may originates from:• Intrinsic field of an obstacle • Currents induced in a conductive obstacle as a result of the

interaction• The obstacle’s magnetic field:

• Intrinsic dipoles (Earth, Mercury, Jupiter, Uranus, Neptune)• Local crust magnetizations (Moon, Mars)

• Conductivity of the obstacle (Mars, Venus)• Conductivity of rocks low• The presence of the conductive material (ionosphere, an ionized

part of the atmosphere) increases conductivity ( ~ne , for magnetized plasmas ec)

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Types of the solar wind interactions

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Earth magnetosphere

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Corotating Jovian magnetosphere

Interaction with the Moon

Induced magnetospheres of

Mars and Venus

Terrestrial magnetosphere

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Field of the solar wind interactions. Why is it important?

• The fundamental scientific questions to address:• Space plasma physics: What is the structure and characteristics of the

near-planet environment? What physics governs the interaction? • Planetology: What is the impact of the interaction (environment) on the

central body?• Non-thermal atmospheric escape (non-magnetized planets)• Auroral phenomena and influence on thermospheres• Surface space weathering (airless bodies)

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Magnetic field measurements. Why are they important?

• Magnetic field measurements are essential to organize and understand energetic charged particle and plasma measurements.

• Magnetic field measurements also represent one of the very few remote sensing tools that provide information about the deep interior.• Magnetic field of Earth, Jupiter, Saturn are generated by currents circulating in their

liquid metallic cores.• Uranus’ and Neptune’s magnetic fields are generated closer to the surface by electrical

currents flowing in high-conductivity crustal ‘‘oceans.’’• Mercury is currently magnetized by the remains of an ancient dynamo• Subsurface oceans on Europa, Ganymede, Callisto were first sensed by a

magnetometer

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Instrumentation to study near-planet space. Particles

• Particle distribution functions: amount of particles of a certain kind from a certain direction at a certain energy in each measurement point

• Types of instruments• Ion and electron spectrometers• Ion mass analyzers• Energetic neutrals imagers• Energetic particle telescopes• Radiation monitors

• Energy ranges• meV - 10s eV: thermal plasma• 10s eV - 10s keV: hot plasma• 10s keV - Mev: energetic particles• MeV - 100s MeV: radiation flux

Mars-96 / ASPERA

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f = f (M, φ, θ, E, x, y, z)

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Instrumentation to study near-planet space. Field and waves

• Thermal plasma density and temperature• Langmuir probes• Density 0.1 - 100 cm-3

• T ~ 0.1 - 10 eV

• Magnetic and electric field vectors and magnitude. Frequency spectra

• Typical instruments• Magnetometers• Electric field experiments• Correlators with particle fluxes

• Typical magnitudes• B-field: 0.01 nT - few 10 000 nT• E-field: 0.01 - 10 mV / m

Ørsted satellite (1999)

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Basic platform requirements

• Particle measurements (energetic particles)• Unobscured omnidirectional (4) field of view• Avoidance of thruster plumes and firing• Spacecraft potential control

• Thermal plasma measurements (plasma density/temperature)• Minimizing effect of the spacecraft on thermal plasma: booms/sticks

• Fields and plasma wave measurements• Minimizing effect of the spacecraft

• Magnetic cleanliness• Booms

• Electro-Magnetic Compatibility (EMC) programs. Some what more stringent than usual (not discussed here)

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Unobscured omnidirectional field of view

• The main and the most challenging requirement

• Can be fully (4) fulfilled only on spinning platforms

• Possible solutions for 3-axis stabilized platforms • 2 hemispheric identical sensors:

mass increase!• Fan-type field of view (180° over

polar angle) on mechanical scanners and attenuators: attitude disturbances

• Spun sections on 3-axis stabilized platforms: enormously expensive

Lewis et al., 2009

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Galileo despun platform

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Mechanical scanners (1)

• Typical moving mass 4 kg, L ~ 0.1 m, ~ 1 rpm • Typical spacecraft mass 0.5 - 1 tons, L ~ 1 m, ~ 10-4 rpm

Spin axis

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Mechanical scanners (2)

0.02°

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Spin-stabilized platforms (spinners)

• Mission examples• JAXA Mercury Magnetospheric Orbiter• ESA Cluster (Earth magnetosphere)• Swedish Freja (Earth magnetosphere)

• Typical spin rates 10 - 20 rpm• Only limited imaging experiments can be

carried out• High intensity emissions / large fields

of view• Auroral / EUV imaging• Scanning photometers

MMO

Cluster

Freja

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Thruster plumes and firing

• Operating even attitude thrusters (1 - 10 N) increase gas pressure around spacecraft.

• It may result in discharge in instruments ion optics using high voltage of few kV

• Hydrazine / Nitrogen thetroxide may contaminate open particle detectors

• Usually weak requirement • Can be fulfilled by proper

accommodation and thruster shields (conflict with blocking of field-of-view)

Rosetta / Schläppi et al., 2010

Attitude maneuver

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Spacecraft potential

• Due to release of photoelectrons (discharging) and accommodation of electrons and ions from the ambient plasmas (charging), spacecraft surfaces get charged and are under a potential relative to the ambient plasma

• Typical values between -10..-20 to +30…+50 V• In energetic plasma on night side the potential may reach -500…-1000 V• The spacecraft potential affects the particle measurement at the

respective energies: energy cut-off at ~q Vsc

• Differential charging over the spacecraft affects particle trajectories

• The surfaces (MLI) surrounding instruments must be conductive.• Spacecraft potential control systems (electron emitters) may be required. • If not possible, the spacecraft potential should be measured.

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Thermal plasma measurements (1)

• Langmuir probes: small spheres (5-10 cm diam.) biased at different voltages. The measurable is the current to the sphere (volt-amp characteristics)

• From voltage - current curve one deduces:• Plasma density and temperature• Spacecraft potential (voltage when the current = 0)

• Spacecraft potential affects the surrounding plasma and the influence should be minimized

Rosetta simulations / Sjögren, 2009

32 m

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Thermal plasma measurements (2)

• Rigid (quasi-rigid) booms / sticks are required• The length depends on the spacecraft size and plasma parameters (the

denser plasma, the shorter boom)• The longer, the better. Minimum 1 m

Cassini Langmuir probe

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Magnetic field measurements

• It is practically impossible to reduce the stray spacecraft magnetic field from a platform to the smallest required levels.• Solar arrays, motors, actuators, power

systems, magnetic materials, etc • The magnetic cleanliness programs on the

early planetary missions were enormously expensive (will never repeat again).

• Pioneer 10 / 11 (launched 1973) achieved 0.01 nT at the 3 m distance (practical limit)

• Long booms are required: B ~ 1/r3 • Double magnetometer techniques: shorter

booms with two magnetometers to obtain the spacecraft stray field (extra mass)

Voyager-1 (1977)

14 m

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Electric field measurements

• A space voltmeter: the potential difference between two terminals (probes) is measured.

• The electrostatic spacecraft potential (1 - 10 V) and V ~ Vsc Dsc/r

• To measure fields of Emin ~ 0.01 mV/m

• Booms of 30m are required!

V = V1 - V2 (measured), E = V / L

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L ~ DscVsc

Emin

~ 30m

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General boom designs (1)

• Rigid tubular booms max. 3 segments mostly for magnetometers

• Scissor booms on MAGSAT (1979)• Optical mirrors are mounted on the

magnetometer sensor platform to ‘‘transfer’’ its orientation to the main body of the spacecraft using infrared beams.

• Truss-like “astromast” designs (Polar / WIND)

6 m

6 m

MAGSAT

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General boom designs (2)

• Wire booms deployed by centrifugal force for E-field experiments and Langmuir probes

Langmuir probe E-field wire booms

Magnetometer and star camera

Swedish Astrid-2

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A typical plasma science spacecraft

ESA-JAXA BepiColombo / Mercury Magnetospheric Orbiter

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Plasma instruments vs. remote sensing

• Main conclusion: Requirements (and thus platform design drivers) are different and in general not compatible.

• Trade-off may not be always possible

Requirement Space plasma measurements Remote sensinginstruments

Unobscured hemispheric FoV Critical. Challenging to fulfill Not requiredSpin-stabilized platforms /scanners

Critical. Challenging to fulfill Not compatible

Thruster avoidance Moderate. Easy to fulfill Critical. Easy to fulfillSpacecraft potential Minor Not requiredMinimizing spacecraftinfluence (booms)

Critical. Challenging to fulfill May not be compatible

Magnetic cleanliness Critical. Challenging/expensive to fulfill Not requiredEMC program Critical. Relatively easy to fulfill Moderate. Easy to fulfill

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Very few dedicated space plasma missions (planetary)

• Mars: Nozomi (ISAS, Japan, 1998)• Mars: MAVEN (NASA, 2013)

• Not a spinner!• Mercury: BepiColombo MMO Mercury

Magnetospheic orbiter (JAXA, 2014)• Piggy-backing on ESA BepiColombo

Mercury Planetary Orbiter

Nozomi

MAVEN

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Possible “main stream” solutions

• Piggy-backing on “planetary-proper” missions• Small scale national / bilateral dedicated missions

• Proposals from the Swedish Institute of Space Physics • 3 missions to Mars

• MOPS, a microsat on Phobos-Grunt (discussions with NPO Lavochkin)

• Mjolnir, a microsat on the ESA Cosmic vision MEMOS (proposal)• Solaris, a microsat on a NASA discovery mission (proposal)

• 2 missions to the Moon• Lunar Explorer, a Swedish microsat (proposal)• A mission within the Chinese space program (under discussion)

• A microsat on Venus Express (mission idea)

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Moon space plasma mission (1)

• A small space plasma mission to the Moon: Swedish Space Corporation feasibility study of 1996

• Payload: Particle instruments, magnetic and electric field measurements including waves

• Study conclusion: a small space plasma mission at the Moon is doable and can be conducted on the moderate (national) level.

• Estimated cast: ca. 23 M€ (229 MSEK) in 1996

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Moon space plasma mission (2)

Basic mission characteristics from the feasibility study• Launch: Kosmos-3M/Tsiklon• TTI (Translunar Trajectory Injection)

• From an eccentric LEO• V = 1300 - 2200 m/s (depending on

launcher)• Lunar Orbit Insertion (LOI)

• Direct insertion from TTI• V = 1200-1600 m/s depending on the

final orbit• Propulsion system for TTI/LOI (2 alternatives)

• Solid (STAR 24A) /Mono-propellant• Bi-propellant/ Bi-propellant

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Moon space plasma mission (3)

Basic mission characteristics from the feasibility study• A spinning platform with spin axis pointing

to the Sun• 166 kg total mass at the Moon inc. 36 kg

of payload with booms• Equatorial orbit 400 x 5000 km to sample

the lunar wake• Communications

• Omnidirec. LGA S-band to 9-m G/S antenna (ESRANGE): 5-6 kbps

• 40 cm HGA S-band to 9-m G/S antenna (ESRANGE): 133 kps

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Mars Orbiting Plasma Surveyor (MOPS). Overview

• Dedicated space plasma mission to Mars• Earth - pointing spin stabilized platform• Direct communication with the Earth• Wet mass: 76.1 kg• Dry mass: 60.0 kg (inc. 5% margin)• Payload mass: 10 kg

• Piggy-back on a mission to Mars• Separation right after MOI• Hohmann transfer onto a working orbit (500 km

x 10000 km, equatorial)• Life time: 1 Martian year (687 days)• Operations in the eclipse

• Pre-phase A technical study completed by Swedish Space Corporation, Solna, Sweden. Example mother ship - Russian Phobos-Grunt

• The project is technically feasible

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“Art house” ideas. Impact probes

• A small (nano) satellite to conduct measurements until not- surviving impact

• Greatly reduced platform masses• Only for airless bodies (Moon, Callisto, Ganymede, Pluto)• Feasible for fly-by missions or scientific objectives requiring

measurements at the surface

Chandrayaan-1 / MIP

Pluto probe (proposal). 2.8 kg / ø22 x 7 cm

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Feasible AND interesting new targets (beside the Earth)

• Mercury, Mars, comets, Saturn covered • Venus: A dedicated space plasma mission on a spin-stabilized platform• Jupiter. Jupiter Magentospheric Orbiter (JAXA)

• Solar sail• Combined with a mission to Trojans

• Uranus orbiter: Identified in the recent the 2011 Planetary and Astronomy Decadal Survey• Mission to a new type of object “Icy Giants”• Not a dedicated space plasma mission but the Uranus’ magnetosphere is

unique: magnetic moment rotates around solar wind direction