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Plasma in the solar system: science and missions Stas Barabash Swedish Institute of Space Physics (IRF) Kiruna, Sweden. Swedish Institute of Space Physics. Established 1957 A governmental research institute under the auspice of Ministry of Education. Annual budget ~ 9 M€
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Plasma in the solar system: science and missions Stas Barabash Swedish Institute of Space Physics (IRF) Kiruna, Sweden
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
Swedish missions Odin 2001 Magnetospheric physics: Viking, Freja, Astrid-1/2, Munin Technology demonstrator: PRISMA Atmospheric physics / Astronomy: Odin PRISMA, 2008 Astrid-2, 1999 Viking, 1986 Astrid-1, 1995 Munin, 2000 Freja, 1992
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% a-particles) with a velocity of 450 km/s and density about 70 cm-3 (Mercury) to 3 cm-3 at Mars
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 ( s ~ne , for magnetized plasmas we >> nc)
Corotating Jovian magnetosphere Induced magnetospheres of Mars and Venus Earth magnetosphere Interaction with the Moon Terrestrial magnetosphere
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)
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
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
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)
Basic platform requirements • Particle measurements (energetic particles) • Unobscured omnidirectional (4p) 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)
Unobscured omnidirectional field of view Lewis et al., 2009 • The main and the most challenging requirement • Can be fully (4p) 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
Mechanical scanners (1) • Typical moving mass 4 kg, L ~ 0.1 m, w ~ 1 rpm • Typical spacecraft mass 0.5 - 1 tons, L ~ 1 m, w ~ 10-4 rpm Spin axis
Mechanical scanners (2) 0.02°
Spin-stabilized platforms (spinners) MMO • 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 Cluster Freja
Thruster plumes and firing Rosetta / Schläppi et al., 2010 • 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) Attitude maneuver
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.
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
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
Magnetic field measurements Voyager-1 (1977) • 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) 14 m
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
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 MAGSAT 6 m
General boom designs (2) • Wire booms deployed by centrifugal force for E-field experiments and Langmuir probes Magnetometer and star camera Langmuir probe E-field wire booms Swedish Astrid-2
A typical plasma science spacecraft ESA-JAXA BepiColombo / Mercury Magnetospheric Orbiter
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
Very few dedicated space plasma missions (planetary) Nozomi • 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 MAVEN
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)
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
Moon space plasma mission (2) Basic mission characteristics from the feasibility study • Launch: Kosmos-3M/Tsiklon • TTI (Translunar Trajectory Injection) • From an eccentric LEO • DV = 1300 - 2200 m/s (depending on launcher) • Lunar Orbit Insertion (LOI) • Direct insertion from TTI • DV = 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
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
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
“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 Pluto probe (proposal). 2.8 kg / ø22 x 7 cm Chandrayaan-1 / MIP
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