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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 PI missions since 1978 Experiment PROMICS-1 PROMICS-2 V3 ASPER A TICS/MATE PROMICS-3 PIPPI/EMIL/MIO ASPER A- C IMI MEDUSA, P IA MEDUSA, D INA ASPER A- 3 NUADU (Co-PI) ICA ASPER A- 4 SARA PRIMA YPP DIM MINA LINA MIPA ENA Mission Prognoz-7 Prognoz-8 Vik ing Phobos-1/2 Freja Interball-1/2 Astrid -1 Mars-96 Nozomi Astrid -2 Munin Mars Express Double Star Rosetta Venus Express Chandrayaan-1 PRISMA Yin ghuo Phobos-Grunt Mars 2013 Luna-Globe BC MP O BC MM O Launch, Org/Country 1978, USSR 1980, USSR 1986, Sweden 1988, USSR 1992, Sweden 1995/96, Russia 1995, Sweden 1996, Russia 1998, Japan 1999, Sweden 2000, Sweden 2003, ESA 2004, China 2004, ESA 2005, ESA 2007, ISRO 2010, Sweden 2011, China 2011, Russia 2013, China 2014, Russia 2014, ESA 2014, ESA Target Earth's magnetosphere Earth's magnetosphere Earth's magnetosphere Mars / Phobos Earth's magnetosphere Earth's magnetosphere Earth's magnetosphere Mars Mars Earth's magnetosphere Earth's magnetosphere Mars Earth's magnetosphere Comet Churyumov-Gerasimenko Venus Moon Technol. Mars Mars Mars Moon (lander) Mercury Mercury Swedish missions Magnetospheric physics: Viking, Freja, Astrid-1/2, Munin Technology demonstrator: PRISMA Atmospheric physics / Astronomy: Odin Odin 2001 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 QuickTime™ and a Sorenson Video decompressor are needed to see this picture. 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) Types of the solar wind interactions Corotating Jovian magnetosphere Induced magnetospheres of Mars and Venus Earth magnetosphere QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. Terrestrial magnetosphere Interaction with the Moon 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 nearplanet 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 f f (M, , , E, x, y, z) • 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 Galileo despun platform 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) • 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 Freja MMO Cluster 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 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 • 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 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 L~ DscVsc ~ 30m E min • 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) 6m MAGSAT 6m 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 Requirement Space plasma measurements Unob scur ed hemis pher ic FoV Spin-stabili zed p la tforms / scanne rs Thru ster avo idanc e Spacecraft potentia l Minimi zing spacecraft influence (boo ms ) Magne tic cleanli nes s EMC progra m Criti cal. Chall eng ing to fulfill Criti cal. Chall eng ing to fulfill Remote sensing instruments Not requir ed Not compatible Moderate. Easy to fulfill Minor Criti cal. Chall eng ing to fulfill Criti cal. Easy to fulfill Not requir ed May not be compatible Criti cal. Chall eng ing/exp ensive to fulfill Criti cal. Rela tively ea sy to fulfill Not requir ed Moderate. Easy to fulfill • 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) • 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 Nozomi 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