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Published on February 24, 2008

Author: Altoro

Source: authorstream.com

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Slide1:  Observational Space Physics The main goal of this course is to support the theoretical concepts of basic space physics by the corresponding observations in SPACE Going to space is still rather expensive, so we will NOT follow this teaching method Slide2:  Observational Space Physics 13.03-03.05.2007, given by Dr. Natalia Ganushkina (FMI) 5 credits 2 lectures per week: Tuesdays 14-16, Physicum D112, Thursdays 10-12, Physicum D114 Exam in the end: verbal Lecturer is happy to answer any questions on Tuesdays 13-14, and Thursdays 12-13 Mobile: 050-341-2371, E-mail: Natalia.Ganushkina@fmi.fi You are also welcome to come to FMI! Slide3:  Observational Space Physics Outline of the course 1. Introduction: State of Space Physics before the spaceflight era and the beginning of satellite observations 2. Measurement techniques in space: magnetic and electric fields, particles, waves, imaging 3. Regions and phenomena: Observations 4. Space weather 5. Current and future space missions Slide4:  There are things that are known and things that are unknown; in between is exploration. Movie Shows the Changing Faces of an Infant Star XZ Tauri Slide5:  Some missions flying and to be flown Slide6:  Chronology of Space Exploration: 1912-1949, 3 during 38 years, failures 0 Balloon flight - Europe - (1912) Discovered cosmic rays. NRL V-2 rocket - USA - (1946) First observation of the Sun's UV spectrum. NRL V-2 rocket - USA - (1949) First observation of solar x rays. http://www.solarviews.com/eng/craft1.htm Slide7:  Sputnik-1 - USSR - (1957) First artificial satellite. Explorer III - USA - (1958) Discovered Earth's radiation belt. Pioneer 0 - USA Lunar Orbiter - (August 17, 1958) First stage exploded. Pioneer 1 - USA Lunar Orbiter - (October 11, 1958) Failed to reach escape velocity. Pioneer 3 - USA Lunar Flyby - (December 6, 1958) Failed to reach escape velocity. Luna 1 - USSR Lunar Flyby - 361 kg - (January 2, 1959) Luna 1 was the first lunar flyby. It discovered the solar wind and is now in a solar orbit. Pioneer 4 - USA Distant Lunar Flyby - 5.9 kg - (March 3, 1959) Space probe is now in a solar orbit. Luna 2 - USSR Lunar Hard Lander - 387 kg - (September 12, 1959) Luna 2 was the first spacecraft to impact the surface of the moon on September 14, 1959. Luna 3 - USSR Lunar Far Side Flyby - 278.5 kg - (October 4, 1959) Encountered the Moon on October 7, 1959 and returned the first image of the Moon's hidden side. Space probe is now in a decayed earth-moon orbit. Pioneer 5 - USA Solar Monitor - (March 11, 1960) Space probe is now in a solar orbit. Chronology of Space Exploration: 1957-1960, 12 during 4 years, failures 5 Slide8:  Mars 1960A - USSR Mars Probe - (October 10, 1960) Failed to reach Earth orbit. Mars 1960B - USSR Mars Probe - (October 14, 1960) Failed to reach Earth orbit. Chronology of Space Exploration: 1957-1960, 12 during 4 years, failures 5, cont’d Slide9:  Chronology of Space Exploration: 1961-1965, 22 during 5 years, failures 11 Venera 1 - USSR Venus Flyby - 643.5 kg - (February 12, 1961) Now in a solar orbit. Aerobee Rocket - USA - (1962) Observed the first x-ray star. Ranger 3 - USA Lunar Hard Lander - 327 kg - (January 26, 1962) Lunar probe missed the moon and is now in a solar orbit. Ranger 4 - USA Lunar Hard Lander - 328 kg - (April 23, 1962) First US lunar impact of the Moon. Mariner 2 - USA Venus Flyby - 201 kg - (August 27, 1962 - January 3, 1963) On December 14, 1962, Mariner 2 arrived at Venus at a distance of 34,800 kilometers and scanned its surface with infrared and microwave radiometers, capturing data that showed Venus's surface to be about 425°C (800°F). Three weeks after the Venus flyby Mariner 2 went off the air on January 3, 1963. It is now in a solar orbit. Ranger 5 - USA Lunar Flyby - 340 kg - (October 18, 1962) Ranger 5 was to be a lander but became a flyby because of a spacecraft failure. It is now in a solar orbit. Mars 1962A - USSR Mars Flyby - (October 24, 1962) Spacecraft failed to leave Earth orbit after the final rocket stage exploded. Mars 1 - USSR Mars Flyby - 893 kg - (November 1, 1962) Communications failed en route. Mars 1962B - USSR Mars Lander - (November 4, 1962) Failed to leave Earth orbit. Slide10:  Chronology of Space Exploration: 1961-1965, 22 during 5 years, failures 11, cont’d Luna 4 - USSR Lunar Probe - 1,422 kg - (April 2, 1963) Lunar 4 was intended to be a lunar lander but missed the Moon. It is now in an Earth Moon orbit. Ranger 6 - USA Lunar Hard Lander - 361.8 kg - (January 30, 1964) Cameras failed; lunar probe impacted the surface of the Moon. Zond 1 - USSR Venus Flyby - 890 kg - (April 2, 1964) Communication lost en route; now in a solar orbit. Ranger 7 - USA Lunar Hard Lander - 362 kg - (July 28, 1964) Arrived on July 31, 1964, sent pictures back at a close range, and impacted the Moon. Mariner 3 - USA Mars Flyby - 260 kg - (November 5, 1964) Mars flyby attempt. Solar panels did not open, preventing flyby. Mariner 3 is now in a solar orbit. Mariner 4 - USA Mars Flyby - 260 kg - (November 28, 1964 - December 20, 1967) Mariner 4 arrived at Mars on July 14, 1965 and passed within 9,920 kilometers of the planet's surface. It returned 22 close-up photos showing a cratered surface. The thin atmosphere was confirmed to be composed of carbon dioxide in the range of 5-10 mbar. A small intrinsic magnetic field was detected. Mariner 4 is now in a solar orbit. Zond 2 - USSR Mars Flyby - (November 30, 1964) Contact was lost en route. Slide11:  Chronology of Space Exploration: 1961-1965, 22 during 5 years, failures 11, cont’d Ranger 8 - USA Lunar Hard Lander - 366 kg - (February 17, 1965) Ranger 8 arrived at the moon on February 20, 1965. It sent back high-resolution pictures until it impacted in Mare Tranquillitatis. Ranger 9 - USA Lunar Hard Lander - 366 kg - (March 21, 1965) Lunar probe sent pictures of its impact on the moon. Luna 5 - USSR Lunar Soft Lander - 1,474 kg - (May 9, 1965) The lunar soft-lander failed and impacted the moon. Luna 6 - USSR Lunar Soft Lander - 1,440 kg - (June 8, 1965) Missed the moon and is now in a solar orbit. Zond 3 - USSR Lunar Flyby - 959 kg - (July 18, 1965) Returned pictures of the lunar far side. It is now in a solar orbit. Luna 7 - USSR Lunar Soft Lander - 1,504 kg - (October 4, 1965) Failed and impacted the moon. Slide12:  Chronology of Space Exploration: rest of the list see at http://www.solarviews.com/eng/craft1.htm Year Period Total Failures 1912-1949 38 years 3 0 1957-1960 4 years 12 5 1961-1965 5 years 22 11 1966-1970 5 years 45 6 1971-1975 5 years 30 6 1976-1980 5 years 10 0 1981-1985 5 years 9 0 1986-1990 5 years 7 1 1991-1995 5 years 4 1 1996-2000 5 years 13 3 2001-2005 5 years 13 0 Slide13:  Selected Space Missions Current Missions Advanced Composition Explorer (ACE) ACE observes of particles of solar, interplanetary, interstellar, and galactic origins, spanning the energy range from that of KeV solar wind ions to galactic cosmic ray nuclei up to 600 MeV/nucleon. It is a major mission in the Explorer program. (Launched August 25, 1997) Cluster Cluster is a European Space Agency program with major NASA involvement. The four Cluster spacecraft carry out three-dimensional measurements in the Earth's magnetosphere, covering both large- and small-scale phenomena in the sunward and tail regions. The first 2 spacecraft were launched on 2000 July 16; the 2nd pair were launched on August 9, 2000. Fast Auroral Snapshot Explorer (FAST) FAST studies the detailed plasma physics of the Earth's auroral regions. Ground support campaigns coordinate satellite measurements with ground observations of the Aurora Borealis, commonly referred to as the Northern Lights. The science instruments on board FAST are helping scientists to learn about the interaction of the solar wind with Earth's magnetosphere. (Launched 1996 August 21) Slide14:  Current Missions GEOTAIL The GEOTAIL mission is a collaborative project undertaken by the Japanese Institute of Space and Astronautical Science (ISAS) and NASA. Its primary objective is to study the tail of the Earth's magnetosphere. The information gathered is allowing scientists to model and more accurately predict Earth-Sun interactions and their effects on space exploration, communications and technology systems. (Launched 1992 July 24) Polar Polar is the second of two NASA spacecraft in the Global Geospace Science (GGS) initiative and part of the ISTP Project. GGS is designed to improve greatly the understanding of the flow of energy, mass and momentum in the solar-terrestrial environment with particular emphasis on geospace. (Launched February 24, 1996) Solar and Heliospheric Observatory (SOHO) SOHO, a joint venture of the European Space Agency and NASA, is a solar observatory studying the structure, chemical composition, and dynamics of the solar interior; the structure (density, temperature and velocity fields) and dynamics of the outer solar atmosphere; and the solar wind and its relation to the solar atmosphere. (Launched December 2, 1995) Selected Space Missions Slide15:  Current missions Solar Terrestrial Relations Observatory (STEREO) Coronal mass ejections (CMEs) are powerful eruptions in which as much as ten billion tons of the Sun's atmosphere can be blown into interplanetary space. The goal of STEREO is to understand the origin coronal mass ejections and their consequences for Earth. The mission will consist of two spacecraft, one leading and the other lagging Earth in its orbit. The spacecraft will each carry instrumentation for solar imaging and for in-situ sampling of the solar wind. STEREO is a Solar Terrestrial Probe mission. (Launch Date: 10/25/06 Ulysses The Ulysses Mission is the first spacecraft to explore interplanetary space at high solar latitudes, orbiting the Sun nearly perpendicular to the plane in which the planets orbit. The spacecraft and spacecraft operations team are provided by the European Space Agency (ESA); the launch of the spacecraft, radio tracking, and data management operations are provided by NASA. Scientific experiments are provided by investigation teams both in Europe and the USA. (Launched October 6, 1990) Wind Wind studies the solar wind and its impact on the near-Earth environment. (Launched November 1, 1994 Selected Space Missions Slide16:  Future missions Magnetospheric MultiScale (MMS) MMS will determine the small-scale basic plasma processes which transport, accelerate and energize plasmas in thin boundary and current layers – and which control the structure and dynamics of the Earth's magnetosphere. MMS will for the first time measure the 3D structure and dynamics of the key magnetospheric boundary regions, from the subsolar magnetopause to the distant tail. (Launch Date: 10/31/13) Time History of Events and Macroscale Interactions during Substorms (THEMIS) THEMIS is a study of the onset of magnetic storms within the tail of the Earth's magnetosphere. THEMIS will fly five microsatellite probes through different regions of the magnetosphere and observe the onset and evolution of storms. THEMIS will determine the causes of the global reconfigurations of the Earth's magnetosphere that are evidenced in auroral activity. (Launch Date: 02/17/07) Two Wide-Angle Imaging Neutral-Atom Spectrometers (TWINS) TWINS will provide stereo imaging of the Earth's magnetosphere, the region surrounding the planet controlled by its magnetic field and containing the Van Allen radiation belts and other energetic charged particles. (Launch Date: 10/1/07) Selected Space Missions Slide17:  Past missions Dynamics Explorer - 1 The DE mission's general objective was to investigate the strong interactive processes coupling the hot, tenuous, convecting plasmas of the magnetosphere and the cooler, denser plasmas and gases corotating in the earth's ionosphere, upper atmosphere, and plasmasphere. Two satellites, DE-1 and DE-2, were launched together on August 3, 1981 and were placed in polar coplanar orbits, permitting simultaneous measurements at high and low altitudes in the same field-line region. DE-2 reentered the atmosphere on February 19, 1983; DE-1 operations were terminated on February 28, 1991. Equator-S Equator-S was a German Space Agency project, with contributions from ESA and NASA, related to the International Solar-Terrestrial Physics program. The mission provided high-resolution plasma, magnetic, and electric field measurements in several regions not adequately covered by any of the existing ISTP missions. The spacecraft was launched December 2, 1997, and stopped transmitting data on May 1, 1998. Selected Space Missions Slide18:  Past missions Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) IMAGE studied the global response of the magnetosphere to changes in the solar wind. Major changes occur to the configuration of the magnetosphere as a result of changes in and on the sun, which in turn change the solar wind. IMAGE used neutral atom, ultraviolet, and radio imaging techniques to detect and gather data on these changes. (Launched March 25, 2000; operations ended January 2006) Interplanetary Monitoring Platform-8 (IMP-8) IMP-8 was instrumented for interplanetary, magnetotail, and magnetospheric boundary studies of cosmic rays, energetic solar particles, plasma, and electric and magnetic fields. The objectives of the mission were to provide solar wind parameters as input for magnetospheric studies and as a 1-AU baseline for deep space studies, and to continue solar cycle variation studies with a single set of well-calibrated and understood instruments. (Launched October 26, 1973; science mission terminated October 26, 2001) Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) SAMPEX is investigating the composition of local interstellar matter and solar material and the transport of magnetospheric charged particles into the Earth's atmosphere. (Launched July 3, 1992) Selected Space Missions Slide19:  Solar Sail Solar sails are a proposed form of spacecraft propulsion using large membrane mirrors. (Spacecraft propulsion is used to change the velocity of spacecraft). Unlike rockets, solar sails require no fuel. Although the thrust is small, it continues as long as the sun shines and the sail is deployed. The science of solar sails is well-proven, but the technology to manage large solar sails is still undeveloped. Mission planners are not yet willing to risk multimillion dollar missions on unproven solar sail unfolding and steering mechanisms. This neglect has inspired some enthusiasts to attempt private development of the technology, such as the Cosmos 1. The concept was first proposed by German astronomer Johannes Kepler in the seventeenth century. It was again proposed by Friedrich Zander in the late 1920s and gradually refined over the decades. Slide20:  Proposal in response to Call for proposals for the first planning cycle of Cosmic Vision 2015--2025 D/SCI/DJS/SV/val/21851 WARP Waves and Relativistic Particles Issue 1.0 April 25, 2007 Slide21:  The spacecraft deploys a large membrane mirror which reflects light from the Sun or some other source. The radiation pressure on the mirror provides a minuscule amount of thrust by reflecting photons. Tilting the reflective sail at an angle from the Sun produces thrust at an angle that bisects the angle between the Sun and the spacecraft. Sails orbit, and therefore do not need to hover or move directly toward or away from the sun. Almost all missions would use the sail to change orbit, rather than thrusting directly away from a planet or the sun. The sail is rotated slowly as the sail orbits around a planet so the thrust is in the direction of the orbital movement to move to a higher orbit or against it to move to a lower orbit. When an orbit is far enough away from a planet, the sail then begins similar maneuvers in orbit around the sun. The best sort of missions for a solar sail involves a dive near the sun, where the light is intense, and sail efficiencies are high. Solar Sail: How does it work? Slide22:  Solar sails are impractical for orbital and interplanetary missions because they move on an indirect course. Most near-term planetary missions involve robotic exploration craft, in which the directness of the course is simply unimportant compared to the small fuel mass and fast transit times of a solar sail. Solar sails capture energy primarily from the "solar wind“. These particles would impart a small amount of momentum upon striking the sail, but this effect would be small compared to the force due to radiation pressure from light reflected from the sail. The force due to light pressure is about 5000 times as strong as that due to solar wind. Radiation pressure is an unproven effect that may violate the thermodynamical Carnot rule. The solution is that when reflected by a solar sail, a photon undergoes a Doppler shift; its wavelength increases (and energy decreases) by a factor dependent on the velocity of the sail, transferring energy from the sun-photon system to the sail. Solar sail craft would have to "tack" or use some other means of propulsion when traveling toward the sun during an intrasystem flight. In fact, a solar sail is equally useful traveling between elliptical orbits toward or away from the sun. This is because the unit-mass energy of an elliptical orbit increases with distance from the primary body. So to go from Earth to, say, Venus, a spacecraft would have to lose orbital energy, which could be accomplished by the sail dragging against the sun's radiation. Solar Sail: Critics Slide23:  No solar sails have been successfully deployed as primary propulsion systems, but research in the area is continuing. On August 9, 2004 Japanese ISAS successfully deployed two prototype solar sails from a sounding rocket. A clover type sail was deployed at 122 km altitude and a fan type sail was deployed at 169 km altitude. Both sails used 7.5 micrometer thick film. A joint private project between Planetary Society, Cosmos Studios and Russian Academy of Science launched Cosmos 1 on June 21, 2005, from a submarine in the Barents Sea, but the Volna rocket failed, and the spacecraft failed to reach orbit. A solar sail would have been used to gradually raise the spacecraft to a higher earth orbit. The mission would have lasted for one month. A suborbital prototype test by the group failed in 2001 as well, also because of rocket failure. A 15-meter-diameter solar sail (SSP, solar sail sub payload, soraseiru sabupeiro-do) was launched together with ASTRO-F on a M-V rocket on February 21, 2006, and made it to orbit. It deployed from the stage, but opened incompletely. Solar Sail: Current progress Slide24:  The Wind from the Sun by Arthur C. Clarke, a short story (in an anthology of the same name) describing a solar sail craft Earth-Moon race. Dust of Far Suns, by Jack Vance, also published as Sail 25, depicts a crew of space cadets on a training mission aboard a malfunction-ridden solar sail craft. The Mote in God's Eye (1975) by Larry Niven and Jerry Pournelle depicts an interstellar alien spacecraft driven by laser-powered light sails. Rocheworld by Robert L. Forward, a novel about an interstellar mission driven by laser-powered light sails. Solar sails appeared in Star Wars Episode II: Attack of the Clones, in which Count Dooku has a combination hyperdrive and starsail spacecraft dubbed the Solar Sailer. A solar sail appears in the Star Trek: Deep Space Nine episode "Explorers", as the primary propulsion system of the "Bajoran solar-sail vessel". The vessel inadvertantly exceeds the speed of light by sailing on a stream of tachyons. Solar Sails in Fiction Slide25:  Electric Sail (1) Electric sail (also called electric solar wind sail) is a proposed form of spacecraft propulsion using the dynamic pressure of the solar wind as a source of thrust. Principles of operation and design The electric sail consists of a number of thin, long and conducting tethers which are kept in a high positive potential by an onboard electron gun. The positively charged tethers repel solar wind protons, thus deflecting their paths and extracting momentum from them. Simultaneously they also attract electron from the solar wind plasma. The arriving electron current is compensated by the electron gun. A way to deploy the tethers is to rotate the spacecraft and have the centrifugal force keep them stretched. Potentiometers between each tether and the spacecraft can be used to fine-tune the tether potentials and thus the solar wind force individually and thus control the attitude of the spacecraft. Slide26:  Electric Sail (2) Intrinsic limitations The electric sail probably cannot be used inside planetary magnetospheres because there is no solar wind there, only slower plasma flows and magnetic fields. While modest variation of the thrust direction can be achieved by inclining the sail, the thrust vector always points more or less radially outward from the Sun. Applications Fast mission (>50 km/s or 10 AU/year) out of the Solar system and heliosphere for small or modest payload As a brake for small interstellar probe which has been accelerated to high speed by some other means such as laser lightsail Inward-spiralling mission to study the Sun at closer distance Two-way mission to inner Solar System objects such as asteroids Off-Lagrange point solar wind monitoring spacecraft for predicting space weather with longer warning time than 1 hour The electric sail - opening up the solar system?:  The electric sail - opening up the solar system? Pekka Janhunen Finnish Meteorological Institute, Space Research (Kumpula Space Centre) Acknowledgements: Arto Sandroos, Simo-Pekka Hannula, Yossi Ezer, Eero Haimi, Tomi Suhonen, Aarne Halme, Pasi Tarvainen, Erkki Heikkola, Mikhail Zavyalov, Slava Linkin, Robert Hoyt, Mikhail Uspensky, Jouni Polkko, Rami Vainio, Petri Toivanen, Juha-Pekka Luntama, Markku Mäkelä, etc., etc. What is the 'Electric Sail':  What is the 'Electric Sail' Device for sailing with the solar wind “Cousin” of the Solar Sail, but uses solar wind dynamic pressure instead of solar radiation pressure Finnish invention (Janhunen, 2004, Janhunen, 2006, Janhunen and Sandroos, 2007) Exotic but seemingly feasible technical construction May enable unprecedentedly high final speeds (50-100 km/s, 10-20 AU/year) for small probes Also commercial applications can be envisioned Working principle:  Working principle Thin and long positively charged tethers, forming obstacle for solar wind protons and transferring momentum from them Electron gun maintains the positive potential Radial, centrifugal deployment Thrust on each tether depends on its voltage, which is tuned individually by potentiometers Thus, flown like a helicopter (attack angle <--> potential) Typical parameters:  Typical parameters Solar wind dynamic pressure rv2 ~ 2 nPa at 1 AU Tether ‘electric radius’ ~ Debye length lDe ~ 20 m N=50-100, L=20 km, rw=10 mm F ~ rv2 NL lDe~0.1-0.2 N a = F/m~1-3 mm/s2 Electron current I = NL en(2eV0/me)1/2 2 rw~10-50 mA V0=15-25 kV dF/dz~50-100 nN/m Needed hardware:  Needed hardware Tethers and their reels (50-100) Solar-powered electron gun/guns (~500 W) Spin initiation, several possibilities: conventional propulsion unit with arms (jettisoned), or obtain spin from solar wind by 'pumping' procedure Potentiometers & tunable length for tethers S/C attitude/spin control thrusters (low power) Sensors for guiding+navigation: tether orientation sensors accelerometer electron detector for measuring s/c potential (optional) tether current measurement (optional) Tethers and their reels:  Tethers and their reels Multiple wire because of micrometeoroids N=50-100, d=20 mm, nmult=4, L=20 km “Hoytether” approach Transverse spacing 5-30 mm Small ballast weight to initiate deployment Tensile strength and conductivity Inner solar system: conductivity important Outer solar system: tensile strength more important Low deployment speed (some mm/s) Probably need to fine-tune length also during flight The path forward:  The path forward “Phase-A” study TEKES or ESA (GSTP) funding (~ 2 years) Test mission EU FP7 funding? Demo mission for IHP (Interstellar Heliopause Probe) ESA: E-sail would be enabling technology for IHP IHP 15 years flighttime to heliopause boundary (150 AU) Measure interstellar plasma and magnetic field Measure heliosphere structure Test “Pioneer anomaly” (fundamental physics) The team:  The team FMI/Kumpula Space Centre (lead) TKK/Material Science (tethers) TKK/Automation Technology (reels and sensors) Numerola Oy, Jyväskylä (modelling) Space Research Institute IKI, Moscow (electron gun) University of Pisa, Italy (orbit calculations) University of Bergen, Norway (electron and ion detectors for diagnostics) What is not possible:  What is not possible Stopping at remote outer solar system target Basically impossible to stop from 50 km/s Returning from outer solar system Inward spiralling slow beyond Mars orbit Having propulsion inside magnetosphere No solar wind there Using heavy payloads Conductivity and tensile strength problem with >100 km long tethers Possible improvement, however: if RF electron heating successful, thrust >1 N may be possible What is possible:  What is possible Turning on and off propulsion at any time This is an improvement over solar sail Regulating thrust between zero and some maximum value, which depends on solar wind conditions and Sun distance Generalisation of the above Modest controlling of the thrust vector angle (+-20 degrees, possibly even +-30 degrees?) In solar sail, control possibility about 2 times higher Applications:  Applications ESA IHP (“Interstellar Heliopause Probe”) Fast (>50 km/s) flyby missions of outer solar system targets, e.g. Pluto (~ 50 kg payload) Sample return from asteroids or Martian moons Or other type of mission to inner solar system Off-Lagrange-point solar wind monitor “Reliable” forecast with ~ 4 hour warning time Fuel factory commercial application (Much later:) “Brake” for ultrafast interstellar probe? Long-term commercial application:  Long-term commercial application “Commercial” = Earth-orbiting satellite E-sail cannot be used directly (magnetosphere!) Orbital fuel factory: Water miner at ice-containing asteroid Electric Sail logistics chain for H2O retrieval LH2/LOX fuel factory at high Earth orbit (L3/L4/L5) Reusable orbital transfer vehicles Fuel factory benefits: Cheapen all space activities (except going to LEO) Cheaper manned Mars, etc. Technical issues?:  Technical issues? Meteoroid cuts (under control) Tether cut may be fatal if causes tether collision Won't happen if tethers not in same plane Getting stuck of damaged tether when retracting? Need to make prototype tether to test this If problem, can use tether worked from flat ribbon Thrust controllable up to a maximum which depends on solar wind which is unpredictable Stochastic nature of orbit design Oscillations due to thermal expansion in eclipse? Eclipsing can be avoided in many missions, anyway Conclusions:  Conclusions E-sail is a spinoff of basic research of space plasma physics (traditional AVA stronghold) E-sail technology looks very promising But in technology, nothing is proven under everything is proven, i.e. until it flies (or fails:-) May enable almost sci-fi class speeds (>50 km/s) High speed for small probes, or economical material fetching for larger payloads High payload mass fraction in the latter case International consortium already existing

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