Propulsion and power generation by bare electrodynamic tethers are revisited in a unified way and issues and
constraints are addressed. In comparing electrodynamic tethers, which do not use propellant, with other propellantconsuming systems, mission duration is a discriminator that defines crossover points for systems with equal initial masses. Bare tethers operating in low Earth orbit can be more competitive than optimum ion thrusters in missions exceeding two-three days for orbital deboost and three weeks for boosting operations. If the tether produces useful onboard power during deboost, the crossover point reaches to about 10 days. Power generation by means of a bare electrodynamic tether in combination with chemical propulsion to maintain orbital altitude of the system is more efficient than use of the same chemicals (liquid hydrogen and liquid oxygen) in a fuel cell to produce power for missions longer than one week. Issues associated with tether temperature, bowing, deployment, and arcing are also discussed.
Heating/cooling rates reach about 4 K/s for a 0.05-mm-thick tape and a fraction of Kelvin/second for the ProSEDS
(0.6-mm-radius) wire; under dominant ohmic effects, temperatures areover200K (night) and 380 K (day) for the tape and 320 and 415 K for that wire. Tether applications other than propulsion and power are briefly discussed.

Electrodynamic Tether Applications and Constraints

Effect of ZnO nanoparticles on thermoelectric properties of cement composite for waste heat harvesting

Over 2500 active satellites are in orbit as of October 2020, with an increase of ~1000 smallsats in the past two years. Since 2012, over 1700 smallsats have been launched into orbit. It is projected that by 2025, there will be 1000 smallsats launched per year. Currently, these satellites do not have sufficient delta v capabilities for missions beyond Earth orbit. They are confined to their pre-selected orbit and in most cases, they cannot avoid collisions. Propulsion systems on smallsats provide orbital manoeuvring, station keeping, collision avoidance and safer de-orbit strategies. In return, this enables longer duration, higher functionality missions beyond Earth orbit. This article has reviewed electrostatic, electrothermal and electromagnetic propulsion methods based on state of the art research and the current knowledge base. Performance metrics by which these space propulsion systems can be evaluated are presented. The article outlines some of the existing limitations and shortcomings of current electric propulsion thruster systems and technologies. Moreover, the discussion contributes to the discourse by identifying potential research avenues to improve and advance electric propulsion systems for smallsats. The article has placed emphasis on space propulsion systems that are electric and enable interplanetary missions, while alternative approaches to propulsion have also received attention in the text, including light sails and nuclear electric propulsion amongst others.

Electric Propulsion Methods for Small Satellites: A Review

Electric Sail Thrust Model from a Geometrical Perspective

A bare electrodynamic tether (EDT) is a conductive thin wire or tape tens of kilometres long, which is kept taut in space by gravity gradient or spinning, and is left bare of insulation to collect (and carry) current as a cylindrical Langmuir probe in an ambient magnetized plasma. An EDT is a probe in mesothermal flow at highly positive (or negative) bias, with a large or extremely large 2D sheath, which may show effects from the magnetic self-field of its current and have electrons adiabatically trapped in its ram front. Beyond technical applications ranging from propellantless propulsion to power generation in orbit, EDTs allow broad scientific uses such as generating electron beams and artificial auroras, exciting Alfven waves and whistlers, modifying the radiation belts and exploring interplanetary space and the Jovian magnetosphere. Asymptotic analysis, numerical simulations, ground and space tests and past and planned missions on EDTs are briefly reviewed.

/pdf/a-review-of-electrodynamic-tethers-for-science-applications-3e0gkqd3m7.pdf

A review of electrodynamic tethers for science applications

Optimum sizing of bare-tape tethers for de-orbiting satellites at end of mission

An electric solar sail (e-sail) is a promising propellantless propulsion concept for the exploration of the Solar System. An e-sail consists of an array of bare conductive tethers at very high positive/negative bias, capable of extracting solar-wind momentum by Coulomb deflection of protons. The present work focuses on the positivebias case with a potential profile that must be correctly modeled. Ion scattering does occur at some point of the profile and the resulting thrust is determined; that thrust scales slower with distance to the Sun, than it was previously suggested in the literature. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Propulsive Force in an Electric Solar Sail

A two-stage mission to place a spacecraft (SC) below the Jovian radiation belts, using a spinning bare tether with plasma contactors at both ends to provide propulsion and power, is proposed. Capture by Lorentz drag on the tether, at the periapsis of a barely hyperbolic equatorial orbit, is followed by a sequence of orbits at near-constant periapsis, drag finally bringing the SC down to a circular orbit below the halo ring. Although increasing both tether heating and bowing, retrograde motion can substantially reduce accumulated dose as compared with prograde motion, at equal tether-to-SC mass ratio. In the second stage, the tether is cut to a segment one order of magnitude smaller, with a single plasma contactor, making the SC to slowly spiral inward over several months while generating large onboard power, which would allow multiple scientific applications, including in situ study of Jovian grains, auroral sounding of upper atmosphere, and space- and time-resolved observations of surface and subsurface.

/pdf/a-proposed-two-stage-two-tether-scientific-mission-at-wq1soy4chy.pdf

A Proposed Two-Stage Two-Tether Scientific Mission at Jupiter

At the beginning of the Space Age, both propulsion and power generation in the spacecraft has been the main issue for consideration. Considerable research has been carried out on technologies by several Space Agencies to reach outer planets and generate electric power for the systems and subsystems in the spacecraft (SC). Various types of power source such as solar photovoltaic, Radioisotope power systems (RPS) have been used by Space Agencies. New technology such as reactor based, electric solar sail and electrodynamic bare tethers might be used in the future for both propulsion and power generation. Mainly, both NASA and Russian Agency worked separately using nuclear technology to obtain more efficiency in their systems for deep space exploration. Radioisotope Power Systems (RPS), is a nuclear-powered system to generate electric power to feed communication and scientific systems on a spacecraft. Radioisotope Thermoelectric Generators (RTGs), a type of Radioisotope Power System, were used in the past as electric power supplies for some navigational and meteorological missions, and most outer-planet missions. Radioisotope power systems use the natural decay of radionuclides produced by a nuclear reactor. The expensive, man-made Plutonium-238 (238Pu) is the appropriate source of energy used in RPS fueling; its long half-life (~87 years) guarantees long time missions. The limited avability of Plutonium-238 is inadequate to support scheduled NASA mission beyond 2018. After the Cold War, throughout the Non-Proliferation of Nuclear Weapons Treaty, the production and processing of these resources have been severally reduced. There is a high-priority recommendation to reestablish production to solve the severe 238Pu demand problem (National Reseach Council, 2009). The isotope initially selected for terrestrial and space power applications was Cerium-144 because it is one of the most useful fission products available from nuclear reactor (Furlog, 1999; Lange, 2008). Its short half-life (about 290 days) made Cerium-144 compatible with a possible short-time mission. However, the high radiation associated with a powerful beta/gamma emission produces several problems with the payload interaction and safety in the case of reentry orbit. The development of RTGs was assigned to The Atomic Energy Commission in 1955. The first system developed for space situation was the System for Nuclear Auxiliary Power (SNAP). The Cerium-144 fueled SNAP-1 power system was never used in space. The first flight with a RTG was SNAP-3 in 1961 delivering 11.6 kW over a 280 days period, using as fueling Polonium-210 (Po-210) isotope. Po-210 is an alpha emitter with

/pdf/radioisotope-power-systems-for-space-applications-1tmyefvbsr.pdf

Antonio Sanchez-Torres

Papers

Optimum sizing of bare-tape tethers for de-orbiting satellites at end of mission

Propulsive Force in an Electric Solar Sail

A Proposed Two-Stage Two-Tether Scientific Mission at Jupiter

Radioisotope Power Systems for Space Applications

Drag and propulsive forces in electric sails with negative polarity