New electrodynamic tether technology

New Electrodynarnic Tether Technology (NETT) is an experiment we proposed to ESA as part of the Columbus Precursor Flights. It was designed to fly as an exposed payload in the Spacelab carrier. Its primary objective is performance testing for the innovative bare tether concept. The experiment also includes two scientific objectives, specific for uninsulated tethers: i) detection of artificial auroral effects produced by secondary electron emission, and ii) detection of VLF wave emission. Additional objectives of the project are space performance of an electron-emitting hollow cathode and engineering verification of an open-loop deployment strategy.

Science with an electrodynamic tether

Ionospheric interaction experiments using a conductive, fully bare tether are discussed. With an optimal design, requiring 1.15 mm diameter and 7.5 km full length for a collected current of 0.87 A at day conditions, the tether radiates 0.33 watts as Fast Magnetosonic waves and 0.16 watts as Alfven waves. Secondary keV electrons are produced over a 6.5 km length, giving raise to noticeable auroral effects in the D-layer, at low geomagnetic latitudes. A preliminary design of the experiment, to be implemented on either a satellite or a Station, has been carried out. An ejector gives an initial velocity to an end mass, a free spool of tether unwinding from that mass during a first stage of deployment; other phases are monitored through the tether velocity, driving a reel with an unwinding device.

Short, high current electrodynamic tether

An electrodynamic tether experiment, to be carried out in the Russian spacecraft Almaz, is proposed. A 10 km tether would be deployed downwards; the lower 8 km would be nonconductive, the upper 2 km would be conductive, bare, and 2.2 mm in diameter, and would act as a thruster, with power supply at the top. This hybrid arrangement allows for other, onelectrodynamic experiments,reducing costs; it also limits the induced electromotive force, reducing the power to be handled. The current-voltage characteristic of contactors would be measured. With the anode switched off, the wire itself should collect a current over 5 A at day conditions, providing a thrust of 0.11 N at a 0.77 kW power.

Magnetantrieb für Raumfahrzeuge

Einfache Metallseile könnten Raumfahrzeuge mit billigem Strom versorgen, zu Antrieb und Steuerung beitragen und der Besatzung die Annehmlichkeiten künstlicher Schwerkraft verschaffen. Dahinterstecken elementare Naturgesetze aus Mechanik und Elektrodynamik

An anodeless (bare) tether experiment

NETT (New Electrodynamic Tether Technology) is an experiment proposed to ESA in 1991 as part of the Columbus Precursor Flights. It was originally intended to fly as an exposed payload in the Shuttle cargo bay. The main purpose was to demonstrate the electrodynamical capabilities of the innovative "bare tether" concept. The proposed conceptual design was recommended by a Scientific Panel of ESA, meeting in Heidelberg in March 1992. Unfortunately, the Precursor Flights have all but been scuttled, particularly as far as exposed payloads are concerned. The experiment, horever, is being considered in accomodation studies (APLSS, PIERS) for the European modulus of the future Space Station. Additionally, it might be possible to fly the bare tether in a Russian spacecraft.

An extended electron beam for auroral studies

An electrically floating metallic bare tether in a low Earth orbit would be highly negative with respect to the ambient plasma over most of its length, and would be bombarded by ambient ions. This would liberate secondary electrons, which, after acceleration through the same voltage, would form a magnetically guided two-sided planar e-beam. Upon impact on the atmospheric E-layer, at about 120-140 Km altitude auroral effects (ionization and light emission) can be expected. This paper examines in a preliminary way the feasibility of using this effect as an upper atmospheric probe. It is concluded that significant perturbations can be produced along the illuminated planar sheet of the atmosphere, with ionization rates of several thousand cm-3 sec1. Observation of the induced optical emission is made difficult by the narrowness and high moving speed of the illuminated zone, but it is shown that vertical resolution of single spectral lines is possible, as is wider spectral coverage with no vertical resolution.

Expectations from EMET and OESEE ground listening of possible EM events generated by the TSS 1R

On 22nd February '96, the space mission STS 75 started ,from the NASA facilities at Cape Canaveral. Such a mission consists in the launch of the shuttle Columbia in order to carry out two experiments in the space: the TSS 1R (Tethered Satellite Sistem 1 Refliight) and the USMP (United States Microgravity Payload). The TSS 1R is a replica of a similar mission TSS 1 '92. The TSS space programme is a bilateral scientific cooperation between the USA space agency NASA (National Aeronautics and Space Agency) and the ASI (Italian Space Agency. The TSS 1R system consists on the shuttle Columbia which deploys, up-ward, by means a conducting tether 20 km long, a spherical satellite (1.5 mt diameter) containing scientific instrumentation. This system, orbiting at about 300 km from the Earth's surface, represents, presently, the largest experimental space structure, Due to its dimensions, flexibility and conducting properties of the tether, the system interacts, in a quite complex manner, wih the earth magnetic field and the ionospheric plasma, in a way that the total system behaves as an electromagnetic radiating antenna as well as an electric power generator. Twelve scientific experiments have been assessed by US and Italian scientists in order to study the electro dynamic behaviour of the structure orbiting in the ionos phere. Two experiments have been prepared in the attempt to receive on the Earth's surface possible electromagnetic events radiated by the TSS 1R. The project EMET (Electro Magnetic Emissions from Tether),USA and the project OESEE (Observations on the Earth Surface of Electromagnetic Emissions) Italy, consist in a coordinated programme of passive detection of such possible EM emissions. This detection will supply the verification of some thoretical hypotheses on the electrodynamic interactions between the orbiting system, the Earth's magnetic field and the ionospheric plasma with two principal aims as the technological assesment of the system concept as well as a deeper knowledge of the ionosphere properties for future space applications. A theoretical model that keeps the peculiarities of tether emissionsis being developed for signal prediction at constant tether current. As a step previous to the calculation of the expected ground signal , the Alfven-wave signature left by the tether far back in the ionosphere has been determined. The scientific expectations from the combined effort to measure the entity of those perturbations will be outlined taking in to account the used ground track sensor systems.

Two-temperature model of the coronal irradiated pellets

A two electron-temperature, quasi-steady model of the corona of a laser-ablated pellet is considered. Ablation pressure, critical radius and mass flow rate are determined. Results are close to those obtained with heat flux saturation well below the free-streaming limit.

Technology of bare tether current collection

The outstanding problem for useful applications of electrodynamic tethers is obtaining sufficient electron current from the ionospheric plasma. Bare tether collectors, in which the conducting tether itself, left uninsulated over kilometers of its length, acts as the collecting anode, promise to attain currents of 10 A or more from reasonably sized systems. Current collection by a bare tether is also relatively insensitive to drops in electron density, which are regularly encountered on each revolution of an orbit. This makes nighttime operation feasible. We show how the bare tether's high efficiency of current collection and ability to adjust to density variations follow from the orbital motion limited collection law of thin cylinders. We consider both upwardly deployed (power generation mode) and downwardly deployed (reboost mode) tethers, and present results that indicate how bare tether systems would perform as their magnetic and plasma environment varies in low earth orbit.