New ESAIL Video: Deploy Tethers!

An ESAIL may start out slowly, but it could turn out to be the fastest man-made vehicle ever constructed. The European Union is funding a three-year project to build an ESAIL craft.

The following video shows the basic deployment strategy and propulsion of the ESAIL.

A full-scale electric sail consists of a number (50-100) of long (e.g., 20 km), thin (e.g., 25 microns) conducting tethers (wires). The spacecraft contains a solar-powered electron gun (typical power a few hundred watts) which is used to keep the spacecraft and the wires in a high (typically 20 kV) positive potential. The electric field of the wires extends a few tens of metres into the surrounding solar wind plasma. Therefore the solar wind ions "see" the wires as rather thick, about 100 m wide obstacles. A technical concept exists for deploying (opening) the wires in a relatively simple way and guiding or "flying" the resulting spacecraft electrically.

The solar wind dynamic pressure varies but is on average about 2 nPa at Earth distance from the Sun. This is about 5000 times weaker than the solar radiation pressure. Due to the very large effective area and very low weight per unit length of a thin metal wire, the electric sail is still efficient, however. A 20-km long electric sail wire weighs only a few hundred grams and fits in a small reel, but when opened in space and connected to the spacecraft's electron gun, it can produce several square kilometre effective solar wind sail area which is capable of extracting about 10 millinewton force from the solar wind. For example, by equipping a 1000 kg spacecraft with 100 such wires, one may produce acceleration of about 1 mm/s^2. After acting for one year, this acceleration would produce a significant final speed of 30 km/s. Smaller payloads could be moved quite fast in space using the electric sail, a Pluto flyby could occur in less than five years, for example. Alternatively, one might choose to move medium size payloads at ordinary 5-10 km/s speed, but with lowered propulsion costs because the mass that has to launched from Earth is small in the electric sail.


(ESAIL illustration)

Science fiction fans may be reminded of the magships from Falling Stars, the 1998 novel by Michael Flynn, which use a magsail:

"How fast will this thing go?" the rigger wondered.

"Depends on current density, orientation, and a bunch of other factors programmed into the RAM pins here." He flourished the goat-case, careful not to shake it. "If you're sailing large before the wind, your acceleration is about a thousandth of a gee."

"That don' sound so fast, friend."

Jimmy grinned, having said almost the same thing to Hobie last year. "Not compared to an SSTO main engine, right. Get a couple of gees squashing your bag during a lift, right? The sail gives a gentler push, but it keeps on pushing. You don't run out of fuel unless the sun goes out; in which case fuel is not your major concern. Bottom line is: a magsail can get you to Mars in about the same time it took the Mayflower to cross the Atlantic."

Via Electric Solar Wind Sail (E-sail); thanks to Jim Bowling for the tip and the reference.

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