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NASA begins testing solar wind sail technology


A system that creates momentum for a spacecraft by repelling protons in the solar wind could get us to the edge of the Solar System in a fraction of the time it now takes. Bill Condie reports.

NASA has begun testing components of a new propulsion system that could see spacecraft ride the solar wind into interstellar space.

The system, called the Heliopause Electrostatic Rapid Transit System, would consist of 10 to 20 electrically charged, bare aluminium wires radiating from the centre of a spacecraft to form a circular “E-Sail”.

The wires would electrostatically repel the fast-moving protons of the solar wind, with the momentum produced creating the spacecraft’s thrust.

“The Sun releases protons and electrons into the solar wind at very high speeds – 400 to 750 kilometres per second,” said Bruce Wiegmann, leading engineer on the project.

“The E-Sail would use these protons to propel the spacecraft.”

Each tether would be just one millimetre thick but about 20 kilometres long.

The spacecraft would rotate at one revolution per hour, with centrifugal forces stretching the wires into position.

The craft would be steered by modulating each wire’s individual voltage, altering the force applied to different portions of the E-Sail.

The tests in the High Intensity Solar Environment Test system, at NASA’s Marshall Space Flight Center in Huntsville, Alabama, are designed to discover the rate of proton and electron collisions with a positively charged wire.

A charged stainless steel wire will be placed in a controlled plasma chamber simulating plasma in a space to mimic how the aluminium wire would behave in space.

Engineers will use the data to improve their models that will then be scaled up.

Scientists expect the system to be very fast. It took NASA’s Voyager 1 spacecraft 35 years to reach the heliopause (the edge of the bubble of space dominated by the Sun), HERTS could make the trip in less than a third the time.

“Our investigation has shown that an interstellar probe mission propelled by an E-Sail could travel to the heliopause in just under 10 years,” Wiegmann says.

“This could revolutionise the scientific returns of these types of missions.”

But the E-Sail could be used for shorter distances too.

“As the team studied this concept, it became clear that the design is flexible and adaptable,” said Wiegmann.
“Mission and vehicle designers can trade off wire length, number of wires and voltage levels to fit their needs – inner planetary, outer planetary or heliopause. The E-Sail is very scalable.”

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