Next-generation spacecraft sailing to interstellar space may soon rely on harnessing solar wind to produce momentum, as scientists from NASA begin experimentations in Alabama for an advanced propulsion system.

Designed for very long distance missions, NASA's HERTS E-sail technology (Heliopause Electrostatic Rapid Transit System Electric Sail) can potentially halve the time it takes for spacecraft to go into interstellar space. It could send spacecraft even to the "edge" of our solar system, known as the Heliopause, at a speed faster than ever.

After initial trials are over, the University of Alabama in Huntsville (UAH) will use computer models to examine NASA's results.

How the E-sail Technology Works

The E-sail propulsion system is expected to consist of at least 10 electrically charged, bare aluminum wires that radiate from the inside of the spacecraft to make a circular "E-sail."

Lead E-sail engineer Bruce Wiegmann said the sun ejects electrons and protons into the solar wind at very high speeds of up to 750 kilometers per second (approx. 1.6 million miles per hour), and they will take advantage of this solar power.

The E-sail's special wires are capable of electrostatically repelling rapid-moving protons of the solar wind, with the momentum acting as the spacecraft's thrust. Each tether would only be one millimeter (0.039 inch) thick but 20 kilometers (12.42 miles) in length.

"The E-Sail would use these protons to propel the spacecraft," said Wiegmann.

Spacecraft with the E-sail would be able to rotate at one revolution per hour, with centrifugal forces expanding the special wires into position. It would then be navigated by controlling each wire's voltage, changing the force applied to different portions of the propulsion.

The tests at the Marshall Space Flight Center in Huntsville will try to discover the rate of electron and proton collisions with a positively charged wire.

Implications for the Future

NASA's Voyager mission is currently exploring the interstellar medium. The use of the E-sail technology could become a breakthrough for these kinds of "ambitious missions," said UAH scientist Gary Zank.

Astronomers expect the new propulsion system to be expeditious. Voyager 1 took 35 years to reach the Heliopause, but HERTS E-sail could do it in a shorter amount of time. Wiegmann said their investigations reveal that spacecraft with E-sail could travel to the Heliopause in just 10 years.

"This could revolutionize the scientific returns of these types of missions," said Wiegmann.

What's more impressive is that the propulsion system could be used for shorter missions, too. Wiegmann said the design is extremely flexible and adaptable. It could be used for missions in the Heliopause, within the inner interplanetary system, as well as on the outer interplanetary, he added.

The HERTS study was funded in 2015 by the Space Technology Mission Directorate (STMD). It was one of the Phase II NASA Innovative Advanced Concepts (NIAC) projects.

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