Revolutionary Space Transportation System Begins Testing

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Forget Solar Sails -- Try an E-sail Instead 

​It's one of the biggest problems in space transportation ...

Time.

It takes a lot of time for conventional, chemical rockets to get to where they are going.

For example, just to get to Mars, low energy Hohmann transfer orbits can take seven months or more for spacecraft to reach their target.

And the outer ​solar system?

Cassini, a probe sent to Saturn in 2004, took four years to reach that planet.​

Voyager 1 took over 35 years -- 35 years! -- to travel through the heliopause, about 100 times the distance from the sun as the Earth,  before it eventually passed into interstellar space in 2012. 

That's a problem. One that NASA has been trying to solve for decades.

Ion engines. Nuclear Thermal Rockets.​ Even solar Sails. All have been studied as ways to improve space transportation speeds

But a new concept may provide a revoutionary solution.​

Testing has started at NASA’s Marshall Space Flight Center in Huntsville, Alabama, on the Heliopause Electrostatic Rapid Transit System (HERTS), a propellant-less E-Sail propulsion system, that would harness solar wind to travel into interstellar space.

Unlike the more commonly known Solar Sail, which uses sunlight for propulsion, the E-Sail would actually harness the eletrostatic charge of the solar wind - the protons and electrons, in other words.

As Bruce Wiegmann, an engineer in Marshall’s Advanced Concepts Office and the principal investigator for the HERTS E-Sail stated:

The sun releases protons and electrons into the solar wind at very high speeds -- 400 to 750 kilometers per second.  The E-Sail would use these protons to propel the spacecraft.

The spacecraft would have 10 to 20 electrically charged, bare aluminum wires that would extend radially from the center of the vehicle and essentially produce a large, circular E-Sail that would electrostatically repel the fast moving protons of the solar wind.

As the protons are repelled by the positively charged wires, they would impart momentum to the spacecraft and create thrust.

Each tether is extremely thin, only 1 millimeter -- the width of a standard paperclip -- and very long, nearly 12 and a half miles -- almost 219 football fields. As the spacecraft slowly rotates at one revolution per hour, centrifugal forces will stretch the tethers into position.

As a result, the sail would have an effective area of about 232 square miles, slightly smaller than the city of Chicago. The effective area would increase to more than 463 square miles-- similar to Los Angeles -- at 5 AU - or about the distance of the asteroid belt from the Sun.

Why an E-sail and not just a Solar Sail?

Well, solar sails work through the interaction of photons -- not protons. At 5 AU, the energy of the solar photons dissipates and solar sails would no longer be accelerate.  The protons and electrons that make up the solar wind, however, keep going.

As a result, Wiegmann believes the E-Sail would continue to accelerate well beyond that distance and into deep space. As he said:

The same concerns don’t apply to the protons in the solar wind. With the continuous flow of protons, and the increased area, the E-Sail will continue to accelerate to 16-20 AU -- at least three times farther than the solar sail. This will create much higher speeds.

That means a journey like the one Voyager 1 took  -- a 35 year jaunt to travel 121 AU before reaching interstellar space - could be reached in as little as ten years.

Which is what makes this such a revolutionary space transportation system.

According to Wiegmann:

Our investigation has shown that an interstellar probe mission propelled by an E-Sail could travel to the heliopause in just under 10 years. This could revolutionize the scientific returns of these types of missions.

The whole idea builds upon the electric sail invention of Dr. Pekka Janhunen of the Finnish Meteorological Institute. The current technologies required for an E-Sail integrated propulsion system are in their infancy, but if the results from plasma testing prove promising, follow on projects could be funded.

To help explain the idea, the team produced this short animation​:

The Testing

The testing, which is taking place in the High Intensity Solar Environment Test system, is designed to test the viability of this idea by looking at the rate of proton and electron collisions with a positively charged wire.

Within a controlled plasma chamber simulating plasma in a space, the NASA team is using a stainless steel wire as an analog for the lightweight aluminum wire. Though denser than aluminum, stainless steel’s non-corrosive properties will mimic that of aluminum in space and allow more testing with no degradation.

In addition to measuring how much the wires will deflect as they are hit by the protons, Engineers are also measuring the build up of electrons that would be attracted to the wire.

That build up can be a problem, so there needs to be a way to discharge the elecrons to maintain the correct electrical charge on the tethers. 

The earliest actual use of the technology is probably at least a decade away, though, so it will still be a while before you will see this revolutionary space transportation system in action.

Ahhh - Time.​

For more information on the Heliopause Electrostatic Rapid Transit System, visit:

http://www.nasa.gov/feature/heliopause-electrostatic-rapid-transit-system-herts

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