NASA has started work on a giant solar sail, which would use electrically charged protons from solar wind to reach enormous speeds – and make interstellar travel a reality.
The unmanned E-Sail (electric sail) concept is called the Heliopause Electrostatic Rapid Transit System (HERTS), with the “heliopause” part referencing the outer regions of the Solar System where the Sun’s influence ends and interstellar space begins – a region the Voyager spacecraft has taken more than three decades to reach. HERTS, measuring a huge 40 kilometers (25 miles) across, would cut the journey to a third of 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,” said NASA engineer Bruce Wiegmann, principle investigator for the HERTS E-Sail, in a statement. “This could revolutionize the scientific returns of these types of missions.”
Now, you’ve probably heard of solar sails before. Japan launched its Ikaros test back in 2010, while The Planetary Society flew its own LightSail design last year. But this concept is slightly different.
Regular solar sails merely use the pressure of the solar wind to generate thrust. While this provides for continual acceleration over long periods of time, at large distances from the Sun – beyond the asteroid belt at 5 AU (astronomical units, 1 AU is the Earth-Sun distance), for example – the rate of acceleration becomes tiny.
The E-Sail differs in that it uses the electrical charge of the protons, rather than their momentum, to generate thrust. “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,” said Wiegmann. “This will create much higher speeds.”
Check out a video explanation of HERTS above.
To harness these protons, HERTS will use 10 to 20 large tethers that are each just 1 millimeter thick but 20 kilometers (12.5 miles) long, expanding from a central point and giving it a total span of 40 kilometers (25 miles). These bare aluminum wires would electrostatically repel the Sun’s protons, creating a small amount of thrust that will accumulate over time in the frictionless environment of space. At the center would be the instrumentation and other equipment of the actual spacecraft.
Of course, the solar wind only flows in one direction, so this would likely be just a one-way mission. But using this method, HERTS could achieve speeds of up to 150 kilometers (90 miles) per second, or 30 AU per year, letting it explore the far reaches of the Solar System in years rather than decades.
If may all sound a bit fanciful, but NASA has now started testing the concept at its Marshall Space Flight Center in Huntsville, Alabama. The tests will study the rate of proton and electron collisions in an electrically charged wire, to see how much thrust could be produced by the E-Sail in space.
HERTS was initially funded through the NASA Innovative Advanced Concepts Program (NIAC) in 2014, a program that acts as a testbed for futuristic proposals. And now, thanks to continual funding, the project could soon see some positive results.
A tentative timeframe suggests HERTS could launch between 2025 and 2030, giving us a brand new way to rapidly explore the outer reaches of the Solar System – and beyond.