Researchers are developing an e-sail propulsion system that could harness solar winds to propel space ship by 2025
This technology would harness the solar wind, streams of protons and electrons, and other charged particles that flow outward from the sun at more than one million mph (1.6 kilometers per hour). Using a large enough sail, the technology would provide thrust from the pressure of the sunlight with absolutely no need for fuel.
“It looks really, really promising for ultra-deep-space exploration,” says Les Johnson on NASA’s Marshall Space Flight Center in Huntsville, Alabama. Johnson is a co-principal investigator of the Heliopause Electrostatic Rapid Transit System (HERTS). The HERTS is an e-sail study and development project that has received two rounds of funding from the NASA Innovative Advanced Concepts (NIAC) program. The team also consists of Pekka Janhunen of the Finnish Meteorological Institute, who was one of the first to formulate the e-sail concept in 2006.
The design in question would consist of 10 to 20 wires that are each o.6 miles to 12 miles long. These wires would be extremely thin at just 25 microns in diameter (for comparison sake, a human hair is about 50 microns wide). The probe itself would be prompted to continually rotate to ensure that the wires stay taut.
A high-voltage, positive bias on the wires, which are oriented normal to the solar wind flow, deflects the streaming protons, resulting in a reaction force on the wires — also directed radially away from the sun. Over periods of months, this small force can accelerate the spacecraft to enormous speeds — on the order of 100-150 km/s (~ 20 to 30 AU/year).
One AU (astronomical unit) is equivalent to the distance from Earth to the sun. Or about 93 million miles. The furthest distance a human-made object has travelled is 134 AU since blasting off in 1977; NASA’s Voyager 1 entered interstellar space in 2012 and is powered by chemical thrusters.
The e-sail concept is similar to solar sailing, a technology that has already been demonstrated in space. Neither of these technologies require any fuel, but solar-sailing harnesses the suns radiation rather than the solar wind. Additionally, solar sailing deploys sails of highly reflective material, as opposed to electrically charged wires. It’s estimated the the e-sail can far surpass solar-sailing technologies; where solar wind can hit interstellar space in just 10 years, twice as fast as the capability of the solar-sail.
Feasibility remains a concern for the e-sail. It’s not 100% clear whether a probe would need to be equipped with special devices to keep it’s wires positively charged, nor is the team sure of how much energy it would require just to accomplish these results. Some models suggests it’s a reasonable amount and the other implies that there’s no realistic way to generate that much energy onboard.
The HERTS team will be conducting plasma-chamber tests to get to the bottom of this issue within the next year. These tests should help to prove a model that best represents reality. If that reality proves positive, we may say e-sail propelling spacecraft sooner than we think.
The proposed HERTS can provide the unique ability to explore the heliopause and the extreme outer solar system on timescales of less than a decade. It is significantly more effective than any other near-to-mid-term propulsion system for deep-space missions, meshes well with heliospheric science payloads, and could be implemented in the 2025-2030 timeframe.
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