The Magnet Sail By Connor O’Keefe Manned interplanetary travel is a project which has retained the interest of the world for several decades now. However, organizations are hesitant to embark on such a journey because of cosmic radiation. The effects of this radiation are mysterious, and nobody is willing to risk lives on a multi-month mission to another planet such as Mars with such little knowledge of the obstacle. The use of a plasma magnet sail is an effective way to bypass this obstacle, due to its energy efficiency and high-speed capability. The basic idea of the plasma magnet sail is to use a vast to receive momentum from and other charged particles to accelerate. This approach is highly cost-effective since great speeds can be reached with the input of relatively small amounts of power. This paper is meant to summarize in part John Slough’s paper discussing the plasma magnet and its capabilities. It is highly condensed in favor of simplicity and conciseness, and it is directed to students and professionals interested in the concept of fast interplanetary travel. Technological Overview A magnetic is a conceptual design for much like a sailboat. The wind is analogous to the charged particles from the and the sail is analogous to the magnetic field induced by a current. The plasma magnet sail is based on the concept of the , however there are a few key differences. The plasma magnet sail requires no added current, theoretically requires no propellant, and most importantly it requires less mass to build. This overview will give a sense of how it works and why it is so important. The Plasma Magnetic Rotor The plasma magnet rotor uses two pairs of polyphase coils (shown in blue and red) which utilize an alternating current (AC) to create a rotating magnetic field (RMF). The AC excites plasma in the RMF which interact with ions that move through the field. This interaction between electrons and ions is what allows the conversion of electrical power to mechanical work. This can be used to create thrust as charged particles (e.g. solar winds) pass through the field.

Figure 1 – Laboratory build (left) and computer Figure 2 – The polyphase coils create a rotating model (right) of what this looks like magnetic field The Traditional Magnetic Sail Figure 3 - Traditional MagSail A spacecraft can utilize a magnetic field to create thrust with ridiculously small amounts of energy, allowing the creation of craft with very high thrust-to-weight ratios. A traditional magnet sail is formed by antennae which extend out in front of the craft, using a current to create a magnetic field that interacts with charged particles coming from behind. It not only enables the craft to accelerate forward quickly, but also backward, allowing the craft to slow down. The method for doing this is explained in the stopping section. Why the Plasma Magnet Sail is Different With a plasma magnet, there is no need for an applied current since the current is induced by the RMF itself. This is important because it allows the creation of a virtually massless sail which is made of solar wind “trapped” by the magnetic field (Figure 4) instead of bulky metal wire sails that carry a current. For one, it minimizes the use of fuel, which makes it a desirable option for an engine. In addition, the magnetic field can be much larger than the motor which it is created by. These are the key innovations presented by this method. The experiments in Slough’s paper show that the size of the magnetic field is inversely proportional to the pressure from solar particles. Therefore, the force from the passing particles is constant even as a hypothetical spacecraft moves away from the sun. This is what gives a spacecraft utilizing this technology the ability to accelerate to such high speed. Figure 4 - Plasma Magnet Sail In addition, the plasma magnet in theory requires no propellant, unlike a classical magnetic sail which requires an applied electrical current to work. Because the Earth’s magnetosphere deflects solar winds, a spacecraft using this technology would need to be orbiting past the moon’s orbit to use the solar wind as propulsion. The spacecraft would then be able to travel outward, following the output of solar wind. An optimal orbit transfer would enable a spacecraft to travel to Mars in a week (Greason) and would allow speeds of up to 0.2% of the speed of light during interstellar transfer.

Mission Logistics The plasma magnet sail has quite a few applications, such as fast travel within the Earth’s magnetosphere, to asteroids, to the Oort cloud, or even to Alpha Centauri. For the purposes of this explanation, it will be used for a mission to Mars. Because the main concern when discussing a Mars mission is cosmic radiation, the fact that the sail enables a week-long trip to Mars is an effective motive for the application of this sail. Cosmic Radiation The plasma magnet sail overcomes the effects of cosmic radiation with its ability to speed through hostile interplanetary space. Since the sail would be able to accelerate using the Earth’s magnetosphere, it can reach high speeds before it even leaves the protection of the magnetosphere. Stopping Another issue that comes to mind is stopping such a fast spacecraft. It is obvious that the sail would be viable on its own for stopping during interstellar travel due to its ability to receive opposing thrust from the destination star. But the method for stopping without the help of another star is not as simple. Jeff Greason proposed a solution to this issue: To use particle beams aimed at the magnetic field to slow the spacecraft down. This would require the installation of a particle beam using matter from the destination to shoot at the incoming spacecraft’s magnetic field. In the case of a Mars mission, particle accelerators could be installed on either Phobos or Deimos, extracting matter from them and shooting it at the spacecraft’s magnetic field to slow it down. This would not be very difficult to aim, since at this point the magnetic field would be hundreds of thousands of miles in diameter. The beam would need to shoot matter equal to the mass of the spacecraft in order to slow it to a reasonable speed, so depending on the mass of the spacecraft and the size of the body being exploited for matter, this may or may not be viable. Works Cited Slough, John “The plasma magnet” (2006). NASA Institute for Advanced Concepts Phase 1 Final Report. Greason, Jeff “Missions Enabled by plasma magnet Sails”, Presentation at the Tennessee Valley Interstellar Workshop, 2017. https://www.youtube.com/watch?v=0vVOtrAnIxM Gilster, Paul “The Plasma Magnet Drive: A Simple, Cheap Drive for the Solar System and Beyond”, Centauri Dreams - Imagining and Planning Interstellar Exploration, https://www.centauri-dreams.org/2017/12/29/the-plasma-magnet-drive-a-simple- cheap-drive-for-the-solar-system-and-beyond/ Figure 1, 2, 3 – Slough, John Figure 4 – Gilster, Paul