A new concept, the magnetic sail, or "magsail," which propels spacecraft by using the magnetic field generated by a loop of superconducting cable to deflect interplanetary or interstellar plasma winds, is proposed. The performance of such a device is evaluated using both a plasma particle model and a fluid model, and the results of a series of investigations are presented. It is found that a magsail sailing on the solar wind at a radius of one astronautical unit can attain accelerations on the order of 0.01 m/s 2 , much greater than that available from a conventional solar lightsail, and also greater than the acceleration due to the sun's gravitational attraction. A net tangential force, or "lift," can also be generated. Lift-to-drag ratios of about 0.3 appear attainable. Equations are derived whereby orbital transfers using magsail propulsion can be calculated analytically. It is found that a magsail can transfer payloads to and from any two circular orbits in the solar system in a flight time slightly larger than the Hohmann ballistic transfer time. The magsail can accomplish these missions at any time, unrestricted by the usual ballistic transfer launch window. The necessary magsail/payload mass ratios are less than 0.15.
NomenclatureA = cross-sectional area of magsail wire, m 2 a = semimajor axis of magsail orbit, a.u. B m = magnetic field at the magsail center, T B 0 = ambient interplanetary magnetic field, T C = characteristic radius of magsail action, m D = drag force exerted by plasma wind on magsail, N d = diameter of magsail wire E = canonical energy of magsail orbit e = eccentricity of magsail orbit h -canonical angular momentum of magsail orbit / = magsail loop current, A / = magsail loop current density, A/m 2 L -lift force exerted by plasma wind on magsail, N M = mass of magsail, kg P = Semilatus rectum of the magsail orbit, a.u. P m -magnetic pressure of the magsail field, Pa P mb = magnetic pressure at the magnetosphere boundary, Pa R c -collection radius of the magsail, m R m = radius of the magsail loop, m R s = radius of spacecraft from sun, a.u. RQ = initial diplacement of proton off magsail axis, m t -time of flight of magsail orbit, l/2v yr V = velocity of the plasma wind, m/s V x = velocity of proton parallel to magsail loop axis, m/s V y = velocity of proton perpendicular to magsail loop axis, m/s V sc -velocity of magsail spacecraft, 2?r a.u./yr W = magsail spacecraft weight ratio a.= fraction of sun's gravitational attraction felt by magsail spacecraft > = polar angle off dipole axis 0 .= true anomaly of magsail spacecraft within its orbit p = density of the plasma wind, kg/m 3 p m = magsail loop mass density, kg/m 3 0 = angle between plasma freestream and the normal to the magnetospheric boundary