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

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The concept of a coherent Space Exploration Initiative (SEI) architecture is defined and is shown to be largely unsatisfied by the conventional Earth-orbital assembly/Mars orbital rendezvous mission plan that has dominated most recent analysis. Coherency's primary requirements of simplicity, robustness, and cost effectiveness are then used to derive a secondary set of mission features that converge on an alternative mission architecture known as "Mars Direct.

The planet Mars, while cold and arid today, once possessed a warm and wet climate, as evidenced by extensive fluvial features observable on its surface. It is believed that the warm climate of the primitive Mars was created by a strong greenhouse effect caused by a thick CO 2 atmosphere. Mars lost its warm climate when most of the available volatile CO 2 was fixed into the form of carbonate rock due to the action of cycling water. It is believed, however, that sufficient CO 2 to form a 300 to 600 mb atmosphere may still exist in volatile form, either adsorbed into the regolith or frozen out at the south pole. This CO 2 may be released by planetary warming, and as the CO 2 atmosphere thickens, positive feedback is produced which can accelerate the warming trend. Thus it is conceivable, that by taking advantage of the positive feedback inherent in Mars' atmosphere/regolith CO 2 system, that engineering efforts can produce drastic changes in climate and pressure on a planetary scale.

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