Alternate Propulsion Technologies and Methods
Figure 26: Artist’s concept of the use of a solar sail above the Earth’s surface (NASA, 2011).
Several types of propulsion methods are not examined within this essay. As the conditions for viability reside upon the ability of a propulsion system to transport high mass payloads over interplanetary distances within a reasonable time frame, multiple propulsion systems are either inherently or currently unable to meet these constraints. Examples of inherently unviable systems include chemical thermal combustion rockets; these propulsion systems, which have extremely high thrust levels and thrust to weight ratios, have abysmally low exhaust velocity and Isp levels. Unless massive changes occur within the design and performance of these systems, they will remain unviable for the applications this report assesses. Other propulsion systems not fully analyzed includes field propulsion technologies. These systems utilize intrinsic space phenomenon for use as propulsion; a primary example of this technology is the solar sail. Using photonic energy emitted from the sun, the sail refracts the force of the photons and converts the kinetic energy into propulsion (NASA, 2011). Alternate forms of sail type propulsion include magnetic and electric sails; the former utilizes superconducting magnets to form a virtual sail, reflecting charged solar particles and providing propulsion, while the latter uses long tendrils of electric wires to generate an electric field, and is propelled by the momentum of the solar wind (Finnish Meteorological Institute, 2010; Janhunen, 2010; Zubrin & Martin, 1999). While requiring no fuel, the miniscule amount of thrust provided, in addition to the theoretical concept, low payload mass, and unacceptable transit durations, results in the unviability of this system. Alternative forms of propulsion systems not included are speculative or unproven theoretical propulsion methods. An alternate type of field propulsion relies upon an unsubstantiated theoretical effect, but it, and other such unproven concepts including warp, diametric, and disjunction drives, are not included due to complete current and near future inoperability.