The Microwave Thermal Thruster and its application to The Launch = problem :-) This document contains a vast wealth of related rocketry material and = I recommend skimming it to anyone with any interest in rocketry. Kevin Parkin's PhD thesis on using ground based microwave phased array = energy sources to send a Hydrogen "fuel" based craft to orbit. Calculated Isp (figure of merit) * is around 825 seconds - compared to = eg a figure of about 450 seconds for the Space Shuttles main engines = and about 260 seconds for the Shuttle's Solid Rocket Boosters. A = significant factor in the Isp improvement is that half the fuel supply = stays at home and is functionally delivered to the rocket's hot end by = microwave beam. Summary page http://etd.caltech.edu/etd/available/etd-06022006-160023/ 40 MB PDF / 261 pages. http://etd.caltech.edu/etd/available/etd-06022006-160023/unrestrict= ed/Parkin-Thesis.pdf Isp =3D specific impulse =3D kg.force x seconds thrust achievable per = kg.mass of propellant. Cancelling kg.f with kg.m gives units of = seconds. Bitter arguments rage about the legitimacy of doing this. = Doing otherwise leads to an equally good figure in velocity units and = g bigger (g =3D gravitational constant in m/s/s or units of your = choice). Truth be know seconds is actually an entirely legitimate unit = and it's just that nobody has properly interpreted the meaning of the = expression (and nobody ever listens when i explain it to them :-) ). = Think of it as the number of seconds for which a unit mass of = propellant can produce a force that cancels it's own "weight" in a = convenient reference gravity field. Abstract Nuclear thermal thrusters long ago bypassed the 50-year-old specific = impulse (Isp) limitation of conventional thrusters, using nuclear = powered heat exchangers in place of conventional combustion to heat a = hydrogen propellant. These heat exchanger thrusters experimentally = achieved an Isp of 825 seconds, but with a thrust-to-weight ratio = (T/W) of less than ten they have thus far been too heavy to propel = rockets into orbit. This thesis proposes a new idea to achieve both high Isp and high = T/W: The Microwave Thermal Thruster. This thruster covers the = underside of a rocket aeroshell with a lightweight microwave absorbent = heat exchange layer that may double as a re-entry heat shield. By = illuminating the layer with microwaves directed from a ground-based = phased array, an Isp of 700=96900 seconds and T/W of 50=96150 is possible = using a hydrogen propellant. The single propellant simplifies vehicle = design, and the high Isp increases payload fraction and structural = margins. These factors combined could have a profound effect on the = economics of building and reusing rockets. A laboratory-scale microwave thermal heat exchanger is constructed = using a single channel in a cylindrical microwave resonant cavity, and = new type of coupled electromagnetic-conduction-convection model is = developed to simulate it. The resonant cavity approach to small-scale = testing reveals several drawbacks, including an unexpected oscillatory = behavior. Stable operation of the laboratory-scale thruster is = nevertheless successful, and the simulations are consistent with the = experimental results. In addition to proposing a new type of propulsion and demonstrating = it, this thesis provides three other principal contributions: The = first is a new perspective on the launch problem, placing it in a = wider economic context. The second is a new type of ascent trajectory = that significantly reduces the diameter, and hence cost, of the = ground-based phased array. The third is an eclectic collection of = data, techniques, and ideas that constitute a Microwave Thermal Rocket = as it is presently conceived, in turn selecting and motivating the = particular experimental and computational analyses undertaken. -- = http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist