A motor failure, generally explosive, where all the propellant is burned in a much shorter time than planned. This can be a nozzle blow-out (loud, but basically harmless), an end-cap blow-out (where all of the pyrotechnic force blows FORWARD which usually does a pretty good job of removing any internal structure including the recovery system) or a casing rupture which has unpredictable, but usually devastating, effects. Another form of CATO is an ejection failure caused by either the delay train failing to burn or the ejection charge not firing, but the result is the same the model prangs. A CATO does not necessarily burn all of the fuel in a rocket motor (especially true for composite fuels, which do not burn well when not under pressure). For this reason you should be especially careful when approaching a CATO. Origin Opinions on the meaning of the acronym range widely. Some say it's not an acronym at all, but simply a contraction of 'catastrophic' and should be pronounced 'Cat-o' (which sounds better than 'cata' over PA systems -). Others maintain that it is an acronym but disagree on the meaning, offering a broad spectrum of 'CAtastrophic Take Off,' 'Catastrophically Aborted Take Off,' 'Catastrophe At Take Off' and the self referential 'CATO At Take Off.' The acronym crowd pron In Hobby Rocketry, any propellant other than black powder. In military parlance (where the term originated) the term is used to denote propellants that are mixtures of oxidizers and fuels and to distinguish them from Single, Double, and Triple base propellants (which are either monopropellants or mixtures of monopropellants). Note that by the military definition, black powder is itself a composite propellant because it consists of separate oxidizers (KNO3 and sulfur) and fuel (charcoal). Further note that by the hobby definition, single/double/triple base propellants are composites because they are not black powder. No ambiguity arises, however, since the military doesn't use black powder (in rockets, anyway), and no hobby rocket motors use single, double or triple base propellants. See also "Single Base Propellants", "Double Base Propellants" and "Triple Base Propellants" For any given motor and Drag Form Factor (q.v.) the liftoff mass for which a rocket will reach maximum altitude in dense atmosphere. At first this might seem to be just the lowest possible mass, but there is a two edged nature to mass covering both powered flight and coasting. Lower mass will give higher burnout velocity, but will dissipate its momentum to drag faster (think of a feather). Conversely, a heavier rocket will have more momentum at burnout to coast farther, but too much mass will hold down both burnout altitude and velocity. Hence, there is a "knee" on the liftoff mass vs. altitude graph. For very low impulse motors (say "B" and below) this "knee" is right around the mass of the motor itself, so the rule of thumb is "the lighter the better." The higher impulses, though, have more leeway, and careful calculations should be made to determine the optimum mass for altitude attempts. In a multi-stage rocket with no staging delays, only the dead mass in the upper stage participates in coasting. Extra dead mass in lower stages cannot enhance coast distance, and so lower stages should be as light as possible. Strictly speaking, an undelayed staged rocket has no optimum liftoff mass, but the mass of the last stage may be optimized with respect to the(sub-optimal) lower stages. In dense atmosphere, the best single stage configuration is more efficient than the best multi stage configuration, provided all the propellant can be contained in one stage. Indeed, there are many instances when cluster rockets out perform staged rockets. The opposite is true for rockets operating in the thin atmosphere of high altitudes. In that environment, staged rockets are more efficient (propellant-wise) than single-staged rockets, and lighter rockets always perform better. There is no optimum mass in a complete vacuum. A dimensionless number used by fluid flow engineers to characterize the way a fluid (gas or liquid) will behave when passing over a solid surface. The number combines the fluid's density, viscosity and velocity with the length it's traveled along the surface. No matter what the fluid is or what size the surface, the flow conditions (laminar, turbulent, detached, etc.) should be the same at the same Rn. Discovered by Osborne Reynolds inthe 19th Century while studying the flow of water in pipes andchannels, it has proven most useful to aerodynamic engineers and naval architects in scaling up wind/water tunnel test results to full size. Carl Dowd, a model aviator and NASA engineer, found it helpful to think of Rn as the "coarseness" of the air seen by a body. Move the body faster, and more particles will pass over it in a given unit of time, increasing Rn. Make the body larger, and there will be more particles over the body at any instant, increasing Rn.