General tendencies of development in rocket propulsion.

Advanced flight propulsion technology is in an important transition – from chemical to nuclear energy.

Twenty years from now most space vehicles should be nuclear powered and nuclear engines will probably be widely used in the atmosphere as well on both aircraft and missiles.

Mean while chemical rockets will carry major operational burden of powering space vehicles and missiles for a list ten years, and they are entering their, most promising era. Operationally, the record of chemical-fuel rocket engines gets better every year, engine costs go down in many ways, reliability goes up, and general confidence increases. New designs, the logical extension of existing types, will be lighter, simpler, and more compact.

One important new design area in liquid rockets is new shares and arrangements of nozzles and combustion chambers.

New materials, higher operating pressures, and new propellants such as liquid hydrogen all are contributing to higher-performance engines. Significant progress has been made is development of storable, liquid-propellant engines hermetically sealed, instantly ready for use after long periods of coasting in space or storage on the ground.

Liquid rockets. Which up to now have been a maze of valves, pumps, sensors, and pipes, are being greatly simplified.

The number and variety of new developments with solid-propellant rockets are even greater that in liquid-engine design. The high reliability already demonstrated by solid rockets is cited as a major reason why they make good boosters for large space payloads. In general, the take off groups weight of any space vehicle would be considerably larger if it were powered by solid-fuel rockets rather than liquid-fuel rockets. Even so, the total cost of boosters operations might well be lower if the solid engines were employed.

Very large total weights have been proposed for some solid-fuel boosters systems, such as fourteen million pounds and more to put a 250,000-pound payload in orbit.

Under most schemes solid-fuel rockets delivering from 400,000 to one million pounds thrust would be clustered to form the large boosters, and three or four stages would be required to form an adequate vehicle. Each of the engines in the clusters would be more than six feet in diameter and probably fifty feet or so in length. The development of engines in the million and multimillion pounds trust category is of particular significance in view of the research work on missiles with antipodal capabilities and the plants for the military use of space.

The solid rockets used in very large boosters would probably be of relatively conservative design. Beyond these, smaller, higher-performance engines are also under development. They result primarily from improvements in two areas – higher-energy propellants and lighter-combustion cases, nozzles, thrust termination devices, and other items which make up the empty weight of the engine. The spherical engine geometry will provide the lightest engine for any given structural material, and engines of this sphere are being tested. Many different kinds of materials are being investigated in an effort to lower the weight of solid rockets cases, including steel wire plastics, die steel, glass filament, and many others.

Major performance improvements are also predicted by engineers working with hybrid rockets, using both liquid and solid propellants. The so-called tri-propellant hybrids are credited by some researches with about seventy five per cent of the performance potential of the nuclear rocket, while high-energy liquid-fuel rockets using liquid hydrogen have about fifty percent of its potential. The tri-propellant hybrid engine operation in its simplest form consists of adding hydrogen or some light gas to the exhaust flow of a solid-fuel rocket to lower its molecular weight. The lowering of the molecular of the particles in the exhaust flow is a powerful tool for increasing the specific impulse of the propellant. When the specific impulse increases, the total thrust produced by a given weight propellant will increase and the performance of any given vehicle will improve. It can carry more weight or its final speed can be raised.