Why are jet aircraft more common than rocket aircraft?
Rockets are currently extremely expensive to operate, limiting their applications to specialized fields such as space and orbital work. A much larger market is available once a rocket's operational cost can be lowered. For example a small aircraft capable of flying people from Chicago to Beijing in 45 minutes would appeal to a large market if available at reasonable costs.
A rocket propelled aircraft's costs are primarily related to complexity and size. The smaller a rocket, the less it costs to develop and fly. This cost decrease is due largely to a decrease in complexity, but also due to a decrease in the worst case disaster severity; the safety requirements for a 747 are much larger than those of a Cessna two seater.
Added complexity increases cost exponentially as each part needs to be designed, tested, and maintained in relation to all the other parts. If the heat shielding is too massive, you need more propellant, which cascades to larger engines, bigger wings, etc. leading to a still larger heat shield. So in addition to a lower parts count, the parts should be less interrelated to achieve lower costs.
Solid rockets are by far the simplest forms of rockets. They do not require finely tuned injectors, propellant mixing, pumping, storage and movement in tanks, hard starts, etc. Historically, solid rockets have been held back by their lower performance - primarily due to the entire propellant supply being necessarily contained inside the engine itself. Solid rockets typically also have lower Isp (a measure of engine propellant efficiency) than liquid propellants, and so higher mass fractions are required to achieve the same engine work.
Our new technologies allow for extreme improvements in the mass fraction of solid rocket engines, decouples the propulsion system design from the rest of the vehicle, while increasing safety and not greatly increasing the complexity of the rocket engine. The propellant can be stored indefinitely, and relatively inexpensive operations are possible.
Our Approach
The Universal Transport Systems' patent-pending approach is to use a pump to take solid propellant, pump gas generators, and coolants from low pressure outside the engine to the high pressure inside the engine. This is done in a way that virtually eliminates the normal problems of pump parts wearing out. Furthermore, solid propellant does not require tanks to maintain shape at low pressures, so tank mass is completely eliminated. Solids also can be shaped to provide aerodynamic lift while outside the engine, eliminating some of the thrust required to simply stay in the air. In this case the propellant is towed behind the aircraft - towing requires 1/10 the engine power of vertically lifting the propellant.
Safety is also increased. First, because of the dramatic mass savings, high safety factors may be used in the engine designs. Instead of the normal 1.5 factor of safety, a factor of 3 is used. The propellant has a greatly reduced probability of fire or explosion because the propellant is kept external to the engine at ambient pressure (most good solid rocket fuels are not very flammable at normal pressures). Also, if the engine stalls the propellant is immediately ejected from the rocket, either by residual pressure in the engine chamber or by drag forces on the propellant still external to the craft (there is nothing holding the fuel inside the engine other than the injector pressure). This makes concentrating on the survival of the pilots, particiants and payloads much easier. Finally, in the extreme event that something unexpected does happen to the propellant, most of it is hundreds of meters away from the aircraft and unable to cause damage or injury to things inside the aircraft.
This new technology enables extremely large mass fractions. Using a safety factor of 3 times the yield strength in titanium, a design mass fraction of 100 has been achieved - the rocket engine could carry 100 times its mass in propellant. Assuming an average Isp of 250 seconds, this would allow a maximum velocity change of more than 11,000 m/s - allowing flight to any point on the globe, without staging.
Another advantage of this system is that the heat shield and aerodynamic qualities of the aircraft are decoupled from the propulsion system. When the propellant is used up or is ejected by stopping the engine, it needs no heat shield as no tank remains behind. The wings do not need to provide enough lift to lift the propellant load, because it can have a useful lift to drag ratio. Control surface authority is not impacted by the propellant loads because the propellant is never present during unpowered flight. During powered flight the propellant hangs from the engine and so does not affect aerodynamic controls. Another seldom considered advantage is that during takeoff the propellant is not supported by the wings or the wheels - so the landing gear, wings, and brakes can be sized for the aircraft weight, not the propellant weight.
Enabling Smaller Rocket Aircraft
Until now, useful rocket powered aircraft had a very large minimum size - the fuel tanks simply could not be made efficiently when small. Because of this technology, a smaller rocket powered light aircraft is possible. This puts high performance rocket powered aircraft in the reach of a privately funded startup like Universal Transport Systems, and greatly reduces the cost of the smallest useful aircraft.
