Limiting factors in air and space propulsion systems affect both design and operation of the engines and the energy derived from a fuel source. Translation of the fuel source to energy (combustion) always requires an oxidizer. The process of breaking the energy-laden bonds of the fuel has classically been achieved using the oxygen in air for air-breathing engines or an onboard source of oxidizer for spaceflight. This is a critical limitation for a possible single-stage vehicle, because the weight of the fuel and oxidizer needed to achieve the necessary speed and altitude for orbit is excessive. This problem was overcome using multi-stage engines that are discarded sequentially during vertical ascent. However, the relative inefficiency of fuels currently available perpetuates the requirement for multi-stage engines to achieve orbit. Multi-stage rockets still require onboard fuel and oxidizer at lift-off that can account for over 95% of the lift-off weight. Only with more efficient fuels and propulsion systems will it become possible to achieve orbit and spaceflight without this limitation. More effective spacecraft designs incorporating a propulsion system powered by a more efficient fuel would greatly reduce the oxidizer to payload ratio. This could be accomplished with a vehicle that uses air while in the atmosphere and switches to onboard oxidizer only after reaching the upper limit of the atmosphere. This more efficient fuel is now available. The use of silanes (silicone hydrites) provides the fuel necessary to achieve this radically different and efficient means of propulsion, using both the oxygen and the 80% nitrogen of our atmosphere for combustion.