What is it about?
Improving rocket ascent Isp with multiple modes integrated into a single gas path is the subject of this paper. Examining the shortcomings of prior concepts and systematically integrating major features of existing technical work is the innovation pathway. What is desired is a propulsion system capable of SSTO for highest reusability simultaneously with highest mass fraction delivered for lowest operational costs so as to minimize access to orbit costs. Nuclear thermal rockets already offer the highest Isp of launch-capable pure rocket propulsion systems, whereas the Supercharged Ejector Scramjet (SESJ, and afterburning supersonic Rocket Fan are the highest launch to hypersonic Isp chemical combined cycle systems proposed so it is logical to attempt to integrate those cycles. The new proposed propulsion concept is called the Nuclear Thermal Turbo Rocket (NTTR), which is a supercharged air-augmented nuclear thermal rocket architecture.
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Why is it important?
Access to orbit costs are the primary obstacle to off-Earth development. Many proposals have been put forth to improve costs, but the only method to bring costs down dramatically is to lower investment and realize a large return on that investment in concert. Most proposals cannot satisfy one or both of these requirements. Functionally what this implies is a simple (low dry mass) Single Stage to Orbit (SSTO) Reusable Launch Vehicle (RLV) with high payload mass fraction. What is proposed is the first such architecture satisfying all of the above, with a payload fraction to orbit estimated to be as high as 28% with further enhancements possible.
Perspectives
Access to space has been a barrier to many proposed developments that would benefit all of humankind - such as asteroid mining and solar power satellites. Alternatives to traditional rockets including such technologies as tethers and nuclear pulse propulsion (Orion) have serious drawbacks that to date have not been resolved. Even marginal performance enhancements to launch vehicles have drawn much publicity and corporate investment, such as Reaction Engine's SABRE and associated Skylon project since reusability is such a large factor in improving economics. Nuclear Thermal Rockets (NTRs) are currently being actively investigated for in-space propulsion to enable manned interplanetary missions by NASA and others. Launch applications of NTRs have been abandoned long ago due to large deficits in thrust to weight ratios making missions marginal, and in-space missions need to loft a propulsion system which reduces mission payload. Simultaneously, developments in the hypersonic propulsion field has matured design tools such that integration with nuclear thermal propulsion (NTP) has recently become possible. Application of high speed airbreathing propulsion is highly synergistic with NTP as the rocket uses hydrogen as a propellant, combustion of which enhances the overall propulsion efficiency across a large portion of the ascent. Overall, the performance of such airbreathing nuclear rocket combined cycles is so high that mass budget for radiation shielding can be large enough to reduce exposure of both payload and launch site to effectively the same as background radiation - mitigating concerns regarding the use of nuclear power for launch missions. A new era of space access is possible with innovations such as the Nuclear Thermal Turbo Rocket.
John Bucknell
Revolution Rockets
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This page is a summary of: The Nuclear Thermal Turbo Rocket - A Conceptual High-Performance Earth-to-Orbit Propulsion System, July 2015, American Institute of Aeronautics and Astronautics (AIAA),
DOI: 10.2514/6.2015-3958.
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