• Specific considerations for reusable systems. Design considerations that are important to enable efficient booster reusability along with associated accessibility and maintenance goals are listed below.1
— Strive to isolate booster ground processing from dependence on facilities and ground support equipment by incorporating frequently used ground checkout equipment into the booster. Routine, scheduled turnaround ideally replenishes only consumables. Eliminate “flight readiness-style” booster certification for every flight. Provide aircraft-style vehicle-type certificate for repetitive flight operations.
— Booster subsystems should be independently power up-able and easily accessible when maintenance is required. This allows work to be performed in parallel with other systems and avoids processing conflicts.
— Avoid closed launch vehicle compartments, which require purges before personnel entry and complicate access and closeout requirements.
— When common propellants can be used, primary and secondary propulsion systems should be highly integrated, using common storage tanks, feed lines, etc. This reduces handling requirements for multiple propellants and reduces interfaces.
— Thermal protection systems should be robust and maintenance-free. Avoid thermal protection systems that are prone to in-flight degradation or that absorb moisture.
— Fewer rocket engines, preferably between two and four main engine, provide multiple operability benefits, such as reducing confined spaces which inherently require purges, reducing servicing and ground interfaces and reducing the number of systems for leak detection.
— IVHM can provide component and system health monitoring to identify those items requiring maintenance. It is critical that IVHM include the nonintrusive detection of fluid leakage and other techniques to reduce the large amount of unplanned maintenance that may be between flights. See Appendix E.
— Provide designs that limit the need for leak-test verification for fluids and gases in both static and dynamic applications by the use of all-welded systems whenever possible. Provide designs for electrical power and data transmission that reduce the use of cable connectors to minimize troubleshooting and repair.
— Where possible, use environmentally benign technologies. Avoid the use of hypergolics for auxiliary propulsion, main engine start, or power generation, if possible. If hypergolics must be used for the reaction control system, incorporate them as modular subsystems allowing for easy removal and replacement. Also avoid toxic freons and ammonia. Avoid the need for vehicle purges wherever possible.
— Avoid hydraulics for engine thrust vector control and to actuate aerodynamic control surfaces, landing gear, etc.; use electric actuators for these functions.
— A reusable flyback booster has a relatively short mission duration, permitting use of batteries rather than propellants for power generation.
— Implement a flight vehicle on-board system that provides its own power management, requiring only one vehicle-to-ground interface at each ground-facility station.
— Equipment should be mounted so that it is readily accessible. Avoid mounting equipment in closed compartments where access can result in collateral damage and unplanned work. Locate equipment on walls with external access or in open compartments that permit easy personnel access. Use aircraft-like access panels.
— Launchpad fluid, electrical, and communications interfaces should be implemented through rise-off disconnects located at the base of the booster and LES. If a mobile launch platform is used, its services should be connected to launchpad infrastructure with auto couplers.
— All subsystems and components should be qualified for the specified life of the reusable vehicle. Where this is not possible, and when removal and replacement over a reduced number of flights is required, these subsystems/components need to be readily accessible for ease of removal and replacement and post-installation checkout.
1 See also Huether, Spears, McCleskey, and Rhodes, “Space Shuttle to Reusable Launch Vehicle,” presented to the Thirty-Second Space Congress, Canaveral Council of Technical Societies, 1995; NASA, An Operational Assessment of Concepts and Technologies for Highly Reusable Space Transportation, Highly Reusable Space Transportation Study Integration Task Force, Operations, NASA Centers, November 1998.