Suchergebnisse

The goal of the Dual-Expander Aerospike Nozzle, a modification to traditional engine architectures, is to find those missions and designs for which it has a competitive advantage over traditional upper stage engines such as the RL10. Previous work focused on developing an initial design to demonstrate the feasibility of the Dual-Expander Aerospike Nozzle. This research expanded the original cycle model in preparation for optimizing the engine's specific impulse and thrust-to-weight ratio. The changes to the model allowed automated parametric and optimization studies. Preliminary parametric studies varying oxidizer-to-fuel ratio, total mass flow, and chamber length showed significant improvements. Drawing on modeling lessons from previous research, this research developed a new engine simulation capable of achieving a specific impulse comparable to the RL10. Parametric studies using the new model verified the Dual-Expander Aerospike Nozzle architecture conforms to rocket engine theory while exceeding the RL10's performance. Finally, this research concluded by optimizing the Dual-Expander Aerospike Nozzle engine for three US government missions: the Next Generation Engine program, the X-37 mission, and the Space Launch System. The optimized Next Generation Engine design delivers 35,000 lbf of vacuum thrust at 469.4 seconds of vacuum specific impulse with a thrust-to-weight ratio of 127.2 in an engine that is one quarter the size of a comparable RL10. For the X-37 mission, the optimized design operates at 6,600 lbf of vacuum thrust and has a vacuum specific impulse of 457.2 seconds with a thrust-to-weight ratio of 107.5. The Space Launch System design produces a vacuum thrust of 100,000 lbf with a vacuum specific impulse of 465.9 seconds and a thrust-to-weight ratio of 110.2. When configured in a cluster of three engines, the Dual-Expander Aerospike Nozzle matches the J2-X vacuum thrust with a 4% increase in specific impulse.

Abstract
How does the way companies elicit ratings from consumers affect the ratings that they receive? In 10 pre-registered experiments, we find that consumers rate subpar experiences more positively overall when they are also asked to rate specific aspects of those experiences (e.g., a restaurant's food, service, and ambiance). Studies 1–4 established the basic effect across different scenarios and experiences. Study 5 found that the effect is limited to being asked to rate specific features of an experience, rather than providing open-ended comments about those features. Studies 6–9 provided evidence that the effect does not emerge because rating positive aspects of a subpar experience reminds consumers that their experiences had some good features. Rather, it emerges because consumers want to avoid incorporating negative information into both the overall and the attribute ratings. Lastly, study 10 found that asking consumers to rate attributes of a subpar experience reduces the predictive validity of their overall rating. We discuss implications of this work and reconcile it with conflicting findings in the literature.