Engineering topics

Riehl, John

Publications and source records attributed to Riehl, John.

4 records

NASA NTRS2002

SRM-Assisted Trajectory for the GTX Reference Vehicle

A goal of the GTX effort has been to demonstrate the feasibility of a single stage-to-orbit (SSTO) vehicle that delivers a small payload to low earth orbit. The small payload class was chosen in order to minimize the risk and cost of development of this revolutionary system. A preliminary design study by the GTX team has resulted in the current configuration that offers considerable promise for meeting the stated goal. The size and gross lift-off weight resulting from scaling the current design to closure however may be considered impractical for the small payload. In lieu of evolving the project' reference vehicle to a large-payload class, this paper offers the alternative of using solid-rocket motors in order to close the vehicle at a practical scale. This approach offers a near-term, quasi-reusable system that easily evolves to reusable SSTO following subsequent development and optimization. This paper presents an overview of the impact of the addition of SRM's to the GTX reference vehicle#s performance and trajectory. The overall methods of vehicle modeling and trajectory optimization will also be presented. A key element in the trajectory optimization is the use of the program OTIS 3.10 that provides rapid convergence and a great deal of flexibility to the user. This paper will also present the methods used to implement GTX requirements into OTIS modeling.

Riehl, John↗

NASA NTRS2002

SRM-Assisted Trajectory for the GTX Reference Vehicle

A goal of the GTX effort has been to demonstrate the feasibility of a single stage- to- orbit (SSTO) vehicle that delivers a small payload to low earth orbit. The small payload class was chosen in order to minimize the risk and cost of development of this revolutionary system. A preliminary design study by the GTX team has resulted in the current configuration that offers considerable promise for meeting the stated goal. The size and gross lift-off weight resulting from scaling the current design to closure however may be considered impractical for the small payload. In lieu of evolving the project's reference vehicle to a large-payload class, this paper offers the alternative of using solid-rocket motors in order to close the vehicle at a practical scale. This approach offers a near-term, quasi-reusable system that easily evolves to reusable SSTO following subsequent development and optimization. This paper presents an overview of the impact of the addition of SRM's to the GTX reference vehicle's performance and trajectory. The overall methods of vehicle modeling and trajectory optimization will also be presented. A key element in the trajectory optimization is the use of the program OTIS 3.10 that provides rapid convergence and a great deal of flexibility to the user. This paper will also present the methods used to implement GTX requirements into OTIS modeling.

Riehl, John↗

NASA NTRS1999

Characterization of In-Situ BN Interface Formed by Nitridation of Nextel 312

Treatment of Nextel (TM) 312 in a reactive environment has been used as a low cost approach to the formation of BN on the fiber surface. Although the BN enriched surface region is extremely thin (less than 40 run), it is effective in providing debonding and composite behavior. Variation in mechanical behavior of Nextel (TM) 312/BN/Blackglas (TM) composites has been noted among panels fabricated with AF-10 cloth treated in different nitridation runs, Understanding this variation became the rationale for undertaking a detailed characterization of the nitrided fiber using field emission scanning electron microscopy, low voltage energy dispersive x-ray and Auger electron spectroscopy. Chemical composition and surface morphology are discussed in relation to observed mechanical behavior of NeXtel (TM) 312/Blackglas (TM) composites tested in bending.

Hurwitz, Fances I.↗

NASA NTRS1998

Electric Propulsion Options for a Magnetospheric Mapping Mission

The Twin Electric Magnetospheric Probes Exploring on Spiral Trajectories mission concept was proposed as a Middle Explorer class mission. A pre-phase-A design was developed which utilizes the advantages of electric propulsion for Earth scientific spacecraft use. This paper presents propulsion system analyses performed for the proposal. The proposed mission required two spacecraft to explore near circular orbits 0.1 to 15 Earth radii in both high and low inclination orbits. Since the use of chemical propulsion would require launch vehicles outside the Middle Explorer class a reduction in launch mass was sought using ion, Hall, and arcjet electric propulsion system. Xenon ion technology proved to be the best propulsion option for the mission requirements requiring only two Pegasus XL launchers. The Hall thruster provided an alternative solution but required two larger, Taurus launch vehicles. Arcjet thrusters did not allow for significant launch vehicle reduction in the Middle Explorer class.

Oleson, Steven↗