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Results for “ion trajectory dynamical stability”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Localized tearing modes in the magnetotail driven by curvature effects

The stability of collisionless tearing modes is examined in the presence of curvature drift resonances and the trapped particle effects. A kinetic description for both electrons and ions is employed to investigate the stability of a two-dimensional equilibrium model. The main features of the study are to treat the ion dynamics properly by incorporating effects associated with particle trajectories in the tail fields and to include the linear coupling of trapped particle modes. Generalized dispersion relations are derived in several parameter regimes by considering two important sublayers of the reconnecting region. For a typical choice of parameters appropriate to the current sheet region, we demonstrate that localized tearing modes driven by ion curvature drift resonance effects are excited in the current sheet region with growth time of the order of a few seconds. Also, we examine nonlocal characteristics of tearing modes driven by curvature effects and show that modes growing in a fraction of a second arise when mode widths are larger than the current sheet width. Further, we show that trapped particle effects, in an interesting frequency regime, significantly enhance the growth rate of the tearing mode. The relevance of this theory for substorm onset phase and other features of the substorms is briefly discussed.

Sundaram, A. K.↗
NASA NTRS1987

Types of planetary tori

While satellite tori are morphologically similar, they divide into dynamically distinct groups whose global balances of ions and neutrals are presently modeled in order to determine how a torus behaves as a consequence of whether it generates itself and whether it disperses or recombines in place. Six possible types of behavior result; attention is given to the equilibrium and stability of each type. The behavior of a perturbation is characterized by a trajectory in the two-dimensional space formed by the ion density and neutral density perturbations. The equilibrium is stable if a perturbation follows its trajectory toward the origin, but is unstable if the motion is away from it. An attempt is made to classify the Jupiter and Saturn tori in this light.

Huang, T. S.↗
NASA NTRS2003

Ultrasail

Ultrasail is a complete sail system for the launch, deployment, stabilization and control of very large solar sails enabling reduced mission times for interplanetary and deep space spacecraft. Ultrasail is an innovative, non-traditional approach to propulsion technology achieved by combining propulsion and control systems developed for formation-flying microsatellites with an innovative solar sail architecture to achieve sq km-class controllable sail areas, sail subsystem area densities of 1 gm per sq m, and thrust levels equivalent to 400 kW ion thruster systems used for comparable deep space missions. Ultrasail can conceivably even achieve outer planetary rendezvous, a deep space capability now reserved for high-mass nuclear and chemical systems. Ultrasail is a Delta IV-launched multi-blade spin-stabilized system with blade lengths as long as 50 km, reminiscent of the MacNeal Heliogyro. The primary innovation is the near-elimination of sail supporting structures by attaching the sail tip to a rigid formation-flying microsatellite truss which deploys the sail blade, and which then articulates the blade to provide attitude control, including spin stabilization and precession of the spin axis. These tip microsatellites are controlled by a solar-powered 3-axis microthruster system (electric or cold gas) to maintain proper sail film tension during deployment and spin-up. The satellite mass also provides a stabilizing centrifugal force on the blade while in rotation. Understanding the dynamics of individual blades is key to the overall dynamics of Ultrasail. Forces and torques that must be modeled include those due to solar pressure, those generated by the microsatellite at the blade tip and by torques applied at the blade root. Centrifugal forces also play a significant role in the deployment and maintenance of the sail configuration. To capture the dynamics of the overall system, the equations of motion for the blades have been derived. Using these differential equations, a control law will be derived to maneuver Ultrasail. This law involves the pitching of the individual blades thereby moving the distribution of the radiation pressure on each individual blade and inducing a resultant torque on the system. The direction of the angular momentum vector and its rate of precession can be controlled through the pitch angle of the blades. The Ultrasail trajectory is also being studied. Optimal or near-optimal trajectories are being generated to showcase Ultrasail performance. Various missions, e.g. outer planet and solar polar missions for observation of the Sun, are currently being investigated to demonstrate the performance enhancements generated by Ultrasail technology. Calculus-of-variations-based optimization software is used to produce optimal Ultrasail trajectories. The performance of these trajectories is being compared to optimal results generated with other propulsion models, including chemical propulsion, ion propulsion, and competing solar sail concepts. Results of these studies will quantify the performance of Ultrasail compared to existing solar sail concepts for high energy missions.

Burton, R.↗
NASA NTRS1999

Computer Simulation Studies of Ion Channel Gating: Characteristics of the M2 Channel of Influenza-A Virus in a Phospholipid Bilayer

The 25 amino acids long, transmembrane fragment of the Influenza virus M2 protein forms a homotetrameric channel that transports protons across lipid bilayers. It has been postulated that high efficiency and selectivity of this process is due to gating by four histidine residues that occlude the channel lumen in the closed state. Two mechanisms of gating have been postulated. In one mechanism, the proton is "shuttled" through the gate by attaching to the delta nitrogen atom on the extracellular side of the imidazole ring, followed by the release of the proton attached to the epsilon nitrogen atom on the opposite side. In the second mechanism, the four histidines move away from each other due to electrostatic repulsion upon protonation, thus opening the gate sufficiently that a wire of water molecules can penetrate the gate. Then, protons are transported by "hopping" along the wire. In this paper, both mechanisms are evaluated in a series of molecular dynamics simulations by investigating stability of different protonation states of the channel that are involved in these mechanisms. For the shuttle mechanism, these are states with all epsilon protonated histidines, one biprotonated residue or one histidine protonated in the delta position. For the gate opening mechanism, this is the state in which all four histidines are biprotonated. In addition, a state with two biprotonated histidines is considered. For each system, composed of the protein channel embedded in phospholipid bilayer located between two water lamellae, a molecular dynamics trajectory of approximately 1.3 ns (after equilibration) was obtained. It is found that the states involved in the shuttle mechanism are stable during the simulations. Furthermore, the orientations and dynamics of water molecules near the gate are conducive to proton transfers involved in the shuttle. In contract, the fully biprotonated state, implicated in the gate opening mechanism, is not stable and the channel looses its structural integrity. If only two histidines are biprotonated the channel deforms but remains intact with the gate mostly closed. In summary, the results of this study lend support to the shuttle mechanism but not to the gate opening mechanism of proton gating in M2.

Schweighofer, Karl J.↗
NASA NTRS2018

Modeling of Orbital and Attitude Dynamics of Nanosatellites Controlled via Active Electrostatic Charging

The large-scale exploration of airless bodies, such as asteroids and moons, is gaining interest, however it is limited by mobility issues: the lack of atmosphere, low gravity, and unknown soil properties pose difficult challenges for many forms of traditional locomotion. The environment in proximity of these bodies is also electrically charged due to interactions with solar wind and UV radiation. The EGlider (Electrostatic Glider) concept would be able to overcome these mobility issues by leveraging the natural environment, allowing operations in close proximity of the surface, while enabling long duration missions by minimizing propellant consumption. The EGlider is an advanced concept for small satellite mobility and propulsion, which relies on the electric fields naturally present around airless bodies in order to generate forces and torques useful for maneuvering. It does so by extending electrically charged appendages, which enable it to electrostatically soar above the surface. By differentially charging its electrodes it can also produce torques to control its attitude. The charges are maintained by continuous active ion or electron emission from the spacecraft, in order to cancel out the neutralizing influx of charges from surrounding plasma. An investigation of the spacecraft-plasma interaction was carried out. This included studying the effect of electrode geometry and calculating the charge-to-mass ratios required to enable several mission scenarios. Long, thin wire electrodes were identified to be the most power-efficient and would allow power-to-weight ratios achievable with current nanosatellite technologies. High electrode potential represents the main limiting factor for the system design. In order to test the feasibility of active control by means of differential charging, a simple 2D interaction model was developed, and a feedback controller to stabilize the vehicle was tested in a simulation environment. The results confirmed that good performance could be obtained for both position and attitude control. Finally, a dedicated software was developed for future simulation and testing of control strategies for the EGlider. This software allows to study the trajectory and attitude of an arbitrarily configured spacecraft in the proximity of an arbitrarily defined main airless body. The spacecraft can be assembled from basic parts, each with specified electrical, mass and optical properties. Efficient models allow to calculate gravitational and electrical interactions with the rotating main body and the local plasma field, as well as solar radiation pressure effects. Control models can be implemented as simple plug-in functions and easily tested. The preliminary validation campaign showed good matching with the reference cases that have been analyzed.

Corpino, Sabrina↗