646 research outputs found

    Space shuttle: Basic supersonic force data for a Grumman delta wing orbiter configuration ROS-NB1

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    Supersonic force data for scale model of space shuttle delta wing orbite

    Effect of maximum lift to drag ratio on optimal aeroassisted plane change

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    Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76843/1/AIAA-1985-1817-421.pd

    The darboux point and the conjugate point on optimal deorbit for reentry trajectories

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    The concept of the Darboux point at which an extremal loses its global optimality is extended to the case of discontinuous control. Using Contensou's domain of maneuverability, the condition for optimal switching at a corner is derived and the optimality of the trajectory in the neighborhood of a Darboux point is analyzed. The theory is applied to the problems of minimum-fuel planar and noncoplanar deorbit from elliptical orbits for atmospheric entry at a prescribed angle. In each case, the global optimal trajectory is assessed and it is found that in these nonlinear problems the Darboux point and the conjugate point are distinct. The global optimality is always lost before local optimality.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25561/1/0000103.pd

    Optimal aeroassisted transfer between coplanar elliptical orbits

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    This paper presents the solution for minimum-fuel, free-time transfer between coplanar elliptical orbits with the possible use of a planetary atmosphere to generate a decelerative braking force. The optimal pure propulsive two-impulse transfer is first considered. It is shown that the solution is obtained by solving a set of three equations for three unknowns. Reduction of the general equations is made for the case of symmetrical transfer and a complete first-order solution is provided for the case of transfer from nearly circular orbit. In aeroassisted transfer atmospheric braking at the perigee can be used to circularize the orbit, and in the circular configuration the orbit can be arbitrarily rotated without fuel consumption. It is shown that complete circularization of this intermediary orbit is optimal only when the rotation angle is large, and an explicit formula for evaluating this critical angle is provided. A complete solution is presented for the case of optimal rotation of an orbit. Finally, an example of optimal aeroassisted transfer is provided for the case of a transfer from a low-energy orbit to a high-energy orbit.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26152/1/0000229.pd

    Interplanetary Trajectory Design for NASA's Common Probe Study

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    The Galileo Probe, Pioneer-Venus probes, and SPRITE concept all share a number of common characteristics. They all follow a similar entry and descent sequence, using an aeroshell to protect against entry environments, and parachutes to aid in extrusion and descent speed control of the descent vehicle containing the science instruments. The descent vehicles all contained similar instruments (e.g. mass spectrometers and atmosphere structure sensors), and data was either relayed back to a carrier spacecraft (Galileo Probe, SPRITE) or transmitted direct to Earth (Pioneer-Venus). Based on these similar characteristics, NASA initiated a study to investigate a common probe' that might be designed to perform similar science in a variety of planetary environments. This concept would leverage a common aeroshell design, and descent vehicle designs that could be made as similar as possible (the primary exception being that Venus will require a pressure vessel due to the extreme pressures and temperatures seen in the lower portion of the descent). To support the Common Probe study, GSFC and JPL performed a series of interplanetary trajectory analyses to help develop the mission designs for Venus, Jupiter, Saturn, Uranus, and Neptune. Primary considerations in the trajectory modeling included: a maximum of 12-year time of flight (for outer planet destinations), generation of both steep and shallow entry trajectories to each destination (where steep and shallow resulted in approximately 150 g and 50 g peak deceleration during entry at each location), and consideration of the data relay. Gravity assists and trajectories with low delta-V requirements (typically much less than 500 m/s) were also incorporated into the design process to enable launch on existing vehicles such as the Atlas V

    Silicon vacancy containing two hydrogen atoms studied with electron paramagnetic resonance and infrared absorption spectroscopy, Phys

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    Float-zone and Czochralski-grown silicon crystals have been implanted with protons or deuterons. Electronparamagnetic-resonance measurements performed during illumination with light at 1064 nm reveal a signal, labeled DK5, in addition to the well-known signal from VO*-the excited spin-triplet state of the oxygenvacancy defect. The DK5 signal originates from a spin-triplet state of a vacancy-type defect with monoclinic-I ͑near-orthorhombic-I͒ symmetry. In contrast to the VO* signal, DK5 has about the same intensity in the spectra recorded on oxygen-lean and oxygen-rich samples, which indicates that the DK5 defect is not oxygen related. However, the close resemblance between the D tensors of DK5 and VO* strongly suggests that the electron-spin distributions are similar in the two defects. Moreover, anisotropic hyperfine splittings from two proton spins are partially resolved in the DK5 signal. The signal is assigned to VH 2 * , the excited spin-triplet state of the silicon vacancy containing two hydrogen atoms, which is the simplest defect consistent with the observed properties. The isochronal annealing behavior of DK5 coincides with that of two infrared-absorption lines at 2063 and 2077 cm Ϫ1 , which, like DK5, are observable only during illumination. These lines are assigned to Si-H stretch modes of VH 2 *

    Disturbed flow in an aquatic environment may create a sensory refuge for aggregated prey

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    Predators use olfactory cues moved within water and air to locate prey. Because prey aggregations may produce more cue and be easier to detect, predation could limit aggregation size. However, disturbance in the flow may diminish the reliability of odour as a prey cue, impeding predator foraging success and efficiency. We explore how different cue concentrations (as a proxy for prey group size) affect risk to prey by fish predators in disturbed (more turbulent or mixed) and non-disturbed (less mixed) flowing water. We find that increasing odour cue concentration increases predation risk and disturbing the flow reduces predation risk. At high cue concentration fish were able to locate the cue source in both disturbed and non-disturbed flow, but at medium concentrations, predators only located the cue source more often than expected by chance in non-disturbed flow. This suggests that objects disturbing flow provide a sensory refuge allowing prey to form larger groups, but that group sizes may be limited by level of disturbance to the flow
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