Analysis of flight vehicle stiffened section skin stability in shear

The skin panels of riveted cylindrical sections of flight vehicles in shear are considered. The objective of the analysis based on the finite element method is to verify the recommendations available for determining critical stresses of similar structural elements and to obtain new results for practical calculations.     

The Radiation Assessment Detector (RAD) Investigation

The Radiation Assessment Detector (RAD) on the Mars Science Laboratory (MSL) is an energetic particle detector designed to measure a broad spectrum of energetic particle radiation. It will make the first-ever direct radiation measurements on the surface of Mars, detecting galactic cosmic rays, solar energetic particles, secondary neutrons, and other secondary particles created both in the atmosphere and in the Martian regolith. The radiation environment on Mars, both past and present, may have implications for habitability and the ability to sustain life. Radiation exposure is also a major concern for future human missions. The RAD instrument combines charged- and neutral-particle detection capability over a wide dynamic range in a compact, low-mass, low-power instrument. These capabilities are required in order to measure all the important components of the radiation environment. RAD consists of the RAD Sensor Head (RSH) and the RAD Electronics Box (REB) integrated together in a small, compact volume. The RSH contains a solid-state detector telescope with three silicon PIN diodes for charged particle detection, a thallium doped Cesium Iodide scintillator, plastic scintillators for neutron detection and anti-coincidence shielding, and the front-end electronics. The REB contains three circuit boards, one with a novel mixed-signal ASIC for processing analog signals and an associated control FPGA, another with a second FPGA to communicate with the rover and perform onboard analysis of science data, and a third board with power supplies and power cycling or “sleep”-control electronics. The latter enables autonomous operation, independent of commands from the rover. RAD is a highly capable and highly configurable instrument that paves the way for future compact energetic particle detectors in space.     

固体火箭发动机无损检测和无损评价技术的现状

无损检测和评价技术在固体火箭发动机研制中起着重要的作用,该文介绍了国外固体发动机无损检测和评价技术的新进展,论述了无损检测和评价技术是保证固体发动机质量和可靠性的关键技术之一,并预示了未来的发展趋势。     

A superposed epoch study of the effects of solar wind stream interface events on the upper mesospheric and lower thermospheric temperature

The response of mesosphere and lower thermosphere (MLT) temperature to energetic particle precipitation over the Earth’s polar regions is not uniform due to complex phenomena within the MLT environment. Nevertheless, the modification of MLT temperatures may require an event-based study to be better observed. This work examines the influence of precipitation, triggered by solar wind stream interfaces (SI) event from 2002 to 2007, on polar MLT temperature. We first test the relationship between the ionospheric absorption measured by the SANAE IV (South African National Antarctic Expedition IV) riometer and the layer of energetic particle precipitation from POES (Polar Orbiting Environmental Satellites). The combined particle measurements from POES 15, 16, 17 and 18 were obtained close in time to the pass of the SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) temperature retrieval. Here, a superposed epoch technique is described and implemented to obtain average temperature profiles during SI-triggered particle precipitation. The superposed epoch average shows no significant temperature decrease below 100 km prior to the onset of SI-triggered precipitation, whereas a clear superposed average temperature decrease is observed at 95 km after the SI impact. A case study of SI event also yields similar observations. Results indicate that cooling effects due to the production of mesospheric odd hydrogen might be major contributors to temperature decrease under compressed solar wind stream.     

The gravireaction of Ceratodon protonemata treated with gibberellic acid.

Moss protonemata exhibit negative gravitropism and the amyloplasts of the apical cell seem to play a key role in protonemal gravisensitivity. However, the mechanisms of this process are still poorly understood. Previously, we have shown that Ceratodon protonemata grown on agar-medium demonstrated greater gravicurvature than protonemata grown on medium with 11 mM glucose. In this study, we have examined whether gibberellic acid (GA), which promotes alpha-amylase expression, influences graviresponse of C. purpureus protonemata (strains WT-4 and WT-U) and how this event interacts with exogenous soluble sugars. After gravistimulation the WT-4 strain curved about twice as fast as the WT-U strain. However, responses of both strains to added substances were similar. High concentration of glucose (0.11 M) caused a decrease in protonema curvature, while the same concentration of sucrose did not significantly change the angles of curvature compared with controls. GA at 0.1 mM and higher concentrations inhibited gravitropism, and caused some apical cells to swell. The possible involvement of the carbohydrates in gravitropism is discussed.     

Simultaneous Response of the Mid-Latitude Ionosphere to a Sudden Commencement of Strong Magnetic Storms

Using the new technology of global GPS detection of ionospheric disturbances (GLOBDET), it is found that a sharp increase of the time derivative of the magnetic field strength during magnetic storms is accompanied by a simultaneous decrease of the mid-latitude total electron content (TEC) over the entire dayside of the globe. The corresponding negative correlation coefficient is no less than 0.8, and the delay relative to the sudden commencement of magnetic storm is about 3–10 min. The effect is especially clearly pronounced for magnetic storms with sudden commencements (SSC). The analysis is carried out for a set of 90 to 300 GPS stations for 10 days (January 6 and April 23, 1998; April 6, June 8, July 13, 14, and 15, 2000; March 31, April 4 and 11, 2001) with various levels of geomagnetic activity (D _st and K _p varied from –6 to –295 nT and from 0 to 9, respectively). The amplitude of the response in the total electron content for the events considered was 0.1–0.4 × 10¹⁶ m^–2 (which is a deviation of 0.2–2.6% from the TEC background value). The velocity of the disturbance motion from the dayside to the nightside was about 10–20 km/s. The results obtained agree with the data of ionospheric parameter measurements conducted earlier by methods with high temporal resolution.     

Periodic motions of a nearly dynamically symmetric satellite in the neighborhood of hyperboloidal precession

The motion of a satellite close to a dynamically symmetric solid body in a Newtonian gravitational field over a circular orbit is studied. The system of differential equations describing the body’s motion is close to a system with cyclic coordinate. New classes of periodic motions are constructed in the neighborhood of a known partial solution to an unperturbed problem, hyperboloidal precession of a dynamically symmetric satellite. In the resonance case, when the ratio of one frequency of small oscillations of a reduced system with two degrees of freedom in the neighborhood of a stable equilibrium position to the frequency of cyclic coordinate variation is close to an integer number, there exist one or three families of periodic motions that are analytic in terms of fractional powers of a small parameter. A study of stability of these motions was performed with the help of KAM (Kolmogorov-Arnold-Moser) theoty. Faling the described resonance there exists a unique family of periodic motions that is analytic in terms of integer powers of a small parameter. The check-up of stability of these motrons was carried out. We distinguished the cases of parametric resonance, resonances of the third and fourth orders, and a non-resonant case. In the resonance cases our study relies on well-known results on stability of Hamiltonian systems during resonances [1]. In the non-resonant case we use the KAM theory [2].     

Fluctuations of Current onto Flat Probes of the ZOND–ZARYAD Instrument Mounted on the MIR Orbital Complex

Flat probes of the ZOND–ZARYAD instrument, which operated on the MIR orbital complex (OC), form a counterprobe (reference surface) configuration in which the alternating component of the net probe current is measured. There is no potential difference between the spacecraft (SC) body and the probes; that is, the probes are at the floating potential (FP). By measuring the alternating component of the probe current, one cannot estimate the FP value, but we can observe small-scale FP dynamics of a single probe in the OC near-surface region and estimate the fluctuations of currents flowing onto the SC. The alternating component of the current on the probes in the OC near-surface region varies in a wide range depending on ionospheric plasma parameters, the probe orientation with respect to the velocity vector, the magnetic field vector, and the direction to the Sun in the illuminated part of the orbit. In addition to the amplitude dynamics, the frequency dynamics of the alternating component of the current onto the probes is observed.