Electron beam experiments in Japanese satellites and rockets

Electron beam experiments in space that have been done and planned in Japan are reviewed. 200eV, 1mA electron beam is emitted from a satellite and several types of wave excitation such as UHF and ω_ce have been observed. The satellite potential and the energy spectrum of returning electrons are measured by Langmuir probes and electrostatic energy analyser. In rocket experiments of K-10-11, K-10-12, K-9M-57, K-9M-58, K-9M-61 and K-9M-66, several types of electron guns were used whose power ranges from 1mW to 1KW. The rocket potential was measured by Langmuir probes and floating probes and optical line emission measurement and wave measurements were also done. The rocket potential was not so high as expected from the balance with ionospheric plasma but strongly affected by the plasma production by the emitted electron beam and return electrons.     

Fluid electrolyte and hormonal changes in conditioned and unconditioned men under hypokinesia

It has been suggested that hypokinesia (diminished muscular activity) may induce more changes in fluid electrolyte metabolism and hormonal concentration of blood plasma in conditioned than unconditioned men. Thus, the objective of this investigation was to determine the effect of 7 days of hypokinesis (HK) on fluid-electrolyte excretion and hormonal content of blood in 12 physically healthy men aged 19-23 years. They were divided into two equal groups according to their physical conditioning. For the simulation of the hypokinetic effect the men were kept under a rigorous bed rest regime. During the background period (BGP), that is prior to the exposure to HK, and under HK, the rate of elimination of fluid, sodium and potassium, and the content of blood plasma aldosterone and cortisol was measured. The amount of excretion of fluid and electrolytes increased while blood plasma aldosterone content decreased. In the conditioned men, a greater excretion of fluid and electrolytes and a greater reduction of plasma aldosterone concentration was observed. It was concluded that hypokinesia induced substantial changes in fluid-electrolyte excretion and hormonal content of blood plasma in both conditioned and unconditioned men.     

Blended control, predictor-corrector guidance algorithm: an enabling technology for Mars aerocapture

A guidance scheme designed for coping with significant dispersion in the vehicle's state and atmospheric conditions is presented. In order to expand the flyable aerocapture envelope, control of the vehicle is realized through bank angle and angle-of-attack modulation. Thus, blended control of the vehicle is achieved, where the lateral and vertical motions of the vehicle are decoupled. The overall implementation approach is described, together with the guidance algorithm macrologic and structure. Results of guidance algorithm tests in the presence of various single and multiple off-nominal conditions are presented and discussed.     

A Kalman Filter Based Tracking Scheme with Input Estimation

Beginning with the derivation of a least squares estimator that yields an estimate of the acceleration input vector, this paper first develops a detector for sensing target maneuvers and then develops the combination of the estimator, detector, and a "simple" Kalman filter to form a tracker for maneuvering targets. Finally, some simulation results are presented. A relationship between the actual residuals, assuming target maneuvers, and the theoretical residuals of the "simple" Kalman filter that assumes no maneuvers, is first formulated. The estimator then computes a constant acceleration input vector that best fits that relationship. The result is a least squares estimator of the input vector which can be used to update the "simple" Kalman filter. Since typical targets spend considerable periods of time in the constant course and speed mode, a detector is used to guard against automatic updating of the "simple" Kalman filter. A maneuver is declared, and updating performed, only if the norm of the estimated input vector exceeds a threshold. The tracking sclheme is easy to implement and its capability is illustrated in three tracking examples.     

Technical and legal issues surrounding space debris—India''s position in the UN

This article briefly presents the historical background, as seen by ISRO and India, to the growing problem of space debris. It describes the technical aspects of ISRO's activities in the field of space debris, and the grey areas in technical understanding, which may impede legal discussions. Analysis of the cost and technical aspects of reorbiting satellites from geostationary Earth orbit (GEO) is detailed, since this is an important area for India and other developing countries. The article also briefly describes ISRO's views of the applicability and relevance of the existing space treaties to a possible future legal regime for space debris. Debates are currently taking place in the UN and other multilateral fora on the subject of space debris and the situation is dynamic. The main aim of this article is to inform readers of ISRO's and India's position in the UN on the subject of space debris, in terms of its technical, political and legal aspects. Certain issues of importance from the legal point of view, though not of immediate urgency, are also discussed.     

Fluid electrolyte excretion during different hypokinetic body positions of trained subjects

The aim of this study was to evaluate the effect of different body positions on renal excretion of fluid and electrolytes after exposure to 364 days of decreased number of steps per day (hypokinesia, HK). The studies were performed on 18 endurance trained male volunteers aged 19-24 years who had an average of VO2max 67 ml/kg body/min. All volunteers were divided into three equal groups: the 1st group subjected to 12 h orthostatic position (OP) and 12 h clinostatic position (CP)/day, the 2nd group exposed to 8 h orthostatic position and 14 h clinostatic position/day, and the 3rd group submitted to 10 h orthostatic position and 16 h clinostatic position/day for 364 days. For the simulation of the hypokinetic effect all volunteers were kept under an average of 3000 steps/day for 364 days. Diuresis and the concentrations of sodium, potassium, chloride, calcium and magnesium as well as excretion of creatine were determined in 24-h urine samples. By the end of the hypokinetic period all volunteers, regardless of their body position during HK, manifested a significant increase in renal excretion of fluid and electrolytes as compared to prehypokinetic period values. It was concluded that prolonged restriction of motor activity induced a significant increase in renal excretion of fluid and electrolytes in endurance trained subjects regardless to their body position and duration thereof per day.     

Super-helix model: a physiological model for gravitaxis of Paramecium.

A new model explaining the gravitactic behavior of Paramecium is derived on the basis of its mechanism of gravity sensing. Paramecium is know to have depolarizing mechanoreceptor ion channels in the anterior and hyperpolarizing channels in the posterior of the cell. This arrangement may lead to bidirectional changes of the membrane potential due to the selective deformation of the anterior and posterior cell membrane responding to the orientation of the cell with respect to the gravity vector; i.e., negative- and positive-going shifts of the potential due to the upward and downward orientation, respectively. The orientation dependent changes in membrane potential, in combination with the close coupling between the membrane potential and ciliary locomotor activity, may allow the changes in swimming direction along the otherwise simple helical swimming path in the following manner: an upward shift of the axis of helical swimming occurs by decreasing the pitch angle due to channel-dependent hyperpolarization in upward-orienting cells, and an upward shift of the swimming helix occurs by increasing the cell's pitch angle due to depolarization in downward-orienting cells. Computer simulation of the model demonstrated that the cell can swim upward along the "super-helical" trajectory consisting of a small helix winding helically along an axis parallel to the gravity vector.     

Auroral plasmas in the evening sector: Satellite observations and theoretical interpretations

Space Science Reviews - Observations and theoretical interpretations of auroral plasma distributions have led to a spectacular advance, in the latter part of the 1970's, in understanding the...     

Sliding-mode controller design for spacecraft attitude trackingmaneuvers

A robust sliding-mode control law that deals with spacecraft attitude tracking problems is presented. Two important natural properties related to the spacecraft model of motion are discussed. It is shown that by using these properties and the second method of Lyapunov theory, the system stability in the sliding mode can be easily achieved. The success of the sliding-mode controller and its robustness relating to uncertainties are illustrated by an example of multiaxial attitude tracking maneuvers     

Detumbling and reorientation maneuvers and stabilization of NASASCOLE system

The questions of rotational maneuver and vibration stabilization of the NASA Spacecraft Control Laboratory Experiment (SCOLE) system is considered. The mathematical model of the SCOLE system includes the rigid body dynamics as well as the elastic dynamics representing transverse and torsional deformations of the elastic beam connecting the orbiter and end body (reflector). For the rotational maneuver, a new control law (orbiter control law) is derived using an orbiter input torque vector. Detumbling and reorientation maneuvers of the SCOLE system are accomplished using this control law; however, this excites the elastic modes of the beam. The orbiter control law asymptotically linearizes the flexible dynamics. Using the linearized model, a linear feedback control law is designed for vibration suppression. An observer is designed for estimating the state variables using sensor outputs which are also used for the synthesis of the control law. Simulation results are presented to show that in the closed-loop system detumbling and reorientation maneuvers can be accomplished and the effect of control and observation spillover is insignificant