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.     

Deuterium-free water (1H2O) in complex life-support systems of long-term space missions

Heavy water containing deuterium displays toxic property. It is stated that any quantity of a heavy isotope of hydrogen--deuterium--is undesirable to animals and plants. It was earlier shown by us that physical-chemical life support systems on board the "MIR" station fractionate (change) isotopes of hydrogen, oxygen and carbon. Therefore, the problem of regenerative systems in habitable space objects should include removal, from water, of a heavy stable isotope of hydrogen--deuterium. In this article we consider one method of obtaining deuterium-free water--decomposition of distillate water in an electrolyser to hydrogen and oxygen with subsequent synthesis in a catalytic or high-temperature reactor. The influence of deuterium-free water on the growth and development of Arabidopsis thaliana and Japanese quail is investigated. It is shown that with the help of the electrolysis method it is possible to fabricate water containing 80% less deuterium in comparison with SMOW. Experimentally, it is proved on a culture of Arabidopsis thaliana and Japanese quail that water with reduced contents of deuterium (80%) displays positive biological activity.     

Near Earth Current Meander (Necm) Model of Substorms

We propose that the appropriate instability to trigger a substorm is a tailward meander (in the equatorial plane) of the strong current filament that develops during the growth phase. From this single assumption follows the entire sequence of events for a substorm. The main particle acceleration mechanism in the plasma sheet is curvature drift with a dawn-dusk electric field, leading to the production of auroral arcs. Eventually the curvature becomes so high that the ions cannot negotiate the sharp turn at the field-reversal region, locally, at a certain time. The particle motion becomes chaotic, causing a local outward meander of the cross-tail current. An induction electric field is produced by Lenz's law, E ^ind=–A/t. An outward meander with B _z>0 will cause E×B flow everywhere out from the disturbance; this reaction is a macroscopic instability which we designate the electromotive instability. The response of the plasma is through charge separation and a scalar potential, E ^es=–. Both types of electric fields have components parallel to B in a realistic magnetic field. For MHD theory to hold the net E must be small; this usually seems to happen (because MHD often does hold), but not always. Part of the response is the formation of field-aligned currents producing the well-known substorm current diversion. This is a direct result of a strong E ^ind (the cause) needed to overcome the mirror force of the current carriers; this enables charge separation to produce an opposing electrostatic field E ^es (the effect). Satellite data confirm the reality of a strong E in the plasma sheet by counter-streaming of electrons and ions, and by the inverse ion time dispersion, up to several 100 keV. The electron precipitation is associated with the westward traveling surge (WTS) and the ion with omega () bands, respectively. However, with zero curl, E ^es cannot modify the emf =Edl=–d^M/dt of the inductive electric field E ^ind (a property of vector fields); the charge separation that produces a reduction of E must enhance the transverse component E . The new plasma flow becomes a switch for access to the free energy of the stressed magnetotail. On the tailward side the dusk-dawn electric field with EJ<0 will cause tailward motion of the plasma and a plasmoid may be created; it will move in the direction of least magnetic pressure, tailward. On the earthward side the enhanced dawn-dusk induction electric field with EJ>0 will cause injection into the inner plasma sheet, repeatedly observed at moderate energies of 1–50 keV. This same electric field near the emerging X-line will accelerate particles non-adiabatically to moderate energies. With high magnetic moments in a weak magnetic field, electrons (ions) can benefit from gradient and curvature drift to attain high energies (by the ratio of the magnetic field magnitude) in seconds (minutes).     

Human characteristics of pair assembly work in a microgravity environment

This research focuses on analyzing the human characteristics of pair assembly work in a microgravity environment. To obtain the necessary data, two groups of test subjects participated in an experiment in a pseudomicrogravity environment, and how such factors as work allotment, sizes of assembled objects, and conditions of parts influence the work efficiency were studied. The results show when the assembled object is smaller that it is easier to change the object's position and that workers can move it to an appropriate site and work easily. If the assembly object is attached to an object with very large mass, the work allotment does not result in a difference in work time. As for positioning the objects, step-saving processes can shorten the work time. For instance, if a part can be put so that both ends automatically touch the proper spots, time can be shortened.     

Plasma transport during substorm growth phase and relation to breakup

For <_bi,_be, the electron and ion bounce frequencies, the response of a plasma to an externally applied electromagnetic perturbation is nonlocal. This implies, via the quasi-neutrality equation, the development of an electrostatic potential which is constant for a given magnetic field line. In the near equatorial region the corresponding potential electric field is shown to oppose the effect of the induced electric field associated with the externally applied perturbation. Thus the effect of the induced electric field is partially shielded; the total azimuthal electric field (i.e. induced plus potential) tends to be small, which explains why the radial flow velocity is slow during quasi-steady conditions prevailing during the growth phase and after the active phase. The nonlocal response of the plasma also leads to the development of a parallel current that may generate current driven Alfvén (CDA) waves, which mode convert into shear Alfvén (SA) waves. CDA/SA waves are systematically observed at early breakup; they grow very fast and produce a parallel diffusion of electrons. As soon as the diffusion time is shorter than the bounce time (_d<_b), the nonlocal response vanishes. Thus the shielding disappears, and an enhanced transport is restored at the rate fixed by the induced electric field alone. We show that fast flows effectively occur when CDA waves have enough power to diffuse electrons (over _d<_b). Electron parallel diffusion also leads to an interruption of the parallel current and therefore to a disruption of the perpendicular current.     

On-line Vehicle Motion Estimation from Visual Terrain Information Part II: Ground Velocity and Position Estimation

An algorithm, combining velocity/height estimates, obtained from an airborne body fixed image shift estimator with auxiliary on-board measurements and sparsely stored terrain profile information constitutes an entirely passive autonomous navigation system suitable for moderate-g flight missions. Two versions are addressed. The "naive estimator," in which altitude estimates are multiplied by velocity/height estimaters, yields ground velocity. Position, obtained by integration, diverges with time. The "extended Kalman filter" (EKF) version, in which velocity and position are defined as state space components, locks on the stored terrain profile and does not diverge with time. It degenerates into the "naive estimator" if the terrain is completely flat. Numerical examples indicate excellent performance potential of the EKF estimator.     

On-Line Vehicle Motion Estimation from Visual Terrain Information Part I: Recursive Image Registration

This paper addresses estimation of motion from the optical flow observed by an airborne down looking electro-optical sensor. The paper is in two parts. Part I addresses the development and analysis of a velocity-to-height ratio estimation algorithm and its principal error characteristics. In part II, it is shown how the information provided by the motion estimator can be integrated with additional on-board sensors to provide a complete autonomous navigation system. Part I as presented here is a summary version of the full length paper.? The algorithm implements recursive registration of successive images by using the gradient of a similarity function between them to control the tracking of their relative shift. The shift estimate provides velocity/height information. Substantial saving in memory and computation as compared to conventional full frame registration is achieved by using only a single line in the TV frame. Stochastic mathematical models for the image, terrain and vehicle velocity perturbations are used in the analysis. The choice of the most appropriate similarity function in the registration algorithm is addressed. Performance analysis indicates very small error variances, as illustrated by numerical examples.     

Post: Polar stratospheric telescope

The tropopause, typically at 16 to 18 km altitude at the lower latitudes, dips to 8 km in the polar regions. This makes the cold, dry and nonturbulent lower stratosphere accessible to tethered aerostats. Tethered aerostats can fly as high as 12 km and are extremely reliable, lasting for many years. In contrast to free-flying balloons, they can stay on station for weeks at a time, and payloads can be safely recovered for maintenance and adjustment and relaunched in a matter of hours. We propose to use such a platform, located first in the Arctic (near Fairbanks, Alaska) and, potentially, later in the Antarctic, to operate a new technology 6-meter, diluted aperture telescope with diffraction-limited performance in the near infrared. Thanks to the low ambient temperature (220 K), thermal emission from the optics is of the same order as that of the zodiacal light in the 2 to 3 micron band. Since this wavelength interval is the darkest part of the zodiacal light spectrum from optical wavelengths to 100 microns, the combination of high resolution images and a very dark sky make it the spectral region of choice for observing the redshifted light from galaxies and clusters of galaxies at moderate to high redshifts.Affiliated to the Astrophysics Division, Space Science Department, European Space Agency     

M-FISH analysis of chromosome aberrations in human fibroblasts exposed to energetic iron ions in vitro.

Confluent human fibroblast cells were exposed to 6 Gy gamma-rays or 200 MeV/nucleon Fe ions at 0.7 or 3 Gy. The cells were allowed to repair for 24 hours after exposure and chromosomes were collected using a premature chromosome condensation technique with calyculin-A. Chromosome aberrations were analyzed using the multicolor FISH (mFISH) technique that allows identification of both complex and truly incomplete exchanges. Results showed that both doses of the Fe ions produced higher ratios of complex to simple exchanges and lower ratio of complete to incomplete exchanges than the 6 Gy gamma-exposure. The ratios of aberration yields were similar for the two doses of Fe ions. After 0.7 Gy of Fe ions, most complex aberrations were found to involve three or four chromosomes, indicating this is the maximum number of chromosome domains traversed by a single Fe ion track.