Biological nitrogen fixation under primordial Martian partial pressures of dinitrogen.

Early Earth and early Mars were similar enough such that past geochemical and climatic conditions on Mars may have also been favorable for the origin of life. However, one of the most striking differences between the two planets was the low partial pressure of dinitrogen (pN2) on early Mars (18 mb). On Earth, nitrogen is a key biological element and in many ecosystems the low availability of fixed nitrogen compounds is the main factor limiting growth. Biological fixation of dinitrogen on Earth is a crucial source of fixed nitrogen. Could the low availability of dinitrogen in the primordial Martian atmosphere have prevented the existence, or evolution of Martian microbiota? Azotobacter vinelandii and Azomonas agilis were grown in nitrogen free synthetic medium under various partial pressures of dinitrogen ranging from 780-0 mb (total atmosphere=1 bar). Below 400 mb the biomass, cell number, and growth rate decreased with decreasing pN2. Both microorganisms were capable of growth at a pN2 as low as 5 mb, but no growth was observed at a pN2 < or = 1 mb. The data appear to indicate that biological nitrogen fixation could have occurred on primordial Mars (pN2=18 mb) making it possible for a biotic system to have played a role in the Martian nitrogen cycle. It is possible that nitrogen may have played a key role in the early evolution of life on Mars, and that later a lack of available nitrogen on that planet (currently, pN2=0.2 mb) may have been involved in its subsequent extinction.     

Current status and future plans for the general antiparticle spectrometer (GAPS)

We discuss current progress and future plans for the general antiparticle spectrometer experiment (GAPS). GAPS detects antideuterons through the X-rays and pions emitted during the deexcitation of exotic atoms formed when the antideuterons are slowed down and stopped in targets. GAPS provides an exceptionally sensitive means to detect cosmic-ray antideuterons. Cosmic-ray antideuterons can provide indirect evidence for the existence of dark matter in such form as neutralinos or Kaluza–Klein particles. We describe results of accelerator testing of GAPS prototypes, tentative design concepts for a flight GAPS detector, and near-term plans for flying a GAPS prototype on a balloon.     

Methods for rotor aerodynamic and dynamic analysis

The complex problems associated with the aerodynamics of blade/vortex interactions, the dynamics of a blade displaced out of its plane of rotation, and the position control of a hovering helicopter are discussed. Simplified models help to describe, and appear to be adequate for analysing, many aspects of these problems. Free wake analyses are shown to be of importance in determining blade loads and performance for hovering flight or for wind turbines. Unsteady aerodynamics and careful definition of the wake formation are required when computing vibratory airloads in forward flight.     

Nondestructive testing of honeycomb structures by computerized,thermographic systems

Complex honeycomb space structures (i.e. antennas, solar panels, etc.) must be inspected and accurately tested before flight.The thermography can be employed with success for the detection of the position of defects (delaminations, noneffective bondings, cracks, etc.) and for the evaluation of their size and geometry in all the cases in which the defect acts as a thermal resistance due to the low conductivity of the air filling the defect volume.The basic idea is to create in the specimen a heat flow distribution that is altered by the presence of the defect.The surface temperature distribution is then measured by means of a thermograph and is correlated with the presence of the defect.A numerical analysis and preliminary experiments have been carried out which show the feasibility of the method as applied to honeycomb structures.     

Effect of Observation Errors on Satellite Attitude Estimation

A study of the effect of observation errors on the best least squares estimate of satellite attitude based on two sets of direction measurements, where one set contains two independent measurements which are corrupted by zero-mean normally distributed additive errors, is summarized. Using Monte-Carlo techniques, the statistics of the estimated rotation of the satellite, from a known reference, were obtained. It was found that one of the parameterizations of the rotation, namely, the vector z, is best suited for estimation, since ?z is normally distributed with zero mean and its standard deviation is independent of the two direction measurements.     

Survey of High-Power Microwave Filters

A summary of research and development work on high-power microwave filters is given here: first, design considerations in high-power microwave filters?power handling capacity, waveform distortion, multimode suppression, and stop and pass band characteristics; second, a discussion of filtering devices and techniques in two broad categories-dominant mode filters and harmonic filters (discussion covers methods of operation and significant characteristics of each filter developed to date); and third, a discussion of applications and limitations of filters in various systems and interference situations. Also included are the availability, cost, size, weight, etc. as functions of frequency for the various filter types.     

Theory of Operation of an Elastically Supported Tuned Gyroscope

Detailed derivation of the transfer function for a multigimbal, elastically supported, tuned gyro is presented and comparison made between its characteristics and those of a classical two-axis, free-rotor gyro. Knowledge of the gyro transfer function is necessary for the purpose of servo analysis of the system in which the gyro is used; also, the transfer function is a basis of evaluation of errors caused by angular inputs that occur at twice spin frequency.     

The bimodal magnetosphere and ring current, radiation belt, and tail transducers

It has generally been assumed that a geomagnetic storm is entirely driven by external forces—e.g., solar wind E_y = V_x × B_z, V_x, V²_x (where the components of the electric field, E, the magnetic field, B, and velocity, V, are given in GSE coordinates)—which would imply that particle injections in the ring current (RC) or outer radiation belts should be highly correlated. However the data from ISTP are showing that the magnetosphere can have at least two very different responses to the same solar wind (SW) conditions: a classic, enhanced RC with Dst response, or a 1000-fold increase in the outer radiation belt MeV electrons (ORBE). August 29, October 14 and 23, 1996 are examples of Dst storms, whereas April 15, 1996 and January 10, 1997 are examples of MeV storms. It is this second response that is so deadly to some geosynchronous spacecraft, whereas geomagnetic storms are categorized by the first response. Neither of these appear to be correlated to the SW conditions driving substorms. Why should the SW energy appear in the radiation belts or the ring current independently? We hypothesize that the RC couples to the electric power available (E_y), the ORBE couple to the mechanical power available (V_x), and the Tail couples to the magnetic energy (B_z) available in the SW. The transducer for RC may be subauroral parallel potentials, the transducer for ORBE may be the cusp, while the Tail substorm transducer is yet a third independent mechanism for extracting SW energy. Evidence for this theory comes from the novel POLAR satellite that traverses the cusp, the plasmasheet and the radiation belts.