The double-pulsar binary J0737–3039

A recent multibeam pulsar survey of the outer Galactic plane at Parkes has discovered the first-known double-pulsar binary, a very compact double neutron star system in which both stars are observable as radio pulsars. In this review, we briefly describe the discovery and the studies which have been enabled by the unique properties of the system. These range from the most precise confirmation yet of the theory of general relativity, with the possibility of even more new tests and the measurement of second-order post-Newtonian effects, to studies of the magnetospheres and emission properties of the two pulsars. The discovery also results in a significant increase in the expected rate of occurrence of the mergers of double neutron star systems, and hence the rate of detection of such events by the new ground-based gravitational wave detectors.     

Modeling the Modification of the Nighttime High-Latitude F-Region by Powerful HF Radiowaves

A mathematical model of the high-latitude F-region, taking the ionospheric plasma convection into account, is used for modeling a response of the auroral F-region to irradiation by powerful high-frequency (HF) radiowaves. The model enables us to calculate the time variations in the profiles of the electron concentration, the velocity of positive ions, and the ion and electron temperatures in the part of a magnetic-flux tube moving over an artificial ionospheric heater under the action of a convective electric field. The modeling was carried out for a part of the magnetic flux tube intersecting the F-layer irradiated by the Norwegian heater at Tromsö when it is located near the midnight magnetic meridian. The calculations were made for the equinox conditions under the high solar and low geomagnetic activity. The results of our modeling show that substantial variations in the profiles of the electron temperature, the velocity of positive ions, and the electron concentration can be produced in the nighttime high-latitude F-layer due to HF heating. The perturbation caused by a 20 s rectangular pulse should exist for about 20 min at the level of the F-layer maximum. The disturbed plasma volume can leave the region irradiated by the heater and move away for over 500 km within the above-mentioned time period.     

The conceptual design of a hybrid life support system based on the evaluation and comparison of terrestrial testbeds.

This report summarizes a trade study of different options of a bioregenerative Life Support System (LSS) and a subsequent conceptual design of a hybrid LSS. The evaluation was based mainly on the terrestrial testbed projects MELISSA (ESA) and BIOS (Russia). In addition, some methods suggested by the Advanced Life Support Project (NASA) were considered. Computer models, including mass flows were established for each of the systems with the goal of closing system loops to the extent possible. In order to cope with the differences in the supported crew size and provided nutrition, all systems were scaled for supporting a crew of six for a 780 day Mars mission (180 days transport to Mars; 600 days surface period) as given in the NASA Design Reference Mission Scenario [Hoffman, S.J., Kaplan, D.L. Human exploration of Mars: the Reference Mission of the NASA Mars Exploratory Study, 1997]. All models were scaled to provide the same daily allowances, as of calories, to the crew. Equivalent System Mass (ESM) analysis was used to compare the investigated system models against each other. Following the comparison of the terrestrial systems, the system specific subsystem options for Food Supply, Solid Waste Processing, Water Management and Atmosphere Revitalization were evaluated in a separate trade study. The best subsystem technologies from the trade study were integrated into an overall design solution based on mass flow relationships. The optimized LSS is mainly a bioregenerative system, complemented by a few physico-chemical elements, with a total ESM of 18,088 kg, which is about 4 times higher than that of a pure physico-chemical LSS, as designed in an earlier study.     

Generating requirements for complex embedded systems using State Analysis

It has become clear that spacecraft system complexity is reaching a threshold where customary methods of control are no longer affordable or sufficiently reliable. At the heart of this problem are the conventional approaches to systems and software engineering based on subsystem-level functional decomposition, which fail to scale in the tangled web of interactions typically encountered in complex spacecraft designs. Furthermore, there is a fundamental gap between the requirements on software specified by systems engineers and the implementation of these requirements by software engineers. Software engineers must perform the translation of requirements into software code, hoping to accurately capture the systems engineer's understanding of the system behavior, which is not always explicitly specified. This gap opens up the possibility for misinterpretation of the systems engineer's intent, potentially leading to software errors. This problem is addressed by a systems engineering methodology called State Analysis, which provides a process for capturing system and software requirements in the form of explicit models. This paper describes how requirements for complex aerospace systems can be developed using State Analysis, using representative spacecraft examples.     

Synthesis of biomass and utilization of plants wastes in a physical model of biological life-support system

The paper considers problems of biosynthesis of higher plants' biomass and "biological incineration" of plant wastes in a working physical model of biological LSS. The plant wastes are "biologically incinerated" in a special heterotrophic block involving Californian worms, mushrooms and straw. The block processes plant wastes (straw, haulms) to produce soil-like substrate (SLS) on which plants (wheat, radish) are grown. Gas exchange in such a system consists of respiratory gas exchange of SLS and photosynthesis and respiration of plants. Specifics of gas exchange dynamics of high plants--SLS complex has been considered. Relationship between such a gas exchange and PAR irradiance and age of plants has been established. Nitrogen and iron were found to the first to limit plants' growth on SLS when process conditions are deranged. The SLS microflora has been found to have different kinds of ammonifying and denitrifying bacteria which is indicative of intensive transformation of nitrogen-containing compounds. The number of physiological groups of microorganisms in SLS was, on the whole, steady. As a result, organic substances--products of exchange of plants and microorganisms were not accumulated in the medium, but mineralized and assimilated by the biocenosis. Experiments showed that the developed model of a man-made ecosystem realized complete utilization of plant wastes and involved them into the intrasystem turnover.     

Comments on the Communication and Data Problems Associated with a Mars Trip During a Conjunction Phase

The analysis and comments presented in this paper are meant to establish the general communication parameters associated with Martian flyby probes and with lander and manned vehicles. Fundamental data transfer problems are reviewed to define comparisons and trends of tradeoffs for future studies. Selected focal points are based upon the long propagation path length, with inherent time delays, and the high noise produced by the sun. These problems are magnified because large quantities of data must be obtained to satisfy the needs of the scientific community and the curiosity of an interested public. A comparison of two communication systems is provided: the microwave spectrum and the optical spectrum, as represented by the microwaves at 2.3 GHz and the laser at 6328 ?. A method of cost effectiveness or value received from space missions (a criterion of power input for data quantity received) is also presented.     

Surface characteristics of spacecraft components affect the aggregation of microorganisms and may lead to different survival rates of bacteria on Mars landers

Layers of dormant endospores of Bacillus subtilis HA101 were applied to eight different spacecraft materials and exposed to martian conditions of low pressure (8.5 mbar), low temperature (-10 degrees C), and high CO(2) gas composition and irradiated with a Mars-normal ultraviolet (UV-visible- near-infrared spectrum. Bacterial layers were exposed to either 1 min or 1 h of Mars-normal UV irradiation, which simulated clear-sky conditions on equatorial Mars (0.1 tau). When exposed to 1 min of Mars UV irradiation, the numbers of viable endospores of B. subtilis were reduced three to four orders of magnitude for two brands of aluminum (Al), stainless steel, chemfilm-treated Al, clear-anodized Al, and black-anodized Al coupons. In contrast, bacterial survival was reduced only one to two orders of magnitude for endospores on the non-metal materials astroquartz and graphite composite when bacterial endospores were exposed to 1 min of Mars UV irradiation. When bacterial monolayers were exposed to 1 h of Mars UV irradiation, no viable bacteria were recovered from the six metal coupons listed above. In contrast, bacterial survival was reduced only two to three orders of magnitude for spore layers on astroquartz and graphite composite exposed to 1 h of Mars UV irradiation. Scanning electron microscopy images of the bacterial monolayers on all eight spacecraft materials revealed that endospores of B. subtilis formed large aggregates of multilayered spores on astroquartz and graphite composite, but not on the other six spacecraft materials. It is likely that the formation of multilayered aggregates of endospores on astroquartz and graphite composite is responsible for the enhanced survival of bacterial cells on these materials.     

Microgravity effects on water supply and substrate properties in porous matrix root support systems.

The control of water content and water movement in granular substrate-based plant root systems in microgravity is a complex problem. Improper water and oxygen delivery to plant roots has delayed studies of the effects of microgravity on plant development and the use of plants in physical and mental life support systems. Our international effort (USA, Russia and Bulgaria) has upgraded the plant growth facilities on the Mir Orbital Station (OS) and used them to study the full life cycle of plants. The Bulgarian-Russian-developed Svet Space Greenhouse (SG) system was upgraded on the Mir OS in 1996. The US developed Gas Exchange Measurement System (GEMS) greatly extends the range of environmental parameters monitored. The Svet-GEMS complex was used to grow a fully developed wheat crop during 1996. The growth rate and development of these plants compared well with earth grown plants indicating that the root zone water and oxygen stresses that have limited plant development in previous long-duration experiments have been overcome. However, management of the root environment during this experiment involved several significant changes in control settings as the relationship between the water delivery system, water status sensors, and the substrate changed during the growth cycles.     

One year old and growing: a status report of the International Space Station and its partners.

The International Space Station (ISS), as the largest international science and engineering program in history, features unprecedented technical, cost, scheduling, managerial, and international complexity. A number of major milestones have been accomplished to date, including the construction of major elements of flight hardware, the development of operations and sustaining engineering centers, astronaut training, and eight Space Shuttle/Mir docking missions. International partner contributions and levels of participation have been baselined, and negotiations and discussions are nearing completion regarding bartering arrangements for services and new hardware. As ISS is successfully executed, it can pave the way for more inspiring cooperative achievements in the future.