Dose equivalent, absorbed dose and charge spectrum investigation in low Earth orbit.

Particle intensity, dose equivalent and absorbed dose have been measured on board the space shuttle Endeavour during STS-108 in December 2001 by Dublin Institute for Advanced Studies (DIAS). The dose estimates are based on very accurate measurements of recoils produced in CR-39 by cosmic ray primary and secondary protons and heavier nuclei and by secondary neutrons. The corresponding LET spectra were used to determine dose equivalent and absorbed dose values. Estimates of the total flux of Z > or = 2 nuclei have been undertaken and a preliminary charge spectrum was measured. Some comparisons are made with preliminary data obtained on STS-105 (ISS Expedition) and other missions using CR-39 detectors.     

GPS based onboard and onground orbit operations for small satellites

In extension to common applications such as groundtrack displays and antenna steering, the SGP4 orbit model is proposed for operational orbit determination in small satellite missions. SGP4 is an analytical orbit model for Low-Earth orbiting satellites that is widely used for the propagation of NORAD twoline elements. Twoline elements may hence be generated completely independent of NORAD. Their use as exclusive source of orbital information simplifies the operations concept and reduces mission costs through the extensive use of existing low-cost mission support software. Due to small computer resource requirements of 8–10kByte, the SGP4 model may also be applied for onboard orbit computations making use of e.g. a 80186 processor, thus ensuring full compatibility of ground-based and onboard operations. The proposed approach is particularly suited in combination with a space-borne GPS receiver, were the C/A-code navigation solutions are treated as measurements that are adjusted in a least-squares sense using the SGP4 model. As consequence, inherent drawbacks of the pure navigation solutions such as data gaps and scatter as well as limited velocity accuracy are avoided, while the operational navigation activities are kept at a minimum. The feasibility of the concept is illustrated based on real GPS navigation data from the TOPEX/Poseidon and the MIR space station with an inherent data quality of 50–100 m. It is shown that 3 hours of data within a 4 day period are sufficient to keep the position error within 4 km, that is considered sufficient for most applications.     

Possible mechanisms of plant cell wall changes at microgravity.

Space and clinostatic experiments revealed that changes of plant cell wall structure and its function depend on type of tissue and duration of influence. It was shown that clinostat conditions reproduce the part of weightlessness biological effects. It is established that various responses of wall structural-metabolic organization occur at microgravity: changes of cell walls ultrastructure and organelles structure; decrease of synthesis of primary plant cell wall; rearrangements of polysaccharides content. It is shown that mechanisms of plant cell wall changes at microgravity are connected with decrease of cellulose crystallization, activation of pectolytic enzymes and rearrangement of calcium balance of apoplast and cytoplasm.     

New instrumentation for optical measuring of oxygen in gas or dissolved in liquids.

The optical oxygen sensor is a novel device for the determination of oxygen in gases or dissolved in liquids. It is based on the measurement principle of fluorescence quenching, which is completely different from that of polarographic oxygen sensors (today the most widespread devices of oxygen detection). The new instrument offers features and advantages, which render it not only a realistic alternative, but, for specific applications, make it superior to existing electrochemical methods. The system is based on low-cost semiconductor devices (light-emitting diodes, photodiodes, low-cost analogue and digital components) and new LED-compatible oxygen-sensitive membranes. The flow cell of the instrument may be thermostatted and the sensor can be calibrated by a simple two-point calibration procedure. The optical oxygen sensor is particularly suitable for measuring dissolved oxygen in respirometry, since no oxygen is consumed by the device and the signal is independent of sample flowrate or stirring speed. Typical fields of application are monitoring of oxygen in ground and drinking water, in process control in bioreactors and in breath gas and blood gas analysis.     

Injuries to plants from controlled environment contaminants.

The use of controlled environments is subject to problems from contaminants emitted from materials of the system and from plants. Many contaminants are difficult to identify because injurious dosages are very low, there is a lack of information on what compounds injure plants, because species and cultivars differ greatly in their sensitivity to injury and injury symptoms often are not distinctive. Plastics have been shown to emit many different volatile compounds. The compound, di-butyl phthalate, contained in certain flexible plastics, has been shown to be very toxic to plants. Other injuries have been produced by caulking compounds and bonded screening. Paints have been shown to release xylene that is toxic to plants. Steam for humidification can cause problems because of hydroxylamines and other compounds added to steam used for heating to control fungal growth in return lines. Mercury, from broken thermometers is a particular problem in growth chambers because small quantities can collect in cracks and slowly volatilize to slow growth of plants. Plants themselves release large quantities of volatile hydrocarbons, with ethylene being the commonly recognized chemical that can be damaging when allowed to accumulate. People release large quantities of carbon dioxide which can cause variations in the rate of growth of plants. Contaminant problems can be controlled through filtering of the air or ventilation with make-up air, however the potential for problems is always present and careful testing should be undertaken with the particular species and cultivars being grown insure that there are no toxic agents altering growth in each particular controlled environment being utilized.     

Molecular alterations in tumorigenic human bronchial and breast epithelial cells induced by high LET radiation.

Carcinogenesis is a multi-stage process with sequence of genetic events governing the phenotypic expression of a series of transformation steps leading to the development of metastatic cancer. In the present study, immortalized human bronchial (BEP2D) and breast (MCF-10F) cells were irradiated with graded doses of either 150 keV/micrometer alpha particles or 1 GeV/nucleon 56Fe ions. Transformed cells developed through a series of successive steps before becoming tumorigenic in nude mice. Cell fusion studies indicated that radiation-induced tumorigenic phenotype in BEP2D cells could be completely suppressed by fusion with non-tumorigenic BEP2D cells. The differential expressions of known genes between tumorigenic bronchial and breast cells induced by alpha particles and their respective control cultures were compared using cDNA expression array. Among the 11 genes identified to be differentially expressed in BEP2D cells, three (DCC, DNA-PK and p21(CIP1)) were shown to be consistently down-regulated by 2 to 4 fold in all the 5 tumor cell lines examined. In contrast, their expressions in the fusion cell lines were comparable to control BEP2D cells. Similarly, expression levels of a series of genes were found to be altered in a step-wise manner among tumorigenic MCF-10F cells. The results are highly suggestive that functional alterations of these genes may be causally related to the carcinogenic process.     

An introduction to gravity perception in plants and fungi--a multiplicity of mechanisms.

The origin and subsequent evolution of life on Earth has taken place within an environment of which a 1g gravitational force is a part. Thus, all living organisms accommodate this variable in their structure and function. Evolution has also selected mechanisms to sense gravity which, in consequence, give particular orientations to living process. It is anticipated that the higher the evolutionary status of an organism, the greater the chance that it will possess multiple mechanisms of gravisensing because evolution discards nothing that assists fitness, but only adds to existing processes. A multiplicity of mechanisms permits gravity to participate in a wide range of developmental programmes, such as taxes, morphisms and tropisms, through the action of different sensors and distinct transduction/response pathways.     

Chromosome instability of HPRT-mutant subclones induced by ionising radiation of various LET.

The induction of HPRT-mutations and survival of Chinese hamster cells (line B11ii-FAF28, clone 431) were studied after irradiation by 4He and 12C-ions of various LET (20-360 keV/micrometers), produced by the U-200 heavy ion accelerator. The RBE increases with LET up to the maximum at 100-200 keV/micrometers and then decreases. Cytogenetic analysis was performed on the HPRT-mutant subclones selected from unirradiated Chinese hamster V-79 cells and from HPRT-mutant subclones that arose after exposure to gamma-rays, 1 GeV protons and 14N-ions (LET-77 keV/micrometers), produced by the synchrophasotron and the U-400M heavy ion accelerator. Slow growing mutant subclones were observed. The cytogenetic properties of individual clones were highly heterogeneous and chromosome instability was observed in both spontaneous and radiation-induced mutants. Chromosome instability was highest among spontaneous mutants and decreased with increasing LET.     

Design of the TRIO system-on-chip for aerospace

Several design and testing aspects of the TRIO smart sensor data acquisition chip, developed by JHU/APL for NASA spacecraft applications are presented. TRIO includes a 10 bit self-corrected analog-to-digital converter (ADC), 16/32 analog inputs, a front end multiplexer with selectable aquisition time, a current source, memory, serial and parallel bus, and control logic. So far TRIO is used in many missions including Contour, Messenger, Stereo, Pluto, and the generic JPL X2000 spacecraft bus.     

Controlled solar sail transfers into the near-sun orbits

We present results of numerical simulations of trajectories of a space probe with a flat solar sail which moves from a circular Earth orbit to near-Sun regions. We consider the upper limit of the sail temperature as the basic restriction. We also examine the planar (ecliptic) solar sail transfer with gravity-assist flybys around planets.