Dosimetric mapping inside BIORACK

The experiment was flown in different locations inside BIORACK on the D1 mission. It contained different plastic detectors (cellulose nitrate, Lexan, and CR 39) and emulsions to measure the high LET components of the radiation environment. For low LET measurements thermoluminescence dosimeters (L iF) were used. The paper gives data about total dose, charge, energy, and LET spectra so far obtained. These data are compared with data of previous spaceflights.     

Embryogenesis and organogenesis of Carausius morosus under spaceflight conditions

The influence of cosmic radiation and/or microgravity on insect development was studied during the 7 day German Spacelab Mission D1. Eggs of Carausius morosus of five stages differing in sensitivity to radiation and in capacity to regeneration were allowed to continue their development in the BIORACK 22°C incubator, either at microgravity conditions or on the 1 g reference centrifuge. Using the Biostack concept - eggs in monolayers were sandwiched between visual track detectors - and the 1 g reference centrifuge, we were able to separate radiation effects from microgravity effects and also from combined effects of these two factors in space. After retrieval, hatching rates, growth kinetics and anomaly frequencies were determined in the different test samples. The early stages of development turned out to be highly sensitive to single hits of cosmic ray particles as well as to the temporary exposure to microgravity during their development. In some cases, the combined action of radiation and microgravity even amplified the effects exerted by the single parameters of space. Hits by single HZE particles caused early effects, such as body anomalies, as well as late effects, such as retarded growth after hatching. Microgravity exposure lead to a reduced hatching rate. A synergistic action of HZE particle hits and microgravity was established in the unexpectedly high frequency of anomal larvae. However, it cannot be excluded, that cosmic background radiation or low LET HZE particles are also causally involved in damage observed in the microgravity samples.     

Radiation stability of organic matter in liquid and frozen H2O, NH3 and water-ammonia mixtures

The redox properties of irradiated liquid and frozen H₂O, NH₃ and H₂O/NH₃ mixtures at 298 K and 77 K, resp., towards some simple organic molecules have been checked by injecting carrierfree ¹¹C atoms and analyzing their chemical state by means of radiochromatography. The reactions and the stability of organic products versus radiation dose (in this study by MeV protons) depend on temperature, phase state, mobility of radicals, their concentration and reactivity. Especially dangerous are the reactive OH and O₂H radicals which oxidize organic material to inorganic CO₂. Highest stability has been found at low temperatures (solid state, reduced mobility of radicals) and for systems containing H-donors (H₂O/NH₃ mixtures), which reduce the concentration of oxidizing radicals. The fact that many bodies in space consist of H₂O-ice with NH₃ and CH₄ additives at temperatures between 10 and 150 K is promising in view of the survival of organic matter under high doses of radiation.     

Radiation protection problems for the space station and approaches to their mitigation.

With the advent of a permanent manned space station the longstanding problems of radiation protection in manned spaceflight have acquired an immediacy. This paper endeavors to emphasize the gaps of our knowledge which must be closed for effective radiation protection. The information that is required includes the accurate determination of the exposure inside the space station to the various components of tile ionizing radiation, the evaluation of the biological importance of the different radiation qualities and the depth dose distribution of the less penetrating component. There is also the possibility of an interaction with weightlessness. It is necessary to establish adequate radiation protection standards and a system of dosimetric surveillance. There is a need for studies of possible methods of hardening selective shielding of the space station. Spaceflight experiments, which might contribute to the solution of some of these problems are discussed.     

Auxin polar transport in Arabidopsis under simulated microgravity conditions — Relevance to growth and development

Activity of auxin polar transport in inflorescence axes of Arabidopsis thaliana grown under simulated microgravity conditions was studied in relation to the growth and development. Seeds were germinated and allowed to grow on an agar medium in test tubes on a horizontal clinostat. Horizontal clinostat rotation substantially reduced the growth of inflorescence axes and the productivity of seeds of Arabidopsis thaliana (ecotypes Landsberg erecta and Columbia), although it little affected seed germination, development of rosette leaves and flowering. The activity of auxin polar transport in inflorescence axes decreased when Arabidopsis plants were grown on a horizontal clinostat from germination stage, being ca. 60% of 1 g control. On the other hand, the auxin polar transport in inflorescence axes of Arabidopsis grown in 1 g conditions was not affected when the segments were exposed to various gravistimuli, including 3-dimensional clinorotation, during transport experiments. Pin-formed mutant of Arabidopsis, having a unique structure of the inflorescence axis with no flower and extremely low levels of the activity of auxin polar transport in inflorescence axes and endogenous auxin, did not continue its vegetative growth under clinostat rotation. These facts suggest that the development of the system of auxin polar transport in Arabidopsis is affected by microgravity, resulting in the inhibition of growth and development, especially during reproductive growth.     

Spaceflight experiments with Arabidopsis starch-deficient mutants support a statolith-based model for graviperception.

In order to help resolve some of the controversy associated with ground-based research that has supported the starch-statolith theory of gravity perception in plants, we performed spaceflight experiments with Arabidopsis in Biorack during the January 1997 and May 1997 missions of the Space Shuttle. Seedlings of wild-type (WT) Arabidopsis, two reduced-starch strains, and a starchless mutant were grown in microgravity and then were given either a 30, 60, or 90 minute gravity stimulus on a centrifuge. By the 90 min 1-g stimulus, the WT exhibited the greatest magnitude of curvature and the starchless mutant exhibited the smallest curvature while the two reduced starch mutants had an intermediate magnitude of curvature. In addition, space-grown plants had two structural features that distinguished them from the controls: a greater number of root hairs and an anomalous hypocotyl hook structure. However, the morphological changes observed in the flight seedlings are likely to be due to the effects of ethylene present in the spacecraft. (Additional ground-based studies demonstrated that this level of ethylene did not significantly affect gravitropism nor did it affect the relative gravitropic sensitivity among the four strains.) Nevertheless, this experiment on gravitropism was performed the "right way" in that brief gravitational stimuli were provided, and the seedlings were allowed to express the response without further gravity stimuli. Our spaceflight results support previous ground-based studies of these and other mutants since increasing amounts of starch correlated positively with increasing sensitivity to gravity.     

Hypervelocity acceleration techniques: A review of exisiting capabilities and prospects for future developments

During the last few decades various techniques have made it possible to accelerate microparticles (10⁻⁶ – 10⁻¹⁵ gr) up to tens of km/sec and macroparticles (1 gr or so) up to 10 km/sec, thus furthering our understanding of many impact related phenomena occurring on the surfaces of celestial bodies.

This review will deal with existing techniques for the acceleration of hypervelocity projectiles. The performance of electrostatic accelerators, electromagnetic rail guns and related systems, plasma drag accelerators, light gas guns and explosive accelerating techniques is reviewed, and the capabilities and limitations of each type are briefly discussed. An attempt is made to assess the future promise of existing techniques and the realism of some current suggestions.     

Designing space vehicle shields for meteoroid protection: A new analysis

Dual-layer meteroid shields consisting of sacrificial bumper plates spaced some distance outboard from the vehicle hull are the most effective structures yet conceived for protecting space vehicles from supervelocity meteroid impacts. This paper presents a new analysis for designing dual-layer shields. The analysis is based upon energy and momentum conservation, fundamental electromagnetic radiation physics, and observation of results from extensive experimental impact investigations conducted at relatively low velocities (near 7 km/s). One important conclusion is that most of the kinetic energy of a meteoroid striking a dual-layer shield is expended as radiation at the stagnation zone on the face plate of the underlying structure. The analysis includes systematic procedures to evaluate the response of shield designs for a given impact threat. Similar applications of the analysis can be used to support a mathematically rigorous procedure for optimum shield design. The research described here supported the Halley Intercept Mission Project at the Jet Propulsion Laboratory, C.I.T., under Contract No. NAS 7–100, sponsored by the National Aeronautics and Space Administration.