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HUMEX, a study on the survivability and adaptation of humans to long-duration exploratory missions, part I: lunar missions.

The European Space Agency has recently initiated a study of the human responses, limits and needs with regard to the stress environments of interplanetary and planetary missions. Emphasis has been laid on human health and performance care as well as advanced life support developments including bioregenerative life support systems and environmental monitoring. The overall study goals were as follows: (i) to define reference scenarios for a European participation in human exploration and to estimate their influence on the life sciences and life support requirements; (ii) for selected mission scenarios, to critically assess the limiting factors for human health, wellbeing, and performance and to recommend relevant countermeasures; (iii) for selected mission scenarios, to critically assess the potential of advanced life support developments and to propose a European strategy including terrestrial applications; (iv) to critically assess the feasibility of existing facilities and technologies on ground and in space as testbeds in preparation for human exploratory missions and to develop a test plan for ground and space campaigns; (v) to develop a roadmap for a future European strategy towards human exploratory missions, including preparatory activities and terrestrial applications and benefits. This paper covers the part of the HUMEX study dealing with lunar missions. A lunar base at the south pole where long-time sunlight and potential water ice deposits could be assumed was selected as the Moon reference scenario. The impact on human health, performance and well being has been investigated from the view point of the effects of microgravity (during space travel), reduced gravity (on the Moon) and abrupt gravity changes (during launch and landing), of the effects of cosmic radiation including solar particle events, of psychological issues as well as general health care. Countermeasures as well as necessary research using ground-based test beds and/or the International Space Station have been defined. Likewise advanced life support systems with a high degree of autonomy and regenerative capacity and synergy effects were considered where bioregenerative life support systems and biodiagnostic systems become essential. Finally, a European strategy leading to a potential European participation in future human exploratory missions has been recommended.

Adaptation, Physiological↗

Experiment "Seeds" on Biokosmos 9. Dosimetric part.

The aim of the experiment "Seeds" on the Sowjetic satellite Biokosmos 9 was the observation of mutagenic effects caused at special loci of seeds of Arabidopsis thaliana and assigned to particles of the Cosmic radiation. Two types of exposure units were flown: A low-shielding unit Type I, mounted at the surface of the satellite (1.4 g/cm2 shielding) and, for comparison, an identical item inside (16 g/cm2 shielding), using nuclear emulsion as track detectors. A Type II unit, flown inside (18g/cm2 shielding) was mounted with AgCl track detectors. The layout will be briefly described. A first set of dosimetric data from the physical evaluation of the experiment will be presented. The subdivision into charge- and LET-groups shows a rather high contribution of the intermediate LET-group (350-1000 MeV/cm) due to medium heavy particles (Z = 6-10) and to enders of light (p, alpha) particles.

Arabidopsis↗

Doses due to the South Atlantic Anomaly during the Euromir'95 mission measured by an on-board TLD system.

During the Euromir'95 mission, a specially designed microprocessor-controlled thermoluminescent detector (TLD) system, called the 'Pille'95', was used by ESA astronaut Thomas Reiter to measure the cosmic radiation dose inside the Mir space station. One of the experiment's objectives was to determine the dose fraction on Mir due to the South Atlantic Anomaly (SAA) on an orbit inclined at 51.6 degrees and at an altitude of about 400 km. Using an hourly measuring period for 170 h in automatic mode, dose components both of galactic (independent of SAA) and SAA origin were determined. It was found that the maximum dose due to crossing the SAA was equal to 55 microGy. Averaging all the measurements it was calculated that the mean dose rate inside the Mir was 12-14 microGy h-1 and that half of this value was caused by the SAA.

Astronauts↗

Health physics concerns in commercial aviation.

Airline pilots and flight attendants are occupationally exposed to cosmic radiation. There has been uncertainty about how to handle the radiation protection requirements of their unique situation. Calculated dose equivalents associated with typical flight routes and crewmember work patterns have recently been published. The results show that flight attendants and pilots on ordinary subsonic aircraft can receive annual doses approaching 10 mSv y-1. I argue that flight crewmembers should receive specific education regarding the risks to their health from radiation exposure. I also argue that a suitable dosimeter system should be employed to provide crewmembers with information on their total doses. This is of particular importance for pregnant crewmembers who risk exceeding recommended fetal dose limits by working some routes during their pregnancy. In addition to airline crewmembers, business "frequent flyers" may receive significant occupational exposures while traveling. They too need appropriate education in order to assist them in assessing their risks from such exposures. Finally, flying during a large solar proton event would significantly increase the dose that would be received. During such an event, the total dose to the fetus of a pregnant crewmember or passenger might exceed the 0.5 mSv recommended monthly maximum. Warnings and action plans for these special circumstances should be improved.

Aviation↗

Investigations of doses on board commercial passenger aircraft using CR-39 and thermoluminescent detectors.

Measurements of cosmic radiation dose rates (from the neutron and the non-neutron components) on board passenger aircraft were performed using environmental packages with thermoluminescent TL and CR-39 etched track detectors. The packages were calibrated at the CERN-EU high-energy Reference Field Facility and evaluated at the Institute of Nuclear Physics in Krakow (TL + CR-39) and at the German Aerospace Centre in Cologne (CR-39). Detector packages were exposed on board passenger aircraft operated by LOT Polish Airlines, flown between February and May 2001. The values of effective dose rate determined, averaged over the measuring period, ranged between 2.9 and 4.4 microSv h(-1). The results of environmental measurements agreed to within 10% with values calculated from the CARI-6 code.

Aircraft↗

Study with a multi-threshold HZE-particle dosimeter using plastic detectors.

During the Apollo 16 and 17 missions two units of the Biostack experiment were exposed to cosmic radiation. In this experiment plastic detector sheets were used for recording and tracing the heavy ions. In some of these sheets the integral energy loss spectrum was measured. The measurements were performed in two different cellulose nitrate materials and in Lexan polycarbonate under 4 g cm-2 and 20 g cm-2 absorber thickness. The individual materials have different energy loss thresholds for the registration of heavy ions. The measured number of particles per cm2 with an restricted energy loss REL greater than REL0, follows a power law a REL(b) with b= -2.18 +/- 0.1 while the value of a depends on the exposure time and the absorber thickness. Calculations show that more than 70% of the fluence in the measured REL region is coming from particles with Z> or =20.

Collodion↗

Cytogenetic investigations in flight personnel.

During long-distance flights at high altitudes flight personnel are exposed to cosmic radiation. In order to determine whether there are biological effects of such low dose radiation exposure in aircrew, chromosomal aberrations were investigated in 59 female cabin attendants and a matched control group of 31 members of station personnel. The mean number of dicentric chromosomes amounts to 1.3 (95% CI 1.0-1.6) per 1000 cells in cabin attendants and 1.4 (95% CI 1.0-1.9) per 1000 cells in controls. In an additional control group of 56 female clerks from Berlin the mean frequency of dicentric chromosomes was 1.3 (95% CI 1.0-1.6). Neither in dicentric frequency and distribution nor in other aberrations was a significant difference between the groups of flight and station personnel found. The high frequency of multi-aberrant cells was remarkable in flight personnel as well as in station personnel. The reason for this phenomenon is unknown and needs further investigation.

Adult↗

Extra dose due to extravehicular activity during the NASA4 mission measured by an on-board TLD system.

A microprocessor-controlled on-board TLD system, 'Pille'96', was used during the NASA4 (1997) mission to monitor the cosmic radiation dose inside the Mir Space Station and to measure the extra dose to two astronauts in the course of their extravehicular activity (EVA). For the EVA dose measurements, CaSO4:Dy bulb dosemeters were located in specially designed pockets of the ORLAN spacesuits. During an EVA lasting 6 h, the dose ratio inside and outside Mir was measured. During the EVA, Mir crossed the South Atlantic Anomaly (SAA) three times. Taking into account the influence of these three crossings the mean EVA/internal dose rate ratio was 3.2. Internal dose mapping using CaSO4:Dy dosemeters gave mean dose rates ranging from 9.3 to 18.3 microGy h-1 at locations where the shielding effect was not the same. Evaluation results of the high temperature region of LiF dosemeters are given to estimate the mean LET.

Calcium Sulfate↗

The Italian national survey of aircrew exposure: II. On-board measurements and results.

The Italian survey of aircrew exposure has been carried out with different advanced dosimetric systems, as described in part I of this paper. The key strategy of the survey was to obtain on-board comparison of measurements for both passive and real-time detectors flown together with passengers. The survey has been carried out in the period of solar minimum (1995-1997), in which the exposure to galactic cosmic rays reaches its maximum value. Even though carrying out the survey in the period of solar minimum was entirely coincidental, this circumstance has been used to good advantage to obtain a comprehensive set of data of the galactic cosmic radiation with little or no disturbance by the solar activity modulation. This comprehensive set of data covers flight routes between -20 degrees and 75 degrees geographic latitude at different civil aviation altitudes. The survey obtained with different advanced dosimetric systems has been supplemented by a large variety of data gathered with passive stacks on different short-range and long-range flights at supersonic and subsonic altitudes. Some of the most important conclusions which can be drawn from the survey are: (i) aircrew of civil aviation receive annual doses within the range of 1 mSv to 6 mSv; (ii) data from different periods of solar minimum agree well, since the discrepancies encountered seem mainly due to the different dosimetric systems used; (iii) repeated measurements on the same route are highly consistent.

Aircraft↗

Serum antioxidant status of civil aircrew.

Objective. To study the serum antioxidant status in civil aircrew members who had more than 4000 h of cumulative flight hours, therefore exposed to a higher dose of cosmic radiation comparing to the dose received by ground residents. Method. Differences in the serum levels of total antioxidant capacity (TAOC), superoxide dismutase (SOD) and malondialdehyde (MDA) were investigated in 230 crew members, 37 local ground residents in Xinjiang, and 37 ground residents in Tianjin. Result. Significantly higher levels of all the three serum indexes were found in civil aircrew members. Serum levels of TAOC and SOD were higher in Xinjiang than in Tianjin ground residents, although no difference was found for MDA. Positive correlations were observed among the three serum indexes in this study. Conclusion. The elevated serum level of MDA in civil aircrew members deserves a proper attention by health care policy makers.

Adult↗

Proliferation kinetics of paramecium tetraurelia in balloon-borne experiments.

Experiments were carried out to demonstrate the effect of cosmic radiation, at a balloon-flight ceiling of about 36,500 m (120,000 ft) on single-cell organism proliferation. Paramecium tetraurelia were placed in air-tight containers and maintained at 25 degrees +/- 0.1 degrees C. Cellular growth was determined by cell count, either after recovery or during the flight, by means of an automatic fixation device. Dosimetry was performed by a tissue equivalent proportional counter and was of about 0.5 mrad/h. Flight ceiling duration ranged from 48 min - 22 h. A secondary stimulating effect of growth rate, preceded by a temporary decrease, was observed after recovery. Because of the high bacterial concentration in the trans-Mediterranean flight culture medium, the temporary drop of the growth rate, due to the radiolysis products, disappears. We consider that the stimulating effect can be the result of enzymatic intracellular scavenging of radiolysis products generated in the cell.

Altitude↗

Mutation induction in human lymphoid cells by energetic heavy ions.

One of the concerns for extended space flight outside the magnetosphere is exposure to galactic cosmic radiation. In the series of studies presented herein, the mutagenic effectiveness of high energy heavy ions is examined using human B-lymphoblastoid cells across an LET range from 32keV/micrometer to 190 keV/micrometer. Mutations were scored for an autosomal locus, thymidine kinase (tk), and for an X-linked locus, hypoxanthine phosphoribosyltransferase (hprt). For each of the radiations studied, the autosomal locus is more sensitive to mutation induction than is the X-linked locus. When mutational yields are expressed in terms of particle fluence, the two loci respond quite differently across the range of LET. The action cross section for mutation induction peaks at 61 keV/micrometer for the tk locus and then declines for particles of higher LET, including Fe ions. For the hprt locus, the action cross section for mutation is maximal at 95 keV/micrometer but is relatively constant across the range from 61 keV/micrometer to 190 keV/micrometer. The yields of hprt-deficient mutants obtained after HZE exposure to TK6 lymphoblasts may be compared directly with published data on the induction of hprt-deficient mutants in human neonatal fibroblasts exposed to similar ions. The action cross section for induction of hprt-deficient mutants by energetic Fe ions is more than 10-fold lower for lymphoblastoid cells than for fibroblasts.

Cell Line↗

Induction and rejoining of DNA double-strand breaks in CHO cells after heavy ion irradiation.

DNA double-strand breaks (DSBs) are the crucial events ultimately leading to cell inactivation. Aimed at understanding the biological action of the charged particle component of cosmic radiation, the induction of DSBs and their repairability was evaluated in Chinese hamster ovary (CHO-K1) cells after exposure to accelerated particles. Irradiations were performed with various ion species including O, Ni and Ca, covering a LET range from 20 to 2000 keV/micrometer. DSBs were determined for plateau-phase cells using the electrophoretic elution of radiation-induced DNA fragments in a static electric field combined with fluorescence scanning of ethidium bromide stained gels. Assuming a DSB yield of 22 DSB per Gy per cell, as derived from X-irradiation, cross-sections for DSB production were calculated from the corresponding fluence-effect curves at a fraction of 0.7 of DNA retained. The same ordinate was used as a reference for the calculation of relative biological efficiency (RBE) for DSB induction. At low LETs (< or = 20 keV/micrometer) RBE values slightly above unity were obtained, but a decrease of RBE was observed with increasing LET. In the region of 100-200 keV/micrometer the RBE for initial DSB induction was clearly below unity. Rejoining of DSBs was assessed by measuring the fraction of DNA retained following post-irradiation incubation of cells under culture conditions. After exposure to Ca ions, DSB rejoining was considerably impaired compared to X-rays.

Animals↗

Equivalent dose measurements on board an Armenian Airline flight and Concorde (correction of Concord) (9-17 km).

The results of investigations of the neutron component (E=1-10 MeV) of cosmic radiation on board the "Armenian Airlines" aircrafts using nuclear photoemulsion are presented. The emulsions were exposed on the flights from Yerevan to Moscow, St.-Petersburg, Beirut, Athens, Frankfurt, Amsterdam, Paris and Sofia, and on Concord supersonic flights from Paris to New York. The dependence of the neutron fluxes, and on absorbed and equivalent doses on the flight parameters were investigated. On the flights of the supersonic Concord, with an altitude of 17 km, the neutron fluxes were essentially higher in comparison to those measured on Armenian airliners. It is interesting to note, that the neutron flux and equivalent dose rate decrease with altitude up to 470 km in space, for example, on board the STS-57. The shape of the differential energy spectrum for fast neutrons is the same on all Armenian airlines flights, but significantly different at 17 km altitude, where the flux in the energy region above 3 MeV is increasing.

Aerospace Medicine↗

Dispersion of single-walled carbon nanotubes in a non-polar polymer, poly(4-methyl-1-pentene).

Poly(4-methyl-1-pentene), PMP, a high melting polymer composed of hydrogen and carbon, has the potential to become an alternative to polyethylene (PE) as shielding material against Galactic Cosmic Radiation (GCR). PMP exhibits higher thermal stability than PE and is transparent in the UV/visible region of the electromagnetic spectrum. Single walled carbon nanotubes (SWNTs) were pretreated with a polar solvent, N, N-Dimethylformimide (DMF), and then dispersed in a halogenated hydrocarbon, cyclohexyl chloride, which also dissolved the non polar polymer, PMP. The composites were characterized via differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), microhardness measurements, and optical microscopy. DMA data revealed that the carbon nanotubes contributed to the enhancement of the high temperature alpha(c) relaxation which is thought to arise from motion around crystalline regions in the matrix. The storage modulus (60 Hz) increased from 2409 MPa in the neat PMP to 3716 MPa at -50 degrees C. The magnitude of the increase diminished near and above the glass transition region; the glassy matrix restricted motion of the crystalline regions. DSC data showed an increase in the percent crystallinity of the composite (75%) as compared to the neat polymer (68%). Low concentrations of nanotubes, when well dispersed, produced nanocomposites with varying degrees of transparency.

Calorimetry, Differential Scanning↗

Evaluation of DNA damage in flight personnel by Comet assay.

There have been some suggestions that air-crew are at a higher-than-normal risk of developing cancer, since they are exposed to potential genotoxic factors. These include cosmic radiations, airborne pollutants such as the combustion products of jet propulsion, ozone, and electromagnetic fields. We used the Comet assay to investigate DNA damage in flight personnel with the aim of assessing potential health hazards in this occupational category. We studied 40 civil air-crew members who had been flying long-haul routes for at least 5 years, and compared them with a homogeneous control group of 40 healthy male ground staff. The Comet assay, or single-cell gel electrophoresis (SCGE), detects DNA single- and double-strand breaks (DSBs) and alkali-labile lesions in individual cells, and is a powerful and sensitive technique for detecting genetic damage induced by different genotoxic agents. Taking into consideration occupational risk and possible confounding factors, this assay showed a small increase, that did not reach statistical significance, of DNA damage in long-haul crew members compared to controls, indicating a lack of evident genotoxic effects. An association, although again not statistically significant, was found between reduced DNA damage and use of protective drugs (antioxidants).

Aircraft↗

Germination, growth rates, and electron microscope analysis of tomato seeds flown on the LDEF.

The purpose of the experiment was to determine cosmic rays long-term effects on living tissue. A batch of tomato seeds were flown in orbit aboard the Long Duration Exposure Facility (LDEF) for almost 6 y. During this time, the seeds received an abundant exposure to cosmic radiation. Upon the return of the LDEF to Earth, the seeds were distributed throughout the United States and 30 foreign countries for analysis. Our university analysis included germination and growth rates as well as scanning electron microscopy (SEM) and X-ray analysis of the control as well as space exposed tomato seeds. In analyzing the seeds under the electron microscope, usual observations were performed on the nutritional and epidermis layer of the seed. These layers appeared to be more porous in the space exposed seeds than on Earth-based control seeds. This unusual characteristic may explain the increases in the space seeds growth pattern. (Several test results showed that the space-exposed seeds germinated sooner than Earth-based seeds. Also, the space-exposed seeds grew at a faster rate.) The porous nutritional region may allow the seeds to receive necessary nutrients and liquids more readily, thus enabling the plant to grow at a faster rate. Roots, leaves and stems were cut into small sections and mounted. After sputter coating the specimens with argon/gold palladium plasma, they were viewed under the electron microscope. Many micrographs were taken. The X-ray analysis displayed possible identifications of calcium, potassium, chlorine, copper, aluminum, silicon, phosphate, carbon, and sometimes sulfur and iron. The highest concentrations were shown in potassium and calcium. As a result of the electron interaction and X-ray production within the open seeds, the traditional layers of the space-exposed seed gave peaks of Mg, P and S, while the Earth seed gave an iron peak, which was not detected in the space-exposed seed because of electron beam positioning difference. The space-exposed seed and the Earth-control seed specimens displayed high concentrations of copper.

Cosmic Radiation↗

Heavy-ion-induced mutations in the gpt delta transgenic mouse: comparison of mutation spectra induced by heavy-ion, X-ray, and gamma-ray radiation.

Heavy-ion radiation accounts for the major component of absorbed cosmic radiation and is thus regarded as a significant risk during long-term manned space missions. To evaluate the genetic damage induced by heavy particle radiation, gpt delta transgenic mice were exposed to carbon particle irradiation and the induced mutations were compared with those induced by reference radiations, i.e., X-rays and gamma-rays. In the transgenic mouse model, deletions and point mutations were individually identified as Spi(-) and gpt mutations, respectively. Two days after 10 Gy of whole-body irradiation, the mutant frequencies (MFs) of Spi(-) and gpt were determined. Carbon particle irradiation significantly increased Spi(-) MF in the liver, spleen, and kidney but not in the testis, suggesting an organ-specific induction of mutations by heavy-ion irradiation. In the liver, the potency of inducing Spi(-) mutation was highest for carbon particles (3.3-fold increase) followed by X-rays (2.1-fold increase) and gamma-rays (1.3-fold increase), while the potency of inducing gpt mutations was highest for gamma-rays (3.3-fold increase) followed by X-rays (2.1-fold increase) and carbon particles (1.6-fold increase). DNA sequence analysis revealed that carbon particles induced deletions that were mainly more than 1,000 base pairs in size, whereas gamma-rays induced deletions of less than 100 base pairs and base substitutions. X-rays induced various-sized deletions and base substitutions. These results suggest that heavy-ion beam irradiation is effective at inducing deletions via DNA double-strand breaks but less effective than X-ray and gamma-ray irradiation at producing oxidative DNA damage by free radicals.

Aerospace Medicine↗