Changes in operational procedures to improve spaceflight experiments in plant biology in the European Modular Cultivation System

The microgravity environment aboard orbiting spacecraft has provided a unique laboratory to explore topics in basic plant biology as well as applied research on the use of plants in bioregenerative life support systems. Our group has utilized the European Modular Cultivation System (EMCS) aboard the International Space Station (ISS) to study plant growth, development, tropisms, and gene expression in a series of spaceflight experiments. The most current project performed on the ISS was termed Seedling Growth-1 (SG-1) which builds on the previous TROPI (for tropisms) experiments performed in 2006 and 2010. Major technical and operational changes in SG-1 (launched in March 2013) compared to the TROPI experiments include: (1) improvements in lighting conditions within the EMCS to optimize the environment for phototropism studies, (2) the use of infrared illumination to provide high-quality images of the seedlings, (3) modifications in procedures used in flight to improve the focus and overall quality of the images, and (4) changes in the atmospheric conditions in the EMCS incubator. In SG-1, a novel red-light-based phototropism in roots and hypocotyls of seedlings that was noted in TROPI was confirmed and now can be more precisely characterized based on the improvements in procedures. The lessons learned from sequential experiments in the TROPI hardware provide insights to other researchers developing space experiments in plant biology.     

Modeling gravity effects on water retention and gas transport characteristics in plant growth substrates

Growing plants to facilitate life in outer space, for example on the International Space Station (ISS) or at planned deep-space human outposts on the Moon or Mars, has received much attention with regard to NASA’s advanced life support system research. With the objective of in situ resource utilization to conserve energy and to limit transport costs, native materials mined on Moon or Mars are of primary interest for plant growth media in a future outpost, while terrestrial porous substrates with optimal growth media characteristics will be useful for onboard plant growth during space missions. Due to limited experimental opportunities and prohibitive costs, liquid and gas behavior in porous substrates under reduced gravity conditions has been less studied and hence remains poorly understood. Based on ground-based measurements, this study examined water retention, oxygen diffusivity and air permeability characteristics of six plant growth substrates for potential applications in space, including two terrestrial analogs for lunar and Martian soils and four particulate substrates widely used in reduced gravity experiments. To simulate reduced gravity water characteristics, the predictions for ground-based measurements (1 − g) were scaled to two reduced gravity conditions, Martian gravity (0.38 − g) and lunar gravity (0.16 − g), following the observations in previous reduced gravity studies. We described the observed gas diffusivity with a recently developed model combined with a new approach that estimates the gas percolation threshold based on the pore size distribution. The model successfully captured measured data for all investigated media and demonstrated the implications of the poorly-understood shift in gas percolation threshold with improved gas percolation in reduced gravity. Finally, using a substrate-structure parameter related to the gaseous phase, we adequately described the air permeability under reduced gravity conditions.     

Indications and counterindications for applying different versions of closed ecosystems for space and terrestrial problems of life support.

Different versions of manned closed ecosystems (CES) based on photosynthesis of unicellular and/or higher plants and chemosynthesis or bacteria are considered. Different versions of CES have been compared for applying them on Earth, Moon, Mars and Venus orbital stations, for Mars missions and planetary stations as well as to provide high-quality life in extreme conditions on the Earth. In microgravity [correction of mycrogravity] we recommend CES with unicellular organisms based on photosynthesis or chemosynthesis (depending of the availability of the light or electric energy). For the planetary stations with Moon gravity and higher CES with higher plants are recommended. Improvement of indoor air quality by CES biotechnology is considered.     

太阳电池电路深空探测服役环境与关键技术分析

针对月球、火星、木星等不同的深空探测任务，本文通过在轨服役环境分析，说明了火星探测火星表面光谱计算方法、火星光谱太阳电池设计思路、火星表面除尘技术路线及木星探测低温低光强技术风险。结合工程技术经验，给出了特殊任务应用条件下单片太阳电池推算整板输出功率的计算方法，解决了我国尚无特殊条件的瞬态大太阳模拟器作为整板输出功率测试地面模拟光源的工程难题，为相关科研人员提供参考。     

NASA历表在深空导航中的发展和比较

利用不同版本的数值历表,对我国正在进行的探月工程以及后续的金星、火星和木星等深空探测中的导航问题进行分析和讨论。对DE405、DE421和DE430的动力学模型及其使用的观测数据进行了分析比较,考察了历表的精度和稳定性。并根据DE430历表简单讨论了木星在我国深空探测站的可视问题,为以后深空导航提供参考。简单讨论了中科院国家天文台行星无线电研究团组基于月球无线电测距(LRR)发展我国自己的历表以及开展基于月球深空导航计划的可行性。     

Improved environment radiation models

The two components of the space radiation environment, galactic cosmic rays and solar energetic particles, are of special importance for the planning of space missions and designing space vehicles for flights in the inner heliosphere. There is a constant need for developing and updating the models for calculating the fluxes of these particles for purposes of forecasting radiation conditions anticipated for future flights, including missions to the Moon and Mars.     

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.     

Improvements in the re-flight of spaceflight experiments on plant tropisms

In order to effectively study phototropism, the directed growth in response to light, we performed a series of experiments in microgravity to better understand light response without the “complications” of a 1-g stimulus. These experiments were named TROPI (for tropisms) and were performed on the European Modular Cultivation System (EMCS), a laboratory facility on the International Space Station (ISS). TROPI-1 was performed in 2006, and while it was a successful experiment, there were a number of technical difficulties. We had the opportunity to perform TROPI-2 in 2010 and were able to optimize experimental conditions as well as to extend the studies of phototropism to fractional gravity created by the EMCS centrifuge. This paper focuses on how the technical improvements in TROPI-2 allowed for a better experiment with increased scientific return. Major modifications in TROPI-2 compared to TROPI-1 included the use of spaceflight hardware that was off-gassed for a longer period and reduced seed storage (less than 2 months) in hardware. These changes resulted in increased seed germination and more vigorous growth of seedlings. While phototropism in response to red illumination was observed in hypocotyls of seedlings grown in microgravity during TROPI-1, there was a greater magnitude of red-light-based phototropic curvature in TROPI-2. Direct downlinking of digital images from the ISS in TROPI-2, rather than the use of analog tapes in TROPI-1, resulted in better quality images and simplified data analyses. In TROPI-2, improved cryo-procedures and the use of the GLACIER freezer during transport of samples back to Earth maintained the low temperature necessary to obtain good-quality RNA required for use in gene profiling studies.     

Vision and Voyages for Deep Space Exploration

More than 50 years of space exploration has not only satisfied human curiosity and built up international cooperation, but also improved life on Earth. Space exploration is an open-ended process which started 50 years ago. It enables access to unknown terrains with robots and humans, thereby opening new frontiers. Progress of goal deep space exploration was reviewed. China's current deep space missions are also briefly introduced. Focused on the vision and voyages for China's deep space exploration in 5 or 10 years. Like the Chinese Lunar Exploration Program (CLEP), we embark on a journey to Mars. We will spend few decades on Mars with the robotic explorers. Unlike CLEP, scientists proposed to build Moon research station by 2030.      

Global approach to simulation: a gateway to long-term human presence in space.

The establishment of an autonomous European manned space capability is an objective set up by the ESA Council Meeting at the ministerial level, in 1985/1987. ESA's Long-Term Programme Office (LTPO), charged of the preparation of the programme for a European Manned Space Infrastructure (EMSI), started during 1988 to build up an intellectual framework in the domain of long-duration manned space missions. EMSI scope was eventually extended to embrace Moon/Mars missions and bases. Several exploratory studies on problems related to human factors in long-duration space missions were initiated by LTPO. The work of an ad-hoc group of experts (SIMIS Group) has been focused during 1989/1990 on the planning for simulation of such missions with a broad mandate, covering the physiological, psychological and operational aspects of long-duration exposure to microgravity and isolation/confinement. Preliminary results of SIMIS activities are reported. The HYDREMSI experiment, carried out in a terrestrial, analogous environment for 72 days during 1989, is described as an example of the envisaged simulations.     

A lunar laboratory

An international research laboratory can be established on the Moon in the early years of the 21st Century. It can be built using the transportation system now envisioned by the National Aeronautics and Space Administration, which includes a space station for Earth orbital logistics and orbital transfer vehicles for Earth-Moon transportation. A scientific laboratory on the Moon would permit extended surface and subsurface geological exploration; long-duration experiments defining the lunar environment and its modification by surface activity; new classes of observations in astronomy; space plasma and fundamental physics experiments; and lunar resource development. The discovery of a lunar source for propellants may reduce the cost of constructing large facilities in space and enhance other space programs such as Mars exploration.     

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.     

China's Lunar and Deep Space Exploration Program for the Next Decade (2020-2030)

China has carried out four unmanned missions to the Moon since it launched Chang'E-1, the first lunar orbiter in 2007. With the implementation of the Chang'E-5 mission this year, the three phases of the lunar exploration program, namely orbiting, landing and returning, have been completed. In the plan of follow-up unmanned lunar exploration missions, it is planned to establish an experimental lunar research station at the lunar south pole by 2030 through the implementation of several missions, laying a foundation for the establishment of practical lunar research station in the future. China successfully launched its first Mars probe on 23 July 2020, followed in future by an asteroid mission, second Mars mission, and a mission to explore Jupiter and its moons.      

Electrostatic space radiation shielding

For the success of NASA’s new vision for space exploration to Moon, Mars and beyond, exposures from the hazards of severe space radiation in deep space long duration missions is ‘a must solve’ problem. The payload penalty demands a very stringent requirement on the design of the spacecrafts for human deep space missions. The exploration beyond low Earth orbit (LEO) to enable routine access of space will require protection from the hazards of the accumulated exposures of space radiation, Galactic Cosmic Rays (GCR) and Solar Particle Events (SPE), and minimizing the production of secondary radiation is a great advantage. There is a need to look to new horizons for newer technologies. The present investigation revisits electrostatic active radiation shielding and explores the feasibility of using the electrostatic shielding in concert with the state-of-the-art materials shielding and protection technologies. The full space radiation environment has been used, for the first time, to explore the feasibility of electrostatic shielding. The goal is to repel enough positive charge ions so that they miss the spacecraft without attracting thermal electrons. Conclusions are drawn for the future directions of space radiation protection.     

Estimation and assessment of Mars contamination.

Since the beginning of the exploration of Mars, more than fourty years ago, thirty-six missions have been launched, including fifty-nine different space systems such as fly-by spacecraft, orbiters, cruise modules, landing or penetrating systems. Taking into account failures at launch, about three missions out of four have been successfully sent toward the Red Planet. The fact today is that Mars orbital environment includes orbiters and perhaps debris, and that its atmosphere and its surface include terrestrial compounds and dormant microorganisms. Coming from the UN Outer Space Treaty [United Nations Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies (the "Outer Space Treaty") referenced 610 UNTS 205 - resolution 2222(XXI) of December 1966] and according to the COSPAR planetary protection policy recommendations [COSPAR Planetary Protection Policy (20 October 2002), accepted by the Council and Bureau, as moved for adoption by SC F and PPP, prepared by the COSPAR/IAU Workshop on Planetary Protection, 4/02 with updates 10/0, 2002], Mars environment has to be preserved so as not to jeopardize the scientific investigations, and the level of terrestrial material brought on and around Mars theoretically has to comply with this policy. It is useful to evaluate what and how many materials, compounds and microorganisms are on Mars, to list what is in orbit and to identify where all these items are. Considering assumptions about materials, spores and gas location and dispersion on Mars, average contamination levels can be estimated. It is clear now that as long as missions are sent to other extraterrestrial bodies, it is not possible to keep them perfectly clean. Mars is one of the most concerned body, and the large number of missions achieved, on-going and planned now raise the question about its possible contamination, not necessarily from a biological point of view, but with respect to all types of contamination. Answering this question, will help to assess the potential effects of such contamination on scientific results and will address concerns relative to any ethical considerations about the contamination of other planets.     

Neuroplasticity changes during space flight.

Neuroplasticity refers to the ability of neurons to alter some functional property in response to alterations in input. Most of the inputs received by the brain and thus the neurons are coming from the overall sensory system. The lack of gravity during space flight or even the reduction of gravity during the planned Mars missions are and will change these inputs. The often observed "loop swimming" of some aquatic species is under discussion to be based on sensory input changes as well as the observed motion sickness of astronauts and cosmonauts. Several reports are published regarding these changes being based on alterations of general neurophysiological parameters. In this paper a summing-up of recent results obtained in the last years during space flight missions will be presented. Beside data obtained from astronauts and cosmonauts, main focus of this paper will be on animal model system data.     

Predicting the effects of gas diffusivity on photosynthesis and transpiration of plants grown under hypobaria

As part of a Bio-regenerative Life Support System (BLSS) for long-term space missions, plants will likely be grown at reduced pressure. This low pressure will minimize structural requirements for growth chambers on missions to the Moon or Mars. However, at reduced pressures the diffusivity of gases increases. This will affect the rates at which CO₂ is assimilated and water is transpired through stomata. To understand quantitatively the possible effects of reduced pressure on plant growth, CO₂ and H₂O transport were calculated for atmospheres of various total pressures (101, 66, 33, 22, 11 kPa) and CO₂ concentrations (0.04, 0.1 and 0.18 kPa). The diffusivity of a gas is inversely proportional to total pressure and shows dramatic increases at pressures below 33 kPa (1/3 atm). A mathematical relationship based on the principle of thermodynamics was applied to low pressure conditions and can be used for calculating the transpiration and photosynthesis of plants grown in hypobaria. At 33 kPa total pressure, the stomatal conductance increases by a factor of three with the boundary layer conductance increasing by a factor of ∼1.7, since the leaf conductance is a function of both stomatal and the boundary layer conductance, the overall conductance will increase resulting in significantly higher levels of transpiration as the pressure drops. The conductance of gases is also regulated by stomatal aperture in an inverse relationship. The higher CO₂ concentration inside the leaf air space during low pressure treatments may result in higher CO₂ assimilation and partial stomata closure, resulting in a decrease in transpiration rate. The results of this analysis offer guidelines for experiments in pressure and high CO₂ environments to establish ideal conditions for minimizing transpiration and maximizing the plant biomass yield in BLSS.     

Materials trade study for lunar/gateway missions.

The National Aeronautics and Space Administration (NASA) administrator has identified protection from radiation hazards as one of the two biggest problems of the agency with respect to human deep space missions. The intensity and strength of cosmic radiation in deep space makes this a 'must solve' problem for space missions. The Moon and two Earth-Moon Lagrange points near Moon are being proposed as hubs for deep space missions. The focus of this study is to identify approaches to protecting astronauts and habitats from adverse effects from space radiation both for single missions and multiple missions for career astronauts to these destinations. As the great cost of added radiation shielding is a potential limiting factor in deep space missions, reduction of mass, without compromising safety, is of paramount importance. The choice of material and selection of the crew profile play major roles in design and mission operations. Material trade studies in shield design over multi-segmented missions involving multiple work and living areas in the transport and duty phase of space mission's to two Earth-Moon co-linear Lagrange points (L1) between Earth and the Moon and (L2) on back side of the moon as seen from Earth, and to the Moon have been studied. It is found that, for single missions, current state-of-the-art knowledge of material provides adequate shielding. On the other hand, the choice of shield material is absolutely critical for career astronauts and revolutionary materials need to be developed for these missions. This study also provides a guide to the effectiveness of multifunctional materials in preparation for more detailed geometry studies in progress.     

Object injection in geodesic conditions: In-flight and on-ground testing issues

In absence of forces, any object moves along the straightest possible path in space–time, called geodesic. The presence of a gravity field generates a space–time distortion that reflects on a curvature of the geodesics. Outer space yields a privileged environment to achieve high levels of geodesic purity, thanks to the absence of many non-gravitational force disturbances typical of the Earth, mainly due to the atmosphere, micro-seismic activity, stray electro-magnetic fields, etc. Many experiments in the field of Fundamental Physics, General Relativity and Earth Observation are performed through space missions, in which objects are either set in geodesic conditions or their deviation from a geodesic is measured. In both cases, stray non-gravitational forces acting on them must be reduced to a negligible level.     

Planetary protection issues and the future exploration of Mars.

A primary scientific theme for the Space Exploration Initiative (SEI) is the search for life, extant or extinct, on Mars. Because of this, concerns about Planetary Protection (PP), the prevention of biological cross-contamination between Earth and other planets during solar system exploration missions, have arisen. A recent workshop assessed the necessity for, and impact of, PP requirements on the unmanned and human missions to Mars comprising the SEI. The following ground-rules were adopted: 1) information needed for assessing PP issues must be obtained during the unmanned precursor mission phase prior to human landings; 2) returned Mars samples will be considered biologically hazardous until proven otherwise; 3) deposition of microbes on Mars and exposure of the crew to Martian materials are inevitable when humans land; and, 4) human landings are unlikely until it is demonstrated that there is no harmful effect of Martian materials on terrestrial life forms. These ground-rules dictated the development of a conservative PP strategy for precursor missions. Key features of the proposed strategy include: 1) for prevention of forward contamination, all orbiters will follow Mars Observer PP procedures for assembly, trajectory, and lifetime. All landers will follow Viking PP procedures for assembly, microbial load reduction, and bioshield; and, 2) for prevention of back contamination, all sample return missions will have PP requirements which include fail-safe sample sealing, breaking contact chain with the Martian surface, and containment and quarantine analysis in an Earth-based lab. In addition to deliberating on scientific and technical issues, the workshop made several recommendations for dealing with forward and back contamination concerns from non-scientific perspectives.