Implementing planetary protection requirements for sample return missions.

NASA is committed to exploring space while avoiding the biological contamination of other solar system bodies and protecting the Earth against potential harm from materials returned from space. NASA's planetary protection program evaluates missions (with external advice from the US National Research Council and others) and imposes particular constraints on individual missions to achieve these objectives. In 1997 the National Research Council's Space Studies Board published the report, Mars Sample Return: Issues and Recommendations, which reported advice to NASA on Mars sample return missions, complementing their 1992 report, The Biological Contamination of Mars Issues and Recommendations. Meanwhile, NASA has requested a new Space Studies Board study to address sample returns from bodies other than Mars. This study recognizes the variety of worlds that have been opened up to NASA and its partners by small, relatively inexpensive, missions of the Discovery class, as well as the reshaping of our ideas about life in the solar system that have been occasioned by the Galileo spacecraft's discovery that an ocean under the ice on Jupiter's moon Europa might, indeed, exist. This paper will report on NASA's planned implementation of planetary protection provisions based on these recent National Research Council recommendations, and will suggest measures for incorporation in the planetary protection policy of COSPAR.     

Radiation protection guidance for activities in low-Earth orbit.

Scientific Committee 75 (SC 75) of the National Council on Radiation Protection and Measurements (NCRP) was assembled for the purpose of providing guidance to NASA concerning radiation protection in low-Earth orbit. The report of SC 75 was published in December 2000 as NCRP Report No. 132. In this presentation an overview of the findings and recommendations of the committee report will be presented.     

A Novel Magnetic Configuration for Space Radiation Active Shielding

Space radiation has been identified as the main health hazard to crews involved in manned Mars missions. Active shielding is more effective than passive shielding to the very energetic particles from cosmic rays. Particle motion in a magnetic field is studied based on the single-particle theory and Monte Carlo method. By comparing the shielding efficiency of different magnetic field configurations, a novel active magnetic shielding configuration with lower mass cost and power consumption is proposed for manned Mars missions. The new magnetic configuration can shield 92.8% of protons and 84.4% of alpha particles with E < 4 GeV·n-1, when considering the passive shielding contribution of 10.0 g·cm-2 Al Shielding, the required magnetic stiffness can be reduced from 27 Tm to 16 Tm. The detailed analysis of mass cost and power consumption shows that active shielding will be a promising means to protect crews from space radiation exposure in manned Mars missions.      

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.     

Near-Earth radiation model deficiencies as seen on CRRES.

The Space Radiation (SPACERAD) experiments on the Combined Release and Radiation Effects Satellite (CRRES) gathered 14 months of radiation particle data in an 18 degrees inclination orbit between 350 km and 36000 km from July 1990 to October 1991. When compared to the NASA radiation belt models AP8 and AE8, the data show the proton model (AP8) does not take into account a second belt formed after major solar flare/shock injection events, and the electron model (AE8) is misleading, at best, in calculating dose in near-Earth orbits. The second proton belt, although softer in energy than the main proton belt, can produce upsets in proton sensitive chips and would produce significant dose in satellites orbiting in it. The MeV electrons observed on CRRES show a significant particle population above 5 MeV (not in the AE8 model) which must be included in any meaningful dose predictions for satellites operating between L-shells of 1.7 and 3.0 RE.     

载人深空探测任务的空间环境工程关键问题

对载人深空探测过程中将遭受的太阳宇宙射线、银河宇宙射线、微重力、尘与尘暴、深空微生物等环境进行分析。对不同深空环境给航天员带来的威胁进行了探讨。从物理屏蔽防护、辐射风险的监测和预警、辐射防护药物、航天员选拨等角度对采取的措施进行了阐述。从空间辐射对航天员的损伤机理、抗辐射和微重力药物开发、空间辐射屏蔽防护结构与材料、航天服自清洁、抗微生物侵蚀材料的研发等多个角度对需要进一步开展的工作进行了讨论。     

Comparison of organ dose and dose equivalent for human phantoms of CAM vs. MAX

For the evaluation of organ dose and dose equivalent of astronauts on space shuttle and the International Space Station (ISS) missions, the CAMERA models of CAM (Computerized Anatomical Male) and CAF (Computerized Anatomical Female) of human tissue shielding have been implemented and used in radiation transport model calculations at NASA. One of new human geometry models to meet the “reference person” of International Commission on Radiological Protection (ICRP) is based on detailed Voxel (volumetric and pixel) phantom models denoted for male and female as MAX (Male Adult voXel) and FAX (Female Adult voXel), respectively. We compared the CAM model predictions of organ doses to those of MAX model, since the MAX model represents the male adult body with much higher fidelity than the CAM model currently used at NASA. Directional body-shielding mass was evaluated for over 1500 target points of MAX for specified organs considered to be sensitive to the induction of stochastic effects. Radiation exposures to solar particle event (SPE), trapped protons, and galactic cosmic ray (GCR) were assessed at the specific sites in the MAX phantom by coupling space radiation transport models with the relevant body-shielding mass. The development of multiple-point body-shielding distributions at each organ made it possible to estimate the mean and variance of organ doses at the specific organ. For the estimate of doses to the blood forming organs (BFOs), data on active marrow distributions in adult were used to weight the bone marrow sites over the human body. The discrete number of target points of MAX organs resulted in a reduced organ dose and dose equivalent compared to the results of CAM organs especially for SPE, and should be further investigated. Differences of effective doses between the two approaches were found to be small (<5%) for GCR.     

A new Mars radiation environment model with visualization.

A new model for the radiation environment to be found on the planet Mars due to Galactic Cosmic Rays (OCR) has been developed at the NASA Langley Research Center. Solar modulated primary particles rescaled for Mars conditions are transported through the Martian atmosphere, with temporal properties modeled with variable timescales, down to the surface, with altitude and backscattering patterns taken into account. The Martian atmosphere has been modeled by using the Mars Global Reference Atmospheric Model--version 2001 (Mars-GRAM 2001). The altitude to compute the atmospheric thickness profile has been determined by using a model for the topography based on the data provided by the Mars Orbiter Laser Altimeter (MOLA) instrument on board the Mars Global Surveyor (MGS) spacecraft. The Mars surface composition has been modeled based on averages over the measurements obtained from orbiting spacecraft and at various landing sites, taking into account the possible volatile inventory (e.g., CO2 ice, H2O ice) along with its time variation throughout the Martian year. Particle transport has been performed with the HZETRN heavy ion code. The Mars Radiation Environment Model has been made available worldwide through the Space Ionizing Radiation Effects and Shielding Tools (SIREST) website, a project of NASA Langley Research Center.     

Comparison of the mean quality factors for astronauts calculated using the Q-functions proposed by ICRP,ICRU, and NASA

For the estimation of the radiation risk for astronauts, not only the organ absorbed doses but also their mean quality factors must be evaluated. Three functions have been proposed by different organizations for expressing the radiation quality, including the Q(L), Q(y), and Q_NASA(Z, E) relationships as defined in International Committee of Radiological Protection (ICRP) Publication 60, International Commission on Radiation Units and Measurements (ICRU) Report 40, and National Aeronautics and Space Administration (NASA) TP-2011-216155, respectively. The Q(L) relationship is the most simple and widely used for space dosimetry, but the use of the latter two functions enables consideration of the difference in the track structure of various charged particles during the risk estimation.     

Achieving and documenting closure in plant growth facilities.

As NASA proceeds with its effort to develop a Controlled Ecological Life Support System (CELSS) that will provide life support to crews during long duration space missions, it must address the question of facility and system closure. Here we discuss the concept of closure as it pertains to CELSS and describe engineering specifications, construction problems and monitoring procedures used in the development and operation of a closed plant growth facility for the CELSS program. A plant growth facility is one of several modules required for a CELSS. A prototype of this module at Kennedy Space Center is the large (7m tall x 3.5m diameter) Biomass Production Chamber (BPC), the central facility of the CELSS Breadboard Project. The BPC is atmospherically sealed to a leak rate of approximately 5% of its total volume per 24 hours. This paper will discuss the requirements for atmospheric closure in this facility, present CO2 and trace gas data from initial tests of the BPC with and without plants, and describe how the chamber was sealed atmospherically. Implications that research conducted in this type of facility will have for the CELSS program are discussed.     

A parametric study of space radiation exposures to critical body organs for low earth orbit missions.

The geomagnetically-trapped and galactic cosmic radiation environments are two of the major sources of naturally-occurring space radiation exposure to astronauts in low earth orbit. The exposure is dependent primarily on altitude, spacecraft shielding, crew stay-times, and solar cycle effects for a 28.5 deg orbital inclination. Based on Space Shuttle experience, the calculated results of a parametric study are presented for several mission scenarios using a computerized anatomical man model and are compared with the NASA crew exposure limits for several critical body organs.     

Radiation environments and absorbed dose estimations on manned space missions.

In order to make an assessment of radiation risk during manned missions in space, it is necessary first to have as accurate an estimation as possible of the radiation environment within the spacecraft to which the astronauts will be exposed. Then, with this knowledge and the inclusion of body self-shielding, estimations can be made of absorbed doses for various body organs (skin, eye, blood-forming organs, etc.). A review is presented of our present knowledge of the radiation environments and absorbed doses expected for several space mission scenarios selected for our development of the new radiation protection guidelines. The scenarios selected are a 90-day mission at an altitude (450 km) and orbital inclinations (28.5 degrees, 57 degrees and 90 degrees) appropriate for NASA's Space Station, a 15-day sortie to geosynchronous orbit and a 90-day lunar mission. All scenarios chosen yielded dose equivalents between five and ten rem to the blood forming organs if no large solar particle event were encountered. Such particle events could add considerable exposure particularly to the skin and eye for all scenarios except the one at 28.5 degrees orbital inclination.     

A consensus approach to planetary protection requirements: recommendations for Mars lander missions.

Over the last several years, the nature of the surface conditions on the planet Mars, our knowledge of the growth capabilities of Earth organisms under extreme conditions, and future opportunities for Mars exploration have been under extensive review in the United States and elsewhere. As part of these examinations, in 1992 the US Space Studies Board made a series of recommendations to NASA on the requirements that should be implemented on future missions that will explore Mars. In particular, significant changes were recommended in the requirements for Mars landers, changes that significantly alleviated the burden of planetary protection implementation for these missions. In this paper we propose a resolution implementing this new set of recommendations, for adoption by COSPAR at its 30th meeting in Hamburg. We also discuss future directions and study areas for planetary protection, in light of changing plans for Mars exploration.     

Analysis of the space radiation doses obtained simultaneously at two different locations outside the ISS

Space weather and related ionizing radiation has been recognized as one of the main health concerns for the International Space Station (ISS) crew. The estimation of the radiation effect on humans outside the ISS requires at first order accurate knowledge of their accumulated absorbed dose rates, which depend on the global space radiation distribution, solar cycle and local variations generated by the 3D mass distribution surrounding the ISS. The R3DE (Radiation Risks Radiometer-Dosimeter for the EXPOSE-E platform) on the European Technological Exposure Facility (EuTEF) worked successfully outside of the European Columbus module between February 2008 and September 2009. A very similar instrument named R3DR for the EXPOSE-R platform worked outside the Russian Zvezda module of the ISS between March 2009 and August 2010. Both are Liulin-type detectors, Bulgarian-built miniature spectrometer-dosimeters. The acquired approximately 5 million deposited energy spectra from which the flux and absorbed dose rate were calculated with 10 s resolution behind less than 0.41 g cm⁻² shielding. This paper analyses the spectra collected in 2009 by the R3DE/R instruments and the long-term variations in the different radiation environments of Galactic Cosmic Rays (GCR), inner radiation belt trapped protons in the region of the South Atlantic Anomaly (SAA) and relativistic electrons from the Outer Radiation Belt (ORB). The R3DE instrument, heavily shielded by the surrounding structures, measured smaller primary fluxes and dose rates from energetic protons from the SAA and relativistic electrons from the ORB but higher values from GCRs because of the contribution from secondary particles. The main conclusion from this investigation is that the dose rates from different radiation sources around the International Space Station (ISS) have a large special and temporal dynamic range. The collected data can be interpreted as possible doses obtained by the cosmonauts and astronauts during Extra Vehicular Activities (EVA) because the R3DE/R instruments shielding is very similar to the Russian and American space suits average shielding (,  and ). Fast, active measurements are required to assess accurately the dose accumulated by astronauts during EVA.     

Issues and problems for radiobiological research in space.

The uniqueness of the space radiation field creates specific problems in the evaluation of hazards to men and materials. Comprehensive measurements of all physical parameters are necessary but not sufficient. Particular attention has to be paid to variables like solar flares by applying fast-responding active dosimetry. The assessment of biological consequences poses even more problems. There are no human data for the kinds of particles seen in space and they will presumably never be available. The only reasonable approach is therefore to use the information obtained for other radiations and check their applicability for the space situation. This involves both the study of fundamental processes in ground experiments as well as their verification in space missions. Special emphasis has to be laid on the modification of radiation effects by flight-dynamic factors and microgravity. Radiation protection guidelines for space flights cannot simply be transformed from existent regulations designed for radiation workers on earth but have to be tailored to the specific situation in space.     

Planetary Protection Policy (U.S.A.).

Through existing treaty obligations of the United States, NASA is committed to exploring space while avoiding biological contamination of the planets, and to the protection of the Earth against harm from materials returned from space. Because of the similarities between Mars and Earth, plans for the exploration of Mars evoke discussions of these Planetary Protection issues. US Planetary Protection Policy will be focused on the preservation of these goals in an arena that will change with the growth of scientific knowledge about the martian environment. Early opportunities to gain the appropriate data will be used to guide later policy implementation. Because human presence on Mars will result in the end of Earth's separation from the martian environment, it is expected that precursor robotic missions will address critical planetary protection concerns before humans arrive.     

Radiation effects in space.

The radiation protection guidelines of the National Aeronautics and Space Administration (NASA) are under review by Scientific Committee 75 of the National Council Protection and Measurements. The re-evaluation of the current guidelines is necessary, first, because of the increase in information about radiation risks since 1970 when the original recommendations were made and second, the population at risk has changed. For example, women have joined the ranks of the astronauts. Two types of radiation, protons and heavy ions, are of particular concern in space. Unfortunately, there is less information about the effects on tissues and cancer by these radiations than by other radiations. The choice of Quality Factors (Q) for obtaining dose equivalents for these radiations, is an important aspect of the risk estimate for space travel. There are not sufficient data for the induction of late effects by either protons or by heavy ions. The current information suggests a RBE for the relative protons of about 1, whereas, a RBE of 20 for tumor induction by heavy ions, such as iron-56, appears appropriate. The recommendations for the dose equivalent career limits for skin and the lens of the eye have been reduced but the 30-day and annual limits have been raised.