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NASA NTRS1992

Radiation health for a Mars mission

Uncertainties in risk assessments for exposure of a Mars mission crew to space radiation place limitations on mission design and operation. Large shielding penalties are imposed in order to obtain acceptable safety margins. Galactic cosmic rays (GCR) and solar particle events (SPE) are the major concern. A warning system and 'safe-haven' are needed to protect the crew from large SPE which produce lethal doses. A model developed at NASA Johnson Space Center (JSC) to describe solar modulation of GCR intensities reduces that uncertainty to less than 10 percent. Radiation transport models used to design spacecraft shielding have large uncertainties in nuclear fragmentation cross sections for GCR which interact with spacecraft materials. Planned space measurements of linear energy transfer (LET) spectra behind various shielding thicknesses will reduce uncertainties in dose-versus-shielding thickness relationships to 5-10 percent. The largest remaining uncertainty is in biological effects of space radiation. Data on effects of energetic ions in human are nonexistent. Experimental research on effects in animals and cell is needed to allow extrapolation to the risk of carcinogenesis in humans.

Robbins, Donald E.↗
NASA NTRS1996

Light ion components of the galactic cosmic rays: Nuclear interactions and transport theory

Light nuclei are present in the primary galactic cosmic rays (GCR) and are produced in thick targets due to projectile or target fragmentation from both nucleon and heavy induced reactions. In the primary GCR, He-4 is the most abundant nucleus after H-1. However, there are also a substantial fluxes of H-2 and He-3. In this paper we describe theoretical models based on quantum multiple scattering theory for the description of light ion nuclear interactions. The energy dependence of the light ion fragmentation cross section is considered with comparisons of inclusive yields and secondary momentum distributions to experiments described. We also analyze the importance of a fast component of lights ions from proton and neutron induced target fragementation. These theoretical models have been incorporated into the cosmic ray transport code HZETRN and will be used to analyze the role of shielding materials in modulating the production and the energy spectrum of light ions.

Cucinotta, F. A.↗
NASA NTRS1995

Shielding materials for highly penetrating space radiations

Interplanetary travel involves the transfer from an Earth orbit to a solar orbit. Once outside the Earth's magnetosphere, the major sources of particulate radiation are solar cosmic rays (SCR's) and galactic cosmic rays (GCR's). Intense fluxes of SCR's come from solar flares and consist primarily of protons with energies up to 1 GeV. The GCR consists of a low flux of nuclei with energies up to 10(exp 10) GeV. About 70 percent of the GCR are protons, but a small amount (0.6 percent) are nuclei with atomic numbers greater than 10. High energy charged particles (HZE) interact with matter by transferring energy to atomic electrons in a Coulomb process and by reacting with an atomic nucleus. Energy transferred in the first process increases with the square of the atomic number, so particles with high atomic numbers would be expected to lose large amounts of energy by this process. Nuclear reactions produced by (HZE) particles produce high-energy secondary particles which in turn lose energy to the material. The HZE nuclei are a major concern for radiation protection of humans during interplanetary missions because of the very high specific ionization of both primary and secondary particles. Computer codes have been developed to calculate the deposition of energy by very energetic charged particles in various materials. Calculations show that there is a significant buildup of secondary particles from nuclear fragmentation and Coulomb dissociation processes. A large portion of these particles are neutrons. Since neutrons carry no charge, they only lose energy by collision or reaction with a nucleus. Neutrons with high energies transfer large amounts of energy by inelastic collisions with nuclei. However, as the neutron energy decreases, elastic collisions become much more effective for energy loss. The lighter the nucleus, the greater the fraction of the neutron's kinetic energy that can be lost in an elastic collision. Thus, hydrogen-containing materials such as polymers are most effective in reducing the energy of neutrons. Once neutrons are reduced to very low energies, the probability for undergoing a reaction with a nucleus (the cross section) becomes very high. The product of such a reaction is often radioactive and can involve the release of a significant amount of energy. Thus, it is important to provide protection from low energy neutrons during a long duration space flight. Among the light elements, lithium and boron each have an isotope with a large thermal neutron capture cross section, Li-6 and B-10. However, B-10 is more abundant in the naturally-occurring element than Li-6, has a thermal neutron capture cross section four times that of Li-6, and produces the stable products, He-4 and Li-7 in the interaction while Li-6 produces radioactive tritium (H-3). Thus, boron is the best light-weight material for thermal neutron absorption in spacecraft. The work on this project was focused in two areas: computer design where existing computer codes were used, and in some cases modified, to calculate the propagation and interactions of high energy charged particles through various media, and materials development where boron was incorporated into high performance materials.

Kiefer, Richard L.↗
NASA NTRS1996

Study of Analytic Statistical Model for Decay of Light and Medium Mass Nuclei in Nuclear Fragmentation

The angular momentum independent statistical decay model is often applied using a Monte-Carlo simulation to describe the decay of prefragment nuclei in heavy ion reactions. This paper presents an analytical approach to the decay problem of nuclei with mass number less than 60, which is important for galactic cosmic ray (GCR) studies. This decay problem of nuclei with mass number less than 60 incorporates well-known levels of the lightest nuclei (A less than 11) to improve convergence and accuracy. A sensitivity study of the model level density function is used to determine the impact on mass and charge distributions in nuclear fragmentation. This angular momentum independent statistical decay model also describes the momentum and energy distribution of emitted particles (n, p, d, t, h, and a) from a prefragment nucleus.

Cucinotta, Francis A.↗
NASA NTRS1997

Shielding Strategies for Human Space Exploration

A group of twenty-nine scientists and engineers convened a 'Workshop on Shielding Strategies for Human Space Exploration' at the Lyndon B. Johnson Space Center in Houston, Texas. The provision of shielding for a Mars mission or a Lunar base from the hazards of space radiations is a critical technology since astronaut radiation safety depends on it and shielding safety factors to control risk uncertainty appear to be great. The purpose of the workshop was to define requirements for the development and evaluation of high performance shield materials and designs and to develop ideas regarding approaches to radiation shielding. The workshop was organized to review the recent experience on shielding strategies gained in studies of the 'Space Exploration Initiative (SEI),' to review the current knowledge base for making shield assessment, to examine a basis for new shielding strategies, and to recommend a strategy for developing the required technologies for a return to the moon or for Mars exploration. The uniqueness of the current workshop arises from the expected long duration of the missions without the protective cover of the geomagnetic field in which the usually small and even neglected effects of the galactic cosmic rays (GCR) can no longer be ignored. It is the peculiarity of these radiations for which the inter-action physics and biological action are yet to be fully understood.

Wilson J. W.↗
NASA NTRS1997

A SPDS Node to Support the Systematic Interpretation of Cosmic Ray Data

The purpose of this project was to establish and maintain a Space Physics Data System (SPDS) node that supports the analysis and interpretation of current and future galactic cosmic ray (GCR) measurements by (1) providing on-line databases relevant to GCR propagation studies; (2) providing other on-line services, such as anonymous FTP access, mail list service and pointers to e-mail address books, to support the cosmic ray community; (3) providing a mechanism for those in the community who might wish to submit similar contributions for public access; (4) maintaining the node to assure that the databases remain current; and (5) investigating other possibilities, such as CD-ROM, for public dissemination of the data products. Shortly after the original grant to support these activities was established at Louisiana State University a detailed study of alternate choices for the node hardware was initiated. The chosen hardware was an Apple Workgroup Server 9150/120 consisting of a 120 MHz PowerPC 601 processor, 32 MB of memory, two I GB disks and one 2 GB disk. This hardware was ordered and installed and has been operating reliably ever since. A preliminary version of the database server was available during the first year effort and was used as part of the very successful SPDS demonstration during the Rome, Italy International Cosmic Ray Conference. For this server version we were able to establish the html and anonymous FTP server software, develop a Web page structure which can be easily modified to include new items, provide an on-line database of charge changing total cross sections, include the cross section prediction software of Silberberg & Tsao as well as Webber, Kish and Schrier for download access, and provide an on-line bibliography of the cross section measurement references by the Transport Collaboration. The preliminary version of this SPDS Cosmic Ray node was examined by members of the C&H SPDS committee and returned comments were used to refine the implementation.

Source record↗
NASA NTRS1999

Evaluation of Spacecraft Shielding Effectiveness for Radiation Protection

The potential for serious health risks from solar particle events (SPE) and galactic cosmic rays (GCR) is a critical issue in the NASA strategic plan for the Human Exploration and Development of Space (HEDS). The excess cost to protect against the GCR and SPE due to current uncertainties in radiation transmission properties and cancer biology could be exceedingly large based on the excess launch costs to shield against uncertainties. The development of advanced shielding concepts is an important risk mitigation area with the potential to significantly reduce risk below conventional mission designs. A key issue in spacecraft material selection is the understanding of nuclear reactions on the transmission properties of materials. High-energy nuclear particles undergo nuclear reactions in passing through materials and tissue altering their composition and producing new radiation types. Spacecraft and planetary habitat designers can utilize radiation transport codes to identify optimal materials for lowering exposures and to optimize spacecraft design to reduce astronaut exposures. To reach these objectives will require providing design engineers with accurate data bases and computationally efficient software for describing the transmission properties of space radiation in materials. Our program will reduce the uncertainty in the transmission properties of space radiation by improving the theoretical description of nuclear reactions and radiation transport, and provide accurate physical descriptions of the track structure of microscopic energy deposition.

Cucinotta, Francis A.↗
NASA NTRS1998

Radiation Effects and Protection for Moon and Mars Missions

Manned and robotic missions to the Earth's moon and Mars are exposed to a continuous flux of Galactic Cosmic Rays (GCR) and occasional, but intense, fluxes of Solar Energetic Particles (SEP). These natural radiations impose hazards to manned exploration, but also present some constraints to the design of robotic missions. The hazards to interplanetary flight crews and their uncertainties have been studied recently by a National Research Council Committee (Space Studies Board 1996). Considering the present uncertainty estimates, thick spacecraft shielding would be needed for manned missions, some of which could be accomplished with onboard equipment and expendables. For manned and robotic missions, the effects of radiation on electronics, sensors, and controls require special consideration in spacecraft design. This paper describes the GCR and SEP particle fluxes, secondary particles behind shielding, uncertainties in radiobiological effects and their impact on manned spacecraft design, as well as the major effects on spacecraft equipment. The principal calculational tools and considerations to mitigate the radiation effects are discussed, and work in progress to reduce uncertainties is included.

Parnell, Thomas A.↗
NASA NTRS1999

Martian Radiation Environment Experiment (MARIE)

Space radiation presents a very serious hazard to crews of interplanetary human missions. The two sources of this radiation are the galactic cosmic rays (GCR) and solar energetic particle (SEP) events. The GCR provides a steady source of low dose rate radiation that is primarily responsible for stochastic effects, such as cancer, and can effect the response of the central nervous system. Nuclear interactions of these components with the Martian atmosphere produces substantial flux of neutrons with high Radio Biological Effectiveness. The uncertainty in the knowledge of many fragmentation cross sections and their energy dependence required by radiation transport codes, uncertainties in the ambient radiation environment, and knowledge of the Martian atmosphere, lead to large enough uncertainties in the knowledge of calculated radiation dose in both free space (cruise phase), in Martian orbit, and on Martian surface. Direct measurements of radiation levels, the relative contributions of protons, neutrons, and heavy ions, and Martian atmospheric characteristics is thus a prerequisite for any human mission. An integrated suite of two spectrometers to provide these data will be described. The Orbiter spectrometer will measure the energy spectrum of SEP events from 15 to 500 MeV/n, and when combined with data from other space based instruments, such as the Advanced Composition Explorer (ACE), would provide accurate GCR spectra also. The Lander spectrometer would measure the absorbed dose rate, dose equivalent dose rate, and the linear energy transfer (LET) spectra and is capable of separating the relative contribution of these quantities from protons, neutrons, and high Z particles. There are two separate flight instruments, one for the Orbiter and one for the Lander, based on a common design of the backplane, the central processing unit (CPU), power supply, and onboard data storage. The Orbiter instrument consists of an energetic particle spectrometer that can measure the elemental energy spectra of charged particles over energy range of 15-500 MeV/n. The spectrometer will be mounted on the science deck and has an angular acceptance of 50 degrees. As the spacecraft orbits Mars, the axis of this field of view sweeps a cone of directions on the sky. During each orbit, the angle between the axis of the spectrometer's field of view and the mean interplanetary field direction varies from 90 degrees to 180 degrees. The Lander instrument is designed: (1) to measure the accumulated absorbed dose and dose rate in tissue as a function of time, (2) to determine the radiation quality factor, (3) to determine the energy deposition spectrum from 0.1 keV/micron to 1500 keV/micron, and (4) to separate the contribution of protons, neutrons, and HZE particles to these quantities.

Badhwar, Gautam D.↗
NASA NTRS1999

Accelerator-Based Studies of Heavy Ion Interactions Relevant to Space Biomedicine

Evaluation of the effects of space radiation on the crews of long duration space missions must take into account the interactions of high energy atomic nuclei in spacecraft and planetary habitat shielding and in the bodies of the astronauts. These heavy ions (i.e. heavier than hydrogen), while relatively small in number compared to the total galactic cosmic ray (GCR) charged particle flux, can produce disproportionately large effects by virtue of their high local energy deposition: a single traversal by a heavy charged particle can kill or, what may be worse, severely damage a cell. Research into the pertinent physics and biology of heavy ion interactions has consequently been assigned a high priority in a recent report by a task group of the National Research Council. Fragmentation of the incident heavy ions in shielding or in the human body will modify an initially well known radiation field and thereby complicate both spacecraft shielding design and the evaluation of potential radiation hazards. Since it is impractical to empirically test the radiation transport properties of each possible shielding material and configuration, a great deal of effort is going into the development of models of charged particle fragmentation and transport. Accurate nuclear fragmentation cross sections (probabilities), either in the form of measurements with thin targets or theoretical calculations, are needed for input to the transport models, and fluence measurements (numbers of fragments produced by interactions in thick targets) are needed both to validate the models and to test specific shielding materials and designs. Fluence data are also needed to characterize the incident radiation field in accelerator radiobiology experiments. For a number of years, nuclear fragmentation measurements at GCR-like energies have been carried out at heavy ion accelerators including the LBL Bevalac, Saturne (France), the Synchrophasotron and Nuklotron (Dubna, Russia), SIS-18 (GSI, Germany), the Alternating Gradient Synchrotron at Brookhaven National Laboratory (BNL AGS) and the Heavy Ion Medical Accelerator (HIMAC) in Chiba, Japan. Until fairly recently most of these experiments were done to investigate fundamental problems in nuclear physics, but with the increasing interest in heavy charged particles on the part of the space flight, radiobiology and radiotherapy communities, an increasing number of experiments are being directed at these areas. Some of these measurements are discussed in references therein. Over the past several years, our group has taken cross section and fluence data at the AGS and HIMAC for several incident beams with nuclear charge, Z, between 6 and 26 at energies between 290 and 1050 MeV/nucleon. Iron (Z = 26) has been studied most extensively, since it is the heaviest ion present in significant numbers in the GCR. Targets have included tissue-equivalent and proposed shielding materials, as well as a variety of elemental targets for cross section measurements. Most of the data were taken along the beam axis, but measurements have been made off-axis, as well. Here we present selected data and briefly discuss some implications for spacecraft and planetary habitat design.

Miller, J.↗
NASA NTRS1999

Impact of Track Structure Effects on Shielding and Dosimetry

Galactic cosmic rays (GCR) consisting of nuclei of all the known elements with kinetic energies extending from tens to millions of MeV pose a significant health hazard to future deep space operations. Even half of the radiation exposures expected in ISS will result from GCR components. The biological actions of these radiations are known to depend on the details of the energy deposition (not just linear energy transfer, LET, but the lateral dispersion of energy deposition about the particle track). Energy deposits in tissues are dominated by the transfer of tens to hundreds of eV to the tissue's atomic electrons. In the case of low LET radiations, the collisions are separated by large dimensions compared to the size of important biomolecular structures. If such events are also separated in time, then the radiation adds little to the background of radicals occurring from ordinary metabolic processes and causes little or no biological injury. Hence, dose rate is a strong determinant of the action of low LET exposures. The GCR exposures are dominated by ions of high charge and energy (HZE) characterized by many collisions with atomic electrons over biomolecular dimensions, resulting in high radical- density events associated with a few isolated ion paths through the cell and minimal dose rate dependence at ordinary exposure levels. The HZE energy deposit declines quickly laterally and merges with the background radical density in the track periphery for which the exact lateral distribution of the energy deposit is the determinant of the biological injury. Although little data exists on human exposures from HZE radiations, limited studies in mice and mammalian cell cultures allow evaluation of the effects of track structure on shield attenuation properties and evaluation of implications for dosimetry. The most complete mammalian cell HZE exposure data sets have been modeled including the C3H10T1/2 survival and transformation data of Yang et al., the V79 survival and mutation data of various groups, and the Harderian gland tumor data of Alpen et al. Model results for the Harderian gland tumor data in comparison with data from Alpen et al. The Harderian target cell initiation cross section compares closely with the transformation cross section found for the C3H10T1/2 cell transformation data of Yang et al. The most notable feature of the cross sections are the multivalued cross sections for a given LET which implies the corresponding relative biological effectiveness (RBE) is dependent not only on the LET but also the ion type. This fact is at variance with the latest ICRP recommended quality factor which is a defined function of only the LET.

Wilson, J. W.↗
NASA NTRS1999

Quantitation of Radiation Induced Deletion and Recombination Events Associated with Repeated DNA Sequences

Manned exploration of space exposes the explorers to a complex and novel radiation environment. The galactic cosmic ray and trapped belt radiation (predominantly proton) components of this environment are relatively constant, and the variations with the solar cycle are well understood and predictable. The level of radiation encountered in low earth orbits is determined by several factors, including altitude, inclination of orbit with respect to the equator, and spacecraft shielding. At higher altitudes, and on a Mars mission, the level of radiation exposure will increase significantly. A significant fraction of the dose may be delivered by solar particle events which vary dramatically in dose rate and incident particle spectrum. High-LET radiation is of particular concern. High-LET radiation, a component of galactic cosmic rays (GCR), is comprised of a variety of charged particles of various energies (10 MeV/n to 10 GeV/n), including about 87% photons, 12% helium ions, and heavy ions (including iron). These high energy particles can cause significant damage to target cells. The different particle types and energies result in different patterns of energy deposition at the molecular and cellular level in a primary target cell. They can also cause significant damage to other, nearby cells as a result of secondary particles. Protons, for instance produce secondaries that include photons, neutrons, pions, heavy particles, as well as gamma rays. Heavy ions deposit energy in a "track" in which the magnitude of the damage varies as the particle loses energy. Heavy ions produce secondary delta rays, or electrons. The distribution of damage through tissue is described by a Bragg curve which will be characteristic for different energies. Needless to say there are differences in the RBE of protons and a particles. High-LET heavy ions are particularly damaging to cells as they do continual damage throughout their track. Differences in these energy deposition patterns can significantly influence the nature of DNA damage and the ability of cellular systems to repair such damage. It has been suspected that these differences also affect the spatial distribution of damage within the DNA of the interphase cell nucleus and produce corresponding differences in endpoints related to health effects. The interaction of a single high-LET particle with chromatin has been suggested to cause multiple double strand breaks within a relatively short distance. In part this is due to the organization of DNA into chromatin fibers in which distant regions of the DNA helix can be physically juxtaposed by the various levels of coiling of the DNA. This prediction was confirmed by the detection of the generation of double strand DNA fragments of 100-2000 bp following exposure to high-LET ions (including iron).

Sinden, Richard R.↗
NASA NTRS1999

Solar-Cosmic-Ray-Produced Nuclides in Extraterrestrial Matter

There are two main types of cosmic rays that have sufficient energy to induce nuclear reactions -- the galactic cosmic rays (GCR) and solar cosmic rays (also called solar energetic particles). Both types of particles can have production rates and production ratios in the small objects often found in cold and hot deserts that are different from those seen for most meteorites, which typically have radii of approx. 10-100 centimeters. GCR production rates are often lower than those for most meteorites. GCR production ratios, such as Ne-22/Ne-21, are also often different in small objects. Smaller meteoroids also are more likely to have nuclides made by solar-cosmic-ray (SCR) particles than typically-sized meteorites. The very small meteorite Salem had large amounts of SCR-produced radionuclides. Meteorites recovered in Antarctica are more likely to contain SCR-produced nuclides than other meteorites. Martian and lunar meteorites are also likely to have SCR-produced nuclides. Production rates and profiles for SCR-produced nuclides in meteoroids have been calculated previously. However, the cross sections for the nuclear reactions making many SCR-produced nuclides, such as Be-10 were not well measured then. New rates and profiles are calculated here using good cross sections for the reactions making these nuclides.

Reedy, Robert C.↗
NASA NTRS2000

Estimating Cosmic Ray Spectral Parameters from Simulated Detector Responses

A simple power law model consisting of a single spectral index al is believed to be an adequate description of the galactic cosmic ray (GCR) proton flux at energies below 100 TeV, with a transition at kink energy Ek to a steeper spectral index a2>al above Ek. The maximum likelihood procedure is developed for estimating these three spectral parameters of the broken power law energy spectrum from simulated detector responses. These estimates and their surrounding statistical uncertainty are being used to derive the requirements in energy resolution, calorimeter size, and energy response of a proposed sampling calorimeter for the Advanced Cosmic-ray Composition Experiment for the Space Station (ACCESS). This study thereby permits instrument developers to make important trade studies in design parameters as a function of the science objectives, which is particularly important for space-based detectors where physical parameters, such as dimension and weight, impose rigorous practical limits to the design envelope.

Howell, Leonard↗
NASA NTRS2000

Solar-Cosmic-Ray-Produced Nuclides in Extraterrestrial Matter

There are two main types of cosmic rays that have sufficient energy to induce nuclear reactions -- the galactic cosmic rays (GCR) and solar cosmic rays (also called solar energetic particles). Both types of particles can have production rates and production ratios in the small objects often found in cold and hot deserts that are different from those seen for most meteorites, which typically have radii of approx.10-100 centimeters. GCR production rates are often lower than those for most meteorites. GCR production ratios, such as Ne-22/Ne-21, are also often different in small objects. Smaller meteoroids also are more likely to have nuclides made by solar-cosmic-ray (SCR) particles than typically-sized meteorites. The very small meteorite Salem had large amounts of SCR-produced radionuclides. Meteorites recovered in Antarctica are more likely to contain SCR-produced nuclides than other meteorites. Martian and lunar meteorites are also likely to have SCR-produced nuclides. Production rates and profiles for SCR-produced nuclides in meteoroids have been calculated previously. However, the cross sections for the nuclear reactions making many SCR-produced nuclides, such as Be-10, were not well measured then. New rates and profiles are calculated here using good cross sections for the reactions making these nuclides.

Reedy, Robert C.↗
NASA NTRS2000

Radiation Physics for Space and High Altitude Air Travel

Galactic cosmic rays (GCR) are of extra-solar origin consisting of high-energy hydrogen, helium, and heavy ions. The GCR are modified by physical processes as they traverse through the solar system, spacecraft shielding, atmospheres, and tissues producing copious amounts of secondary radiation including fragmentation products, neutrons, mesons, and muons. We discuss physical models and measurements relevant for estimating biological risks in space and high-altitude air travel. Ambient and internal spacecraft computational models for the International Space Station and a Mars mission are discussed. Risk assessment is traditionally based on linear addition of components. We discuss alternative models that include stochastic treatments of columnar damage by heavy ion tracks and multi-cellular damage following nuclear fragmentation in tissue.

Cucinotta, F. A.↗
NASA NTRS2001

Composite Materials for Radiation Shielding During Deep Space Missions

Minimizing radiation exposure from the galactic cosmic ray (GCR) environment during deep space missions is essential to human health and sensitive instrument survivability. Given the fabrication constraints of space transportation vehicles protective shielding is, consequently, a complicated materials issue. These concerns are presented and considered in view of some novel composite materials being developed/suggested for GCR shielding applications. Advantages and disadvantages of the composites will be discussed as well as the need for coordinated testing/evaluation and modeling efforts.

Grugel, R. N.↗
NASA NTRS2000

Estimating Cosmic Ray Spectral Parameters From Simulated Detector Responses With Detector Design Implications

A simple power law model consisting of a single spectral index alpha (sub 1), is believed to be an adequate description of the galactic cosmic ray (GCR) proton flux at energies below 10(exp 13) eV, with a transition at knee energy E(sub k) to a steeper spectral index alpha(sub 2) greater than alpha(sub 1) above E(sub k). The maximum likelihood procedure is developed for estimating these three spectral parameters of the broken power law energy spectrum from simulated detector responses. These estimates and their surrounding statistical uncertainty are being used to derive the requirements in energy resolution, calorimeter size, and energy response of a proposed sampling calorimeter for the Advanced Cosmic ray Composition Experiment for the Space Station (ACCESS). This study thereby permits instrument developers to make important trade studies in design parameters as a function of the science objectives, which is particularly important for space-based detectors where physical parameters, such as dimension and weight, impose rigorous practical limits to the design envelope.

Howell, L. W.↗