| 1. |
- El-Jaby, S., et al.
(författare)
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ISSCREM: International Space Station cosmic radiation exposure model
- 2013
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Ingår i: IEEE Aerospace Conference Proceedings. - 1095-323X. - 9781467318112
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Konferensbidrag (refereegranskat)abstract
- A semi-empirical model is derived from operational data collected aboard the International Space Station (ISS) with the U.S. tissue equivalent proportional counter (TEPC). The model provides daily and cumulative mission predictions of the operational dose equivalent that space-crew may receive from galactic cosmic radiation (GCR) and trapped radiation (TR) sources as a function of the ISS orbit. The parametric model for GCR exposure correlates the TEPC dose equivalent rate to the cutoff rigidity at ISS altitudes while the TR parametric model relates this quantity to the mean atmospheric density at the crossing of the South Atlantic Anomaly (SAA). The influences of solar activity, flux asymmetry inside the SAA, detector orientation, and position aboard the ISS on the dose equivalent have been examined. The model has been successfully benchmarked against measured data for GCR and TR exposures to within ±10% and ±20%, respectively, over periods of time ranging from a single day to a full mission. In addition, preliminary estimates of the protection quantity of effective dose equivalent have been simulated using the PHITS Monte Carlo transport code. These simulations indicate that the TEPC dose equivalent is a conservative estimate of the effective dose equivalent.
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| 2. |
- Block, Jan, et al.
(författare)
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Using Monte Carlo simulation as support for decision making while negotiating a PBL contract
- 2014
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Ingår i: IEEE Aerospace Conference. Proceedings. - 1095-323X.
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Tidskriftsartikel (refereegranskat)abstract
- In connection with performance-based logistics (PBL) contracts for aircraft fleets it is very important to carefully analyse both operations and maintenance before and during the contract negotiation phase. Monte Carlo Simulation is a valuable methodology in this context since it allows delimiting and exploring a complex parameter space in a transparent and relatively easily visualized manner. With timely analyses it is possible to identify both technical and economic risks and minimize the possible consequences, a process that benefits both parties in the negotiation process. This paper describes a part of this process in connection with the negotiation of a PBL contract for the Swedish Air Force SAAB 105 (SK 60) trainer fleet between Saab AB and the Swedish Defence Materiel Administration (FMV). The information used in the simulations was largely empirical data derived from previous operations of the aircraft system. The main factors that were simulated were operational requirements, fleet size, spares inventories, turn-around times, failure rates and influence of extraneous factors (e. g. weather). The simulations resulted in considerable savings due to reduction of the active fleet size, and increased reclamation of surplus spares and units from retired aircraft.
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| 3. |
- Felicetti, Leonard, et al.
(författare)
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A comparison among classical and SDRE techniques in formation flying orbital control
- 2013
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Ingår i: 2013 IEEE Aerospace Conference. - Piscataway, NJ : IEEE Communications Society. - 9781467318112
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Konferensbidrag (refereegranskat)abstract
- A key point in formation flying mission design is represented by the accuracy and the cost of maintaining the requested orbital configuration. In fact, the relative geometry among spacecraft should be kept within tight limits in order to accomplish payload missions. At the same time, this effort requires to accommodate onboard the relevant amount of propellant, which should be correctly evaluated. The quest for optimal control strategy faces the non linear nature of the orbital dynamics, furthermore affected by perturbations that can be only modeled and therefore not perfectly known. As a result, traditional optimal strategies as the Linear Quadratic Controller (LQR), which design can be achieved under the hypothesis of simplified (as an example linearized) dynamics, not always meet the objective. Innovative approaches, like the State Dependent Riccati Equation (SDRE) technique, allow to better take into account, at an increasing level of approximations, the real dynamics. The paper presents extensive results of the simulations carried out for two different problems in formation flying control: the maintaining of a desired relative geometry and the acquisition of a requested configuration. A relevant point, also with respect to currently available literature, is the fact that the considered reference orbits have an eccentricity different from zero
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| 4. |
- Ghaemi, Hirad, 1980, et al.
(författare)
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CLEAN technique in strip-map SAR for high-quality imaging
- 2009
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Ingår i: IEEE Aerospace Conference Proceedings. - 1095-323X. - 9781424426225 ; , s. Art. no. 4839474-
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Konferensbidrag (refereegranskat)abstract
- The maximum obtainable resolution of a strip-map synthetic aperture radar (SAR) system can be retained by simply avoiding weighting, or tapering, data samples in the along-track compression process. However, this will lead to hazardous artifacts caused by strong sidelobes of the corresponding adjacent scatterers whose interference might severely weaken the desired targets or even introduce false targets. On the other hand, some residual artifacts, even after tapering process, may still deteriorate the quality (contrast) of the SAR image. These issues can be remedied by applying the so-called CLEAN technique, which can mitigate these ill-effects in strip-map SAR imagery while maintaining the maximum resolution. This, indeed, is carried out as a post processing step, i.e., after the azimuth compression is accomplished, in the SAR system. The objective of this paper is to extend the CLEAN technique to strip-map SAR system to produce high-quality images with a very good along-track resolution. The algorithm is then applied to data from a ground-based circular SAR (CSAR) system to verify its implementation as well as this new application of the CLEAN technique.
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| 5. |
- Mortazavi, S. A.R., et al.
(författare)
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Can Reactivation of SARS-CoV-2 Decrease the Chance of Success of Future Deep Space Missions?
- 2021
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Ingår i: IEEE Aerospace Conference Proceedings. - 1095-323X. ; 2021-March
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Konferensbidrag (refereegranskat)abstract
- Korean CDC experts first reported the likelihood of reactivation in COVIOD-19 patients. They hypothesized that like childhood chicken pox infections which lie dormant for tens of years only to cause shingles in seniors, SARS-CoV-2 can reactivate. However, as testing for the virus had been flawed at that time, U.S. infectious disease experts were skeptical about the reports of second COVID-19 infections. New reports have addressed the urgent need to conduct large-scale studies to better understand the potential recurrence of SARS-CoV-2 in COVID-19 patients. Moreover, some case studies show possible reactivation of SARS-CoV-2 in a family cluster. Given this consideration, major space stressors such as microgravity and space radiation and their interactions which are not fully known, so far can increase the risk of reactivation of SARS-CoV-2 in future space missions, an event that can easily impact the success of any space mission. Since about 80% of infected people are either asymptomatic or show only mild symptoms, in a near future, it would be likely that astronauts who start their mission even after complex medical examinations, experience reactivation of the virus during their mission. Moreover, we have previously addressed the potential higher fatality of COVID-19 infections in space due to 1) uselessness of social distancing due to microgravity 2) immune system dysregulation 3) possibly higher mutation rates of the novel coronavirus (SARS-CoV-2) as a RNA virus 4) higher risk of reactivation of the virus 5) existence of strong selective pressure and 6) decreased maximum oxygen uptake.
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| 6. |
- Mortazavi, S. M. J., et al.
(författare)
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Can Adaptive Response and Evolution Make Survival of Extremophile Bacteria Possible on Mars?
- 2020
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Ingår i: 2020 IEEE AEROSPACE CONFERENCE (AEROCONF 2020). - 1095-323X. - 9781728127347
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Konferensbidrag (refereegranskat)abstract
- The humidity on the surface of the red planet, Mars, drops steeply during the daytime as the temperature rises. In this situation, Martian microorganisms should have the capability to cope with desiccation. Extremophiles are microorganisms that are capable of surviving in extreme environmental conditions. It has previously been shown that a pre-exposure to low levels of either ionizing or non-ionizing radiation can induce resistance against subsequent exposure to high levels of different stressors (e.g. high doses of ionizing radiation) in a wide variety of living systems. Moreover, it has been shown that E. coli bacteria repeatedly exposed to a dose needed for 1% survival, and increasing the dose each time due to increased radioresistance for the same survival (1%), generates extremely radioresistant bacteria through directed evolution. Mortazavi et al. have warned that in a similar manner with extremophiles such as Deinococcus radiodurans, it would be very likely that this type of human-directed radioresistance makes E. coli bacteria resistant to all physical and chemical agents (generation of serious life-threatening micro-organisms). There are reports about the possibility of the existence of microbes in the salty puddles of Mars. On Mars, with its thin atmosphere and lack of the protective magnetic field, higher levels of space radiation cause more genetic mutations. Interestingly, these mutations in bacteria, which can make them resistant against radiation, can also make them resistant against desiccation. Moreover, the adaptive response to radiation in bacteria might play an important role in this process. As stated in a NASA report, the cells in the astronauts will be traversed by multiple protons before exposure to HZE particles. This sequential exposure might significantly increase the resistance against radiation. The same exposure in bacteria might not only induce resistance against the high levels of damage caused by HZEs, but also to other life-threatening factors for bacteria such as desiccation. In this paper, the current understanding of extremophiles and their capability of surviving in extreme environmental conditions as well as current findings about radioadaptive responses in bacteria will be discussed.
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| 7. |
- Mortazavi, S. M. J., et al.
(författare)
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Does Exposure of Astronauts' Brains to High-LET Radiation in Deep Space Threaten the Success of the Mission?
- 2020
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Ingår i: 2020 IEEE AEROSPACE CONFERENCE (AEROCONF 2020). - 1095-323X. - 9781728127347
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Konferensbidrag (refereegranskat)abstract
- Astronauts' exposure to radiation is different from exposure to radiation on Earth. Besides cancer, cardiovascular disease and acute radiation syndrome, there are concerns over the potential behavioral and cognitive impairments caused by exposure of the astronauts' central nervous system to high levels of space radiation. Therefore, potential behavioral and cognitive i mpairments caused by astronauts' brains exposure to high levels of space radiation and the possibility of developing dementia and other motor neuron diseases are getting more attention. As NASA is interested in studies on radium deposition in human brain, and exposure of the brain to high linear energy transfer (LET) alpha particles, we have assessed the cognitive effects of long-term exposure of human brain to alpha particles which partly mimics astronauts' exposure to high charge and energy (HZE) particles during upcoming mars missions. Dr. John Boice, President of NCRP, and his colleagues' have stated that human brain exposed for years to alpha particles on Earth may be more relevant to a Mars mission in contrast with the mouse brain exposed to heavy ions for a few minutes. Interestingly, both Boice and NASA did not pay enough attention to this fact that radium as well as many other alpha emitters tend to accumulate in the bone, and the alpha particles whose energies are typically -5 MeV have a very short range (maximum lOs of um), so the radiation dose due to the alpha emitters would be localized to volumes near the cranium rather than being uniformly distributed throughout the cerebral and cerebellar parenchyma. Extraordinary high levels of Ra-226 have previously been reported in high background radiation areas of Ramsar, where people are consuming locally grown foods. In this paper, we will present data which provide a human brain radiation exposure analogue for upcoming Mars missions. Normally the dose to the functional parts of the brain are not likely to be significant, even with higher uptakes of the radium or other alpha-emitting isotopes in the cranium. Therefore, only residents with calcium-rich diet were selected for the study. Measurements of background gamma radiation was performed in their bedrooms, dining rooms, vegetable yards and gardens with citrus fruit trees of the dwellings in areas with high levels of Ra-226 in the soil and at a nearby control area with the same socio-economic factors. Moreover, the food frequency, reaction time, working memory and computational abilities as well as the Radium Ingestion Index (RII) of 47 participants (22 males and 24 females) from the hot areas, where the annual radiation absorbed dose from background radiation is up to 260 mSv/y, were studied, and the same things were studied for 17 participants (4 males and 13 females) from a nearby normal background radiation area with the same socioeconomic factors as at the hot areas. Our study showed that exposure of human brain to high LET particles did not affect the working memory. However, individuals with higher levels of radium ingestion had significantly increased reaction times. The increased reaction time in individuals with higher exposure levels to alpha particles emitted from ingested Ra-226 is an important finding, since similar conditions might occur in deep space, when astronauts' brain cells are exposed to HZE particles. As the astronauts face numerous challenges in isolated and confined space environment, they should be able to respond quickly to different hazards. However, further studies are needed to verify if the fmdings in high radiation dose areas in Ramsar are relevant for deep space mission.
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| 8. |
- Mortazavi, S. M. J., et al.
(författare)
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Radioadaptation of Astronauts' Microbiome and Bodies in a Deep Space Mission to Mars and Beyond
- 2020
-
Ingår i: 2020 IEEE AEROSPACE CONFERENCE (AEROCONF 2020). - 1095-323X. - 9781728127347
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Konferensbidrag (refereegranskat)abstract
- During manned space missions, humans will be accompanied by microorganisms. This prompts us to study the characteristics of bacteria grown in space [1]. It has been shown that a pre-exposure to low levels of either ionizing or non-ionizing radiation can make microorganisms more resistant not only to high doses of ionizing radiation but to any factor that threatens their survival (e.g. antibiotics) [2,3]. This phenomenon that is called "adaptive response" (i.e. increased resistance in living organisms pre-exposed to a low level stressor such as a low dose of ionizing radiation) [4] significantly increases the risk of serious infections in deep space missions. It's worth noting that both animal and human data confirm the disruption of the immune system during spaceflight [5]. In addition, the virulence of bacteria can also be increased significantly in space [4], hence this kind of adaptive response which increases the resistance of bacteria can endanger the astronauts' lives in space. On the other hand, A NASA report notes that as astronauts' cells will be exposed to multiple protons before being traversed by HZE particles, they can show adaptive responses. Given this consideration, it would be realistic to expect co-radioadaptation of astronauts' microbiome and their body in a deep space journey to Mars and beyond. The complexity of these phenomena and current uncertainties, which highlight the need for further studies before any long-term manned mission, will be discussed in this paper.
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| 9. |
- Ota, S., et al.
(författare)
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Neutron Production in the Lunar Subsurface from Galactic Cosmic Rays
- 2009
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Ingår i: IEEE Aerospace Conference Proceedings. - 1095-323X. - 9781424438877
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Konferensbidrag (refereegranskat)abstract
- The neutron production from galactic cosmic ray (GCR) protons and alpha particles in the lunar subsurface was estimated using the three-dimensional Monte Carlo simulation code PHITS. The PHITS simulations of equilibrium neutron density profiles in the lunar subsurface were compared with experimental data by the Apollo 17 Lunar Neutron Probe Experiment. By use of the latest GCR spectra based on BESS measurements and well-benchmarked nuclear interaction models, our calculations well reproduced the data within the experimental error of 15% (measurement) + 30% (systematic) at the region shallower than 300 g/cm2. However, our calculation showed 10-20% higher values in the deeper region.
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| 10. |
- Sihver, Lembit, 1962, et al.
(författare)
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A comparison of total reaction cross section models used in FLUKA, GEANT4 and PHITS
- 2012
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Ingår i: Aerospace Conference, 2012 IEEE. ; , s. 1-10, s. 1 - 10
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Konferensbidrag (refereegranskat)abstract
- Understanding the interactions and propagations of high energy protons and heavy ions are essential when trying to estimate the biological effects of Galactic Cosmic Rays (GCR) and Solar Particle Events (SPE) on personnel on interplanetary missions, and when preparing the construction of a lunar base. To be able to calculate the secondary particles, including neutrons, and to estimate shielding properties of different materials and radiation risks inside complex geometries, particle and heavy ion transport codes are needed. The interactions of the GCR and SPE with matter include many complex properties and many factors influence the calculated results. In all particle and heavy ion transport codes, the probability function that a projectile particle will collide with a nucleus within a certain distance x in the matter depends on the total reaction cross sections, which also scale the calculated partial fragmentation cross sections. It is therefore crucial that accurate total reaction cross section models are used in the transport calculations. FLUKA, GEANT4 and PHITS are three major multi-purpose three-dimensional Monte Carlo particle and heavy ion transport codes widely used for fundamental research, radioprotection, radiotherapy, and space dosimetry. In this paper, a systematic comparison of the total reaction cross section models used as default in these three codes is performed for a variety of systems of importance for space dosimetry, and the need for future improvements and benchmarking against experimental results is discussed. The need for benchmarking and improvements of the partial nuclear reaction and evaporation models, as well as how impact parameter functions, switching time between the dynamical/pre-equilibrium and the de-excitation/evaporation stages, low energy data libraries, etc., influence the final results, is also briefly be discussed.
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