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- 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. |
- 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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