104 research outputs found
Two and three impulses phasing strategy with a spacecraft orbiting on an Earth–Moon NRHO
No full textThe increasing interests in Moon exploration have led in recent years to international collaborations between space agencies aimed to assemble and operate the Gateway, an orbiting spaceport located on a Near Rectilinear Halo Orbit (NRHO) about the second libration point of the Earth–Moon system (EML-2). In this context, transfer strategies between the Earth and the spaceport cover a key role for both assembly and resupply missions. The presented work is thus focused on one leg of the transfer: the phasing maneuver. This work is conducted under the hypotheses of the Circular Restricted Three-Body problem (CR3BP) in which the Earth and the Moon are the only bodies that influence the spacecraft motion. The primaries are assumed to have a circular motion around their common barycenter. Under these hypotheses, is demonstrated the existence of periodic orbits, such as the Halo orbit family, that are exploited to design a proposed phasing maneuver. Two strategies are investigated: Halo parking orbit to NRHO two-impulses transfer and direct phasing with manifold exploitation. The first strategy is an optimal two-impulses transfer departing an EML-2 southern Halo and targeting the baseline NRHO. The second strategy considers the chaser already injected on the Gateway's NRHO. Poincare maps are employed to identify unstable/stable manifolds intersections in search of low-energy phasing trajectories that leave the reference orbit along the unstable branch before re-entering it via the stable one. Three-impulses transfers with similar costs are found patching together these arcs. The two strategies are thus compared to highlight their advantages and disadvantages with the perspective of a real autonomous cargo mission around the Moon to refurnish the orbiting station
Two and Three Impulses Phasing Strategy with a Spacecraft Orbiting on a Earth-Moon NRHO
No full textThe increasing interests in Moon exploration has led in recent years to international collaborations between space agencies aimed to assemble and operate the Gateway, an orbiting spaceport located on a Near Rectilinear Halo Orbit (NRHO) about the second libration point of the Earth-Moon system (EML2). In this context, transfer strategies between the Earth and the spaceport cover a key role for both assembly and resupply missions. The presented work is thus focused on one leg of the transfer: the phasing manoeuvre. This work is conducted under the hypotheses of the Circular Restricted Three Body problem (CR3BP) in which the Earth and the Moon are the only bodies that influence the spacecraft motion. The primaries are assumed to have a circular motion around their common barycentre. Under these hypotheses, is demonstrated the existence of periodic orbits, such as the Halo orbit family, that are exploited to design a proposed phasing manoeuvre. Two strategies are investigated: Halo parking orbit to NRHO two-impulse transfer and direct phasing with manifold exploitation. The first strategy is an optimal two-impulse transfer departing an EML-2 southern Halo and targeting the baseline NRHO. The second strategy considers the chaser already injected on the Gateway's NRHO. Poincare maps are employed to identify unstable/stable manifolds intersections in search of low-energy phasing trajectories that leave the reference orbit along the unstable branch before re-entering it via the stable one. Three-impulse transfers with similar costs are found patching together these arcs. The two strategies are thus compared to highlight their advantages and disadvantages with the perspective of a real autonomous cargo mission around the Moon to refurnish the orbiting station
Exploiting Coherent Patterns for the Analysis of Qualitative Motion and the Design of Bounded Orbits Around Small Bodies
Get PDFMissions around small bodies present many challenges from their design to the operations, due to the highly non-linear and uncertain dynamics, the limited Δv budget and constraints coming from orbit determination and mission design. Within this context, mathematical tools to enhance the understanding of the dynamics behavior can be proven useful to support the mission design process. Chaos indicators are adopted to reveal patterns of time-dependent dynamical systems and to enable the identification of practical stability regions, which are then exploited to design bounded orbits in the proximity of small bodies. The methodology is applied to study the MMX and Hera missions. In the MMX context, the final goal is to obtain bounded orbits useful for the global surface mapping and gravity potential determination of Phobos. On the other hand, concerning the Hera mission, a qualitative analysis of the natural motion about the Didymos binary asteroid system is carried out to compute bounded orbits convenient for the global characterization of the two asteroids and to investigate potential landing trajectories. Sensitivity analyses via Monte Carlo simulations are performed to prove the robustness of the different bounded orbits
Estimació de la incertesa de mesura dels procediments de referència primaris per a la mesura de la concentració catalítica dels enzims en un laboratori de referència
Get PDFAquest treball s'ha realitzat al Laboratori de Referència d'Enzimologia Clínica (LREC) de la Unitat de Bioquímica de Medicina. El LREC és un laboratori de referència acreditat per les normes ISO 17025 i ISO 15195, i forma part de la xarxa internacional de laboratoris de referència del Joint Committee for Traceability in Laboratory Medicine (JCTLM). Un dels requisits dels laboratoris de referència es conèixer la contribució de les diferents fonts d'incertesa a la incertesa de mesura, el que es coneix amb el nom de "compilació de la incertesa". L'objectiu d'aquest treball és l'estimació de la incertesa de mesura, mitjançant un estudi de compilació de la incertesa, de dos procediments de mesura de referència primaris: - el procediment de referència primari per la mesura de l'enzim γ-glutamil transferasa (GGT), com a exemple de procediment amb una única reacció. -el procediment de referència primari per la mesura de l'enzim creatina cinasa (CK), com a exemple de procediment amb més d'una reacció. El càlcul de la incertesa s'ha realitzat a partir dels documents "Evaluation of measurement data - Guide to the expresion of uncertainty", més conegut com GUM i desenvolupat pel Joint Committee for Guides in Metrology (JCGM), i "Quantifying uncertainty in analytical measurement", recomanat per l'Eurachem. Això va implicar fer un estudi exhaustiu dels procediments de mesura de referència, que va consistir en els següents passos: a) definir el mesurant; b) identificar totes les possibles fonts d'incertesa; c) calcular la incertesa estàndard de cada font, mitjançant una avaluació de tipus A o de tipus B, d) calcular els coeficients de sensibilitat, els quals descriuen com varia el resultat del mesurant al produir canvis en cadascuna de les fonts de incertesa; e) calcular la incertesa combinada, tenint en compte la presència o no de fonts correlacionades i f) calcular la incertesa expandida amb un nivell de confiança d'aproximadament el 95 %. El valor de la incertesa de mesura estimada per el procediment de mesura de la GGT és d'un 2,2 % amb un factor de cobertura (k) de 2. De totes les fonts d'incertesa estudiades únicament 8 han contribuït a la incertesa de mesura. Aquestes fonts d'incertesa, ordenades per la importància en la contribució, són: la variabilitat expressada com la imprecisió en condicions intermèdies de mesura amb un 35,6 %, l'interferent glicina amb un 22,8 %, l'exactitud de les absorbàncies amb un 17,1 %, la longitud d'ona amb un 12,4 %, el pH amb un 8,61 %, la linealitat amb un 1,60 %, la fracció de volum de mostra amb un 1,18 %, i la temperatura amb un 0,68 %. La incertesa de mesura estimada del procediment de mesura de la CK és d'1,9 % (k=2). Les principals fonts d'incertesa amb una contribució significativa a la incertesa de mesura són: la variabilitat expressada com la imprecisió en condicions intermèdies de mesura amb un 50,1 %, l'exactitud de les absorbàncies amb un 23,2 %, el pH amb un 22,4 %, la fracció de volum de mostra amb un 2,16 %, la temperatura amb un 1,35 %, la longitud d'ona amb un 0,37 % i la linealitat amb un 0,34 %.This work has been carried out in the Laboratori de Referència d'Enzimologia Clinica (LREC) from de biochemistry and molecular biology department of the Universitat Autònoma de Barcelona (UAB). The LREC is a reference laboratory that is accredited for the ISO 17025 and ISO 15195 standards, and also it is part of the international network of references laboratories of the Joint Committee for Traceability in Laboratory Medicine (JCTLM). One of the requirements of the reference laboratories is to know the contribution of the different sources of uncertainty to the measurement uncertainty, the so called "uncertainty budget". The aim of this work is the estimation of the measurement uncertainty, through an uncertainty budget study, of two primary reference measurement procedures: - the primary reference procedure for the measurement of the catalytic concentration of γ-glutamyltransferase (GGT), as an example of procedure with one reaction. - the primary reference procedure for the measurement of catalytic concentration of creatine kinase (CK), as an example of procedure with different reactions. The calculation of the uncertainty has been based on the documents "Evaluation of measurement data - Guide to the expression of uncertainty," which is known as GUM and was developed by the Joint Committee for Guides in Metrology (JCGM), and "Quantifying uncertainty in analytical measurement ", which is recommended by the Eurachem. So for the uncertainty estimation a comprehensive study of the reference measurement procedures was done. This study consisted of the following steps: a) definition of the measurand; b) identification of all possible sources of uncertainty; c) quantification of the standard uncertainty of each potential source of uncertainty identified, with a type A or type B evaluation; d) calculation of sensitivity coefficient, which describe how the value of the measurand varies with changes in each sources of uncertainty; e) calculation of combined uncertainty considering the presence or not of correlated sources of uncertainty, and f) calculation of expanded uncertainty with a level of confidence of approximately 95 %. The value of the measurement uncertainty estimated for the measurement procedure of GGT is 2,2 % with a coverage factor (k) of 2. From all the sources of uncertainty identified only 8 have contributed to the measurement uncertainty. This sources of uncertainty, ordered by importance in the contribution, are the following: the variability expressed as imprecision in intermediated conditions with a 35,6 %, the inhibition by glycine with a 22,8 %, the absorbance accuracy with a 17,1 %, the wavelength adjustment with a 12,4 %, the pH with a 8,61 %, the linearity with a 1,60 %, the sample volume fraction with a 1,18 % and the temperature with a 0,68 %. The measurement uncertainty estimated for the measurement procedure of CK is 1,9 % (k = 2). The main sources of uncertainty with a significant contribution to the measurement uncertainty are: the variability expressed as imprecision in intermediated conditions with a 50,1 %, the absorbance accuracy with a 23,2 %, the pH with a 22,4 %, the sample volume fraction with a 2,16 %, the temperature with a 1,35 %, the wavelength adjustment with a 0,37 % and the linearity with 0,34 %
Certificación de la concentración de masa de la isoenzima 2 de la creatina-quinasa del material de referencia BCR 608
Get PDFConsultable des del TDXTítol obtingut de la portada digitalitzadaEn la actualidad no se ha descrito ningún procedimiento de medida de referencia para la medición de la concentración de masa de la isoenzima 2 de la creatina-quinasa, por lo que para la asignación de un valor de concentración de masa al material de referencia BCR 608 se siguió la siguiente estrategia: en la campaña de certificación se midió la concentración de masa del material mediante inmunoanálisis de distintas características, utilizando como calibrador una solución purificada de creatina-quinasa 2 a la que previamente se le había asignado un valor de concentración de proteína mediante el procedimiento de Doetsch, utilizando como calibrador el material de referencia SRM 927b con un valor de concentración de proteína certificado. La creatina-quinasa 2 se purificó a partir de músculo cardiaco humano. A la solución purificada se le asignó un valor de concentración de proteína por el procedimiento de Doetsch de 124,3 mg/L, diluyéndose hasta una concentración de 80,362 mg/L para poder ser utilizada como calibrador en los distintos inmunoanálisis. El valor certificado de concentración de masa de la creatina-quinasa 2 del material de referencia BCR 608 fue de 94,5 mg/L con una incertidumbre asociada de 9,6 mg/L.This report describes the certification of a mass concentration value to the already prepared creatine kinase 2 reference material (BCR 608) with a catalytic concentration assigned value. At present, a mass creatine kinase 2 reference method have not been described. For this reason, we measured the BCR 608 mass concentration in different immunoassays using a creatine kinase 2 purified solution as a calibrator. Previously, the protein concentration of the creatine kinase 2 solution was measured by Doestch method using the reference material SRM 927b as calibrator. Creatine kinase 2 was purified from human heart. A protein concentration value of 124.30 mg/L was assigned to the solution of purified creatine kinase 2 by Doetsch method, and then this solution was diluted to obtain a liquid standard of known protein concentration (80.36 mg/L) to calibrate the immunoassays. The mass concentration of creatine kinase 2 in the BCR 608 reference material was certified to be 94.5 mg/L with an associated uncertainty of 9.6 mg/L
Easily retrievable objects among the NEO population
No full textAsteroids and comets are of strategic importance for science in an effort to understand the formation, evolution and composition of the Solar System. Near-Earth Objects (NEOs) are of particular interest because of their accessibility from Earth, but also because of their speculated wealth of material resources. The exploitation of these resources has long been discussed as a means to lower the cost of future space endeavours. In this paper, we consider the currently known NEO population and define a family of so-called Easily Retrievable Objects (EROs), objects that can be transported from accessible heliocentric orbits into the Earth’s neighbourhood at affordable costs. The asteroid retrieval transfers are sought from the continuum of low energy transfers enabled by the dynamics of invariant manifolds; specifically, the retrieval transfers target planar, vertical Lyapunov and halo orbit families associated with the collinear equilibrium points of the Sun-Earth Circular Restricted Three Body problem. The judicious use of these dynamical features provides the best opportunity to find extremely low energy Earth transfers for asteroid material. A catalogue of asteroid retrieval candidates is then presented. Despite the highly incomplete census of very small asteroids, the ERO catalogue can already be populated with 12 different objects retrievable with less than 500 m/s of Δv. Moreover, the approach proposed represents a robust search and ranking methodology for future retrieval candidates that can be automatically applied to the growing survey of NEOs
End-of-life disposal concepts for libration point and highly elliptical orbit missions
Get PDFLibration Point Orbits (LPOs) and Highly Elliptical Orbits (HEOs) are often selected for astrophysics and solar terrestrial missions. No guidelines currently exist for their end-of life, however it is a critical aspect to other spacecraft and on ground safety. This paper presents an analysis of possible disposal strategies for LPO and HEO missions as a result of an ESA study. The dynamical models and the design approach are presented. Five missions are selected: Herschel, Gaia, SOHO as LPOs, and INTEGRAL and XMM-Newton as HEOs. A trade-off is made considering technical feasibility, as well as the sustainability context and the collision probability
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