DOCSLIB.ORG

University of Southampton Research Repository Eprints Soton

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
University of Southampton Research Repository Eprints Soton University of Southampton Research Repository ePrints Soton Copyright © and Moral Rights for this thesis are retained by the author and/or other copyright owners. A copy can be downloaded for personal non-commercial research or study, without prior permission or charge. This thesis cannot be reproduced or quoted extensively from without first obtaining permission in writing from the copyright holder/s. The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the copyright holders. When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given e.g. AUTHOR (year of submission) "Full thesis title", University of Southampton, name of the University School or Department, PhD Thesis, pagination http://eprints.soton.ac.uk UNIVERSITY OF SOUTHAMPTON FACULTY OF ENGINEERING AND THE ENVIRONMENT Aeronautics, Astronautics and Computational Engineering Fractionated Satellites: A Systems Engineering Analysis by Benjamin Samuel Schwarz Thesis for the degree of Doctor of Philosophy JULY 2014 i UNIVERSITY OF SOUTHAMPTON ABSTRACT FACULTY OF ENGINEERING AND THE ENVIRONMENT Aeronautics, Astronautics and Computational Engineering Thesis for the degree of Doctor of Philosophy FRACTIONATED SATELLITES: A SYSTEMS ENGINEERING ANALYSIS Benjamin Samuel Schwarz The current method of operating space-based assets involves the design and launch of large, monolithic spacecraft. These spacecraft are not responsive to failures or changes in mission requirements, as both require the launch of a completely new spacecraft. The concept of fractionated spacecraft was introduced in 2006 by the US Defence Advanced Research Projects Agency (DARPA) as a way of designing and operating space systems which is more responsive than current methods. The fractionated concept involves the decomposition of the traditional monolithic satellite into a number of free-flying spacecraft connected wirelessly. The free-flying satellites each carry a subset of the required subsystems and share their fractionated resources to achieve the mission objectives. Since 2006, studies of this concept have focused on analyses of the value and utility provided by fractionated spacecraft or on design studies of specific systems. This thesis addresses two key questions: Firstly, is fractionation a mission enabling technology? Secondly, can design rules and guidelines be developed for fractionated satellites to allow continuity of measurements to be maintained and launched mass minimised? The first question is addressed by studying a payload and system for measuring coastal salinity from space. This provides an initial opportunity to assess the fractionated concept from a systems engineering point of view. The second question is addressed by undertaking a more general analysis of fractionated architectures, building on the knowledge gained in development of the fractionated coastal salinity measurement system. A computer model was developed to simulate the lifetime of different fractionated architectures when subjected to subsystem failures. A local search algorithm was used to find fractionated architectures which gave the best compromise between mass launched versus the operational time over a 50 year lifetime. The results from the application of this model showed that architectures that are highly fractionated, containing several homogeneous satellites, best achieved this compromise. These findings provide a contrast to the heterogeneously fractionated architectures proposed by DARPA. When a fractionated architecture is first implemented, the technology required to fractionate all the spacecraft subsystems may not be available. Consequently, the key to the implementation of these first fractionated architectures will be to ensure that there is redundancy in the fractionated subsystems spread across the architecture. ii Table of contents Table of contents ............................................................................................................................... iii List of tables ........................................................................................................................................ v List of figures ...................................................................................................................................... vi DECLARATION OF AUTHORSHIP ..................................................................................................... x Acknowledgments ............................................................................................................................. xii Nomenclature .................................................................................................................................. xiii Acronyms ......................................................................................................................................... xvi 1. Introduction ................................................................................................................................ 1 1.1. What is a fractionated satellite? ......................................................................................... 1 1.1.1. Why use a fractionated approach? ............................................................................. 2 1.1.2. A fractionated response to failed spacecraft .............................................................. 3 1.1.3. Value ........................................................................................................................... 4 1.1.4. The Pleiades fractionated system ............................................................................... 6 1.2. Conclusions and research problem ..................................................................................... 6 1.2.1. The research problem ................................................................................................. 7 1.2.2. Structure of the thesis................................................................................................. 9 2. Fractionation: A mission enabling technology? ........................................................................ 10 2.1. Sea surface salinity and its measurement ........................................................................ 10 2.1.1. Why measure coastal salinity? .................................................................................. 10 2.1.2. Ocean salinity measurement by remote sensing ...................................................... 11 2.1.3. Aperture synthesis techniques for remote sensing .................................................. 14 2.1.4. Other ocean salinity measurement systems ............................................................. 20 2.1.5. Conclusions ............................................................................................................... 21 2.2. Design drivers and requirements ...................................................................................... 21 2.3. Method ............................................................................................................................. 22 2.3.1. Extending the Doppler Radiometer concept ............................................................ 23 2.4. Results ............................................................................................................................... 24 2.5. A fractionated coastal salinity measurement system ....................................................... 35 2.5.1. Requirements and system architecture .................................................................... 36 2.5.2. Summary and conclusions ........................................................................................ 47 3. Developing design principles for fractionated space systems .................................................. 51 3.1. Introduction ...................................................................................................................... 51 iii 3.2. Model structure ................................................................................................................ 53 3.3. The fractionation of spacecraft subsystems ..................................................................... 53 3.3.1. Communications ....................................................................................................... 54 3.3.2. On-board data handling ............................................................................................ 55 3.3.3. Power ........................................................................................................................ 56 3.3.4. Attitude determination and control system ............................................................. 56 3.3.5. Orbital control system .............................................................................................. 58 3.3.6. Mass and power values used in the model ............................................................... 58 3.4. Architecture evaluation .................................................................................................... 60 3.4.1. Fractionated architectures ........................................................................................ 60 3.4.2. Architecture simulation ............................................................................................ 62 3.4.3. Outputs from the architecture evaluation ...............................................................
Load more

Recommended publications
  • Distributed Or Monolithic? a Computational Architecture
    TO APPEAR IN IEEE SYSTEMS JOURNAL, DOI: 10.1109/JSYST.2016.2594290 1 Distributed or Monolithic? A Computational Architecture Decision Framework Mohsen Mosleh, Kia Dalili, and Babak Heydari Abstract—Distributed architectures have become ubiquitous in Distributed architecture is a common approach to increase many complex technical and socio-technical systems because of system flexibility and responsiveness. In a distributed architec- their role in improving uncertainty management, accommodating ture, subsystems are often physically separated and exchange multiple stakeholders, and increasing scalability and evolvability. This departure from monolithic architectures provides a system resources through standard interfaces. Advances in networking with more flexibility and robustness in response to uncertainties technology, together with increasing system flexibility require- that it may confront during its lifetime. Distributed architecture ments, has made distributed architecture a ubiquitous theme does not provide benefits only, as it can increase cost and in many complex technical systems. Examples can be seen complexity of the system and result in potential instabilities. in many engineering systems: Distributed Generation, which The mechanisms behind this trade-off, however, are analogous to those of the widely-studied transition from integrated to modular is an approach to employ numerous small-scale decentralized architectures. In this paper, we use a conceptual decision frame- technologies to produce electricity close to the end users of work that unifies modularity and distributed architecture on a power, as opposed to the use of few large-scale monolithic five-stage systems architecture spectrum. We add an extensive and centralized power plants [2]; Wireless Sensor Networks, computational layer to the framework and explain how this can in which spatially distributed autonomous sensors collect data enhance decision making about the level of modularity of the architecture.
    [Show full text]
  • Front Cover Image
    Front Cover Image: Top Right: The Mars Science laboratory Curiosity Rover successfully landed in Gale Crater on August 6, 2012. Credit: NASA /Jet Propulsion Laboratory. Upper Middle: The Dragon spacecraft became the first commercial vehicle in history to successfully attach to the International Space Station May 25, 2012. Credit: Space Exploration Technologies (SpaceX). Lower Middle: The Dawn Spacecraft enters orbit about asteroid Vesta on July 16, 2011. Credit: Orbital Sciences Corporation and NASA/Jet Propulsion Laboratory, California Institute of Technology. Lower Right: GRAIL-A and GRAIL-B spacecraft, which entered lunar orbit on December 31, 2011 and January 1, 2012, fly in formation above the moon. Credit: Lockheed Martin and NASA/Jet Propulsion Laboratory, California Institute of Technology. Lower Left: The Dawn Spacecraft launch took place September 27, 2007. Credit: Orbital Sciences Corporation and NASA/Jet Propulsion Laboratory, California Institute of Technology. Program sponsored and provided by: Table of Contents Registration ..................................................................................................................................... 3 Schedule of Events .......................................................................................................................... 4 Conference Center Layout .............................................................................................................. 6 Special Events ................................................................................................................................
    [Show full text]
  • Download Article (PDF)
    Proceedings of the 2nd International Conference On Systems Engineering and Modeling (ICSEM-13) Hybrid Approach to Optimize the Cluster Flying Orbit for Fractionated Spacecraft Based on PSO-SQP Algorithm Shenghui Wan1, a, Junling Song 2,b, Jian Chen 1,c , Min Hu2,b 1China Satellite Maritime TTC Department, Jiangyin, China 2Academy of Equipment, Beijing, China [email protected], [email protected], [email protected] Keywords: Fractionated spacecraft; Cluster flying orbit; Relative orbital elements; Particle swarm optimization; Sequential quadratic programming. Abstract. This template This paper investigates the optimal cluster flight orbit design issue for the fractionated spacecraft according to three main goals: keeping the cluster as stable as possible, preventing the collisions within the cluster, maintaining the inter-satellite distance within the maximum region. Firstly, the relative orbital elements are adopted to describe the relative motion. Then, the formation design requirements are formulated in terms of the relative orbital elements, the constrained optimization problem is solved using the hybrid particle swarm optimization algorithm integrated with sequential quadratic programming local search. The simulation results show that the hybrid PSO-SQP algorithm is effective. Introduction Fractionated spacecraft has been well concerned in recent five years because of its unique technical merits. The concept of the fractionated spacecraft is to separate the traditional monolithic satellite into free-flying service modules and different payloads, which are connected by self-organizing network wirelessly. DARPA began a program called the System F6 (Future, Fast, Flexible, Fractionated, Free-Flying Spacecraft) in 2008. The fractionated spacecraft usually consist of tens and scores of modules and the modules often operate in close proximity, which make the cluster flying orbit design issue more challenging [1].
    [Show full text]
  • A Methodology for the Optimization of Disaggregated Space System Conceptual Designs Robert E
    Air Force Institute of Technology AFIT Scholar Theses and Dissertations Student Graduate Works 6-18-2015 A Methodology for the Optimization of Disaggregated Space System Conceptual Designs Robert E. Thompson Follow this and additional works at: https://scholar.afit.edu/etd Recommended Citation Thompson, Robert E., "A Methodology for the Optimization of Disaggregated Space System Conceptual Designs" (2015). Theses and Dissertations. 199. https://scholar.afit.edu/etd/199 This Dissertation is brought to you for free and open access by the Student Graduate Works at AFIT Scholar. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of AFIT Scholar. For more information, please contact [email protected]. A METHODOLOGY FOR THE OPTIMIZATION OF DISAGGREGATED SPACE SYSTEM CONCEPTUAL DESIGNS DISSERTATION Robert E. Thompson, Major, USAF AFIT-ENV-DS-15-J-062 DEPARTMENT OF THE AIR FORCE AIR UNIVERSITY AIR FORCE INSTITUTE OF TECHNOLOGY Wright-Patterson Air Force Base, Ohio DISTRIBUTION STATEMENT A. APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED. The views expressed in this thesis are those of the author and do not reflect the official policy or position of the United States Air Force, Department of Defense, or the United States Government. This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States. AFIT-ENV-DS-15-J-062 A METHODOLOGY FOR THE OPTIMIZATION OF DISAGGREGATED SPACE SYSTEM CONCEPTUAL DESIGNS DISSERTATION Presented to the Faculty Department of Systems Engineering and Management Graduate School of Engineering and Management Air Force Institute of Technology Air University Air Education and Training Command In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy Robert E.
    [Show full text]
  • Modular Rapidly Manufactured Small Satellite (MRMSS)
    Modular Rapidly Manufactured Small Satellite (MRMSS) Greenfield T. Trinh1, Daniel Cellucci2, Will Langford3, Stephen Im4, Ali Guarneros Luna5, Kenneth C. Cheung6 NASA Ames Research Center, Mountain View, CA, 94035 The Modular Rapidly Manufactured Small Satellite (MRMSS) project applies modular building block system to space applications. The need to reduce mass for spaceflight applications and reuse resources is a critical technology for long dura- tion space missions. Mass reduction and reuse of material will help bring down costs for spaceflight missions and open up more possibilities for exploration and research. The MRMSS project consists of two major components: A basic research component demonstrating electronic digital materials, and a technology demonstration applying the modular building block based systems concept to the CubeSat form factor. This paper describes the core technologies developed to enable the modular system as well the first flight demonstration on a sounding rocket. I. Introduction Digital materials are materials with "a discrete set of components, discrete number of allowable relative positions and orientations, and explicit control of the placement of individual components"[1] [2]. The motivation behind the MRMSS project’s application to spacecraft structures stems from the need to reduce mass carried into orbit and reuse of the material once it has served its original purpose. Ongoing research at NASA Ames seeks ways to make spacecraft systems more versatile, and the CubeSat platform is a appropriately suited for demonstrating this concept due to its inherent modularity. By defining each side of the CubeSat as a single modular unit, we have developed a system that is scalable, modular, and modifiable.
    [Show full text]
  • Distributed Spacecraft Missions (DSM) Technology Development at NASA Goddard Space Flight Center
    Distributed Spacecraft Missions (DSM) Technology Development at NASA Goddard Space Flight Center Jacqueline Le Moigne, NASA Goddard Space Flight Center IGARSS 2018 Distributed Spacecraft Missions What is a Distributed Spacecraft Mission (DSM)? A DSM is a mission that involves multiple spacecraft to achieve one or more common goals. Drivers o Enable new science measurements o Improve existing science measurements o Reduce the cost, risk and implementation schedule of all future NASA missions o Investigate the minimum requirements and capabilities to cost effectively manage future multiple platform missions and to cost effectively develop and deploy such missions NASA Goddard DSM Activities 2 Design Intellligent and Reference Missions DSM Definitions, DSM Collaborative Taxonomy, Survey, (DRM) Framework for Constellations (ICC): An Earth Science Technology 2 Types of DSM, Scientist Interviews, Roadmap Software Architecture Identification of Main Use Case and DSM Constellations (DRM- Design and cFS-Based based on DSM Technology RFI C) and Precision Communications Challenges RFI Concepts Formation Flying Protocols (DRM-PFF) Development Strategic IRAD Development 2013 2014 2015 2016 2017 2018 Transitional Development Projects SST’16 with EPSCoR with Earth and ESTO/AIST14 CANYVAL-X: Stanford Univ.: NMSU and UNM: Heliophysics “Trade-space Analysis CubeSat Astronomy by DiGital Distributed Virtual Telescope for Conceptual Tool for Designing NASA and Yonsei Timing and Localization X-Ray Observations Missions Design Univ. using Virtual System (demonstrate
    [Show full text]
  • Distributed Spacecraft Missions (Dsm) Technology Development at Nasa Goddard Space Flight Center
    DISTRIBUTED SPACECRAFT MISSIONS (DSM) TECHNOLOGY DEVELOPMENT AT NASA GODDARD SPACE FLIGHT CENTER Jacqueline Le Moigne NASA Goddard Space Flight Center, Greenbelt, MD 20771 ABSTRACT mission adds to the complexity of the mission, not only in the development phase but also in the operational For the last 5 years, NASA Goddard has been phase, and this complexity translates into additional investigating Distributed Spacecraft Missions (DSM) costs and risk to the mission. Therefore, it is only now system architectures, surveying past, current and that new technologies and capabilities such as smallsats, potential mission concepts, developing several cubesats, hosted payloads, onboard computing, better taxonomies and identifying some key technologies that space communications, and ground systems automation will enable future DSM mission design, development, have appeared and became mature, that DSM seem to be operations and management. This paper summarizes this feasible for a reasonable and potentially lower cost and Initiative and the talk will provide details about specific risk than monolithic missions. Goddard DSM projects that are currently underway and The objective of the Goddard Initiative is to make that are relevant to future Earth Science missions. marked and demonstrable progress in developing and/or maturing the technologies that will be necessary to Index Terms— Distributed Spacecraft Missions design, develop, launch and operate DSMs. The DSM (DSM), Constellations, Precision Formation Flying activity is a multi-year project-level initiative that targets delivery, integration, and demonstration of mission- 1. INTRODUCTION enabling technologies and key capabilities that will A “Distributed Spacecraft Mission (DSM)” is a mission significantly advance the spatial, spectral, temporal, and that involves multiple spacecraft to achieve one or more angular resolution of Earth and space common goals.
    [Show full text]
  • Quantitative Analysis of Satellite Architecture Choices: a Geosynchronous Imaging Satellite Example
    QUANTITATIVE ANALYSIS OF SATELLITE ARCHITECTURE CHOICES: A GEOSYNCHRONOUS IMAGING SATELLITE EXAMPLE Matthew Daniels Stanford University, [email protected] M. ElisaBeth Paté-Cornell Stanford University ABSTRACT Firms operating satellites have a choice between two broad classes of satellite architectures: consolidated and distributed. In a consolidated satellite architecture multiple instruments are aggregated onto a single spacecraft. A distributed (or disaggregated) architecture separates satellite capabilities -- including payloads -- across multiple heterogeneous smaller spacecraft in the same orbit. Vehicles in a distributed satellite architecture may share a common wireless network. For a firm that operates scientific or national security satellites, there may be four classes of potential advantages associated with a distributed architecture: (1) capabilities can be deployed incrementally instead of waiting until the last payload is ready for launch; (2) failures in orbit can be fixed more quicKly and with smaller units; (3) new technologies can be inserted more efficiently by phased integration of new payloads; and (4) the system is more flexible in terms of responses to adversarial interactions in space, and may therefore provide more flexibility for deterrence. Quantitative approaches are useful to assess the value of these benefits for specific mission types. We present here a quantitative frameworK to assess tradeoffs between consolidated and distributed satellite architecture for national space programs. We use optimization and risK models to show when distributed satellite architectures can provide a more resilient and valuable way of implementing certain critical space systems, such as weather satellites and strategic missile launch warning satellites. This work allows comparison of mission approaches on the basis of expected utility maximization and selection of strategies that best exploit the technical and operational characteristics of each satellite architecture.
    [Show full text]
  • Aligning Perspectives and Methods for Value-Driven Design
    Aligning Perspectives and Methods for Value-Driven Design Adam M. Ross, M. Gregory O’Neill, Daniel E. Hastings, and Donna H. Rhodes September 1, 2010 Track 100 -MIL-4: Emerging Trends AIAA Space 2010 Outline • Introduction • Defining Value • Economic Background • Overview of VCDMs • Spacecraft Mission Examples • Discussion seari.mit.edu © 2010 Massachusetts Institute of Technology 2 Introduction • What is the most valuable system for our mission? – Value is perceived by stakeholder(s) of interest – Value can be comprised of both direct and indirect benefits and costs • Formulating a response: “valuation” methods – “Traditional” requirement- and cost-centric approaches – Value-driven design approaches • Theory: economics, decision analysis, psychology, behavioral economics, and complex engineering design • Operationalization: value-centric design methodologies (VCDMs) Objective Domain Engineering Design Domain Stakeholder Most Valuable Candidate “Valuation” Value System Design System Designs Method • Relevancy: notable efforts in the aerospace sector – DARPA System F6 Program and valuation of fractionated spacecraft – Four industry-lead teams developed and applied VCDMs seari.mit.edu © 2010 Massachusetts Institute of Technology 3 Defining Value • “Value” definition includes several important factors – Cost/Resources HlitidfiitiHolistic definition of f“ “creati ng val ue” – Satisfaction/Utility Balancing and increasing the net level of – Importance/Priority (1) satisfaction, with (2) available resources, while addressing (3) its degree of importance • Value in design is subjective and context-dependent – Example: “value” of heated seats in Maine winter vs. Florida summer • Evolution of definition in economic theory – Value in use vs. value in exchange – Scarcity vs. labor requirement – Willingness to pay (i.e., “pr ice ” vs. wea lth) – Supply-side vs. demand-side – Marginal utility vs.
    [Show full text]
  • Final Conference Program
    The World’s Forum for Aerospace Leadership 21st AAS/AIAA Space Flight Mechanics Meeting 13–17 February 2011, New Orleans, Louisiana AAS General Chair Angela Bowes AMA Inc./NASA LaRC AIAA General Chair Dr. Peter C. Lai The Aerospace Corporation AAS Technical Chair Dr. Moriba Jah AFRL/RVSV AIAA Technical Chair Dr. Yanping Guo Johns Hopkins University Applied Physics Laboratory Cover image: NASA/JPL-Caltech/Univ. of Wisconsin This is one segment of an infrared portrait of dust and stars radiating in the inner Milky Way. More than 800,000 frames from NASA’s Spitzer Space Telescope were stitched together to create the full image, capturing more than 50 percent of our entire galaxy. This is a three-color composite that shows infrared observations from two Spitzer instruments. Blue represents 3.6-micron light and green shows light of 8 microns, both captured by Spitzer’s infrared array camera. Red is 24-micron light detected by Spitzer’s multiband imaging photometer. This combines observations from the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) and MIPSGAL projects. Images, maps, and information in the conference program are used with the consent of all parties to AAS/AIAA. Cover design and conference program printing sponsored by The Aerospace Corporation. Table of Contents General Information ........................................................................................................................ 3 Registration ....................................................................................................................................
    [Show full text]
  • Astro2020 APC White Papers a Realistic Roadmap to Formation Flying Space Interferometry
    Astro2020 APC White Papers A Realistic Roadmap to Formation Flying Space Interferometry Type of Activity: Ground Based Project Space Based Project Infrastructure Activity Technological Development4 Activity State of the Profession Consideration4 Other Principal Author: Name: John Monnier Institution: University of Michigan Email: [email protected] Phone: 734-763-5822 Endorsers: (names, institutions, emails) Alicia Aarnio, University of North Carolina Greensboro, [email protected] Olivier Absil, University of Liege,` [email protected] Narsireddy Anugu, University of Exeter, [email protected] Ellyn Baines, Naval Research Lab, [email protected] Amelia Bayo, Universidad de Valparaiso, [email protected] Jean-Philippe Berger, Univ. Grenoble Alpes, IPAG, [email protected] L. Ilsedore Cleeves, University of Virginia, [email protected] Daniel Dale, U. Wyoming, [email protected] William Danchi, NASA Goddard Space Flight Center, [email protected] W.J. de Wit, ESO, [email protected] Denis Defrere,` University of Liege,` [email protected] Shawn Domagal-Goldman, NASA-GSFC, [email protected] Martin Elvis, CfA Harvard & Smithsonian, [email protected] Dirk Froebrich, University of Kent, [email protected] Mario Gai, Istituto Nazionale di AstroFisica,, [email protected] Poshak Gandhi, School of Physics & Astronomy, [email protected] arXiv:1907.09583v1 [astro-ph.IM] 22 Jul 2019 Paulo Garcia, Universidade do Porto, Portugal, [email protected] Tyler Gardner, University of Michigan, [email protected]
    [Show full text]
  • Appendix B Acronyms and Abbreviations
    Appendix B Acronyms and Abbreviations Units of Measure and some Physical Constants A . ampere --- unit of electric current [named after André M. Ampère (1775---1836), French physicist]. 1 A represents a flow of one coulomb of electricity per second (or: 1A = 1C/s) Ah ............ amperehour Å . angstrom --- unit of length (used in particular for the short wavelength spectrum); 1Å= 10---10 m [named after Anders Jonas Ängström (1814--- 1874), Swedish physicist and astronomer] amu. atomic mass unit (1.6605402 10---27 kg) are............) unit of area (1 are = 100 m2 arcmin......... arcminute [1’ = (1/60)º or 1 arcmin = 2.908882 x 10---4 radian] arcsec.......... arcsecond [1” = (1/60)’ or 1 arcsec = 4.848137 x 10---6 radian= 0.000278º] au . astronomical unit --- unit of length, namely the mean Earth/sun distance [=1.495978706 1013 cm, which is the semimajor axis of the Earth’s orbit around the sun (or about 150 million km)] bar............) pressure, (1 bar = 105 Nm---2 Bq . Becquerel [named after Alexandre Edmond Becquerel, a French physi- cist (1820---1891)]. The Bq is a SI unit used to measure a radioactivity. One Becquerel is that quantity of a radioactive material that will have 1 transformations in one second. c . velocity of light in vacuum (299,792,458 m/s) cd . candela (unit of luminous intensity). The candela is the luminous inten- sity, in a given direction, of a source that emits monochromatic radi- ation of frequency 540 × 1012 Hz and that has a radiant intensity in that direction of 1/683 watt per steradian. cm...........
    [Show full text]