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Microgravity Educator Guide

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  • MicrogravityA Teachers Guide With Activities

    in Science, Mathematics, and Technology

    National Aeronautics and Space Administration

    Office of Life and Microgravity Sciences and ApplicationsMicrogravity Research Division

    Office of Human Resources and EducationEducation Division

    This publication is in the Public Domain and is not protected by copyright.Permission is not required for duplication.

    EG-1997-08-110-HQ

  • Acknowledgements This publication was developed for the NationalAeronautics and Space Administration with theassistance of the many educators of theAerospace Education Services Program,Oklahoma State University.

    Writers:

    Melissa J. B. Rogers, MSTAL-CUT CompanyNASA Lewis Research CenterCleveland, OH

    Gregory L. Vogt, Ed-D.Teaching From Space ProgramNASA Johnson Space CenterHouston, TX

    Michael J. Wargo, Sc.D.Microgravity Research DivisionNASA HeadquartersWashington, DC

  • Activity Contributors

    Microgravity In The ClassroomAccelerometersAround The WorldInertial BalanceCandle DropCrystallization ModelGregory L. Vogt, Ed.D.Teaching From Space ProgramNASA Johnson Space Center

    Gravity-Driven Fluid FlowCharles E. Bugg, Ph.D. Professor EmeritusUniversity of Alabama, BirminghamandChairman and Chief Executive OfficerBiocrypt Pharmaceuticals, Inc.

    Craig D. Smith, Ph.D.ManagerX-Ray Crystallography LaboratoryCenter for MacromolecularCrystallographyUniversity of Alabama at Birmingham

    Surface Tension-Driven FlowsGregory L. Vogt, Ed.D.Teaching From Space ProgramNASA Johnson Space Center

    R. Glynn Holt, Ph.D.Research Assistant ProfessorBoston UniversityAeronautics and Mechanical EngineeringDepartment

    Temperature Effects on SurfaceTensionMichael F. SchatzSchool of PhysicsGeorgia Institute of Technology

    Stephen J. VanHookCenter for Nonlinear DynamicsDepartment of PhysicsUniversity of Texas at Austin

    Candle FlamesHoward D. Ross, Ph.D.ChiefMicrogravity Combustion BranchNASA Lewis Research Center

    Crystal Growth and Buoyancy-DrivenConvection CurrentsRoger L. Kroes, Ph.D.ResearcherMicrogravity Science DivisionNASA Marshall Space Flight Center

    Donald A. Reiss, Ph.D.ResearcherMicrogravity Science DivisionNASA Marshall Space Flight Center

    Rapid CrystallizationMicroscopic Observation of CrystalsDavid Mathiesen, Ph.D.Assistant ProfessorCase Western Reserve UniversityandAlternate Payload SpecialistUSML-2 Mission

    Zeolite Crystal GrowthAlbert Sacco, Jr.HeadDepartment of Chemical EngineeringWorchester Polytechnical InstituteandPayload SpecialistUSML-2 Mission

  • Microgravity A Teachers Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 58 (), 912 () i

    As opportunities for extended space flight havebecome available, microgravity research inphysical and biological sciences has grown inimportance. Using the Space Shuttle and soon theInternational Space Station, scientists are able toadd long term control of gravitys effects to theshort list of variables they are to manipulate intheir experiments. Although most people areaware of the floating effects of astronauts andthings in orbiting spacecraft, few understand whatcauses microgravity much less how it can beutilized for research.

    The purpose of this curriculum supplement guideis to define and explain microgravity and showhow microgravity can help us learn about thephenomena of our world. The front section of theguide is designed to provide teachers of science,mathematics, and technology at many levels witha foundation in microgravity science andapplications. It begins with backgroundinformation for the teacher on what microgravityis and how it is created. This is followed withinformation on the domains of microgravityscience research; biotechnology, combustionscience, fluid physics, fundamental physics,materials science, and microgravity researchgeared toward exploration. The backgroundsection concludes with a history of microgravityresearch and the expectations microgravityscientists have for research on the InternationalSpace Station.

    Following the background information areclassroom activities that enable students toexperiment with the forces and processesmicrogravity scientists are investigating today.The activities employ simple and inexpensivematerials and apparatus that are widely availablein schools. The activities emphasize hands-oninvolvement, prediction, data collection andinterpretation, teamwork, and problem solving.Activity features include objectives, materials andtools lists, management suggestions, assessmentideas, extensions, instructions and illustrations,student work sheets, and student readers.Because many of the activities anddemonstrations apply to more than one subjectarea, a matrix chart relates activities to nationalstandards in science and mathematics and toscience process skills.

    Finally, the guide concludes with a suggestedreading list, NASA educational resourcesincluding electronic resources, and an evaluationquestionnaire. We would appreciate yourassistance in improving this guide in futureeditions by completing the questionnaire andmaking suggestions for changes and additions.The evaluation can be sent to us by mail orelectronically submitted through the Internet sitelisted on the form.

    How To Use This Guide

  • Microgravity A Teachers Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 58 (), 912 ()ii

    Note on Measurement andFormat

    In developing this guide, metric units ofmeasurement were employed. In a fewexceptions, notably within the Materials andTools lists, British units have been listed. In theUnited States, metric-sized parts such as screwsand wood stock are not as accessible as theirBritish equivalents. Therefore, British units havebeen used to facilitate obtaining requiredmaterials.

    The main text of this guide uses large printlocated in a wide column. Subjects relating tomathematics, physical science, and technologyare highlighted in bold. Definitions, questions fordiscussion, and examples are provided in smallerprint in the narrow column of each page. Eacharea highlighted in the text has a correspondingsection in the narrow column. This correspondingsection first lists applicable Mathematics andScience Content Standards, indicated by gradelevel: Grades 58, o Grades 9-12. We haveattempted to position the appropriate discussionas close as possible to the relevant highlightedtext. A key word or phrase in each margindiscussion is also highlighted for ease inidentifying related text.

  • Microgravity A Teachers Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 58 (), 912 () iii

    Table of ContentsIntroduction

    First, What is Gravity? ............................................................................................... 1What is Microgravity? ................................................................................................ 1Creating Microgravity ................................................................................................ 3

    Drop Facilities ..................................................................................................... 7Aircraft ................................................................................................................ 8Rockets ............................................................................................................... 9Orbiting Spacecraft ........................................................................................... 10

    Microgravity Science Primer .......................................................................................... 13The Microgravity Environment of Orbiting Spacecraft ............................................. 15Biotechnology .......................................................................................................... 16

    Protein Crystal Growth ..................................................................................... 18Mammalian Cell and Tissue Culture ................................................................ 19Fundamental Biotechnology ............................................................................ 21

    Combustion Science ............................................................................................... 21Premixed Gas Flames ..................................................................................... 25Gaseous Diffusion Flames ............................................................................... 25Liquid Fuel Droplets and Sprays ...................................................................... 25Fuel Particles and Dust Clouds........................................................................ 26Flame Spread Along Surfaces ......................................................................... 26Smoldering Combustion................................................................................... 27Combustion Synthesis ..................................................................................... 27

    Fluid Physics ........................................................................................................... 28Complex Fluids ................................................................................................ 29Multiphase Flow and Heat Transfer ................................................................. 31Interfacial Phenomena ..................................................................................... 32Dynamics and Stability ..................................................................................... 33

    Fundamental Physics .............................................................................................. 34Materials Science .................................................................................................... 37

    Electronic Materials .......................................................................................... 39Glasses and Ceramics ..................................................................................... 40Metals and Alloys ............................................................................................. 41Polymers .......................................................................................................... 43

    Microgravity Research and Exploration ................................................................... 44

  • Microgravity A Teachers Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 58 (), 912 ()iv

    Microgravity Science Space Flights ...............................................................................46International Microgravity Laboratory-1, January 1992 .......................................49United States Microgravity Laboratory-1, June 1992 ..........................................49Spacelab-J, September 1992 ..............................................................................51United States Microgravity Payload-1, October 1992 .........................................52United States Microgravity Payload-2, March 1994 ............................................53International Microgravity Laboratory-2, July 1994 .............................................55United States Microgravity Laboratory-2, October 1995 .....................................57United States Microgravity Payload-3, February 1996 ........................................59Life and Microgravity Spacelab, June 1996 ........................................................62Shuffle/Mir Science Program, March 1995 to May 1998 .....................................64

    Future Directions ............................................................................................................68

    Glossary .........................................................................................................................71

    Activities .........................................................................................................................75

    NASA Resources for Educators ...................................................................................167

    NASA Educational Materials ........................................................................................168

  • Microgravity A Teachers Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 58 (), 912 ()

    1

    IntroductionSpace flight is important for rnany reasons. Spaceflight carries scientific instruments and humanresearchers high above the ground, permitting usto see Earth as a planet and to study the complexinteractions of atmosphere, oceans, land, energy,and living things. Space flight lifts scientificinstruments above the filtering effects of theatmosphere, making the entire electromagneticspectrum available and allowing us to see moreclearly the distant planets, stars, and galaxies.Space flight permits us to travel directly to otherworlds to see them close up and sample theircompositions. Finally, space flight allowsscientists to investigate the fundamental states ofmattersolids, liquids, and gasesand theforces that affect them in a microgravityenvironment.

    The study of the states of matter and theirinteractions in microgravity is an excitingopportunity to expand the frontiers of science.Areas of investgation include biotechnology,combustion scie,lce, fluid physics, fundamentalphysics, materials science, and ways in whichthese areas of research can be used to advanceefforts to explore the Moon and Mars.

    Microgravity is the subject of this teachers guide.This publication identifies the underlyingmathematics, physics, and technology principlesthat apply to microgravity. Supplementaryinformation is included in other NASA educationalproducts.

    First, What is Gravity?Gravitational attraction is a fundamental propertyof matter that exists throughout the knownuniverse. Physicists identify gravity as one of thefour types of forces in the universe. The othersare the strong and weak nuclear forces and theelectromagnetic force.

    Mathematics Standards

    o Mathematical Connectionso Mathematics as Communication

    Number and Number Relationships Number Systems and Number Theory

    Science Standards

    o Physical Science o Unifying Concepts and Processes

    The electromagnetic spectrum is generally separated intodifferent radiation categories defined by frequency (units ofHertz) or wavelength (units of meters). Wavelength is commonlyrepresented hy the symbol .

    Example:

    NameXraysUltravioletVisible LightInfraredMicrowaveTelevisionAM Radio

    Mathematics Standards

    o Algebrao Conceptual Underpinnings of Calculus

    Geometryo Geometry from an Algebraic Perspective

    o Mathematical Connections o Mathematics as Reasoning

    o Trigonometry

    Science Standards

    o Physical Science o Unifying Concepts and Processes

    An impressed force is an action exerted upon a body,in order to change its state, either of rest, or of uni-

    ApproximateWavelength (m)= 10-15 to 10-9

    = 10-8 to 10-7

    = 10-7 to 10-6

    = 10-6 to 10-3

    = 10-3 to 10-1

    = 10-1 to 1= 10-2 to 103

  • Microgravity A Teachers Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 58 (), 912 ()

    2

    form motion in a straight line. A body force acts on the entiremass as a result of an external effect not due to direct contact;gravity is a body force. A surface force is a contact force that actsacross an internal or external surface of a body.

    Mathematics Standards

    o Algebrao Conceptual Underpinnings of Calculus

    Geometryo Geometry from an Algebraic Perspective

    o Mathematical Connections o Mathematics as Reasoning

    o Trigonometry

    Science Standards

    o Physical Science o Unifying Concepts and Processes

    Velocity is the rate at which the position of an object changeswith time; it is a vector quantity. Speed is the magnitude ofvelocity.

    Mathematics Standards

    o Mathematical Connections o Mathematics as Reasoning

    Science Standards

    o History and Nature of Science o Science as Inquiry o Unifying Concepts and Processes

    Newtons discovery of the universal nature of the force ofgravity was remarkable. To take the familiar force that makes anapple fall to Earth and be able to recognize it as the same forcethat keeps the planets on their quiet and predictable pathsrepresents one of the major achievements of human intellectualendeavor. This ability to see beyond the obvious and familiar isthe mark of a true visionary. Sir Issac Newtons pioneering workepitomizes this quality.

    Mathematics Standards

    o Algebra Computation and Estimation

    o Functions o Mathematical as Communication Number and Number Relationships Patterns and Functions

    Science Standards

    o Unifying Concepts and Processes

    More than 300 years ago the great Englishscientist Sir Isaac Newton published theimportant generalization that mathematicallydescribes this universal force of gravity. Newtonwas the first to realize that gravity extends wellbeyond the domain of Earth. The basis of thisrealization stems from the first of three laws heformulated to describe the motion of objects. Partof Newtons first law, the law of inertia, states thatobiects in motion travel in a straight line at aconstant velocity unless acted upon by a netforce. According to this law, the planets in spaceshould travel in straight lines. However, as earlyas the time of Aristotle, scholars knew that theplanets travelled on curved paths. Newtonreasoned that the closed orbits of the planets arethe result of a net force acting upon each of them.That force, he concluded, is the same force thatcauses an apple to fall to the groundgravity.

    Newtons experimental research into the force ofgravity resulted in his elegant mathematicalstatement that is known today as the Law ofUniversal Gravitation. According to Newton, everymass in the universe attracts every other mass.The attractive force between any two objects isdirectly proportional to the product of the twomasses being considered and inverselyproportional to the square of the distanceseparating them. If we let F represent this force, rrepresent the distance between the centers of themasses, and m1 and m2 represent the magnitudesof the masses, the relationship stated can bewritten symbolically as:

    From this relationship, we can see that the greaterthe masses of the attracting objects, the greaterthe force of attraction between them. We can alsosee that the farther apart the objects are fromeach other, the less the attraction. If the distancebetween the objects doubles, the attractionbetween them diminishes by a factor of four, andif the distance triples, the attraction is only one-ninth as much.

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    3

    The eighteenth-century English physicist HenryCavendish later quantified Newtons Law ofUniversal Gravitation. He actually measured thegravitational force between two one kilogrammasses separated by a distance of one meter.This attraction was an extremely weak force, butits determination permitted the proportionalrelationship of Newtons law to be converted intoan equality. This measurement yielded theuniversal gravitational constant, G. Cavendishdetermined that the value of G is 6.67 x 10-11 Nm2/kg2. With G added to make the equation, theLaw of Universal Gravitation becomes:

    What is Microgravity?

    The presence of Earth creates a gravitational fieldthat acts to attract objects with a force inverselyproportional to the square of the distancebetween the center of the object and the center ofEarth. When we measure the acceleration of anobject acted upon only by Earths gravity at theEarths surface, we commonly refer to it as one gor one Earth gravity. This acceleration isapproximately 9.8 meters per second squared (m/s2). The mass of an object describes how muchthe object accelerates under a given force. Theweight of an object is the gravitational forceexerted on it by Earth. In British units (commonlyused in the United States), force is given in unitsof pounds. The British unit of masscorresponding to one pound force is the slug.

    While the mass of an object is constant and theweight of an object is constant (ignoringdifferences in g at different locations on theEarths surface), the environment of an objectmay be changed in such a way that its apparentweight changes. Imagine standing on a scale in astationary elevator car. Any vertical accelerationsof the elevator are considered to be positive

    indicates proportionality

    indicates equality

    is an expression

    is an equation

    Mathematics Standards

    o Algebra o Mathematical Connections o Mathematics as Communication Measurement

    Science Standards

    o Science and Technology o Science as Inquiry o Unifying Concepts and Processes

    The internationally recognized Systeme International (Sl) is asystem of measurement units. The Sl units for length (meter) andmass (kg) are taken from the metric system. Many dictionariesand mathematics and science textbooks provide conversion tablesbetween the metric system and other systems of measurement.Units conversion is very important in all areas of life. forexample in currency exchange, airplane navigation, and scientificresearch.

    Units Conversion Examples1 kg 2.2lb 1 in = 2.54cm1 liter 1 qt 1 yd 0.9 m

    Questions for Discussion What common objects have a mass of about 1 kg? What are the dimensions of this sheet of paper in cm and

    inches? How many liters are there in a gallon?

    Mathematics Standards

    Computation and Estimation o Mathematics as Communication Number and Number Relationships Number Systems and Number Theory

  • Microgravity A Teachers Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 58 (), 912 ()

    4

    Science Standards

    o Science as Inquiry o Science in Personal and Social Perspectives o Unifying Concepts and Processes

    Scientific notation makes it easier to read, write, and manipulatenumbers with many digits. This is especially useful tor makingquick estimates and for indicating the number of significantfigures.

    Examples:0.001 = 10-3

    10 = 101

    1000 = 103

    Which is bigger, 6 x 10-3 or 8 x 10-4? 6 x 103 or 8 x 104?How much bigger?

    Mathematics Standards

    o Mathematical Connections o Mathematics as Reasoning

    Science Standards

    o Science and Technology o Science as Inquiry o Unifying Concepts and Processes

    Questions for Discussion How does a scale work ? What does a scale measure? How many different kinds of scales can you list? Do they need gravity for them to work? Would you get different results on the Moon or Mars? How can you measure the mass of an object in

    microgravity?

    upwards. Your weight, W, is determined by yourmass and the acceleration due to gravity at yourlocation.

    If you begin a ride to the top floor of a building,an additional force comes into play due to theacceleration of the elevator. The force that thefloor exerts on you is your apparent weight, P, themagnitude of which the scale will register. Thetotal force acting on you is F=W+P=mae, where aeis the acceleration of you and the elevator andW=mg. Two example calculations of apparentweight are given in the margin of the next page.Note that if the elevator is not accelerating thenthe magnitudes W and P are equal but thedirection in which those forces act are opposite(W=-P). Remember that the sign (positive ornegative) associated with a vector quantity, suchas force, is an indication of the direction in whichthe vector acts or points, with respect to a definedframe of reference. For the reference framedefined above, your weight in the example in themargin is negative because it is the result of anacceleration (gravity) directed downwards(towards Earth).

    Imagine now riding in the elevator to the top floorof a very tall building. At the top, the cablessupporting the car break, causing the car and.you to fall towards the ground. In this example,we discount the effects of air friction and elevatorsafety mechanisms on the falling car. Yourapparent weight P=m(ae-g)=(60 kg)(-9.8 m/s

    2-(-9.8 m/s2)) = O kg m/s2; you are weightless. Theelevator car, the scale, and you would all beaccelerating downward at the same rate, which isdue to gravity alone. If you lifted your feet off theelevator floor, you would float inside the car. Thisis the same experiment that Galileo is purportedto have performed at Pisa, Italy, when he droppeda cannonball and a musketball of different massat the same time from the same height. Both ballshit the ground at the same time, just as theelevator car, the scale, and you would reach theground at the same time.

  • Microgravity A Teachers Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 58 (), 912 ()

    5

    Normalweight

    Heavierthan normal

    Lighterthan normal

    No apparentweight

    Acceleration and weight

    The person in the stationary elevator car experiences normalweight. In the car immediately to the right, apparent weightincreases slightly because of the upward acceleration.Apparent weight decreases slightly in the next car because ofthe downward acceleration. No weight is measured in the lastcar on the right because of free fall.

    For reasons that are discussed later, there aremany advantages to performing scientificexperiments under conditions where the apparentweight of the experiment system is reduced. Thename given to such a research environment ismicrogravity. The prefix micro- (m) derives fromthe original Greek mikros meaning small. By thisdefinition, a microgravity environment is one inwhich the apparent weight of a system is smallcompared to its actual weight due to gravity. Aswe describe how microgravity envifonments canbe produced, bear in mind that many factorscontribute to the experienced accelerations andthat the quality of the microgravity environmentdepends on the mechanism used to create it. Inpractice, the microgravity environments used byscientific researchers range from about onepercent of Earths gravitational acceleration(aboard aircraft in parabolic flight) to better thanone part in a million (for example, onboard Earth-orbiting research satellites).

    Quantitative systems of measurement, such asthe metric system, commonly use micro- to meanone part in a million. Using that definition, theacceleration experienced by an object in a

    Mathematics Standards

    o Algebra Computational and Estimation

    o Conceptual Underpinnings of Calculus o Mathematical Connections o Mathematics as Problem Solving Measurement

    Science Standards

    o Physical Science o Science and Technology o Science as Inquiry o Unifying Concepts and Processes

    F=W+P=maeRewriting yields P=ma

    e-mg=m(a

    e- g).

    If your mass is 60 kg and the elevator is aeceleratingupwards at 1 m/s2, your apparent weight isP=60 kg (+1 m/s2-(-9.8 m/s2))=+648 kg m/s2

    while your weight remainsW=mg=(60 kg)(-9.8 m/s2)=-588 kg m/s2.If the elevator aceelerates downwards at 0.5 m/s2,your apparent weight isP=60 kg (-0.5 m/s2-(-9.8 m/s2))=+558 kg m/s2.

    Mathematics Standards

    o Mathematics as Communications o Mathematics as Reasoning

    Science Standards

    o Science as Inquiry o Science in Personal and Social Perspectives o Unifying Concepts and Processes

    1 micro-g or 1 g = 1 x 10-6 g

    Questions for Discussion What other eommon prefixes or abbreviations tor powers of

    ten do you know or ean you find ? In what everyday places do you see these used ?

    Grocery stores, farms, laboratories, sporting facilities,pharmacies, machine shops.

    Common prefixes for powers of ten:10-9 nano- n10-3 milli- m102 centi- c103 kilo- k106 mega- M109 giga- G

  • Microgravity A Teachers Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 58 (), 912 ()

    6

    Mathematics Standards

    o Algebra Computation and Estimation

    o Conceptual Underpinnings of Calculuso Discrete Mathematics

    o Mathematical Connections o Mathematics as Problem Solving o Mathematics as Reasoning Number and Number Relationships

    Science Standards

    o Unifying Concepts and Processes

    Calculate the times in these examples. Teachers canuse these examples at several different scholasticlevels.

    Provide the equation as:

    Provide the equation as d=(1/2) as t2, and have thestudents re-order the equation.

    Making measurements and calculating results involvethe concepts of accuracy and precision, significant figures, andorders of magnitude. With these concepts in mind, are the droptimes given in the text correct?

    Mathematics Standards

    o Algebra Computation and Estimation o Mathematical Connections o Mathematics as Problem Solving o Mathematics as Reasoning Measurement

    Science Standards

    o Science and Technology o Science as Inquiry o Unifying Concepts and Processes

    Questions for Discussion How far away is the Mooon? How far away is the center of Earth from the center

    of the Moon? Why did we ask the previous question? How far away is the surface of Earth from the surface

    of the Moon What are the elevations of different features of

    Earth and the Moon? How are elevations measured?

    microgravity environment would be one-millionth(10-6) of that experienced at Earths surface. Theuse of the term microgravity in this guide willcorrespond to the first definition. For illustrativepurposes only, we provide the following simpleexample using the quantitative definition. Thisexample attempts to provide insight into whatmight be expected if the local accelerationenvironment would be reduced by six orders ofmagnitude from 1 g to 10-6 g,

    If you dropped a rock from a roof that was fivemeters high, it would take just one second toreach the ground. In a reduced gravityenvironment with one percent of Earthsgravitational pull, the same drop would take 10seconds. In a microgravity environment equal toone-millionth of Earths gravitational pull, thesame drop would take 1,000 seconds or about 17minutes!

    Researchers can create microgravity conditions intwo ways. Because gravitational pull diminisheswith distance, one way to create a microgravityenvironment (following the quantitative definition)is to travel away from Earth. To reach a pointwhere Earths gravitational pull is reduced toonemillionth cf that at the surface, you wouldhave to travel into space a distance of 6.37million kilometers from Earth (almost 17 timesfarther away than the Moon, 1400 times thehighway distance between New York City and LosAngeles, or about 70 million football fields). Thisapproach is impractical, except for automatedspacecraft, because humans have yet to travelfarther away from Earth than the distance to theMoon. However, freefall can be used to create amicrogravity environment consistent with ourprimary definition of microgravity. We discussthis in the next section.

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    7

    Creating Microgravity

    As illustrated in the elevator examples in theprevious section, the effects of gravity (apparentweight) can be removed quite easily by puttinganything (a person, an object, an experiment) intoa state of freefall. This possibility of using Earthsgravity to remove the effects of gravity within asystem were not always evident. Albert Einsteinonce said, I was sitting in a chair in the patentoffice at Bern when all of a sudden a thoughtoccurred to me: If a person falls freely, he will notfeel his own weight. I was startled. This simplethought made a deep impression on me. Itimpelled me toward a theory of gravitation.Working with this knowledge, scientists involvedin early space flights rapidly concluded thatmicro-gravity experiments could be performed bycrew members while in orbit.

    Gravity and Distance

    The inverse square relationship between gravitational force anddistance can be used to determine the acceleration due to gravityat any distance from the center of Earth, r.

    F = Gmem/r

    e2 force of gravity due to Earth on a mass,

    m, at Earths surfaceF = mg g = Gm

    e/r

    e2

    F = Gmem/r2 force of gravity due to Earth on a mass,

    m, at a distance, r, from Earths centerF = ma a = Gm

    e/r2

    gre2 = ar2

    a = gre2/r2 acceleration due to Earths gravity at

    distance, r, from Earths center

    A typical altitude for a Space Shuttle Orbiter orbit is 296 km. TheEarths mean radius is 6.37x106 m. The acceleration due togravity at the Orbiters altitude is

    a = 9.8 m/s2 (6.37x106 m)2 / (6.67x106 m)2 = 8.9 m/s2

    This is about 90% of the acceleration due to gravity at Earthssurface. Using the same equations, you can see that to achieve amicrogravity environment of 10-6 g by moving away from Earth,a research laboratory would have to be located 6.37x109 m fromthe center of Earth.

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    8

    Mathematics Standards

    o Algebra Computation and Estimation

    o Conceptual Underpinnings of Calculuso Discrete Mathematicso Functions

    o Mathematical Connections o Mathematics as Problem Solving o Mathematics as Reasoning Patterns and Functions o Statistics

    Science Standards

    o Physical Science o Science and Technology o Science as Inquiry o Science in Personal and Social Perspectives o Unifying Concepts and Processes

    Questions for Discussion What is the functional relationship between acceleration,

    distance, and time?

    Use the four sets of drop facility data points given in the textand the additional data set (0 meters, 0 seconds). What doesthe (0 meters, 0 seconds) data set represent? Why is it a validdata set to use?

    Suggested solution methods: Use different types of graphpaper Use a computer e urvefitting r)rogrnm Do a dimensionalanalysis.

    Knowing that g=9.8 m/s2, what equation can you write toincolporate acceleration, distance, and time?

    Assume it costs $5,000 per meter of height to build a droptower.

    How much does it cost to build a drop tower to allow drops of1 second, 2 seconds, 4 seconds, 10 seconds?

    Why does it cost so much more for the longer times?

    What would be an inexpensive way to double low-gravity time in a drop tower?

    Shoot the experiment package up from the bottom.

    The use of orbiting spacecraft is one methodused by NASA to create microgravity conditions.In addition, four other methods of creating suchconditions are introduced here and we giveexamples of situations where the student canexperience microgravity.

    Drop FacilitiesResearchers use high-tech facilities based on theelevator analogy to create micro-gravityconditions. The NASA Lewis Research Center hastwo drop facilities. One provides a 132 meterdrop into a hole in the ground similar to a mineshaft. This drop creates a reduced gravityenvironment for 5.2 seconds. A tower at Lewisallows for 2.2 second drops down a 24 meterstructure. The NASA Marshall Space Flight Centerhas a different type of reduced gravity facility.This 100 meter tube allows for drops of 4.5second duration. Other NASA Field Centers andother countries have additional drop facilities ofvarying sizes to serve different purposes. Thelongest drop time currently available (about 10seconds) is at a 490 meter deep vertical mineshaft in Japan that has been converted to a dropfacility. Sensations similar to those resulting froma drop in these reduced gravity facilities can beexperienced on freefall rides in amusement parksor when stepping off of diving platforms.

    Schematic of the NASA Lewis Research Center 2.2 SecondDrop Tower.

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    9

    AircraftAirplanes are used to achieve reduced gravityconditions for periods of about 15 seconds. Thisenvironment is created as the plane flies on aparabolic path. A typical flight lasts two to threehours allowing experiments and crew members totake advantage of about forty periods ofmicrogravity. To accomplish this, the plane climbsrapidly at a 45 degree angle (this phase is calledpull up), traces a parabola (pushover), and thendescends at a 45 degree angle (pull out). Duringthe pull up and pull out segments, crew andexperiments experience accelerations of about 2g. During the parabola, net accelerations drop aslow as 1.5x10-2 g for about 15 seconds. Due tothe experiences of many who have flown onparabolic aircraft, the planes are often referred toas Vomit Comets. Reduced gravity conditionscreated by the same type of parabolic motiondescribed above can be experienced on the seriesof floater hills that are usually located at the endof roller coaster rides and when driving overswells in the road.

    Parabolic Flight Characteristics

    Mathematics Standards

    o Conceptual Underpinnings of Calculuso Functions

    o Mathematical Connections Patterns and Functions

    Science Standards

    o Earth and Space Science o Physical Science o Unifying Concepts and Processes

    Microgravity carriers and other spacecraft follow paths bestdescribed by conic sections. The aircraft and sub-orbital rocketstrace out parabolas. Orbiting spacecraft are free falling onelliptical paths. When a meteoroid is on a path that is influencedby Earth or any other planetary body but does not get capturedby the gravitational field of the body, its motion, as it approachesthen moves away from the body, traces out a hyperbolic path.

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    Rocket Parabolic Flight Profile

    Mathematics Standards

    o Algebra Computation and Estimation

    o Conceptual Underpinnings of Calculuso Discrete Mathematicso Functions

    o Mathematical Connections o Mathematics as Problem Solving o Mathematics as Reasoning Number and Number Relationships

    Science Standards

    o Physical Science o Science and Technology

    o Science as Inquiryo Unifying Concepts and Processes

    Questions for Discussion How does the Shuttle stay in orbit? Use the following two

    equations that descnbe the foree aeting on an object. The firstequation represents the force of gravity acting on the Shuttle.

    Where:

    F1

    = Force of gravity acting on the Shuttle

    G = Universal gravitational constant

    me

    = Mass of Earth

    ms

    = Mass of the Shuttle

    r = Distance from center of Earth to the Shuttle

    RocketsSounding rockets are used to create reducedgravity conditions for several minutes; they followsuborbital, parabolic paths. Freefall exists duringthe rockets coast: after burn out and beforeentering the atmosphere. Acceleration levels areusually around 10-5 g. While most people do notget the opportunity to experience theaccelerations of a rocket launch and subsequentfreefall, springboard divers basically launchthemselves into the air when performing divesand they experience microgravity conditions untilthey enter the water.

    Orbiting SpacecraftAlthough drop facilities, airplanes, and rocketscan establish a reduced gravity environment, allthese facilities share a common problem. After afew seconds or minutes, Earth gets in the wayand freefall stops. To conduct longer scientificinvestigations, another type of freefall is needed.

    To see how it is possible to establish microgravityconditions for long periods of time, one must firstunderstand what keeps a spacecraft in orbit. Askany group of students or adults what keepssatellites and Space Shuttles in orbit and youwill probably get a variety of answers. Twocommon answers are The rocket engines keepfiring to hold it up, and There is no gravity inspace.

    Although the first answer is theoretically possible,the path followed by the spacecraft wouldtechnically not be an orbit. Other than the altitudeinvolved and the specific means of exerting anupward force, little difference exists between aspacecraft with its engines constantly firing andan airplane flying around the world. A satellitecould not carry enough fuel to maintain itsaltitude for more than a few minutes. The secondanswer is also wrong. At the altitude that theSpace Shuttle typically orbits Earth, thegravitational pull on the Shuttle by Earth is about90% of what it is at Earths surface.

    F1 = G

    mem

    s

    r2

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    In a previous section, we indicated that IssacNewton reasoned that the closed orbits of theplanets through space were due to gravityspresence. Newton expanded on his conclusionsabout gravity and hypothesized how an artificialsatellite could be made to orbit Earth. Heenvisioned a very tall mountain extending aboveEarths atmosphere so that friction with the airwould not be a factor. He then imagined a cannonat the top of that mountain firing cannonballsparallel to the ground. Two forces acted uponeach cannonball as it was fired. One force, due tothe explosion of the black powder, propelled thecannonball straight outward. If no other forcewere to act on the cannonball, the shot wouldtravel in a straight line and at a constant velocity.But Newton knew that a second force would acton the cannonball: gravity would cause the pathof the cannonball to bend into an arc ending atEarths surface.

    The second equation represents the force acting on the Shuttlethat causes a centripetal acceleration,

    This is an expression of Newtons second law, F=ma.

    F2

    = Force acting on the Shuttle that causes uniformcircular motion (with centripetal acceleration)

    v = Velocity of the Shuttle

    These two forces are equal: Fl=F

    2

    V =

    In order to stay in a circular orbit at a given distance from thecenter of Earth, r, the Shuttle must travel at a precise velocity, v.

    How does the Shuttle change its altitude? From a detailedequation relating the Shuttle velocity with the Shuttle altitude,one can obtain the following simple relationship for a circularorbit. Certain simplifying assumptions are made in developingthis equation: 1) the radius of the Shuttle orbit is nearly thesame as the radius of Earth, and 2) the total energy of theShuttle in orbit is due to its kinetic energy, 1/2 mv2; the changein potential energy associated with the launch is neglected.

    r = v

    = orbital period. the time it takes thc Shuttle to completeone revolution around Earth

    =

    v = the change in Shuttle velocityr = the change in Shuttle altitude

    v2

    r

    G =m

    em

    s

    r2m

    sv2

    r

    v2 =Gm

    e

    r

    2 r 3/2(Gm

    e) 1/2

    Gm

    r

    e

    Illustration from Isaac Newton, Principia, VII,Book III, p. 551.

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    For example:

    Consider a Shuttle in a circular orbit at 160 nautical miles (296.3km) altitude. Determine the new altitude caused by the Shuttlefiring a thruster that increases its velocity by I m/s.

    First, calculate the orbital period, X, from the above equation.

    = 2(re+2.96 x l05 m)3/2 (Gm

    e) 1/2

    = 2(6.37 x 106m+2.96 x 105 m)3/2 (6.67 x 10-11 m3 x 5.98 x1024kg)l/2

    s2kg

    = 5.41 x 103 s

    Next, use the period and the applied velocity change to calculatethe altitude change.

    = 5.41x103s

    = 1.72xl03 m

    This altitude change is actually seen on the opposite side of theorbit. In order to make the orbit circular at the new altitude, theShuttle needs to apply the same v at the other side of the orbit.

    In the discussion and example just given, we state that theequations given are simple approximations of more complexrelationships between Shuttle velocity and altitude. The morecomplex equations are used by the Shuttle guidance andnavigation teams who track the Shuttles flights. But theequations given here can be used for quick approximations of thetypes of thruster firings needed to achieve certain altitudechanges. This is helpful when an experiment team may want torequest an altitude change. Engineers supporting the experimentteams can determine approximately how much propellant wouldbe required for such an altitude change and whether enoughwould be left for the required de-orbit burns. In this way, theengineers and experiment teams can see if their request isrealistic and if it has any possibility of being implemented.

    Newton considered how additional cannonballswould travel farther from the mountain each timethe cannon fired using more black powder. Witheach shot, the path would lengthen and soon thecannonballs would disappear over the horizon.Eventually, if one fired a cannon with enoughenergy, the cannonball would fall entirely aroundEarth and come back to its starting point. Thecannonball would be in orbit around Earth.Provided no force other than gravity interferedwith the cannonballs motion, it would continuecircling Earth in that orbit.

    This is how the Space Shuttle stays in orbit. Itlaunches on a path that arcs above Earth so thatthe Orbiter travels at the right speed to keep itfalling while maintaining a constant altitude abovethe surface. For example, if the Shuttle climbs toa 320 kilometer high orbit, it must travel at aspeed of about 27,740 kilometers per hour toachieve a stable orbit. At that speed and altitude,the Shuttle executes a falling path parallel to thecurvature of Earth. Because the Space Shuttle isin a state of freefall around Earth and due to theextremely low friction of the upper atmosphere,the Shuttle and its contents are in a high-qualitymicrogravity environment.

    r=

    (1 m/s )

    v

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    MicrogravityScience PrimerWe experience many manifestations of gravity ona day to day basis. If we drop something, it fallstoward Earth. If we release a rock in a container ofwater, the rock settles to the bottom of the con-tainer. We experience other effects of gravityregularly, although we may not think of gravity asplaying a role.

    Consider what happens when a container of wateris heated from below. As the water on the bottomis heated by conduction through the container, itbecomes less dense than the un-heated, coolerwater. Because of gravity, the cooler, more densewater sinks to the bottom of the container and theheated water rises to the top due to buoyancy. Acirculation pattern is produced that mixes the hotwater with the colder water. This is an example ofbuoyancy driven (or gravity driven) convection.The convection causes the water to be heatedmore quickly and uniformly than if it were heatedby conduction alone. This is the same densitydriven convection process to which we refer whenwe state matter-of-factly thathot air rises.

    In addition to mixing, density differences can alsocause things to differentially settle through aprocess called sedimentation. In this process, themore dense components of mixtures ofimmiscible fluids or solid particles in fluids setteto the bottom of a container due to gravity. If youfill a bucket with very wet mud, and then leave thebucket sitting on the ground, over time the moredense soil particles will sink to the bottom of thebucket due to gravity, leaving a layer of water ontop. When you pick up a bottle of Italian saladdressing from the grocery store shelf, you seeseveral different layers in the bottle. The densesolids have settled to the bottom, the vinegarforms a middle layer, and the least dense oil is ontop.

    Science Standards

    o Physical Science o Unifying Concepts and Processes

    Heat transfer occurs through one of three processes or acombination of the three. Conduction is the flow of heat througha body from an area of higher temperature to an area of lowertemperature. Molecules in the hot region increase theirvibrational energy as they are heated. As they collide withmolecules with lower vibrational energy (cooler ones). some ofthe vibrational energy is passed to the cooler ones, their energy isincrcased. and heat is passed on.

    Heat transfer by convection is the movement of heat by motionof a fluid. This motion can he the result of some force, such as apump circulating heated water. and is referred to as forcedconvection. If the motion is the result of difterences in density(thermal or compositional). the convection is referred to asbuoyancy-driven, density-driven. or natural convection.

    Radiation is the emission of energy trom the surface of a body.Energy is emitted in the form of electromagnetic waves orphotons (packets of light). The character (wavelength. energy ofphotons, etc.) of the radiation depends on the temperature.surface area. and characteristics of the body emitting the energy.Electromagnetic waves travel with the speed of light throughempty space and are absorbed (and/or reflected) by objects theyfall on, thus transferring heat. An excellent example of radiativeheating is the suns heat that we experience on Earth.

    Mathemathics Standards

    o Mathematical Conneclions

    Science Standards

    o Earth and Space Science o Physical Science o Unifying Concepts and Processes

    The mass of a body divided hy its volume is its average density.

    Science Standards

    o Physical Science o Unifying Concepts and Processes

    When two or more liquids are immiscible they do not mixchemically.

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    Density Table Units (kg/m3)

    Interstellar space 10-21 - 10-18

    Atmosphere at normal altitudeof Space Shuttle in orbit 1-4x10-11

    Air at 0C and 1 atm 1.3Carbon Dioxide 1.9Balsa 110-140Bone 170-200Cork 220-260The Larch 500-560Lithium 530Applewood 660-840Peat Blocks 840Ice 920Olive Oil 920Sodium 970Water at 0C and 1 atm 1000Rock Salt 2180Graphite 2300-2700Aluninum 2700Basalt 2400-3100Talc 2700-2800Dolomite 2830Diamond 3010-3520Average density of Earth 5520Iron 7860Lead 11340Irdium 22400Osmium 22500Uranium nucleus 3x1017

    Neutron star (center) 1017-1018

    Mathematics Standards

    o Algebrao Functions

    Geometryo Geometry from a Synthetic Perspective

    o Mathematical Connections o Mathematics as Communication o Mathematics as Problem Solving Measurement

    o Trigonometry

    Science Standards

    o Physical Science o Science and Technology o Science in Personal and Social Perspectives o Unifying Concepts and Processes

    Gravity can also mask some phenomena thatscientists wish to study. An example is theprocess of diffusion. Diffusion is the interminglingof solids, liquids, and gases due to differences incomposition. Such intermingling occurs in manysituations, but diffusion effects can be easilyhidden by stronger convective mixing. As anexample, imagine a large room in which all aircirculation systems are turned off and in which agroup of women are spaced ten feet apartstanding in a line. If an open container ofammonia were placed in front of the first womanin line and each woman raised her hand when shesmelled the ammonia, it would take aconsiderable amount of time before everyoneraised her hand. Also, the hand raising wouldoccur sequentially along the line from closest tothe ammonia to furthest from the ammonia. If thesame experiment were performed with a fancirculating air in the room, the hands would beraised more quickly, and not necessarily in thesame order. In the latter case, mixing of theammonia gas with the air in the room is due toboth diffusion and convection (forced convectiondue to the fan) and the effects of the twoprocesses cannot be easily separated. In a similarmanner, buoyancy driven convection can maskdiffusive mixing of components in scientificexperiments.

    Some behavior of liquids can also be masked bygravity. If you pour a liquid into a container onEarth, the liquid conforms to the bottom of thecontainer due to gravity. Depending on the shapeof the container and on the properties of thecontainer and the liquid, some of the liquid maycreep up the walls or become depressed alongthe walls due to the interrelated phenomena ofsurface tension, adhesion, cohesion, andcapillarity.

    The resulting curved surface may be familiar toanyone who has measured water in a smalldiameter glass container (the water cupsupward) or has looked at the level of mercury in aglass thermometer (the mercury cupsdownward). The distance the contact

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    line between the liquid and the container movesup or down the container wall is affected bygravity.

    Experiments performed on Earth often takeadvantage of the effects of gravity discussed. Formany experiments, however, these effects tend tomake the execution of experiments or the analysisof experimental results difficult and sometimeseven impossible. Therefore, many researchersdesign experiments to be performed undermicrogravity conditions. The different scientificresearch areas that are studied in microgravityinclude biotechnology, combustion science, fluidphysics, fundamental physics, and materialsscience. Each of these areas, or disciplines, isdiscussed below. The discipline is defined, someof the specific effects of gravity that illustrate thebenefits of microgravity research are discussed,and some examples of current research arepresented. In addition, a brief discussion of themicrogravity environment of orbiting spacecraft isprovided as is an introduction to the applicationof microgravity research to the exploration anddevelopment of space.

    The MicrogravityEnvironment ofOrbiting SpacecraftWhile freefall reduces the effects of gravity, beingin an orbiting laboratory introduces otheraccelerations that cause effects that areindistinguishable from those due to gravity. Whena spacecraft is in orbit around Earth, the orbit isactually defined by the path of the center of massof the spacecraft around the center of Earth. Anyobject in a location other than on the linetraversed by the center of mass of the spacecraftis actually in a different orbit around Earth.Because of this, all objects not attached to thespacecraft move relative to the orbiter center ofmass. Other relative motions of unattachedobjects are related to aerodynamic drag on the

    Capillarity can be defined as the attraction a fluid has for itselfversus the attraction it has for a solid surface (usually the fluidscontainer). Thc surface tension in a liquid-liquid or liquid-gassystem is the fluids tendency to resist an increase in surface area.Surface tension is temperature dependent. Surface tension,capillarity, adhesion, and cohesion work together to drive thecontact angle between a solid-liquid interface and liquid-liquidinterface when a small diameter tube is dipped into a liquid.When the contact angle =0, the liquid wets the tubccompletely. When 90 (an obtuse angle). the liquid is depressed in thetube and does not wet the walls. The distance belween the liquidsuriace in the container and in the tube is h=2

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    Mathematics Standards

    Computation and Estimation o Mathematical Connections o Mathematics as Communication Measurement

    Science Standards

    Grades 5-8 (); Grades 9-12 (o)

    o Physical Science o Science and Technology o Unifying Concepts and Processes

    Quasi-steady accelerations in spacecraft are related to theposition in the spacecraft, aerodynamic drag, and vehiclerotation. For the Space Shuttle Orbiters, these accelerations areon the order of lx10-6 g and vary with the orbital frequency.

    Mathematics Standards

    Computation and Estimation o Mathematical Connections o Mathematics as Communication Measurement

    Science Standards

    o Physical Science o Science and Technology o Unifying Concepts and Processes

    g-jitter indicates the vibrations expenenced by microgravityexpenments (for example on parabolic aircraft and the SpaceShuttle) that cause effects similar to those that would be causedby a time-varying gravitational field.

    The quasi-steady microgravity environment on the OrbiterColumbia shows the effiects of variations in Earths atmosphericdensity. The primary contribution to the variation is the day/nightdiffierence in atmospheric density. The plot shows that the dragon the Orbiter varies over a ninety minute orbit.

    vehicle and spacecraft rotations. A spacecraft inlow-Earth orbit experiences some amount of dragdue to interactions with the atmosphere. Anobject within the vehicle, however, is protectedfrom the atmosphere by the spacecraft itself anddoes not experience the same deceleration thatthe vehicle does. The floating object andspacecraft therefore are moving relative to eachother. Similarly, rotation of the spacecraft due toorbital motion causes a force to act on objectsfixed to the vehicle but not on objects freelyfloating within it. On average for the SpaceShuttles, the quasi-steady accelerationsresulting from the sources discussed above(position in the spacecraft, aerodynamic drag,and vehicle rotation) are on the order of 1x1 0-6 g,but vary with time due to variations in theatmospheric density around Earth and due tochanges in Shuttle orientation.

    In addition to these quasi-steady accelerations,many operations on spacecraft cause vibrationsof the vehicle and the payloads (experimentapparatus). These vibrations are often referred toas g-jitter because their effects are similar tothose that would be caused by a time-varyinggravitational field. Typical sources for vibrationsare experiment and spacecraft fans and pumps,motion of centrifuges, and thruster firings. With acrew onboard to conduct experiments, additionalvibrations can result from crew activities.

    The combined acceleration levels that result fromthe quasi-steady and vibratory contributions aregenerally referred to as the microgravityenvironment of the spacecraft. On the SpaceShuttles, the types of vibration-causingoperations discussed above tend to create acumulative background microgravity environmentof about 1x10-4 g, considering contributions forall frequencies below 250 Hz.

    BiotechnologyBiotechnology is an applied biological sciencethat involves the research, manipulation, and

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    manufacturing of biological molecules, tissues,and living organisms. With a critical andexpanding role in health, agriculture, andenvironmental protection, biotechnology isexpected to have a significant impact on oureconomy and our lives in the next century.Microgravity research focuses on three principalareasprotein crystal growth, mammalian celland tissue culture, and fundamentalbiotechnology.

    Gravity significantly influences attempts to growprotein crystals and mammalian cell tissue onEarth. Initial research indicates that proteincrystals grown in microgravity can yieldsubstantially better structural information thancan be obtained from crystals grown on Earth.Proteins consist of thousandsor in the case ofviruses, millionsof atoms, which are weaklybound together, forming large molecules. OnEarth, buoyancy-induced convection andsedimentation may inhibit crystal growth. Inmicrogravity, convection and sedimentation aresignificantly reduced, allowing for the creation ofstructurally better and larger crystals.

    The absence of sedimentation means that proteincrystals do not sink to the bottom of their growthcontainer as they do on Earth. Consequently, theyare not as likely to be affected by other crystalsgrowing in the solution. Because convective flowsare also greatly reduced in microgravity, crystalsgrow in a much more quiescent environment,which may be responsible for the improvedstructural order of space-grown crystals.Knowledge gained from studying the process ofprotein crystal growth under microgravityconditions will have implications for proteincrystal growth experiments on Earth.

    Research also shows that mammalian cellsparticularly normal cellsare sensitive toconditions found in ground-based facilities usedto culture (grow) them. Fluid flows caused bygravity can separate the cells from each other,

    Protein crystals grown in microgravity can haveregular, simple shapes and a more highly orderedinternal structure than those grown on Earth.

    1 g g

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    severely limiting the number of cells that willaggregate (come and stay together). But tissuesamples grown in microgravity are much largerand more representative of the way in whichtissues are actually produced inside the humanbody. This suggests that better control of thestresses exerted on cells and tissues can play animportant role in their culture. These stresses aregreatly reduced in microgravity.

    Protein Crystal GrowthThe human body contains over 100,000 differentproteins. These proteins play important roles inthe everyday functions of the body, such as thetransport of oxygen and chemicals in the blood,the formation of the major components of muscleand skin, and the fighting of disease. Researchersin this area seek to determine the structures ofthese proteins, to understand how a proteinsstructure affects its function, and ultimately todesign drugs that intercede in protein activities(penicillin is a well-known example of a drug thatworks by blocking a proteins function).Determining protein structure is the key to thedesign and development of effective drugs.

    The main purpose in growing protein crystals isto advance our knowledge of biological molecularstructures. Researchers can use microgravity tohelp overcome a significant stumbling block inthe determination of molecular structures: thedifficulty of growing crystals suitable forstructural analysis. Scientists use X-raydiffraction to determine the three-dimensionalmolecular structure of a protein. They cancalculate the location of the atoms that make upthe protein based on the intensity and position ofthe spots formed by the diffracted X-rays. Fromhigh resolution diffraction data, scientists candescribe a proteins structure on a molecularscale and determine the parts of the protein thatare important to its functions. Using computeranalysis, scientists can create and manipulatethree-dimensional models of the protein andexamine the intricacies of its structure to create adrug thatfits into a proteins active site, likeinserting a key into a lock to turn off the

    Crystallized protein lysozyme after dialysis to remove smallmolecule contaminants.

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    proteins function. But X-ray diffraction requireslarge, homogeneous crystals (about the size of agrain of table salt) for analysis. Unfortunately,crystals grown in Earths gravity often haveinternal defects that make analysis by X-raydiffraction difficult or impossible. Space Shuttlemissions have shown that crystals of someproteins (and other complex biological moleculessuch as viruses) grown on orbit are larger andhave fewer defects than those grown on Earth.The improved data from the space-grown crystalssignificantly enhance scientists understanding ofthe proteins structure and this information can beused to support structure-based drug design.

    Scientists strive for a better understanding of thefundamental mechanisms by which proteins formcrystals. A central goal of microgravity proteincrystal growth experiments is to determine thebasic science that controls how proteins interactand order themselves during the process ofcrystallization. To accomplish this goal, NASA hasbrought together scientists from the proteincrystallography community, traditional crystalgrowers, and other physical scientists to form amultidisciplinary team in order to address theproblems in a comprehensive manner.

    Mammalian Cell and Tissue CultureMammalian cell tissue culturing is a major area ofresearch for the biotechnology community. Tissueculturing is one of the basic tools of medicalresearch and is key to developing future medicaltechnologies such as ex vivo (outside of thebody) therapy design and tissue transplantation.To date, medical science has been unable to fullyculture human tissue to the mature states ofdifferentiation found in the body.

    The study of normal and cancerous mammaliantissue growth holds enormous promise forapplications in medicine. However, conventionalstatic tissue culture methods form flat sheets ofgrowing cells (due to their settling on the bottomof the container) that differ in appearance andfunction from their three-dimensional counterparts

    Science Standards

    o Physical Science o Unifying Concepts and Processes

    A substance that is homogeneous is uniform in structure and/orcomposition.

    Three different types of protein c rystals grown on theSpace Shuttle Columbia in 1995: satellite tobacco mosaicvirus, lysozyme, and thaumatin.

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    Science Standards

    o Life Science o Unifying Concepts and Processes

    Differentiation is the process (or the result of that process) bywhich cells and/or tissues undergo a progressive specialization ofform or function.

    Mathematics Standards

    o Algebrao Conceptual Underpinnings of Calculuso Geometry from an Algebraic Perspective

    o Mathematical Connections o Mathematics as Problem Solving

    Science Standards

    o Physical Science o Science and Technology o Unifying Concepts and Processes

    The forces acting on a surface can be separated into componentsperpendicular (normal) to and tangential to the surface. Thenormal force causes a normal stress and the tangential force isresponsible for a tangential, or shear, stress acting on the surface.Shear forces cause contiguous parts of a structure or liquid toslide relative to each other.

    growing in a living body. In an effort to enhancethreedimensional tissue formation, scientists havedeveloped a ground-based facility for cell andtissue culture called a bioreactor. This instrumentcultures cells in a slowly rotating horizontalcylinder, which produces lower stress levels onthe growing cells than previous Earth-basedexperimental environments. The continuousrotation of the cylinder allows the sample toescape much of the influence of gravity, butbecause the bioreactor environment tends to berather passive, it is sometimes difficult for thegrowing tissue to find the fresh media (foodsupply) it needs to survive.

    Another reason normal mammalian cells aresensitive to growth conditions found in standardbioreactors is that fluid flow causes shear forcesthat discourage cell aggregation. This limits boththe development of the tissue and the degree towhich it possesses structures and functionssimilar to those found in the human body. Tissuecultures of the size that can be grown in thesebioreactors allow tests of new treatments oncultures grown from cells from the patient ratherthan on patients themselves. In the future, thistechnology will enable quicker, more thoroughtesting of larger numbers of drugs andtreatments. Ultimately, the bioreactor is expectedto produce even better results when used in amicrogravity environment.

    In cooperation with the medical community, thebioreactor design is being used to prepare bettermodels of human colon, prostate, breast, andovarian tumors. Cells grown in conventionalculture systems may not differentiate to form atumor typical of cancer. In the bioreactor,however, these tumors grow into specimens thatresemble the original tumor. Similar results havebeen observed with normal human tissues aswell. Cartilage, bone marrow, heart muscle,skeletal muscle, pancreatic islet cells, liver cells,and kidney cells are examples of the normaltissues currently being grown in rotatingbioreactors by investigators. In addition,

    A bioreactor vessel thatflew on the Space Shuttle Discovery inJuly 1995.

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    laboratory models of heart and kidney diseases,as well as viral infections (including Norwalk virusand Human Immunodeficiency Virus (HIV)) arecurrently being developed using a modified NASAbioreactor experiment design with slightvariations in experimental technique and someadjustments to hardware. Continued use of thebioreactor can improve our knowledge of normaland cancerous tissue development. NASA isbeginning to explore the possibility of culturingtissues in microgravity, where even greaterreduction in stresses on growing tissue samplesmay allow much larger tissue masses to develop.A hioreactor is in use on the Russian SpaceStation Mir in preparation for the InternationalSpace Station.

    Fundamental BiotechnologyElectrophoresis has been studied on a dozenSpace Shuttle flights and has led to additionalresearch in fluid physics in the area ofelectrohydrodynamics. Phase partitioningexperiments, which use interfacial energy (theenergy change associated with the contactbetween two different materials) as the means ofseparation, have flown on six missions.

    Combustion Science

    Combustion, or burning, is a rapid, self-sustaining chemical reaction that releases asignificant amount of heat. Examples of commoncombustion processes are burning candles, forestfires, log fires, the burning of natural gas in homefurnaces, and the burning of gasoline in internalcombustion engines. For combustion to occur,three things must normally be present: a fuel, anoxidizer, and an ignition stimulus. Fuels can besolid, liquid, or gas. Examples of solid fuelsinclude filter paper, wood, and coal. Liquid fuelsinclude gasoline and kerosene. Propane andhydrogen are examples of gaseous fuels.Oxidizers can be solid (such as ammoniumperchlorate, which is used in Space Shuttle boosterrockets), liquid (like hydrogen peroxide), or gaseous

    Science Standards

    o Physical Science o Science and Technology o Sciences in Personal and Social Perspectives o Unifying Concepts and Processes

    Electrophoresis is the separation of a substance based on theelectrical charge of the molecule and its motion in an appliedelectric field.

    Science Standards

    o Physical Science o Science and Technology o Science in Personal and Social Perspectives o Unifying Concepts and Processes

    An exception to the standard combustion process is hypergoliccombustion. In this situation, a fuel and an oxidizerspontaneously react on contact without the need for an ignitionstimulus. The jets used to maintain and change the Shuttlesorientation when in orbit are powered by hypergolic reactions.

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    (like oxygen). Air, which contains oxygen, is aparticularly common oxidizer. An electrical sparkis an example of an ignition stimulus.

    Combustion is a key element in many of modernsocietys critical technologies. Electric powerproduction, home heating, ground transportation,spacecraft and aircraft propulsion, and materialsprocessing are all examples in which combustionis used to convert chemical energy to thermalenergy. Although combustion, which accounts forapproximately 85 percent of the worlds energyusage, is vital to our current way of life, it posesgreat challenges to maintaining a healthyenvironment. Improved understanding ofcombustion will help us deal better with theproblems of pollutants, atmospheric change andglobal warming, unwanted fires and explosions,and the incineration of hazardous wastes. Despitevigorous scientific examination for over a century,researchers still lack full understanding of manyfundamental combustion processes.

    Some objectives of microgravity combustionscience research are to enhance ourunderstanding of the fundamental combustionphenomena that are affected by gravity, to useresearch results to advance combustion scienceand technology on Earth, and to address issues offire safety in space. NASA microgravitycombustion science research combines theresults of experiments conducted in ground-based microgravity facilities and orbitinglaboratories and studies how flames ignite,spread, and extinguish (go out) undermicrogravity conditions.

    Research in microgravity permits a new range ofcombustion experiments in whichbuoyancyinduced flows and sedimentation arevirtually eliminated. The effects of gravitationalforces often impede combustion studiesperformed on Earth. For example, combustiongenerally produces hot gas (due to the energyreieased in the reaction), which is less dense thatthe cooler gases around it. In Earths gravity, the

    The familiar shape of a candle flame on Earth iscaused by buoyancy-driven convection. Inmicrogravity, a candle flame assumes a sphericalshape as fresh oxidizer reaches it by diffusionprocesses.

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    hot gas is pusched up by the denser surroundinggases. As the hot gas rises, it creates buoyancy-induced flow that promotes the mixing of theunburned fuel, oxidizer, and combustionproducts.

    The ability to significantly reduce gravity-drivenflows in microgravity helps scientists in severalways. One advantage is that the quieter andmore symmetric microgravity environment makesthe experiments easier to model (describemathematically), thus providing a better arenafor testing theories. In addition, eliminatingbuoyancy-induced flows allows scientists to studyphenomena that are obscured by the effects ofgravity, such as the underlying mechanisms offuel and heat transport during combustionprocesses. Because buoyancy effects are nearlyeliminated in microgravity, experiments of longerduration and larger scale are possible, and moredetailed observation and examination ofimportant combustion processes can occur.

    Scientists often desire an even mixture of thecomponent parts of fuels so that modelsdeveloped for their experiments can usesimplified sets of equations to represent theprocesses that occur. Sedimentation affectscombustion experiments involving particles ordroplets because, as the components of greaterdensity sink in a gas or liquid, their movementrelative to the other particles creates anasymmetrical flow around the dropping particles.This can complicate the interpretation ofexperimental results. On Earth, scientists mustresort to mechanical supports, levitators, andstirring devices to keep fuels mixed, while fluidsin microgravity stay more evenly mixed withoutsticking together, colliding, or dispersingunevenly.

    Mathematics Standards

    Computation and Estimationo Discrete Mathematics

    o Mathematical Connections o Mathematics as Communication o Mathematics as Problem Solving o Mathematics as Reasoning

    Science Standards

    o Physical Science o Science as Inquiry o Science and Technology o Unifying Concepas and Processes

    The creation and use of mathematical models is a key elementof science, engineering, and technology. Modeling begins withidentifying the physical and chemical phenomena involved in anexperiment. Associated mathematical equations such as equationsof motion are then identified. These governing equations aresolved in order to predict important aspeces of the experimentbehavior, using appropriate values of experiment parameters suchas density, composition, temperature, and pressure. Simplemathematical models can be solved hy hand, while morecomplex experiments are generally modeled using sophisticatedalgorithms on high speed computers.

    In microgravity research, scientists use modeling in preparationfor flight experiments and in analysis of the results. Models andexperiment procedures are fine-tuned based on comparisonsbetween model predictions and the results of ground-basedmicrogravity experiments (for example, drop facilities andparabolic aircraft flights). This preliminary work allowsresearchers to best take advantage of space flight opportunities.

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    To date, combustion science researchers havedemonstrated major differences in the structuresof various types of flames burning undermicrogravity conditions and under 1 g conditions.In addition to the practical implications of theseresults in combustion efficiency, pollutant control,and flammability, these studies establish thatbetter understanding of the individual processesinvolved in the overall combustion process can beobtained by comparing results from microgravityand Earth gravity tests. One clear example of theadvantage of these comparison tests is in the areaof fire safety. Most smoke detectors have beendesigned to detect soot particles in the air, but thesizes of soot particles produced in 1 g aredifferent from those produced in microgravityenvironments. This means that smoke-detectingequipment must be redesigned for use onspacecraft to ensure the safety of equipment andcrew.

    Comparisons of research in microgravity and in1 g have also led to improvements in combustiontechnology on Earth that may reduce pollutantsand improve fuel efficiency. Technologicaladvances include a system that measures thecomposition of gas emissions from factorysmoke stacks so that they can be monitored. Inaddition, a monitor for ammonia, which is onegas that poses dangers to air quality, is alreadybeing produced and is available for industrial use.Engineers have also designed a device that allowsnatural gas appliances to operate more efficientlywhile simultaneously reducing air pollution. Thismay be used in home furnaces, industrialprocessing furnaces, and water heaters in thefuture. Another new technology is the use ofadvanced optical diagnostics and lasers to betterdefine the processes of soot formation so thatsoot-control strategies can be developed. Deviceshave also been developed to measure percentagesof soot in exhausts from all types of engines andcombustors, including those in automobiles andairplanes.

    Transmission Electron Microscope image of laser-heated soot.

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    The combustion science program supportsexperiments in the following research areas:

    Premixed Gas FlamesIn premixed gas flame research, the fuel andoxidizer gases are completely mixed prior toignition. Scientists are interested in flame speed(the rate at which the flame zone travels awayfrom the ignition source and into the unreactedmixture) as a function of both the type of fuel andoxidizer used and the oxidizer-to-fuel ratio. Withsufficiently high or low ratios, the flame does notmove into the unreacted mixture; these criticalratios are referred to as lower and upperflammability limits and are of considerableinterest in terms of both safety and fundamentalscience. Gravity can strongly affect both flamespeed and flammability limits, chiefly throughbuoyancy effects. Scientists in this area are alsoresearching gravitys effects on the stability,extinction, structure, and shape of premixed gasflames.

    Gaseous Diffusion FlamesIn this area of research, the fuel and oxidizergases are initially separate. They tend to diffuseinto each other and will react at their interfaceupon ignition. The structure of these flames undermicrogravity conditions is quite different than onEarth because of buoyancy-induced flows causedby Earths gravity. Scientists study flammabilitylimits, burning rates, and how diffusion flamestructure affects soot formation. Within this area,results of studies of the behavior of gas-jet flamesin a microgravity environment, both in transitionand in turbulent flows, are being used to developmodels with potential applications in creatingeffective strategies to control soot formation inmany practical applications.

    Liquid Fuel Droplets and SpraysIn this research area, scientists study thecombustion of individual liquid fuel dropletssuspended in an oxidizing gas (air, for example).For these experiments, investigators commonlyuse fuels

    Candle flame energy flow. Adapted from The Science of Flamesposter, National Energy Foundation, Salt Lake City, Utah.

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    Ultraviolet images of OH radiation taken at hnIf:vecnndinterval.s during a drrvp tower test of the DropletCombustion Experiment. The diameter of the flame producedby burning a heptane droplet decreases in freefall.

    such as heptane, kerosene, and methanol. Gravityhinders fundamental studies of dropletcombustion on Earth due to flows induced byhigh-density droplets that sink andbuoyancyinduced upward acceleration of hotcombustion products relative to the surroundinggas. These flows cause drops to burn unevenly,making it difficult for scientists to drawmeaningful conclusions from their experiments.

    This area of study also includes the investigationof the combustion of sprays and ordered arraysof fuel droplets in a microgravity environment foran improved understanding of interactionsbetween individual burning droplets in sprays.Knowledge of spray combustion processesresulting from these studies should lead to majorimprovements in the design of combustors usingliquid fuels.

    Fuel Particles and Dust CloudsThis area is particularly important in terms of firesafety because clouds of coal dust have thepotential to cause mine explosions and grain-dustclouds can cause silos and grain elevators toexplode. It is particularly difficult to study thefundamental combustion characteristics of fuel-dust clouds under normal gravity because initiallywelldispersed dust clouds quickly settle due todensity differences between the particles and thesurrounding gas. Because particles stick togetherand collide during the sedimentation process,they form nonuniform fuel-air ratios throughoutthe cloud. In microgravity, fuel-dust cloudsremain evenly mixed, allowing scientists to studythem with much greater experimental control witha goal of mitigating coal mine and grain elevatorhazards.

    Flame Spread Along SurfacesAn important factor in fire safety is inhibiting thespread of flames along both solid and liquidsurfaces. Flame spread involves the reactionbetween an oxidizer gas and a condensed-phasefuel or the vapor produced by the cooking of

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    such a fuel. Research has revealed majordifferences in ignition and flame-spreadingcharacteristics of liquid and solid fuels undermicrogravity and normal gravity conditions.Material flammability tests in 1 g, which arestrongly affected by buoyancy-induced flows, donot match results obtained in microgravity. It istherefore useful to study both flame spread andmaterial flammability characteristics inmicrogravity to ensure fire safety in environmentswith various levels of gravity. The knowledgegained from these studies may also lead to betterunderstanding of dangerous combustionreactions on Earth. Microgravity experimentseliminate complexities associated with buoyancyeffects, providing a more fundamental scenariofor the development of flame-spreading theories.

    Smoldering CombustionSmoldering combustion is a relatively slow,nonflaming combustion process involving anoxidizer gas and a porous solid fuel. Well-knownexamples of smoldering combustion areburning cigarettes and cigars. Smolderingcombustion can also occur on much larger scaleswith fuels such as polyurethane foam. When aporous fuel smolders for a long period of time, itcan create a large volume of gasified fuels, whichare ready to react suddenly if a breeze or someother oxidizer flow occurs. This incites the fuel tomake the transition to full-fledged combustion,often leading to disastrous fires (like thoseinvolving mattresses or sofa cushions). Sinceheat is generated slowly in this process, the rateof combustion is quite sensitive to heat exchange;therefore, buoyancy effects are particularlyimportant. Accordingly, smoldering combustion isexpected to behave quite differently in theabsence of gravity.

    Combustion SynthesisCombustion synthesis, a relatively new area ofresearch, involves creating new materials througha combustion process and is closely tied to workin materials science. One area of particularinterest is referred to as self-deflagrating high-

    View looking down at a piece qf ashless filter paper with a 1centimeter grid on it. On the USMP-3 Shuttle mission, a radiantheater (two concentric rings exposed at the center of the image)was used to ignite samples to study flame spread and smolderingin weak air f1ows under microgravity conditions. In this image,areas where the grid is not seen have been burned, with thecracking and curling edges of the burning paper leaving a cuspedappearance. The flame started at the heater site and propagatedtoward the right where a fan provided a source of fresh air.Charred paper around the burnt area is a darker grey than theuraffected paper. White areas to the right of the heater rings aresoot zones.

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    Science Standards

    o Physical Science o Unifying Concepts and Processes

    A fluid is something that flows. Highly compressible fluids areusually considered gases; essentially incompressible fluids areusually considered liquids. Fluids tend to conform to the shape ofa container. On Earths surface, liquids tend to fill the bottom ofan open or closed container and gases tend to fill closedcontainers.

    temperature synthesis. This occurs when twomaterials usually two solidsare mixedtogether, are reactive with one another, and createa reaction that gives off a large amount of heat.Once the reaction is started, the flame willpropagate through a pressed mixture of theseparticles, resulting in a new material. Much of theinitial research in this groundbreaking areainvolves changing variables such as composition,pressure, and preheat temperature. Manipulatingthese factors leads to interesting variations in theproperties of materials created through thesynthesis process.

    Flame processes are also being used to createfullerenes and nanoparticles. Fullerenes, a newform of carbon, are expensive to produce at thistime and cannot be produced in large quantities,but scientists predict more uses for them will bedeveloped as they become more readily available.Nanoparticles (super-small particles) are also ofgreat interest to materials scientists due to thechanges in the microstructure of compactedmaterials that can be produced by sintering,which result