Microgravity Science Space Flights

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MicrogravityScience SpaceFlightsUntil the mid-20th century, gravity was anunavoidable aspect of research and technology.During the latter half of the century, the use ofdrop towers to reduce the effects of gravitybecame more prevalent, although the extremelyshort periods of time they provided ( 6 seconds)severely restricted the type of research that couldbe performed.Initial microgravity research centered aroundsolving space flight problems created by thereduction in gravity’s effects experienced on orbit.How do you get the proper amount of fuel to arocket engine in space or water to an astronaut ona spacewalk? The brief periods of microgravityavailable in drop towers at the Lewis ResearchCenter and the Marshall Space Flight Center weresufficient to answer these basic questions and todevelop the pressurized systems and other newtechnologies needed to cope with this newenvironment. But, they still were not sufficient toinvestigate the host of other questions that wereraised by having gravity as an experimentalvariable.Skylab, America’s first space station.46The first long-term opportunities to exploremicrogravity and conduct research relatively freeof the effects of gravity came during the latterstages of NASA’s first great era of discovery. TheApollo program presented scientists with thechance to test ideas for using the spaceenvironment for research in materials, fluid, andlife sciences. The current NASA microgravityprogram had its beginning in experimentsconducted in the later flights of Apollo, theApollo-Soyuz Test Project, and onboard Skylab,America’s first space station.Microgravity — A Teacher’s Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5–8 ( ), 9–12 ( )

Preliminary microgravity experiments conductedduring the 1970’s were severely constrained,either by the relatively low power levels and spaceavailable on the Apollo spacecraft, or by the lownumber of flight opportunities provided to Skylab.These experiments, as simple as they were,provided new insights into the roles of fluid andheat flows in materials processing Much of ourunderstanding of the physics underlyingsemiconductor crystal growth, for example, canbe traced back to research initiated on Skylab.Since the early 1980’s, NASA has sent crews andpayloads into orbit on board the Space Shuttle.The Space Shuttle has given microgravityscientists an opportunity to bring theirexperiments to low-Earth orbit on a more regularbasis. The Shuttle introduced significant newcapabilities for microgravity research: larger,scientifically trained crews; a major increase inpayload volume and mass and available power;and the return to Earth of all instruments,samples, and data. The Spacelab module,developed for the Shuttle by the European SpaceAgency, gives researchers a laboratory withenough power and volume to conduct a limitedrange of sophisticated microgravity experimentsin space.Use of the Shuttle for microgravity researchbegan in 1982, on its third flight, and continuestoday on many missions. In fact, most Shuttlemissions that aren’t dedicated to microgravityresearch do carry microgravity experiments assecondary payloads.The Spacelab-1 mission was launched inNovember 1983. The primary purpose of themission was to test the operations of the complexSpacelab and its subsystems. The 71microgravity experiments, conducted usinginstruments from the European Space Agency,produced many interesting and provocativeresults. One investigator used the travelling heatermethod to grow a crystal of gallium antimonidedoped with tellurium (a compound useful forThe Spacelab module in the Orbiter Cargo Bay.Microgravity — A Teacher’s Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5–8 ( ), 9–12 ( )47

making electronic devices). Due to the absence ofgravity-driven convection, the space-growncrystal had a far more uniform distribution oftellurium than could be achieved on Earth. Asecond investigator used molten tin to studydiffusion in low gravity- research that canimprove our understanding of the solidification ofmolten metals.The first Spacelab mission dedicated to United States microgravityscience on USML-I. The coast of Florida appears in the background.Another Shuttle mission using the Spacelabmodule was Spacelab-3, which flew in April 1985.SL-3 was the first mission to include U.S.developed microgravity research instruments inthe Spacelab. One of these instruments supportedan experiment to study the growth of crystals ofmercury iodide-a material of significant interestfor use as a sensitive detector of X-rays andgamma rays. Grown at a high rate for a relativelyshort time, the resulting crystal was as good asthe best crystal grown in the Earth-basedlaboratory. Another U.S. experiment consisted ofa series of tests on fluid behavior using aspherical test cell. The microgravity environmentallowed the researcher to use the test cell tomimic the behavior of the atmosphere over alarge part of Earth’s surface. Results from thisexperiment were used to improve mathematicalmodels of our atmosphere.In October 1985, NASA launched a Spacelabmission sponsored by the Federal Republic ofGermany, designated Spacelab-D1. American andGerman scientists conducted experiments tosynthesize high quality semiconductor crystalsuseful in infrared detectors and lasers. Thesecrystals had improved properties and were moreuniform in composition than their Earth-growncounterparts. Researchers also successfullymeasured critical properties of molten alloys.48Microgravity — A Teacher’s Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5–8 ( ), 9–12 ( )

International MicrogravityLaboratory-1, January 1992More than 220 scientists from the United Statesand 14 other countries contributed to theexperiments flown on the first InternationalMicrogravity Laboratory (IML-1) in January 1992.Several biotechnology experiments concernedwith protein crystal growth enabled NASAscientists to successfully test and compare twodifferent crystal-growing devices.A German device called the Cryostat producedsuperior-quality crystals of proteins from severalmicroorganisms including the satellite tobaccomosaic virus (STMV), which has roles in diseasesaffecting more than 150 crop plants. As a resultof this experiment, scientists now have a muchclearer understanding of the overall structure ofSTMV. This information is useful in efforts todevelop strategies for combating viral damage tocrops.IML-1 also carried experiments designed to probehow microgravity affects the internal structure ofmetal alloys as they solidify. The growthcharacteristics, determined from one of theexperiments, matched the predictions of existingmodels, providing experimental evidence thatcurrent hypotheses about alloy formation arecorrect.Payload Commander Bonnie J. Dunbar and Payload SpecialistLawrence J. DeLucas working in the module on USML-1.United States MicrogravityLaboratory-1, June 1992In June 1992 the first United States MicrogravityLaboratory (USML-1) flew aboard a 14-dayshuttle mission, the longest up to that time. ThisSpacelab-based mission was an important step ina long-term commitment to build a microgravityprogram involving government, academic, andindustrial researchers.The payload included 31 microgravityexperiments using some facilities andinstruments from previous flights, including theProtein Crystal Growth facility, a SpaceMicrogravity — A Teacher’s Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5–8 ( ), 9–12 ( )49

Acceleration Measurement System, and the SolidSurface Combustion Experiment. New experimentfacilities, all designed to be reusable on futuremissions, included the Crystal Growth Furnace(CGF), a Glovebox provided by the EuropeanSpace Agency, the Surface Tension DrivenConvection Experiment apparatus (STDCE), andthe Drop Physics Module.Science Standards ooooEarth and Space ScienceHistory and Nature Of SciencePhysical ScienceUnifying Concepts and ProcessesQuestions for Discussion What are Cd, Hg, Te, Zn? What do these elements have in common?Hint: Look at their position on the periodic table of the elements.Investigators used the CGF to grow crystals offour different semiconductor materials attemperatures as high as 1260 C. One spacegrown CdZnTe crystal developed far fewerimperfections than even the best Earth-growncrystals, results that far exceeded pre-flightexpectations. Thin crystals of HgCdTe grown fromthe vapor phase had mirror-smooth surfaces evenat high magnifications. This type of surface wasnot observed on Earth-grown crystals.Researchers used the STDCE apparatus to explorehow internal movements of a liquid are createdwhen there are spatial differences in temperatureon the liquid’s surface. The results are in closeagreement with advanced theories and modelsthat the experiment researchers developed.In the Drop Physics Module, sound waves wereused to position and manipulate liquid droplets.Surface tension controlled the shape of thedroplets in ways that confirmed theoreticalpredictions. The dynamics of rotating drops ofsilicone oil also conformed to theoreticalpredictions. Experimental and theoretical resultsof this kind are significant because they illustratean important part of the scientific method:hypotheses are formed and carefully plannedexperiments are conducted to test them.Fission sequence of a rotating levitated drop.50Sixteen different investigations run by NASAresearchers used the Glovebox, which provided asafe enclosed working area; it also was equippedwith photographic equipment to provide a visualrecord of investigation operations. The Gloveboxallowed crew members to perform proteincrystallization studies as they would on Earth,including procedures that requireMicrogravity — A Teacher’s Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5–8 ( ), 9–12 ( )

hands-on manipulation. Among other results, useof the Glovebox provided the best-ever crystals ofmalic enzyme that may be useful in developinganti-parasitic drugs.The burning of small candles in the Gloveboxprovided new insights into how flames can existin an environment in which there is no air flow.The results were similar (though much longerlived) to what can be seen by conducting similarexperiments in freefall here on Earth. (See CandleFlames in Microgravity, in the Activities section ofthis guide.) The candles burned for about 45 to60 seconds in the Glovebox experiments.Another Glovebox investigation tested how wireinsulation burns under different conditions,including in perfectly still air (no air flow) and inair flowing through the chamber from differentdirections. This research has yielded extremelyimportant fundamental information and also haspractical applications, including methods forfurther increasing fire safety aboard spacecraft.The crew of scientist astronauts in the Spacelabplayed an important role in maximizing thescience return from this mission. For instance,they attached a flexible type of glovebox, whichprovided an extra level of safety, to the CrystalGrowth Furnace. The furnace was then opened,previously processed samples were removed andan additional sample was inserted. This enabledanother three experiments to be conducted. Twoother unprocessed samples were already in thefurnace.Zeolite crystals can be grown in the Glovebox Facility. Shownhere are photos (at the same scale) of zeolite crystals grown onUSML-I (top) and on Earth (bottom).Spacelab-J,September 1992The Spacelab-J (SL-J) mission flew in September1992. SL-J was the first Space Shuttle missionshared by NASA and Japan’s National SpaceDevelopment Agency (NASDA). NASAmicrogravity experiments focused on proteincrystal growth and collecting acceleration data insupport of the microgravity experiments.Microgravity — A Teacher’s Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5–8 ( ), 9–12 ( )51

NASDA’s science payload consisted of 22experiments focused on materials science andthe behavior of fluids, and 12 human biologyexperiments. NASDA also contributed twoexperiment facilities. One of these, the LargeIsothermal Furnace, was used to explore howvarious aspects of processing affect thestructure and properties of materials. Thesecond apparatus was a Free-FlowElectrophoresis Unit used to separate differenttypes of molecules in a fluid.United States MicrogravityPayload-1, October 1992The first United States Microgravity Payload(USMP-1) flew on a 10-day Space Shuttlemission launched on October 22, 1992. Themission was the first in an ongoing effort thatemploys telescience to conduct experiments ona carrier in the Space Shuttle Cargo Bay.Telescience refers to how microgravityexperiments can be conducted by scientists onthe ground using remote control.USMP experiments are mounted on Mission PeculiarEquipment Support Structures in the Shuttle Cay.rgo Bay.The carrier in the Cargo Bay consisted of twoMission Peculiar Equipment Support Structures.On-board, the two Space AccelerationMeasurement Systems measured how crewmovements, equipment operation, and thrusterfirings affected the microgravity environmentduring the experiments. This information wasrelayed to scientists on the ground, who thencorrelated it with incoming experiment data.A high point of USMP-1 was the first flight ofMEPHISTO, a multi-mission collaborationbetween NASA-supported scientists and Frenchresearchers. MEPHISTO (designed and built bythe French Space Agency, Centre Nationald’Etudes Spatiales or CNES) is designed to studythe solidification process of molten metals andother substances. Three identical samples of onealloy (a combination of tin and bismuth) weresolidified, melted, and resolidified more than 40times, under slightly different conditions eachtime. As each cycle ended, data were transmitted52Microgravity — A Teacher’s Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5–8 ( ), 9–12 ( )

from the Space Shuttle to Marshall Space FlightCenter. There, researchers analyzed theinformation in combination with data from theSpace Acceleration Measurement System andsent back commands for adjustments. In all, theinvestigators relayed more than 5000 commandsdirectly to their instruments on orbit. Researcherscompared experiment data with the predictions oftheoretical models and showed that mathematicalmodels can predict important aspects of theexperiment behavior. This first MEPHISTO effortproved that telescience projects can be carriedout efficiently, with successful results.The lambda point for liquid helium is thecombination of temperature and pressure atwhich normal liquid helium changes to asuperfluid. On Earth, effects of gravity make itvirtually impossible to measure properties ofsubstances very close to this point. On USMP-1,the Lambda Point Experiment cooled liquidhelium to an extremely low temperature—-a littlemore than 2 K above absolute zero. Investigatorsmeasured changes in its properties immediatelybefore it changed from a normal fluid to asuperfluid. Performing the test in microgravityyielded temperature measurements accurate towithin a fraction of one billionth of a degree—several hundred times more accurate than wouldhave been possible in normal gravity. Overall thenew data were five times more accurate than inany previous experiment.United States MicrogravityPayload-2, March 1994The second United States Microgravity Payload(USMP-2) flew aboard the Space ShuttleColumbia for 14 days from March 4 to March 18,1994. Building on the success of telescience inUSMP-1, the Shuttle Cargo Bay carried fourprimary experiments which were controlled byapproximately 10,000 commands relayed byscientists at Marshall Space Flight Center. USMP2 also included two Space AccelerationMeasurement Systems, which provided scientistsScience and mission management teams monitor and controlexperiments from operations centers worldwide.Microgravity — A Teacher’s Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5–8 ( ), 9–12 ( )53

on the ground with nearly instant feedback onhow various kinds of motion-including crewexercise and vibrations from thruster enginesaffected mission experiments. The OrbitalAcceleration Research Experiment in the CargoBay collected supplemental data on acceleration,providing an indication of the quasi-steadyacceleration levels experienced by theexperiments.A dendrite grown in the Isothermal Dendritic GrowthExperiment aboard the USMP-2. This is an example of howmost metals solidify.Science Standards o Physical Science o Unifying Concepts and ProcessesDendrites are branching structures that develop as a moltenmetal solidifies under certain conditions. The root of this word isthe (Greek dendron, meaning tree. Branching structures inbiology (nerve cells) and geology (drainage systems) are alsoreferred to as being dendritic.54Throughout the mission, the Critical Fluid LightScattering Experiment—-nicknamed Zeno—analyzed the behavior of the element xenon as itfluctuated between two different states, liquid andgas. First, a chamber containing liquid xenon washeated. Then, laser beams were passed throughthe chamber as the xenon reached temperaturesnear this transition point. A series ofmeasurements were taken of how the laser beamswere scattered (deflected) as the xenon shiftedfrom one state to another. Researchers expectedthat performing the experiment on orbit wouldprovide more detailed information about how asubstance changes phase than could be obtainedon Earth. In fact, the results producedobservations more than 100 times more precisethan the best measurement on the ground.The Isothermal Dendritic Growth Experiment(IDGE) examined the solidification of a materialthat is a well-established model for metals. Thismaterial is especially useful as a model because itis transparent, so a camera can actually recordwhat happens inside a sample as it freezes. In 59experiments conducted during 9 days, over 100television images of growing dendrites were sentto the ground and examined by the researchteam. Dendritic growth velocities and tip radii ofcurvature were measured. Results obtained undercertain experiment conditions were not consistentwith current theory. This inconsistency was thesubject of subsequent research on USMP-3. Inanother successful demonstration of telescience,the team relayed more than 200 commands to theIDGE, fine-tuning its operations.Microgravity — A Teacher’s Guide with Activities in Science, Mathematics, and Technology,EG-1997-08-110-HQ, Education Standards Grades 5–8 ( ), 9–12 ( )

USMP-2 also included a MEPHISTO experiment.On this mission, the MEPHISTO apparatus wasused for U.S. experiments to test how gravityaffects the formation of crystals from an alloy ofbismuth and tin that behaves much like asemiconductor during crystal growth.Metallurgical analysis of the samples has shownthat interactions between the molten and solidalloy during crystallization play a key role incontrolling the final morphological stability of thealloy.Another USMP-2 materials science experimentused the Advanced Automated DirectionalSolidification Furnace (AADSF). An eleven dayexperiment using the AADSF yielded a large, wellcontrolled sample of the alloy semiconductor,HgCdTe. The results of various analysistechniques performed on the crystal indicate thatvariations in the acceleration environment had amarked effect (due to changing residual fluidflow) on the final distribution of the alloy’scomponents in the crystal.International MicrogravityLaboratory-2, July 1994The second International Microgravity Laboratory(IML-2), with a payload of 82 major experiments,flew in July 1994 on the longest Space Shuttleflight to that time. IML-

Microgravity — A Teacher’s Guide with Activities in Science, Mathematics, and Technology, EG-1997-08-110-HQ, Education Standards Grades 5–8 ( ), 9–12 ( ) 46 Skylab, America’s first space station. Microgravity Science Space Flights Until the mid-20th century, gravity was an unavoidable aspect of research and technology.

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