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boom

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gravity is the force that pulls people

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without gravity sitting in a chair or

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walking down stairs would be difficult

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for example

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when you drop a ball at any point on

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earth it will always fall straight down

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that is gravity at work pulling the ball

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towards the earth's surface

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but there is a difference between

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dropping and throwing a ball

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when a ball is thrown it still falls to

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earth but lands at a point further away

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from where it was thrown

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if a ball could be thrown with enough

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forward velocity

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it would fall around the earth creating

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a low earth orbit

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like the ball the space shuttle is

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actually in a continuous fall around the

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earth

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astronauts and objects inside the

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shuttle are falling at exactly the same

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rate as the shuttle

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thus creating the effects of

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weightlessness

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imagine an astronaut in an elevator on

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earth

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the elevator is going to the top of a

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very tall building

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suddenly when he reaches the top the

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cable breaks

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the elevator begins to fall

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inside the car the astronaut begins to

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float he is weightless

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if he had an apple it would float too

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that is because the car the astronaut

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and the apple are falling at the same

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rate of speed

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you may have experienced moments on

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earth when the effects of gravity seem

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to disappear

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or crest the hill on a roller coaster

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scientists can take advantage of a

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reduced gravity environment to isolate

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the effects gravity has on physical

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chemical and biological processes

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a better understanding of these

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processes can be achieved by studying

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phenomena usually obscured by the

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effects of gravity

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on earth scientists utilize specialized

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facilities such as drop towers and

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aircraft in parabolic dive sequences to

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test experiments for a few seconds at a

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time in an environment which is

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approximately 1 100th of the earth's

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normal gravity level

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however many experiments require even

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smaller gravity levels and longer

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durations of free fall that cannot be

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achieved in these earth-based facilities

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in the constant microgravity environment

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of low earth orbit

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researchers have found that experiments

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in biotechnology

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fluid dynamics and material science have

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produced dramatically different results

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than ground-based research

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one example of this can be seen by

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examining crystals grown in a

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microgravity environment

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these crystals contain fewer flaws and

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imperfections than crystals grown on

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earth

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the result

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higher quality crystals for potential

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applications on earth

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however even in the microgravity

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environment aboard the shuttle there are

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other forces that may affect the results

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of experiments

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disturbances and vibrations caused by

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thruster firings

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crew movements and equipment operation

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can mimic the effects of gravity on

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experiment results

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disturbances that are significant for

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sensitive experiments

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that may negatively affect the results

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of those experiments

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a simple demonstration illustrates how

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an outside force can affect the results

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of an experiment

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the slightest disturbance to just one

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domino will cause the others to fall

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or try this experiment in your kitchen

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the surface tension of a glass of water

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will support common paper clips

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when the glass is bumped the paper clips

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sink to the bottom of the glass

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in order to understand the final data

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from an experiment conducted in

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microgravity

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these disturbances and other parameters

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such as temperature and pressure need to

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be measured

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researchers may then use the data to

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determine if unexpected results were

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caused naturally or by these measured

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at nasa's lewis research center in

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cleveland ohio scientists and engineers

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have developed the space acceleration

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measurement system or sams to measure

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and record vibrations and disturbances

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that may alter experiment results

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sams is designed to measure characterize

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and record low gravity disturbances on

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board the space shuttle

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a single sams unit can monitor three

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experiments directly as well as other

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experiments in close proximity

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the sams hardware consists of a main

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signal processing unit

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and three remote tri-axial sensor heads

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the three sensors on each of these heads

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detect the different disturbances and

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their levels

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the data is sent through cables and

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stored on disks similar to the compact

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discs that are found in homes today the

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sensor heads are mounted on or near an

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experiment

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permitting disturbances affecting that

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experiment to be sampled

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sams has the ability to collect data up

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to 20 feet away from the main unit

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this enhances its versatility and allows

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it to serve a wide variety of

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microgravity science and technology

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experiments

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sams is scheduled to fly as part of the

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second united states microgravity

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payload mission

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usmp2 aboard the space shuttle columbia

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in march of 1994.

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during this mission scientists in the

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payload operations control center or

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park will be able to monitor some of the

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data that the sams unit is collecting in

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real time as the disturbances are

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occurring

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scientists can use this information to

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determine if adjustments need to be made

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to their experiments to avoid any

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unacceptable conditions

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sams will support four materials science

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experiments on the usmp2 mission

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three of these experiments were

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developed or are managed by the nassau

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lewis research center

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the data that sams will collect for

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these experiments could lead to many

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advancements in processed materials such

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as improved industrial casting methods

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the development of superconductors and

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the ability to produce higher quality