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Życie w Kosmosie

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Życie na Marsie

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Low Gravity Platforms

Newton's Law

Windy Einsteina

Creating Microgravity

Tworzenie Mikrograwitacji 

NASA EDUCATION

What is microgravity?

Microgravity, also called weightlessness or zero gravity, is the absence of gravity. It is bested illustrated by astronauts floating in their spacecraft. They are floating because they are in a microgravity environment. Besides astronauts, many people experience microgravity every day by riding roller coasters or jumping off diving boards. It is the "free fall" period of these activities when the microgravity occurs and of course only lasts for a short period of time.

Microgravity Information

What are gravity and microgravity?

Gravity is a force that governs motion throughout the universe. It holds us to the ground, keeps the Moon in orbit around the Earth, and keeps Earth in orbit around the Sun.

First described by Sir Isaac Newton more than 300 years ago, gravity is the attraction between any two masses. It is most obvious when one of the masses is very large, like Earth. The acceleration of an object toward the ground (near Earth’s surface) caused by gravity alone is called normal gravity, or 1g. This acceleration is equal to 32.2 ft/sec² (9.8m/sec²).

As an example, if you drop an apple on Earth, it falls at 1g. If an astronaut on the Space Station drops an apple, it falls too; it just doesn’t look like it’s falling. That’s because the apple, the astronaut and the space station are all falling together. But they’re not falling toward Earth, they’re falling around it at the same rate. Since they’re all falling at the same rate, objects inside of the Station appear to float in a state we call zero gravity (0g), or more accurately, microgravity (1x10^-6 g.)

More generally described by Hawking Center Fellow Niki Eggert to her first grade students:

Gravity is a force that pulls down on you when you are on Earth. It causes things to fall down to the ground and not float away. Micro is a word that means very, very small. In space, there is a tiny bit of gravity. So we call this microgravity. Although it looks like things float in space, they are actually falling at a much slower rate because there is microgravity.

How does ZERO - G achieve microgravity?

Using the same methods that NASA has used for over 45 years to train astronauts, Zero Gravity Corporation (ZERO-G) achieves microgravity through Parabolic Flight.

Parabolic Flight, sometimes referred to as weightless flight, is achieved using ZERO-G’s Boeing 727 aircraft named G-FORCE ONE. Weightlessness occurs by flying G-FORCE ONE through a parabolic flight maneuver. Specially trained pilots fly these maneuvers between approximately 24,000 and 34,000 feet altitude. Each parabola takes 10 miles of airspace to perform and lasts about one minute from start to finish.

The plane is initially pulled up to approximately 45 degrees ’nose high’ and then ’pushed over’ the top to reach the zero-gravity segment of the parabolas. For the next 25 - 30 seconds everything in the plane is weightless. At approximately 30 degrees ’nose low’ a gentle pull-out is started which allows the Flyers to stabilize on the aircraft floor. Finally, the g-force is increased smoothly to about 1.8 g’s until the aircraft reaches a flight altitude of 24,000 feet. The maneuver is then repeated.

The weightlessness experienced by everyone inside the airplane is actually equivalent to the type of "free fall" you experience when sky diving. In this case however, the body of the aircraft surrounds you and protects you from the on-rushing wind. At the end of the free fall period, the aircraft scoops you up and carries you back to the top of the arc to begin the free fall process again.

In addition to achieving zero-g or weightlessness, G-FORCE ONE can also fly a parabola designed to offer Lunar (1/6th) or Martian (1/3rd) gravity. These reduced gravity environments are also created with a modified parabola that is not quite as steep as zero gravity parabolas.

Hawking Center Fellow Chace Johnson explains the Zero Gravity flights in scientific terms to his high school students in the following fashion:

Based on Isaac Newton’s proposed gravitational formula, the force of gravity (Fg) = (G)(m2m2)/d2. Being that (G) is a gravitational constant, the only factors that can affect gravity are mass and distance. In parabolic flight, flyers’ masses do not change and their change in distance from the center of the Earth is negligible. Therefore, their gravitational force (Fg) is neither gone ("zero G") nor diminished considerably ("microgravity"). The average person is only aware of gravity due to an opposing force on his/her body (normal force) or by observing the direction an object falls in comparison with its surroundings (frame of reference). In parabolic flight, flyers become "contained projectiles" where their normal force is removed while their frame of reference stays the same (unless we have drift). Therefore, the illusion of zero-gravity is created.

Could you describe a typical education flight and what it feels like?

Prior to flying aboard G-Force One on an education mission, teachers must complete a professional development workshop with one of our specially trained Hawking Center Educator Fellows. During the workshop, participants learn about Force & Motion; Martian, Lunar and Microgravity concepts/applications; experimental design for G-Force One; classroom applications and experiments; as well as necessary safety precautions for performing experiments in reduced gravity.

ZERO-G recommends at least three weeks but no more than two months between the professional development workshop and the flight day. This time period allows teachers to fully engage students in finalizing experimental design, applying the concepts in the classroom and predicting outcomes for their ZERO-G mission.

On flight day, participating teachers meet with their Hawking Center Educator Fellows who will also be their Team Coach, to finalize experiments and plan the sequence of experiments, or experiment profile, according to the flight profile. They review needed equipment, video recording procedures and anticipated outcomes one more time.

The education flight begins like any other commercial flight. You taxi out to the runway and await permission to take off. Once granted, the captain flies out to the airspace designated by the FAA as ours for the day. About the time the captain of a commercial flight would be turning off the seatbelt sign, you are given the okay to unbuckle your seatbelt and truly “move about the cabin”. Your Team Coach leads you to the floating/experiment area and guides you through set up of your experimental equipment. As instructed by your coach, you will then lay on the padded floor to prepare for the first set of parabolas.

After a few moments of feeling pressed gently into the floor as you experience 1.8 g’s, the Flight Director will call out “Martian 1” and you begin to feel lighter. So light in fact that you may be doing one-finger push-ups with a smile on your face! Two Lunar parabolas follow.

Depending on your experiment profile, the Martian and Lunar parabolas are ideal for human feats. This period also permits teachers an initial opportunity to understand physical movement in reduced gravity environments.

After the first set of parabolas, you experience a one to five minute period of “Straight and Level.” During this time, you and your Team Coach quickly review the experiments you’ve planned for the upcoming parabolas.

The Flight Director then calls “ZERO - 1” and you begin to float right off the floor. It’s like nothing on Earth. Working with your coach and teammates, you perform the experiments as planned making sure to capture the data either through use of the two fixed cameras in each floating section or the assistance of the videographer and/or photographer on board.

Achieving weightlessness is an experience few teachers have tried. Those who have, say it is life-changing and the boost their students need to cement an interest in science, technology, engineering and math education.

A feeling of true freedom and a place where the impossible becomes real, parabolic flight is the only way to create sustained weightlessness without going into space.

What is a typical flight profile?

Flight profiles may vary, however most flights consist of 5 sets of three parabolas each divided by periods of “Straight and Level.”

Can I experience weightlessness on Earth without flying in an aircraft?

No. Parabolic flight is the only way to experience true, sustained weightlessness (up to 30 seconds at a time) without going into space.

How can I get a ticket to weightlessness?

For more information on how you can fly aboard G-Force One, click on the link for your “Opportunities to Go Weightless”.

Other Online Resources

The main Zero Gravity Corporation web site - http://www.GoZeroG.com

The Official Stephen Hawking web site - http://www.hawking.org.uk

Space Florida web site - http://www.SpaceFlorida.gov

NASA Education - http://education.nasa.gov

źródło: http://www.hawkingcenter.org/educators/resources/

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.

More than 300 years ago the great Englishscientist Sir Isaac Newton published theimportant generalization that authematicallydescribes 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 Newton’s 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 ground—gravity.Newton’s 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.

3The eighteenth-century English physicist HenryCavendish later quantified Newton’s 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 Newton’s 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 Earth’s gravity at theEarth’s 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 theEarth’s 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 positiveindicates 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/s2-(-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

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 Earth’s 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 aMathematics microgravity environment would be one-millionth(10-6) of that experienced at Earth’s 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 Earth’sgravitational pull, the same drop would take 10seconds. In a microgravity environment equal toone-millionth of Earth’s 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 Earth’s 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.

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 Earth’sgravity 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.

 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.

Aircraft

Airplanes 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.

Rockets

Sounding rockets are used to create reducedgravity conditions for several minutes; they followsuborbital, parabolic paths. Freefall exists duringthe rocket’s 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 Spacecraft

Spacecraft Although 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 Earth’s surface.

In a previous section, we indicated that IssacNewton reasoned that the closed orbits of theplanets through space were due to gravity’spresence. Newton expanded on his conclusionsabout gravity and hypothesized how an artificialsatellite could be made to orbit Earth. Heenvisioned a very tall mountain extending aboveEarth’s 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 atEarth’s surface.

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 cannonball’s 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.

_____________________________

What is Microgravity?

 
Gravity is a force that governs motion throughout the universe. It holds us to the ground, and it keeps the moon in orbit around Earth and Earth in orbit around the sun.

The Expedition 16 crew members pose for a Christmas photo in the Zvezda Service Module of the International Space Station. Credit: NASA Many people mistakenly think that gravity does not exist in space. However, typical orbital altitudes for human spaceflight vary between 120 - 360 miles above Earth's surface. The gravitational field is still quite strong in these regions, since this is only about 1.8 percent the distance to the moon. Earth's gravitational field at about 250 miles above the surface is 88.8 percent of its strength at the surface. Therefore, orbiting spacecraft, like the space shuttle or space station, are kept in orbit around Earth by gravity.

The nature of gravity was first described by Sir Isaac Newton, more than 300 years ago. Gravity is the attraction between any two masses, most apparent when one mass is very large (like Earth). The acceleration of an object toward the ground caused by gravity alone, near the surface of Earth, is called "normal gravity," or 1g. This acceleration is equal to 32.2 ft/sec2 (9.8 m/sec2).

If you drop an apple on Earth, it falls at 1g. If an astronaut on the space station drops an apple, it falls too. It just doesn't look like it's falling. That's because they're all falling together: the apple, the astronaut and the station. But they're not falling towards Earth, they're falling around it. Because they're all falling at the same rate, objects inside of the station appear to float in a state we call "zero gravity" (0g), or more accurately microgravity (1x10-6 g.)

Creating Microgravity

The condition of microgravity comes about whenever an object is in free fall. That is, it falls faster and faster, accelerating with exactly the acceleration due to gravity (1g). As soon as you drop something (like an apple) it is in a state of free fall. The same is true if you throw something; it immediately starts falling towards Earth. But how does something fall around Earth?

Newton developed a thought experiment to demonstrate this concept. Imagine placing a cannon at the top of a very tall mountain.

Once fired, a cannonball falls to Earth. The greater the speed, the farther it will travel before landing. If fired with the proper speed, the cannonball would achieve a state of continuous free-fall around Earth, which we call orbit. The same principle applies to the space shuttle or space station. While objects inside them appear to be floating and motionless, they are actually traveling at the same orbital speed as their spacecraft: 17,500 miles per hour (28,000 km per hour)!

Objects in a state of free fall or orbit are said to be weightless. The object's mass is the same, but it would register "0" on a scale. Weight varies depending on whether you are on Earth, the moon or in orbit. But your mass stays the same, unless you go on a diet!

NASA uses a variety of facilities to create microgravity conditions. The most famous way is by aircraft flying in parabolic arcs to create microgravity for tests and simulations that last 20-25 seconds. NASA's Johnson Space Center, for example, operates a C-9 Low-G Flight Research aircraft also known as the "Vomit Comet." It make several trips each year to NASA Glenn in support of ground-based microgravity research. It's predecessor, a KC-135 aircraft, was used to shoot the weightless scenes in the movie Apollo 13.

The facilities most likely to be misconstrued as "anti-gravity chambers" are NASA's drop towers. Specifically, NASA Glenn has the Zero Gravity Research Facility. It is a large shaft some 500 feet deep that allows test packages to free fall in a vacuum for just over 5 seconds. In this state of free fall, weightlessness (at or near microgravity) can be obtained. NASA Glenn also has a 2.2 second drop tower.

You may have experienced weightlessness yourself without realizing it. Many amusement park rides create brief periods of free fall. Some rides that operate vertically without any applied forces are actually classified as free fall rides. Most roller coasters have a set of parabolic (rolling) hills that also create brief periods of weightlessness. For less adventurous people, a car ride on the rolling hills of a country road or jumping on a trampoline also create brief experiences of weightlessness.

Źródło: NASA

Physics up above
Oct 1, 2007 6 comments

Once the stuff of science fiction, the International Space Station (ISS) offers a unique test-bed for physics in microgravity conditions. Moreover, describes Bruce Dorminey, experiments carried out on the ISS are paving the way for manned missions to Mars and beyond

Exponentially over budget, plagued by technical glitches and some seven years behind schedule, critics have always found the International Space Station (ISS) to be an easy target. Since NASA first began discussing the station's forerunner some 25 years ago, many astrophysicists and planetary scientists have viewed the ISS as an orbiting "white elephant" siphoning funds from more scientifically adventurous space missions.


Physics up aboveBut that would be to ignore the importance of having a permanently manned space station. While the ISS's interlocking modules, external trusses and solar arrays hardly resemble Arthur C Clarke's majestic rotating wheel in 2001: A Space Odyssey, the station is a product of humankind's quest for both a better life here on Earth and an innate sense of wanderlust. Born a quarter of a century after the Soviet Union launched Sputnik 1, the ISS grew out of an amalgam of designs from previously planned but unexecuted space stations. These include the US Space Station Freedom, Russia's Mir-2 and the stand-alone Columbus research module of the European Space Agency (ESA).

Today, as a joint project of the US, Russian, European, Japanese and Canadian space agencies, the ISS orbits at an altitude of between 370–460 km in the same direction as Earth's rotation. It provides a unique environment in which to study nature in low gravity — from the flow of fluids to the growth of crystal. Moreover, the ISS is proving to be a "research springboard" from which humankind can launch itself further out into the solar system. That is, if more down-to-earth factors such as money and international politics do not get in the way.

A political science
From the outset, critics of US space policy singled out the ISS as a foray into post-Cold War politics, rather than truly an international scientific undertaking. As planetary scientist Wendell Mendell at NASA's Johnson Space Center in Houston explains, "The NASA space programme is a technically driven enterprise intended to explore the unknown. But because it is part of the US government, it is also a political entity. Except for the fact that NASA wanted to build one, in my mind the space station was not well thought out. It was a committee-consensus process, so over the years there were a lot of studies that ended up getting scrapped."


Voyage of explorationOnce the ISS reaches the "assembly complete" stage by 2010 — which was originally scheduled for 2003 — a permanent crew of six will enjoy a pressurized volume of 935 m3 during six-month-long stays. That is about four times larger than the Russian Mir space station, which was manned continuously for almost 10 years before being forced to crash into the atmosphere in 2001, and some five times the size of NASA's 1970s-era Skylab. Unofficially, NASA's expenditure on the ISS is $100bn and counting — spiking through its years of planning and construction. Even so, ISS funding is assured until 2016, and it is likely that the station will operate until at least 2020.

In late 1998 Russia delivered the first segment of the ISS to low Earth orbit, and for a while the assembly appeared to be running on schedule. But with the loss in 2003 of the Space Shuttle Columbia and its crew of seven, the US Congress argued that if astronauts were willing to risk their lives for spaceflight, then NASA needed to make sure that the risk was commensurate with the exploratory and scientific gain. While the ISS might have had a noble purpose, was it really pushing the bounds of exploration in the tradition of, say, the Apollo programme that took us to the Moon nearly 40 years ago?

Even though the aerospace industry seemed excited about the ISS, many manned-spaceflight enthusiasts — ranging from researchers within the space agencies themselves to space buffs among the general public — viewed it as a distraction from more scientifically daring missions. Thus, if the ISS itself was not really pushing the boundaries, then its international partners had two choices: either abandon it altogether; or persevere and use it as jumping-off point for research on how to achieve long-term manned lunar and interplanetary missions. Fortunately they chose the latter option.

High dining
The ISS can tell us a lot about manned-spaceflight operations but, as Mendell points out, the devil is in the details. "Nowadays there is a lot of talk about the problems of garbage and stowage because no-one had thought about those before," he says. "The whole idea of how humans perform in isolated conditions in space for long durations is an important element of study in the ISS."


Weightless workoutsA case in point: after the ISS astronauts have dined on some of their favourite in-orbit offerings — which include shrimp cocktail, chicken fajitas and barbecue-beef brisket all washed down with lemonade — ground control requires that they spend at least 1.5 hours doing resistive exercise. As well as keeping the astronauts' heart muscles functioning optimally, the workout counters the bone loss that humans suffer in microgravity conditions (i.e. a state where the force of gravity is almost undetectable and which is practically the same as weightlessness). In such a low-gravity environment, astronauts can lose up to 2% of their bone structure per month. No-one knows exactly why this happens, but it is thought that a lack of gravitational stress on the skeletal structure somehow slows production of bonebuilding osteoblast cells.

If manned trips to Mars are to be feasible, then space biologists are going to have to solve some very basic problems associated with long-term weightlessness. Thus, during their regular five days per week work schedule, crew members on the ISS spend much of their time helping ground-based investigators carry out hundreds of microgravity experiments.

About 200 experiments have already been carried out on the space station or are still in progress, and at least 500 more are planned over the next five years. They range from Earth observations to proving the worth of technologies for industry, including many that study the effect of microgravity on animal, plant and human biology. Thus far, these experiments have been carried out in the Russian service modules and the US research lab Destiny. However, the Space Shuttle is scheduled to deploy ESA's Columbus laboratory in December of this year and the Japanese Kibo research module in April 2008. Furthermore, the Russians hope to develop and deploy a research module perhaps as early as 2011.

Each ISS partner is responsible for choosing (and funding) its own experiments, which usually begins with some sort of peer-review process to weigh up the merits of individual scientific proposals. It can take anywhere from six months to eight years before these proposals are finally implemented in Earth orbit. While most of the experiments do not require much involvement from astronauts, the crew members often have to start and stop experiments as well as to document results using digital imagery and video for later ground-based analysis. But given that many of the astronauts already have PhDs in a science subject, they are usually very comfortable with the rigours of experimental investigation.

Fuelled by experiment
Recently, much of the focus of ISS experiments has been to refine technologies that will help humankind explore beyond the Moon to Mars, such as those that manage spacecraft fuels. "Right after Sputnik, it dawned on NASA that when gravity goes, liquid fuels are also going to do different things," says Mark Weislogel, a mechanical engineer at Portland State University in Oregon. "The Apollo engineers implemented their designs without the benefit of long-duration microgravity tests. They made a series of good decisions, but they had a measure of luck on their side. With more low-gravity experience, however, we can improve the reliability of systems and reduce the overall mass of a given spacecraft."

Understanding how fluids behave in the absence of gravity is vital when managing spacecraft fuel tanks. But it is also important for life-support systems, liquidwaste disposal, water processing, thermal cooling and potentially even space-based turbine-powered electrical generators. In 2004 Weislogel was the principal investigator on a series of capillary-flow experiments on the ISS, in which he and his co-workers investigated how capillary surface-tension forces drive fluids both in space and on the ground. To study capillary forces in space, ISS astronauts used digitized video to record the movements of silicone oil contained in six 2 kg test vessels. The data are currently being analysed by researchers back on Earth.


Hands off"Suppose you've just released one of your rocket's upper stages and now you're adrift in low gravity," says Weislogel. "It's time to fire the next rocket, but if the tank isn't full, you've got to know where that liquid is. If the engine fires and the liquid isn't over the exit, then you could have a problem." In other words, if microgravity changes the location of fuel in the tank, which in some spacecraft designs has to be mixed in precise ratios from two separate fuel components, the engines may misfire and the fuel tanks could even be damaged. Such scenarios could cause a spacecraft to miss its target, with potentially disastrous consequences.

Fuel tanks tend to be spheroidal in order to make them as strong as possible. But even with the best current designs, low gravity can play havoc when it comes to positioning fuel within a tank. To get round the problem, designers frequently use complicated propellantmanagement devices or baffles to wick the fuel into its optimal position, which is usually near a fuel pump. However, if an Apollo-era device failed, the engine might be knocked out altogether — possibly interfering with the mission's ability to manoeuvre back safely to Earth. Weislogel and co-workers' capillary-flow experiments could reduce such risks. For instance, if the primary fuel system fails, better use of capillary forces could ensure that at least some of the spacecraft's cooling or other systems might still function, even if at a reduced level.

If faulty fuel pumps do not end a mission altogether, there is always the ongoing threat to astronauts from solar flares made up of very energetic protons or of heavy-ion background radiation from galactic cosmic rays (GCRs). In particular, the highly ionizing nature of GCRs can cause proteins in human cells to fragment, which increases the chances of tissue damage and tumours. While the Earth's magnetic field protects ISS crews from much of the Sun's activity, this will not be the case for manned interplanetary missions.

Frank Cucinotta, a radiation biologist and chief scientist for NASA's Radiation Research Program at the Johnson Space Center, says that we have come a long way in our understanding of radiation risks since the days of Yuri Gagarin, who in 1961 became the first man in space. "We now understand how radiation traverses through the materials [both of the spacecraft itself and the astronauts' attire] and tissue," he says. "By studying the damage mechanism, we should be able to develop biological countermeasures such as antioxidants, pharmaceuticals and gene therapy."

The ISS experiment Matroshka-2 (MTR-2), which follows on from an earlier experiment called Matroshka-1, was designed to track radiation fluxes both inside and outside the space station. MTR-2 uses a simulated human torso to mimic human flesh and internal organs. This "phantom" is embedded with dosimeters to measure incoming radiation fluxes, which can then be compared with the latest space-radiation models to better estimate the real risk to humans.


Heavenly bodyMTR-2's principal investigator Guenther Reitz, who heads the department of radiation biology at the German Aerospace Center in Cologne, says fluxes of cosmic-ray exposure outside the ISS have been "overestimated" in the past. He and his colleagues, who are currently working on a paper summarizing their findings for Nature, are encouraged by their initial results. While all humans have different sensitivities to radiation, Reitz says there may be ways, however futuristic, to capitalize on radiation-resistant genetic traits to help make astronauts less susceptible to ambient radiation in space. He says that cosmic rays are a high risk, but they will not stop humans from making interstellar trips beyond our solar system's heliopause.

Breaking the second law
Although the ISS has been a boon for research into the biological impact of life in low Earth orbit, the microgravity conditions on board the station have also provided an important niche for fluids and materials research. One such experiment explores one of the most basic tenets of high-school physics: the second law of thermodynamics, which states that entropy (a measure of disorder) always increases when a system changes from one state to another.

When a crystal forms in microgravity, the individual particles in a system have more freedom to rattle about than they would on the ground. Thus, in space an ordered structure can, somewhat perversely, arise from a higher state of entropy. "Take colloids [microparticles suspended in liquid] into space," says William Meyer, a staff scientist at the National Center for Fluids and Combustion at NASA's Glenn Research Center in Cleveland, "and you automatically take away the sedimentation and jamming effect of gravity."

This can have striking consequences. As principal investigator for the Express Physics of Colloids in Space experiment, in 2004 physicist David Weitz of Harvard University and his colleagues used colloidal engineering to study the microgravity dynamics of polymethyl methacrylate — a particle form of Plexiglass — suspended in an organic solvent. They found that more ordered and larger liquid-crystal-type structures can form on the ISS than on Earth because particles can remain suspended indefinitely in microgravity. This, in turn, leads to crystals that can diffract light more effectively, possibly leading to "perfect mirrors".

An obvious Earth-bound application of a perfect mirror is in fibre-optic telecommunications. For example, if a perfect-mirror coating could be developed, it could prevent signal loss in fibre-optic cables, particularly when such signals (i.e. light) are forced to make sharp turns. Currently, fibre-optic switching is performed electronically by first converting light into electricity, processing the signal and then converting it back into photons again. But according to Meyer, such devices — for example based on a "photonic-band-gap mirror" — would allow the same amount of light to handle a lot more information, thus potentially making fibre-optic communications much more efficient.


Suspension in spaceA less hi-tech, but perhaps more surprising, application of Weitz and co-workers' Plexiglass experiments might be found in detergent products. If detergent and even some food manufacturers had a better understanding of a given product's shelf life (which is often governed by its rate of gravitational collapse), such knowledge could potentially save them millions of dollars. For example, Weitz says that at least one major US detergent manufacturer would like to make its current fabric-softener formulation more polymer-rich so that it makes clothes feel softer. But a higher polymer count can sometimes translate into a less stable product. Thus, one goal of Weitz' ISS research is to simply determine how to avoid product instabilities, while extending a given product's shelf life.

But Weitz is also interested in making materials that can survive long periods in low gravity — materials that will be needed to assure successful interplanetary missions. "We mixed these colloidal particles with some polymer and saw behaviour analogous to that of oil and water in salad dressing," he says. "That helps us understand the stability of common everyday products and why things remain stable. If we're serious about going to Mars, we had better understand if things that normally remain stable on Earth also remain stable in space."

From detergents to Mars
Ironically, the long journey from Earth orbit to Mars may finally begin when the Space Shuttle is retired in 2010. It is due to be replaced by NASA's Crew Exploration Vehicle (CEV), which is now scheduled for a 2014 launch via NASA's planned Ares I rocket. The CEV (see over) will be able to ferry a crew of six to the ISS and back. And both the CEV and ESA's Automated Transfer Vehicle (ATV) will be used to autonomously replenish station cargoes. Currently, Russia's unpiloted Progress spacecraft functions as an ISS resupply vehicle, while Japan is also planning a robotic resupply spacecraft — the H-II Transfer Vehicle (HTV) — for launch in 2009. Later, NASA also plans to use the CEV to take astronauts back to the Moon — a mission now projected for 2020 — with a mission to Mars within a few years.


Orbital ferryNASA's original Apollo schedule called for a lunar base by the mid- to late-1970s. Who would have predicted that 30 years hence, the US agency would be struggling to remount technology just to get back to the lunar surface? If the red planet remains NASA's real goal, however, the ISS will continue to pay intangible dividends simply in terms of learning more about the vagaries of long-duration spaceflight.

For example, astronauts on their way to Mars will need to be more autonomous and resourceful because ground controllers will not be able to monitor and supervise them in real time. "It will be more like communications at the South Pole in the age of the Telex," says Mendell. "The missions will still need back-room support, but we've got to figure out how to do it differently." The ISS is already helping long-term planners tackle such practical issues, but it is doing so from Earth orbit.

Half a century after the launch of Sputnik 1, what can we say of the ISS and of the future human occupation of space? Arthur C Clarke's iconic year 2001 has long since passed, without having delivered Stanley Kubrick's grand cinematic vision of ambitious interplanetary missions and routine trips to the lunar surface. Yet even if humanity stands guilty of squandering its past glories due to a sometimes-indolent space policy, we can be thankful that at least new chapters in the history of manned spaceflight continue to be written. We are now using the ISS to plan our next steps out into the unknown. With the Moon as a way station, first stop will be Mars. And for its role in teaching us how to get there and back, the ISS is proving to be serendipity indeed.

About the author
Bruce Dorminey is a science journalist based in the US and author of Distant Wanderers: The Search for Planets beyond the Solar System (Springer, New York)

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