DOCUMENT RESUME

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AUTHOR Bird, John TITLE The Upper ; Threshold of Space. INSTITUTION National Aeronautics and Space Administration, Washington, D.C. REPORT NO NASA-NP-105 PUB DATE 88 NOTE 40p.; Colored photographs and pages will not reproduce well. PUB TYPE Books (010) -- Reports - Descriptive (141)

EDRS PRICE MF01/PCO2 Plus Postage. DESCRIPTORS * Science; (Aerospace); *Science Materials; Scientific Personnel; *Scientific Research; Scientists; *; *Space Sciences

ABSTRACT This booklet contains illustrations of the upper atmosphere, describes some recent discoveries, and suggests future research questions. It contains many color photographs. Sections include: (1) "Where Does Space Begin?";(2) "Importance of the Upper Atmosphere" (including neutral atmosphere, ionized regions, and balloon and investigations);(3) ""; (4) ""; (5) "Recent Discoveries" (those made by manned and unmanned ); (6) "Future Research" (describing spacelab missions, tethered , the International Solar-Terrestrial Physics Program/Global Geospace Science Mission, and others); (7) "Unanswered Questions"; (8) "Conclusion"; and (9) "Sources" (listing general and technical materials). (YP)

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4 ,01 *V 41. 3 Table of 1 Where does space begin? Contents 3Importance of the upper atmosphere 3 Neutral atmosphere 3 5 6 Mesosphere 6 7 7 Weightlessness 8 Ionized regions 8 9 Magnetosphere 10 Balloon and investigations 13 Airglow 13 What is it? 13 Spacecraft observations 15 Aurora 15 What is it? 16 How does it occur? 19 Recent discoveries 19 Spacecraft glow 20 Spacelab 1 21 Unmanned spacecraft 23 Future research 23 Spacelab missions 23 Earth Observation Mission-1 23 Space Plasma Lab 25Tethered satellite 25 International Solar-Terrestrial Physics Program/ Global Geospace Science Mission 28Other future programs 28 Space Station 28 Lidar 28 Long Duration Exposure Facility 30 Upper Atmosphere Research Satellite 30 Earth Radiation Budget Experiment 33 Unanswered questions 33 Conclusion 34 Sources 35 Acknowledgments 35 Photo credits 35The author 4 44.Pv.

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11R , e are conscious of the weath- Even the thinnest part of our atmosphere Importance er, but largely unaware of the is important. Less than 0.1 percent ofour atmosphere above the . atmosphere (by mass) is above 50 kilome- of the upper However, what happens in ters (31 mi), yet it occupies a volume much this higher atmosphere affects the atmo- larger than Earth. The Sun's rays mustcross atmosphere sphere below the clouds. Indeed, at the bot- this region before reaching us. Further, the tom of the atmosphere, we see only the end upper atmosphere is important to radio result of diverse processes extending from communications. Earth's surface to interplanetary space. Rather than being isolated and indepen- dent, these regions interact and intercon- Neutral Atmosphere nect. They form a chain from the surface of Earththrough the atmosphere and our Just where does the lower atmosphere end solar-terrestrial environmentto the Sun. and the upper atmosphere begin? For the Ultimately, all disturbances in this environ- human body, the upper atmosphere begins ment originate inside the Sun. These distur- a few kilometers above sea level; for a bances spread through the chain via solar spacecraft it could be considered to begin wind and radiation to influence our weath- at about 160 kilometers (99 mi). Without a er, our climate, and even our communica- generally accepted to mark it, the tions. More importantly, the processes in upper atmosphere can best be understood this chain are finely tuned to a delicately by starting on the ground and moving balanced equilibrium compatible with life upward to examine it, layer by layer. Our on Earth. atmosphere is considered to be composed All regions of the atmosphere interact to of layers. We distinguish these layers by provide conditions essential to life and to temperature and by composition. Both protect life in many ways. The atmosphere methods are shown in the illustration on provides life's most fundamental needs for page 2. In the temperature classification survival: pressure, proper temperature, and system, each layer is characterized by its oxygen. Without them there would be no unique temperature variation, or gradient. life on Earth. Without the atmosphere,one Where do the layer names come from? side of our planet would be frozen; the Troposphere is from the Greek word tro- other would be cooked by solar radiation. pos meaning to turn, implying that this Fortunately, the atmosphere transmits just region is turning and creating weather as the right amount of sunlight and contains we know it. Stratosphere comes from the just the right mixture of oxygen, nitrogen, Latin word stratum, meaning layer. and carbon dioxide to sustain life. Mesosphere comes from the Greek word We are inescapably surrounded by the mesos, meaning middle. Tl:ermosphere atmosphere and its influences. Besides ful- comes from the Greek word therme, mean- filling our basic needs, how does theatmo- ing heat. Exosphere means external to the sphere influence us? It determines our cli- atmosphere. mate and weather, including hurricanes, flash floods, tornadoes, and . It Troposphere also influences the flow of pollution, such In the lowest layer, or troposphere, the tem- as acid rain. Variations in weather may perature decreases the higher you go. You Earth as seen from a even influence our moods. may have noticed this if you have ever balloon at 37 km. Most of the atmosphere is been on a mountain. Some mountains below. remain snow-capped all year because of their elevation. The troposphere has many other impor- tant characteristics, including weight and pressure, that are essential for life. Although we are usually oblivious to the air that surrounds us, air exerts a pressure of about 101,000 pascals (14.7 psi). And 3 Concorde air has weight. In fact, a refrigerator con- We may acclimatize or adapt to the thin- tains roughly .45 kilograms (one pound) of ner air, but this involves living at succes- air. Why don't we feel the weight of the sively higher over a period of air? We do not feel the weight because we weeks. It is possible to live about 4.2 kilo- are surrounded by it, just as we do not feel meters (2.6 mi) as do some people in Tibet; the weight of the water in a swimming pool however, at this altitude, we are above vir- when we are in it. If we were not in the air tually all plant and animal life. Our bodies or the water, we could easily notice its are physiologically incompatible with this weight. How? Could you carry a swim- elevation. Without acclimatization or sup- ming pool? No, it has too much weight. plementary oxygen, it is hard to breathe, Similarly, if you were in a huge vacuum and night vision deteriorates. At 4.2 kilo- chamber you would find that a room-size meters (2.6 mi) these effects are immedi- box of air would be heavy. ately apparent, but the threshold level may Other basic conditions for lifeproper be as low as 1.6 kilometers (1 mi) for temperature and oxygenare also found in someone accustomed to sea level. the troposphere, but only near the surface. To climb higher into the sky, let's take a What happens as we go higher? commercial jet. We soon pass the height of From the iop of a mountain at roughly 5 the summit of Mt. Everest at 9 kilometers kilometers (3.1 mi), we can see clouds (5.6 mi) and continue up to a cruising alti- below. Small private usually fly tude of 10.6 kilometers (6.6 mi). From here below this altitude because their rate of we see a few thin wispy clouds around us climb reduces as the air becomes thinner. and puffy white cumulus clouds far below. At this altitude, whether we are in an If the aircraft were not pressurized and unpressurized aircraft or on a mountain, we equipped with its own oxygen supply, we need supplementary oxygen unless we would last a few minutes at most. Winds at return to lower altitudes within a few min- this height are strong, frequently exceeding utes. 161 kilometers (100 mi) per hour. Temperatures are also extreme: 50° C (-58°F) is typical. 4 tS Exosphere The Atmosphere Day Night 300_ _300 iiiiiiiiiiiiSolar radiation F2 peak 200_ y X UV 1R Radio _200 .1A E Region 100 E Thermosphere _100 90 -0 90 80_ Ionosphere _ 80 70 Mesosphere _ 70 60_ _ 60 50_ _ 50 40 _ 40 Stratosphere 30 _ 30 20 Troposphere _ 20 10_, _10 0 0 -90 106 105 104 103 102 Temperature, °C Electron density cm-3

At IIkilometers (6.8 mi), we reach the tern (12.4mi), we are above 90 percent of top of the troposphere. This dividing line is the atmosphere and the sky becomes a dark called the . The exact altitudes violet merging into black. At this height we delimiting the layers of the atmosphere begin to notice the curve of Earth. At 30 change with local air temperature and kilometers (18.6 mi), the extremely low depend on variables such as time of year. pressure means almost no atmosphere is place on Earth, and local weather condi- available to absorb the heat generated by tions. Although there is no precise distinc- our bodies. We are warm when in the sun- tion, the division between the upper and light, but cold when in the shade of the bal- lower atmosphere is often considered to be loon. Our balloon will go no higher near the top of the troposphere. Generally, because the air above is so thin, the amount meteorology is the realm of science that of helium in the balloon is now heavier studies events below this altitude. than the amount of air it is displacing. So is the corresponding science we let out some of the helium and float that studies events of the neutral atmo- safely back to Earth. sphere above this height. The delicate balance of nature continues to be apparent even in the stratosphere. Stratosphere Ozone is an important chemical that exists To venture into the stratosphere, we need a throughout the stratosphere. It absorbs Concorde supersonic airliner, a military jet, harmful ultraviolet radiation from the Sun. a rocket, or a helium balloon. Continuing Even a small dose of ultraviolet radiation up with a helium balloon, we notice that causes sunburn, but in greater doses it the temperature is near 50°C, and all causes mutations and skin cancer. The clouds are now below. The air appears clear maximum concentration of ozone is at 25 because there is no dust or water vapor. We kilometers (15.5 mi) but even there it is a could survive in the stratosphere up to 12.8 minor constituent, or component, of the kilometers (8 mi) by breathing pure oxy- gen.Butbecause we are going higher, we will need to wear spacesuits. At 20 kilome- 5 Lights in our sky

Att'mic oxygen Mdkicular nitogen 300km Airglow

High altitude aurora Atomic oxygen

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"Vs Visable airglow layer 100km Hydroxyl emission layer tasium aurora 50km -Molecular oxygen

atmosphere. Ozone is an example of a Mesosphere trace constituent having an important Far above the reach of aircsaft, and below influence on our lives. Some trace compo- the reach of spacecraft. lies the :meso- nents in the stratosphere can be active and sphere, with its steadily declining tempera- important to the chemical balance. ture making it become the coldest part of Certain ac,:vities threaten to deplete the the atmosphere. A mysterious no-man's protective . Chloroflurocarbons land, this region can be reached by only the for example. can rise to the stratosphere largest helium balloons. where they decompose to produce chlo- The mesosphere is above 99 percent of rine that consumes the ozone. It IA as once the atmosphere and extends from 50 to 80 thought that supersonic aircraft produced kilometers (30 to 5() mi). Even at them. alti- chemicals that would destroy ozone, we tudes, the composition of the air is virtually now know that nitrogen oxides from these the same as at sea level. However, the aircraft actually produce ozone..,us, not minor components are different. In the only can the total amount of ozone be mesosphere, for example. atomic oxygen is expected to change, but also the vertical created in minor amounts by the interaction distribution may change. We do not of ultraviolet light from the Sun on molec- know what the consequences may he. ular oxygen. Clearly, we must learn more about the stratosphere. Thermosphere The next region is the thermosphere. It extends from 80 to 300 kilometers (50 to 180 mi) and is characterized by increasing temperature. As implied by its name, the thermosphere is hot. In fact, it is as hot as 500°C (932°F) to 2000°C (3632°F) depending on the level of activity on the Sun's surface. In and above the thermo- sphere, the composition of the atmosphere is different from the mix of 78 percent 6 iU nitrogen. 21 percent oxygen below. Above wear spacesuits if we open a window. 100 kilometers (62.5 mi), the composition Except for the view, the office is typical. is not uniform, so the region between 100 Looking outside, we see a black sky even and 300 kilometers (60 to 180 mi) is called though it is noon and sunlight fills the the heterosphere, and tne atmosphere office. We are not weightless. We do not below is called the homosphere. The con- even feel lighter. stituents are well mixed in the homosphere. Suddenly, a bright star appears against Minimum orbital altitudethe lowest the black sky. It is a 50 kilo- altitude at which a spacecraft can orbit meters (30 mi) away and approaching at 8 Earth for a reasonable timeis about 150 kilometers (5 mi) per second. A few sec- kilometers (93.2 mi). However, it is possi- onds later it flies by within a kilometer of ble to have an elliptical orbit where the us. We see it clearly but only for a fraction minimum altitude, or perigee, is much of a second, just long enough to see two lower. For example, the Space Shuttle is spacesuited astronauts floating around in it initially sent into orbit at 100 kilometers Why are they weightless if we are not? (62.5 mi), where the main engines burn They are weightless because they are in out. This is twice the maximum balloon free fall. Any object in free fall is weight- altitude. Even though a spacecraft can orbit less unless the object is acted upon by in the thermosphere, there is a slight drag some outside force, such as wind. You are force because of the thin atmosphere. This weightless when you are jumping off a div- causes the spacecraft to slow down gradu- ing hoard. ally until it eventually reenters the lower But how can the astronauts he falling if atmosphere and burns up. But, as orbital they are travelling horizontally? The Space altitude increases, drag decreases, and the Shuttle appears to be flying horizontally spacecraft may stay in orbit longer. because it flies parallel to Earth's surface, but gravity is still pulling it down. The Exosphere resulting path follows the curve of Earth. The exosphere extends from 300 kilome- Does gravity reduce with height? Yes. ters (180 mi) to the undefined region where But even at the top of our 250-kilometer the atmosphere gradually merges with (150-mi) building, gravity is reduced interplanetary gases. Hydrogen and helium only slightly. We have to go hundreds of are the main gases of the exosphere, but the kilometers higher before our weight drops density of these gases is low. significantly.

Weightlessness Now that we are at orbital altitudes, are we above gravity? How high does gravity go? Earth's gravity is cut in half at about 1600 kilometers (960 mi). but gravity exists throughout the universe. To explore this further, imagine an office build;ng 250 kilometers (150 mi) tall. In an office on the top floor we have the same view of Earth that astronauts have from the Shuttle. Inside the pressurized building we are com- fortable, but we would of course need to

U Ionized regions sphere. allow ing communications around the world. Further. all satellite communica- Ionosphere tions must transmit radio waves through Rather than characterizing !aye's of thc thc ionosphere. where complex interactions atmosphere by temperature variations. we OCCUL can identify the series of layers. or regions. YOU may ha% e noticed that radio recep- by the presence and density of electrically tion from stations far away improces at charged particles. night. This is because the D region, which Where do these charged particles conic absorbs radio waves. disappears or k great- from? Atoms contain oppositely charged ly reduced at night tas shown in the illus- particles called protons and electrons. If an tration on page 6). What causes this.) Solar electron. which is negati% el) charged. radiation during the day causes atoms to lea% es an atom. the result is a free electron. separate into ions and electrons in a process The remaining. positkel) charged ..tom is called . At night. the ions tend to called an ion. The density of the free elec recombine with electrons to form neutral irons is referred to as electron density. The particles. causing the D-region ionosphere electron density. or number of electrons in to disappear. But other mechanisms main- a gi% en %olurn: such as a cubic centimeter. tain some ionization at night. is the same as the ion density. Electron den Solar flares can cause radio blackouts. sit) in the atmosphere increases by height. How Radiation from a Bare enhances ion- from nearly zero at 50 kilometels k30 nut ization and therefore enhances electron to a peak at 180 to 300 kilometers k 110 tk, do.sity in the D region on the daylight side 180 mik then it decreases. of Earth. This increase in electron density This region of ions. called the ion° corresponds to an ilk rease in absorption of sphere. is shown in the illustrakion on Fagc radio w a% es in the D region. Since radio 6. Note that the ionosphere is di% idedinto w a% es must cross this legion before the) subregions called C. D. E. and F ,onc- can be reflected to their destination, the) sponding to different electron density %art are absorbed along their path. ations. The term -region- is used ratite' Above 1000 kilometers (621 mm), the than "la) er" because the altitudes of the ionosphere merges into the heliosphere, region% %ary from one location to the ..here helium is found. The hellosphereun The ionosphere. which is composed of tun; merges into the protonsphere at an alti- charged particles. is imbedded within the tude of a few thousand kilometers where thermosphere. %% Nell is composed of neu helium anti hydrogen atoms are dominant. tral particles. As a result. all of these parts Ionized particles are mixed with the much ties are mixed together. lower-density neutral particles of the exo- The ionosphere is important because ions sphere. So. like the exosphere. the iono- and electrons affect radio comes. For exam- sphere gradually merges with interplane- ple. radio waves are reflected by the iono- tary gases. Above the ionosphere most particles are Space Shuttle seen ionized and are therefbre in the plasma from temporarily free- state. Plasma is neither gs, liquid, nor flying Shuttle satellite. solid: it is the fourth state of matter. On an astronomical scale. plasma is common. In fact. over 99 percent by volume of the uni- verse is plasma. For example. the Sun is made of plasma. Fluorescent light contains plasma. and fire is plasma.

8 2 Magnetosphere Deep inside Earth, flows of molten metal sustain a huge magnetic field around Earth. The shape of the magnetic field lines would be similar to those of a simple bar magnet, however, the solar wind causes a distortion. Facing the Sun, the magnetic field is com- pressed by the supersonic solar wind to form a shock w al, e. As shown in the illus- tration top right, the cross-section of this shock w aNe has the shape of a bow and is called a bow shock. On the other side of Earth, the charged particle enl, ironment contained by Earth's magnetic field (the magnetosphere) stretches hundreds of thou- sands of kilometers in a long magnetotail. At its base, the magnetosphere merges into the ionosphere. All particles in the outer magnetosphere are electronically charged while only a fraction is charged in the iono- sphere. The near-Earth space em ironment, including the magnetosphere, the iono- sphere, and the upper atmosphere, is known as geospace. Together with the solar wind and the Sun, the entire system is known as the solar-terrestrial environment. As shown in the illustration to the right, the magnetosphere includes a complex sys- tem of interacting electric and magnetic fields, electric currents, and particle flows. In 1958 doughnut-shaped radiation belts were discovered using satellite Explorer I. These regions are known as the Van Allen radiation belts. Two beltsthe inner and outer radiation beltscontain the most energetic particles of a larger doughnut- shaped region called the plasmasphere. High-powered electrical currents in the magnetosphere are connected through the ionosphere. The aurora (described in detail Top: The magneto- later in this book) gives us visual clues to sphere of Earth is processes occurring in the magnetosphere. shaped by the solar wind.

Above: Regions of the magnetosphere.

9 Photos: Balloon investigations the interstellar environment. If we could see through the dust clouds that block our 1 Helium balloon during Many investigations of the atmosphere iew inisible light. we uould obsene inflation. Two helium have been conducted w ith helium balloons otherwise unknowable portions of our input tubes speed infla- sent into the stratosphere. Investigations own galaxy. tion during this critical utilize the balloon's unique capability to fly The helium balloons required for these phase when the thin at altitudes far above the reach of any air- flights are not at all like regular hot-air plastic is exposed craft, although still far below the reach of balloons. They are hundreds of meters high to wind. any spacecraft. and made from plastic thinner than house- In addition to in-situ stratosphere experi- hold garbage bags. Upon launch, a small 2 Balloon after inflation ments, balloon payloads often carry tele- shown with parachute amount of helium is added to the top of the lying on the ground, scopes and cosmic-ray detectors aloft to balloon. The bottom of the balloon is and the payload on take advantage of the clear sky at these alti- attached t-.) the top of a parachute. The "Tiny Tim." tudes. As shown in the illustration of the parachute is attached to the payload, which sky, only a small part of the electromag- in turn is on a truck. As the balloon rises, it 3 Just after a balloon is netic spectrum reaches the ground. picks up its on deflated portion, then the released, it begins to Harmful radiation such as rays and paraLhute, and finally the payload. pick up the parachute X-rays, as well as most infrared light, is As the balloon rises, the atmospheric and payload. absorbed gradually before it reaches the pressure surrounding it degreases, allowing surface. However, at balloon altitudes the balloon to expand. When it reaches its 4Balloon during ascent, enough radiation is present and transmitted peak altitude, it is fully inflated to a nearly after it is free. The in these IA av elengths to allow gamma ray, spheriLal shape. To bring the payload back parachute and payload X-ray, and infrared photographs of the zos- down, an explosive bolt is fired. This sepa- hang-below. mos. Therefore, with balloon-borne tele- rates the payload and the parachute from scopes, we may literally study the Sun, our the balloon. The balloon is destroyed, and 5 Recovery of a scientific galaxy, and other galaxies in a different the payload floats gently back to the balloon payload. light. ground. For example, infrared light is invisible to Balloons, of course, are not the only way the human eye, but telescopes can pick it to study the upper atmosphere. Other meth- up. This is fortunate because some astro- ods utilize ground-based stations, aircraft, nomical objects give off most of their ener- rockets, satellites, and manned spacecraft. gy as infrared light. However, because this light is absorbed by water in Earth's atmo- sphere, telescopes on the ground can detect little of it. Balloon-borne telescopes fly above most of the water vapor in the atmosphere, and are more sensitive to infrared light. They have another advantage over ground-based telescopes, because the atmosphere itself emits infrared light. Flying high above much of Earth's atmosphere, balloon-borne telescopes have a mach clearer view of the sky. Infrared light can, however, pass through Ground-based instruments include scatter interstellar dust clouds, giv ing an unob- radar facilities that monitor the temperature structed view of the universe not possible and winds in the thermosphere. with visible light. This occurs because the Before we look at satellite and spacecraft infrared wavelength is greater than the investigations, lees look at the structure diameter of the dust particles. The interstel- of the atmosphere beyond ballooning lar particles, less than one micron in diame- altitudes. ter, are about the size of smoke particles. They originate in stars and are ejected into 10 r -\

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-r-P Top: Aurora and airglow from Shuttle mission.

Above: Edge-on view of the airglow layer, showing the dim red aurora above and the clouds below.

Right.Spectacular view of the green-blue southern aurora and the red airglow layer seen from Skylab.

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By 1873 the northern auroral zone was Aurora mapped and was found to be a ring around the north magnetic pole. Spectral measure- ments, that is, measurements of the compo- nent colors, were initially made in the early 1900s. An international campaign during 1957-58 was organized to study the aurora. This led to our current general understand- ing of the aurora, but there are still many unanswered questions. Although auroral displays most frequent- ly occur in northern latitudes of 65 to 70 degrees, they sometimes occur 1.., lower lat- What is it? itudes. For example, a famous display was seen in India and Egypt during 1872. Very Some of nature's most beautiful displays low-latitude are usually red. In are seen in the sky: rainbows, sunsets, and 1938 such a display was chased by a fire stars. Another is the auroraa spectacular brigade sent out to extinguish a fire at light show seen in the night skies at north- Windsor Castle in London. ern latitudes. Colorful bands of light flicker The aurora appears in many different and dance across the sky. People living in forms: arcs with rays, bands, pulsating sur- Alaska are lucky because they can see the faces, and draperies. One of the most com- aurora on almost any clear night. But in mon form is a blue-green flickering drap- summer the nights up north are short, or ery moving across the northern sky. there is no night at all, so the best time to Narrow, vertical, luminous columns with see the aurora is in the winter. Further rapid fluctuations in intensity are common. south, the aurora appears less frequently. The lower border is often intense and People have always been curious about sometimes red. Typically, a display lasts a the aurora, citing it in folklore and mythol- few minutes and occurs a few times per ogy throughout the ages. Scientific studies night. Strangely enough, there have been of the aurora also date a long way back, reliable reports of people hearing the auro- specifically to 1621 and a French scientist ra, although there is yet no scientific expla- named Gassendi. He documented his nation or confirmation. observations in a pLysics book in which he Photos: referred to what he saw as the aurora borealis, meaning northern dawn. The 1 Red auroral rays. aurora is popularly known as northern 2 Mutiple auroral bands. lights. In 1773 the corresponding phenomenon 3 Red corona. in the Southern Hemisphere, aurora aus- trails (southern dawn), was first reported 4 A spectacular view of by Captain Cook. He observed it when he the brown airglow sailed the Indian Ocean. layer and aurora. The high altitude is red. This photo was taken between Antarctica and Australia on Shuttle flight 51-B, SpacJlab 3. 4

15 , 1 8 , Left: Processes involved in a magnetic storm.

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How does it occur? directing the electric currents to the iono- sphere in the polar regions. The electrical To understand the aurora, we must start power is scattered as it is converted to inside the Sun. There, a complex interac- lightthe diffuse aurora. tion of radiation and connection maintains Spectacular auroral displays are caused the gaseous region called the Sun's corona. by bursts of solar w ind particles originating At temperatures over a million degrees in magnetic storms on the Sun. These parti- Celsius, the corona continuously gibes off cles reach Earth directly from the Sun and particles collectively wiled the solar wind. from the far regions of the magnetosphere, When the solar w nd reaches Earth, itinter- especially the magnetotail that is oriented acts with Earth's magnetic field, causing away from the Sun. Earth's magnetic field electric currents that travel along the mag- guides and electric fields in space acceler- netic field lines. Much like a magnet, these ate particles toward the auroral regions. field lines focus dow n at the polar regions, The auroral regions are rings surrounding the north and south magnetic poles and Above: This bright red may be easily seen from space. Their light aurora is rare and is created by the interaction of solar wind occurs only during the particles with ions in Earth's atmosphere. Sun's most intense The colors are characteristic of the com- magnetic storms. ponents of the atmosphere and the altitude. Right: A solar flarethe The power created by a magnetic storm source of intense auro- hitting the ionosphere is about half ral displays. due to particles and about half due to electric currents.

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ecently, much attention has been surface of the Orbital Maneuvering System Recent focused on understanding the (OMS) pods. When theColunzbia thrusters upper atmosphere. One such con- were fired, the glow increased. When a sur- discoveries cern is over spacecraft glow. face was exposed to the direct flow of the Others include the results of Spacelab I and rarified atmosphere, the glow could be unmanned spacecraft experiments. seen. It was particularly evident over the surfaces of the tail and OMS pods. A fanlike glow was also observed Spacecraft glow extending from the tip of the tail to a dis- tance of a few meters. One method used to Since the discovery of a mysterious glow determine the thickness of the glowing over the Shuttle on STS-3 in early 1982, layer was to observe stars in the back- the phenomenon of spacecraft glow has ground while the orbiter was in a slow roll. been under investigation. Surfaces facing By knowing the roll rate and the time it the velocity vector (i.e., into the solar took for a star to disappear behind the wind) were found to be covered with a glow, scientists could calculate the thick- faintly glowing, t!iin orange layer. The ness of the glowing layer. Knowing the layer is visible to the naked eye during the thickness of the layer provides scientists night side of each orbit. with a clue to the cause of the glow. From This phenomenon is of great importance the thickness they can estimate the time because of its impact on future experiments required for the atomic molecular species in the cargo bay and on other satellites such to emit the light. The length of time as the . An example of a depends on what the emitting species is, problem created by spacecraft glow is that and thus the duration of each constituent instruments designed to observe faint stars color helps reveal the source composition. will have a more restricted field of view One species found was atomic oxygen; this since they will be unable to look over the is not surprising because the atmosphere at surfaces of the orbiter. those heights is mostly oxygen. A similar effect was found on the Further studies were conducted on STS-4 Atmosphere Explorer-C satellite. The glow by mission Commander T.K. Mattingly. was caused by an interaction of the thin The object was to find a color spectrum of atmosphere with the satellite, which was the emitted light. The glow was photo- moving at 8 kilometers (5 mi) per second. graphed through a grating device attached As the altitude increased, the effect to the camera. A grating acts like a prism, decreased, suggesting its dependence on splitting light into its constituent colors. If atmospheric density. the relative amount of each color is known, In March 1982 the STS-3 crew, Jack the composition of the material producing Lousma and Gordon Fullerton, took photos the light can be determined. Because the of the glow without realizing it. They pho- glow was faint, photos had to be taken at Firing of the Orbital tographed electron beams from the Vehicle night when the Moon was not visible. This Maneuvering System Charging and Potential experiment during occurred for only 12 minutes of each orbit (OMS) engines caused the night portion of an orbit. When the pho- and only during the early part of the mis- this bright glow at the tos were developed on the ground, the glow sion. Also, since the crew was busy, only a aft end of Space was seen emitting from a region 5 to 10 few photos were taken. Exposure times Shuttle Challenger on centimeters (2 to 4 in) thick just above the ranged from 50 to 400 seconds. On this STS-7. flight the glow was not as bright as observed on STS-3, which was thought to be due to the higher altitude of STS-4. Also, the vehicle orientations were differ- ent. The color of the light was found to be mostly red extending toward infrared.

19 23 Glow appears on the glowing. This experiment will be done tail and engine pod, again. and in the cargo bay of Although not totally understood, the the Shuttle. Earth's air- glow appears to be due to the impact of glow layer is in the high-altitude oxygen atoms with lower background. altitude oxygen molecules. It is not clear whether the oxygen itself is giving off the glow, or whether the oxygen reacts with the surface on impact, causing some other molecule to glow. If the latter is the case, the most likely molecule would be OH, or hydroxyl, which emits red light. However, On STS-5 an improved camera system a combination of processes may be the was used. Astronauts Joe Allen and Robert cause. So far, the mechanism has been nar- Overmyer photographed the glowing layer rowed to three possible chemical reactions of the atmosphere at an altitude of 100 involving OH, carbon monoxide, and kilometers (60 mi). This airglow intensity molecular nitrogen. was used to determine the absolute bright- Many further investigations are planned. ness of the vehicle glow. On this flight, Spectroscopic analysis will be made of the samples of different materials were put on glow on future flights. Scientists will con- the Remote Manipulator System (RMS) tinue working to determine the cause. The arm and the glow was found to be different full extent of the impact on future payloads for each material. A similar experiment will then be realized. was conducted on STS-8. On STS-9 (Spacelab I) the crew took further glow photography, using the same Spacelab 1 camera system as on STS-5. One of the pallet-mounted instruments, called the Spacelab I demonstrated the viability of Imaging Spectrometric Observatory (ISO) utilizing the Shuttle as a scientific labor- also looked for the glow, but the results arc atory for many disciplines, including still being analyzed. It is difficult to distin- atmospheric sciences. guish one source of light from another For example, th,2 ISO obtained dayglow because there are many sources that can spectra by looking both away from and cause the payload to glow. For example, toward Earth. Height profiles of nitric when the thrusters fire, their glow lights up oxide and other constituents were also the payload bay and enhances the vehicle obtained. ISO observations of the mysteri- glow. Thruster firings occur often, and the ous Shuttle glow suggested two possible resulting glow lasts a few seconds, so they mechanisms as the cause. One is surface are an independent problem. Other sources catalysis, in which molecules leave the sur- of light in the payload bay are faint but face and later radiate. The other mechanism show up on film. They include starlight and is plasma discharge, in which the atmo- reflections of the airglow. Even lightning sphere around the vehicle glows like the on the ground was found to light up the aurora from electron impact. cargo bay on STS-9. Recently discovered bands of ultraviolet Another Spacelab I experiment, called light 300 kilometers (180 mi) above Earth's the Far Ultraviolet Space Telescope surface have led to improvements to the (FAUST), ended up with fogged film. The FAUST to keep its film from fogging. glow phenomena may have been the cause. The Atmospheric Emissions Photometric From ground telescopes observing STS-9, Imaging (AEPI) experiment looked at mag- it appeared that the nose of the Shuttle was nesium ions that come from vaporizing meteors. The light from these ions was so strong that one of the scientist-astronauts thought the illumination was possibly due to "resonance scattering." But the Shuttle 20 24 was too far below the horizon for this to temperatures of the thermosphere and trace occur. AEPI and a few other Spacelab I constituents in the magnetosphere. These instruments will be renown on another satellites discovered that particles acceler- mission, called Earth Observation Mission- ate not only downward to the auroral ! (EOM-1). regions, but upward as well. Above 800 Another Spacelab experiment involved kilometers (480 mi) at high latitudes there photography of the recently discovered is a continual flow of hydrogen. helium. wave patterns in -like structures at 85 and oxygen ions, called the polar wind. kilometers (51 mi) altitude. These hydroxyl Using data from Dynamics Explorer-I. clouds are seen in the infrared region and nitrogen was discovered in the magneto- were photographed at night by the sphere. Scientists speculate that this Spacelab crew. In another experiment, the nitrogen comes from the ionosphere,con- astronauts observed light emission from firming the idea that Earth, in addition to hydrogen in the dayside aurora for the first the Sun, is a major source of ions in the time. magnetosphere. For the first time, the aurora was recently seen from space in the shape of a giant Unmanned spacecraft Greek lettertheta,and was found to occur regularly. Photographs of theta-auroras In ddition to the discoveries in the upper were taken in ultraviolet light by Dynamics atmosphere made using the Shuttle, many Explorer-2. important discoveries have been made by Ultraviolet images have been provided unmanned spacecraft. by the Air Force HILAT satellite and bya For example. two Dynamics Explorer Canadian instrument on the Swedish satellites have been monitoring winds and Vikingsatellite.

Dynamics Explorer discovers nitrogen in the A a 0 MIMMINIMAIMiL.--"'"------magnetosphere.

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21' Spacelab missions experiments. All involve the study of plas- Future ma (see Ionosphere section). Spacelab missions will be flown regularly To study the plasma surrounding Earth, research in support of various disciplines, including Space Plasma Lab-1 experiments will sup- those involving the upper atmosphere. port each other with coordinated measure- ments. They all will analyze the same phe- Earth-Observation Mission-1 nomena using different techniques. One The Earth Observation Mission-I (EOM-I) technique will transmit radio beams into will refly some Spacelab-I experiments. the upper atmospheric plasma and measure These include the ISO and AEPI experi- the reflected waves. It will be utilized by an ments that will observe airglow. experiment called Waves in Space Plasma Another Spacelab payload, the (WISP) and will transmit radio waves rang- Atmospheric Trace Molecule Spectroscopy ing from 300 hertz (300 cycles per second) experiment, will look at the Sun just above to 300 million hertz. Different frequencies Earth's horizon. Because the atmosphere will travel different distances into the atmo- will absorb some of the Sun's light, the sphere. By analyzing the reflected beam, remaining light that reaches the instrument the electron density at various altitudes will provide clues about the composition of may be determined. The antenna used for the atmosphere. this experiment will be about 300 meters (330 yards) long. Space Plasma Lab Two of the experiments will inject parti- Passive and active techniques will be used cle beams into space. In the Vehicle to probe Earth's environment from Space Charging and Potential (VCAP) experi- Plasma Laboratory, which will be flown ment, a pulsed electron gun will emit a every 18 months. The first flight of Space beam, and the returning current will be Plasma Lab originally was called Spacelab- measured. The beam causes the vehicle to 6, but was renamed. become electrically charged. This electrical Many details of the first flight have been charge on the surface of the Orbiter will be planned. It is scheduled for launch in the measured with respect to the surrounding early i 990s using the Shuttle. The mission plasma. will last seven days; the orbit will be at an In the second beam injection experiment, altitude of 300 kilometers (180 mi). The Space Experiments with Particle lab will be composed of two pallets and a short module where the astronauts will work. A pallet-only configuration is also Far left: Future stud- possible. These components will be carried ies of Earth's environ- in the cargo bay. This payload has a mass ment will rely heavily of 11,000 kilograms (12 tons) of which on the Shuttle. 3000 kilograms (3.3 tons) are experiments. In either case, payload specialists will be Left: Long Duration Exposure Facility part of the crew. Orientation of the Orbiter (LDEF) during deploy- will be such that the yaw axis is parallel to ment from Shuttle. the magnetic field lines of Earth; that is, the wings will be perpendicular to Earth's surface. Eleven experiments are planned in three categories: injection of radio waves and particle beams into the atmosphere; experi- ments deployed by the RMS, including a free-flying package; and optical sensing

23 27 Accelerators (SEPAC), some investq;ations Multiprobes (MMP) iv ill be deployed in IA ill stud} plasma phenomena in the 1. trini- various locations to measure plasma waves ty of the Orbiter and some will study it simultaneously. from far away. Vehicle charge neutraliza- Other Spacelab instruments will optically tion and beam plasma physics w ill be stud- observe the plasma phenomenon. One of ied close to the Orbiter. In another experi- these, the Wide Angle Michelson Doppler ment, neutral gas iv ill he released from the Imaging Interferometer (WAMDII), was car,bay and an de_ on beam injected developed in Canada. WAMDII is an imag- into it. The interaction iv ill create a glow ing device that iv ill map iv inds and temper- that another experiment iv ill observe. To atures as functions of height, latitude, and analyze the atmosphere down to 100 kilo- time of day. Particular attention will be meters (60 mi), the SEPAC Electron Beam paid to iv inds near auroral forms and near Accelerator will inject pulses to probe the airglow irregularities. The data will com- ionosphere. plement results from a Fabry-Perot interfer- Further inv estigations of the plasma ometer on the Dynamics Explorer satellite, environment surrounding the Orbiter will which have already been published. be done with experiments deployed on the Another imaging experiment is the Remote Manipulator System or its arm. Atmosphere Emissions Photometric One of these experiments is called Imaging (AEPI) experiment, which was Theoretical and Experimental Study of flown on Spacelab 1. It consists of a low Beam Plasma Physics (TEBPP). light-level television camera and a Photon Interactions of beams from other experi- Counting Array. These instruments are ments with the surrounding plasma will be mounted on a two-axis gimbal made from a analyzed with this instrument package, modified Apollo Telescope Mount Star including an energetic particle spectrome- Tracker from Skylab and thus can be ter, pulsed plasma probes, a sweeping plas- steered. The camera has a wide-angle and a ma iv ave receiver, an electron probe, a neu- telephoto lens that iv ill be used to observe tral particle density detector, and a pho- beams injected by other experiments and tometer system. To determine the density natural light sources such as aurora and and composition of ambient ions, the airglow. Energetic Ion Mass Spectrometer (EIMS) Another optical experiment is the includes eleven-channel electron multipli- Energetic Neutral Atom Precipitation ers, a retarding potential analyzer, and a (ENAP) experiment. It will utilize five magnetic analyzer. spectrometers to observe visible and ultra- The Recoverable Plasma Diagnostics violet emissions from a range of altitudes. Package (RPDP) will be an instrument Still another experiment that will examine package deployed by the RMS and set free. light emission at various heights is the It will take measurements as far as 100 Atmospheric Lyman Alpha Emissions kilometers (60 mi) from the Orbiter and (ALAE) experiment. Lyman alpha is an then be retrieved. Other operational modes ultraviolet spectral line, or color, emitted include use of RPDP as a tethered satellite by hydrogen. Examination of this light will or use only on the RMS. Instruments to be reveal the temperature of the hydrogen. included in the package include an ion Space Plasma Lab will be an evolution- mass spectrometer, a triaxial magnetome- ary system to be modified as required by ter, electric and magnetic field sensors, and scientific objectives, but the basic facility a composition analyzer. Nonrecoverable will remain the same. Therefore, the subsatellites called Magnetosphere turnaround time w ill be minimized to yield maximum scientific return, making it a valuable element of the Space Transportation System.

24 28 Tethered satellite A novel plan to explore the atmosphere below the Shuttle involves reeling a satel- lite down from the Shuttle. The satellite will be lowered on the end of a wire, or Tethered satellite dur- tether, up to 100 kilometers (60 mi) long, ing deployment from with payloads weighing up to 500 kilo- the Space Shuttle. grams (1100 lb), according to current pro- posals. Atmospheric composition, magnetic The first flight is planned for the early field variations, plasma flow interactions, 1990s, probably above 125 kilometers (75 aerodynamic measurements, and electrody- mi). Aerodynamic effects below this height namic effects are all of interest. are being considered in the design, but the Previous in-situ studies of this region behavior of such a system is still unknown. have been conducted only by rockets that Subsequent flights would occur about once continually change altitude. The difference a year. An early flight will use a magne- in gravity at the different heights of the tometer to map Earth's magnetic field. The Shuttle and the satellite will cause tension initial electrodynamic experiments will use in the tether. and the satellite on the end a I-meter (3.3-foot) diameter conducting sphere. will remain in a fixed position relative to the Orbiter. Therefore, it would be stable straight up or down from the spacecraft. International Solar-Terrestrial After the experiments are conipleted, the Physics Program/ satellite will be reeled back into the Orbiter Global Geospace Science at 10 meters (33 feet) per second or more. Mission To begin deployment, the satellite could be separated from the Orbiter on a 50-meter Over the next few decades, scientists study- (I65-foot) boom to provide a slight differ- ing the near Earth will ence in gravitational attraction. try to develop a comprehensive understand- Alternatively, it could be given a slight ing of its interactive regions. These regions push with springs. include the magnetosphere and the iono- Various materials have been proposed for sphere. Together with the rest of Earth's the tether: Kevlar, Teflon, copper alloy, and near-space environment, these regions are nylon are some materials that have been known as geospace. investigated. For electrodynamic experi- This ambitious goal to understand ments, a conducting tether will be used; geospace in detail will be realized only other experiments will call for an insulating with a large network of observational sta- tether. tions on the ground and in space. By taking simultaneous complementary observations

25 Logo : International in many places, it w ill be possible to piece Solar-Terrestrial together the puzzle of this complex system. Physics program, a To achieve this goal, the International worldwide cooperative Solar-Terrestrial Physics (ISTP) program is program to study the being developed by NASA, the European Earth-Sun system. Spa Le Agency (ESA), and the Institute of Space and Astronautical Science (ISAS) of Japan. The prime phase of the ISTP pro gram will be 1989 through 1995. A key element of the program is the Global Geospace Science (GGS) mission that involves several complementary space- craft. They will be in different orbits and will have the maneuvering capability of large-orbit modifications. Scientific objec- tives of the GGS mission include tracing and flows into high latitude regions from particle and energy flows from the solar space. It will be in a polar orbit 6 by 250 ind to our atmosphere, determining the Earth radii. This orbit will allow excellent nature and influence of plasma processes, dews of the aurora. Images of the aurora and investigating the origin and loss of will be recorded every minute, so the data plasma near Earth. Plasma atoms are elec- transmission rate for this spacecraft (42 trically charged, or ionized. Theoretical kilobits per second) will be much higher work will involve the synthesis of mathe- than the others. These images of the auro- matical models to simulate geospace. A ra will be obtained at various narrow comprehensive study of geospace as a wavelength bands, from X-ray through whole has not been previously attempted. visible. Six spacecraft are required to monitor the plasma source and storage regions simulta- CRRESThis joint NASA/Air Force neously. Primary sources of plasma in spacecraft will monitor the ring-shaped geospace are the solar wind, which is a current that surrounds Earth. This current continual flow of gases from the Sun, and acts as an energy and particle storage the ionosphere. Primary storage regions are region. The spacecraft will be placed in the tail of the magnetosphere and the elec- at about 6.6 Earth tric currents that surround Earth. To cover radii. CRRES stands for "chemical release these four regions, the six space craft are: radiation effects satellite."

WindThis NASA spacecraft will moni- GeotailThis spacecraft (a joint collab- tor the solar wind upstream from Earth, at oration between NASA and ISAS) will a distance of 6 to 250 Earth radii (6 to 250 orbit from a lunar flyby and back to a dis- times the average Earth radius of 3959 tance of a few Earth radii. It will monitor miles). energy and particle storage mechanisms PolarThis NASA spacecraft w ill mea- in the tail of the magnetosphere, or geo- sure plasma flows from the ionosphere magnetic tail.

SOHO This spacecraft (NASA/ISAS) is designed to investigate the physics of the solar interior, the corona, and the solar wind.

26 3 0 ClusterThis project (NASA/ISAS ) Responsibility for deployment and opera- consists of four small explorer-class craft tion of these facilities will be shared by a positioned in a halo orbit to investigate series of p-ograms. the spatial and temporal characteristics of The DARN program will utilize a net- various small-scaled plasma structures in ork of radar facilities located in northern the solar wind and the magnetosphere. latitudes. These facilities will detect back- One of the cluster craft will be launched scattered radio waves from the ionosphere 18 months in advance to support the GGS that will reveal information about the struc- program for its equatorial science objec- ture of the ionosphere, including irregulari- tives. ties. Other radar facilities in eastern Canada and northern Europe will complement The Geotail spacecraft will be built by DARN. ISAS. The others will be built by NASA. MAINSTEP is a program to study the European labs will contribute by sharing in ionosphere from Halley Station, Antarctica. the responsibility of building instruments Data from the instruments will be incorpo- for the NASA spacecraft. rated into the GGS data base. CANOPUS will study the aurora and the Some of these spacecraft will be ionosphere. This Canadian program will launched from the Shuttles cargo bay. involve observation facilities throughout Payload Assist Modules will then propel northern Canada and will support the GGS them to their required orbits. Liquid propel- mission. lant on board each spacecraft will allow Sondrestrom Radar, located in maneuvering. Other ISTP spacecraft will Greenland, will also support the GGS mis- be launched using expendable launch sion by providing data on the ionosphere. vehicles (ELVs). Numerous orbital geometry configura- Basically, all spacecraft will be similar. tions will exploit the capability of these They will weigh between 600 and 900 kilo- spacecraft for maneuvering. For example, grams (1320 and 1980 lb) and will incorpo- the Wind spacecraft will 11y in two differ- rate spin stabilization at 10 to 20 rpm. They ent types of orbits. One involves a double- will consume 200 to 300 watts of power lunar swingby in which the spacecraft pass- from solar arrays. Data will be stored on es by the Moon on the way out to a dis- tape recorders and played back to the tance of 200 Earth radii. The other possible telemetry system. The spacecraft will be Wind orbit is called the L I halo. In this designed to last at least 3 years. geometry the spacecraft will orbit the Instruments on board the spacecraft will famous L 1 liberation point. At this point in monitor magnetic fields, electric fields, space, 240 Earth radii away, a spacecraft plasma waves, plasma composition. and can maintain its position with respect to energetic particle velocities. Earth while consuming relatively little fuel. A tentative launch schedule has already As a result of the GGS mission, our been planned. CRRES will be launched in knowledge of Earth's environment will be 1989, with both Wind and Polar launched greatly enhanced. It will then be possible to in 1992 to supplement measurements to be make much better predictions of events in made by the ESA-Solar Polar Mission. geospace. SOHO and Cluster will be launched in 1994. In addition to space observations at key points in geospace, complementary ground- based observations will be made. These observations will focus on the processes of upper atmospheric heating by electric cur- rents. To facilitate such observations, radar, magnetometer, and photometer sites throughout the world will be employed. 31 27 Other future programs cloud cover, and other atmospheric param- eters. General purpose facilities for moni- New technologies in areas such as optical toring the atmosphere may include lidar remote sensing have recently advanced to and microwave facilities. The microwave the stage where the troposphere. strato- facility will help us understand the relation- sphere, and mesosphere can be effectively ship between the ocean and the atmo- monitored from orbit. Orbiting platforms sphere. will therefore be ideal for studying the These flights to the Space Station, atmosphere over a range of latitudes, longi- besides its many other missions. will tudes, and altitudes, as well as over long increase the Shuttle launch rate. The periods of time. Shuttle launches may therefore become a source of pollution because of the alu- minum clouds given off by the solid rocket boosters.

Lidar One of the most promising new methods for studying the upper atmosphere in ol es lasers. Lidar, or light detection and ranging, is a technique in which a laser is fired into the sky and the reflection is observed. With Lidar, the height of any atmospheric con- stituent may be determined, inLluding trace constituents. A multiuser Lidar facility on the Shuttle, I and later on the Space Station, w ill monitor the global atmosphere. VertiLal distribu- tions and flow patterns of constituents such as pollutants and w ater v apor will be moni- 4y Y tored and analyzed. Other key measurements w ill include heights of cloud tops and distributions of trace constituents, such as ice, ozone, and Above: Power Tower Space Station water vapor. Because it is dangerous to reference configuration The Space Station will play an important look into a laser beam and because it is of Space Station. role in upper atmospheric research because possible someone on the ground could hap- it will be inhabited by men and women pen to look skyward when the laser is fired, available to service and operate instru- the design must consider the safety of peo- ments. They will adjust experiment align- ple on the ground. ment, focusing, and calibration. The Shuttle will service the station, replacing Long Duration Exposure Facility necessary supplies and expendables such as The Long Duration Exposure Facility liquid coolants for optical detection sys- (LDEF) is another Shuttle-launched multi- tems. Another advantage of the Space use facility for collecting information about Station for atmospheric research will be the the upper atmosphere. Launched on Shuttle many instruments that can make simultane- Mission 41 -C, LDEF is designed to fit the ous measurements of temperature, wind, cargo bay. It is a 12-sided cylindrical frame, 4.3 meters by 9.1 meters (14.2 feet by 30 feet). It weighs 9700 kilograms (10.7 tons). LDEF's surface is covered by an assort- ment of materials that interact with the upper atmosphere while in orbit. After a 28 32 >4, few months. the LDEF is retrieed by the form on the spat.et.raft surface. The effects Astronauts in Spacelab. Shuttle and brought back to Earth. Its test of weightlessness on crystals and seeds materials, mounted on trays on its surface, will be the focus of the other LDEF experi- are sent to scientists for analysis. By study- ments. ing the effects of long exposure to condi- LDEF is gravity-gradient stabilized, that tions in orbit, scientists can determine the is, it is placed in an orientation so that the best materials for protection of future orbit- slight variation in gravity from one end to ing spacecraft and facilities such as the the other keeps it in exactly the same orien- Space Station. tation. This stabilization technique will be LDEF will also carry materials such as used on the Space Station. LDEF is placed glass fiber and plastic composites that may in a vertical orientation by the Shuttle's be used as structural components in future RMS, and held until all vibrations stop. It space structures, as well as materials with is then released. various insulative coatings. Lenses and mirrors will be flown to test their durability against the accumulative effects of radia- tion. Certain LDEF experiments will focus on the problem presented when particles of the atmosphere cause electrical currents to 29 Upper Atmosphere Research help us understand the energy balance Satellite between Earth and space, the Earth NASA's Upper Atmosphere Research Radiation Budget Experiment (ERBE) will Satellite (UARS) program will pros ide data measure the incoming and outgoing radia- on temperatures, w inds, compositior . and tion, part of w hich is sunlight and heat that other conditions in the upper atmosphere. penetrates the atmosphere. Studies will emphasize the stratosphere and Three satellites will be used in the ERBE mesosphere to determine their response to system. Two (NOAA-F and NOAA-G) will natural phenomena, such as solar activity, be launched from California by Atlas rock- as well as to the activities of humans. The ets into 830-kilometer (575-mi) altitude Shuttle will launch UARS into a 630-kilo- polar orbits. The third, the Earth Radiation meter (370-mi) orbit at 57-degrees inclina- Budget Satellite (ERBS), was launched by tion. This high inclination of the orbital the Shuttle into a 57-degree orbit and plane will allow coverage of most of deployed by the RMS. The spacecraft's Earth's surface. The spacecraft is 7 meters own propulsion system lifted it to its final by 3 meters (23 feet by 9.9 feet), weighs altitude of 610 kilometers (379 mi). Below right: Earth 5000 kilograms (5.5 tons), and will con- One instrument to be used is the Radiation Budget sume 1.5 kW of electrical power. Stratospheric Aerosol and Gas Experiment Satellite (ERBS) during (SAGE II). It will look at the Sun tangen- deployment from Earth Radiation Budget Experiment tially through the stratosphere w ith a tele- Shuttle. Blue image is When the Sun's energy reaches Earth, some scope. The spacecraft will see the Sun set reflection of aft flight is reflected and some is absorbed by the on each orbit. The line of observation will deck on window. atmosphere. BeLause Earth emits energy, a descend through successively lower layers balance is established whereby the incom- of the atmosphere. Inside the spacecraft a ing radiation balances the outgoing. This spectrometer, which acts like a prism, balance is called the radiation budget. To 'Jaks up the light into its constituent col- ors. It detects changes in the color of the Sun as the light is absorbed by constituents of the stratosphere. The remaining colors, or spectra, will reveal the presence of ozone, water vapor, nitrogen dioxide, or other chemicals. Thus the composition at different altitudes can be monitored. Another instrument to be used is the ERBE Non-Scanner (ERBE-NS). It includes five sensors: two will provide wide-angle observations of Earth, two will provide a narrow-field view, and one will monitor the Sun's radiation. The third instrument is called the ERBE scanner (ERBE-S). It will measure radia- tion reflected by and emitted from Earth. ERBE data will supersede data from the Nimbus series spacecraft, because the ERBE will be more accurate. Other future programs to study the upper atmosphere include the Magnetic Field Satellite and the Geopotential Research Mission, which will study Earth's gravita- tional field. The mission will use a satellite orbiting the Sun and will provide complementary data.

30 34 Left: (both photos) Upper Atmosphere Research Satellite (UARS).

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v.., -Jo AIthough we basically under- atmosphere influence long-term physical, Unanswered stand the processes occurring in chemical, and biological trends in our envi- the upper atmosphere, many ronment? questions details are missing. We do not One possible source of these long-term know the relative importance of the diverse changes is carbon dioxide in the atmo- processes, nor do we know how the upper sphere. Over the last century, carbon diox- atmosphere interacts with other regions in ide in the atmosphere has been increasing the Earth-Sun system. We know little about as a result of the use of fossil fuels. Today, the composition of the magnetosphere or oil and coal combustion are still our pri- the consequences of solar wind. How, for mary energy sources. The consequences of example, does the upper atmosphere influ- continued dependence on fossil fuels are ence our weather below? What do auroras unknown, but a significant increase in at- tell us about events in the far regions of the mospheric carbon dioxide could result, magnetosphere? causing climatic changes. To reduce this If we can better understand our geospace risk, we may need to limit the use of fossil system, we will better understand similar fuels and instead derive our energy from systems throughout the universe, such as wind, solar, or nuclear sources. those around Jupiter and Mercury or How can we predict the long-term around astronomical objects such as radio changes in the upper atmosphere? Will galaxy NGC 1265. (The magnetosphere of changes in the upper atmosphere result in Far left: Earth viewed NGC 1265 stretches 100,000 light years global heating or cooling? A slight change over North Pole in the into space.) in the energy reaching Earth from the Sun ultraviolet. These con- By studying our own upper atmosphere could result in a one-degree centigrade in- secutive images show we also can learn about the auroras, air- crease in average air temperature, signifi- Me aurora and geo- corona that surround glow, and of other planets. cantly melting the polar caps, increasing Earth. Airglow, for example, was observed on the sea level worldwide, and flooding all Mars by Mariner 6. Intense aurora were coastal areas. Below: Auroral arc discovered in Jupiter's atmosphere, but the Scientists are working on these questions, system obtained by source of the radiation is unknown. and within the next generation we hope we simultaneous observa- Many important questions about space- will have enough answers to prevent disas- tion in ultraviolet and craft glow have been raised recently. What trous changes in our atmosphere. visible light. is the cause of the glow phenomenon? How will it influence future space instru- ments, such as optical instruments designed to see faint light sources? How will it in- fluence placement of instruments in orbit and design of the Space Station system? Most importantly, how will our upper

e have only begun to probe the mysteries of our upper at- Conclusion mosphere. Yet research has already provided a wealth of knowledge on the interactions of the Sun and Earth that occur in the upper atmo- sphere. With a continuing worldwide effort, we are also beginning to understand the in- fluence of technological and industrial achievement on our atmosphere. This re- search will lead to a better understanding of our most precious resourceour environment. 33 1,,,, 4 I' 3..,i eneral

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Adknowledgme is

Tim Eastinan,'Sci ntist, 4 Office pfSpace,ienCeancl.Applications, NASA !Headquarters: Linda D.oherty, Public Affairs Specialist, Public. Affaies.0. 'NASA Marshall Space Flight Center Pamgl, Chief, Physici Branch, NASA Marshall Space Flight Center;, C.R. Chappell, Chief,, : .Solar-Teriestlial Physics Division, 4. NASA Marshall Spate F-liglitCentek%, Hunter Waite; Seidmist,' Spfai-Terrestrial Physics Division, -,--NASA- Marshall Space Flight Center. cary,SwenSoty,Scientist, Lockheed Missiles and Space Corp: kobert,E. Haynes, Publicatidns Officer,;-. 9ASA Headquarters

Photo,Credits

- L.A. Feank and J.D.',Cra.ven,, , University of Ioya General Electric ."GeoPhysicalInstitt4, University-of Alaska. C.R. Chappell; ,1.- Marihall Space Fliifit Center 4 'Harvard College '04ervatofy`'- Ball AFrospace

Jim Riccio, - t Jet CalifornialnstituteloftiTachnold Marielones, '..",f;;; Pubic Miars SPecii4alist.,, 'NASA Headquarters

The AuttPor fi*- \- : John Bird. has, writtehnpnieCOS scientific"-,._,- ., arficles for newSpaPersafid niagaiinei: '... is a scientist working"on and '3,-,-,-

herds the altitude reCord:fdr.,h(ng-- .. . " gliding;--1 1,70G metarS 0,9',Q00 At.,, , -

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