NP-119 Science in Orbit: The Shuttle & Spacelab Experience, 1981-1986

 

Chapter 5

Using Space as a laboratory: Space Plasma Physics

 


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aft view of the space shuttle cargo bay with the earth in the background.


 

[55] Earth's atmosphere varies with altitude, and its several regions have distinct compositions and physical properties. The ionosphere, where the gas is partly ionized or electrified, extends from approximately 60 to 1,000 kilometers (40 to 600 miles) above Earth's surface; it is an excellent place to study how electrified gases (plasmas) behave. Most of the universe is in the plasma state. By studying the space environment in Earth's neighborhood, we gain clues about processes around distant planets, stars, and other celestial objects.

Scientists have sent rockets and satellites to explore the ionosphere, and they have gathered data whenever and wherever auroras (the ghostly Northern and Southern Lights) and other plasma events occur naturally. However, it is impossible to create on the ground a laboratory as vast and variable as the ionosphere. To understand this complex environment, we must make space our laboratory.

As the Shuttle orbits Earth at altitudes of 240 to 400 kilometers (150 to 250 miles), it is immersed in ionospheric plasma. While in this environment, the Shuttle/Spacelab can be used to deploy small satellites and retrieve them, expose detectors directly to natural plasma, disturb the plasma with beams of energetic particles, and operate in coordination with ground-based facilities and other satellites. During a Shuttle/Spacelab mission, the ionosphere becomes a laboratory for studying processes that occur near Earth and throughout the universe, and the vehicle itself becomes an instrument for experiments. The space plasma environment is studied by three techniques: active experiments, in-situ probes, and remote sensing.

Active experiments introduce agents (particles, waves, chemicals) into the ionosphere to trace, modify, or stimulate the environment. The Shuttle itself stimulates the environment as it passes through the plasma, creating a wake and other disturbances. By carrying both active and passive probes, Spacelab functions as a laboratory and an observatory, simultaneously able to stimulate the space environment in a controlled manner and monitor the resultant effects.

In-situ probes are needed to diagnose the characteristics and changes in ambient plasma populations near the Shuttle. Spacelab has carried a variety of passive probes which operated independently or in concert with active experiments.

 


Studies of plasma near Earth may help us understand the plasma environments around other planets and their moons.

Studies of plasma near Earth may help us understand the plasma environments around other planets and their moons.


Scientists gather data from auroras and other natural plasma events.

Scientists gather data from auroras and other natural plasma events.

 

[56] Remote sensors are used to detect the effects of active experiments or to study natural atmospheric phenomena at greater distances from the Shuttle. Emissions of light accompany many processes that are difficult to study from the ground because the atmosphere obscures them. On Spacelab, instruments have a global view and can detect faint light emitted by atmospheric chemicals, by energetic processes such as auroras, or by active experiments.

 

Active Experiments: Spacelab is ideally suited for active experiments. Instead of waiting for nature to perform, scientists can create artificial auroras, particle beams, plasma waves, and wakes. Ordinarily unseen magnetic field lines and wind patterns may become visible in clouds of color produced by chemical releases, enabling us to watch and photograph the form and motion of space plasmas.

In active experiments, investigators introduce a known stimulus and measure the environment's response to test hypotheses about the natural processes of particle acceleration, wave and wind movement, chemical releases, and energy release. Three types of active experiments have been accomplished during Shuttle missions: particle beam and wave injections, wake and sheath generation, and chemical releases. Passive instruments for measuring changes in plasma conditions were necessary companions to all active experiments.

 

Beam and Wave Injection: Beam injection experiments help scientists trace the invisible electric and magnetic fields that envelop Earth. Electron beams emitted from Spacelab travel along magnetic fields. By measuring the paths of the beams, scientists can discover how particles are accelerated and guided in the plasma environment.

Waves are generated naturally in plasma by the constant mixing and flowing of plasmas and by sudden disturbances, such as lightning or particle beam injections. Thus, emitted particle beams or radio waves trigger wave motions in the natural plasma. Plasma waves are important mechanisms for transferring energy from one plasma regime to another, where it may be deposited, absorbed, or transformed and carried elsewhere. Comparisons of wave input and output yield information about energy exchange.

 


Electron beams emitted during the Spacelab 2 mission interact with natural plasma in the vicinity of the Shuttle.

Electron beams emitted during the Spacelab 2 mission interact with natural plasma in the vicinity of the Shuttle.


In a laboratory, electron beam experiments are confined by walls; the Shuttle is making it possible for scientists to do similar plasma physics experiments in the vast, unconfined laboratory of space.

In a laboratory, electron beam experiments are confined by walls; the Shuttle is making it possible for scientists to do similar plasma physics experiments in the vast, unconfined laboratory of space.


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This computer image maps a plume of particles after an emission by the Space Experiments with Particle Accelerators (SEPAC).

This computer image maps a plume of particles after an emission by the Space Experiments with Particle Accelerators (SEPAC).

 

Beam and wave injections are helping scientists understand processes such as auroras that occur when beams of particles from space collide with atmospheric particles around Earth's magnetic poles. These experiments also may reveal clues to particle beam activity detected in solar flares and in the vicinity of other planets (Jupiter and Saturn ).

The Space Experiments with Particle Accelerators (SEPAC) flown on the Spacelab 1 mission used the Shuttle as a platform for active space plasma research. The investigation used a particle accelerator that could emit electron beams from 1,000 to 7,500 volts and up to 1.6 amps and a magnetoplasma dynamic arc jet which emitted pulses of argon ions. Several passive probes were carried to observe the shape of the beam and to measure wave and particle interactions.

When the electron beam accelerator was operated above current levels of about 100 milliamps, the character of the beam changed dramatically because of strong turbulence. The beam spread rapidly in space, and many electrons from the beam scattered back to the Shuttle, causing a bright glow on the surfaces and in the thin atmosphere surrounding the Shuttle. Indeed, the Shuttle actually charged positive as it sought to attract electrons from the ionsphere to balance the current shot forth in the electron beam.

The charge buildup on the Shuttle was neutralized momentarily by injecting a plume of neutral gas simultaneously with the electron beam. To the surprise of the investigators, the gas neutralized the charge instantly, and the vehicle charge remained neutral for several milliseconds after the simultaneous emissions. This indicates that injections of neutral gas may be an effective way to eliminate spacecraft charges.

Another surprise was that during neutral gas injection, electron density increased, indicating that neutral atoms were being torn apart and converted into ions and electrons by interaction with the ambient ionospheric plasma. Passive detectors measured ionization 10 to 100 times greater than the ambient electron density. The instant reaction of these relatively benign neutral atoms with the natural space plasma is evidence that the ionosphere can become dynamic and turbulent. In addition, a plasma generator was used to inject pulses of ions and electrons which neutralized the Shuttle's electrical charging.

[58] Other evidence of the strong beam plasma interactions was observed by a joint experiment that used an electron spectrometer to measure modifications in electron populations. Spacecraft charging was observed, as well as processes that accelerated electrons to more than four times their injection energy.

Particle beams were also injected by the Spacelab 1 Phenomena Induced by Charged Particle Beams (PICPAB) experiment. An electron and ion accelerator mounted on a pallet generated beams while passive diagnostic instruments on the pallet and deployed through the Spacelab scientific airlock measured resultant effects. When the beams were injected, plasma wave activity was measured in the vicinity of the airlock, and the beams created several instabilities in the natural magnetic and electric fields. Changes in the electric and magnetic fields were also recorded during emissions by the other particle accelerator. There were large variations of the Shuttle/Spacelab charge with respect to the ambient plasma potential, and it took from a few milliseconds to several seconds after the beam was switched off for the vehicle potential to neutralize.

Spacelab 2 carried another beam-injection experiment, the Vehicle Charging and Potential Experiment (VCAP), which studied beam injections near the Shuttle and operated jointly with a deployed satellite so that the beams could be studied as they propagated further into space. (Both sets of instruments had an earlier trial flight on the OSS-1/STS-3 mission.) An electron generator mounted on the pallet emitted electrons in a stead stream to create beams and in pulsed modes to create waves of known frequencies. The maximum beam current was 100 milliamps and its energy was 1,000 electron volts, resulting in a beam power approximately equal to that of a 1 00-watt light bulb. The Vehicle Charging and Potential Experiment also studied how the beam injections charged the Shuttle and affected plasma in its vicinity.

For the joint experiments, the Plasma Diagnostics Package (PDP) was deployed as a free flyer about 300 meters (0.25 miles) away from the Shuttle. The satellite consisted of complementary instruments for simultaneous measurements of plasma characteristics such as magnetic and electric fields, particle distributions, radio waves, and plasma composition, density, and temperature. During the tree flight, the crew completed intricate maneuvers to align the satellite and the Shuttle along the same geomagnetic field line, like beads on an imaginary string. At the moment the Shuttle...

 


The Plasma Diagnostics Package (PDP) was released as a free flyer to measure plasma characteristics away from the Shuttle.

The Plasma Diagnostics Package (PDP) was released as a free flyer to measure plasma characteristics away from the Shuttle.



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The radio spectrogram from a PDP receiver shows that an electron beam interacted with plasma to generate a whistler radio emission. This experiment duplicated a natural phenomenon; similar whistler emissions are often generated by natural electron beams along auroral field lines.

The radio spectrogram from a PDP receiver shows that an electron beam interacted with plasma to generate a whistler radio emission. This experiment duplicated a natural phenomenon; similar whistler emissions are often generated by natural electron beams along auroral field lines.

 

....crossed the magnetic field, an electron beam was e emitted, and the satellite measured the characteristics of the beam as it traveled along the magnetic field and spread into the ionosphere.

The spectrum of waves from the beam appears as an intense broadband emission. An unusual feature of the beam may be caused by whistler radiation, plasma waves that travel at specific angles to magnetic fields. The whistler radiation seen by the PDP near the electron beam is analogous to the auroral hiss radiation seen by satellites passing over the Earth's auroral zones. This sort of beam to-wave energy conversion is a fundamental process responsible for radio emissions from other planets and astronomical systems.

Another time when the satellite and Shuttle were aligned along the magnetic field, the beam was pulsed to create plasma waves similar to low-frequency radio signals. The satellite measurements during the beam and wave injections indicate that the beam heated ions in the natural plasma and created turbulent motion, density variations, and strong electric fields. Since similar processes occur during auroras and magnetic storms, these beam injection experiments strengthened the link between active experiments and the physics of auroral beams.

The joint PDP-VCAP experiments on Spacelab 2 were the culmination of a series of earlier experiments. The first joint measurements to study the effects of an electron beam on the space environment, and vice versa, were performed in a large ionospheric simulation chamber on the ground. These preliminary experiments provided valuable experience in operating both sets of instruments and also in selecting suitable operating modes for the electron beam. For the OSS 1 mission, planners drew upon the chamber test experience to improve the flight plan for PDP operations on the remote manipulator arm. When OSS- 1 results proved to be of great interest to space plasma physicists, the next logical step was proposed: to conduct joint experiments and study beam effects over a greater range beyond the 12-meter (40-toot) reach of the arm. Releasing the PDP as a tree flyer during the Spacelab 2 mission was already planned; the VC AP experiment was added to the payload to follow up on....

 


Space experiments with the PDP were the cilmination of years of testing and planning in ground-based plasma laboratories. Here in the Johnson Space Center plasma chamber, the PDP is engulfed by a glowing column of energetic electrons emitted by the electron generator that was flown with the PDP on two Shuttle missions.

Space experiments with the PDP were the culmination of years of testing and planning in ground-based plasma laboratories. Here in the Johnson Space Center plasma chamber, the PDP is engulfed by a glowing column of energetic electrons emitted by the electron generator that was flown with the PDP on two Shuttle missions.

 

[60] ....the OSS- 1 success and study beam effects over a greater distance. This on going iteration of an experiment in light of cumulative experience is one of the primary advantages of the Shuttle for science; it allows scientists to refine their objectives, equipment, and procedures through reflights in much the same way as they perfect experiments by repetition on the ground.

 

Wake and Sheath Generation: As it travels through space, the Shuttle affects the density, temperature, and electrical properties of the surrounding plasma. An electric field sheath develops around the vehicle and, like a boat, the Shuttle creates a wake in the plasma. The wake is depleted of plasma as the Shuttle collides with and displaces the gas, and various instabilities occur as the wake region is refilled with plasma.

 


Plasma distributions were mapped as the manipulator arm moved the PDP around the Shuttle.

Plasma distributions were mapped as the manipulator arm moved the PDP around the Shuttle.

Many other celestial objects such as moons, asteroids, and comets also travel through gases of charged particles. Wake and sheath experiments can help scientists determine flow patterns around natural bodies, such as the moon lo that passes through Jupiter's plasma environment.

Wake and sheath experiments aid in evaluations of the Shuttle's effect on Spacelab investigations which study a medium that is being disturbed by the vehicle that carries them. This knowledge is pertinent for planning future experiments, interpreting data, and designing other large space structures and observatories that also will be traveling through the ionosphere.

Experiments in simulation chambers and a few remote observations of plasma activities around comets, planets, and moons led to theories about large body interactions with plasmas. The PDP's first flight on a pallet in the Shuttle payload bay and on the Remote Manipulator System (RMS) during the OSS-1 mission gave scientists a chance to' make direct measurements around a large body moving through space. These measurements yielded several discoveries: a large gas cloud enveloped the Shuttle, trailing out to unknown distances; a broadband electrical noise was emitted around the Shuttle; and ion and electron interactions occurred between ambient plasmas and molecules released from Shuttle water dumps and thruster firings. The plasma disruptions created by the Shuttle were more complex than expected, and another mission....

 


The gas cloud given off by the orbiter produces reactions that modify the density of nearby plasma.

The gas cloud given off by the orbiter produces reactions that modify the density of nearby plasma. Ions created from a charge-exchange reaction with the plasma produce electrostatic waves that are evident at more than 300 meters (0.25 miles) from the orbiter along magnetic fields. The plasma wake of the Shuttle results in an ion tail similar to the tails of comets.

 

[61] ...was warranted to extend observations.

To continue the inquiry begun on the OSS-1 mission, the PDP was flown on the Spacelab 2 mission. This time, it was moved about on the RMS out to distances of 12 meters (40 feet) to map the surrounding plasma environment. The Shuttle made several intricate maneuvers so that the satellite could study diverse plasma effects around the Shuttle. Measurements indicated that the thermal ion distributions around the spacecraft are much more complex than predicted. Frequently, an unexpectedly intense background level of ion current due to incoming hot ions was measured. Surprisingly, the ions often appeared to change energies, an indication of high ion temperatures and turbulent plasma activity. These effects have not been observed by satellites and rockets; the new observations demonstrate the significant impact of a large, gas-emitting space vehicle like the Shuttle on the ionosphere.

As on the prior mission, the satellite instruments again detected the emissions from material. . outgassing, thruster firings, water dumps, and a cloud of neutral gas that expanded away from the Shuttle. The gaseous cloud modified the ionosphere at large distances through chemical interactions between ions and neutral atoms. Water vapor was detected in the immediate vicinity of the Shuttle out to several hundred meters. These contaminants were especially dominant in the Shuttle's wake, and natural plasma ions of nitrogen (N2+), nitric oxide (NO+), and oxygen (O+) were depleted. These contaminants interfere with measurements of natural plasma made from the Shuttle payload bay.

The PDP never sampled undisturbed natural plasma because the ionosphere was perturbed out to the distance covered by the PDP during its free flight. Investigators are comparing the Shuttle to a comet, which creates a deep wake and turbulence as it moves through plasma. The gas cloud enveloping the Shuttle is large enough to be....

 


The top panel of these two spectrograms shows the angle of diffracted partivles as they fill the wake left by the Shuttle.

The top panel of these two spectrograms shows the angle of diffracted particles as they fill the wake left by the Shuttle. The bottom panel shows the distribution of ion energy over time. By studying intensity changes at different angles, investigators are trying to determine the physical processes occurring as the particles refill the wake. Similar processes may occur in the wakes of celestial bodies moving through space.

 

[62]...similar to a comet's surrounding cloud; also, the Shuttle appears to release molecules, such as water, that react with ions from the natural plasma and form new molecular species. This may be similar to the process by which comets react with ions from the ambient plasma to create their long tails.

An attempt to map the multiple ion streams and wake around the Shuttle yielded fascinating observations of plasma flows, density variations, and turbulence associated with the wake. With the plasma satellite extended 10 meters (33 feet) on the arm, the Shuttle performed a roll maneuver, sweeping the satellite through the wake. Measurements obtained during these maneuvers indicated that ions from the ambient ionosphere were accelerated into the wake from above and below the vehicle.

Investigators are trying to determine how particles are accelerated rapidly enough to refill the plasma void in the Shuttle's wake. Various explanations are under consideration. One possibility is that a strong electric field, which is created by density differences between the depleted wake and the ambient ionosphere, accelerates the ions into the void. This expansion process has been observed in laboratory experiments but never in a natural plasma environment. Plasma physicists believe that it may be a common process around large natural celestial bodies moving through various types of space plasmas.

 


This series of computer-enhanced optical images shows the effects of a Shuttle engine firing. The visible emission results from the neutralization of ionospheric ions and electrons by carbon dioxide in the Shuttle's exhaust. As the plasma returns to normal, the red airglow fades.

This series of computer-enhanced optical images shows the effects of a Shuttle engine firing. The visible emission results from the neutralization of ionospheric ions and electrons by carbon dioxide in the Shuttle's exhaust. As the plasma returns to normal, the red airglow fades.

 

The Millstone Hill radar antenna mapped variations in electron density during the plasma depletion experiment. These panels show pre-event conditions (a) and the resultant perturbations at 14 minutes (b), 40 minutes (c), and 107 minutes (d) after the Shuttle thruster firing.

The Millstone Hill radar antenna mapped variations in electron density during the plasma depletion experiment. These panels show pre-event conditions (a) and the resultant perturbations at 14 minutes (b), 40 minutes (c), and 107 minutes (d) after the Shuttle thruster firing.

 

[63] Chemical Releases: Chemical releases in the ionosphere often result in luminous particle interactions that "paint" invisible magnetic fields, currents, and waves in vivid color. Hidden features of the structure, chemistry, and dynamics of the atmosphere are revealed by visible movements of vapors and plasma.

One Spacelab 2 investigation took advantage of chemicals that the Shuttle routinely releases when thrusters are fired to maintain or change altitude: exhaust consisting mainly of water vapor, carbon dioxide, and hydrogen. The effects of these releases are temporary and are not detrimental to the environment, but they do cause some interesting physical and electrical changes in the ionosphere.

The exhaust triggers chemical reactions that cause electrons to combine with ions in the upper atmosphere, leaving temporarily depleted plasma areas or "holes." The most visible effect of the holes is a taint red airglow emission associated with carbon dioxide molecules. Radar and radio measure meets at ground observatories can detect other traits of these holes, such as elevated electron temperature, reduced electron concentrations, drifts of nearby plasma into the hole, and disrupted or enhanced radio wave propagation.

The Shuttle's ability to fire the engines to release exhaust at specific times and locations allowed Spacelab 2 scientists to monitor the areas of depleted plasma from three separate observatories on the ground. There were two nighttime engine burns during which optical emissions could be monitored. Within seconds after the burn over the Millstone Hill Incoherent Scatter Observatory in Westford, Connecticut, the red airglow emission at 630 nanometers increased sharply, reached a maximum 3 minutes later, and gradually decayed for 10 to 15 minutes. The airglow cloud grew to 300 kilometers (186 miles) in diameter and then faded back to normal. Radar data indicated that electron density was depleted and the hole spread in altitude and latitude for one hour. During a relatively smaller daytime exhaust release over the same site, radar data indicated that electron densities were reduced, confirming that even small releases affect the ambient plasma.

The goal of another engine burn, over the University of Tasmania low-frequency radio observatories in Hobart, Tasmania, was to test the concept of conducting low-frequency radio astronomy through an artificially created window in the ionosphere. To the disappointment of astronomers who study radio emissions in an effort to learn about distant celestial objects, radio waves in the band less than 3 megahertz are blocked by the ionosphere. After the burn over Hobart, electron densities were reduced by 20 to 30 percent, and cosmic signals at 1.7 megahertz were received through the plasma hole. The experiment thus succeeded in demonstrating that plasma depletions may indeed open new astronomical windows.

Complementing the ground-based observations, measurements made by instruments aboard the Shuttle indicated that ambient plasma activity was enhanced for several minutes after each thruster firing. Depletions in plasma density, airglow enhancements, increases in turbulence, and variations in spacecraft potential were recorded.

 

Passive Monitors: Through active experiments and on-site diagnostic instruments, space scientists have learned a great deal about how the natural plasma environment acts when disturbed. However, Spacelab gives scientists another advantage: a global view of the atmosphere that is not possible from the ground. The Shuttle/Spacelab serves as an excellent platform for atmospheric observations.

From space, the light emissions from the atmosphere make it a giant television screen that shows charging chemical reactions. Even though these events occur far from the Shuttle, sensitive onboard instruments can make images of the tell-tale light emissions associated with chemical reactions.

The Atmospheric Emission Photometric Imager (AEPI) flown on Spacelab 1 was designed to study global patterns in magnetic fields and other features occurring naturally in the atmosphere. Images of the....

 


A photometric imaging experiment was flown on Spacelab 1 to study faint natural and artificial atmospheric emissions. This optical image reveals sunlit ionized magnesium in Earth's atmopshere.

A photometric imaging experiment was flown on Spacelab 1 to study faint natural and artificial atmospheric emissions. This optical image reveals sunlit ionized magnesium in Earth's atmosphere.

 

Earth's magnetic field in the vicinity of the Shuttle was computed and superimposed over the magnesium emission seen at 100-200 kilometers (60-125 miles) altitude.

Earth's magnetic field in the vicinity of the Shuttle was computed and superimposed over the magnesium emission seen at 100-200 kilometers (60-125 miles) altitude. Since magnesium emissions appear to align with the magnetic field, they can be used as a visible tracer of magnetic fields.

 

The glow that surrounds the Shuttle as it travels through space continues to mystify plasma physicists as well as scientists in other disciplines.

The glow that surrounds the Shuttle as it travels through space continues to mystify plasma physicists as well as scientists in other disciplines.

 

[64] ....atmosphere were produced by two low light-level television cameras with special lenses and filters. The filters help the instrument detect faint emissions from metastable oxygen, magnesium ions, and other atmospheric elements in the 200 to 750 nanometer spectral region.

Magnesium ions deposited at altitudes of 100 to 200 kilometers (60 to 125 miles) by meteors burning up during entry were imaged by AEPI as they scattered sunlight. By comparing the images to magnetic field data taken at the same time, investigators were able to show that the magnesium clouds were aligned along the magnetic fields for 1,600 to 2,400 kilometers (1,000 to 1,500 miles). Now scientists can use magnesium deposits to trace magnetic fields.

Observations also were made of atmospheric airglow created as molecules react with sunlight and of the glow associated with the Shuttle. It has been suggested that hydroxyl (OH) is a candidate species for producing the troublesome Shuttle glow which may interfere with some astronomical observations. However, hydroxyl may not be the dominant species involved in Shuttle glow, because it was detected in photographs of Earth's airglow but was absent in photographs of Shuttle glow. The glow has been studied on other missions by scientists from different disciplines who have proposed various theories concerning the glow. Other candidates that may be involved in the glow reaction include nitrogen dioxide (NO2), carbon monoxide (CO), and nitrogen (N2)

From Spacelab, scientists have an unusual view of the aurora which occurs in an altitude range of approximately 60 to 1,000 kilometers (40 to 600 miles). To date, most views of the aurora have been from the ground or from satellites in orbits far above the aurora. The orbit and inclination of the Spacelab 3 mission gave scientists a....

 


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These auroral photographs taken from the Space Shuttle show how a rare red emission from atomic oxygen (630 nanometer) changes as it dances across the atmosphere, reaching an altitude of more than 450 kilometers (280 miles). The uniform white band along the horizon is the atmospheric airglow layer at 95 kilometers (60 miles) altitude.

 

These auroral photographs taken from the Space Shuttle show how a rare red emission from atomic oxygen (630 nanometer) changes as it dances across the atmosphere, reaching an altitude of more than 450 kilometers (280 miles). The uniform white band along the horizon is the atmospheric airglow layer at 95 kilometers (60 miles) altitude.

 

These auroral photographs taken from the Space Shuttle show how a rare red emission from atomic oxygen (630 nanometer) changes as it dances across the atmosphere, reaching an altitude of more than 450 kilometers (280 miles). The uniform white band along the horizon is the atmospheric airglow layer at 95 kilometers (60 miles) altitude.

 

...closer, side view of the aurora. The Shuttle's cameras were used to record 5 hours of videotapes and 274 still photographs. In conjunction with orbital motion, the video and photo graphs were taken so that they overlapped and could be viewed stereoscopically.

The aurora is not just a glowing spot in the sky; it is a bright oval encircling the polar region. Both Earth's magnetic and electric fields modulate the aurora to produce the bright curtain and ribbon-like forms as well as the dim diffuse aurora. The aurora is the only natural visible manifestation of the magnetosphere, and by studying changes in its form and motion scientists can infer changes in the pat terns of Earth's electromagnetic field.

As light shows danced across the polar cap of the Southern Hemisphere, Spacelab 3 scientists recorded features that had never been seen before, including the first views from outside the atmosphere of thin horizontal layers of enhanced aurora. The layers, once thought to be rare, were recorded on two of the three Shuttle passes over the aurora. This first observation of enhanced aurora from space eliminates concerns that the ground based observations might have been optical illusions caused by atmospheric refraction.

Also for the first time, thin vertical layers were observed in diffuse auroras.

 


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The first observations from space of enhanced auroras were made during the Spacelab 3 mission.

The first observations from space of enhanced auroras were made during the Spacelab 3 mission. The thin band of light parallel to Earth's horizon is an edge-on view of the airglow layer at 95 kilometers (60 miles) altitude. A rayed auroral arc just above the airglow layer bends inward and passes under the Shuttle in the foreground. The rays in the arc extend upward approximately 60 to 200 kilometers (37 to 124 miles). A very thin band of brighter enhanced auroral emission less than 2 kilometers (1.2 miles) high runs through the aurora near the base of the rays.

 

This observation is possible only from space, ideally in near Earth orbit, because diffuse auroras cover a wide range of latitudes; when viewed from the ground or from above by satellites, they appear as a uniform glow. From the vantage point of the Shuttle, scientists got an edge-on view of diffuse auroras and could see the various thicknesses and layers within. The mission resulted in an extensive catalogue of known auroral features, including a collection of images of tall red rays extending over a wide geographical range. Scientists are using these images to see how auroral features vary with location over Earth.

 

An Unbounded Laboratory: To fully understand the space plasma environment enveloping Earth, plasma physicists must join with solar and atmospheric physicists to study the integrated solar-terrestrial system. Solar-terrestrial physics encompasses the entire sun-Earth system, including the detailed study of solar processes, the relationship between changes at the sun and resulting changes in Earth's magnetosphere and atmosphere, and the detailed physics of the Earth's magnetosphere/ionosphere/atmosphere system. The solar observations and radiation measurements, active space plasma experiments, and atmospheric and auroral observations of Spacelab 1, Spacelab 2, and Spacelab 3 are major steps in studying the integrated solar-terrestrial system.

Scientists are using their Shuttle/Spacelab experience to plan research for the Space Station and other observatories. The Space Station offers investigators a laboratory to continue the exciting manned research and observations initiated on the Shuttle/Spacelab. Some instruments will be attached to the station, making possible real-time observations of the sun and coordinated active experiments. Scientists in....

 


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Scientists watched images of the aurora that were recorded and transmitted during Spacelab 3.

Scientists watched images of the aurora that were recorded and transmitted during Spacelab 3.

 

...space and on the ground will be able to coordinate observations of important events, such as solar flares or magnetic storms, and track effects as they propagate from the sun to Earth's magnetosphere and atmosphere.

With the close interaction of well-trained scientist crewmembers, more elaborate active experiments similar to those achieved aboard Spacelab 2 will be accomplished. Instruments on the Space Station, free-flying and tethered satellites, the Shuttle, and orbital platforms can make thorough simultaneous measurements of controlled perturbations of space plasma.

Plasma physics studies will continue with two major facilities now being planned. The Space Plasma Laboratory will incorporate several proven experiments, such as the Space Experiments with Particle Accelerators (SEPAC) and the Atmospheric Emissions Photometric Imager (AEPI) from Spacelab 1 and the Plasma Diagnostic Package (PDP) from Spacelab 2, as well as new instruments such as a special pair of extremely long whip antennas to transmit very low-frequency radio waves into the magnetosphere. The Space Plasma Laboratory instruments will probe the invisible cocoon that shelters our world from deep space. The Tethered Satellite, built by the United States and Italy, will study plasma phenomena by trolling an instrument package from the Shuttle through the atmosphere.

Since solar terrestrial phenomena affect the entire Earth, the international cooperation of the Spacelab era must continue aboard the Space Station and in other research on co-orbiting and polar platforms. NASA has plans for the Solar-Terrestrial Observatory and the Earth Observation System, both of which will help us study the integrated sun-Earth system. Instruments aboard platforms will be able to make global observations at varying local times, altitudes, and latitudes. This is necessary for tracking events as they occur around the world and for mapping atmospheric constituents and conditions. Besides global coverage, the platforms will provide continuous viewing of the sun and Earth and its magnetosphere and atmosphere. This will allow scientists to monitor events as they evolve and observe conditions during different solar cycles.

The Space Station along with co-orbiting platform observatories will further research by offering manned operations, large and complementary instrumentation, on-orbit calibration and repair, deployment and retrieval of subsatellites, and a data system to bring all the information together. When we establish a permanent presence in space, we will have a vast laboratory at our disposal.

 


Scientists use the data from space to characterize the Earth's plasma environment and interpret the results of active experiments there.

Scientists use the data from space to characterize the Earth's plasma environment and interpret the results of active experiments there.


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Shuttle/Spacelab missions provide opportunities for scientists to gain valuable experience in space experimentation and formulate important questions to be answered by long-term Space Station experiments. In this artist's concept, the Tethered Satellite System studies the plasma surrounding Earth.

Shuttle/Spacelab missions provide opportunities for scientists to gain valuable experience in space experimentation and formulate important questions to be answered by long-term Space Station experiments. In this artist's concept, the Tethered Satellite System studies the plasma surrounding Earth.

 

[69] Space Plasma Physics Investigations

.

OSS-1/STS-3

Plasma Diagnostics Package (PDP)

S. Shawhan, University of lowa, lowa

.

Vehicle Charging and Potential Experiment (VCAP)

P.M. Banks, Stanford University, Stanford, California

.

Spacelab 1/STS-9

Atmospheric Emission Photometric Imaging (AEPI)

S.B. Mende, Lockheed Solar Observatory, Palo Alto, California

.

Electron Spectrometer

K. Wilhelm, Max Planck Institute, Stuttgart, Germany

.

Magnetometer

R. Schmidt, Academy of Sciences, Vienna, Austria

.

Phenomena Induced by Charged Particle Beams (PICAB)

C. Beghin, National Center for Scientific Research, Paris, France

.

Space Experiments with Particle Accelerators (SEMC)

T. Obayashi, Institute of Space and Astronautical Sciences, Tokyo, Japan

.

Spacelab 3/51-B

Auroral Imaging Experiment

T. J. Hallinan, University of Alaska, Fairbanks, Alaska

.

Spacelab 2/51-F

Plasma Depletion Experiments

M. Mendillo, Boston University Boston, Massachusetts, and

P.A. Bernhardt, Los Alamos National Laboratory, Los Alamos, New Mexico

.

Plasma Diagnostics Package (PDP)*

L.A. Frank, University of lowa, lowa City, lowa

.

Vehicle Charging and Potential Experiment (VCAP)*

P.M. Banks, Stanford University, Stanford, California

.

* Reflight


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