Space Sciences

Research in space sciences and the development of innovative spacecraft instrumentation and systems continue to be vigorous activities at SwRI. Institute scientists collaborate with the engineering and technical staff on the design and fabrication of scientific instruments, spacecraft computers, and power supplies for flight on interplanetary probes, Earth-orbiting spacecraft, and sounding rockets. Strong theoretical and observational research programs are maintained in space physics, planetary science, stellar astronomy, and solar physics.

The Cassini spacecraft, weighing more than 5,600 kilograms, was assembled at the Kennedy Space Center at Cape Canaveral. In addition to its role as the principal investigator institution for the Cassini Plasma Spectrometer, SwRI also leads the Ion and Neutral Mass Spectrometer (INMS) science team. Developed at NASA's Goddard Space Flight Center, INMS will measure neutral species and low-energy ions in key regions of the Saturn system, and will characterize the composition and structure of the upper atmosphere of Titan and its interaction with the planet's magnetosphere.

On October 15, 1997, a Titan IV B rocket, the nation's largest expendable launch vehicle, sent the Cassini spacecraft to Saturn, where it will begin its four-year mission when it arrives in June 2004. The Cassini Plasma Spectrometer (CAPS), one of 12 scientific instruments aboard, was developed under SwRI leadership. Over the past year, Institute scientists and engineers carried out environmental tests and calibrations of CAPS, culminating in the delivery of the flight unit to Kennedy Space Center for integration with the spacecraft. CAPS will contribute to researchers' understanding of the chemical composition, and perhaps the origin and history, of the Saturnian system. It also will permit detailed studies of Saturn's aurora, ionosphere, and magnetosphere.

SwRI is also the team leader for another Cassini instrument, the Ion and Neutral Mass Spectrometer (INMS), a quadrupole mass spectrometer developed at NASA's Goddard Space Flight Center. The INMS will measure neutral species and low-energy ions in key regions of the Saturn system, with a primary focus on characterizing the composition and structure of the upper atmosphere of the Saturnian moon, Titan, and its interaction with the planet's magnetosphere. INMS will also furnish data on the neutral and plasma environments of Saturn's ring system and icy moons and on the positive ions and neutral species in Saturn's inner magnetosphere.

Since being selected in 1996 as principal investigator institution for the Imager for Magnetosphere-to-Aurora Global Exploration (IMAGE) mission, SwRI has guided the project successfully through a rigorous mission confirmation review and through critical design reviews of the science instruments and spacecraft subsystems. The project has entered its next phase, where detailed designs will be developed and proto-flight instruments will be built. The first of NASA's medium-class Explorer missions, IMAGE is scheduled for launch in January 2000. During its two-year mission, IMAGE will use a combination of neutral atom, ultraviolet, and radio wave imaging to provide the first global images of key regions of the Earth's magnetosphere. These images will allow researchers to overcome the spatial and temporal limitations of localized in situ measurements and to investigate the effects of the Sun's variable activity on the global structure and dynamics of the magnetosphere. The team led by SwRI consists of investigators from nine U.S. and five foreign institutions. In addition to overall responsibility for managing the IMAGE project, including spacecraft development and operation, SwRI is building the medium energy neutral atom imager and the central instrument data processor, through which all of the instruments will communicate with the spacecraft and the ground.

In August 1997, SwRI delivered an integration model of the Plasma Experiment for Planetary Exploration (PEPE) to the Jet Propulsion Laboratory for installation on the Deep Space 1 spacecraft. PEPE, an advanced plasma instrument, will measure the energy and direction of arrival of ions and electrons and determine ion composition in the space environments near Mars, an asteroid, and a comet.

SwRI is playing a key role in NASA's New Millennium technology demonstration program by contributing the Plasma Experiment for Planetary Exploration (PEPE), one of only two scientific instruments to be flown on the Deep Space 1 mission. In collaboration with Los Alamos National Laboratory, the Institute has led the design, fabrication, and testing of PEPE, a time-of-flight ion mass spectrometer that also measures electrons. Several novel technologies have been developed or applied as part of the PEPE program. Delivery of the flight unit is scheduled for late 1997. Following the 1998 launch of Deep Space 1, PEPE will be used to investigate gases around an asteroid, plasma wakes at Mars, and the coma of the comet West-Kohoutek-Ikemura. One of the most advanced plasma sensors ever to fly, PEPE is based on the Miniaturized Optimized Smart Sensor (MOSS), an ultracompact plasma sensor developed at SwRI with internal research funding. PEPE's performance compares to that of CAPS, yet it has only one-quarter of the mass and requires only half the power. Managed by NASA's Jet Propulsion Laboratory, the New Millennium program was established to develop and validate advanced technologies, spacecraft designs, and operations concepts for solar system exploration and the study of Earth from space.

Rosetta is a European Space Agency (ESA) mission to the comet Wirtanen. Scheduled for launch in 2003, Rosetta will carry two SwRI-developed instruments, the Ion Electron Spectrometer (IES) and the Alice ultraviolet spectrograph. IES and Alice represent a new generation of highly miniaturized spaceborne instruments that use innovative technologies in sensor optics, component packaging, and high-voltage power supplies to achieve excellent sensitivity and resolution while minimizing costs and spacecraft resource requirements. IES does not include time-of-flight instrumentation, but otherwise is based on the PEPE design. Its small size (1.3 kg) and low power requirement (2.0 watts) reflect further innovations. SwRI is also involved in another Rosetta experiment, the ROSINA dual mass spectrometer, being developed under the leadership of the University of Bern, Switzerland. The Institute's role is to provide a sophisticated, high-speed waveform capture system that will be used to obtain time-of-flight measurements.

Another instrument developed at SwRI is the Miniaturized Electrostatic Dual top-hat Spherical Analyzer, or MEDUSA. A combined ion-electron electrostatic analyzer with a mass of 1.5 kg that requires only 4 watts of power, MEDUSA will be flown in late 1997 on the Swedish microsatellite Astrid-2 and in late 1998 on MUNIN, a Swedish "nanosatellite" that is roughly the size of a shoe box.

This image, acquired with the Röntgensatellit X-ray telescope, shows the distribution of X-ray emissions across Jupiter's Earth-facing hemisphere. The emissions have been averaged over several rotations of the planet. The emissions in the auroral regions are strongest; however, emissions at the middle and low latitudes are surprisingly bright and are evidence that charged particle precipitation occurs at low as well as high latitudes. SwRI scientists have studied Jovian X-ray emissions since 1992.

SwRI's Extreme Ultraviolet Spectrograph (EUVS) was flown successfully on a sounding rocket in March 1997 to observe comet Hale-Bopp. The instrument performed as expected and provided high-resolution spectral information about the comet. On earlier flights, the EUVS observed Venus, Jupiter, the lunar atmosphere, a variety of stellar targets, and the torus of neutral and ionized gas along the orbit of the Jovian moon Io at the time of the Shoemaker-Levy 9 impacts. Since SwRI began operating this instrument in 1994, the EUVS spectral resolution has been increased tenfold and its sensitivity has been tripled. This enhanced capability makes it possible to detect and identify more chemical species in the atmosphere of the target body.

Jupiter continues to provide Institute planetary scientists with a rich object of study. Images of Jovian X-ray emissions acquired with the Earth-orbiting Röntgensatellit over the past three years have revealed emissions from the planet's lower latitudes as well as from the auroral zones in its polar regions. The precipitation of sulfur and oxygen ions from Jupiter's inner radiation belts into the equatorial upper atmosphere is thought to produce the low-latitude X-rays. Results of a modeling study published by SwRI researchers in the April 1997 issue of Science indicate that the energy deposited by charged particle precipitation at low latitudes, as calculated from the intensity of the observed emissions, can account for a significant portion of the high temperatures observed by the Galileo probe during its December 1995 descent into Jupiter's equatorial upper atmosphere.

SwRI also is involved in the Galileo Solid State Imaging (SSI) investigation. SSI images are being studied for information about the surface geology of Jupiter's moons Europa, Ganymede, and Callisto, with particular emphasis on their crater populations. These studies will help researchers reconstruct the satellites' geological history, as well as provide valuable information about the populations of asteroids and comets responsible for the cratering.

The observational and theoretical investigation of smaller solar system bodies, asteroids, and comets is a key element in SwRI's planetary research program. Analysis of Galileo images of the asteroids Gaspra and Ida has revealed significant space weathering effects on the reflectance spectra of asteroid surfaces, while images of the carbon-rich asteroid Mathilde, acquired by the Near-Earth Asteroid Rendezvous spacecraft during its June 1997 flyby, have furnished SwRI researchers with valuable data on Mathilde's cratering history and on its mass and composition. In addition to such space-based investigations, SwRI also is conducting a search with ground-based telescopes for asteroid satellites. The use of a new optical technology known as adaptive optics removes the blurring caused by the Earth's atmosphere and makes it possible to distinguish faint objects that are near bright asteroids.

Large-scale computer simulations are the primary tool used by Institute scientists for theoretical studies of the dynamic behavior of asteroids and comets. Among the subjects addressed by this research is the role played by comets in the formation of the outer planets and in the delivery of water and organics to the Earth shortly after its formation. The results of one numerical simulation performed at SwRI predicted the existence of a previously unsuspected disk of comets surrounding the planetary system. This prediction, published in the June 1997 issue of Science, has since been confirmed observationally. In addition, SwRI scientists recently have developed a new, extremely fast computer algorithm that will allow them to conduct modeling studies of the formation of the Earth and the planets with unprecedented resolution and speed. Known as SyMBA for the Symplectic Massive Body Algorithm, this code is more than 10 times faster than any other existing computer algorithm for such studies.

The Institute's space science program recently has expanded to include stellar astronomy and solar physics as well as planetary science and space physics. Stellar astronomy studies center on the investigation of stellar evolution and formation through observational and theoretical studies of massive stars (stars from 10 to 100 times the mass of the Sun). According to most theories, massive stars should be clumped together in tight groups. However, SwRI analysis of data acquired with NASA's shuttle-borne Ultraviolet Imaging Telescope indicates that massive stars are more widely distributed than previously thought. Because these stars eventually end their lives as supernovas, their wide distribution means that energy and processed material from the violent supernova explosions can "stir up" the interstellar medium throughout a galaxy.

In the field of solar physics, SwRI is participating in the ESA/NASA Solar and Heliospheric Observatory (SOHO) mission. Through their analysis of data from SOHO's Solar Ultraviolet Measurements of Emitted Radiation experiment, Institute scientists are helping to determine the acceleration mechanisms of the high-speed solar wind and to study the detailed structure of the coronal holes, or open magnetic field regions near the solar poles from which the high-speed wind originates. In addition, SwRI researchers conducted a successful sounding rocket experiment in May 1997 to measure the helium abundance in the Sun's corona and to study solar wind acceleration mechanisms. The rocket payload consisted of two ultraviolet spectrometers and four extreme ultraviolet imagers, which used new multi-layer mirror technology. All of the instruments functioned as expected and produced high signal-to-noise spectra and images, including the first full-disk hydrogen Lyman alpha image of the Sun since the mid-1970s Skylab mission and the first observations of helium in the outer corona. Such measurements will help scientists better understand the Sun's variable activity and its effects on the Earth and other planets.

The Institute is developing a RAD6000^TM-based processor system for the Gravity Probe B relativity gyroscope experiment. Gravity Probe B is being developed by NASA and Stanford University to test two unverified predictions of Einstein's general theory of relativity. The experiment will monitor small changes in the direction of spin of four gyroscopes contained in a satellite flying at an altitude of 400 miles in a circular polar orbit. Changes in the gyroscopes' motion will allow Stanford researchers to probe how space and time are warped by the presence of the Earth and also to investigate how the Earth's rotation drags space-time around with it. These effects have profound implications for the nature of matter and structure of the universe. The SwRI-developed processor system will control spacecraft functions, oversee the gyroscope system, and collect data from the experiment's sensors.

The Institute has completed construction and testing of the first of 15 custom computer systems bound for the International Space Station Alpha (ISSA). Based on the RAD6000^TM processor, the furnace facility control units aboard ISSA include 128 megabytes of memory, more than that of most large workstations. The units will control up to four high-temperature furnaces to be used on the space station for microgravity research.

An advanced data acquisition and control system developed by SwRI successfully managed the activities of the Optical Properties Monitor during experiments on the Russian Mir space station. The Optical Properties Monitor is a multipurpose, in-space optical laboratory for the study of materials including thermal control surfaces, optical materials and coatings, and solar power materials. During this mission, selected materials were exposed to low-Earth orbit and the Mir-induced environment for in situ monitoring and post-flight analyses of the effects of these environments. The data acquisition and control system was used to direct electromechanical operations, including filter wheels, lens banks, and sample carousels. The system also collected and stored the data.

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