bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of Connective Tissue Growth Factor in Mediating Hypertrophy of Human Proximal Tubular Cells Induced by Angiotensin II
Authors: Liu Bi-Cheng , Sun Jing , Chen Qi , Ma Kun-Ling , Ruan Xiong-Zhong , Phillips Aled O.
Published: October 2003

Background/Aims: Cellular hypertrophy is an early important pathological feature of renal diseases such as diabetic nephropathy and remnant kidney. Recent studies have demonstrated that angiotensin II (Ang II) might be a major contributor in regulating cell hypertrophy. However, the exact mechanism is still unclear. The aim of our present work was to investigate the possible role of a newly clarified fibrogenic factor, connective tissue growth factor (CTGF), in mediating the effect of Ang II-induced tubular cell hypertrophy. Methods: The cell line HK2 was grown in Dulbecco’s modified Eagle’s medium containing 10% heat-inactivated fetal calf serum. After the cells were rested in serum-free medium for 24 h, the dose and time response of CTGF mRNA expression to Ang II stimulation was observed by RT-PCR, and protein synthesis was observed by Western blotting. The effect of anti-CTGF on Ang II (10–7M)-induced [3H]-leucine incorporation, total protein content (Coomassie brilliant blue G250 method) and change in cellular size [determined by a scanning electronic microscope (SEM)] was also observed. The influence of anti-CTGF antibody on the cell cycle was analyzed by using a fluorescence-activated cell sorter flow cytometer. Results: The results showed that Ang II induced expression of CTGF mRNA in a time- and dose-dependent manner (p < 0.05 and 0.01, respectively). Stimulation of cells with Ang II (10–7M) for 48 h resulted in a 92% increase in [3H]-leucine incorporation (5,584 cpm/105 cells at 0 h vs. 10,741 cpm/105 cells at 48 h; p = 0.01), which was significantly abolished by treatment with anti-CTGF antibody. Ang II (10–7M) significantly increased the total protein content in HK2 cells (control: 0.169 ± 0.011 mg/105 cells vs. Ang II: 0.202 ± 0.010 mg/105 cells; p = 0.03), which was markedly inhibited by cotreatment with anti-CTGF antibody. The average cellular diameter determined by SEM showed that the increase in cell size induced by Ang II could be significantly inhibited by anti-CTGF antibody (control: 11.92 ± 1.62 µm, Ang II group: 20.63 ± 3.83 µm, Ang II + anti-CTGF group: 16.43 ± 3.23 µm; p < 0.01, respectively). Furthermore, the flow cytometer study showed that Ang II arrested the cell cycle at G0–G1 phase, which was significantly reversed by treatment with anti-CTGF antibody (G0–G1 percentage: in Ang II group: 76 ± 1.8%, in Ang II + anti-CTGF group: 71 ± 1.78%; p = 0.04). Conclusion: Our data are the first to clearly demonstrate that CTGF might be an important mediator of Ang II-induced renal hypertrophy, which suggests that inhibiting the production of CTGF might be the new strategy in early prevention of renal fibrosis.
Interaction between Nitric Oxide and Cyclooxygenase Pathways in Endothelial Cells
Authors: Vassalle Cristina , Domenici Claudio , Lubrano Valter , L’Abbate Antonio
Published: October 2003

Nitric oxide (NO) and cyclooxygenase (COX) derived prostaglandins (PGs) are involved in vascular homeostasis. Contradictory results have been obtained in previous studies on the putative ‘cross-talk’ between these two pathways. Our aim was to evaluate the interaction between NO and PG release in human microvascular endothelial cells (HMEC-1) and in umbilical vein endothelial cells (HUVEC). Methods: Medium samples were assayed for nitrite/nitrate (NOx) and L-citrulline levels while lysed cells were assayed for endothelial NO synthase (eNOS), as markers of NO production. Prostaglandin E2 (PGE2) and 6-keto-prostaglandin F1α (6-keto-PGF1α) were assessed as indicators of COX activity. Results: The NO donor sodium nitroprusside and L-arginine increased PGs levels in both cell types. NG-monomethyl-L-arginine (L-NMMA) significantly inhibited 6-keto-PGF1α release without significantly reducing PGE2 levels. Indomethacin increased both NOx, eNOS and L-citrulline levels. PGE2 treatment did not modify NOx values. Conclusion: The stimulation of PGs by NO may represent an additional pathway used by exogenous nitrovasodilators to elicit vasodilation. Reduction of PGs by inhibition of COX was compensated by enhanced NO. Conversely, PGsdid not compensatedecreased NO following L-NMMA treatment. Treatment with the vasodilatator prostaglandin E2 did not modifyNOx levels.
Current status of lung transplantation
Authors: Lau C.L. , Patterson G.A.
Published: October 2003

Two decades have passed since the first successful clinical lung transplant was performed in 1983, and, in the interim, lung transplantation has become the preferred treatment option for a variety of end-stage pulmonary diseases. Remarkable progress has been made in the field through refinement of technique and improved understanding of transplant immunology and microbiology.

Unfortunately, donor shortages continue to limit the more widespread application of lung transplantation. In order to address this issue, marginal donors, living lobar and split lung donor techniques, and nonheartbeating donors have been used clinically to increase the number of donor lungs available.

Chronic rejection of the lung allograft is currently the major hurdle limiting long-term survival. To date, prevention of known risk factors and treatment strategies have not lessened the devastating toll this process has on lung transplant survival. Better understanding of the cause of chronic rejection is needed in order to develop novel strategies for its treatment. Promotion of immune tolerance is a promising area that could potentially eliminate chronic rejection.

The present article discusses recent advances in lung transplantation. It also details the major issues facing the field today. Only through continued clinical and experimental investigation will lung transplantation eventually reach its full potential.
Respiratory failure
Authors: Roussos C. , Koutsoukou A.
Published: October 2003

Respiratory failure occurs due mainly either to lung failure resulting in hypoxaemia or pump failure resulting in alveolar hypoventilation and hypercapnia. Hypercapnic respiratory failure may be the result of mechanical defects, central nervous system depression, imbalance of energy demands and supplies and/or adaptation of central controllers.

Hypercapnic respiratory failure may occur either acutely, insidiously or acutely upon chronic carbon dioxide retention. In all these conditions, pathophysiologically, the common denominator is reduced alveolar ventilation for a given carbon dioxide production.

Acute hypercapnic respiratory failure is usually caused by defects in the central nervous system, impairment of neuromuscular transmission, mechanical defect of the ribcage and fatigue of the respiratory muscles.

The pathophysiological mechanisms responsible for chronic carbon dioxide retention are not yet clear. The most attractive hypothesis for this disorder is the theory of “natural wisdom”. Patients facing a load have two options, either to push hard in order to maintain normal arterial carbon dioxide and oxygen tensions at the cost of eventually becoming fatigued and exhausted or to breathe at a lower minute ventilation, avoiding dyspnoea, fatigue and exhaustion but at the expense of reduced alveolar ventilation. Based on most recent work, the favoured hypothesis is that a threshold inspiratory load may exist, which, when exceeded, results in injury to the muscles and, consequently, an adaptive response is elicited to prevent and/or reduce this damage. This consists of cytokine production, which, in turn, modulates the respiratory controllers, either directly through the blood or probably the small afferents orviathe hypothalamic-pituitary-adrenal axis. Modulation of the pattern of breathing, however, ultimately results in alveolar hypoventilation and carbon dioxide retention.
Alternative energy conservation technologies in industrial freezers operating under frosting conditions
Authors: Mago P J , Sherif S A
Published: October 2003

The objective of this paper is to provide an overview of some alternative energy conservation technologies in industrial freezers and refrigerated facilities that are prone to coil frosting problems. This effort will particularly target three distinct techniques, namely the use of heat pipe assisted heat exchangers, employing dampered coils and operating freezer coils at excessively high face velocities. The feasibility of these technologies will be explored both experimentally and analytically. The results will be supported by visual observations and images taken inside the laboratory freezer under study.
Determination of stiffness and damping sensitivity for computer numerically controlled machine tool drives
Authors: Holroyd G , Pislaru C , Ford D G
Published: October 2003

A generalized eigenvalue method is used to determine the undamped and damped natural frequencies, coefficients of damping and mode shapes of a computer numerically controlled (CNC) machine tool drive. The calculated results compare well with the measured results obtained by using vibration analysis equipment. Then the sensitivity of the various modes to changes in the stiffness and damping characteristics of the machine drives is estimated. These values prove to be useful in adjusting the parameters of a hybrid model for a CNC machine tool axis drive in order to alter the simulated results in accordance with the measured results.
Computational study of the gas flow through a critical nozzle
Authors: Kim H-D , Kim J-H , Park K-A , Setoguchi T , Matsuo S
Published: October 2003

The critical nozzle is defined as a device to measure the mass flow with only the nozzle supply conditions making use of the flow choking phenomenon at the nozzle throat. The discharge coefficient and critical pressure ratio of the gas flow through the critical nozzle are strongly dependent on the Reynolds number, based on the diameter of the nozzle throat and nozzle supply conditions. Recently a critical nozzle with a small diameter has been extensively used to measure mass flow in a variety of industrial fields. For low Reynolds numbers, prediction of the discharge coefficient and critical pressure is very important since the viscous effects near walls significantly affect the mass flow through the critical nozzle, which is associated with working gas consumption and operation conditions of the critical nozzle. In the present study, computational work using the axisymmetric, compressible, Navier-Stokes equations is carried out to predict the discharge coefficient and critical pressure ratio of gas flow through the critical nozzle. In order to investigate the effect of the working gas and turbulence model on the discharge coefficient, several kinds of gases and several turbulence models are employed. The Reynolds number effects are investigated with several nozzles with different throat diameters. The diffuser angle is varied in order to investigate the effects on the discharge coefficient and critical pressure ratio. The computational results are compared with the previous experimental ones. It is known that the standard k-ε turbulence model with the standard wall function gives the best prediction of the discharge coefficient. The discharge coefficient and critical pressure ratio are given by functions of the Reynolds number and boundary layer integral properties. It is also found that the diffuser angle affects the critical pressure ratio.
Development of a damping seat slide to reduce whiplash injury
Authors: Schmitt K-U , Muser M , Heggendorn M , Niederer P , Walz F
Published: October 2003

To prevent whiplash injury, a new seat slide was developed. In the case of a rear-end impact, the device allows the vehicle seat to slide backwards while damping this motion. Deformable steel profiles serve as damping elements. To activate the device, a trigger system is used which detects an acceleration threshold.

Sled test experiments were performed to analyse the behaviour of the new system. The tests were conducted to mimic rear-end collisions with a delta-V of 16 km/h. A BioRID dummy was used as a human surrogate. The results indicate the beneficial influence of the damping seat slide on the occupant kinematics. In particular, the so-called S-shape deformation of the neck assessed by the neck injury criterion (NIC) is reduced. Comparing a standard car seat with and without the damping seat slide, it was shown that the NIC is reduced by approximately 40 per cent. Hence it was shown that besides the head restraint and the recliner that are used in other whiplash protection systems, the seat slide has the potential to prevent whiplash injury.
Artificial Gravity
Authors: Young Laurence R.
Published: October 2003

Artificial gravity (AG) is not gravity at all. It is not a field force or a “force at a distance.” Neither does its strength obey the inverse square law of attraction that determines the orbital motion of planets. However, in terms of its action on any mass, it is indistinguishable from “real gravity.” Instead of gravitational pull, it exerts a centrifugal force, proportional to the mass that is being accelerated centripetally in a rotating device. Although the effect of AG on an extended body differs from that of true gravity, the effects on any given mass are equivalent. Thus AG is simply the imposition of acceleration on a body to recover the forces that are eliminated by the free fall of orbital flight. Probably the most serious health threat to humans during interplanetary flight comes from radiation exposure en route and on some extraterrestrial surface. Beyond that, prolonged exposure to weightlessness itself can result in deconditioning many of the body's systems. For space voyages of several years, such as those envisioned for exploration of Mars, the human requires some sort of “countermeasure” to reduce or eliminate this deconditioning.

The notion of creating a substitute for gravity through centrifugation was introduced early in the conception of human space travel. The popularization of AG, however, is attributable to the science fiction community. Only two space missions early in the program were devoted to animal studies. Human in‐flight results were anecdotal.

The envelope of operation for AG is limited by several factors. The “comfort zone” for AG with a rotational radius of up to 1000 feet is bounded by several constraints. Theminimum gravitational level, normally measured at the rim of a centrifuge, is the key parameter in the design space. Themaximum gravitational acceleration levelis also a factor if short‐radius intermittent AG is used.

Themaximum angular velocityof the AG device is limited by the Coriolis forces encountered when walking or when moving objects, and by the motion sickness and disorientation experienced with certain kinds of head movements. Coriolis accelerations are real inertial accelerations that occur when moving within a rotating framework. The choice of AG design depends on whether continuous or intermitent AG is to be used. These choices are discussed.
Astronomy‐Infrared
Authors: Werner Michael , Harwit Martin
Published: October 2003

This article describes the astrophysical questions that can be addressed at infrared wavelengths, the advantages of pursuing infrared astronomy from space, the enabling technologies, and the missions that have been flown and are planned to exploit the unique potential of this wavelength range. The infrared band covers three decades—from ∼1 μm to ∼1000 μm—that encompass a very wide range of instrumental techniques and scientific issues. Discussion here has been limited to rocket‐ and satellite‐borne missions aimed primarily at astrophysical targets and have omitted the infrared instruments that have been carried on planetary probes. The short‐wavelength limit of the detailed discussion is drawn at 2.5 μm but note that the Near Infrared Camera and Multi‐Object Spectrograph (NICMOS) instrument on the Hubble Space Telescope (HST) have operated very successfully in the 1 to 2.5‐μm band; these wavelengths are also among those studied by the Diffuse Infrared Background Experiment (DIRBE) on the Cosmic Background Explorer (COBE). Wavelengths longer than ∼200 μm have been probed extensively from space only by the highly successful COBE spacecraft. COBE observations of the nearby Universe are discussed but we cannot do justice to its extraordinary spatial and spectral measurements of the cosmologically critical cosmic microwave background radiation (CMBR).

An introductory section describes the astrophysical uniqueness of the infrared and the tremendous benefits to be gained by carrying infrared instrumentation above the atmosphere. Next three key technical areas of particular importance for infrared astronomy—detectors, cryogenics, and optics—and the way they have been adapted to the space environment are presented. Next, comes a review of previous and near‐term missions for infrared astronomy from space, emphasizing the evolution of both science and technology since the first rocket experiments of the 1960s. The final mission discussed in detail is the Space Infrared Telescope Facility (SIRTF), which was scheduled for launch in 2003. SIRTF's advanced technology and great scientific potential will mark the end of the first phase of exploration of the Universe in the infrared band. But SIRTF is also a beginning, because it sets the stage for the missions of the next decade. Finally, a summary of the technological challenges and scientific opportunities of these upcoming programs are given.
Optical Astrometry from Space
Authors: Kovalevsky Jean
Published: October 2003

Astrometry plays a very particular part in the realm of astronomy. One can define astrometry as the part of astronomy that measures the apparent positions of celestial bodies on the sky. And, because these positions vary with time, the objective is to describe and study these motions that, for stars, provide two essential parameters: the proper motion and the parallax from which the distance is derived. As an extension, one ascribes also to astrometry the measurement of apparent dimensions and shapes of celestial bodies. However, in this article, the determination of star positions, the primary goal of space astrometry is considered.

The physical quantities that are measured by astrometry are angles that are often very small. Radians are not used in astrometry; the basic units are degrees and seconds of arc (denoted″). Smaller units are necessary, and astrometrists are currently using milliseconds of arc and now are starting to use one millionth part of a second of arc. Some basics that have to be known for further understanding are given.

Before describing what space has brought to astrometry and what it is expected to bring in the future, it is necessary, for comparison, to present the achievements of ground‐based astrometric observations. One must distinguish two classes of instruments that differ by the area of the sky measured. Descriptions of the instrument are mentioned in space missions have been launched: Hipparcos and facilities on the Hubble Space Telescope. These are described.

The successful entry of astrometry among space astronomical techniques is a powerful incentive to devise and propose to space agencies new more powerful, more effective space astrometric missions with a better science return to cost ratio. Many projects have been presented during the last decade. Some have already been thoroughly studied, and engineered descriptions of a possible realization exist. The two most ambitious projects are described. However, they have not yet been built, so the information given here is provisional. Other projects will only be mentioned, even if some might be launched before those more sophisticated.
Biological Responses and Adaptation to Spaceflight: Living in Space—An International Enterprise
Authors: Nicogossian Arnauld
Published: October 2003

Attempting to predict human responses to space travel, physicians and researchers of the 1950s speculated that microgravity and spaceflight itself would present significant challenges‐if not barriers—to the human body. They hypothesized that the combined stresses of launch acceleration, weightlessness, radiation, and heavy deceleration upon reentry would be incapacitating. At the very least, they predicted that the bodily systems sensitive to gravity‐based cues would function improperly or not at all. Given this grim forecast, the initial focus was to demonstrate that life, away from Earth, could survive space travel and subsequent return to Earth's gravity. Faced with this challenge, both the United States and Soviet Union turned first to ground simulations, such as immobilization studies, and then to the study of animal test subjects launched on board high‐altitude balloons, suborbital, and orbital rockets. What followed is a series of biological satellites that carried a variety of living specimens, from isolated cell cultures to whole instrumented organisms. The Soviet Union relied primarily on canines to provide such data, whereas the United States chose primates for such experimentation.

This article attempt to present a concise overview of life in space, physiological responses to this new environment, and associated health implications for future space travelers. Consideration must be given to the hostile, and yet dynamic environment of space; to the craft that protects the crew members from the harsh environment, allowing them to navigate in space; and to life itself as it adjusts to this novel environment. Today it is known that some adaptive changes, such as immune and hormonal responses, are primarily the response to the stresses of confinement, isolation, and spacecraft design, not necessarily to the unique effects of the space environment.
Comets
Authors: Cochran Anita L.
Published: October 2003

Comets are small icy/dusty bodies left over from the formation of the solar system and represent the least altered bodies from the epoch of formation. They formed in the outer parts of our planetary system; some still reside in their primordial reservoir known as the Kuiper belt; those formed in the Uranus‐Neptune region were ejected to a spherical reservoir known as the Oort cloud; those formed near Jupiter and Saturn were ejected from our solar system entirely.

The nuclei of comets are small (typically a few km) bodies composed of ices and dust. Of the ices 80% is water ice. The dust is composed of organics and silicates. As the nucleus is heated, the ices sublime and flow outward from the nucleus. The dust/gas mixture forms a large coma and even larger tails.

To date, several spacecraft have visited comets and have made measurements
in situ
, but we have yet to retrieve samples and return them for study in laboratories. The vast majority of our knowledge of cometary composition comes, however, from remote observations obtained with ground‐based or Earth‐orbital telescopes. These data are gathered using spectroscopic and photometric techniques on a wide variety of comets. The spectrum of a comet is characterized predominantly by molecular emission coupled with an underlying continuum of sunlight reflecting from the dust.

Every single day, about 100 tons of interplanetary material hits the upper atmosphere of Earth, and some of that material reaches the surface. A large percentage of the smallest particles originates in comets as dust grains that are released when ices sublime. These small cometary particles represent no hazard to Earth. Many of them are fluffy aggregates that “float” in the upper stratosphere for long periods of time and are occasionally collected for study by specially equipped high‐flying aircraft.

Much can be learned about the nature of comets via observations from the ground and Earth orbit. However, one can never see the nucleus of the comet in this way, and information is inferred about its nature by using models. To study the nuclei of comets, it is necessary to send spacecraft to them. These spacecraft missions can range from simple flybys, to rendezvous missions, to landings and sample returns. The completed and planned cometary missions of the U.S. and other nations are described.
Earth Orbiting Satellite Theory
Authors: Steven Nerem R.
Published: October 2003

The objective of this article is to provide an introduction to the theory of satellite orbital motion. Although the discussion focuses on Earth‐orbiting satellites, the theory is equally valid for computations around other primary bodies including the Moon, the Sun, and the planets. The majority of the discussion focuses on the problem of two bodies. The solution provides sufficient accuracy for many problems in astrodynamics. Perturbations from the two‐body problem are discussed because a number of applications require greater accuracy. The solution of these more complex problems is generally accomplished using numerical integration techniques, which is beyond the scope of this chapter.
Immunology and Infection in Space
Authors: Shearer William T. , Sonnenfeld Gerald
Published: October 2003

This article on alterations of immune responses in space travel is intended to provide a review of the background and rationale for the hypothesis that immune function of humans on long‐term space flight missions will be sufficiently altered that immune compromise occurs, thus rendering astronauts subject to opportunistic infections, particularly activation of latent viruses and the development of malignancies. The article reviews published information on the evidence of immune compromise in humans and animals flown in space and in human and animal earth‐bound models of spaceflight. These alterations in immune function are discussed in the context of model secondary immunodeficiency states where external forces predispose humans to repetitive infection, debilitation, and cancer. An attempt will be made to quantitate the degree of immune impairment observed in space travelers and earth‐bound equivalent model subjects and to predict what the astronauts on the Mars Mission might experience in terms of the occurrence of reactivated viral infections and the development of malignancy. Because this article includes many technical terms that may not be familiar to the reader, a glossary of immunological terms is included.
Mercury
Authors: Nelson Robert M.
Published: October 2003

Mercury, our solar system's innermost planet, is shrouded in mystery, despite the fact that it is Earth's third closest planetary neighbor and is one of the five planets known to the ancients. It is fairly easy to see. It appears to an Earth‐based observer at approximately 2‐month intervals as a bright object visible to the naked eye near the Sun, shortly before sunrise or after sunset. However, despite its nearness and its brightness, it ranks only behind the most distant planet, Pluto, in our understanding of its interior structure, its surface composition, and the dynamic interactions between its surface, its tenuous atmosphere, and its magnetosphere. These topics are subjects of this article. The physical processes that have governed Mercury's origin and evolution are poorly understood. The planet has many unusual qualities, including an unexpected magnetic field and a remarkably high density (mass to volume ratio). It has even been suggested that water ice may be present just under the surface at some places on the planet, even though its surface is the closest to the Sun of all of the planets. Because Mercury is close to the Sun, the response of the planet's environment to solar activity is also expected to be greatest of all of the planets.

Mercury has the most extreme daily temperature fluctuation of all of the planets. Understanding more about Mercury is important for testing models of planetary formation, and the results of these research activities will have great impact on models of the origin and evolution of the solar system. Obstacles to exploration of mercury conclude the discussion.
Nuclear Rockets and Ramjets
Authors: Finger Harold B.
Published: October 2003

The objective of this article is to describe the design concepts of and the programs to develop our nuclear rocket propulsion capability for spaceflight and the nuclear ramjet systems intended for missile delivery and to describe the mission capabilities they could provide. In both systems, the nuclear reactor replaces the combustion chamber as the source of high‐temperature energy used to provide the thrust in place of their chemical alternatives. The nuclear rocket was, and still is, considered for deep space missions, including missions, such as human flight to Mars, whereas the stimulus for the nuclear ramjet was its potential performance as a high‐speed, almost limitless range, low‐altitude and, therefore, almost undetectable missile delivery system. In the early phases of research on the nuclear rocket, it too had been considered as a possible missile system.

The hardware weight of the entire system must be limited so that the various mission benefits resulting from the nuclear energy source are not counterbalanced by that total weight. Major design and development requirements include selecting materials that have high‐temperature strength and are compatible with hydrogen propellant in the rocket and air in the ramjet, appropriate neutronic characteristics, controlled and stable start‐up and operation, component design and reliability, and are safe. All of these matters must be and were comprehensively researched and developed to provide systems that could achieve the desired performance. These were all high priority tasks in both the nuclear rocket and nuclear ramjet programs, and they are discussed in this article, as are the important management organizations and technical capabilities established to carry them out.

Though significant progress was made in these programs, neither the nuclear rocket nor the nuclear ramjet program was carried to actual application in its proposed and anticipated missions. In the nuclear rocket case, the space program has not yet committed to mission objectives that require the high payload and deep space capability of that system. However, nuclear rocket propulsion continues to be recognized as necessary for large, deep space missions. In the nuclear ramjet case, existing chemical rocket systems provide all of the military missile requirements that are foreseen. Similar to the nuclear ramjet development, the extensive work that had been done on nuclear‐powered turbojet engines, that is mentioned here, was also discontinued because chemically fueled turbojets provide all of the capability that was required.
Planetary Exploration Spacecraft Design
Authors: Jones Ross M.
Published: October 2003

Having only begun in the early 1960s, planetary‐exploration spacecraft design is a fairly new art. Between 1962 and 1973, NASA designed, built, and launched 10 spacecraft named Mariner to explore Venus, Mars, and Mercury for the first time. In 1962, the Jet Propulsion Laboratory (JPL) launched the Mariner 2 spacecraft to explore Venus. In 1965, Mariner 4 flew by Mars and captured the first close‐up photos of another planet.

Each year since 1962, NASA, the USSR, Japan, or the European Space Agency has launched at least one planetary‐exploration spacecraft. Two of the best known are NASA's Voyagers, which were launched in 1977, two years after NASA's Viking mission sent landers and orbiters to Mars. Today, 24 years after launch, Voyager 2 has completed a tour of Jupiter, Saturn, Uranus, and Neptune, and still returns data from a distance of 64 AU. NASA spacecraft have visited every planet in the solar system except Pluto, and orbited Venus, Mars, and Jupiter. In 1975, the USSR's Venera 9 and 10 spacecraft sent the first photos from the surface of another planet (Venus); in 1986, the European Space Agency's Giotto spacecraft captured the first detailed photos of a comet's nucleus (Halley's). The NASA/JPL Cassini spacecraft is due to enter Saturn orbit in 2004. The NASA/APL MESSENGER spacecraft is due to orbit Mercury in 2009. MESSENGER is being built by the Johns Hopkins Applied Physics Laboratory (APL), which also built the Near Earth Asteroid Rendezvous 10 (NEAR) spacecraft that orbited and touched down on the asteroid Eros in February 2001.

This article addresses the important elements of planetary‐exploration spacecraft (PES) design. The scope of this article includes those spacecraft that fly by, orbit, or land on other planets, asteroids, or comets. Planetary‐exploration spacecraft are truly fascinating machines, and their missions are some of humankind's most audacious endeavors. Spacecraft elements are described in some detail, and the principal focus is on the system design and the technical subsystems. Ground stations, launch vehicles, science, and navigational elements are not addressed.
Pluto and Charon
Authors: Young Eliot , Young Leslie
Published: October 2003

Pluto is a small, cold planet on the outskirts of the known solar system. Pluto's diameter (∼2370 km) is roughly equivalent to the distance from New York to Las Vegas, or about two‐thirds the size of our Moon. Pluto has one known moon of its own, Charon, whose diameter (∼1250 km) is slightly more than half of Pluto's. Unlike seven of the other eight planets (Uranus is the exception), Pluto rotates on its side, as does Charon in its orbit around Pluto. Charon's distance from Pluto is 19,636 km, compared to the Earth–Moon distance of 384,400 km.

Despite their proximity, Pluto and Charon are covered by bright frosts of differing compositions: H
2
O ice covers Charon, whereas Pluto's surface is predominantly N
2
frost that has traces of methane and carbon monoxide ices. Both objects have densities near 2 gm/cm
3
, implying a roughly even mixture of rock and H
2
O ice for their bulk compositions.

The Pluto/Charon system has a highly elliptical orbit around the Sun. A Pluto recedes from the Sun, much of its thin N
2
atmosphere will condense as frost on the surface. This periodic redeposition of fresh frost takes place every Pluto year (248 Earth‐years) and is the reason that Pluto's surface has one of the highest albedos in the solar system.

The Pluto/Charon system currently represents one of the wide open frontiers in the solar system. No spacecraft has visited Pluto/Charon (although NASA has plans for an upcoming Pluto–Kuiper Belt mission). The angular diameter of Pluto is only a tenth of an arcsecond at best, which is just about the resolving limit of the Hubble Space Telescope (HST) and ground‐based observatories that have adaptive optics capabilities. Consequently much of what is known about the Pluto/Charon system has been pieced together from indirect clues or observations taken during unique observing geometries.

Much has been determined by infrared spectroscopy. A rare opportunity to study Pluto's atmosphere takes place when Pluto passes directly between Earth and a star (stellar occulations). The 1988 occulation provided the most detailed and direct information about Pluto’s atmosphere.
Rocket Propulsion Theory
Authors: Hawk Clark W.
Published: October 2003

A rocket is defined as an “engine or motor that develops thrust by ejecting a stream of matter rearward, or the missile or vehicle powered by such an engine.” Since the reaction principle involved assumes a self‐contained source of energy, a rocket can operate in any medium including space outside the earth's atmosphere, where there is no oxygen to support combustion. This article gives the history of the use of rockets. The laws governing these operations are discussed. The rocket is an energy conversion device that converts potential energy to thermal energy. The energy source can be chemical, electrical, beamed (solar or laser), or nuclear. Nozzle theory is described.
Saturn System
Authors: Fink Uwe
Published: October 2003

Saturn has intrigued human beings ever since they noticed that it belongs to the group of objects called
planets
, which move relative to the “fixed stars” in the sky. Saturn is the slowest moving of the ancient planets. It takes fully 29.46 years to return to the same position in the sky. Two orbits of Saturn are thus very close to an integral number of 59 Earth years, so that the phenomena of Saturn repeat on roughly the same yearly date after an interval of 59 years. This was recognized by the ancient Babylonians and Greeks. Thus, Saturn was associated with the measurement of time being it was named
Cronos
(time) in Greek legend and served as the father of the lord of planets Jupiter (Zeus). The Romans celebrated the winter feast
Saturnalia
in his honor, and the name Saturn today is fixed in our language in the word
Saturday
.

The physical models used to determine the bulk composition and interior are discussed. Atmospheric composition appearance and colors rotational rate and circulation are also discussed.

Which all of the major planets have faint ring systems, rings of Saturn are so bright and extensive that Saturn is undoubtedly the most spectacular telescopic object in the sky. When viewed with a good telescope, Saturn seems to float mysteriously and serenely in the vast reaches of space. When the rings of Saturn are opened to their maximum, they provide 1.3 times as much light as the ball of the planet. Thirty satellites are presently known. Features of the principal satellites are detailed. Physical details of Titan (the largest moon) are discussed. Voyager spacecraft has returned data on the atmosphere of Titan.
Sun
Authors: Chupp Edward L.
Published: October 2003

The Sun is only one of several billion stars in our galaxy, but as a special example, it is important to understand how it compares to other stars. Following the development of stellar spectroscopy, techniques became available to classify stars by their locations on the Hertzsprung–Russell (HR) diagram, which is a plot of stellar luminosity as a function of spectral type. To place a star on the HR diagram, the star's distance must be known, so its absolute luminosity can be determined from the measured luminous flux using the inverse square law. The star's spectral type is determined by measuring the star's “color” and characterizing its spectrum. The sun is a “G” class star. Stars that have higher surface temperatures, for example, are “O” class, and “M” class stars have lower surface temperatures. All normal stars span a temperature range from ∼40,000 K to ∼4000 K. Actually a star's spectral class is determined by comparing its spectrum with the spectra of a set of standard stars. Some physical properties of the Sun and the way the properties are determined are given here.

From direct measurement of isotope ratios, we know that the Sun's age is ∼4.5 billion years, and from the theory of stellar evolution, that it may live at least another 5 billion years. When its current internal energy source is depleted, it will expand and become a red giant and eventually a dwarf star similar to those on the HR diagram. However the goal here is to describe the present Sun in some detail.

The current understanding of the Sun draws on advances in both ground‐based observing techniques and sophisticated space instrumentation, as well as in theoretical computer models using the observations as input. This article first briefly describes some important ground‐based observations and identifies several space missions whose main purpose has been to advance knowledge of Earth’s nearest star. Next, the structure of the Sun and its atmosphere is described in more detail, beginning at the center of the Sun and emphasizing current understanding in appropriate detail. A major goal of this work is to give an up‐to‐date summary of our knowledge of solar activity. The new science of helioseismology is discussed, and space weather, as it affects Earth, is also covered briefly later. For each topic, a brief history will be given with a summary of current knowledge followed by identification of important unsolved problems. References for further study will be given for each topic discussed.
Space Radiation
Authors: Dicello J.F. , Cucinotta F.A.
Published: October 2003

The most critical biomedical risks of space habitation are (1) carcinogenesis caused by radiation, (2) loss of bone mass or density, (3) poor psychosocial adaptation, and (4) clinical manifestations of trauma or acute medical problems. Because of the unique problems and the potential long‐term consequences, radiation is frequently considered the most serious of these for long‐duration space missions, and cancer is the major risk followed by damage to the central nervous system. Radiative hazards in space have been discussed in depth by a Task Group of the National Research Council along with overall research strategies.

The term radiation in the present context refers specifically to directly and indirectly ionizing radiation, including X rays, gamma rays, neutrons, ions, and other somewhat esoteric particles such as muons and pions. Radiation is a natural part of our environment on the surface of Earth. Biological organisms in general, and humans in particular, have adapted to the normal radiative environment at Earth's surface and certainly have even benefited from the radiation. At the same time, those radiations also initiate biological damage ranging from sunburn to cancer. Earth's atmosphere and its magnetic field act as excellent radiative shields by reducing the levels of radiation. As one goes farther away from Earth's surface into orbit or toward outer space, the radiative level generally increases in intensity and changes in the types and energies of the radiation. It is known that the radiative dose rates for personnel in space are significantly higher than on Earth's surface. There has been little experience with regard to the biological consequences of healthy people exposed to these types of radiation for protracted periods of time. Best estimates indicate, however, that the additional exposure to higher energy radiation beyond that on Earth's surface or above the present allowable limits for radiation workers could result in significant risks of cancer or other serious diseases.

Because of higher level of exposures and the potential for long‐term negative consequences, radiation has been categorized as the worst biomedical risk of long‐duration space missions. At the same time, using an appropriate programmatic strategy and focused research, the risks of radiation in space should be reduced to levels comparable to or less than those of other hazards.
Interplanetary Medium
Authors: Manweiler Jerry W.
Published: October 2003

In the commonness of life on Earth, most would expect that the composition of space beyond our atmosphere might be planets, comets, asteroids, and an occasional meteor. In reality, the space between the planets and other larger objects of our solar system is richly composed of a variety of complex phenomena, which on Earth drive weather, affect communications, and provide beautiful displays with the aurora.

Long considered an empty void, the vast space between the planets and our Sun is actually filled with a tenuous gas comprised of neutral and ionized particles along with small dust grains. The source of the ionized particles comprising this gas is mostly outflows and outbursts of the Sun. Some of this gas is due to outflow of particles from planets, comets, and asteroids. Finally, some of this gas comes from the infall of particles of gas and dust from the surrounding interstellar space. In this article, the boundaries, composition, sources, and dynamics of the particles filling the interplanetary medium are explored.
Electromagnetic Propulsion
Authors: McNab Ian R.
Published: October 2003

Sporadic attempts have been made for more than 150 years to use electrical energy to launch projectiles at high velocities. Throughout the world during the last 20 years, most of the funding invested in electromagnetic (EM) launcher development has been for military applications. In most cases, the perceived advantage has been attaining higher velocities than can be achieved with propellant guns, leading to enhanced lethality. The elimination of gun propellants would also reduce vulnerability as well as allowing an increased number of stored rounds and enabling extended missions. The EM rail gun has been the preferred choice for this application because it has already repeatedly demonstrated muzzle velocities well above those of conventional guns—typically 2500 m/s versus 1750 m/s. The military challenge is to fit the electric pulsed power equipment into a battleworthy vehicle, especially if it needs to be compact. The main potential applications are direct fire tank guns, long‐range artillery, and air and missile defense.

Several electrical or electromagnetic (EM) concepts have been suggested, as described here, but their potential for space applications is, as yet, limited. However, the technological bases are now being created on which future EM launch systems for space exploration could be based in the twenty‐first century. Such systems could include launch to space from the surface of Earth, the Moon or asteroids, Maglev launch assist for large rocket systems and, possibly, EM thrusters for space transportation. Electrical ion engines have been used in space, and the Hall plasma thruster is under development for NASA.

The interest in electric launchers for military applications has led to improved understanding and advances in many technical areas. Most military applications for EM launchers require gigawatt power levels for pulse lengths of a few milliseconds to accelerate a useful projectile in a launcher of acceptable length. Coupled with the need for compact and robust equipment, this is a challenging goal for the pulsed power system. The desire to achieve muzzle velocities significantly greater than those of conventional guns—from 2–3 km/s—also requires developing the launcher and projectile. Recent progress in these areas could be the basis for future space applications.
Russian Space Stations
Authors: Semyonov Yuri P. , Gorshkov L.
Published: October 2003

The Soviet and Russian long duration orbital space stations, Salyut and Mir, were operated from 1971 to 2001. During this period, eight stations were placed into orbit. This article discusses the history and goals of these stations. While the stations were in operation, a variety of improvements were made to extend their operational lifetimes and improve their performance. Experience in on‐orbit operations enabled the Energia Rocket and Space Corporation (Energia RSC) to develop a Russian space‐station concept. This concept was most fully embodied by the Mir space station and the Russian segment of the International Space Station.

The basic principles behind the Energia RSC concept, as actually developed and implemented, are discussed.

The major goals of space‐station use are as follows: research on the behavior of the human body, space research, remote sensing of Earth's surface and atmosphere, basic research in materials science and the production of materials and biological substances under microgravity conditions and research and development of proposed materials and techniques for future projects.