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At least 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Human parathyroid hormone-(1-38) restores cancellous bone to the immobilized, osteopenic proximal tibial metaphysis in rats

The purpose of this study was to determine if human parathyroid hormone-(1-38) (hPTH(1-38)) can restore cancellous bone mass to the established osteopenic, immobilized proximal tibial metaphyses of female rats. The right hindlimbs of 6-month-old female Sprague-Dawley rats were immobilized by bandaging the right hindlimbs to the abdomen. After 30 days of right hindlimb immobilization, the rats were subcutaneously injected with 200 micrograms hPTH(1-38)/kg/day for 15 days (short-term treatment) or 75 days (longer-term treatment). Static bone histomorphometry was performed on the primary spongiosa, and both static and dynamic histomorphometry were performed on the secondary spongiosa of the right proximal tibial metaphyses. Immobilization for 30 days without treatment decreased trabecular bone area, number, and thickness in both primary and secondary spongiosa, and induced an increase in eroded perimeter and a decrease in tissue referent-bone formation rate in the secondary spongiosa. These changes reached a new steady state thereafter. Treatment with 200 micrograms hPTH(1-38)/kg/day for 15 days, beginning 30 days after immobilization, significantly increased trabecular bone area, thickness, and number in both primary and secondary spongiosa despite continuous immobilization when compared with controls. The short-term PTH treatment (15 days) significantly increased labeling perimeter, mineral apposition rate, and tissue referent-bone formation rate in the secondary spongiosa and stimulated longitudinal bone growth as compared with the controls. Longer PTH treatment (75 days) further increased trabecular bone area, thickness, and number as compared with controls and groups given short-term PTH treatment (15 days). The bone formation indices in the secondary spongiosa of the longer-term treated rats were lower than those of the short-term treated group, but they were still higher than those of controls. Our findings indicate that PTH treatment stimulates cancellous bone formation, and restores and adds extra cancellous bone to the established, disuse-osteopenic proximal tibial metaphysis of female rats with continuously immobilized right hindlimbs. These results suggest that PTH may be useful in treating disuse-induced osteoporosis in humans.

NASA Program Space Physiology and Countermeasures↗
NASA NTRS1993

Decreased catecholamine secretion from the adrenal medullae of chronically diabetic BB-Wistar rats

Many humans with IDDM eventually lose the capacity to secrete epinephrine from their adrenal medullae. The mechanism for this pathological change is unknown. We hypothesized that this abnormality is attributable to neuropathic changes in the greater splanchnic nerves or in the chromaffin cells that they innervate. To study this hypothesis, we isolated rat adrenal glands, perfused them ex vivo, and measured the epinephrine content of the perfusate under various conditions of stimulation. We used transmural electrical stimulation (20-80 V, at 10 Hz) to induce epinephrine secretion indirectly by selectively activating residual splanchnic nerve terminals within the isolated glands. Under these conditions, epinephrine secretion was severely attenuated in glands from female BB-Wistar rats with diabetes of 4 mo duration compared with their age-matched, nondiabetic controls. These perfused diabetic adrenal medullae also demonstrated decreased catecholamine release in response to direct chromaffin cell depolarization with 20 mM K+, evidence that a functional alteration exists within the chromaffin cells themselves. Nonetheless, total catecholamine content of adrenal medullae from these diabetic rats was not significantly different from controls, indicating that the secretory defect was not simply attributable to a difference in the amount of catecholamines stored and available for release. Herein, we also provide histological evidence of degenerative changes within the cholinergic nerve terminals that innervate these glands.

NASA Discipline Musculoskeletal↗
NASA NTRS1992

Altering the cellular mechanical force balance results in integrated changes in cell, cytoskeletal and nuclear shape

Studies were carried out with capillary endothelial cells cultured on fibronectin (FN)-coated dishes in order to analyze the mechanism of cell and nuclear shape control by extracellular matrix (ECM). To examine the role of the cytoskeleton in shape determination independent of changes in transmembrane osmotic pressure, membranes of adherent cells were permeabilized with saponin (25 micrograms/ml) using a buffer that maintains the functional integrity of contractile microfilaments. Real-time videomicroscopic studies revealed that addition of 250 microM ATP resulted in time-dependent retraction and rounding of permeabilized cells and nuclei in a manner similar to that observed in intact living cells following detachment using trypsin-EDTA. Computerized image analysis confirmed that permeabilized cells remained essentially rigid in the absence of ATP and that retraction was stimulated in a dose-dependent manner as the concentration of ATP was raised from 10 to 250 microM. Maximal rounding occurred by 30 min with projected cell and nuclear areas being reduced by 69 and 41%, respectively. ATP-induced rounding was also accompanied by a redistribution of microfilaments resulting in formation of a dense net of F-actin surrounding retracted nuclei. Importantly, ATP-stimulated changes in cell, cytoskeletal, and nuclear form were prevented in permeabilized cells using a synthetic myosin peptide (IRICRKG) that has been previously shown to inhibit actomyosin filament sliding in muscle. In contrast, both the rate and extent of cell and nuclear rounding were increased in permeabilized cells exposed to ATP when the soluble FN peptide, GRGDSP, was used to dislodge immobilized FN from cell surface integrin receptors.(ABSTRACT TRUNCATED AT 250 WORDS).

Non-NASA Center↗
NASA NTRS1992

Glucose transporters and maximal transport are increased in endurance-trained rat soleus

Voluntary wheel running induces an increase in the concentration of the regulatable glucose transporter (GLUT4) in rat plantaris muscle but not in soleus muscle (K. J. Rodnick, J. O. Holloszy, C. E. Mondon, and D. E. James. Diabetes 39: 1425-1429, 1990). Wheel running also causes hypertrophy of the soleus in rats. This study was undertaken to ascertain whether endurance training that induces enzymatic adaptations but no hypertrophy results in an increase in the concentration of GLUT4 protein in rat soleus (slow-twitch red) muscle and, if it does, to determine whether there is a concomitant increase in maximal glucose transport activity. Female rats were trained by treadmill running at 25 m/min up a 15% grade, 90 min/day, 6 days/wk for 3 wk. This training program induced increases of 52% in citrate synthase activity, 66% in hexokinase activity, and 47% in immunoreactive GLUT4 protein concentration in soleus muscles without causing hypertrophy. Glucose transport activity stimulated maximally with insulin plus contractile activity was increased to roughly the same extent (44%) as GLUT4 protein content in soleus muscle by the treadmill exercise training. In a second set of experiments, we examined whether a swim-training program increases glucose transport activity in the soleus in the presence of a maximally effective concentration of insulin. The swimming program induced a 44% increase in immunoreactive GLUT4 protein concentration. Glucose transport activity maximally stimulated with insulin was 62% greater in soleus muscle of the swimmers than in untrained controls. Training did not alter the basal rate of 2-deoxyglucose uptake.(ABSTRACT TRUNCATED AT 250 WORDS).

Non-NASA Center↗
NASA NTRS1992

Immunological characterization of pulmonary intravascular macrophages

Pulmonary intravascular macrophages (PIMs) are lung macrophages found apposed to the endothelium of pulmonary capillaries. In many species, they are responsible for the clearance of blood-borne particulates and pathogens; however, little else is known about their roles as immunologic effector cells. We compared PIMs with pulmonary alveolar macrophages (PAMs) to determine the relative immunological activities of these two cell populations. Our results suggested that both populations possess similar phagocytic and bactericidal activities. In assays measuring cytotoxicity, PIMs were more cytotoxic than PAMs against virally infected target cells; however, differences between these macrophage populations were not as marked when noninfected targets were used. LPS-stimulated PIMs produced more T-cell proliferative cytokines than PAMs, and both populations of nonstimulated macrophages produced similar amounts of the cytokines. In contrast, PAMs produced more TNF alpha and NO2- than PIMs when both populations were stimulated with LPS; however, nonstimulated PAMs and PIMs produced similar amounts of TNF alpha and NO2. These data suggest that bovine PIMs are immunologically active. Differences between the degrees of activity of PIMs and PAMs indicate that these macrophage populations may have different roles in lung surveillance.

NASA Discipline Cell Biology↗
NASA NTRS1992

Electrical acustimulation relieves vection-induced motion sickness

The aim of this study was to examine the effects of electrical acustimulation on gastric myoelectric activity and severity of symptoms of motion sickness. In experiment 1, 16 Chinese subjects received electrical acustimulation in one of two sessions. In experiment 2, 45 white and black American subjects were randomly divided into three groups: acustimulation, sham acustimulation, and control. Each subject sat in an optokinetic drum for 15 minutes baseline and 15 minutes of drum rotation. Subjects' electrogastrograms and subjective symptoms of motion sickness were obtained. In experiment 1, the mean symptom score and tachyarrhythmia during acustimulation sessions were significantly lower than during no-acustimulation sessions. In experiment 2, the mean symptom score of the acustimulation group was significantly lower than that of the sham-stimulation group and the control group; tachyarrhythmia in the acustimulation group was significantly less than that of the control group but not the sham-stimulation group. In conclusion, electrical acustimulation reduces the severity of symptoms of motion sickness and appears to decrease gastric tachyarrhythmia.

Non-NASA Center↗
NASA NTRS1992

Abnormalities in intracellular calcium regulation and contractile function in myocardium from dogs with pacing-induced heart failure

24 d of rapid ventricular pacing induced dilated cardiomyopathy with both systolic and diastolic dysfunction in conscious, chronically instrumented dogs. We studied mechanical properties and intracellular calcium (Ca2+i) transients of trabeculae carneae isolated from 15 control dogs (n = 32) and 11 dogs with pacing-induced cardiac failure (n = 26). Muscles were stretched to maximum length at 30 degrees C and stimulated at 0.33 Hz; a subset (n = 17 control, n = 17 myopathic) was loaded with the [Ca2+]i indicator aequorin. Peak tension was depressed in the myopathic muscles, even in the presence of maximally effective (i.e., 16 mM) [Ca2+] in the perfusate. However, peak [Ca2+]i was similar (0.80 +/- 0.13 vs. 0.71 +/- 0.05 microM; [Ca2+]o = 2.5 mM), suggesting that a decrease in Cai2+ availability was not responsible for the decreased contractility. The time for decline from the peak of the Cai2+ transient was prolonged in the myopathic group, which correlated with prolongation of isometric contraction and relaxation. However, similar end-diastolic [Ca2+]i was achieved in both groups (0.29 +/- 0.05 vs. 0.31 +/- 0.02 microM), indicating that Cai2+ homeostasis can be maintained in myopathic hearts. The inotropic response of the myopathic muscles to milrinone was depressed compared with the controls. However, when cAMP production was stimulated by pretreatment with forskolin, the response of the myopathic muscles to milrinone was improved. Our findings provide direct evidence that abnormal [Ca2+]i handling is an important cause of contractile dysfunction in dogs with pacing-induced heart failure and suggest that deficient production of cAMP may be an important cause of these changes in excitation-contraction coupling.

Non-NASA Center↗
NASA NTRS1992

Exercise training, glucose transporters, and glucose transport in rat skeletal muscles

It was previously found that voluntary wheel running induces an increase in the insulin-sensitive glucose transporter, i.e., the GLUT4 isoform, in rat plantaris muscle (K. J. Rodnick, J. O. Holloszy, C. E. Mondon, and D. E. James. Diabetes 39: 1425-1429, 1990). The present study was undertaken to determine whether 1) the increase in muscle GLUT4 protein is associated with an increase in maximally stimulated glucose transport activity, 2) a conversion of type IIb to type IIa or type I muscle fibers plays a role in the increase in GLUT4 protein, and 3) an increase in the GLUT1 isoform is a component of the adaptation of muscle to endurance exercise. Five weeks of voluntary wheel running that resulted in a 33% increase in citrate synthase activity induced a 50% increase in GLUT4 protein in epitrochlearis muscles of female Sprague-Dawley rats. The rate of 2-deoxy-glucose transport maximally stimulated with insulin or insulin plus contractions was increased approximately 40% (P less than 0.05). There was no change in muscle fiber type composition, evaluated by myosin ATPase staining, in the epitrochlearis. There was also no change in GLUT1 protein concentration. We conclude that an increase in GLUT4, but not of GLUT1 protein, is a component of the adaptive response of muscle to endurance exercise and that the increase in GLUT4 protein is associated with an increased capacity for glucose transport.

NASA Discipline Cell Biology↗
NASA NTRS1992

Opioid agonists binding and responses in SH-SY5Y cells

SH-SY5Y (human neuroblastoma) cultured cells, known to have mu-opioid receptors, have been used to assess and compare the ability of eight representative mu-selective compounds from diverse opioid families to recognize and activate these receptors. A wide range of receptor affinities spanning a factor of 10,000 was found between the highest affinity fentanyl analogs (Ki = 0.1nM) and the lowest affinity analog, meperidine (Ki = 1 microM). A similar range was found for inhibition of PGE1-stimulated cAMP accumulation with a rank order of activities that closely paralleled binding affinities. Maximum inhibition of cAMP accumulation by each compound was about 80%. Maximum stimulation of GTPase activity (approximately 50%) was also similar for all compounds except the lowest affinity meperidine. Both effects were naloxone reversible. These results provide further evidence that mu-receptors are coupled to inhibition of adenylate cyclase and that the SH-SY5Y cell line is a good system for assessment of mu-agonists functional responses.

Non-NASA Center↗
NASA NTRS1990

Osteoclast cytosolic calcium, regulated by voltage-gated calcium channels and extracellular calcium, controls podosome assembly and bone resorption

The mechanisms of Ca2+ entry and their effects on cell function were investigated in cultured chicken osteoclasts and putative osteoclasts produced by fusion of mononuclear cell precursors. Voltage-gated Ca2+ channels (VGCC) were detected by the effects of membrane depolarization with K+, BAY K 8644, and dihydropyridine antagonists. K+ produced dose-dependent increases of cytosolic calcium ([Ca2+]i) in osteoclasts on glass coverslips. Half-maximal effects were achieved at 70 mM K+. The effects of K+ were completely inhibited by dihydropyridine derivative Ca2+ channel blocking agents. BAY K 8644 (5 X 10(-6) M), a VGCC agonist, stimulated Ca2+ entry which was inhibited by nicardipine. VGCCs were inactivated by the attachment of osteoclasts to bone, indicating a rapid phenotypic change in Ca2+ entry mechanisms associated with adhesion of osteoclasts to their resorption substrate. Increasing extracellular Ca2+ ([Ca2+]e) induced Ca2+ release from intracellular stores and Ca2+ influx. The Ca2+ release was blocked by dantrolene (10(-5) M), and the influx by La3+. The effects of [Ca2+]e on [Ca2+]i suggests the presence of a Ca2+ receptor on the osteoclast cell membrane that could be coupled to mechanisms regulating cell function. Expression of the [Ca2+]e effect on [Ca2+]i was similar in the presence or absence of bone matrix substrate. Each of the mechanisms producing increases in [Ca2+]i, (membrane depolarization, BAY K 8644, and [Ca2+]e) reduced expression of the osteoclast-specific adhesion structure, the podosome. The decrease in podosome expression was mirrored by a 50% decrease in bone resorptive activity. Thus, stimulated increases of osteoclast [Ca2+]i lead to cytoskeletal changes affecting cell adhesion and decreasing bone resorptive activity.

NASA Discipline Musculoskeletal↗
NASA NTRS2005

Vision for Micro Technology Space Missions

It is exciting to contemplate the various space mission applications that Micro Electro Mechanical Systems (MEMS) technology could enable in the next 10-20 years. The primary objective of this chapter is to both stimulate ideas for MEMS technology infusion on future NASA space missions and to spur adoption of the MEMS technology in the minds of mission designers. This chapter is also intended to inform non-space oriented MEMS technologists, researchers and decision makers about the rich potential application set that future NASA Science and Exploration missions will provide. The motivation for this chapter is therefore to lead the reader down a path to identify and it is exciting to contemplate the various space mission applications that Micro Electro Mechanical Systems (MEMS) technology could enable in the next 10-20 years. The primary objective of this chapter is to both stimulate ideas for MEMS technology infusion on future NASA space missions and to spur adoption of the MEMS technology in the minds of mission designers. This chapter is also intended to inform non-space oriented MEMS technologists, researchers and decision makers about the rich potential application set that future NASA Science and Exploration missions will provide. The motivation for this chapter is therefore to lead the reader down a path to identify and consider potential long-term, perhaps disruptive or revolutionary, impacts that MEMS technology may have for future civilian space applications. A general discussion of the potential for MEMS in space applications is followed by a brief showcasing of a few selected examples of recent MEMS technology developments for future space missions. Using these recent developments as a point of departure, a vision is then presented of several areas where MEMS technology might eventually be exploited in future Science and Exploration mission applications. Lastly, as a stimulus for future research and development, this chapter summarizes a set of barriers to progress, design challenges and key issues that must be overcome in order for the community to move on, from the current nascent phase of developing and infusing MEMS technology into space missions, in order to achieve its full future potential.

Dennehy, Neil↗
NASA NTRS2005

In Situ Resource Utilization (ISRU) Experiments for Mars Exploration

In situ resource utilization can best be described as living off the land. In our case the land is the planet Mars. ISRU is based on the idea that some fraction of the consumables, life support and propellant materials do not have to be flown from earth. Rather, they can be manufactured or extracted from resources already present on Mars. The primary resources on Mars are the atmosphere, polar caps and regolith. The atmosphere of Mars is mostly carbon dioxide as shown in the table below. The proportion of oxygen on the other hand is quite small. Still, there is quite a bit of oxygen in the Martian atmosphere, but it is unfortunately tied up with carbon. Thus, one of the goals of ISRU is the separation of breathable oxygen from the carbon dioxide. Several means of separation have been proposed. We have begun experiments on another approach for production of oxygen with carbon monoxide as a useful by product. Our work on a CO2 separator is described later in this report. Regolith melting is another means of obtaining materials. Two materials of interest are iron and silicon. Iron oxide is plentiful on Mars and is of obvious importance for structural components. Silicon is the foundation of solid state devices. Power generation on Mars may be accomplished using silicon solar cells. There is discussion of the feasibility of in situ production of solar cells. This would require a means of extracting silicon from the regolith. We have conducted several experiments concerning melting and glassification of the Mars soil simulant. Other summer faculty fellows have tried various means of processing the stimulant material. These include furnace melting, microwave melting and laser ablation. We have conducted several furnace melting experiments in both air and carbon dioxide environments. We have also carried out experiments to test spark melting in a carbon dioxide atmosphere. These experiments suggest the possibility of using arc melting in a reducing atmosphere. It is important to keep in mind that we are working with a soil stimulant. Any simulant, no matter how chemically similar it is to Martian regolith, may differ in mineralogy. The underlying assumption in this work is that once a glass is formed, any differences between simulant and regolith are unimportant. The exact means of forming the glass do, however, depend on the mineralogy of the regolith. A sample return mission is required to help answer these questions.

Marone, Matt↗
NASA NTRS2005

Fluid-structural dynamics of ground-based and microgravity caloric tests

Microgravity caloric tests aboard the 1983 SpaceLab1 mission produced nystagmus results with an intensity comparable to those elicited during post- and pre- flight tests, thus contradicting the basic premise of Barany's convection hypothesis for caloric stimulation. In this work, we present a dynamic fluid structural analysis of the caloric stimulation of the lateral semicircular canal based on two simultaneous driving forces for the endolymphatic flow: natural convection driven by the temperature-dependent density variation in the bulk fluid and expansive convection caused by direct volumetric displacement of the endolymph during the thermal irrigation. Direct numerical simulations indicate that on earth, the natural convection mechanism is dominant. But in the microgravity environment of orbiting spacecraft, where buoyancy effects are mitigated, expansive convection becomes the sole mechanism for producing cupular displacement. A series of transient 1 g and microgravity case studies are presented to delineate the differences between the dynamics of the 1 g and microgravity endolymphatic flows. The impact of these different flow dynamics on the endolymph-cupula fluid-structural interactions is also analyzed based on the time evolutions of cupular displacement and velocity and the transcupular pressure differences.

Gravitation↗
NASA NTRS2006

Structure and Function of the Snail Statocyst System after a 16-Day Flight on Foton-M-2

In terrestrial gastropod snail Helix lucorum L. we studied the changes after a 16-day exposure to microgravity in: behavior, neural responses to adequate motion stimulation, intersensory interactions between the photosensory pathways and the statocyst receptors, and in expression of the HPeP gene in the statocyst receptors. In behavioral experiments it was found that the latency of body position change to sudden orientation change (flip from horizontal to downwards position) was significantly reduced in the postflight snails. Extracellularly recorded neural responses of the statocyst nerve to adequate motion stimulation in the postflight snails were independent of the motion direction while in the control animals an orientation selectivity was observed. Significant differences in the HPeP gene mRNA expression pattern in the statocyst receptor neurons were observed in postflight (30h) and control snails. Obtained results confirm the possibility to elucidate the influence of microgravity exposure on mechanisms and function of gravireceptors using this simple model animal.

Balaban, P. M.↗
NASA NTRS1999

Encapsulation system for the immunoisolation of living cells

The present invention is drawn to a composition of matter comprising high viscosity sodium alginate, cellulose sulfate and a multi-component polycation. Additionally, the present invention provides methods for making capsules, measuring capsule permeability to immunologically-relevant proteins and treating disease in an animal using encapsulated cells. Over one thousand combinations of polyanions and polycations were examined as polymer candidates suitable for encapsulation of living cells and thirty-three pairs were effective. The combination of sodium alginate, cellulose sulfate, poly(methylene-co-guanidine) hydrochloride, calcium chloride, and sodium chloride produced the most desirable results. Pancreatic islets encapsulated in this multicomponent capsule demonstrated glucose-stimulated insulin secretion in vitro and reversed diabetes without stimulating immune reaction in mice. The capsule formulation and system of the present invention allows independent adjustments of capsule size, wall thickness, mechanical strength and permeability, and offers distinct advantages for immunoisolating cells.

Wang, Taylor G.↗
NASA NTRS1986

Apparatus for detecting at least one predetermined condition and providing an informational signal in response thereto in a medication infusion system

A medication infusion system provides redundant safety and includes condition detecting and informational alarm signal generating apparatus for indicating if (1) a fluid leak occurs in different portions of the system; (2) a programmable input from a patient or physician would result in exceeding a safe dosage limit; (3) the reservoir containing medication has been filled; (4) the intended medication pumping does not correlate with the pumping actually effected; (5) battery voltage is low; (6) the medication reserve is low; and (7) the system has been switched off. The apparatus may provide subcutaneous electrical, thermal, or audible stimulation to the patient and also provides a signal which a physician may monitor. The stimulation may be coded to separately identify each above-listed deviation in nominal system performance. In addition, the number of medication requests are correlated with actual medication dispensing to assure proper operation. An identification scheme is provided which matches the patient with his or her corresponding medication.

Fischell, Robert E.↗
NASA NTRS2006

Iron-Tolerant Cyanobacteria: Ecophysiology and Fingerprinting

Although the iron-dependent physiology of marine and freshwater cyanobacterial strains has been the focus of extensive study, very few studies dedicated to the physiology and diversity of cyanobacteria inhabiting iron-depositing hot springs have been conducted. One of the few studies that have been conducted [B. Pierson, 1999] found that cyanobacterial members of iron depositing bacterial mat communities might increase the rate of iron oxidation in situ and that ferrous iron concentrations up to 1 mM significantly stimulated light dependent consumption of bicarbonate, suggesting a specific role for elevated iron in photosynthesis of cyanobacteria inhabiting iron-depositing hot springs. Our recent studies pertaining to the diversity and physiology of cyanobacteria populating iron-depositing hot springs in Great Yellowstone area (Western USA) indicated a number of different isolates exhibiting elevated tolerance to Fe(3+) (up to 1 mM). Moreover, stimulation of growth was observed with increased Fe(3+) (0.02-0.4 mM). Molecular fingerprinting of unialgal isolates revealed a new cyanobacterial genus and species Chroogloeocystis siderophila, an unicellular cyanobacterium with significant EPS sheath harboring colloidal Fe(3+) from iron enriched media. Our preliminary data suggest that some filamentous species of iron-tolerant cyanobacteria are capable of exocytosis of iron precipitated in cytoplasm. Prior to 2.4 Ga global oceans were likely significantly enriched in soluble iron [Lindsay et al, 2003], conditions which are not conducive to growth of most contemporary oxygenic cyanobacteria. Thus, iron-tolerant CB may have played important physiological and evolutionary roles in Earths history.

Brown, I. I.↗
NASA NTRS2008

Lessons Learned from Previous Space-Borne Sounders as a Guide to Future Sounder Development

Space-borne radio sounding is considered to be the gold standard for electron-density (N(sub e)) measurements compared to other techniques even under low-density conditions, such as N(sub e) < 1/cu cm, when other techniques are known to experience difficulties. These reliable measurements are not restricted to in-situ N(sub e) determinations since a spaceborne sounder can provide vertical N(sub e) profiles (N(sub e)(h)) from the spacecraft altitude to the altitude of maximum N(sub e). Near-conjunction studies involving the International Satellites for Ionospheric Studies (ISIS) satellites in the topside ionosphere and Dynamics Explorer 2 (DE 2) near the altitude of the F-region peak density have verified that, even at the greatest distance from the sounder, the ISIS-derived N(sub e)(h) profiles agree with the DE-2 Langmuir-probe measurements to within about 30% over a density range of more than two decades. Space-borne sounders can also provide N(sub e) profiles along the magnetic-field B, by inverting echoes that are ducted along field-aligned irregularities (FAI), and can provide information about the terrain beneath the satellite by examining surface reflections in the frequency range above the ionospheric penetration frequency. Many nations have launched rocket and satellite radio sounders in geospace over more than 4 decades and there have been sounders on space-probes and in orbit around other planets. Here we will summarize some of the lessons learned from these accomplishments by analyzing data from radio sounders on the Alouette and ISIS satellites and the OEDIPUS and other rockets in the terrestrial ionosphere, the IMAGE satellite in the terrestrial magnetosphere, the Ulysses space probe in Jupiter's 10 plasma torus and the MARSIS satellite in orbit around Mars. The emphasis will be on information deduced concerning (1) fundamental plasma processes and gradients in N, and B in the vicinity of the sounders from sounder-stimulated plasma resonances and short-range echoes involving ion as well as electron motions, (2) the importance of the antenna orientation relative to B for the detection of different plasma resonances, (3) sounder-stimulated plasma phenomena, including FAI, when special plasma conditions are satisfied, (4) the minimum power required for long-range echoes, as indicated by echoes from frequency components of the transmitted pulse and by multiple ducted echoes, and (5) the terrain beneath the satellite from surface reflections. Knowledge of these results should enable the optimum design of a future sounder to satisfy specific science requirements with minimal spacecraft resources.

Benson, Robert F.↗