SEARCH · Search NASA

Results for “Tether”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 865 records · Page 48

All sources NASA NTRS DOE OSTI

NASA NTRS1998

A Review of Scientific and Technological Results from the TSS-1R Mission

The Tethered Satellite System (TSS) program was designed to provide a unique opportunity to explore certain space plasma-electrodynamic processes and the orbital mechanics of a gravity-gradient stabilized system of two satellites linked by a long conducting tether. A unique data set was obtained during deployment which has allowed significant science to be accomplished. This paper focuses on results from the TSS-1R mission that are most important to the future technological applications of electrodynamic tethers in space, in particular, the current collection process. Of particular significance is an apparent transition of the physics of current collection when the potential of the collecting body becomes greater than the ram energy of the ionospheric atomic oxygen ions. Previous theoretical models of current collection were electrostatic, assuming that the orbital motion of the system, which is highly subsonic with respect to electron thermal motion, was unimportant. This may still be acceptable for the case of relatively slow-moving sounding rockets. However, the TSS-1R results show that motion relative to the plasma must be accounted for in orbiting systems.

Stone, N. H.↗

NASA NTRS1996

Electron Flow to a Satellite at High Positive Potential

The Tethered Satellite System (TSS) is designed to deploy a 1.6 m diameter spherical satellite a distance of 20 km above the space shuttle orbiter on an insulated conducting tether. Because of the passage of the conducting tether through the earth's magnetic field, an emf is generated producing a positive satellite potential of about 5000 V. Electron flow under the influence of this high positive potential is the focus of the present analysis. The ionospheric parameters at TSS orbit altitude are; thermal velocity of electrons, 1.9 x 10(exp 5) M/S, thermal velocity of the ions, 1.1 x 10(exp 3) m/s, velocity of the satellite 8 x 10(exp 3) m/s. The electrons, with a Debye length, lambda(D) = 0.49 cm, spiral about the earth's magnetic field lines (0.4 Gauss) with a radius of about 3 cm and the ions spiral with a radius of 5 m. Under these conditions, the electron thermal energy, kT is 0.17 eV. The TSS satellite radius, r(p) is 163 Debye lengths. There is an extensive literature on the interaction of satellites with the near-earth ionospheric plasma. The space charge limitation to the electron current collected by a sphere at positive electrical potential was calculated by Langmuir and Blodgett (1924). Parker and Murphy (1967) recognized the importance of the influence of the earth's magnetic field and used the guiding center approximation to calculate the electron current collected by a positive charged satellite. More recently Ma and Schunk (1989) have calculated the time dependent flow of electrons to a spherical satellite at positive potential utilizing numerical methods and Sheldon (1994) used similar methods to solve this problem for the steady state. In order to analyze some of the phenomena that occurred in the ionosphere during the TSS flights, it would be useful to have analytic expressions for these electron flows. The governing equations are very complex and an exact analytical solution is not likely. An approximate analytical solution is feasible however, and the results of one attempt are presented herein.

Sheldon, John W.↗

NASA NTRS1999

The Biomechanics of Exercise Countermeasures

The Penn State Zero-gravity Simulator (PSZS) is a device developed by the Center for Locomotion Studies (CELOS) to enable ground studies of exercise countermeasures for the bone loss that has been shown to occur during long-term exposure to zero gravity (0G). The PSZS simulates 0G exercise by providing a suspension system that holds an individual in a horizontal (supine) position above the floor in order to enable exercise on a wall-mounted treadmill. Due to this orientation, exercise performed in the PSZS is free of the force of -ravity in the direction that would normally contribute to ground reaction forces. In order for movements to be more similar to those in 0G, a constant force suspension of each segment (equal to the segment weight) is provided regardless of limb position. During the preliminary development of the PSZS, CELOS researchers also designed an optional gravity-replacement simulation feature for the PSZS. This feature was a prototype tethering system that consisted of a spring tension system to pull an exercising individual toward the treadmill. The immediate application of the tethering system was to be the provision of gravity-replacement loading so that exercise in 0G- and 1G-loading conditions could be compared, and the PSZS could then be used to evaluate exercise countermeasures for bone loss during space flight. This tethering system would also be a model for the further refinement of gravity-replacement systems provided for astronaut usage while performing prescribed exercise countermeasures for bone loss during long-term space flights.

Cavanagh, Peter R.↗

NASA NTRS2000

Current-Produced Magnetic Field Effects on Current Collection

Current collection by an infinitely long, conducting cylinder in a magnetized plasma, taking into account the magnetic field of the collected current, is discussed. A region of closed magnetic surfaces disconnects the cylinder from infinity. Due to this, the collected current depends on the ratio between this region and the plasma sheath region and, under some conditions, current reduction arises. It is found that the upper-bound limit of current collection is reduced due to this change of magnetic field topology. The effect can be essential even if the orbit-limited model of current collection is valid. This model is used to find the reduction of the total current collected by a cylinder (e.g., a bare tether). Such effect strongly depends on plasma density. The results are applied to a tether system in the ionosphere. For this case, it is found that current reduction can be significant for long tethers in typical dayside ionospheric conditions.

Khazanov, G. V.↗

NASA NTRS2000

Current-Produced Magnetic Field Effects on Current Collection

Current collection by an infinitely long, conducting cylinder in a magnetized plasma, taking into account the magnetic field of the collected current, is discussed. A region of closed magnetic surfaces disconnects the cylinder from infinity. Owing to this, the collected current depends on the ratio between this region and the plasma sheath region and, under some conditions, current reduction arises. It is found that the upper bound limit of current collection is reduced due to this change of magnetic field topology. The effect can be substantial even if the orbit-limited model of current collection is valid. This model is used to find the reduction of the total current collected by a cylinder (e.g., a bare tether). It is shown that this effect strongly depends on plasma density. The results are applied to a tether system in the ionosphere, and it is found that current reduction can be significant for long tethers in typical dayside ionospheric conditions.

Khazanov, G. V.↗

NASA NTRS1996

Sharp Hypervelocity Aerodynamic Research Probe

The objective of this flight demonstration is to deploy a slender-body hypervelocity aerodynamic research probe (SHARP) from an orbiting platform using a tether, deorbit and fly it along its aerothermal performance constraint, and recover it intact in mid-air. To accomplish this objective, two flight demonstrations are proposed. The first flight uses a blunt-body, tethered reentry experiment vehicle (TREV) to prove out tethered deployment technology for accurate entries, a complete SHARP electronics suite, and a new soft mid-air helicopter recovery technique. The second flight takes advantage of this launch and recovery capability to demonstrate revolutionary sharp body concepts for hypervelocity vehicles, enabled by new Ultra-High Temperature Ceramics (UHTCs) recently developed by Ames Research Center. Successful demonstration of sharp body hypersonic vehicle technologies could have radical impact on space flight capabilities, including: enabling global reentry cross range capability from Station, eliminating reentry communications blackout, and allowing new highly efficient launch systems incorporating air breathing propulsion and zeroth staging.

Bull, Jeffrey↗

NASA NTRS2002

Minimum Arc Threshold Voltage Experiments on Extravehicular Mobility Unit Samples

The International Space Station (ISS) is now under construction in Low Earth Orbit (LEO). The process of building the ISS requires that astronauts carry out many Extravehicular Activities. To protect the astronauts form the hazardous space environment, they are required to wear a suit known as the Extravehicular Mobility Unit (EMU). For most Extra-Vehicular Activities (EVAs) the EMU is tethered to ISS via a steel safety tether. During the course of an EVA it is common for the safety tether to contact exposed metal on both the ISS and the EMU. In this case, the single point ground of the EMU would be at the same potential as the ISS with respect to the LEO Plasma. In the event that the metal structure of the ISS begins to charge negative of the plasma potential as a result of electron collection by the ISS photovoltaic arrays, then the EMU would also be driven to a negative potential. Anodized aluminum components on the EMU would then begin to develop a charge across their amortization layer as ions from the plasma are collected. In the case where large negative potentials are applied to the EMU, dielectric breakdown may occur as a large voltage difference is developed across the thin amortization layer (oxide). The resulting arc plasma may in turn couple to the charge accumulated on the nearby ISS anodized debris shields and thereby generate a large current flow through the metal EMU structure. Current flow through the EMU could result in an electrocution hazard for the Crew Member inside the EMU - and therefore represents an important safety concern. To address this concern, a series of experiments have been undertaken. In each experiment specially prepared anodized aluminum samples were placed in a LEO representative plasma and charged until dielectric breakdown occurred in the form of an arc. This process was repeated a number of times for three sets of samples. During each test the arc voltage and current were monitored. A statistical treatment of the arc voltage threshold will be presented. In addition, safe operating voltages for the EMU are suggested.

Schneider, Todd↗

NASA NTRS2003

Plasma Sheath Behavior of the ProSEDS Delta II

The Propulsive Small Expendable Deployer System (ProSEDS) mission is a demonstration of the orbit lowering capabilities of an electrodynamic tether. The system is sequenced through various electrical modes, involving both open circuit and closed circuit configurations, so that the performance capabilities of the system can be studied. Ionospheric electrons are collected on the upper end of the bare tether, conducted through the tether, and returned to the ionosphere at the lower end (Delta I1 2nd stage) via the operation of a Hollow Cathode Plasma Contactor (HCPC). The working gas of the HCPC is xenon. Environmental plasma measurements and sheath potential are obtained from the Differential Ion Flux Probe w/Mass Analysis (DIFPM) and Langmuir Probe and Spacecraft Potential (LPSP) instruments. Each instrument has three sensors symmetrically placed about the strut section of the Delta 2nd stage. A magnetometer is also included in the ProSEDS instrumentation suite. An initial analysis of the rocket stage sheath behavior as a function of ProSEDS configuration (open or closed circuit), ambient ionospheric density, orientation to velocity vector (ram-wake influence), and magnetic field orientation is presented. An initial assessment on how well the plasma contactor grounded the rocket stage is also presented.

Wright, K. H.↗

NASA NTRS2003

Evidence for Gradual External Reconnection Before Explosive Eruption of a Solar Filament

We observe a slowly-evolving quiet region solar eruption of 1999 April 18, using EUV images from the EUV Imaging Telescope (EIT) on the Solar and Heliospheric Observatory (SOHO), and soft X-ray images from the Soft X-ray Telescope (SXT) on Yohkoh. Using difference images, where an early image is subtracted from later images, we examine dimmings and brightenings in the region for evidence of the eruption mechanism. A filament rose slowly at about 1 kilometer per second for six hours before being rapidly ejected at about 16 kilometers per second, leaving flare brightenings and post-flare loops in its wake. Magnetograms from the Michelson Doppler Imager (MDI) on SOHO show that the eruption occurred in a large quadrupo1ar magnetic region, with the filament located on the neutral line of the quadrupole's central inner lobe, between the inner two of the four polarity domains. In step with the slow rise, subtle EIT dimmings commence and gradually increase over the two polarity domains on one side of the filament, i.e. in some of the loops of one of the two side lobes of the quadrupole. Concurrently, soft X-ray brightenings gradually increase in both side lobes. Both of these effects suggest heating in the side-lobe magnetic arcades, which gradually increase over several hours before the fast eruption. Also during the slow pre-eruption phase, SXT dimmings gradually increase in the feet and legs of the central lobe, indicating expansion of the central-lobe magnetic arcade enveloping the filament. During the rapid ejection, these dimmings rapidly grow in darkness and in area, especially in the ends of the sigmoid field that erupts with the filament, and flare brightenings begin underneath the fast-moving but still low-altitude filament. We consider two models for explaining the eruption: "breakout," which says that reconnection occurs high above the filament prior to eruption, and tether cutting, which says that the eruption is unleashed by reconnection beneath the filament. The pre-eruption evolution is consistent with gradual breakout that led to (and perhaps caused) the fast eruption. Tether-cutting reconnection below the filament begins early in the rapid ejection, but our data are not complete enough to determine whether this reconnection began early enough to be the cause of the fast-phase onset. Thus, our observations are consistent with gradual breakout reconnection causing the long slow rise of the filament, but allow the cause of the sudden onset of the explosive fast phase to be either a jump in the breakout reconnection rate or the onset of runaway tether-cutting reconnection, or both.

Sterling, Alphonse C.↗

NASA NTRS2003

Low Earth Orbit Plasma Variability Model

The empirical International Reference Ionosphere is a widely used model for estimating low Earth orbit plasma characteristics for use in spacecraft design and mission analysis. The climatological model provides mean values of plasma density, temperature, composition, and other ionospheric parameters that can be used to estimate the average magnitude of spacecraft charging, current collection for electrodynamic tethers, and other effects on spacecraft design. Mean IRI parameters are not adequate to answer questions such as what is the maximum or minimum value of the spacecraft potential, does the maximum spacecraft potential exceed a program requirement, will an electrodynamic tether provide adequate drag to deorbit a satellite at end of life, and will the tether provide sufficient thrust to reboost a spacecraft at any time in the solar cycle. These questions require estimates of the variability of the ionospheric environment about the mean values. This presentation describes the status of work at MSFC to develop an empirical ionospheric variability model that can be used in conjunction with the climatological IRI model to provide both mean ionospheric parameters and variations of the environment about the mean. Our technique will use an extensive database of satellite and radar observations of the electron density and temperature to derive variances of the data about the model values. The variances will then be incorporated into Fortran wrapper software that calls the IRI-2001 model and provides statistical estimates of the deviation of the environment about the mean IRI values. We will provide an update on the state of the database development and provide examples of analysis and modeling efforts completed specifically for an International Space Station application.

Minow, Joseph I.↗

NASA NTRS2004

Evidence for Gradual External Reconnection Before Explosive Eruption of a Solar Filament

We observe a slowly evolving quiet-region solar eruption of 1999 April 18, using extreme-ultraviolet (EUV) images from the EUV Imaging Telescope (EIT) on the Solar and Heliospheric Observatory (SOHO) and soft X-ray images from the Soft X-ray Telescope (SXT) on Yohkoh. Using difference images, in which an early image is subtracted from later images, we examine dimmings and brightenings in the region for evidence of the eruption mechanism. A filament rose slowly at about 1 km/s for 6 hours before being rapidly ejected at about 16 km/s leaving flare brightenings and postflare loops in its wake. Magnetograms from the Michelson Doppler Imager (MDI) on SOHO show that the eruption occurred in a large quadrupolar magnetic region with the filament located on the neutral line of the quadrupole s central inner lobe between the inner two of the four polarity domains. In step with the slow rise, subtle EIT dimmings commence and gradually increase over the two polarity domains on one side of the filament, i.e., in some of the loops of one of the two sidelobes of the quadrupole. Concurrently, soft X-ray brightenings gradually increase in both sidelobes. Both of these effects suggest heating in the sidelobe magnetic arcades. which gradually increase over several hours before the fast eruption. Also, during the slow pre- eruption phase, SXT dimmings gradually increase in the feet and legs of the central lobe, indicating expansion of the central-lobe magnetic arcade enveloping the filament. During the rapid ejection. these dimmings rapidly grow in darkness and in area, especially in the ends of the sigmoid field that erupts with the filament. and flare brightenings begin underneath the fast-moving but still low-altitude filament. We consider two models for explaining the eruption: "breakout. which says that reconnection occurs high above the filament prior to eruption, and tether cutting, which says that the eruption is unleashed by reconnection beneath the filament. The pre-eruption evolution is consistent with gradual breakout that led to (and perhaps caused) the fast eruption. Tether-cutting reconnection below the filament begins early in the rapid ejection. but our data are not complete enough to determine whether this reconnection began early enough to be the cause of the fast-phase onset. Thus, our observations are consistent with gradual breakout reconnection causing the long slow rise of the filament, but allow the cause of the sudden onset of the explosive fast phase to be either a jump in the breakout reconnection rate or the onset of runaway tether-cutting reconnection. or both.

Sterling, Alphonse C.↗

NASA NTRS2004

Technology Development and Demonstration Concepts for the Space Elevator

During the 1990s several discoveries and advances in the development of carbon nano-tube (CNT) materials indicated that material strengths many times greater than common high-strength composite materials might be possible. Progress in the development of this material led to renewed interest in the space elevator concept for construction of a tether structure from the surface of the Earth through a geostationary orbit (GEO) and thus creating a new approach to Earth-to-orbit transportation infrastructures. To investigate this possibility the author, in 1999, managed for NASA a space elevator work:hop at the Marshall Space Flight Center to explore the potential feasibility of space elevators in the 21 century, and to identify the critical technologies and demonstration missions needed to make development of space elevators feasible. Since that time, a NASA Institute for Advanced Concepts (NIAC) funded study of the Space Elevator proposed a concept for a simpler first space elevator system using more near-term technologies. This paper will review some of the latest ideas for space elevator development, the critical technologies required, and some of the ideas proposed for demonstrating the feasibility for full-scale development of an Earth to GEO space elevator. Critical technologies include CNT composite materials, wireless power transmission, orbital object avoidance, and large-scale tether deployment and control systems. Numerous paths for technology demonstrations have been proposed utilizing ground experiments, air structures. LEO missions, the space shuttle, the international Space Station, GEO demonstration missions, demonstrations at the lunar L1 or L2 points, and other locations. In conclusion, this paper finds that the most critical technologies for an Earth to GEO space elevator include CNT composite materials development and object avoidance technologies; that lack of successful development of these technologies need not preclude continued development of space elevator systems in general; and that the critical technologies required for the Earth to GEO space elevator are not required for similar systems at the Moon, Mars, Europa, or for orbital tether systems at GEO, Luna, and other locations.

Smitherman, David V., Jr.↗

NASA NTRS1996

Activation of a Ca(2+)-dependent protein kinase involves intramolecular binding of a calmodulin-like regulatory domain

Ca(2+)-dependent protein kinases (CDPKs) are regulated by a C-terminal calmodulin-like domain (CaM-LD). The CaM-LD is connected to the kinase by a short junction sequence which contains a pseudosubstrate autoinhibitor. To understand how the CaM-LD regulates a CDPK, a recombinant CDPK (isoform CPK-1 from Arabidopsis, accession no. L14771) was made as a fusion protein in Escherichia coli. We show here that a truncated CDPK lacking a CaM-LD (e.g. mutant delta NC-26H) can be activated by exogenous calmodulin or an isolated CaM-LD (Kact approximately 2 microM). We propose that Ca2+ activation of a CDPK normally occurs through intramolecular binding of the CaM-LD to the junction. When the junction and CaM-LD are made as two separate polypeptides, the CaM-LD can bind the junction in a Ca(2+)-dependent fashion with a dissociation constant (KD) of 6 x 10(-6) M, as determined by kinetic binding analyses. When the junction and CaM-LD are tethered in a single polypeptide (e.g. in protein JC-1), their ability to engage in bimolecular binding is suppressed (e.g. the tethered CaM-LD cannot bind a separate junction). A mutation which disrupts the putative CaM-LD binding sequence (e.g. substitution LRV-1444 to DLPG) appears to block intramolecular binding, as indicated by the restored ability of a tethered CaM-LD to engage in bimolecular binding. This mutation, in the context of a full-length enzyme (mutant KJM46H), appears to block Ca2+ activation. Thus, a disruption of intramolecular binding correlates with a disruption of the Ca2+ activation mechanism. CDPKs provide the first example of a member of the calmodulin superfamily where a target binding sequence is located within the same polypeptide.

Non-NASA Center↗

NASA NTRS2006

MXER Simulation Study (Appendix B)

The task of prediction of the motion of a momentum exchange system with a 9-digit accuracy is extremely challenging, and it is relentlessly testing our ability to gain fundamental insights into the nature of the tether dynamics in this system. It has been show that the modal decomposition approach developed in the first part of this study is a very powerful and precise tool for the simulation of the dynamics of momentum exchange tethers. However, to get a prediction with required accuracy using this tool, one must have precise inputs, including the initial state, system parameters, and the environmental models. In simulations, the tether tip positioning has been observed to be quite sensitive to even small variations of the parameters involved in the calculations. It is therefore imperative that precise estimation and control algorithms be developed to compensate for the inevitable uncertainties and support high precision rendezvous.

Levin, E. M.↗

NASA NTRS2005

SAFER Inspection of Space Shuttle Thermal Protection System

In the aftermath of the space shuttle Columbia accident, it quickly became clear that new methods would need to be developed that would provide the capability to inspect and repair the shuttle's thermal protection system (TPS). A boom extension to the Remote Manipulator System (RMS) with a laser topography sensor package was identified as the primary means for measuring the damage depth in acreage tile as well as scanning Reinforced Carbon- Carbon (RCC) surfaces. However, concern over the system's fault tolerance made it prudent to investigate alternate means of acquiring close range photographs and contour depth measurements in the event of a failure. One method that was identified early was to use the Simplified Aid For EVA Rescue (SAFER) propulsion system to allow EVA access to damaged areas of concern. Several issues were identified as potential hazards to SAFER use for this operation. First, the ability of an astronaut to maintain controlled flight depends upon efficient technique and hardware reliability. If either of these is insufficient during flight operations, a safety tether must be used to rescue the crewmember. This operation can jeopardize the integrity of the Extra-vehicular Mobility Unit (EMU) or delicate TPS materials. Controls were developed to prevent the likelihood of requiring a tether rescue, and procedures were written to maximize the chances for success if it cannot be avoided. Crewmember ability to manage tether cable tension during nominal flight also had to be evaluated to ensure it would not negatively affect propellant consumption. Second, although propellant consumption, flight control, orbital dynamics, and flight complexity can all be accurately evaluated in Virtual Reality (VR) Laboratory at Johnson Space Center, there are some shortcomings. As a crewmember's hand is extended to simulate measurement of tile damage, it will pass through the vehicle without resistance. In reality, this force will push the crewmember away from the vehicle, and could induce a moment which, if strong enough, could saturate the attitude control system in SAFER. This raises the concern that additional propellant will be consumed to maintain controlled flight. To account for this, the fidelity of the Virtual Reality simulation was improved to include the effect of crewmember contact with the vehicle during SAFER flight. In addition, while participating in VR simulations, the subject is in shirt sleeves and sits in a chair. This does not provide a flight-like representation of body position awareness. To prevent inadvertent contact with tile or RCC, other facilities were utilized to establish crew preferences for body attitude and tool configuration. Finally, a study was performed to determine if attitude constraints are needed for the Space shuttle and International Space Station to reduce SAFER flight difficulty.

Scoville, Zebulon C.↗

NASA NTRS2007

NASA Bluetooth Wireless Communications

NASA has been interested in wireless communications for many years, especially when the crew size of the International Space Station (ISS) was reduced to two members. NASA began a study to find ways to improve crew efficiency to make sure the ISS could be maintained with limited crew capacity and still be a valuable research testbed in Low-Earth Orbit (LEO). Currently the ISS audio system requires astronauts to be tethered to the audio system, specifically a device called the Audio Terminal Unit (ATU). Wireless communications would remove the tether and allow astronauts to freely float from experiment to experiment without having to worry about moving and reconnecting the associated cabling or finding the space equivalent of an extension cord. A wireless communication system would also improve safety and reduce system susceptibility to Electromagnetic Interference (EMI). Safety would be improved because a crewmember could quickly escape a fire while maintaining communications with the ground and other crewmembers at any location. In addition, it would allow the crew to overcome the volume limitations of the ISS ATU. This is especially important to the Portable Breathing Apparatus (PBA). The next generation of space vehicles and habitats also demand wireless attention. Orion will carry up to six crewmembers in a relatively small cabin. Yet, wireless could become a driving factor to reduce launch weight and increase habitable volume. Six crewmembers, each tethered to a panel, could result in a wiring mess even in nominal operations. In addition to Orion, research is being conducted to determine if Bluetooth is appropriate for Lunar Habitat applications.

Miller, Robert D.↗

NASA NTRS2008

Deployable Wireless Camera Penetrators

A lightweight, low-power camera dart has been designed and tested for context imaging of sampling sites and ground surveys from an aerobot or an orbiting spacecraft in a microgravity environment. The camera penetrators also can be used to image any line-of-sight surface, such as cliff walls, that is difficult to access. Tethered cameras to inspect the surfaces of planetary bodies use both power and signal transmission lines to operate. A tether adds the possibility of inadvertently anchoring the aerobot, and requires some form of station-keeping capability of the aerobot if extended examination time is required. The new camera penetrators are deployed without a tether, weigh less than 30 grams, and are disposable. They are designed to drop from any altitude with the boost in transmitting power currently demonstrated at approximately 100-m line-of-sight. The penetrators also can be deployed to monitor lander or rover operations from a distance, and can be used for surface surveys or for context information gathering from a touch-and-go sampling site. Thanks to wireless operation, the complexity of the sampling or survey mechanisms may be reduced. The penetrators may be battery powered for short-duration missions, or have solar panels for longer or intermittent duration missions. The imaging device is embedded in the penetrator, which is dropped or projected at the surface of a study site at 90 to the surface. Mirrors can be used in the design to image the ground or the horizon. Some of the camera features were tested using commercial "nanny" or "spy" camera components with the charge-coupled device (CCD) looking at a direction parallel to the ground. Figure 1 shows components of one camera that weighs less than 8 g and occupies a volume of 11 cm3. This camera could transmit a standard television signal, including sound, up to 100 m. Figure 2 shows the CAD models of a version of the penetrator. A low-volume array of such penetrator cameras could be deployed from an aerobot or a spacecraft onto a comet or asteroid. A system of 20 of these penetrators could be designed and built in a 1- to 2-kg mass envelope. Possible future modifications of the camera penetrators, such as the addition of a chemical spray device, would allow the study of simple chemical reactions of reagents sprayed at the landing site and looking at the color changes. Zoom lenses also could be added for future use.

Badescu, Mircea↗

NASA NTRS2010

Grid-Sphere Electrodes for Contact with Ionospheric Plasma

Grid-sphere electrodes have been proposed for use on the positively biased end of electrodynamic space tethers. A grid-sphere electrode is fabricated by embedding a wire mesh in a thin film from which a spherical balloon is formed. The grid-sphere electrode would be deployed from compact stowage by inflating the balloon in space. The thin-film material used to inflate the balloon is formulated to vaporize when exposed to the space environment. This would leave the bare metallic spherical grid electrode attached to the tether, which would present a small cross-sectional area (essentially, the geometric wire shadow area only) to incident neutral atoms and molecules. Most of the neutral particles, which produce dynamic drag when they impact a surface, would pass unimpeded through the open grid spaces. However, partly as a result of buildup of a space charge inside the grid-sphere, and partially, the result of magnetic field effects, the electrode would act almost like a solid surface with respect to the flux of electrons. The net result would be that grid-sphere electrodes would introduce minimal aerodynamic drag, yet have effective electrical-contact surface areas large enough to collect multiampere currents from the ionospheric plasma that are needed for operation of electrodynamic tethers. The vaporizable-balloon concept could also be applied to the deployment of large radio antennas in outer space.

Stone, Nobie H.↗