Status of the NEXT Ion Thruster Long Duration Test

The status of NASA's Evolutionary Xenon Thruster (NEXT) Long Duration Test (LDT) is presented. The test will be conducted with a 36 cm diameter engineering model ion thruster, designated EM3, to validate and qualify the NEXT thruster propellant throughput capability of 450 kg xenon. The ion thruster will be operated at various input powers from the NEXT throttle table. Pretest performance assessments demonstrated that EM3 satisfies all thruster performance requirements. As of June 26, 2005, the ion thruster has accumulated 493 hours of operation and processed 10.2 kg of xenon at a thruster input power of 6.9 kW. Overall ion thruster performance, which includes thrust, thruster input power, specific impulse, and thrust efficiency, has been steady to date with very little variation in performance parameters

Feasibility of Large High-Powered Solar Electric Propulsion Vehicles: Issues and Solutions

Human exploration beyond low Earth orbit will require the use of enabling technologies that are efficient, affordable, and reliable. Solar electric propulsion (SEP) has been proposed by NASA s Human Exploration Framework Team as an option to achieve human exploration missions to near Earth objects (NEOs) because of its favorable mass efficiency as compared to traditional chemical systems. This paper describes the unique challenges and technology hurdles associated with developing a large high-power SEP vehicle. A subsystem level breakdown of factors contributing to the feasibility of SEP as a platform for future exploration missions to NEOs is presented including overall mission feasibility, trip time variables, propellant management issues, solar array power generation, array structure issues, and other areas that warrant investment in additional technology or engineering development

Identifying the science and technology dimensions of emerging public policy issues through horizon scanning

Public policy requires public support, which in turn implies a need to enable the public not just to understand policy but also to be engaged in its development. Where complex science and technology issues are involved in policy making, this takes time, so it is important to identify emerging issues of this type and prepare engagement plans. In our horizon scanning exercise, we used a modified Delphi technique [1]. A wide group of people with interests in the science and policy interface (drawn from policy makers, policy adviser, practitioners, the private sector and academics) elicited a long list of emergent policy issues in which science and technology would feature strongly and which would also necessitate public engagement as policies are developed. This was then refined to a short list of top priorities for policy makers. Thirty issues were identified within broad areas of business and technology; energy and environment; government, politics and education; health, healthcare, population and aging; information, communication, infrastructure and transport; and public safety and national security.Public policy requires public support, which in turn implies a need to enable the public not just to understand policy but also to be engaged in its development. Where complex science and technology issues are involved in policy making, this takes time, so it is important to identify emerging issues of this type and prepare engagement plans. In our horizon scanning exercise, we used a modified Delphi technique [1]. A wide group of people with interests in the science and policy interface (drawn from policy makers, policy adviser, practitioners, the private sector and academics) elicited a long list of emergent policy issues in which science and technology would feature strongly and which would also necessitate public engagement as policies are developed. This was then refined to a short list of top priorities for policy makers. Thirty issues were identified within broad areas of business and technology; energy and environment; government, politics and education; health, healthcare, population and aging; information, communication, infrastructure and transport; and public safety and national security

Power and Propulsion System Design for Near-Earth Object Robotic Exploration

Near-Earth Objects (NEOs) are exciting targets for exploration; they are relatively easy to reach but relatively little is known about them. With solar electric propulsion, a vast number of interesting NEOs can be reached within a few years and with extensive flexibility in launch date. An additional advantage of electric propulsion for these missions is that a spacecraft can be small, enabling a fleet of explorers launched on a single vehicle or as secondary payloads. Commercial, flight-proven Hall thruster systems have great appeal based on their performance and low cost risk, but one issue with these systems is that the power processing units (PPUs) are designed for regulated spacecraft power architectures which are not attractive for small NEO missions. In this study we consider the integrated design of power and propulsion systems that utilize the capabilities of existing PPUs in an unregulated power architecture. Models for solar array and engine performance are combined with low-thrust trajectory analyses to bound spacecraft design parameters for a large class of NEO missions, then detailed array performance models are used to examine the array output voltage and current over a bounded mission set. Operational relationships between the power and electric propulsion systems are discussed, and it is shown that both the SPT-100 and BPT-4000 PPUs can perform missions over a solar range of 0.7 AU to 1.5 AU - encompassing NEOs, Venus, and Mars - within their operable input voltage ranges. A number of design trades to control the array voltage are available, including cell string layout, array offpointing during mission operations, and power draw by the Hall thruster system

G3BP–Caprin1–USP10 complexes mediate stress granule condensation and associate with 40S subunits

Mammalian stress granules (SGs) contain stalled translation preinitiation complexes that are assembled into discrete granules by specific RNA-binding proteins such as G3BP. We now show that cells lacking both G3BP1 and G3BP2 cannot form SGs in response to eukaryotic initiation factor 2α phosphorylation or eIF4A inhibition, but are still SG-competent when challenged with severe heat or osmotic stress. Rescue experiments using G3BP1 mutants show that phosphomimetic G3BP1-S149E fails to rescue SG formation, whereas G3BP1-F33W, a mutant unable to bind G3BP partner proteins Caprin1 or USP10, rescues SG formation. Caprin1/USP10 binding to G3BP is mutually exclusive: Caprin binding promotes, but USP10 binding inhibits, SG formation. G3BP interacts with 40S ribosomal subunits through its RGG motif, which is also required for G3BP-mediated SG formation. We propose that G3BP mediates the condensation of SGs by shifting between two different states that are controlled by the phosphorylation of S149 and by binding to Caprin1 or USP10

Not-so-suspect terrane: Constraints on the crustal evolution of the Rudall Province

Time-constrained isotopic datasets permit the evaluation of tectonic processes, including continental collision, rifting, and the origins of terrane fragments. The Rudall Province, in the Paterson Orogen, is part of the West Australian Craton (WAC) and now lies to the east of the Archaean Pilbara Craton. Components within the Rudall Province have previously been linked to the Arunta Orogen of the North Australian Craton (NAC) based on similarities in timing of magmatism, deformation, and metamorphism and hence have been referred to as suspect terranes, with respect to the WAC. The Rudall Province is divided into three lithotectonic elements known as the Talbot, Connaughton, and Tabletop Terranes. The southern two terranes (Talbot and Connaughton) were affected by magmatism related to collision between the West and North Australian Cratons, during the 1800–1765 Ma Yapungku Orogeny. Zircon crystals in both Talbot and Connaughton terranes have a Hf isotopic and, in the case of inheritance, U–Pb age affinity to detritus that originated from the Capricorn Orogen basement in the WAC. Furthermore, the Hf isotopic composition of c. 1800 Ma magmatic zircons within the Rudall Province has similarity to components within the c. 1800 Ma Bridget Suite of the East Pilbara Terrane, which has an indubitable association to the Pilbara Craton. Hence, sources for all isotopic compositions preserved within the Rudall Province can be found within the proximal WAC. There is no necessity to invoke transfer of exotic NAC lithotectonic elements to the West Australian Craton margin and to suggest an accretionary style of orogenesis for the Rudall Province. The Tabletop Terrane has been regarded as a different far-travelled block with crust distinct from the other components of the Rudall Province. However, the currently available dataset implies that the Tabletop Terrane was derived from crust of similar composition to the Connaughton and Talbot terranes. A distinctive phase of crust formation at 1900 Ma is indicated by zircons, with mantle-like oxygen isotope ratios, within a c. 1450 Ma monzogranite of the Talbot Terrane. This timing of crust formation implies an affinity to a major deep lithospheric source of similar age recognized in the Musgrave Province and Edmund Basin. These data indicate that the major suture between the North and West Australian Cratons lies to the east of the Rudall Province

Not-so-suspect terrane : constraints on the crustal evolution of the Rudall Province

Time-constrained isotopic datasets permit the evaluation of tectonic processes, including continental collision, rifting, and the origins of terrane fragments. The Rudall Province, in the Paterson Orogen, is part of the West Australian Craton (WAC) and now lies to the east of the Archaean Pilbara Craton. Components within the Rudall Province have previously been linked to the Arunta Orogen of the North Australian Craton (NAC) based on similarities in timing of magmatism, deformation, and metamorphism and hence have been referred to as suspect terranes, with respect to the WAC. The Rudall Province is divided into three lithotectonic elements known as the Talbot, Connaughton, and Tabletop Terranes. The southern two terranes (Talbot and Connaughton) were affected by magmatism related to collision between the West and North Australian Cratons, during the 1800-1765. Ma Yapungku Orogeny. Zircon crystals in both Talbot and Connaughton terranes have a Hf isotopic and, in the case of inheritance, U-Pb age affinity to detritus that originated from the Capricorn Orogen basement in the WAC. Furthermore, the Hf isotopic composition of c. 1800. Ma magmatic zircons within the Rudall Province has similarity to components within the c. 1800. Ma Bridget Suite of the East Pilbara Terrane, which has an indubitable association to the Pilbara Craton. Hence, sources for all isotopic compositions preserved within the Rudall Province can be found within the proximal WAC. There is no necessity to invoke transfer of exotic NAC lithotectonic elements to the West Australian Craton margin and to suggest an accretionary style of orogenesis for the Rudall Province.The Tabletop Terrane has been regarded as a different far-travelled block with crust distinct from the other components of the Rudall Province. However, the currently available dataset implies that the Tabletop Terrane was derived from crust of similar composition to the Connaughton and Talbot terranes.A distinctive phase of crust formation at 1900. Ma is indicated by zircons, with mantle-like oxygen isotope ratios, within a c. 1450. Ma monzogranite of the Talbot Terrane. This timing of crust formation implies an affinity to a major deep lithospheric source of similar age recognized in the Musgrave Province and Edmund Basin. These data indicate that the major suture between the North and West Australian Cratons lies to the east of the Rudall Province.19 page(s