摘要:

The previous papers presented at STAIF 2002 and STAIF 2003 discussed the design, fabrication and characterization of the evaporator section and the initial test cell of a planar MEMS loop heat pipe based upon coherent porous silicon or “CPS” technology. The potentially revolutionary advantage of CPS technology is that it is planar and allows for pores or capillaries of absolutely uniform diameter. Coherent porous silicon can be mass‐produced by various MEMS fabrication techniques. The preliminary experiments made with the original test structure exhibited the desired temperature and pressure differences, but these differences were extremely small and oscillatory. This paper describes modifications made to the initial test cell design, which were intended to improve its evacuated, closed loop performance. Included among these changes were the redesign of the compensation chamber and condenser, an increase in the porosity of the coherent porous silicon wick, the fabrication of silicon top “hot” plates with an increased depth of the vapor reservoir and the integration of metal resistive heater elements onto the backside of the top plates to simulate the input heat. Some changes were made in the test sequence to produce more discernable differences in temperatures and pressures. The most recent results of the tests made with the modified system will be presented. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1649571

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

In this paper we present the experimental results of an investigation aiming to demonstrate the role of constraints like substrate temperature and environmental pressure on the evaporation process of wetting droplets. It is clearly shown that increasing the temperature or reducing the pressure enhances the evaporation rate. The effect of changing these two parameters on the wetting behaviour is however not similar. The wetting behaviour is dictated by the surface tensions between the three phases (liquid, vapour and solid). Whilst pressure has little effect on these interfacial tensions, the temperature can greatly change these latter. A force balance at the triple line dictates the anchoring of the three‐phase line; changing any of the interfacial tensions can alter this force balance. Increasing temperature tends to reduce the liquid‐vapour surface tension, which reduces the Young unbalanced force acting on the triple line. These results in promoting the anchoring of this latter. Reducing pressure will enhance evaporation, which will lead to a greater evaporative cooling effect, this will increase the force acting to depin the triple line. The relationship between the evaporation rate and the anchoring of the three‐phase line is discussed. The evaporation rate is found to be constant and proportional to the droplet base as far as the three‐phase line is anchored. After depining of the triple line the evaporation rate is reduced. This can have important implications in various applications where both the evaporation and wetting are to be controlled. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1649572

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Market driven space exploration will have the opportunity to develop to new levels with the coming of space nuclear power and propulsion. NASA’s recently established Prometheus program is expected to receive several billion dollars over the next five years for developing nuclear power and propulsion systems for future spacecraft. Not only is nuclear power and propulsion essential for long distance Jupiter type missions, but it also important for providing greater access to planets and bodies nearer to the Earth. NASA has been working with industrial partners since 1987 through its Research Partnerships Centers (RPCs) to utilize the attributes of space in Low Earth Orbit (LEO). Plans are now being made to utilize the RPCs and industrial partners in extending the duration and boundaries of human space flight to create new opportunities for exploration and discovery. Private investors are considering setting up shops in LEO for commercial purposes. The trend is for more industrial involvement in space. Nuclear power and propulsion will hasten the progress. The objective of this paper is to show the progression of space market driven research and its potential for supporting space exploration given nuclear power and propulsion capabilities. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1649573

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

A small‐scale test apparatus has been built and tested for the CELT pneumatic launch assist concept presented at STAIF 2001. The 7.5 cm (3‐inch) diameter × 305 M (1000 feet) long system accelerates and pneumatically brakes a 6.35 cm diameter projectile with variable weight (1.5 – 5 Kg). The acceleration and braking tube has been instrumented with optical sensors and pressure transducers at 14 stations to take data throughout the runs. Velocity and pressure profiles for runs with various accelerator pressures and projectile weights are given. This test apparatus can serve as an important experimental tool for verifying this concept. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1649574

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Researches on reusable launch vehicle (RLV) in Japan have been conducted mainly by the three space agencies: the National Space Development Agency of Japan (NASDA), the National Aerospace Laboratory of Japan (NAL) and the Institute of Space and Astronautical Science (ISAS). HOPE‐X program by NASDA/NAL, spaceplane/scramjet related researches by NAL, and development studies of ATREX engine and small reusable vehicle testing (RVT) by ISAS are such major activities. After the consecutive launch failures of NASDA’s H‐II and ISAS’s M‐V rockets in 1999–2000, it was concluded that more intensive efforts should be concentrated on the reliability improvement of those major expendable vehicles and that RLV related researches should be promoted to establish fundamental technologies essential to future RLV. In past two years, NASDA succeeded in five consecutive launches of new H‐IIA, and ISAS successfully resumed the launch of M‐V. As for RLV researches, considerable progress has been achieved in the high speed flight demonstration (HSFD) tests of HOPE‐X program, scramjet tests of Mach 4 to 8 by NAL, and ATREX engine and small RVT tests by ISAS. The current three space agencies will be merged into one in October 2003 to establish a new organization named Japan Aerospace Exploration Agency (JAXA). It is expected that the above research activities will be also merged to promote a higher‐level research program on RLV. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1649575

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Japanese launch vehicle technology has reached the global highest level by recent successful launches; therefore, we are now progressing from the catching‐up phase to the new phase. Japanese own technologies shall be improved further under the long‐term strategy for the future transportation system research and development. This paper reports the current status of our space transportation systems such as H‐IIA and M‐V, and the road map for the future space transportation systems. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1649576

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Andrews Space has developed the “Alchemist” Air Collection and Enrichment System (ACES), a dual‐mode propulsion system that enables safe, economical launch systems that take off and land horizontally. Alchemist generates liquid oxygen through separation of atmospheric air using the refrigeration capacity of liquid hydrogen. The key benefit of Alchemist is that it minimizes vehicle takeoff weight. All internal and NASA‐funded activities have shown that ACES, previously proposed for hypersonic combined cycle RLVs, is a higher payoff, lower‐risk technology if LOX generation is performed while the vehicle cruises subsonically. Andrews Space has developed the Alchemist concept from a small system study to viable Next Generation launch system technology, conducting not only feasibility studies but also related hardware tests, and it has planned a detailed risk reduction program which employs an experienced, proven contractor team. Andrews also has participated in preliminary studies of an evolvable Next Generation vehicle architecture—enabled by Alchemist ACES—which could meet civil, military, and commercial space requirements within two decades. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1649577

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The NEMO [NuclearEuropaMobileOcean] mission would explore and return samples and possible life forms from Europa’s sub‐surface oceans to Earth. The NEMO spacecraft would land on Europa two years after leaving Earth, using a compact bi‐modal NTP engine. NEMO’S small nuclear reactor melt probe would then melt a channel through the multi‐km ice sheet to the ocean, which a small robotic submarine would explore, transmitting data by sonic link and optical fiber to the spacecraft for relay to Earth. After its exploration, the submarine would rejoin the melt probe for return to the NEMO spacecraft. Using electricity from the bi‐modal MITEE engine, fresh H2propellant would be manufactured by electrolysis of melt water from surface ice. NEMO would then hop to a new site, exploring ten sites in a year before returning with samples and life forms to Earth, six years after it left. The design and performance of the NEMO spacecraft, MITEE engine, melt probe, and submarine are described. The probe and submarine use existing reactor technology. A NEMO mission could launch shortly after 2013 AD. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1649578

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Conceptual designs of Advanced Radioisotope Power System (ARPS) with Cascaded Thermoelectric Converters (CTCs) are developed and optimized for maximum efficiency operation for End‐Of Mission (EOM) electrical power of at least 100 We. These power systems each employs four General Purpose Heat Source (GPHS) bricks generating 1000 Wthat Beginning‐of‐Life (BOL) and 32 Cascaded Thermoelectric Modules (CTMs). Each CTM consists of a top and a bottom array of thermoelectric unicouples, which are thermally, but not electrically, coupled. The top and bottom arrays of the CTMs are connected electrically in series in two parallel strings with the same nominal voltage of > 28 VDC. The SiGe unicouples in the top array of the CTMs are optimized for nominal hot shoe temperature of 1273 K and constant cold shoe temperature of either 780 K or 980 K, depending on the thermoelectric materials of the unicouples in the bottom array. For a SiGe cold junction temperature of 780 K, the unicouples in the bottom array have p‐legs of TAGS‐85 and n‐legs of 2N‐PbTe and operate at constant hot junction temperature of 765 K and nominal cold junction temperature of 476.4 K. When the SiGe cold junction temperature is 980 K, the unicouples in the bottom arrays of CTMs have p‐legs of CeFe3.5Co0.5Sb12or CeFe3.5Co0.5Sb12and Zn4Sb3, segments and n‐legs of CoSb3and operate at constant hot junction temperature of 965 K and nominal cold junction temperatures of 446.5 K or 493.5 K, respectively. The CTC‐ARPSs have a nominal efficiency of 10.82&percent; – 10.85&percent; and generate BOL power of 108 We. This system efficiency is ∼ 80&percent; higher than that of State‐of‐the‐Art (SOA) Radioisotope Thermoelectric Generators (RTGs), requiring 7 GHPS bricks and generating 105 Weat BOL. The CTC‐ARPSs have specific powers of 8.2 We/kg to 8.8 We/kg, which are 71&percent; to 83&percent; higher, respectively, than that of the SOA‐RTGs, and use ∼ 43&percent; less238PuO2fuel. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1649579

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Plutonium‐238 oxide (238PuO2) is used in the fabrication of general purpose heat sources (GPHS) or light‐weight radioisotope heater units (LWRHUs). The heat sources supply the thermal energy used in radioisotope thermoelectric generators to power spacecraft for deep space missions and to heat critical components in the cold environs of space. Los Alamos National Laboratory has manufactured heat sources for approximately two decades. The aqueous purification of238PuO2is required, due to rigorous total Pu‐content, actinide and non‐actinide metal impurity, and neutron emission rate specifications. The238PuO2aqueous purification process is a new capability at Los Alamos National Laboratory as previously, aqueous purified238PuO2occurred at other DOE complexes. The Pu‐content and actinide and non‐actinide metal impurity specifications are met well within specification in the Los Alamos process, though reduction in neutron emission rates have been challenging. High neutron emission rates are typically attributed to fluoride content in the oxide. The alpha decay from238Pu results in &agr;,n reactions with light elements such as17O,18O, and19F resulting in high neutron emission rates in the purified238PuO2. Simple16O‐exchange takes care of the high NER due to17O, and18O. A new method to reduce the NER due to19F in the purified238PuO2is presented in this paper. The method involves addition of water to purified238PuO2, followed by heating to remove the water and liberating fluoride as HF. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1649580

出版商:AIP    

年代:1904

数据来源: AIP