摘要:

NASA has completed its current technology program on nuclear propulsion ‐ both nuclear thermal propulsion (NTP) and nuclear electric propulsion (NEP). The focus of the NTP studies has been on piloted and cargo missions to Mars (with precursor missions to the Moon) although studies have been conducted to examine the potential uses of NTP for science missions. The focus of the NEP studies shifted from piloted and cargo missions to Mars to space science missions with consideration of combining a science mission with an early demonstration of NEP using the SP‐100 space nuclear reactor power system.

ISSN:0094-243X    

DOI:10.1063/1.2950187

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

NASA has completed a preliminary mission and systems study of nuclear electric propulsion (NEP) systems for “split‐sprint” human exploration and related robotic cargo missions to Mars. This paper describes the study, the mission architecture selected, the NEP system and technology development needs, proposed development schedules, and estimated development costs. Since current administration policy makers have delayed funding for key technology development activities that could make Mars exploration missions a reality in the near future, NASA will have time to evaluate various alternate mission options, and it appears prudent to ensure that Mars mission plans focus on astronaut and mission safety, while reducing costs to acceptable levels. The split‐sprint nuclear electric propulsion system offers trip times comparable to nuclear thermal propulsion (NTP) systems, while providing mission abort opportunities that are not possible with “reference” mission architectures. Thus, NEP systems offer short transit times for the astronauts, reducing the exposure of the crew to intergalactic cosmic radiation. The high specific impulse of the NEP system, which leads to very low propellant requirements, results in significantly lower “initial mass in low earth orbit” (IMLEO). Launch vehicle packaging studies show that the NEP system can be launched, assembled, and deployed, with about one less 240‐metric‐ton heavy lift launch vehicle (HLLV) per mission opportunity ‐ a very large cost savings! Technology development cost of the nuclear reactor for an NEP system would be shared with the proposed nuclear surface power systems, since nuclear systems will be required to provide substantial electrical power on the surface of Mars. The NEP development project plan proposed includes evolutionary technology development for nuclear electric propulsion systems that expands upon SP‐100 (Space Power ‐ 100 kw) technology that has been developed for lunar and Mars surface nuclear power, and small NEP systems for interplanetary probes. System upgrades are expected to evolve that will result in even shorter trip times, improved payload capabilities, and enhanced safety and reliability. Non‐nuclear technology development for the NEP system is estimated to cost about $721 M (1993 $). Nuclear technology development costs are not included in the costs in this report, since these costs will be incurred in the nuclear surface power development program. NEP Phase A/B studies are estimated to cost about $154 M. Flight system hardware development (Phase C/D) is estimated to cost about $2.8 B, and fabrication of flight hardware is estimated to be about $7.8 B for four mission opportunities in 2009, 2011, 2014, and 2016.

ISSN:0094-243X    

DOI:10.1063/1.2950272

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

In this paper, we strive to achieve four goals: (1) to place into the open literature additional basic information relevant to the continuous‐mode space fusion power (for example, fusion‐fuel choice, the importance of plasma‐ion fuel mix, plasma temperature, and four important radiations), (2) to give an example of the application of this information to adapt (using three design principles), and then optimize (using a new design tool) a terrestrial fusion reactor for space propulsion, (3) to describe a candidate deep‐space mission called the Solar Gravity Lens (SGL) mission that demonstrates it is technically reasonable to propose, and intensify, studies for performing an extra‐solar‐ system mission, and (4) to describe the application of new materials and technology (identified in the laboratory but not necessarily developed) that may dramatically improve performance of space‐fusion‐propulsion concepts.

ISSN:0094-243X    

DOI:10.1063/1.2950190

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

In this paper, we strive to achieve three goals: (1) to describe a continuous‐thrusting space‐fusion‐propulsion engine called the Mirror Fusion Propulsion System (MFPS), (2) to describe MFPS' ability to accomplish two candidate outer‐solar‐system (OSS) missions using various levels of advanced technology identified in the laboratory, and (3) to describe some interesting safety features of MFPS that include continuous mission‐abort capability, magnetic‐field‐shielding against solar particle events (SPE), and performance of in‐orbit characterization of the target body's natural resources (prior to human landings) using fusion‐neutrons, x‐rays, and possibly the neutralized thrust beam. The first OSS mission discussed is a mission to the Saturnian system, primarily exploration and resource‐ characterization driven, with emphasis on minimizing the Earth‐to‐Saturn and return‐trip flight times. The other OSS mission discussed is an economically‐driven mission to Uranus, stopping first to perform in‐orbit resource characterization of the major moons of Uranus prior to human landing, and then returning to earth with a payload consisting of3He (removed from the Uranian atmosphere or extracted from the Uranian moons) to be used in a future earth‐based fusion‐power industry.

ISSN:0094-243X    

DOI:10.1063/1.2950203

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A “bi‐modal” nuclear propulsion and power system based on the United States Air Force's (USAF's)* Space Nuclear Thermal Propulsion (SNTP) technology is applied to a set of high energy Solar system exploration missions. Performance comparisons are made to a baseline mission set developed by the Jet Propulsion Laboratory utilizing a nuclear electric propulsion system based on the SP‐100 space power system. Orbiters and probes of Uranus, Neptune, and Pluto, a Grand Tour of the Galilean moons of Jupiter, a Comet Nucleus Sample Return, and a Multiple Mainbelt Asteroid Rendezvous mission are analyzed. The first five missions utilizing SP‐ 100 required a Shuttle‐C or equivalent heavy lift launcher. With the bi‐modal PBR system, the payload goals are deliverable in the same transit times, but on the smaller, existing Titan IV launcher. Furthermore, all optional payloads originally available only at increased transit time are accommodated. Available mass margins for these missions are 20%–85% of the power/propulsion system mass, providing significant robustness. The same missions were analyzed on a Titan III launcher in order to pursue further cost reductions. Substantial payload masses (1000 kg or more) were found to be available in all cases with reasonable transit times, coinciding well with the current “lighter, faster, cheaper” NASA philosophy.

ISSN:0094-243X    

DOI:10.1063/1.2950216

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The Russian Topaz‐IIspace reactor system is being modified for use for the United States ‐ Nuclear Electric Propulsion Space Test Project (NEPSTP). The nuclear reactor fuel consists of annularUO2fuel pellets with 17 mm diameter and 9 mm height. The fuel is fabricated to high purity and high density (96% theoretical density). The reactor core contains 37 single‐cell thermionic fuel elements (TFEs), each with approximately 40 fuel pellets. The fuel pellets are contained within an emitter tube of single crystal Mo‐3%Nb with a tungsten coating on the outer surface to enhance thermionic emission. The fuel has evolved through an ongoing development program to provide low swelling and very high mechanical strength. Extensive irradiation testing, chemical compatibility testing, and vibration testing were conducted in Russia to verify the performance and lifetime capabilities of the fuel and TFE. This paper summarizes the fuel design, fuel development, and performance testing of theUO2fuel for the TOPAZ‐IIreactor.

ISSN:0094-243X    

DOI:10.1063/1.2950235

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The adsorption/desorption characteristics of Cs on sapphire surfaces have been studied using a combination of surface analytical techniques. An approximate initial sticking coefficient for Cs on sapphire has been measured using a reflection mass spectrometric technique and has been found to be 0.9. Thermal Desorption Mass Spectrometry (TDMS) and Auger Electron Spectroscopy (AES) have been used to verify that a significant decrease in sticking coefficient occurs as the Cs coverage reaches a critical submonolayer value. TDMS analysis demonstrates that Cs is stabilized on a clean sapphire surface at a temperature in excess of that experienced by sapphire in a TOPAZ‐IIthermionic fuel element (TFE). Surface contaminants, like carbon, can increase the capacity for Cs adsorption relative to the clean sapphire surface. C contamination eliminates the high temperature state of Cs desorption found on clean sapphire but shifts the bulk of the Cs desorption from 400 to 620 K. Surface C is a difficult contaminant to remove from sapphire, requiring annealing temperatures in excess of 1400 K. Whether Cs is stabilized on sapphire in a TFE environment will most likely depend on the relationship between surface contamination and surface structure.

ISSN:0094-243X    

DOI:10.1063/1.2950249

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

This paper describes some of the current activities of the TOPAZ‐IIInternational Research Program in the areas of materials science and thermionics. In view of the importance of insulator degradation to the issue of thermionic fuel element (TFE) lifetime, the initial focus of our experimental research has been in the area of cesium‐sapphire interactions. Surface interactions of Cs with insulators are of primary importance in causing breakdown and arcing. An experimental facility is described which allows the study of insulator surface electrical conduction in Cs environments typical of the TOPAZ‐IITFE. Some initial experiments regarding the charge state of Cs embedded in a sapphire matrix are described. It is concluded that, at temperatures relevant to TFE applications, Cs is singly ionized in this environment.

ISSN:0094-243X    

DOI:10.1063/1.2950261

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The world's most complete facility for ex‐reactor ultrahigh‐temperature hydrogen exposure testing is located at the Research Institute of SLA “Lutch” in Podolsk, Moscow Region, Russia. This facility has been utilized for a number of years for testing high‐temperature nuclear fuels for the now‐defunct Soviet space program, and recent work was performed there under contract for Babcock & Wilcox. Capabilities of the facility are presented. The work performed for B&W is summarized as one example. (U,Zr,Nb)C fuel spheres with and without ZrC coatings were exposed to flowing hydrogen at 5 atm for 30 minutes at 3150 K, followed by thermal survivability testing at 3500 K in static helium. Both the test facility and the fuel performed superbly.

ISSN:0094-243X    

DOI:10.1063/1.2950267

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Pellets of both hyper‐ and hypostoichiometric uranium dioxide were prepared and tested to determine their relative thermal stability. This paper will discuss the materials tested, the test procedure and the test results. In summary, pellets of hyperstoichiometric uranium oxide (O/U = 2.003–2.005) and hypostoichiometric uranium oxide (O/U = 1.995–1.997) were fabricated. For each stoichiometry, fully dense pellets, pellets with a nominal 10 % porosity, and pellets with a nominal 18 % porosity were prepared.The pellets were thermally treated at 1873 K and 2073 K. The composition, microstructure, and density of the treated samples were characterized. The results after thermal treatment have been compared to the pre‐tested pellets. These results will be presented.

ISSN:0094-243X    

DOI:10.1063/1.2950276

出版商:AIP    

年代:1994

数据来源: AIP