Stephanie D. Leifer

Evaluation of Propulsion Options for Interstellar Missions

This paper describes an evaluation of various propulsion options for robotic interstellar rendezvous missions to stars ranging from 4.5 Light Years (L.Y.) with a 10-year trip time, to 40 L.Y. with a 100-year trip time. Concepts considered included advanced electric propulsion, nuclear (fission, fusion, antimatter) propulsion, beamed energy (e.g., light sails, MagSails) propulsion, electromagnetic catapults, in-situ propellant production concepts (e.g., the interstellar ramjet), and hybrid systems (e.g., antimatter-catalyzed fission/ fusion). The various candidate propulsion options were evaluated using three screening criteria. First, is it possible for the candidate system to achieve the required AV, which can be as much as 0.6 c for a fast, 4.5-L.Y. mission. Second, does the propulsion systems require an extensive, mission-unique supporting infrastructure. Finally, the technology readiness levels of the various subsystem technologies of the propulsion concept are reviewed. This screening process resulted in the selection of beamed energy sail, matter-antimatter, and fusion ramjet concepts as the most promising candidates. Potential mission performance and near-term technology goals of these concepts were then evaluated.

Electrostatic propulsion using C60 molecules

Buckminsterfullerene, a newly discovered allotrope of Thus, a gap in propulsion capability exists for missions carbon (C6 0 ), has demonstrated properties that make it an with a requirement for low-to-moderate specific impulse, ideal candidate as a propellant for electrostatic propulsion. yet at higher propulsion system efficiency than is provided Here, we present a discussion of the potential benefits C60 by state-of-the-art xenon ion engines or arcjets. ion propulsion may provide over conventional ion propulsion and previously suggested methods of cluster 0 8 ion propulsion. These benefits include improved propulsion system power efficiency, especiallylin the

Nuclear safe orbit basing considerations

Consideration is given to one aspect of space nuclear power safety, namely, the radiation dose rate risk due to a reentered reactor. It is found that for nuclear-thermal propulsion NERVA vehicles, the minimum required altitude for initial basing and earth escape is 500 to 600 km; for final end-of-life storage, the required altitude is about 1000 km. For a 10-MWe nuclear-electric propulsion vehicle, the basing node is 800 km and the final end-of-life storage altitude is 1100 km. Radiation levels have been evaluated for both the SP-100 nuclear electric and the NERVA nuclear thermal reactors as a function of operating time, power level, and time after shutdown.

Electric thruster models for multimegawatt nuclear electric propulsion mission design

Three types of electric thrusters currently under development at JPL have potential to support future missions which utilize multimegawatt nuclear electric propulsion. These electric thrusters are the electron bombardment ion thruster, the magnetoplasmadynamic (MPD) thruster, and the electron‐cyclotron‐resonance (ECR) thruster. The electron bombardment ion thruster is a relatively mature technology which has been developed for operation at kilowatt power levels but will require new development for application in the multimegawatt regime. The MPD engine represents a technology which may be very well suited to steady‐state multimegawatt applications but which has been limited to sub‐scale (100’s of kW) and pulsed (MW) testing thus far. The ECR plasma engine represents a class of very promising new concepts which are still in the basic research phase of development, but which may possess important fundamental advantages over other electric thruster technologies. In this paper, models of these thrusters are d...

Venus Mobile Explorer with RPS for active cooling: A feasibility study

This paper presents the findings from a study to evaluate the feasibility of a radioisotope power system (RPS) combined with active cooling to enable a long-duration Venus surface mission. On-board power with active cooling technology featured prominently in both the National Research Councils Decadal Survey and in the 2006 NASA Solar System Exploration Roadmap as mission enabling for the exploration of Venus. Power and cooling system options were reviewed and the most promising concepts were modeled to develop an assessment tool for Venus mission planners considering a variety of future potential missions to Venus, including a Venus Mobile Explorer (either a balloon or rover concept), a long-lived Venus static lander, or a Venus Geophysical Network. The concepts modeled were based on the integration of General Purpose Heat Source (GPHS) modules with different types of Stirling cycle heat engines for power conversion and cooling. Unlike prior investigations which reported on single point design concepts, this assessment tool allows the user to generate either a point design or parametric curves of approximate power and cooling system mass, power level, and number of GPHS modules needed for a “black box” payload housed in a spherical pressure vessel. Input variables include altitude, pressure vessel diameter, payload temperature, and payload power on Venus. Users may also specify the number and type of pressure vessel windows, use of phase-change material for additional (time-dependent) payload cooling, and amount of (rechargeable) battery power for peak power demand operations. Parameter sets that would enable a Venus surface mission with fewer than 16 GPHS modules were identified. Thus, the study provides guidance for design practices that might enable a long-duration Venus surface mission with an attainable quantity of 238Pu, and with achievable operating parameters.

THE NASA ADVANCED PROPULSION CONCEPTS PROGRAM AT THE JET PROPULSION LABORATORY

Research activities in advanced propulsion concepts at the Jet Propulsion Laboratory are reviewed. The concepts, which include high power plasma thrusters such as lithium-fueled Lorentz-Force-Accelerators, MEMS-scale propulsion systems, in-situ propellant utilization techniques, fusion propulsion systems and methods of using antimatter, were selected for study because each offers the potential for either significantly enhancing space transportation capability or enabling bold, ambitious new missions. This has been shown through systems and missions evaluations - the essential tools for determining the benefits and performance drivers of an advanced concept Potential performance of a new concept traditionally has been compared with that of chemical propulsion. However, because of the growing acceptance of electric propulsion in both government and commercial sectors, concepts must now show a significant benefit relative to this technology as well. There is a range of maturity levels represented by the advanced concepts studied under this program, yet each concept faces feasibility issues. Our research is focused on addressing, one-by-one, the key feasibility issues of each concept. In addition to potentially addressing the propulsion needs of missions like those of the Human Exploration and Development of Space (HEDS) initiative, outer planet sample returns and orbiters, or other ambitious deep space endeavors, this research is aiding in fundamental scientific discoveries and developments in other technologies.

A comparison of chemical propulsion, nuclear thermal propulsion, and multimegawatt electric propulsion for Mars missions

Various propulsion systems are considered for a split-mission piloted exploration of Mars in terms of reducing total initial mass in low earth orbit (IMLEO) as well as trip time. Aerobraked nuclear thermal propulsion (NTP), multimegawatt (MMW) nuclear electric propulsion (NEP), and MMW solar electric propulsion (SEP) are discussed and compared to a baseline aerobraked chemical propulsion system. NTP offers low IMLEO, MMW NEP allows both low IMLEO and a short trip time, and both nuclear systems offer better mission characteristics than the chemical system. The MMW SEP is concluded to be less efficient in spite of a lower IMLEO because of the systems higher specific mass and nonconstant power production. It is recommended that MMW NEP and SEP systems be considered for application to Mars cargo missions. The NEP system is concluded to be the most effective propulsion configuration for piloted Mars missions and lunar base missions.