Search

The NEAR mission was a spectacular rehearsal for one of the most exciting and scientifically rewarding missions of the next decade, sample return from near-Earth asteroids. A unique source of information about the early solar system, the formation of the planets, and the connection between stars and our Sun, are meteorites and asteroids. Yet, studies of both are hindered by a lack of unequivocal and detailed information linking the two. Meteorites are rock samples of unknown provenance. We have no information about the geological context of their source. They are also highly non-representative sampling of primitive solar system material because the terrestrial meteorite population is dominated by the ejecta of stochastic impacts and because the atmosphere filters out all but the toughest rocks. Without sample return, asteroids are not amenable to the depth and breadth of techniques available in the laboratory, yet the NEAR images indicate that there are many processes occurring on asteroids – or that could have occurred in the past – that we must understand if the meteorite data are ever to yield a clear image of early solar system processes. Technical developments of the last few years and the discovery of large numbers of NEAs mean that sample return is now within small mission capability. A team of about 20 scientists and engineers from all relevant subject fields are now assembling a mission called Hera. This paper reviews the mission as of fall 2002. 2004 COSPAR. Published by Elsevier Ltd. All rights reserved.

The Orion Crew Exploration Vehicle is the first crewed capsule design to be developed by NASA since Project Apollo. Unlike Apollo, however, the CEV is being designed for service in both Lunar and International Space Station missions. Ascent aborts pose some issues that were not present for Apollo, due to its launch azimuth, nor Space Shuttle, due to its cross range capability. The requirement that a North Atlantic splashdown following an abort be avoidable, in conjunction with the requirement for overlapping abort modes to maximize crew survivability, drives the thrust level of the service module main engine. This paper summarizes 3DOF analysis conducted by NASA to aid in the determination of the appropriate propulsion system for the service module, and the appropriate propellant loading for ISS missions such that crew survivability is maximized.

The evolution of low-thrust propulsion technologies has reached a point where such systems have become an economical option for many space missions. The development of efficient, low trip time control laws has received an increasing amount of attention in recent years, though few studies have examined the subject of inclination changing maneuvers in detail. A method for performing economical inclination changes through the use of an efficiency factor is derived front Lagrange's planetary equations. The efficiency factor can be used to regulate propellant expenditure at the expense of trip time. Such a method can be used for discontinuous-thrust transfers that offer reduced propellant masses and trip-times in comparison to continuous thrust transfers, while utilizing thrusters that operate at a lower specific impulse. Performance comparisons of transfers utilizing this approach with continuous-thrust transfers are generated through trajectory simulation and are presented in this paper.

Solar Electric propulsion (SEP) is examined as a candidate transportation option for human missions to Mars. Focus is given to an Earth-escape staging concept. This concept uses a SEP system to transfer from low earth orbit (LEO) to a high-energy elliptical parking orbit (HEEPO) and a chemical propulsion system to transfer from the HEEPO to a hyperbolic escape trajectory. LEO to Earth escape performance of these combined transportation systems is comparable to that of a nuclear thermal rocket (NTR). As a result, a mass efficient non-nuclear transportation architecture with fast, 180 day, Earth-to-Mars piloted transit times is enabled.

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.

This paper examines the strong interrelationship between assumed technology and mission performance requirements for NEP. Recent systems analysis efforts by NASA, DOE, and various contractors are used to project achievable system performance as a function of technological sophistication for two piloted Mars mission applications. Specific mass regimes for each collection of technologies are presented as a function of power level for piloted applications. Low thrust mission analyses are presented which relate these system performance projections to achievable mission performance. Mission performance ‘‘maps’’ are constructed which link prime mission figures‐of‐merit of time and initial mass with system requirements on power level and specific mass, and hence technology. Both opposition and conjunction class piloted Mars missions are presented for the 2016 opportunity, analogous to those proposed in the ‘‘90‐Day Study’’ and ‘‘Synthesis’’ architecture studies. Mass and time breakdowns are presented for 10 MWe piloted and 5 MWe cargo point designs.