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Calculations have been performed to quantify the cost and delivered mass advantages of aerocapture at all destinations in the Solar System with significant atmospheres. A total of eleven representative missions were defined for the eight possible destinations and complete launch-to-orbit insertion architectures constructed. Direct comparisons were made between aerocapture and competing orbit insertion techniques based on state-of-the-art and advanced chemical propulsion, solar electric propulsion, and aerobraking. The results show that three of the missions cannot be done without aerocapture: Neptune elliptical orbits, Saturn circular orbits, and Jupiter circular orbits. Aerocapture was found to substantially reduce the cost per unit mass delivered into orbit for five other missions based on a heavy launch vehicle: Venus circular orbits (55% reduction in $/kg costs), Venus elliptical orbits (43% reduction); Mars circular orbits (13% reduction), Titan circular orbits (75% reduction), and Uranus circular orbits (69% reduction). These results were found to be relatively insensitive to 30% increases in both the estimated aerocapture system mass and system cost, suggesting that even modestly performing aerocapture systems will yield substantial mission benefits. Two other missions consisting of spacecraft in high eccentricity elliptical orbits at Mars and Jupiter were not shown to be improved by aerocapture. The last mission in the set consisting of an aeroassisted orbit transfer at Earth showed that aerocapture offered a 32% $/kg reduction compared to chemical propulsion, but that aerobraking offered even better performance. Nevertheless, the problems of repeated passes through the Van Allen radiation belts are likely to preclude Earth aerobraking for most applications.

The use of ion propulsion for deep-space missions will become a reality in 1998 with the ight of the ion-propelled, New Millennium Deep Space 1 (DS1) spacecraft. The anticipation of this event is stimulating the call for improved ion propulsion technologies, a trend that is expected to continue. This paper describes the evaluation of possible advanced solar electric propulsion technologies and their potential bene ts to projected near-term and midterm solar system exploration missions. The advanced technologies include high-performance derivatives of the DS1 ion propulsion technology, scaled-down DS1 systems, and direct-drive Hall-effect thruster systems. The results of this study indicate that signi cant near-term bene ts can be obtained by the development of improved versions of the DS1 ion propulsion system (IPSs) components. In addition, if the current trend to smaller planetary spacecraft continues, then missions ying these smaller future spacecraft will bene t substantially from the development of scaled-down IPSs that incorporate advanced technologies in the ion engines and the propellant feed systems. The performance of the direct-drive Hall thruster systems is potentially superior to that of all other midterm options, but this technology has the highest development risk. Signi cantly reduced trip times to small bodies and the outer planets may be possible if technology programs work to retire these risks.

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A detailed Neptune aerocapture systems analysis and spacecraft design study was performed to improve our understanding of the techonology requirement for such a hard mission. The primary objective was to engineer a point design based on blunt body aerosheU technology and quantitatively assess feasibility and performance. This paper reviews the launch vehicle, propulsion, and trajectory options to reach Neptune in the 2015-2020 time frame using aerocapture and all-propulsive vehicles. It establishes the range of entry conditions that would be consistent with delivering a -1900 kg total entry vehicle maximum expected mass to Neptune including a -790 kg orbiter maximum expected mass to the science orbit. Two Neptune probes would be also be delivered prior to the aerocapture maneuver. Results show that inertial entry velocities in the range of 28 to 30 km/s are to be expected for chemical and solar electric propulsion options with several gravity assists (combinations of Venus, Earth and Jupiter gravity assists). Trip times range from approximately 10-11 years for aerocapture orbiters to 15 years for all-propulsive vehicles. This paper shows that the use of aerocapture enables this mission given the payload to deliver around Neptune compared to an all-propulsive orbit insertion approach. However, an all-propulsive chemical insertion option is possible for lower payload masses than the one needed for this science mission. Both approaches require a Delta IV heavy class launch vehicle.