Computer Science
Scientific paper
Jan 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002iaf..confe.678j&link_type=abstract
IAF abstracts, 34th COSPAR Scientific Assembly, The Second World Space Congress, held 10-19 October, 2002 in Houston, TX, USA.,
Computer Science
Scientific paper
insertion of spacecraft into elliptical orbit around target planet is proposed for Neptune orbiter mission. The primary goal of combining nuclear electric propulsion (NEP) and aerocapture orbital insertion is a reduction of a trip time comparing to that of similar mission, which would use nuclear electric propulsion only. One of the limitations of the all NEP orbiter is that at the planetary approach it must match its arrival velocity with Neptune's orbital speed in order to initiate slow capture into the desired orbit using low thrust electric propulsion. Use of aerocapture for insertion into closed elliptical orbit around Neptune through a single aerodynamically controlled atmospheric pass gives advantage of having higher entry velocities than it would be possible in case of all NEP scenario, thus reducing trip time required for interplanetary transfer. propulsion and thermal protection systems. Moreover, because faster interplanetary trip times for combined NEP/Aerocapture orbiter result in a higher entry velocities into the Neptune's atmosphere, they will also drive the increase in aerobrake mass fraction. In addition, aerocapture at Neptune also presents a challenge for aerobrake's guidance system which must target vehicle to the desired atmospheric exit conditions in the presence of significant uncertainties in Neptune's atmospheric density. Hence, there is a need to design a robust nominal aerocapture trajectory capable of accommodating density dispersions and also optimized for minimum thermal protection mass, thus contributing to overall reduction of aerobrake mass fraction. determine the optimal combination between reduction of the trip time and increase in aerobrake mass fraction was undertaken. The initial assumptions on aerobrake thermal protection materials and NEP system characteristics were based on near term state of the art technology, corresponding to 2007-2010 time frame, when such a mission to Neptune could be launched. interplanetary trajectory simulation including capture into orbit around Neptune. In these low thrust trajectory simulations the trust level and the specific impulse of a single electric rocket engine were fixed, thus allowing to optimize number of engines and their thrust time history for a rapid transfer to Neptune. Therefore, for combined NEP/Aerocapture mission use of this approach made possible to determine the change in NEP mass fraction, comparing to that one of all NEP mission scenario where spacecraft velocity at its arrival would have to be matched with Neptune's orbital speed. atmosphere, where vehicle was captured into a highly elliptical orbit, which insures periodical close fly-by of the biggest Neptune's moon Triton, thus allowing its scientific observation. Nominal trajectories found in the process of aerocapture simulations were optimized for minimum mass of aerobrake's thermal protection system and were also shown to withstand significant density variations which are likely to be encountered in Neptune's atmosphere. These nominal trajectories were used to determine sensitivity of aerobrake's thermal protection system mass fraction to the variation of atmospheric entry velocity resulted from shorter trip times to Neptune. that for the same initial mass at the low earth orbit, all NEP mission flight time is 11-12 years, when as for the mission scenario which combines NEP and aerocapture flight time can be reduced to 5-6 years. Such a reduction in mission flight time represents much faster scientific return and it also translates into a higher chance of mission success and significant operational cost savings due to much shorter mission time.
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