Interstellar Heliopause Probe


Аuthors

Loeb H. W.1*, Schartner K. 1**, Dachwald B. 2***, Ohndorf A. 3****, Seboldt W. 3*****

1. Justus-Liebig-Universität,
2. Aachen University of Applied Sciences,
3. German Aerospace Centre DLR,

*e-mail: H.W.Loeb@exp1.physik.uni-giessen.de
**e-mail: Karl-Heinz.Schartner@exp1.physik.uni-giessen.de
***e-mail: dachwald@fh-aachen.de
****e-mail: andreas.ohndorf@dlr.de
*****e-mail: wolfgang.seboldt@dlr.de

Abstract

There is common agreement within the scientific community that in order to understand our local galactic environment it will be necessary to send a spacecraft into the region beyond the solar wind termination shock. Considering distances of 200 AU for a new mission, one needs a spacecraft traveling at a speed of close to 10 AU/yr in order to keep the mission duration in the range of less than 25 yrs, a transfer time postulated by European Space Agency (ESA). Two propulsion options for the mission have been proposed and discussed so far: the solar sail propulsion and the ballistic/radioisotope-electric propulsion (REP). As a further alternative, we here investigate a combination of solar-electric propulsion (SEP) and REP. The SEP stage consists of six 22-cms diameter RIT-22 ion thrusters working with a high specific impulse of 7377 s corresponding to a positive grid voltage of 5 kV. Solar power of 53 kW at begin of mission (BOM) is provided by a light-weight solar array. The REP stage consists of four space-proven 10 cm diameter RIT-10 (radio-frequency ion thruster) that will be operating one after the other for 9 yrs in total. Four advanced radioisotope generators provide 648 W at the beginning of mission (BOM). The scientific instrument package is oriented at earlier studies. For its mass and electric power requirement 35 kg and 35 W are assessed, respectively. Optimized trajectory calculations, are based on our «InTrance» method. The program yields a burn out of the REP stage in a distance of 79.6 AU for a usage of 154 kg of Xenon propellant. With a hyperbolic excess energy C3 = 45.1 km2/s2 a heliocentric probe velocity of 10 AU/yr is reached at this distance, provided a close Jupiter gravity assist adds a velocity increment of 2.7 AU/yr. A transfer time of 23.8 yrs results for this scenario requiring about 450 kg Xenon for the SEP stage, jettisoned at 3 AU. We interpret the solar and SEP/REP as a competing alternative to solar sail and ballistic/REP. Omitting a Jupiter fly-by even allows more launch flexibility, leaving the mission duration in the range of the ESA specification.

Keywords:

radio-frequency ion thruster; solar electric propulsion; interstellar heliopause probe; mission strategy; radioisotope-electric propulsion


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