Pragmatic Trajectory Options Applicable to an Interstellar Probe Mission

Interstellar Probe is a proposed mission concept for in-situ exploration of the nearby interstellar medium (NISM) and heliosphere with realistic technologies and timeframes. Employing currently available technologies, the most promising architectures involve long-duration, RTG-powered spacecraft coupled with multi-stage kick motors on the near complete Space Launch System (SLS) due to the high C3 lift capabilities. The potential architectures studied here are based on existing or near-existing technology for a pragmatic approach towards a launch within the next 20 years. The heavy lift capacity on the SLS Block 2 launcher, for instance, enables heliocentric escape speeds in excess of 8 AU/yr for likely vehicle configurations if utilizing a low-altitude Jupiter gravity assist in conjunction with Atlas V Centaur and STAR48BV upper stages (launching between 2030 to 2042). This speed maximization is vital for a long-distance journey of roughly 120AU out to the NISM and beyond. Science return maximization, however, exists as a more subtle trade where optimal speed locations do not correlate with germane science areas related to the NISM and the heliosphere. Recent data on interstellar space and the general shape and orientation of the heliosphere indicate destinations with higher interest that drive the landscape of a potential Interstellar Probe concept. With a guaranteed departure from the solar system, Interstellar Probe also presents a unique opportunity for planetary science as celestial bodies are available in almost any direction near the ecliptic (which corresponds with local escape speed peaks). Kuiper belt object (KBO) or trans-Neptunian object (TNO) encounters along the way to the NISM are available for high-interest targets, but such cases must correlate with destinations relevant with the primary mission - heliophysics. The present study explores various Jupiter gravity assist transfer options (ballistic and powered) for an examination of destinations throughout the sky over a possible launch timeframe (2030-2042). A novel destination sky map technique for analyzing the system escape possibilities guides outbound selection via multiple criteria factors. Potential spacecraft masses for various concepts (heliophysics-only or with a planetary science augmentation via flying by KBOs or TNOs) are examined. Target opportunities to a specific target of interest (e.g., Quaoar) highlight the trade between maximum escape speed and KBO flybys. The results of this work will support the science definition discussion on departure direction and plausible mass estimates for various architectures in advance of an Interstellar Probe mission.