Interstellar probe – Destination: Universe!

Interstellar Probe: Humanity's exploration of the Galaxy Begins

The classic accepted view of the heliosphere is a quiescent, comet-like shape aligned in the direction of the Sun's travel through the interstellar medium (ISM) extending for 1000's of AUs (AU: astronomical unit). Here we show, based on magnetohydrodynamic (MHD) simulations, that the tension (hoop) force of the twisted magnetic field of the sun confines the solar wind plasma beyond the termination shock and drives jets to the North and South very much like astrophysical jets. These jets are deflected into the tail region by the motion of the Sun through the ISM similar to bent galactic jets moving through the intergalactic medium. The interstellar wind blows the two jets into the tail but is not strong enough to force the lobes into a single comet-like tail, as happens to some astrophysical jets (Morsony et al. 2013). Instead, the interstellar wind flows around the heliosphere and into equatorial region between the two jets. As in some astrophysical jets that are kink unstable (Porth et al. 2014) we show here that the heliospheric jets are turbulent (due to large-scale MHD instabilities and reconnection) and strongly mix the solar wind with the ISM beyond 400 AU. The resulting turbulence has important implications for particle acceleration in the heliosphere. The two-lobe structure is consistent with the energetic neutral atoms (ENAs) images of the heliotail from IBEX (McComas et al. 2013) where two lobes are visible in the North and South and the suggestion from the CASSINI (Krimigis et al. 2009, Dialynas et al. 2013) ENAs that the heliosphere is "tailless".

Magnetized Jets Driven by the Sun, the Structure of the Heliosphere Revisited: Consequences for Draping of BISM ahead of the HP and Time Variability of ENAs

The Interstellar Probe mission presents the ambitious challenge of launching a spacecraft for interstellar exploration by 2030. In this paper, a telecommunications system designed for operations up to 1000 AU and 50 year lifetime is presented. The deep space nature of the mission provides its own set of challenges, then compounded by a long lifetime requirement. Typically, essential parts such as mechanical reaction elements and batteries used for spacecraft pointing and communications are not expected to survive until end-of-life. Fortunately, the timeline of the Interstellar Probe mission coincides with an entrance into a golden age of astronomy. Very large radio antennas and arrays currently built and in construction extend our capability for deep space communication, providing an opportunity for collaboration between NASA and the NRAO. Performances of these apertures towards deep space communications are analyzed and prove to be critical in maximizing current capability for interstellar communications. Additionally, increased commercialization of space has led to an advancement in the efficiency of light-weight antenna reflectors, enabling consideration of larger aperture spacecraft antenna while minimizing mass. Capitalizing on these resources, a pragmatic system for interstellar communications based on current and near term capability is presented.

Interstellar Communications

A detailed overview of the knowledge gaps in our understanding of the heliospheric interaction with the largely unexplored Very Local Interstellar Medium (VLISM) are provided along with predictions of with the scientific discoveries that await. The new measurements required to make progress in this expanding frontier of space physics are discussed and include in-situ plasma and pick-up ion measurements throughout the heliosheath, direct sampling of the VLISM properties such as elemental and isotopic composition, densities, flows, and temperatures of neutral gas, dust and plasma, and remote energetic neutral atom (ENA) and Lyman-alpha (LYA) imaging from vantage points that can uniquely discern the heliospheric shape and bring new information on the interaction with interstellar hydrogen. The implementation of a pragmatic Interstellar Probe mission with a nominal design life to reach 375 Astronomical Units (au) with likely operation out to 550 au are reported as a result of a 4-year NASA funded mission study. 

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Future Exploration of the Outer Heliosphere and Very Local Interstellar Medium by Interstellar Probe

Since the beginning of space exploration, one of the most ambitious goals has been to explore beyond the boundaries of our solar system. Ground and Earth-orbit based systems have given a deep understanding of the overall characteristics of the heliosphere in the local interstellar medium and how the characteristics of our solar system are similar to and different from other systems. Viewing the heliosphere from outside will allow, for the first time, a more complete understanding of how a star system evolves and interacts with the Universe. Interstellar missions have been studied for decades. The primary reasons we have not yet explored this region are critical limitations in technology. These include a lack of propulsion that can achieve the high speeds needed to get to the heliospheric boundary in reasonable time, reliable systems that can function for the long lifetime needed, reasonable communications capabilities at interstellar range, and constraints on mission resources such as power when more than 100 AU from the Earth. Recent developments in launch systems, execution of long-lived missions such as New Horizons, new radioisotope power systems, and advanced communications systems have for the first time allowed for a practical, feasible near-term mission that can achieve the goal of exploring outside the solar system. We present recent results of a concept study that examined possible missions that could be launched as early as 2030 using existing, or near-existing, technology. These possible missions support significant payloads for heliospheric science, with the potential for additions to the payload for planetary investigations or astrophysics. The concept study includes a detailed look at possible trajectories in launch years from 2030 to 2040 with flyout speeds at least twice that of Voyager 1 and 2, and significant opportunities for tuning the flyout direction to maximize the heliophysics return as well as allow encounters with outer planets or Kuiper Belt Objects. We present a summary of trade studies performed to investigate the constraints and design space for an interstellar probe. These trades include a comparison of trajectories that include gravity assists at Jupiter and at the Sun to increase speed, optimization of the telecommunications architecture to balance data downlink rate with power usage, and spacecraft control methods to allow precise pointing for telecommnications while minimizing propellant usage for an extremely long-lived mission. We present a spacecraft design that can support the potential payloads designed to operate reliably for 50 years, while allowing for communications from 1000 AU.

Interstellar Probe: A Practical Mission to Escape the Heliosphere

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 $C_{3}$ 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.

Wayne Schlei

Papers

Interstellar Probe: A Practical Mission to Escape the Heliosphere

Pragmatic Trajectory Options Applicable to an Interstellar Probe Mission