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Lecture Starts at 16:40
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PSW #2,462
September 9, 2022
A First Interstellar Probe: Next Step to the Starts
Ralph L. McNutt, Jr.
Applied Physics Laboratory/Johns Hopkins University
“Interstellar Probe” (IsP) is a proposed scientific mission to capture a unified view of our heliosphere and its surroundings in interstellar space. IsP is envisioned to address four primary questions. (1) What are the processes within the heliosphere responsible for the formation of the heliospheric boundary? (2) What are the physical processes at work in the heliosheath? (3) What are the global dynamics of the heliosphere? And (4) what are the conditions in, and characteristics of, the very local interstellar medium, and the Sun’s influence on it? The IsP will carry state of the art instruments designed specifically to investigate these properties of the heliosphere, the solar wind and the very near interstellar medium to answer these questions.
To study and select a menu of “appropriate” science drivers, required measurements, and example payload instruments for such a mission, an internal Johns Hopkins Applied Physics Laboratory team and a large number of external and unpaid volunteers were assembled and participated in four workshops held annually from 2018 through 2021. The work let to the assembly of a science traceability matrix, and Working Groups crafted a notional set of remote-sensing and in situ instruments to address both a baseline heliophysics mission and an “augmented” mission with additional planetary science and astrophysics science goals.
Detailed engineering and trade-off studies were carried out and showed that an interstellar probe mission supporting the science objectives can be designed, built, and launched by the early 2030s. The nominal mission proposal uses a super heavy lift launch vehicle (such as a Space Launch System Block 2 Cargo vehicle with additional 3rd and 4th stages) to propel a payload spacecraft of approximately 860 kg carrying about 90 kg of instruments. With a close Jupiter gravity assist, a spacecraft with these parameters launched on a super heavy life vehicle in 2036 would exit the solar system at about twice the current speed of Voyager 1 and in 50 years would reach ~350 AU from the center of the solar system. Powered by two next-generation radioisotope thermoelectric generators and with a communications system designed to return data from as far as 1,000 AU, it would be able to send data back to earth for well over that amount of time and would constitute the next step past the Voyagers.
The IsP would be a large strategic mission for NASA, and it is envisioned that a future NASA Science and Technology Definition Team, as well as members of the upcoming Solar and Space Physics Decadal Survey could draw upon the IsP report as a “menu” from which to select and/or reject science goals, solar-system-flyout direction, and potential instruments for a scientific payload for an Interstellar Probe that could be readied in this decade and launched within the next.
This lecture will discuss the IsP, including its science objectives, potential instrumentation, possible launch and trajectory scenarios, and other aspects of a mission with a design and running life that could be as long as one hundred years, possibly longer.
The 498 page IsP study proposal, including science details, instrument examples, system trade-offs, and cost and reliability estimates, is available for download without charge at interstellarprobe.jhuapl.edu.
Ralph L. McNutt, Jr. is a Physicist and Member of the Principal Professional Staff in the Space Exploration Sector of The Johns Hopkins Applied Physics Laboratory (APL), and he is the Principal Investigator on the Pragmatic Interstellar Probe proposal. Concurrently is a co-Investigator on NASA’s Voyager, New Horizons, and Parker Solar Probe missions (currently operating) and on NASA’s Europa Clipper mission (now under development).
Ralph is an author on over 220 papers. He co-chaired National Academies 2009 Studies on Radioisotope Power Systems and NASA’s 2017 Large Strategic Science Missions.
Among other honors and awards Ralph is a Member and Trustee of the International Academy of Astronautics, he is a recipient of the APL Lifetime Publication Award, the NASA Silver Achievement Medal to the Parker Solar Probe Team, the IAA Laurels for Team Achievement Awards for the Parker Solar Probe, New Horizons and MESSENGER missions, and he is the recipient of thirteen NASA Group Achievement Awards. Planet 172191 Ralphmcnutt is named for him.
Ralph earned his BS in Physics at Texas A&M University and his PhD in Physics at the Massachusetts Institute of Technology.
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Since the local interstellar medium and the heliosphere it surrounds are three dimensional, it seems to me launching four or more identical probes in different directions from the Solar System with particle and field instruments, plasma and dust detectors as well as radio science instruments would be the way to go. Using a solar sail and a gravity assist from Jupiter plus adding an extra booster rocket to the launch vehicle to speed them along into the interstellar medium at at least double the velocity of Voyager 1 would be in reach if technology available now or in the near future. To simply and lighten them, spin stabilization could be used to keep the probes antenna pointed at Earth while the instruments can scan in all directions. As for power, I imagine using RTG's based on Americium 241 and a Stirling engine would ensure enough power to operate the spacecraft for well beyond 1,000 A.U and fifty years of mission operations. Efficiency of the RTG's used by Voyager has a seven percent efficiency rating while improved RTG's have increased it to thirty percent.