Nov. 5 marked the first anniversary of Voyager 2’s great escape from the solar system. It was on that day in 2018 when the spacecraft passed through the heliopause, the boundary between the part of space surrounding the sun dominated by the solar wind and interstellar space, some 18 billion kilometers from Earth. Scientists marked the anniversary by publishing a series of papers in the journal Nature Astronomy about data Voyager 2 has returned since its entry into interstellar space, and comparing it to Voyager 1, which passed through the heliopause in 2012.
Both Voyagers, launched in 1977, are still operating, but neither will last forever. Within a decade, the nuclear batteries on the two spacecraft will decay to the point where they can’t produce enough power to keep alive their instruments and communications system, ending their missions.
Given a taste of interstellar space, scientists are looking for ways to follow up on the Voyagers. In 2014, a study by Caltech’s Keck Institute for Space Studies examined the feasibility of sending a mission directly into interstellar space and the scientific benefits of doing so.
“Not only is there a compelling scientific reason to go to the interstellar medium, but there’s plenty of science to be done on the way,” said Leon Alkalai of JPL during a panel discussion at the end of this year’s International Astronautical Congress (IAC) in Washington. That science outlined in the study ranges from planetary flybys to searches for Kuiper Belt objects in the outer solar system.
Since that study, Alkalai said a small team at JPL (“zealots, in a way,” as he put it) have been looking at interstellar mission concepts. They’re not alone: last year the Applied Physics Lab (APL) of Johns Voyager’s stellar achievement Hopkins University started its own “Interstellar Probe” mission study that will be incorporated into planning for the next heliophysics decadal survey in the early 2020s. The European Space Agency has also supported studies, including a paper presented at its recent “Voyage 2050” workshop that included contributions from China.
There’s little doubt such a mission could reap a bounty of science, and there’s no shortage of technical approaches to developing the mission, including one concept that would slingshot the probe around the sun. But the biggest obstacle for an interstellar mission (besides its cost, which the panel studiously avoided bringing up) is the timescales involved.
“This will be a long mission. It will take on the order of 30 to 50 years to get out there,” said Robert F. Wimmer-Schweingruber of the University of Kiel in Germany. That poses unique challenges for spacecraft that, traditionally, typically last no more than a couple decades even when extended past their prime mission.
That includes how such missions are run. “This is a long-term effort, and I think we’ll have to divide an interstellar probe into multiple phases,” he suggested. That would start with planetary discoveries and searches for Kuiper Belt objects before passing the heliopause into interstellar space. Each phase would have a different science team. “That should be the opportunity for old men like us to step down and hand over the mission to another principal investigator.”
He had a point with the “old men” remark. The entire panel for that IAC session featured senior male scientists and engineers, with no sign of younger and more diverse voices being involved in concepts for a mission that will span their entire professional careers.
At one point, Ralph McNutt of APL asked those in the audience born after 1990 to stand. “Once we get this thing launched,” he told them, “you are the people who are going to end up being some of the best candidates for keeping the darn thing running. Don’t screw it up.”
But if a multigenerational mission like this is to succeed, those younger generations need to play a bigger role sooner, rather than later. Otherwise, they may decide to do something else.
“Foust Forward” appears in every issue of SpaceNews magazine. This column ran in the Nov. 11, 2019 issue.
Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. His Foust Forward column appears in every issue of the magazine.