The Grand Tour | Armchair Cosmology

Congress has left Washington D.C. on recess without voting on even a short-term authorization bill for NASA. This is hardly surprising, but unquestionably disruptive to a number of missions that require decades to plan and execute. Ideal orbital alignments don’t keep congressional calendars.

The success of NASA’s most storied deep space probes, Voyager 1 and 2, hinged on hitting a window that only arrives once every two centuries. This golden opportunity to closely observe the outer planets was nearly squandered due to budget constraints and lobbying from contractors on other projects.

The concept of a “Grand Tour” mission began with two unlikely and fortuitous discoveries. In 1961, a 25 year old graduate student named Michael Minovitch tackled the three-body problem, which had puzzled physicists and mathematicians for 300 years. The challenge was to understand how the gravity of two bodies such as the sun and a planet might influence the path of a third body such as a comet– or in this case, a spacecraft.

Minovitch, during his summer internship at the Jet Propulsion Laboratory, convinced his superiors to check the accuracy of data he’d worked on at UCLA. Remarkably, the intern had succeeded where Newton had failed. Granted, Newton didn’t have access to an IBM 7090 computer, but it was a great achievement nonetheless. With the the three-body problem solved, It was possible to plot the trajectory of a spacecraft to employ planetary gravity and slingshot to Jupiter in two years rather than the 30 or 40.

The orbital mechanics of gravitational assist were discovered during the heat of the space race. The Apollo mission was justifiably absorbing most of the bandwidth at NASA. The rare opening that the sling shot effect provided wasn’t recognized until four years later when Gary Flandro, another summer intern at JPL, began plotting potential flight trajectories over the next decade. He was stunned to find that Jupiter, Saturn, Uranus, and Neptune would all align on one side of the sun in the late 1970s– an event that wouldn’t happen again for another 176 years.

A “Grand Tour” of the outer planets was conceivable and, with the backdrop of the Apollo budget bubble, seemed possible. The initial proposal was a grandiose mission with multiple spacecrafts consisting of orbiters and landers that utilized Saturn V rockets for launch. Unfortunately, NASA’s budget would peak in 1966 and drop precipitously in the following years. The fiscal year 1971 budget received a 15% cut, and the production of the Saturn V was suspended. Due to President Nixon’s budgetary pullback, his general perception of the Apollo program as a Kennedy pet project, and the development of the space shuttle, the “Grand Tour” was shelved.

NASA and JPL had to accept the economic reality and reconfigure the mission. They scaled back the design to a Mariner class spacecraft supplemented with subsystems from the Viking program. The Voyager team, led by Chief Scientist Ed Stone, kept their eye on the “Grand Tour” launch date. Despite the stated mission being reduced to a Jupiter and Saturn flyby, they upgraded the plutonium battery with the hope that the probes would survive long enough to reach Uranus and Neptune.

37 years later, the Voyagers continue to provide new insights into our solar system as they pass into interstellar space. Ed Stone reflected in an interview with the Guardian, “When I started on Voyager my two daughters were young… By the time they were in college we had passed Saturn and were on our way to Uranus. They got married and the Voyagers just kept going, and we had grandchildren and Voyager just kept going and our grandchildren are now aware of what’s happening to the Voyagers just like our children were.”

The mission persisted through struggles very reminiscent of today’s issues, from the cost overruns of the James Webb Space Telescope to the competition for budget dollars between the SLS heavy lift rocket and the Commercial Crew Program. The Voyager team’s vision and generational stamina allowed the probes to discover 22 new moons, the presence of a volcano on Io, an aurora on multiple planets. Those stalwart spacecrafts survived drastic spending cuts, all the bureaucratic wrangling, and a host of technical failures. Yet, they’ve managed to reach the edge of our star system and sail into the interstellar unknown. It’s enough to give hope that the pathfinders will keep pushing the horizon off the map.