More From JPL's Linda and Tom Spilker

Episode Summary

Executive Summary: Planetary Radio centers on a proposed outer-solar-system mission, Argo, with Linda and Tom Spilker explaining how a Neptune flyby could study Neptune, Triton, rings, and Kuiper Belt targets while showcasing the technical hurdles of launch mass, gravity assists, power, and communications. The episode also highlights Bill Nye on how satellite data help Earth, plus brief news, Q&A, and skywatch segments.

Main Topics: Proposed Neptune mission Argo: Tom and Linda Spilker describe the science goals of a proposed mission to Neptune, named Argo, emphasizing how a return visit could reveal changes since Voyager 2 and enable follow-on Kuiper Belt exploration. How planetary missions are conceived and approved: The Spilkers explain that missions begin with community science objectives, then must be translated into engineering concepts, mission architecture, cost, and feasibility before NASA funding is even possible. Engineering challenges for an outer-solar-system mission: Discussion focuses on launch mass, trajectory design using gravity assists, powering the spacecraft beyond Saturn, and telecom/data-return constraints at Neptune distances. Bill Nye on Earth science from space: Bill Nye argues that satellite-based GPS measurements are directly useful for understanding land subsidence in Louisiana’s delta and for making hard policy decisions about levees and abandonment. Space news roundup: Matt Kaplan covers Atlantis’s successful delivery of the Columbus lab, the upcoming Endeavour launch, and the nearing end of Ulysses, which has far outlived its planned lifetime. Q&A and skywatch/trivia segments: Emily Lakdawalla answers a moon-phase question, and Bruce Betts offers skywatching tips, a space history note, a random fact about NASA’s A-Train, and the trivia contest result.

Key Arguments: A Neptune mission is scientifically valuable because Voyager 2 provided only a brief snapshot; a new mission could track atmospheric, seasonal, and geological changes over time. Neptune’s gravity makes it a powerful trajectory tool, potentially enabling much larger Kuiper Belt accessibility than a Pluto flyby mission. Mission design starts with agreed science objectives; only then can engineers determine instruments, trajectory, power, telecom, and cost. Beyond Saturn, solar power is insufficient for a viable mission, making RTGs (radioisotope thermoelectric generators) central to feasibility. Outer-solar-system missions may use gravity assists from Jupiter and possibly Saturn to accumulate enough energy for Neptune arrival. Satellite data are not just for space exploration; they can inform urgent Earth-based policy decisions, such as whether to reinforce or retreat from subsiding deltas. The mission concept remains early-stage and depends on future funding and NASA’s willingness to permit RTG use.

Data Points: Voyager 2 Neptune encounter: 1989 - The only spacecraft flyby of Neptune discussed as the baseline for comparison with Argo. Voyager 2 pre-encounter imaging duration: a few months - Used to explain the limited data available before the brief Neptune encounter. Close observational window at Neptune: a few brief days - The period during which Voyager 2 could carefully track clouds and Triton features. New dark spot timescale: 5–6 years after Voyager flyby - Tom Spilker notes the great dark spot disappeared within this period and later reappeared elsewhere. Neptune trajectory steering via gravity assist: up to about 60 degrees - Used to show how Neptune can dramatically redirect a spacecraft compared with Pluto. Kuiper Belt accessibility increase: about 4,000 times more volume - Argo’s Neptune gravity assist could open far more target options than New Horizons’ Pluto flyby. Launch/mission history referenced: 2007 - Bruce Betts notes New Horizons’ Jupiter flyby in space history. New Horizons distance: 9 AU - Bruce Betts says New Horizons is already nine times Earth-Sun distance from the Sun. Moon phase cycle: 29.5 days - Emily Lakdawalla explains the lunar phase cycle length. Moon orbital period around Earth: a little more than 27 days - Part of the explanation for why moon phases shift by seven or eight days. Delta subsidence rate: at least 0.1 cm per year - Bill Nye cites GPS-based measurements of the Achafalaya River Delta sinking. House height difference example: 6 inches / 15 cm - Bill Nye uses a personal anecdote to illustrate the significance of small elevation differences. Shuttle Atlantis mileage over 13 days: over 5 million miles - News item describing Atlantis’s Columbus delivery mission. Distance comparison: about 10 round trips to the moon - Equivalent mileage for Atlantis’s 13-day mission. Ulysses mission duration: 17 years in space - The mission is described as nearing its end after much longer than planned. Ulysses planned vs actual duration: almost four times as long as planned - Its extended operation due to longevity and power source endurance. June/seasonal clue: 73? no explicit metric - No reliable numeric data beyond those already listed. Carried by three spacecraft in the A-Train middle: 3 - Bruce Betts says three of the five A-Train spacecraft observe within seconds of each other. A-Train total spacecraft: 5 - Bruce Betts describes NASA’s Earth-observing constellation.

Pivotal Quotes: "We only got a snapshot of Neptune from that flyby." — Tom Spilker: Explaining why a return mission is needed after Voyager 2. "Neptune's gravity. We can change up to about 60 degrees." — Tom Spilker: Describing how Argo could use Neptune for a major trajectory change toward the Kuiper Belt. "We believe in the PBJ, the passion, beauty, and joy of space exploration." — Bill Nye: Planetary Society pitch for public support and membership.

Implications: Argo illustrates how future outer-planet missions hinge on science return, RTG policy, and trajectory design; if approved, it could greatly expand Kuiper Belt exploration. The episode also reinforces that space data have direct practical value on Earth.