Ulysses Mission Operations Manager Nigel Angold on the End of the Solar Polar Journey

Episode Summary

Executive Summary: This Planetary Radio episode centers on the nearing end of the Ulysses mission, highlighting its 18-year pioneering study of the Sun’s poles, its engineering durability, and the international collaboration that sustained it. The show also answers a Mars timekeeping question and features Bruce Betts’ night-sky notes, a trivia contest about naming a Saturn car, and a wrap-up on Planetary Society activities.

Main Topics: Ulysses mission nearing end after 18 years: Nigel Angold explains that Ulysses continues taking data but is expected to end soon as hydrazine fuel runs low and may freeze; the mission far exceeded its original five-year design life. Scientific legacy of solar polar observations: The interview emphasizes Ulysses’ unique polar orbit over the Sun, which enabled unprecedented measurements of the solar wind and magnetic-field reversal across a solar cycle. Engineering robustness and spacecraft design: Angold describes how Ulysses was built for radiation and simplicity, with only one major mechanical issue—the antenna-induced wobble—mitigated through operational workarounds. International collaboration and mission operations: Ulysses is presented as an early example of large-scale ESA-NASA cooperation, with mixed contributions from Europe and the U.S. and a long operational presence at JPL. Mars timekeeping and mission clocks: Emily Lochtawala explains why spacecraft use Earth-based time systems, while Mars landers also track local solar time for operations tied to daylight and power conditions. Night sky update and listener trivia: Bruce Betts discusses Jupiter visibility, satellite tracking resources, and the Saturn-car naming contest, then introduces a new trivia question about Cosmos 1’s solar sail.

Key Arguments: Ulysses lasted far beyond its planned five-year lifetime because careful operations and robust design preserved the spacecraft for 18 years. Flying over the Sun’s poles provided a unique perspective unavailable from ecliptic-plane missions and revealed information about solar wind and magnetic-field structure. The mission’s simple, radiation-hardened design made it durable, but its limited onboard software flexibility reflects its 1970s/80s heritage. International collaboration was essential to Ulysses and became easier over time through email and the internet. Mars missions keep Earth-based spacecraft clocks for command timing, but also use local solar time when surface lighting and operations depend on the Martian day-night cycle.

Data Points: Original mission duration: 5 years - Ulysses was designed to last five years before extensions. Actual mission duration at time of episode: 18 years - Angold discusses Ulysses after nearly 18 years of operation. Hydrazine consumption to prevent freezing: about 0.5 kg per month - Fuel is circulated through a cold spot to keep it from freezing. Expected remaining time: a few months - Angold says fuel depletion/freeze means only limited time remains. Solar cycle length: 11 years - Ulysses observed a full solar cycle and magnetic reversal. Hale cycle length: 22 years - The magnetic reversal cycle of the Sun is described as 22 years. Solar wind speed at lower latitudes: around 400 km/s - Typical ecliptic-plane measurements before Ulysses' Solar wind speed at higher latitudes: around 750 km/s - Ulysses found faster solar wind near the Sun’s poles. Mars day length difference: about 3% longer than Earth - Emily explains why Earth-style 24-hour clocks still work well for Mars operations. Question response window: by 2 p.m. Monday, September 1 - Deadline for the next trivia contest entry.

Pivotal Quotes: "the rumours of your death were greatly exaggerated" — Matt Kaplan: Opening exchange acknowledging Ulysses is still operating despite earlier reports of impending end. "the beauty of a mission like Ulysses is it's making unique measurements because it's flying over the poles of the Sun" — Nigel Angold: Explaining why Ulysses’ polar trajectory produced unique science. "We believe in the PBJ, the passion, beauty, and joy of space exploration." — Bill Nye: Member appeal and mission statement for the Planetary Society.

Implications: Ulysses demonstrates how robust design and international cooperation can extend mission value far beyond expectations. Its findings continue shaping solar physics, while Mars operations and public outreach segments show how mission planning and audience engagement remain central to planetary exploration.