Landing on Mars: How Hard Can It Be?

Episode Summary

Executive Summary: This Planetary Radio episode centers on the engineering challenges of landing Phoenix on Mars, featuring Rob Manning’s deep dive into entry, descent, and landing (EDL) failures and fixes. It also includes a Phoenix status update, a night-sky segment, a trivia contest, and brief space-news wrapups on shuttle, Deep Impact, and GLAST missions.

Main Topics: Rob Manning on the difficulty of Mars landings: Manning explains why EDL is one of the hardest problems in planetary exploration, emphasizing that every Mars landing requires extensive testing, simulation, and humility because spacecraft often behave in unexpected ways. Phoenix EDL design changes and troubleshooting: He describes major Phoenix engineering changes, including turning off thrusters due to unstable plume interactions, redesigning thruster interfaces, and validating radar and parachute behavior through tests and simulations. Phoenix landing performance and post-landing mystery: The episode notes that Phoenix landed successfully, but the parachute opened late and the spacecraft appears to have gone farther downrange than expected, prompting investigation into atmospheric density assumptions and trajectory modeling. Phoenix science operations and instrument issues: Emily Lochtawala reports on dirt contamination on the lander deck and at the TEGA/TIGA instrument, which may be preventing sample delivery into the tiny oven, while other instruments continue operating. Broader planetary mission updates: The host briefly covers Space Shuttle Discovery’s final ISS spacewalk, the renamed Deep Impact extended missions, and a delayed GLAST launch, situating Phoenix within a wider landscape of active space exploration. Night sky and upcoming Mars opportunities: Bruce Betts discusses Mars and Saturn in the evening sky, Jupiter in the pre-dawn sky, and outlines upcoming Mars launch windows for MSL, Phobos-Grunt, and ExoMars.

Key Arguments: Mars landings are exceptionally hard because spacecraft dynamics in the atmosphere are difficult to model and test. Phoenix required major late-stage design changes because hypersonic thrusters in the backshell wake field could behave unpredictably, so they were turned off. Even seemingly small components, such as radar systems and thruster mountings, can become mission-critical failure points during EDL. The spacecraft is often 'smarter' than engineers expect; unexpected behavior in software, sensors, or aerodynamics can change landing outcomes. Phoenix’s late parachute deployment did not necessarily cause a late touchdown because a lower, slower descent can offset the timing difference. The newly returned data suggest Phoenix may have landed farther downtrack than planned, possibly indicating that atmospheric density at the site was underestimated. Despite instrument issues, the Phoenix mission remains scientifically productive and continues to operate other tools while TEGA/TIGA is troubleshot. Future Mars missions, especially MSL, are adopting and extending Phoenix test procedures to reduce landing risk.

Data Points: Phoenix guests at PlanetFest: about 700 guests - Attendance at the Planetary Society’s PlanetFest celebration where Rob Manning spoke Parachute delay: about 7 seconds late - Phoenix’s parachute opened later than expected during descent Landing timing accuracy: within about 1 second - Observed landing time was close to the press announcement estimate TCM5 maneuver: very tiny maneuver - A trajectory correction made by aiming at the null vector before firing thrusters Odyssey telemetry rate: 32 kilobits per second - Used in reconstructing the landing data after Phoenix descent Phoenix vertical velocity: about 5.5 miles per hour - Trivia answer for Phoenix’s descent speed at landing Phoenix horizontal velocity: less than 0.2 miles per hour - Trivia answer for Phoenix’s near-zero lateral speed at landing TEGA oven width: about 1 millimeter - Emily Lochtawala explains why the sample screen uses millimeter-sized holes TEGA oven length: about 3 centimeters - Size of the quartz oven in the thermal and evolved gas analyzer TEGA shake rate: 5 to 100 times per second - Range of shaking frequencies used to move samples through the screen Mars launch window cadence: about every 26 months - Bruce Betts explains the orbital timing that creates Mars launch opportunities 2009 Mars opportunity missions: 2 scheduled launches - Mars Science Laboratory and Phobos-Grunt were planned for that launch window Public PlanetFest total guests: about 350 remaining late in the evening - Portion of attendees still present during Manning’s talk after Phoenix landing June 14: planned return to Earth for Discovery crew - Space Shuttle Discovery astronauts were expected back on the ground on June 14 June 11: earliest GLAST launch date - NASA delayed launch pending booster repairs

Pivotal Quotes: "They're really hard. And it's really hard to get it right." — Rob Manning: Describing the core challenge of Mars entry, descent, and landing "We found out that when you fired a rocket to go move the vehicle this way, it went this way." — Rob Manning: Explaining why thrusters were deemed too unpredictable for Phoenix EDL "It says the spacecraft is smarter than we are." — Matt Kaplan: Summarizing the lesson from Phoenix’s landing behavior and telemetry

Implications: Phoenix showed that Mars landings can succeed only through exhaustive testing and real-time adaptation. The data and anomalies will inform MSL and future missions, improving EDL design, while Phoenix’s instruments continue returning science despite operational setbacks.