Fred Jansen: How to land on a comet

The Epic Quest of the Rosetta Spacecraft

The Origin of the Solar System

• The speaker introduces the Rosetta spacecraft mission, emphasizing its goal to land on a comet and explaining the need to understand solar system origins.

• Formation of the sun and planets occurred from a primordial cloud of gas and dust; comets played a crucial role in delivering water and organic materials to Earth.

• Comets are likened to simpler puzzles compared to complex life emergence, highlighting their significance in early Earth conditions.

Comet Dynamics and Their Role

• Jupiter and Saturn's gravitational interactions reshaped the solar system, pushing comets into the Kuiper Belt where they remain largely unchanged for billions of years.

• Comets have two distinct tails: a dust tail influenced by solar wind and an ion tail following magnetic fields, with key features like coma and nucleus.

Importance of Studying Comets

• Comets preserve original materials from solar system formation, making them ideal subjects for studying Earth's beginnings and potential life origins.

• ESA initiated its Horizon 2000 program in 1983, leading to missions like Giotto that confirmed comets as valuable research targets.

Development of the Rosetta Mission

• The Rosetta mission was approved in 1993 after successful findings from previous comet studies; it faced delays due to Ariane rocket issues but launched in 2004.

• Churyumov-Gerasimenko was selected as a target because it is relatively new to the solar system since being deflected by Jupiter in 1959.

Achievements of Rosetta

• Notable first achievements include orbiting a comet, landing on one, navigating using surface landmarks instead of traditional methods, and operating beyond Jupiter's orbit using solar power.

• The spacecraft utilized gravitational slingshots around Earth, Mars, and asteroids for efficient travel without excessive fuel consumption.

Hibernation Phase Before Arrival

Approaching the Comet: The Rosetta Mission

Initial Maneuvers and Testing

• In May 2014, the Rosetta spacecraft approached the comet, initiating rendezvous maneuvers. During its journey, it flew by Earth to test its cameras, capturing images like a "selfie" of Mars.

• Upon waking from hibernation in January 2014, Rosetta was two million kilometers from the comet but traveling at a speed significantly faster than required.

Braking and Navigation Challenges

• The spacecraft was moving 2,800 km/h faster than the comet's velocity, necessitating eight braking maneuvers. One significant maneuver lasted seven hours and consumed 218 kg of fuel amidst concerns over propulsion system leaks.

• The true rotation period of the comet is approximately 12.5 hours; flight dynamics engineers anticipated challenges in landing due to its irregular shape.

Mapping for Landing Site Selection

• Detailed mapping of the comet became essential to identify a suitable landing area that was flat and within a 500-meter diameter—this was crucial given their landing error margin.

• Photoclinometry was employed to map the surface using shadows cast by sunlight on rocks. This technique allowed for comprehensive coverage of the comet's surface features.

Time Constraints in Decision Making

• The entire process from mapping to selecting a final landing site took only 60 days—a stark contrast to typical Mars missions which involve years of planning with large teams.

• Commands were prepared for Rosetta to deploy Philae once an appropriate landing site was identified.

Precision Requirements for Landing

• For successful deployment, Rosetta had to be precisely positioned in space while aiming towards the comet since Philae operated passively during descent.

• The trajectory for landing lasted seven hours; even minor errors in velocity could result in significant misalignment upon arrival at such vast distances from Earth.

Scientific Instruments and Findings

• Rosetta carried various instruments capable of analyzing gas composition, dust particles, and magnetic fields among other scientific measurements related to the comet's environment.

• Data collected showed variations in gas density correlating with solar heating effects on different parts of the comet as it rotated—indicating active outgassing processes.

Discoveries About Dust Particles

• Analysis revealed organic compounds present on or near the comet’s surface; findings included sodium and magnesium concentrations dating back to early solar system formation events.

• Imaging results showcased unexpected geological features resembling boulders and dunes—similarities drawn with formations found on Mars despite comets lacking atmospheres necessary for wind-driven processes.

Comet Exploration Insights

Comet Activity and Structure

• The comet exhibits intriguing features, including a pit from which three jets are observed, indicating active regions where material evaporates into space.

• A notable crack in the neck of the comet measures one kilometer long and 2.5 meters wide; some speculate it may split when approaching the sun, complicating exploration efforts.

Lander Design and Functionality

• The lander is equipped with various instruments similar to those on Rosetta, aimed at comparing findings in space with those on the comet for ground truth measurements.

• Images captured by the OSIRIS camera show the lander's descent towards the comet's surface, highlighting its proximity just before landing.

Landing Sequence and Challenges

• Post-landing images reveal that while the lander was expected to settle, it actually bounced off due to hitting a crater edge during its first contact.

• Initially designed to bounce, this feature was discarded for cost reasons; however, unexpected bouncing occurred during landing.

Data Collection and Findings

• Magnetometer data indicates a change in rotation velocity after impact with a crater edge during landing; this suggests an element of luck in their current position.

• An iconic image shows a leg of the lander on the comet's surface; ongoing efforts aim to locate and reactivate the lander as it remains unresponsive.

Comet Composition and Activity Levels

• The comet has half the density of water, suggesting it appears solid but is less dense than expected; significant activity increases were noted last summer.