Japan: Moon lander Slim comes back to life and resumes mission
Japan’s SLIM lunar lander, which initially came to rest on its side with solar panels facing away from the Sun, has revived after changing lighting angles allowed it to regain power and resume limited operations. Commenters unpack how a lost engine nozzle led to the awkward landing, why the craft lacks self-righting mechanisms or night-survival hardware given its modest budget and tech-demo goals, and how its precise touchdown near the target still marks a significant success despite constrained science returns. Broader context includes why lunar landings remain hard, tradeoffs between robustness and cost, and shortcomings in mainstream reporting of such technical missions.
Lander orientation and power “glitch”
- SLIM is still lying on its side; it never righted itself.
- The “glitch” reported as “fixed” appears to be loss of power due to solar panels facing away from the Sun.
- As the Moon rotated, sunlight eventually hit the side-mounted panels, allowing batteries to recharge and communications to resume.
- Some commenters object to calling this a “fix,” since no active correction was performed; others note “glitch” is just being used as “non-functional state.”
Landing dynamics and design
- SLIM has no dedicated self-righting actuators; it’s “basically a box,” with only attitude thrusters that are risky to fire now.
- It was designed to land on its side after a planned quarter-turn; instead, it rotated an extra quarter-turn, leaving engine nozzles pointing upward and solar panels on a lateral side.
- A referenced explanation says a lost nozzle during final descent reduced thrust on one side, causing the tip-over, though still achieving ~50 m landing accuracy near the target.
- Debate over “upside down” vs “sideways” hinges on which orientation (flight vs final rest) is considered the reference.
Mission scope and expected lifetime
- SLIM is a technology demonstrator for high-precision landings on slopes; surface observations are considered a bonus.
- It was not designed to survive lunar night; expected temperatures of –130°C to –250°C and lack of radioactive heaters likely mean it will not “survive” structurally or electronically.
- Remaining time before lunar night is short, so team is focusing on optical observations of nearby rocks; power is constrained due to suboptimal panel angle.
Rovers and surface operations
- Two tiny deployed robots (one ball-like roller, one hopper) continue limited surface work and imaging; one can communicate directly with Earth.
- Idea of using them to push SLIM upright is dismissed as unrealistic given their size.
Why lunar landings remain difficult
- Thread notes that most failures occur during descent due to small, unanticipated issues that lack on-site human intervention.
- Several comments contrast expensive, heavily risk-mitigated historical programs with today’s comparatively low-budget, higher-risk missions.
Media and discussion tone
- Multiple commenters criticize mainstream coverage as technically shallow or confusing.
- Others note strong “armchair engineering” in the thread but are broadly impressed SLIM revived at all, with humor (Kerbal Space Program, “send commands upside down,” Monty Python) interspersed.