Japan's precision moon lander has hit its target, but appears to be upside-down
Japan’s SLIM spacecraft has achieved an exceptionally accurate “pinpoint” landing on the Moon, touching down within roughly 100 meters of its target but ending up tipped on its nose, likely after one of its main engines lost thrust about 50 meters above the surface. Commenters weigh this mixed outcome: the lander’s solar panels are currently facing the wrong way, threatening its long‑term operation, yet it still deployed two tiny rovers — including one that photographed the stricken craft — and demonstrated a major advance in landing precision. Much of the debate centers on whether it is fair to call the mission a “success” or even “perfect” when the vehicle is not upright, and on the broader trade-offs in lander design, redundancy, and mission goals.
Orientation of the lander
- Multiple comments note the probe “appears” upside-down based on a photo, but some stress that wording is cautious until sensors are reconciled.
- Others clarify it is more like ~90° tipped onto its nose, not thrusters-up 180°, and that media headlines oversimplify.
- There’s confusion vs. correction over what “upside down” means; some argue the “up” side is simply facing away from the camera.
Precision vs. accuracy and mission assessment
- Big focus on semantics: several commenters argue the landing is accurate (hit the intended area) but not precise (precision requires multiple attempts).
- Others frame it as “accurate but not reliable” or note “consistency” would be the right word in a target-shooting analogy.
- Debate over calling the pinpoint landing a “perfect score,” with some saying that’s justified for targeting alone, others calling it rhetorical overreach.
Landing mechanics and engine anomaly
- Thread highlights that one main engine lost thrust ~50 m above the surface, making a hot/imbalanced landing likely.
- Discussion of SLIM’s “two-step” landing (rear-leg first, then pivot forward) and possible failure modes: over-rotation, bounce-back, or hitting a rock asymmetrically.
- Some push back on armchair criticism, noting lunar gravity, structural stiffness, and terrain variability make this hard to simulate perfectly.
Recovery prospects and self-righting
- People ask why RCS thrusters aren’t used to flip the probe. Replies note all thrusters are on a now-spaceward-facing plate; using them post-impact could be unsafe or ineffective.
- Added context that designing mechanical self-righting systems would cost mass and complexity; trade-off vs. science payload is debated.
- Solar panels currently face the wrong way; hope expressed that changing sun angle may revive the craft, but outcome is unclear.
Comparisons, context, and design philosophy
- Mentions of other robotic lunar attempts (Chang’e series, Chandrayaan, Beresheet, Luna-25, Peregrine, Japanese missions Omotenashi/Hakuto-R).
- Some see this as validation of more “forgiving” landing concepts (e.g., airbags), though others note those are mostly Mars-specific and not straightforward for the Moon.
- Overall sentiment: landing on the Moon is hard; despite the tip-over, many view the pinpoint targeting and deployment of small rovers as a significant achievement.
Language, naming, and media style
- Critique of verbose lead sentences in coverage; some propose clearer alternatives.
- Discussion of “pinpoint landing” meaning target accuracy only.
- Notes on SLIM’s English acronym vs. its Japanese name and the broader use of English branding in Japan.