Why it's so challenging to land upright on the moon
Landing a spacecraft upright on the Moon turns out to be far harder than it looks, mostly because low gravity, no atmosphere, uneven terrain and tight mass budgets leave almost no margin for horizontal drift or sensor failures. Commenters contrast recent private and national missions that have tipped over or barely survived with Apollo-era successes, arguing that today’s lower budgets, higher precision goals and full automation make the problem fundamentally different rather than “solved.” Ideas ranging from self-righting or spherical landers to lunar GPS, pre-built landing pads and massive vehicles like Starship are weighed against practical constraints of mass, cost, reliability and the need to protect fragile payloads.
What Counts as a “Successful” Lunar Landing?
- Debate over whether a landing is “successful” if a craft tips over.
- Some argue success = primary payload survives and functions, not just upright posture.
- Others insist that if the intended landing configuration isn’t achieved, it’s a failure.
- For crewed missions, tipping over is seen as potentially catastrophic.
Simulations, Autopilots, and Reinforcement Learning
- Multiple links to browser lander games and OpenAI Gym’s LunarLander.
- RL can land in simulation but is described as brittle and prone to exploiting sim quirks, so not trusted for real rockets.
- Human-designed guidance algorithms are viewed as more reliable despite higher development cost.
Navigation, Guidance, and “Moon GPS”
- Suggestions for lunar GPS or beacons; pushback that Apollo succeeded with celestial navigation and radar.
- Clarification: stars give attitude, not precise position/velocity; modern systems rely on radar and vision for terminal guidance.
- Keeping lunar satellites in stable orbits is described as fuel-expensive due to lumpy gravity.
Design Trade-offs: Shape, Legs, and Self-Righting
- Many armchair proposals: airbags, spheres, tetrahedrons, Weeble-like shapes, ultra-wide or deployable legs, sideways landers, self-righting mechanisms.
- Engineers in the thread emphasize constraints: mass to the Moon is extremely expensive; deployment mechanisms add failure modes; thermal, power, and comms requirements make “omni-face” designs hard.
- Historical examples (Mars airbags, Soviet Luna probes, Pathfinder tetrahedron) cited, but noted as mass-limited or not scalable to larger payloads.
Starship, Mass Budgets, and Refueling
- Claim: most problems get easier with a larger mass budget; Starship’s refueling-based architecture offers huge payload capacity.
- Counter-claim: mass budget doesn’t fix basic stability issues of a tall vehicle or fundamental physics.
- Disagreement on how many refueling launches are required (ranges from ~6 to ~20, “unclear”).
Abort Modes and Risk Management
- Discussion of “abort-to-orbit” and analogous Shuttle abort modes.
- For uncrewed landers like IM-1, no abort capability meant they were committed once descent began.
- Thread highlights that IM-1 landed without functioning altimetry due to a procedural error; many see QC/checklists as the real failure, not basic lander geometry.
Meta: History, Difficulty, and Public Perception
- Past successes (Apollo, Soviet and Chinese missions) used as both inspiration and misleading comparison: earlier programs had larger budgets and lower precision goals.
- Some criticize “epidemic” framing of recent failures as misunderstanding statistics.
- Several comments mock simplistic “why don’t they just…” solutions while acknowledging that HN naturally gravitates to such speculation.