NASA lays out how SpaceX will refuel Starships in low-Earth orbit
NASA’s plan to use SpaceX’s Starship for Artemis hinges on complex in-orbit refueling, prompting debate over how propellant transfer in microgravity will work, how many tanker launches are practical, and whether pressure-fed systems and gentle spin maneuvers are sufficient. Commenters contrast Starship’s ambitious, iterative development and promised low-cost, high-cadence reuse with the delayed, expensive SLS/Orion stack, arguing over whether relying on an unproven system is visionary or reckless. The thread also raises concerns about environmental impact, the necessity of orbital depots for sustainable Moon and Mars missions, and whether large-scale human spaceflight delivers enough long-term value compared with robotic exploration.
Propellant transfer and vehicle dynamics
- Discussion on how Starship will transfer cryogenic propellant in microgravity: pressure-fed “free flow” from a donor to receiver, with tank pressurization and propellant-settling thrusters.
- Concerns about mixed liquid/gas phases in 0g and whether pressure alone can provide reliable transfer.
- Some expect gentle vehicle spin or milli‑g accelerations to settle propellant; others note spinning massive, partially filled vehicles is nontrivial and may shift centers of mass during transfer.
- Debate over using simple pumps or venturi-like devices vs. keeping the system pressure-fed and mechanically simpler; no consensus.
Refueling logistics, boil‑off, and launch cadence
- NASA/SpaceX aim to demonstrate multi-week propellant storage and transfer in LEO; key unknown is boil‑off rate of cryogenic propellants.
- Estimates in the thread: a first lunar mission could require on the order of ~10–15 tanker flights within a 3–4 week window.
- Some argue this implies an aggressive but plausible cadence (launch every ~2 days) if reuse and pads are mature; others see it as operationally fragile and error-prone.
- Boil‑off mitigation ideas discussed: tank orientation, shading vs. sun-heating, and active cooling with radiators; effectiveness is considered uncertain.
Artemis architecture, Gateway, and Mars ambitions
- Several comments argue in‑orbit refueling is not strictly needed for the Moon, but Artemis deliberately uses it to develop tech for Mars.
- Criticism that SLS and Orion are late, expensive, underpowered, and drive awkward choices (e.g., near-rectilinear halo orbit for Gateway).
- Some see Gateway’s value in deep-space habitation and comms; others think a LEO depot or relay satellites would be more straightforward.
SpaceX Starship: optimism vs. skepticism
- Supporters point to rapid iterative testing, Falcon 9’s reuse track record, and the scalability of many daily flights as making mass depoting and Mars cargo feasible.
- Skeptics emphasize missed timelines, incomplete demonstrations (no fully orbital, fully successful Starship yet), and argue long-range performance claims lack empirical backing.
- Disagreement over whether the program is merely “late but progressing” or dangerously overpromised.
Environmental and operational concerns
- Questions raised about atmospheric pollution from many daily launches; some note methane/oxygen exhaust is cleaner than solid or kerosene systems, but overall high‑rate launch impacts are considered under-studied.
- Ground operations (inspection, refurbishment, legal/safety overhead) are seen by some as a major hidden cost; others argue heavy automation and multiple vehicles/pads can amortize this.
Human vs. robotic exploration
- One side questions the real value of human spaceflight vs. robotics, calling some crewed missions “make work.”
- Others counter that for highly complex operations, humans may still be cheaper and more capable than elaborate robotics, especially as launch costs fall.