4 ms·
Prior to Starship, just getting large enough structures and mass into space has been the limiting factor. There is a minimum diameter for spin gravity to avoid
by maccam94 5y ago
Prior to Starship, just getting large enough structures and mass into space has been the limiting factor. There is a minimum diameter for spin gravity to avoid disorienting vestibular side-effects. Spinning two spacecraft attached by a tether might work for short-term use cases, but I don't know how feasible it is to keep that stable for months or years. Transporting adequate volumes of water shielding is probably infeasible for SpaceX's planned Mars mission profile:
- you need 1 meter of water shielding to reduce radiation to safe levels[0]
- each cubic meter of water is 1 metric ton
- Starship's circumference is ~28 meters
Assuming you only shield 4 meters of the length of the ship, not counting the top and bottom cross sections of the cylinder, you've already blown past the 100T payload capacity of Starship.
[0]: https://space.stackexchange.com/a/1826 https://space.stackexchange.com/a/1826
- nojokes 5y agoYou can use multiple deliveries when water is added in orbit.
- maccam94 5y agoYes, that works fine for a space station, but not so much for a rocket that needs to accelerate and decelerate it on a trip to Mars (and back).
- nojokes 5y agoEspecially for such rocket because you may need also additional fueling.
- maccam94 5y agoStarship already requires in-orbit fueling to fully refill its tanks for the outbound journey to Mars when loaded to its 100T payload limit. It cannot carry additional fuel to accelerate and decelerate another 100T+ of water shielding. SpaceX currently plans that Starship will return to Earth from the Martian surface without in-orbit refueling. I don't know the payload capacity for that trip offhand, but again water shielding would exceed the 100T mark and it would be an incredible amount of added complexity to do in-orbit refueling there with the limited fuel generation infrastructure.
- seaorg 5y agoMultiple launches. Assemble and fuel a big spinning water bottle in orbit. Maybe tether maybe not. Spin up and establish cycle orbit. Done. Basic physics and orbital mechanics. https://en.m.wikipedia.org/wiki/Mars_cycler https://en.m.wikipedia.org/wiki/Mars_cycler
- seaorg 5y agoActually, assemble multiple water-filled cylinders in earth orbit and then put those in staggered cycle orbits. Power requirements are low so all you’d need is a regular engine with a large fuel tank. Once those are in cycle orbit you now have giant water cylinders that you can catch every once in a while to ride to earth/Mars. Forever. With a tiny energy budget for corrections. Just wait till one passes by and slip your vessel inside it. Man I am good.