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Orbital refueling
- Thread starter Cosmacelf
- Start date
Ultimately it's not a whole lot different from docking. SpaceX has that down. Their initial ideas seem pretty sound. Elon showed the idea in one of his Mars presentations. You dock two ships together, thrust in a certain direction, which causes the fuel to move into the ship that needs it. The process still has to be tested though.
A number of entities are working the the satellite refueling problem FWIW. Northrop Grumman (via their Orbital acquisition from years ago) is probably in the lead with MEV. (While it does have a few missions under its belt it hasn't actually transferred propellant on orbit yet).
A big reason refueling hasn't happened yet is because no vehicle on orbit has been designed for refueling (except for some new sats that wouldn't need refueling anyway). The practical impact to that is a service sat has a massively complicated task in front of it, not the least of which is Step 2: remove the safety wire from the satellite's fill/drain valves.
(Step 1 is "catch satellite"). SpaceX is in a favorable place where the entire system can be designed from the start with liquid transfer in mind.
Yes, that was the plan, but now it appears to have changed. Of course they are still probably at least a year away from doing a test so by then the current plan may change again.
Watched a silly movie called "Moonfall" on a plane to Australia. It had a number of complimentary comments about Elon and SpaceX, and one of the minor plot points was that they used a SpaceX orbital refueling station to save Earth.
Having said that, don't go out of your way to see it unless you're a fan of Halle Berry.
Having said that, don't go out of your way to see it unless you're a fan of Halle Berry.
I started that film but could not finish it. It was beyond silly, it was moronic. Set in the present day, it repeatedly violated the basic laws of physics and did not just stretch the bounds of credulity, it exploded them. It was a non-stop insult to one’s intelligence.
The reference to a SpaceX orbital refueling station was not a mitigating factor.
I think I will Love it. Exactly the kind of crap I love. The more the stupid the better, as long it doesn't pretend to be a sci-fi movie, like say the "Independence Day"
Terminator857
Active Member
It will be cool when we have a space station that can hold fuel. No need to make several trips for refueling for super heavy as the fuel is already waiting in space.
I foresee SpaceX getting a billion dollar contract award for garbage cleanup. Future space stations may have be designed to clean up debri and or increased armor for protection.
Oof... obviously entertainment is subjective... but most movies require some degree of "suspension of disbelief"... for folks that have no idea of the science/laws of physics involved, such plot devices may not be distracting. For some of us that have at least a decent grasp of such things, movies that don't just take minor liberties but instead re-write such laws completely can be awfully distracting... I tend to be more in @ecarfan 's camp...
It really depends on whether the movie has other redeeming qualities for me. For instance, The Space Between Us, had a horrendous plot hole such that somehow there was no speed of light communication lag between Mars and Earth. If you could ignore that, the movie was a very sweet teen romance and I'm a sucker for romances.
Ben W
Chess Grandmaster (Supervised)
I would imagine that the main benefit of acceleration is to settle the fuel in the tank so it can be pumped without bubbles. It might be quite expensive/wasteful to use continuous thrust to do "passive" pumping; I would imagine it might work better to dock the craft together and spin them slowly around each other to settle the fuel using centripetal acceleration, then actively pump from one to the other (visualize a countertop soap dispenser where gravity settles the soap to the bottom but it pumps out the top), then un-spin. That would also allow the transfer to be done more slowly, with smaller pumps and pipes, without wasting fuel.
I also wonder whether it might make sense to keep on-orbit fuel and oxidizer depots separate, to minimize the chance of O2 and CH4 combining and exploding from an accidental collision or space junk impact. And/or have alternating tankers transport fuel and then oxidizer as payload, rather than have each tanker transport both. (Obviously some of both will be needed as landing propellant.)
I like your centripetal accel idea for settling the liquid in the craft. However, I would expect that there would be dedicated orbital refilling craft that are used as permanent depots that would not routinely re-enter and land. They would just need propellant for maneuvering and solar arrays to maintain power. Other Starships would repeatedly launch, refill the depot ships, then re-enter to reload.
Ben W
Chess Grandmaster (Supervised)
I expect that for the foreseeable future, the orbital depots will simply be constellations of individual Starship tankers, modified slightly for long-term fuel storage. I'm not sure what the benefit would be of connecting multiple tankers together, and it would probably add unnecessary complexity and risk to construct larger tanks on-orbit. (Safer to construct and test the tanks on the ground, and launch them in one piece.) Even if a tanker-size depot is nearly full, it shouldn't take much thrust to spin to settle fuel in the attached tanker. Much easier than spinning the ISS, but even that happened recently by accident! Probably 0.1g is more than enough; that's about three revolutions per minute, with a 9-meter radius, assuming the tankers mate side-to-side. Cold-gas or ullage thrusters should be easily capable of that.
On a related topic, I think the best way to send crewed Starships to Mars will end up being in pairs, tethered nose-to-nose with a ~300m Xylon tether, and spun for artificial gravity. (Earth gravity on leaving Earth's orbit, tapering to Mars gravity on arrival.) The catch arms would already be designed for exactly that load, so they could be the tether attachment points. I'll be very curious to see whether this is what they end up doing. (Or if not, why not.)
