43

Short answer: Space stations have been refueled on orbit, as well as some small demonstration missions. Long answer: There is only a limited number of objects that this is even an option. There are 3 types of docking which have generally happened. Those involving manned spacecraft but not a space station, those involving a space station, and those with ...


30

Unfortunately sending propellant ahead to pick up on route will not help. The same amount of propellant will be needed regardless if both are accelerated together or separately. Also if launched separately it adds to the complexity of the mission as a docking will be required. Any type of docking requires both ship and propellant store to be traveling on the ...


19

This is basically the approach being considered for getting all of the hardware to Mars for a crewed mission. However instead of refueling an upper stage that was used to get you to orbit, it is considered much easier with almost the same benefit to launch an entire fueled stage with engines instead of just the tanks with propellant. The only penalty is ...


18

If you think less about fuel and more about the other amenities for a long distance mission, you are awfully close to the concept of a cycler. The basic idea is that you take a big vessel, on which astronauts can live for a long time and accelerate it on a trajectory that regularly passes by the places you want to travel in between. You do this without a ...


16

The real problem is that, in space travel, your speed determines your trajectory, and therefore two objects can't follow the same trajectory at different velocities. Precisely, a faster interplanetary trajectory will give you a more elliptic, elongated orbit around the sun, while a slower one will be more round (and I don't even consider the case of gravity ...


14

The propulsion system of the Service Module (public relations name: Zvezda), part of the Russian side of the ISS, is refueled by Russian Progress spacecraft, and formerly by European Automated/Ariane Transfer Vehicle (ATV) spacecraft. Both Progress and ATV spacecraft deliver approximately 850 kg of propellant to the ISS. The Service Module uses storable ...


12

The ISS is periodically refueled by its cargo supply ships. NASA's Robotic Refueling Mission has experimented with refueling satellites. DARPA's Orbital Express demonstrated hydrazine refueling (among other autonomous orbital maintenance operations) between two satellites in 2007.


11

ESA is working on such an engine. an ESA-led team has built and fired an electric thruster to ingest scarce air molecules from the top of the atmosphere for propellant, opening the way to satellites flying in very low orbits for years on end The molecules collected by the intake designed by QuinteScience in Poland are given electric charges so that ...


10

In addition to the standard operational refueling missions that are part of normal station-keeping operations, there have also been experiments performed that studied in-space refueling. In particular, three phases of the NASA Robotic Refueling Mission have been completed, which simulated on-orbit refueling of a satellite not designed for refueling. A module ...


8

You can find most of the information you need on the picture below which comes from Reddit. Crucially, if you add up the relevant lines, delta-V from Mars to Earth-Mars transfer is about 5.92 km/s. Assuming they produce the vacuum raptor (not planned for the very first starship missions) Starship will have an $I_{sp}$ around 380s, so by the rocket equation,...


8

There isn't much information publicly available, but the MEV appears to dock to the one component many satellites have in common: the rocket engine nozzle. An extensible probe from the MEV (on the left) enters the rocket nozzle and (presumably) expands its tip. Frame from a video on the Space Logistics website, annotation mine. A line in the fact sheet ...


8

The reason for the acceleration is not so much to cause the transfer of the liquids, but to get the liquid to be at one end of the tank where the pump inlet is. Remember in zero-g, the liquid is not going to stay at one part of tank but will slosh all over and mix with "air" or whatever gas is in the tank along with the liquid fuel. Without a little bit of ...


8

No. (Unless it has been done as part of a secret mission.) NASA's Space Technology Mission Directorate had plans for just that called Cryogenic Propellant Storage & Transfer (CPST), which would have launched a mission to demonstrate both the transfer of cryogenic propellent, and its storage in space for a long period of time. Unfortunately it was ...


8

I didn't see this referenced anywhere so I'm including it for completeness. Feel free to merge it in with another answer. STS-41G (launched October 5 1984) included a secondary payload called the Orbital Refueling System (ORS). Here's a description from the Press Kit ORBITAL REFUELING SYSTEM (ORS) The Orbital Refueling System experiment is a demonstration ...


8

Several things that KSP does not model: The challenges of actually docking two things mechanically together without a handy human such that the plumbing works (leaks have a tendency to go bang) The extra instrumentation required to dock with enough reliability to not risk the mission (need duplicate equipment). Notably for the ISS many craft just take ...


7

This is a short answer but in KSP pumping fuel is totally costless, whereas in reality pumping fuel between stages is difficult even in the case where the stages are mated together on the ground. This is especially true when the propellants are cryogenic and therefore more akin to a thick slush than easily-pumped liquid. On the other hand, I have found a ...


6

Shuttle orbital manuevering / attitude system tankage used screens to ensure that fluid always remained at the tank exit. Sufficient fluid would cling to the screens to get the engines started. The screens are shown in this schematic of an Orbital Maneuvering System tank. In this case the screens are only at the aft because this system always provided thrust ...


6

Rather than having fuel tanks you meet on the way the better way would be preposition fuel tankers at the start and end of the trip i.e Earth and Mars orbit. You put fuel tankers in Earth's orbit as its the easiest place to refuel (in this scenario) and means you can make use of small rocket launches (crew, ship, and fuel separately) instead of needing one ...


5

I think it’s because they want to use the same pipe work they use for tanking on the ground in orbit. I imagine the Starship will have an LOX inlet/outlet on one side and a Methane inlet/outlet on the other and all Starship will be built in the same way. If you back one Starship onto another with the heatshields pointing in the same direction the LOX pipe ...


5

Theoretically possible, but not planned. Refuelling in the sense of replacing expended fuel in the propulsion system is possible in theory. This answer provides a nice schematic of the propulsion system, and according to the legend at least there is a valve for filling up the propellant tanks. Presumably, you could "top it off" again once the fuels is ...


5

The difference in loading a flown booster and a brand new booster is the same. SpaceX starts loading RP1 and first stage LOX at T-35 min. RP1 fueling on the first stage finishes around the T-3 min and second stage around T-2 min time. For LOX fueling, they never really finish loading, they will keep topping off the LOX that's boiled off til about liftoff. So ...


5

So the basic fact is that the delta-V from LEO to LLO (low lunar orbit) using a high-thrust system is about 4 km/s and using a low thrust system it's about 8. source So, using something like a vacuum raptor engine ($I_{sp}$ 382s) you need a mass ratio of about 2:1. That is, for every ton you want to deliver to LLO you need 2 tons of methalox in LEO. Using ...


4

For the Salyut 6 space station, both Progress cargos and the station used bladder tanks. The tanks were pressurised using nitrogen. The nitrogen could be recovered once the operation was done (at least on the station side). To vent the pipes, they just let them open, exposed to vacuum for a week then purged with nitrogen. Source:The Story of Space Station ...


4

Ullage (i.e. getting the fuel at the end the tank you want it to be at and the pressurant at the other end) for large rocket stages in free-fall is usually handled with small auxiliary thrusters. For small thrusters, it's practical to use bladder pressurization or some other solution; you use the small thrusters to slightly accelerate the large stage, and ...


4

So long as the object you wish to slow is made of metal you can slow it by putting a ring of magnets around it. How fast this will work depends on the metals involved. I do not believe this can bring it to an actual stop, however--the slower it turns the less braking force. Edit: Yes, you can stop it--if your ring is spinning the velocity won't go to ...


4

The presentations Musk made at the IAC suggested 6 tankers to one spaceship, for a Mars mission. Two tankers to one spaceship for a lunar mission.


4

My reading of the Aviation Week article on this seemed to suggest that while Landsat-7 was not designed to be refueled, when they looked at its design, they found a fuel line, they could patch into that could be used to fill the tanks again. They need to cut away the insulation to get to the pipe, and then will probably use some variant of a vampire tap to ...


3

For missions that require more fuel than the standard ACES stage contains, they propose to launch 2 rockets, one with the ACES stage and payload, one with extra LOX en LH. They also propose using the ACES stage and XEUS lander as space tugs, keeping them in space for a long time instead of having to launch a new one for every mission. That's what the '...


3

The big problem with sending supplies and fuel ahead is that there's many ways it could go wrong which would end up with the crew being dead. There's no major advantage to sending supplies ahead of the mission to orbit another body, and a lot of risk. The thought is that you can split the cargoes and launch them in smaller, cheap rockets rather than ...


3

The ISS can be refueled with UDMH and N2O4 by visiting vehicles, initially the ATV: http://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration/ATV/Premiere_for_Europe_Jules_Verne_refuels_the_ISS The propellant transfer is done through the docking connector, through pipes that run outside the pressurized portions of the ISS.


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