Has in-space refueling been done?

Question

Before the Apollo program committed to the lunar orbit rendezvous mode, one of the Earth orbit rendezvous proposals involved launching two Saturn Vs, one with the Apollo spacecraft and large lunar descent stage, with little or no oxidizer in the S-IVB translunar stage, and the second carrying a large LOX tank. The two would rendezvous in Earth orbit and transfer LOX before TLI.

As it happened, the much cheaper but slightly riskier single-launch LOR plan won out and there was no in-flight fuel transfer in Apollo.

Has any space mission done a rendezvous specifically for propellant transfer?

I assume in most cases it's far cheaper to launch on one larger rocket than on two smaller ones -- if you have a larger one.

Answer 1

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 unmanned spacecraft. In the first category there are the following missions that I'm aware of.

• Gemini 8/ Agena- No fuel transfer attempted.
• Soyuz/ Soyuz- No fuel transfer attempted. This type was tried early on.
• Apollo/LEM- No fuel transfer attempted.
• Apollo/ Soyuz- No fuel transfer attempted.
• Hubble Space Telescope- Has no propulsion, thus no refueling was possible.
• Other Shuttle satellite servicing missions- I have found a few other missions, but none with fuel transfers.

As for space station dockings, here's a list of all of the space stations that have existed:

• Salyut stations- Contained an engine. The first 4 had no means of refueling, however, Salyut 6 and 7 was refueled on orbit.
• Skylab- Would have been possible to refuel via an EVA, but this doesn't seem to have been done.
• Mir- Frequently refueled by Progress spacecraft.
• International Space Station (ISS)- Frequently refueled

In addition, a few tests have been done with unmanned spacecraft to demonstrate refueling. One of these was done on the ISS (Robotic Refueling Mission), which demonstrates how to fuel with a spacecraft not designed to be refueled. The other is the Orbital Express mission, sponsored by the US government to demonstrate such refueling capacity, which refueled using purposely build spacecraft on orbit.

There are plans for two additional spacecraft to assist with refueling other spacecraft, namely:

• Space Infrastructure Servicing (SIS)
• Mission Extension Vehicle (MEV)

Answer 2

• 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.

Answer 3

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 of Shuttle-human-tended capabilities to refuel already orbiting satellites once their self-contained thruster systems have depleted fuel reserves. This demonstration is a precursor to actual Shuttle refueling missions for satellites.

The ORS has been designed to deliver about 550 lb. of fuel to a retrieved satellite. The system, developed by the Engineering Directorate at Johnson Space Center, will be tested on 41-G in various stages leading to a full hydrazine transfer between two different tanks on the ORS support structure.

For the final fuel transfer stage, mission specialists David Leestma and Kathryn Sullivan will don their spacesuits and proceed to the aft end of the payload bay where the ORS equipment is mounted on an MPESS (Mission Peculiar Experiment Support Structure) along with the Large Format Camera. There the crewmembers will open the tool kit and remove the hydrazine servicing tool which will already be hooked up to the fuel supply tank. The crewmembers will connect it to the ground fill panel of a simulated satellite panel, thus completing the fuel supply link. After pressure checking the hookup, the crewmembers will return to the cabin.

The actual transfer of the hydrazine, which is a very toxic and corrosive material, will be controlled from the aft flight deck experiment control panels. The ORS is equipped with sensors which provide pressure and temperature values and switch and valve positions.

ISTR this project got cancelled as too hazardous after the STS-51L failure. I always found that name Mission Peculiar Experiment Support Structure amusing.