In July 2004, Astronaut Mike Fincke melted some solder aboard the International Space Station. The behavior of the solder’s rosin in zero gravity is fascinating to watch.

The solder, heated, became a molten blob with a droplet of rosin clinging tight to the outside. Solder melts: that’s not too surprising. It’s the behavior of the rosin that amazed. As the temperature increased, the droplet began to spin, round and round, faster and faster, like a miniature carnival ride.

[Thanks, Rachel!]

Laura Cochrane

Laura Cochrane


  • Drax

    why does the droplet sit at the bottom of the solder when done, looks like it does on the others too.. if there was no gravity wouldn’t it just be random where it stopped?

    • Colin Knapp

      My guess is it is attracted to the heat coming off the paper clip (since that loses it’s heat more slowly) hence why it’s getting ‘pulled’ to the bottom.

    • Dean W. Armstrong

      I would guess the rosin has some surface tension–and we can confirm it does because the liquid rosin keeps itself together as a fairly well-defined droplet–and the surface tension drives it “down” the wire. I suppose it would also if it had gotten near the “top” near the point of solidification it would have gone there. Interestingly, the rosin is intended as a wetting agent for the solder, to reduce its surface tension.

    • jammitweapon

      Liquids, like molten solder, will flow from the coolest area to the hottest. If heat was applied to the paper clip, it would be hotter than the solder blob. If you’ve ever sweated copper water pipe, you know to heat the joint so the solder will be “sucked” into it. This is the reason why you want to heat the joint and not the solder.

  • Vadimk

    hmm, floating molten solder, but they do make him were some snazzy safety gear.

  • Kris Lee

    Those were very brave men.

  • Charlie

    Pretty neat, but industry will have to be in a spun habitat. People have been really trying to replace lead and tin solder and have not had much success, to much tin you get fine crystals growing that create electrical shorts.
    I think maybe paint type of rosen and rosen free lead solder might work better. Also maybe a little iron in the lead and a magnet on the other side of a circuit board. Surface tension, once adhesion begins should do the trick afterward.

    Super experimental choice! Great going!

    • jammitweapon

      It is possible to tin/lead solder without a flux of any type. You just have to do it in an oxygen free environment. If you have some flux free plumbing solder you can try this. Apply oil to a scrubbing pad. Use this oily pad to clean both the solder and the copper. Make sure to leave a layer of oil on both surface when you clean. Solder through the oily layer like normal. The oil prevents oxygen from getting to your freshly cleaned surfaces. Take care of oil smoke and prepare for the chance of an oil fire.

  • Patrick Burns

    So… it begs the question, how are astronauts going to do any electronic repairs in space on future missions?

    • Phil

      The answer is extremely simple – astronauts already have done electronics repairs on a regular basis.

      Sergei Krikalev did soldering on the Mir space station in the early 1990s to make assorted repairs.

      Brian Duffy did a controlled soldering experiment in a glovebox on the STS-57 shuttle mission in 1993.

      Bill Shepherd did some soldering on the first crew to the International Space Station in 2000.

      Don Pettit did some educational demonstrations with a soldering iron during his first spaceflight in 2002.

      Those are off of the top of my head.

      The preferable repair method in space is using solderless crimps for obvious safety reasons (and it’s been done dozens of times on the shuttle). But sometimes soldering is the better approach.

  • majorproblem

    Isn’t this just another example similar to what happens if you put droplets of water on a hot stove plate? (Leidenfrost effect says a quick google:

  • Jim Gage

    spinning rosin… outgassing due to combustion. A mini rocket engine.

  • docbrown56

    Three things, like the monkey in the middle of a dance contest : 1) at the 17sec. spot,(the small object that flew off, went to the next paperclip blob, orbited, then flew off screen), 2nd) even in space centrifical forces should have pulled the two blobs apart, 3rd) why didn’t the metal solder-blob slip off the metal wire? I smell thesis ,or is that theses? Also did you notice how those blobs almost looked like the interaction between EARTH and MOON? Just sayin’ .