Kind: captions
Language: en
[Applause]
should I put this down yeah of course
all right we're about to do some welding
goggle
[Music]
up here on Earth if you want to get two
metals to fuse you have to heat them up
past their melting point but in space
it's a different story as we found out
the hard
way on the 3rd of June 19 1965 astronaut
Ed White conducted the first ever
American spacewalk aboard geminy 4
tethered via a long goldplated hose he
propelled himself outside the capsule by
shooting pressurized oxygen from a
handheld gun he enjoyed it so much that
flight control literally had to order
him back into the spacecraft the flight
director says get back in back in back
in Roger we've been trying to talk to
you for a while here returning to the
vehicle he commented it was the saddest
moment of his life little did he know
what would happen next inside the
spacecraft the crew was faced with a
problem the hatch would not close for
about an hour there was no word from
gmany 4 said he's busy and he'd rather
not talk to us flying over Africa they
actually went out of range of
communication with the ground chimy 4
Houston Capcom give me your
status but after a lot of wrenching and
Brute Force they got it closed and
everything was fine the original Mission
called for another depressurization
where they would open up the hatch and
throw away a bunch of bulky gear things
they needed only for the spacewalk but
the pilot mcdot radioed to say that
under no circumstances were they going
to open the hatch again flight thought
it was because the astronauts wanted to
keep the Eva suit and gas guns as
souvenirs the astronauts eventually
returned to Earth safely with the extra
gear literally stuffed into the foot
Wells of their cramped craft so what
caused the hatch to stick well NASA
engineers at the time identified that
the failure was due to something called
cold welding you see in space if two
metals come into contact they can
actually fuse together without the need
for heat or melting of either piece the
reason for this is due to the
fundamental structure of metals which is
a little bit like this candy bar in that
they contain a lattice of positively
charged ions like the peanuts embedded
in a sea of freely moving negative
electrons like the caramel now here on
Earth the surface layers of a metal
react with the oxygen in the atmosphere
to create a protective oxide layer and
this actually prevents two pieces of
metal from joining together but in space
this oxide layer can be worn
away like if two pieces of metal are
sliding over each other as in hinges and
then the bare pieces of metal with a
little bit of force or
impact can actually fuse
together so the electrons from one piece
of metal can flow into the other
as physicist Richard fean put it the
atoms have no way of knowing that
they're in different pieces this
obviously has huge implications for the
construction and maintenance of
spacecraft like the International Space
Station so why don't we hear about more
disasters like this happening in space
all the time I mean why isn't the ISS
already a big welded mess well the truth
is that cold welding is not as big of a
problem as scientists originally thought
it was I mean experiments on the ground
in vacuum Chambers and in space have
shown that perfectly clean metal
surfaces when pressed together in the
absence of atmosphere will weld together
but in practice the metals that are used
in spacecraft are never that clean I
mean they have those oxide layers on
them not to mention other contaminants
dirt and grease and it would take a long
time for all of those things to be
eliminated so that bare metal touches in
space so the gemin 4 hatch problem was
not actually caused by cold welding it
was just a sticky door but that's not to
say that cold welding never happens for
example in 1991 the Galileo spacecraft
was on its way to Jupiter now when
scientists tried to unfurl its High Gain
antenna which was meant to open like an
umbrella it got stuck three of the 18
ribs of the antenna refused to open and
this was due in part to the fact that
they were cold welded the pins were
stuck in place and nothing the
scientists could do would open it it and
so in the end they had to scramble to
find a way to use the low gain antenna
to send back data from Jupiter something
that it was never meant to do a 2009
report by the European Space Agency
recommended three main ways to reduce
the risks of cold welding number one
where possible use Plastics or Ceramics
to avoid sliding metal onm metal
contacts second if you have to use metal
and metal try to use two different
Metals maybe two different metal alloys
because that reduces the risks of those
Metals melding together and third use
durable Coatings that resist wear to
avoid bare metal on metal contact but
cold welding is not always a bad thing
scientists have actually found it
incredibly useful in fabricating
nanotechnology you know traditional
welding techniques used on that sort of
tiny scale can often go wrong because
you're trying to pinpoint heat onto tiny
nanowires and you can end up pretty
quickly with a melted mess on your hands
so in conditions very similar to the
vacuum of outer space scientists have
shown that single Crystal Gold Nano
wires fuse to each other in seconds
using no heat just the cold welding
technique and those welds are perfect
the crystallin structure is identical to
the rest of the nanowire as are the
mechanical and electrical properties so
although cold welding is a bit of a
potential problem in space it's actually
incredibly useful here on Earth to
manufacture nanotechnology
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