0:00:04 > 0:00:07NASA's space shuttle is the most complex machine ever built,
0:00:07 > 0:00:11making it one of the world's most expensive vehicles.
0:00:15 > 0:00:19But then, it does travel 25 times faster than a speeding bullet,
0:00:19 > 0:00:24and it carries cargoes worth tens of millions of dollars.
0:00:24 > 0:00:28It's the world's first reusable spaceship.
0:00:28 > 0:00:31On each mission, it flies around four million miles.
0:00:33 > 0:00:37But no matter how clever the rocket scientists behind it are,
0:00:37 > 0:00:40this incredible feat of engineering wouldn't have been possible without...
0:00:40 > 0:00:41a church organ...
0:00:43 > 0:00:45..a German U-boat...
0:00:45 > 0:00:47..tram tracks...
0:00:48 > 0:00:49..a camera...
0:00:49 > 0:00:50It's mega!
0:00:50 > 0:00:53..and a cannonball.
0:01:07 > 0:01:11For NASA engineers, the Apollo moon missions were a tough act to follow.
0:01:12 > 0:01:14Even as man walked on the moon,
0:01:14 > 0:01:18the question was, "What would NASA do next?"
0:01:18 > 0:01:20The answer was the space shuttle.
0:01:22 > 0:01:26It launches into the Florida sky from the pads behind me.
0:01:26 > 0:01:30And as the world's first reusable space vehicle,
0:01:30 > 0:01:33it's made the final frontier just another destination.
0:01:33 > 0:01:37A fleet of five shuttles has blasted off
0:01:37 > 0:01:41from the Kennedy Space Centre more than 130 times.
0:01:41 > 0:01:44They've delivered well over 1,000 tonnes of cargo,
0:01:44 > 0:01:49including most of the International Space Station and the Hubble Telescope.
0:01:49 > 0:01:54Not bad for a delivery truck, albeit quite an expensive one.
0:01:54 > 0:01:58A new one will set you back a cool 1.7 billion.
0:01:59 > 0:02:04And taking it out for a spin costs about 450 million.
0:02:06 > 0:02:11But NASA designed the shuttle to reduce the cost of space exploration.
0:02:11 > 0:02:14So the shuttle is reusable,
0:02:14 > 0:02:18an ingenious jack of all trades, part plane, part rocket.
0:02:25 > 0:02:27I've come to look behind the scenes.
0:02:27 > 0:02:31Only astronauts or rocket engineers get close to the shuttle.
0:02:31 > 0:02:36This is the place where it starts. So next stop, space.
0:02:36 > 0:02:40But as they prepare for the shuttle's last ever launches,
0:02:40 > 0:02:44NASA has given me special access to see how it really works.
0:02:44 > 0:02:46You just picked it up!
0:02:46 > 0:02:51The shuttle is a combination of specialised parts put together
0:02:51 > 0:02:57for every trip and then rolled out to the launch pad - rather slowly.
0:03:00 > 0:03:04The shuttle isn't the white plane. That's the Orbiter,
0:03:04 > 0:03:08the bit which carries the astronauts to space.
0:03:08 > 0:03:12To get them there calls for two different rocket systems
0:03:12 > 0:03:14and a huge orange tank to store liquid fuel,
0:03:14 > 0:03:17all of which are jettisoned before reaching space.
0:03:19 > 0:03:21The whole assembly is the shuttle.
0:03:25 > 0:03:29The main rocket engines are at the rear of the Orbiter.
0:03:29 > 0:03:32They burn furiously during the shuttle's
0:03:32 > 0:03:33eight-and-a-half minute ascent into orbit.
0:03:36 > 0:03:43They are extremely powerful - 37 million horsepower, to be precise.
0:03:43 > 0:03:45And they propel the 2,000 tonne shuttle
0:03:45 > 0:03:49up to 650km above the Earth's surface.
0:03:58 > 0:04:03NASA has allowed me into the workshop where they overhaul the engines.
0:04:04 > 0:04:07- This our main engine shop. - This is where it all happens?
0:04:07 > 0:04:10This is where we prepare all these motors after they've flown
0:04:10 > 0:04:14- to reinstall and get ready to go again.- And these are they?
0:04:15 > 0:04:20'Mike Cosgrove is no ordinary grease monkey.
0:04:20 > 0:04:23'He's one of NASA's elite rocket scientists.'
0:04:23 > 0:04:26These are the next set of engines we're going to be installing.
0:04:26 > 0:04:28We're finishing up the processing on those,
0:04:28 > 0:04:32they've flown and gone through our shop here, and they've been completely refurbished
0:04:32 > 0:04:35and we're just putting the final touches.
0:04:35 > 0:04:37- So this'll be used next? - This'll be used next.
0:04:37 > 0:04:41- This isn't a one-shot deal is it? - No, this is a reusable engine.
0:04:41 > 0:04:45- Some of these motors have flown up to 25 times.- Four million miles...
0:04:45 > 0:04:48- Per trip.- This could be a hundred-million-mile job? - Absolutely.
0:04:48 > 0:04:49Probably time for a service.
0:04:49 > 0:04:53These engines don't just travel enormous distances,
0:04:53 > 0:04:57they withstand extreme temperatures.
0:04:57 > 0:05:00Without any protection they would self-destruct.
0:05:01 > 0:05:07Temperatures exceed 3,300 degrees C or 6,000 degrees Fahrenheit.
0:05:07 > 0:05:10At 6,000 degrees, what would they do?
0:05:10 > 0:05:12- Normal metals would melt.- Yeah. Gone.
0:05:12 > 0:05:15'And that is a problem.
0:05:16 > 0:05:21'Engines that melt will never do the job they're supposed to do.
0:05:21 > 0:05:24'It's like trying to make a kettle out of chocolate.'
0:05:24 > 0:05:26And we start with the very definition of uselessness -
0:05:26 > 0:05:27a chocolate kettle.
0:05:27 > 0:05:30Chocolate kettles, of course, famously useless
0:05:30 > 0:05:32because in order to heat water to be hot enough
0:05:32 > 0:05:33to make a decent cup of tea,
0:05:33 > 0:05:36well, on the way you'll melt the kettle.
0:05:36 > 0:05:37Chocolate is designed to melt in the mouth.
0:05:37 > 0:05:41In other words, at just below body temperature.
0:05:41 > 0:05:45So just to prove a point, I shall now try to make a lovely cup of tea.
0:05:47 > 0:05:51Yes, clearly already it is having trouble.
0:05:51 > 0:05:55Yep, its reputation is clearly deserved. Useless.
0:05:59 > 0:06:03Just as easily as my kettle, at shuttle operating temperatures,
0:06:03 > 0:06:06even metals would melt like chocolate.
0:06:09 > 0:06:12For the solution, NASA turned to a 19th-century machine
0:06:12 > 0:06:15that transformed church music.
0:06:18 > 0:06:20Church organs need a flow of air.
0:06:20 > 0:06:25Until a little over 100 years ago, it was pumped by hand.
0:06:25 > 0:06:28Right, to work, this is the lever, those are the bellows.
0:06:28 > 0:06:31I pump the lever. It puts air into the system.
0:06:35 > 0:06:39And there you have it, the original Hammond organ.
0:06:39 > 0:06:41Sorry, couldn't resist it.
0:06:42 > 0:06:45HITS WRONG NOTES
0:06:46 > 0:06:53Of course, inevitably, after a time, along came a machine to replace,
0:06:53 > 0:06:56well, me, the person who pumps the organ.
0:06:57 > 0:07:02It was an internal combustion engine, still in its infancy in the 1880s.
0:07:02 > 0:07:06The one first used to pump air into church organs
0:07:06 > 0:07:09also introduced an invention that would help NASA.
0:07:11 > 0:07:14And it would have been a machine very much like this one
0:07:14 > 0:07:17that replaced me driving the bellows to provide air for the organ.
0:07:17 > 0:07:20It's a single-cylinder internal combustion engine.
0:07:20 > 0:07:23But it had a problem, like all internal combustion engines,
0:07:23 > 0:07:25and the clue is in the name "internal combustion".
0:07:25 > 0:07:29It's an explosion going on inside it, here.
0:07:29 > 0:07:34And that makes the engine hot, dangerously hot.
0:07:34 > 0:07:37So it's jacketed with water. There's a water jacket around it.
0:07:37 > 0:07:39Another cylinder full of water to cool.
0:07:39 > 0:07:46Cold water is constantly circulating round the hot engine, removing the heat.
0:07:46 > 0:07:50This was the first cooling system for an internal combustion engine.
0:07:50 > 0:07:55It's a primitive version of what NASA uses on the shuttle.
0:07:56 > 0:08:00But while water can cool one of these engines,
0:08:00 > 0:08:04it's never going to do the job for NASA.
0:08:04 > 0:08:09At shuttle temperatures, most metals would get so hot,
0:08:09 > 0:08:11they wouldn't just melt, they would vaporise.
0:08:11 > 0:08:17So the rocket scientists had to take engine cooling to a whole new level.
0:08:19 > 0:08:23Luckily, NASA already had a great coolant on tap.
0:08:23 > 0:08:29Inside the giant orange tank is the fuel - super-cold liquid hydrogen.
0:08:29 > 0:08:36At minus 253 degrees Celsius, it is perfect for cooling engines.
0:08:36 > 0:08:40This is where you see the big fireball come out the backside.
0:08:40 > 0:08:42This is the bit we've all seen on the television...
0:08:42 > 0:08:44How are we going to cool this bad boy down?
0:08:44 > 0:08:47What we're going to do is take a tap off that liquid hydrogen
0:08:47 > 0:08:50that's being pumped around to the engine,
0:08:50 > 0:08:57and we're going to duct it down the side of the nozzle here, through these distribution tubes.
0:08:57 > 0:08:59It's going to fill up this manifold
0:08:59 > 0:09:03and then it's going flow back up through 1,080 tubes
0:09:03 > 0:09:07into the main combustion chamber and burn it.
0:09:07 > 0:09:11So the actual fuel that you're using is sent along these pipes here,
0:09:11 > 0:09:14- and I thought these were just marks.- These are tubes.
0:09:14 > 0:09:17..which cools this down, protects it from the heat
0:09:17 > 0:09:20- of the engine...- Correct.- ..and then it goes in and is burnt...
0:09:20 > 0:09:25- Correct.- ..which is one of the secrets to the incredible efficiency of this engine,
0:09:25 > 0:09:28- because you're using the fuel before you've burnt it.- Correct.
0:09:28 > 0:09:32The reason shuttle engines don't melt is because of a principle
0:09:32 > 0:09:36first used in an engine like this to drive the bellows of a church organ.
0:09:36 > 0:09:40A cooling system - the removal of heat.
0:09:40 > 0:09:43The shuttle's fuel-cooling system is so efficient
0:09:43 > 0:09:48it keeps the engines at a cool 54 degrees Celsius.
0:09:48 > 0:09:52But can all this rocket science help me boil water with a chocolate kettle?
0:09:52 > 0:09:57To test NASA's system, I've built a radical new prototype.
0:09:57 > 0:10:00What we have here is something pretty special,
0:10:00 > 0:10:05because this is a chocolate kettle inspired by NASA.
0:10:05 > 0:10:10I've gone one better, in fact. This isn't just a chocolate kettle, it's a chocolate ice-cream kettle.
0:10:10 > 0:10:13Because that's what that is - chocolate ice cream.
0:10:13 > 0:10:19The challenge is to stop my ice cream from melting as the water heats up.
0:10:21 > 0:10:25Here's how it's working. This is the fuel for the burner down here, liquid propane.
0:10:26 > 0:10:29It's rushing along this narrow tube here, up here.
0:10:29 > 0:10:35Just like the shuttle, I'm using freezing-cold fuel to do the cooling for me.
0:10:35 > 0:10:40It then carries its way around here, down here, into the burner. That's the actual fuel I'm using.
0:10:42 > 0:10:47Because it's staying cool up here, despite this being full of now boiling water...
0:10:49 > 0:10:53..my ice cream is staying frozen.
0:10:54 > 0:10:56That's NASA, that is.
0:10:57 > 0:11:02100 degrees on the inside, below zero on the outside,
0:11:02 > 0:11:06but it still isn't a perfect kettle.
0:11:06 > 0:11:09One thing... I didn't design any way of pouring it out.
0:11:09 > 0:11:13That's refinement, I'll work on that.
0:11:13 > 0:11:18Just like my ice cream, the space shuttle main engines don't melt,
0:11:18 > 0:11:24even though they should be getting really, really hot.
0:11:34 > 0:11:39But even the staggering power produced by the most efficient engine in the world
0:11:39 > 0:11:44isn't enough on its own to get the shuttle into space.
0:11:45 > 0:11:49At liftoff, the shuttle is just too heavy.
0:11:49 > 0:11:55The engineers needed more power, but they had to limit the weight.
0:11:55 > 0:12:00It's a tricky thing to get right. To get more power, you need more engines and more fuel.
0:12:00 > 0:12:04More engines and more fuel means it's heavier.
0:12:04 > 0:12:07So the shuttle is fitted with these -
0:12:07 > 0:12:09boosters.
0:12:09 > 0:12:12These are solid rocket boosters or SRBs.
0:12:12 > 0:12:15They have a great power-to-weight ratio.
0:12:15 > 0:12:20And as the name suggests, the fuel they burn isn't liquid, it's solid.
0:12:22 > 0:12:24And it's very, very explosive.
0:12:26 > 0:12:29The height of a 15-storey building,
0:12:29 > 0:12:33these are the largest solid rocket boosters ever flown.
0:12:33 > 0:12:39When the fuel is lit, all those elements produce about 1,300 tonnes of thrust,
0:12:39 > 0:12:43about the same as 17,000 Formula One car engines.
0:12:45 > 0:12:51To get that amount of power, the fuel has to burn at incredible temperatures.
0:12:51 > 0:12:54The secret ingredient takes us back to tram tracks.
0:12:58 > 0:13:04In the 19th century, tram tracks were just bolted next to one another,
0:13:04 > 0:13:08and the gaps between them made for a bumpy ride.
0:13:09 > 0:13:13Then in the 1890s, German chemist Hans Goldschmidt
0:13:13 > 0:13:17invented a way to weld tracks together.
0:13:17 > 0:13:21Goldschmidt discovered that he could create an intense heat,
0:13:21 > 0:13:25by burning something you might not expect to burn at all -
0:13:25 > 0:13:26aluminium.
0:13:27 > 0:13:33First used in Essen, Germany, aluminium welding made for a much smoother ride
0:13:33 > 0:13:38and revolutionized tram lines across the world.
0:13:41 > 0:13:45It's the intense heat of burning aluminium that NASA exploits.
0:13:45 > 0:13:52Burning even a small amount can be hot enough not just to fuse steel, but to cut through it,
0:13:52 > 0:13:54which is why I have one of these.
0:13:54 > 0:14:00It's an aluminium lance, made out of aluminium foil as you'd find in the kitchen.
0:14:00 > 0:14:04Lots and lots of it rolled very tightly here into fine tubes,
0:14:04 > 0:14:07wrapped in yet more aluminium foil.
0:14:07 > 0:14:11This is something you shouldn't be trying at home in your kitchen.
0:14:11 > 0:14:15But you probably don't have the other ingredient you need - compressed oxygen.
0:14:15 > 0:14:18That's over there in the tanks.
0:14:18 > 0:14:21So oxygen flows from tanks, along my aluminium lance, up here.
0:14:21 > 0:14:24I ignite it, the aluminium burns.
0:14:25 > 0:14:30In theory, once lit, this should burn at...
0:14:30 > 0:14:33at least 2,500 degrees C.
0:14:33 > 0:14:36So it should be around about half as hot as the sun.
0:14:36 > 0:14:41But can my home-made lance make an impact on solid steel?
0:14:42 > 0:14:46Right, only one way to find out. Enough talking. Let's do it.
0:15:12 > 0:15:16Sometimes you can look at theories and numbers on paper,
0:15:16 > 0:15:19and sometimes you just need to see solid evidence.
0:15:19 > 0:15:23And I think that counts. Clearly, that was pretty hot.
0:15:25 > 0:15:27Burning aluminium provides enough
0:15:27 > 0:15:32heat to cut through steel and weld tram tracks together.
0:15:34 > 0:15:38And it's the vital ingredient for the shuttle's solid rocket boosters.
0:15:38 > 0:15:41Of course, the SRBs aren't just full of aluminium foil.
0:15:41 > 0:15:44There is other stuff in there as well,
0:15:44 > 0:15:46though you wouldn't want to wrap your sandwiches in it.
0:15:46 > 0:15:48Ammonium perchlorate -
0:15:48 > 0:15:51to provide oxygen for combustion -
0:15:51 > 0:15:53iron oxide, rust, to help it burn.
0:15:53 > 0:15:55EXPLOSION
0:15:55 > 0:15:58It's the powdered aluminium, though,
0:15:58 > 0:16:00that creates super-high temperatures.
0:16:00 > 0:16:04High temperatures turn the solid fuel into vast amounts of gas.
0:16:04 > 0:16:08And it's this gas that makes the rocket move.
0:16:08 > 0:16:12Because when a lot of gas is forced through a narrow nozzle,
0:16:12 > 0:16:14you get thrust.
0:16:15 > 0:16:18It's the same thing that happens when you let go of a balloon.
0:16:18 > 0:16:21The air inside is squeezed and shoots out this way.
0:16:21 > 0:16:25That's a push. There's an equal and opposite reaction
0:16:25 > 0:16:28which means a push this way.
0:16:28 > 0:16:31So the balloon...goes that way...
0:16:31 > 0:16:32..sorry!
0:16:35 > 0:16:39The challenge for NASA was to make a rocket that has as much thrust as possible
0:16:39 > 0:16:42right at the start,
0:16:42 > 0:16:44when the shuttle is at its heaviest.
0:16:50 > 0:16:54In an attempt to find out how they do that,
0:16:54 > 0:16:56I've asked rocket man David Beeton
0:16:56 > 0:17:01to help me build my very own Great British space fleet...
0:17:01 > 0:17:02of two.
0:17:02 > 0:17:05And, just like the shuttle's rocket boosters,
0:17:05 > 0:17:08we are using solid fuel made with powdered aluminium.
0:17:10 > 0:17:14- So this is the fuel...can I hold it?- Yeah.- Is it dangerous?- No.
0:17:14 > 0:17:17'There is the same amount of fuel in each rocket,
0:17:17 > 0:17:20'which will burn along its entire length.
0:17:20 > 0:17:24'But the fuel with the hole down the middle should burn faster.
0:17:24 > 0:17:28'More fuel will be on fire at once,
0:17:28 > 0:17:32'so the rocket should fly faster right from the word go.'
0:17:34 > 0:17:37So because that's burning faster, the same load,
0:17:37 > 0:17:41because it's burning faster, the power is given more quickly.
0:17:41 > 0:17:44This will give a really good peak of power, and as it burns out,
0:17:44 > 0:17:46it will progressively increase the thrust.
0:17:46 > 0:17:49- Will that make a visible difference? - Oh, yes.
0:17:49 > 0:17:50Can we test it?
0:17:50 > 0:17:52- We can.- Can we have a race?
0:17:52 > 0:17:54I would think so.
0:17:58 > 0:18:02'So, other than the position of the ignition groove -
0:18:02 > 0:18:07'and the colour - these two rockets are identical.'
0:18:07 > 0:18:09If I drop this it's bad, isn't it?
0:18:09 > 0:18:12- It could be bad, yes. - OK, fine.
0:18:12 > 0:18:16So, to get this right, this one has the faster burning charge.
0:18:16 > 0:18:18That has the faster burning motor. That's yours.
0:18:21 > 0:18:23Rocket science!
0:18:23 > 0:18:26That's OK.
0:18:28 > 0:18:31- Yes.- Oh, yes.
0:18:34 > 0:18:36Job done.
0:18:36 > 0:18:40This is mine. Look at that one.
0:18:40 > 0:18:43EXPLOSION SOUND EFFECT
0:18:45 > 0:18:47We'll arm the system.
0:18:51 > 0:18:54Five, four,
0:18:54 > 0:18:57three, two, one,
0:18:57 > 0:18:59Go!
0:19:03 > 0:19:05In just ten seconds,
0:19:05 > 0:19:09the red rocket shoots 600 metres into the air.
0:19:09 > 0:19:13I think that was quite clear that the red one was a lot faster!
0:19:16 > 0:19:19The red rocket's fuel burns much faster,
0:19:19 > 0:19:23because more of the fuel is on fire at once.
0:19:27 > 0:19:31This means more hot gas is produced in a shorter time,
0:19:31 > 0:19:34which gives this rocket more thrust.
0:19:41 > 0:19:45The blue rocket eventually reaches roughly the same height,
0:19:45 > 0:19:48but it takes much longer to get there,
0:19:48 > 0:19:51even though it had a bit of a head start.
0:19:59 > 0:20:01- It was visibly quicker.- It was.
0:20:01 > 0:20:02And that's just a faster burn.
0:20:02 > 0:20:05- That's just the fast burn. - Same energy released,
0:20:05 > 0:20:07just more quickly.
0:20:07 > 0:20:10- Got to find them now, obviously. - Yes.
0:20:10 > 0:20:14NASA's shuttle engineers need maximum thrust,
0:20:14 > 0:20:18so they go for a bigger, faster burn...like the red rocket.
0:20:20 > 0:20:25At launch, each booster is burning fuel at the unbelievable rate
0:20:25 > 0:20:29of five tonnes every second.
0:20:31 > 0:20:33They burn for about two minutes,
0:20:33 > 0:20:35then they are jettisoned.
0:20:45 > 0:20:4830 miles up, they fall away from the shuttle...
0:20:50 > 0:20:53..and back to earth.
0:21:00 > 0:21:02They crash-land into the Atlantic Ocean.
0:21:07 > 0:21:11Here - and this is the beauty of the system -
0:21:11 > 0:21:15NASA picks them up for refuelling back on dry land.
0:21:17 > 0:21:21So, thanks to a welding technique that smoothed out tram journeys,
0:21:21 > 0:21:25the thrust provided by the solid rocket boosters
0:21:25 > 0:21:28is enough to get the shuttle off the launch pad,
0:21:28 > 0:21:31and on a journey of its own...
0:21:31 > 0:21:34hundreds of miles into space.
0:21:34 > 0:21:37But the rockets are so powerful
0:21:37 > 0:21:41that they create a very dangerous problem of their own...
0:21:44 > 0:21:46..at lift off.
0:21:47 > 0:21:51The exhaust gases that generate thrust
0:21:51 > 0:21:54also generate phenomenal sound energy.
0:21:54 > 0:22:00This is so powerful, it can have fatal consequences.
0:22:04 > 0:22:07And this is the launch pad, where it all happens.
0:22:09 > 0:22:14During a launch, this place is just alive with energy, flames,
0:22:14 > 0:22:18searing gases, incredible amounts of noise.
0:22:18 > 0:22:21I'm underneath where the shuttle sits on the launch pad -
0:22:21 > 0:22:22this is the flame trench.
0:22:22 > 0:22:25I can only be here because the shuttle isn't in place right now.
0:22:25 > 0:22:29You certainly wouldn't want to be here when the countdown hits zero.
0:22:29 > 0:22:33And this trench was used in some Apollo missions as well.
0:22:33 > 0:22:37Just to think of the incredible amounts of energy these walls
0:22:37 > 0:22:40have taken over the years,
0:22:40 > 0:22:42it kind of boggles the mind.
0:22:45 > 0:22:48The firing rockets create a thunderous sound
0:22:48 > 0:22:51that slams into the bottom of this trench.
0:22:51 > 0:22:53This sound is energy.
0:22:53 > 0:22:59And systems engineer John Lorch knows how powerful this can be.
0:22:59 > 0:23:01Even way back, three miles away,
0:23:01 > 0:23:04you can feel that energy just popping in your chest,
0:23:04 > 0:23:08you know, and it's just amazing the amount of energy.
0:23:08 > 0:23:12Unchecked, all this energy would bounce off the ground,
0:23:12 > 0:23:16straight back up towards the shuttle.
0:23:19 > 0:23:23The vibrations would be so powerful, they would wreak havoc.
0:23:23 > 0:23:29On the first ever shuttle mission, they ripped heat-resistant tiles off the surface of the Orbiter.
0:23:29 > 0:23:33That time, the Orbiter returned to earth safely.
0:23:33 > 0:23:36But it could have burned up on re-entry.
0:23:40 > 0:23:42So the engineers needed to find a way
0:23:42 > 0:23:45to protect the shuttle from reflected energy.
0:23:45 > 0:23:49To do that, they had to absorb the sound energy that roared down here
0:23:49 > 0:23:52and then bounced back up and hit the shuttle itself.
0:23:52 > 0:23:56Back at the Hammond space centre, UK,
0:23:56 > 0:23:59I can't replicate the shuttle's thunderous sound.
0:23:59 > 0:24:03But I CAN give you a taste of its destructive power.
0:24:03 > 0:24:07I'm going to build a wall here and then I'm going to knock it over
0:24:07 > 0:24:10with a pulse just of air - phewf -
0:24:10 > 0:24:13like that, only bigger.
0:24:13 > 0:24:15A lot bigger.
0:24:18 > 0:24:22I've just used the half one on the end, look, I've made a neat job of that.
0:24:23 > 0:24:26'That's the wall built.'
0:24:26 > 0:24:30'And over here is what I hope is going to blow it over -
0:24:30 > 0:24:32'a vortex cannon.'
0:24:35 > 0:24:38'First, we need to do a little test run.'
0:24:38 > 0:24:40Three, two, one...
0:24:40 > 0:24:43EXPLOSION
0:24:52 > 0:24:56That is up there amongst the most amazing things I've ever seen!
0:24:56 > 0:24:59EXPLOSION
0:24:59 > 0:25:01An explosion in the base of the cannon
0:25:01 > 0:25:05creates a single pulse of air, the shape of a doughnut.
0:25:05 > 0:25:08Unlike sound, that moves in a wave,
0:25:08 > 0:25:13the vortex flies through the air like a missile.
0:25:13 > 0:25:18The vortex has a lot of energy but can it knock over my wall?
0:25:19 > 0:25:23Jim's charging it with acetylene ready to make our explosion.
0:25:23 > 0:25:26Don't overdo it, will you?
0:25:26 > 0:25:30This is going to have to be one hefty puff of air.
0:25:33 > 0:25:34Thank you very much.
0:25:34 > 0:25:37If we're ready, everyone? In three, two, one...
0:25:37 > 0:25:39EXPLOSION
0:25:43 > 0:25:45It's just air.
0:25:52 > 0:25:56In slow motion, we can see the vortex
0:25:56 > 0:25:59as it travels through the air at over 200 mph.
0:26:06 > 0:26:10And, as you can see, it creates a fair amount of destruction.
0:26:26 > 0:26:28The shuttle's problem is much bigger.
0:26:30 > 0:26:35Its exhaust gases jet out at about 2,500 mph,
0:26:35 > 0:26:40producing vast amounts of sound energy as vibrations.
0:26:40 > 0:26:44The engineers needed to find a way to protect the shuttle.
0:26:44 > 0:26:48NASA turned to a system that connects the shuttle to U-Boats...
0:26:50 > 0:26:52..via bubbles.
0:26:52 > 0:26:55Acoustics expert, Tim Leighton,
0:26:55 > 0:26:58from the university of Southampton shows me how.
0:26:59 > 0:27:03What we have here is our very own mini sonar system.
0:27:03 > 0:27:07A tube of water, a speaker at the bottom that plays cheeps of sound,
0:27:07 > 0:27:13and at the top, an underwater microphone that will pick them up.
0:27:13 > 0:27:19You can hear the sound cheeps and they are represented on screen.
0:27:19 > 0:27:22I'm going to introduce bubbles in here,
0:27:22 > 0:27:25because bubbles are really powerful at absorbing sound.
0:27:25 > 0:27:27This is the key thing to watch?
0:27:27 > 0:27:30That cheep is going to disappear. So here we go.
0:27:30 > 0:27:34So you're literally just blowing bubbles in with this machine?
0:27:34 > 0:27:36Oh, right, I can hear that.
0:27:36 > 0:27:40But look at the screen. And it's gone.
0:27:41 > 0:27:46The bubbles you see in the pipe are killing off that sound entirely.
0:27:46 > 0:27:50We're still playing the sound cheeps through the water.
0:27:50 > 0:27:55But even the smallest bubbles are stopping the microphone from picking them up.
0:27:55 > 0:27:57There's nothing in there now.
0:27:57 > 0:28:00- Are they enough to stop it?- Yep.
0:28:00 > 0:28:01But there's hardly any!
0:28:01 > 0:28:05So these tiny, tiny, almost microscopic bubbles
0:28:05 > 0:28:07are completely killing the sound on there.
0:28:09 > 0:28:13The bubbles soak up the sound by getting hot.
0:28:15 > 0:28:18So literally, the sound leaves here, which is just this wave,
0:28:18 > 0:28:21this movement coming up through here.
0:28:21 > 0:28:23When it encounters bubbles of air in the water,
0:28:23 > 0:28:26the wave squashes the bubbles of air, that heats them up.
0:28:26 > 0:28:29So the energy in the sound wave is turned into energy in heat.
0:28:31 > 0:28:33So bubbles absorb sound.
0:28:33 > 0:28:36But how does that help submarines?
0:28:37 > 0:28:41World War II. The German U-Boat fleet is under attack.
0:28:41 > 0:28:44The Germans want to make their subs untraceable
0:28:44 > 0:28:47to the Allied destroyers and their sonar systems.
0:28:47 > 0:28:51The Allied sonar worked by sending out sound cheeps from their ships
0:28:51 > 0:28:55and then waiting for the echo to bounce back from a solid object.
0:28:55 > 0:28:57This told them where German subs were.
0:28:57 > 0:29:02If the Germans could absorb the sonar cheeps - no echo.
0:29:02 > 0:29:04They would be invisible.
0:29:04 > 0:29:08So they created rubber tiles to glue to the sides of their subs.
0:29:10 > 0:29:12Tiles with bubbles in them.
0:29:13 > 0:29:19This is a genuine World War II lining
0:29:19 > 0:29:23from a German submarine.
0:29:23 > 0:29:25And you see it's stuck onto the submarine this way.
0:29:25 > 0:29:30This side is smooth. But this side has holes in, has voids in.
0:29:30 > 0:29:35'The holes trap air, creating thousands of little bubbles.'
0:29:35 > 0:29:37When a sonar ping comes and hits this,
0:29:37 > 0:29:42these absorb the sound in the same way that those bubbles did.
0:29:42 > 0:29:46So bubbles can make German U-Boats invisible.
0:29:46 > 0:29:50But the shuttle isn't underwater, obviously,
0:29:50 > 0:29:54and it has a bit more than just cheeps of sound to deal with.
0:29:54 > 0:30:01To absorb the phenomenal noise of firing rocket engines,
0:30:01 > 0:30:04NASA turned sound absorption on its head.
0:30:04 > 0:30:10Instead of air in water, they put water in air.
0:30:10 > 0:30:13Tim's got another tube with just air in it.
0:30:13 > 0:30:17We're still sending cheeps of sound through it.
0:30:17 > 0:30:21But this time, we're going to try to block them
0:30:21 > 0:30:23with a mist of water droplets.
0:30:23 > 0:30:26- This one into this one, yeah? - Water into ice.
0:30:26 > 0:30:30OK, so I pour that in there and it makes fog.
0:30:30 > 0:30:33I can't see where I'm pouring. Hopefully it's into the tube.
0:30:33 > 0:30:37That's going in, isn't it? I feel like a wizard.
0:30:37 > 0:30:41And my spell seems to be working. Oh, look at that!
0:30:41 > 0:30:44Absolutely knocked it right back.
0:30:44 > 0:30:48So this is just fog, I'm not tipping the actual water in.
0:30:48 > 0:30:51'The microscopic droplets of water in the air are vibrating,
0:30:51 > 0:30:54'turning sound energy into heat.
0:30:54 > 0:31:00'NASA protects the Orbiter in pretty much the same way.
0:31:00 > 0:31:04'Though, needless to say, NASA's system is a bit more complicated.'
0:31:04 > 0:31:06It looks like a warehouse.
0:31:06 > 0:31:08It's actually the mobile launcher platform.
0:31:08 > 0:31:11The shuttle assembly sits on top.
0:31:11 > 0:31:13Those three, they're the Rainbirds.
0:31:13 > 0:31:16And at peak flow, nine seconds after launch,
0:31:16 > 0:31:22water hurtles through those at a rate of 900,000 gallons -
0:31:22 > 0:31:26that's 3.5 million litres - a minute.
0:31:26 > 0:31:30Releasing so much water, so quickly, through the Rainbirds
0:31:30 > 0:31:34forms millions of water droplets suspended in air.
0:31:34 > 0:31:40And it's these water drops that absorb the phenomenal sound energy.
0:31:42 > 0:31:46The system for unleashing that amount of water
0:31:46 > 0:31:49is unbelievably simple...
0:31:51 > 0:31:52A water tower.
0:31:52 > 0:31:56At heart, this is, essentially, a really big version
0:31:56 > 0:31:59of the kind of water tank you'd see outside a town or city.
0:31:59 > 0:32:01This is really just an elegant,
0:32:01 > 0:32:04simple design to get that flow rate we need.
0:32:04 > 0:32:09'When the valves open, more than a million litres of water plummets.
0:32:09 > 0:32:14'It sprays beneath the rocket engines and absorbs the thunderous sound.
0:32:14 > 0:32:19'So can water work against the vortex cannon?'
0:32:21 > 0:32:25Time to see if what's good enough for the shuttle is good enough for my wall.
0:32:25 > 0:32:27First, obviously, we've got to rebuild it.
0:32:34 > 0:32:36Lovely!
0:32:36 > 0:32:40'Next we need water. This is our Rainbird.
0:32:42 > 0:32:46'The blast I'm about to fire has exactly the same power as before.'
0:32:49 > 0:32:52'But this time, there's a curtain of water
0:32:52 > 0:32:56'between the cannon and the blocks.'
0:32:56 > 0:32:59OK. If we're ready, everybody?
0:32:59 > 0:33:01In three, two, one...
0:33:01 > 0:33:03EXPLOSION
0:33:06 > 0:33:07EXPLOSION
0:33:11 > 0:33:14In slow motion, you can see how the pulse of air
0:33:14 > 0:33:17hits the water and loses energy.
0:33:22 > 0:33:24EXPLOSION
0:33:26 > 0:33:28Look at that!
0:33:28 > 0:33:32I think we can safely say top marks, NASA, well done.
0:33:32 > 0:33:34Their theory works, as I've just proved.
0:33:34 > 0:33:38They'll be grateful. And it really did work.
0:33:40 > 0:33:45By using billions of drops of water to disrupt the energy pulse,
0:33:45 > 0:33:50the NASA engineers are able to protect their precious Orbiter and its payloads.
0:33:50 > 0:33:54And it's all thanks to the power of the bubble.
0:34:00 > 0:34:03Eight-and-a-half minutes after lift-off,
0:34:03 > 0:34:07the Orbiter is more than 190 miles above Earth.
0:34:07 > 0:34:10It's in space.
0:34:13 > 0:34:18Only minutes later, the crew is getting ready to start its mission.
0:34:25 > 0:34:29The Orbiter was designed, basically, to be a delivery van...
0:34:29 > 0:34:33a very expensive, technologically advanced delivery van.
0:34:33 > 0:34:35Its job is to deliver things into space.
0:34:35 > 0:34:37So far it's put satellites, telescopes,
0:34:37 > 0:34:40and most of the International Space Station up there.
0:34:42 > 0:34:46But you can't just pop open the back and pull out your cargo.
0:34:46 > 0:34:51Especially when it's a satellite or a chunk of space station.
0:34:51 > 0:34:57Not the easiest objects to move. And expensive if you drop something.
0:34:57 > 0:35:00So every shuttle cargo bay is armed with a helping hand.
0:35:00 > 0:35:08Back on earth, NASA has a full scale replica of the shuttle's cargo bay.
0:35:08 > 0:35:11Even if the astronauts could physically lift
0:35:11 > 0:35:12and manhandle the cargo,
0:35:12 > 0:35:15spacewalking is very dangerous.
0:35:15 > 0:35:17So NASA turned to robots for help.
0:35:17 > 0:35:21Specifically, a robot arm, called the Canadarm -
0:35:21 > 0:35:25built by those famous space scientists, the Canadians.
0:35:25 > 0:35:27They faced a real problem...
0:35:27 > 0:35:30how do you grab hold of something in space,
0:35:30 > 0:35:34without accidentally knocking it across the galaxy?
0:35:34 > 0:35:38The answer was found in a camera lens.
0:35:41 > 0:35:44Camera lenses, just like our eyes, have irises in them
0:35:44 > 0:35:48that control the amount of light allowed through the lens.
0:35:48 > 0:35:52In a camera lens, they're made up of interlocking metal plates,
0:35:52 > 0:35:57which, when twisted, change the size of the aperture in the middle.
0:35:57 > 0:36:01But how did this end up on the Canadarm,
0:36:01 > 0:36:04on board the Space Shuttle?
0:36:04 > 0:36:09The first designs for the Canadarm gripped objects, much like a hand.
0:36:09 > 0:36:15But engineers quickly realised there was a fundamental problem.
0:36:15 > 0:36:20The smallest of accidental nudges could send any cargo hurtling off.
0:36:20 > 0:36:24There is no air resistance in space, so once something starts moving,
0:36:24 > 0:36:26it doesn't stop.
0:36:28 > 0:36:33For some reason, NASA wouldn't let me play with their 100 million arm,
0:36:33 > 0:36:35in orbit.
0:36:35 > 0:36:39So to find out just how big a problem this really is,
0:36:39 > 0:36:44I've asked Neil Billingham to introduce me to one of his robots.
0:36:46 > 0:36:50So I move it like that? So that's forward.
0:36:50 > 0:36:53Ooh, it's faintly spooky.
0:36:53 > 0:36:56'What I'm doing is pretty much what shuttle astronauts
0:36:56 > 0:36:57'have to do in space.'
0:37:00 > 0:37:03'And I'm beginning to get the hang of it.'
0:37:07 > 0:37:11See if I can scratch my nose with it - it's annoying me.
0:37:15 > 0:37:18That's the best thing I've ever played with. It's mega!
0:37:20 > 0:37:24'On Earth, the claw on the end can open and close,
0:37:24 > 0:37:27'making it a perfect tool for grabbing things.'
0:37:27 > 0:37:30That closes the gripper, the other one opens it.
0:37:30 > 0:37:33Glad I didn't do that when my nose was in it!
0:37:33 > 0:37:35This claw arrangement, clearly a very useful,
0:37:35 > 0:37:39multipurpose device here on Earth.
0:37:39 > 0:37:41How would it work in space? Well, we can find out,
0:37:41 > 0:37:45because I've constructed here my very own satellite.
0:37:45 > 0:37:51The helium balloon behaves like a weightless satellite in space.
0:37:51 > 0:37:55So it's very hard to grab hold of.
0:37:55 > 0:37:57And I'm not just making this up.
0:37:57 > 0:37:59Peter Stibrany is a Canadarm expert.
0:37:59 > 0:38:02OK, it's in position. I'm going to go for a grip.
0:38:03 > 0:38:05Well, that's not worked at all.
0:38:05 > 0:38:06That's also given it a shove.
0:38:06 > 0:38:09I presume, in space, that would be really bad news.
0:38:09 > 0:38:14Certainly you could push your target away from you.
0:38:14 > 0:38:16And if we were in space, that would have just kept going.
0:38:16 > 0:38:19'One wrong move on the real, 15 metre-long arm,
0:38:19 > 0:38:24'and I could send millions of dollars worth of satellite racing out of reach.
0:38:24 > 0:38:27'Somebody would be cross.'
0:38:27 > 0:38:32'NASA needed a new way to grab hold of things in space.
0:38:32 > 0:38:35'One with 100% accuracy.
0:38:35 > 0:38:41'Then an engineer working on the robot arm had a Eureka moment.
0:38:41 > 0:38:44'A keen photographer, his inspiration was the camera iris.'
0:38:46 > 0:38:51'And I have a mini version of what he helped design to go into space.
0:38:51 > 0:38:56'Like a camera iris, it rotates, but instead of interlocking plates,
0:38:56 > 0:39:00'it has three wires that close in.'
0:39:00 > 0:39:03And almost straight away, I've captured what I'm after.
0:39:03 > 0:39:07And I reckon...
0:39:07 > 0:39:11that's my space telescope caught! It took me seconds to do it.
0:39:11 > 0:39:16Why is it so much easier with that than an ordinary grab?
0:39:16 > 0:39:20The initial volume that it can grab is very large.
0:39:20 > 0:39:23So just make sure your target is somewhere in there,
0:39:23 > 0:39:25you don't have a lot of alignment.
0:39:25 > 0:39:31Once locked tight, astronauts can easily manoeuvre a chosen satellite.
0:39:32 > 0:39:35Thanks to a simple camera iris,
0:39:35 > 0:39:39the Canadarm is now a vital part of all shuttle missions.
0:39:43 > 0:39:46But once the mission is complete,
0:39:46 > 0:39:50there is still the pressing problem of getting back to Earth...
0:39:50 > 0:39:53in one piece.
0:39:58 > 0:40:04The return journey is one of the most dangerous parts of any shuttle mission.
0:40:04 > 0:40:09And it can be fatal, as every astronaut is all too aware.
0:40:13 > 0:40:18In 2003, the Orbiter Columbia burned up
0:40:18 > 0:40:20as it re-entered Earth's atmosphere,
0:40:20 > 0:40:22killing all seven crew members.
0:40:28 > 0:40:30The problem is the incredible speed.
0:40:30 > 0:40:37At re-entry the Orbiter is travelling at 17,000 mph.
0:40:42 > 0:40:46High speeds in space are not a problem, there's no atmosphere.
0:40:46 > 0:40:51But start hitting trillions of tiny particles in the upper atmosphere and things change.
0:40:51 > 0:40:55Hitting all those particles creates friction. A lot of friction.
0:40:55 > 0:40:57And that generates heat.
0:40:57 > 0:41:00Aeroplanes, missiles and bullets are usually streamlined,
0:41:00 > 0:41:02so they can slip through the air
0:41:02 > 0:41:04creating as little friction as possible.
0:41:04 > 0:41:07Early scientists thought that would work for rockets.
0:41:08 > 0:41:13But in the 1950s, space scientist Harvey Allen,
0:41:13 > 0:41:17realised that rocket speeds come with their own problem.
0:41:17 > 0:41:20Travel at five times the speed of sound and above
0:41:20 > 0:41:22and the friction is too intense.
0:41:22 > 0:41:24No matter how sleek the design,
0:41:24 > 0:41:29no known substance could survive the heat for long.
0:41:29 > 0:41:33Allen's solution was, at first hearing, pretty radical.
0:41:33 > 0:41:39Rather than make the nose of anything needing to re-enter the atmosphere sharp and sleek,
0:41:39 > 0:41:44he said to make it blunt, deliberately un-aerodynamic.
0:41:44 > 0:41:49And that's why the Orbiter's blunt nose can be connected
0:41:49 > 0:41:54back to a very un-aerodynamic flying object - the cannonball.
0:41:54 > 0:41:58We now know a round cannonball is not the perfect flying shape.
0:41:58 > 0:42:00But its ultimate aim is not to fly,
0:42:00 > 0:42:03it's to smash as much of something as possible.
0:42:07 > 0:42:12But how does smashing into air help the Orbiter on re-entry?
0:42:14 > 0:42:18This is the University of Manchester.
0:42:18 > 0:42:22But it's a very specific little corner of the University
0:42:22 > 0:42:26because these machines are dedicated to serving
0:42:26 > 0:42:29another very, very special machine through there.
0:42:29 > 0:42:30It's a wind tunnel.
0:42:30 > 0:42:35But these winds will be travelling at hypersonic speeds. Up to Mach 6.
0:42:35 > 0:42:39That's six times the speed of sound.
0:42:39 > 0:42:41Obviously, that kind of performance
0:42:41 > 0:42:46involves the release and control of stupendous amounts of energy,
0:42:46 > 0:42:49which is why the actual wind tunnel itself
0:42:49 > 0:42:52isn't as big as some of you might have been used to.
0:42:52 > 0:42:58So to go inside it, I have one mini Orbiter with a pointy nose,
0:42:58 > 0:43:00and one with a blunt nose.
0:43:00 > 0:43:04Kostas Kontis is head of aerospace research.
0:43:04 > 0:43:09First, I want to see exactly why a pointy-nosed design
0:43:09 > 0:43:11is such a bad idea for the Orbiter.
0:43:11 > 0:43:14I guess it's got to be fairly firmly fixed.
0:43:14 > 0:43:18Of course. You don't want them to fly around. It's quite dangerous.
0:43:18 > 0:43:21What if this tunnel goes off while my hand's in there?
0:43:21 > 0:43:23Probably you would lose your hand.
0:43:23 > 0:43:25It would just be blown away.
0:43:25 > 0:43:28I don't want that to happen. Let's get this done quickly.
0:43:30 > 0:43:34'At these speeds, you can only see what's happening
0:43:34 > 0:43:37'with an elaborate system of mirrors, lenses,
0:43:37 > 0:43:39'and high-speed photography.'
0:43:42 > 0:43:46So if we can switch off the lights, please.
0:43:46 > 0:43:50- There's a lot of energy about to be released.- That's right, yes.
0:43:50 > 0:43:56'A 3.700 mph jet of air, to be precise.'
0:43:56 > 0:43:57Fire!
0:43:57 > 0:44:00LOUD WHIRRING
0:44:06 > 0:44:08That was strangely frightening.
0:44:08 > 0:44:11Right let's get that image up and have a look.
0:44:11 > 0:44:13So this is with the pointed nose,
0:44:13 > 0:44:16and with this system you can actually see the shockwave.
0:44:16 > 0:44:20'The air around the nose is compressed so much
0:44:20 > 0:44:24'that it forms super-heated shockwaves.'
0:44:24 > 0:44:29It actually hits the wings. So that's the tricky part.
0:44:29 > 0:44:33Because it's quite dangerous, the temperatures are very high.
0:44:33 > 0:44:37So this shockwave punches through the air, goes over the wings.
0:44:37 > 0:44:40And I thought that was good, it's making a tiny hole, it's sleek.
0:44:40 > 0:44:42But where that line hits the wing,
0:44:42 > 0:44:46there's a lot of energy being deposited right there.
0:44:46 > 0:44:51'The wing tips are exposed to high-speed air, so lots of friction.
0:44:51 > 0:44:53'And at Orbiter speeds,
0:44:53 > 0:44:57'the shockwave itself reaches thousands of degrees Celsius.'
0:44:57 > 0:45:02- So, because of the shape of its nose, it can tear its own wings off. - Exactly, yes.
0:45:02 > 0:45:05And the wings are rather important.
0:45:05 > 0:45:09Up until re-entry, the shuttle has been a rocket.
0:45:09 > 0:45:14But now, it's a plane that has to glide back to earth.
0:45:14 > 0:45:19So counter to what we would expect, the pointy shape doesn't work.
0:45:19 > 0:45:22So how will the blunt nose fare?
0:45:25 > 0:45:27Fire!
0:45:33 > 0:45:36- OK, that's it.- OK, lights up.
0:45:36 > 0:45:41Right, moment of truth. This is where we see, hopefully, some difference. Go on then.
0:45:41 > 0:45:44- OK. Let's pres the button.- OK.
0:45:44 > 0:45:47Whoa! Well, that couldn't be clearer, could it?
0:45:47 > 0:45:52'With a blunt nose, the shockwave misses the wings completely,
0:45:52 > 0:45:56'and deflects high-speed air away from the Orbiter's wings.
0:45:56 > 0:45:59'So no friction.'
0:45:59 > 0:46:02It's completely counterintuitive. I just would not guess that,
0:46:02 > 0:46:05if I was to design something to re-enter the atmosphere.
0:46:05 > 0:46:08I would immediately think, well, pointed is best.
0:46:08 > 0:46:10That's against what your instinct tells you.
0:46:10 > 0:46:15So, thanks to a cannonball, blunt is best for re-entry.
0:46:15 > 0:46:19But, as is seen in this footage from the Orbiter's cockpit,
0:46:19 > 0:46:23The shockwave around the craft glows intensely.
0:46:23 > 0:46:28At Mach 25, it's superheated to 5,500 degrees C.
0:46:28 > 0:46:32It might not touch the Orbiter, but as you can imagine,
0:46:32 > 0:46:35it still makes it pretty warm.
0:46:35 > 0:46:40So, at NASA's Kennedy Space Centre, scientist Martin Wilson is in charge
0:46:40 > 0:46:44of producing heat-resistant tiles to protect the space vehicle.
0:46:45 > 0:46:48Heat. It's very hot.
0:46:48 > 0:46:50So this, essentially, is a kiln?
0:46:50 > 0:46:52Yes, this is one of the kilns that we use
0:46:52 > 0:46:57in the heat treatments of the tiles during manufacture.
0:46:57 > 0:46:59And what sort of temperature is it in there?
0:46:59 > 0:47:04The temperature inside the kiln is 2,200 degrees, 1,160 Centigrade.
0:47:04 > 0:47:08These are actually the materials from which the tiles are made.
0:47:08 > 0:47:10- You just picked it up! - It's pure silica.
0:47:10 > 0:47:14- But it's just come out of there. Seconds ago.- Still very, very hot.
0:47:14 > 0:47:16Have you got special hands? Can I do that?
0:47:16 > 0:47:19No, you can do that. Touch it only by the corners.
0:47:19 > 0:47:23That's just come out of that kiln. That's astonishing.
0:47:23 > 0:47:26You can still see the energy bouncing around inside it.
0:47:26 > 0:47:29'Silica cools down very fast at its edges.
0:47:29 > 0:47:35'But because the tiles are effectively a silica foam,
0:47:35 > 0:47:38'they are also full of air.
0:47:38 > 0:47:41'This makes them great insulators.
0:47:41 > 0:47:45'So, thanks to these heat-resistant tiles and cannonballs,
0:47:45 > 0:47:50'the Orbiter completes re-entry, and glides in for landing.
0:47:50 > 0:47:53'It touches down at just 220 mph.'
0:47:55 > 0:47:59So after a journey of some four million miles,
0:47:59 > 0:48:02at about 23 times the speed of sound, the Orbiter,
0:48:02 > 0:48:05the final part of the Shuttle,
0:48:05 > 0:48:07is safely here back on Earth.
0:48:07 > 0:48:13Over three decades, NASA's shuttle fleet has travelled
0:48:13 > 0:48:14over 500 million miles.
0:48:14 > 0:48:20It's taken mankind into space to orbit our world,
0:48:20 > 0:48:23and push the frontiers of our knowledge.
0:48:23 > 0:48:26It owes its engineering DNA to...
0:48:26 > 0:48:28a church organ,
0:48:28 > 0:48:30a German U-boat,
0:48:30 > 0:48:32tram tracks, a camera
0:48:32 > 0:48:35and a cannonball.
0:48:50 > 0:48:53Subtitles by Red Bee Media Ltd
0:48:53 > 0:48:57E-mail subtitling@bbc.co.uk