Missile Technology on the Cheap.

Whoosh! The gleaming projectile hurtles towards the stars, trailing vapour and open mouths.

Well, sort of.

Rockets are popular. Big, powerful and, above all, expensive. Shuttle launches cost billions of dollars a shot, and unmanned launches aren't much cheaper. You can, of course, do it yourself. Burt Rutan has his own company that builds rockets as well as aircraft, and the British Starchaser team are working on their own system for launching tourists and satellites.

Unfortunately, 'real' rocketry is far beyond the scope most pockets, and even modest-sized liquid and solid-fuelled rockets are too expensive for the casual hobbyist. They are more in the realm of the dedicated enthusiast. Toyshops sell kits by companies like Estes, and high-power models are also available online, but they are still a bit of a stretch for the casual pocket, costing up to several tens of pounds per launch. This instructable describes three ways of getting into rocketry on a pocket-money budget.

... and think what a rocket actually is. Newton's Third Law of Motion states that, for every action, there is an equal and opposite reaction. That's how a rocket works; push something out the back, the rest of the rocket gets pushed forwards. The faster it gets pushed out, the faster the rocket goes. Here's the important point: nowhere does Newton mention fire. He doesn't say 'throw hot stuff out the back to go forwards'; he just says 'throw stuff out the back to go forwards'. It doesn't have to be a blast of burning gases. Water will do the job just as well. This really is rocket science.

But, Water Rockets?

Yes, water rockets. The easiest way to find out what we're talking about is to try it. Time for an experiment.

Buy a can of cheap fizzy drink (make it as cheap as you can, because you aren't going to drink it), put on old clothes and go outside. Give the can a good shake, then throw it on the ground. Throw it at something pointy, like stones, so that the can bursts. What happens? Fizzy drink goes everywhere, that's what happens (that's why you're wearing those old clothes), but so does the can. When the pressure in the can shoots drink one way, the can goes the other way. That is a rocket. All we need is a more controllable way of putting the pressure in and letting it out again when we want to.

Time to Build a Rocket.

This is important: if you are going to make a rocket, you must be aware of the dangers. Water rockets are fast and can hit hard. You should take all the precautions you see fit. You have been warned.

Building a rocket isn't as hard as it sounds, but we will need some specialist items:

> A fizzy pop bottle (any size, but it must have contained something fizzy - the bottles that hold still drinks are not as strong)

> A cork or rubber bung the right size to fit very snuggly into the neck of the bottle (they can be bought from some brewing supply shops, found in junk shops or scrounged off friendly science teachers)

> A bicycle pump (foot or hand, either is fine)

> A football inflation adaptor (the long spike that connects onto the pump and slides into the football's bladder - they cost a few pence from sports shops)

> Some water

> A couple of bricks

> Safety goggles are also a very good idea, as the plastic bottles can burst, although this is rare. You are more likely to get clipped by a flying bung or a ricocheting rocket

The most difficult part is getting the adaptor through the bung. If you are using a cork, you will have to drill through the cork (use the narrowest drill-bit you can), insert the adaptor and seal around it with silicon sealer. Some people use a rubber bung. To pierce the bung, heat a narrow nail to red heat with a blow torch (holding it with pliers!), push it through the bung and pull it straight back out. Very quickly, push the adaptor through the same hole while the rubber is still hot. After a few moments, the rubber will have cooled and set to make a good seal around the adaptor. Now it's time to test it.

(Alternative method (which I have not tried) is to freeze the rubber bung (24 hours in your icebox), and then drill it with a narrow bit.)

Stand the empty bottle right way up in a bucket, push in the bung and connect your pump. Give several pumps. The bottle should creak and shift slightly as the pressure builds. Stop and listen. Can you hear a hiss? Quiet, high-pitched hisses are fine, because the bottle does not need to hold pressure very long. Louder, deeper hisses are also not usually cause for panic, but if you can't cure them with extra sealant you will have to pump very fast to launch your rocket.

Pump some more. And more. It should not take long, but after about ten to twenty pumps (depending on pump and bottle), the bung will suddenly shoot out of the bottle with a bang. Your basic rocket is finished.

Launching the Water Rocket.

Launching a water rocket is an outdoors activity, as they have been known to go up to 100m high, and this Researcher lost a couple a street or two away from the schoolyard they were launched from.

Half-fill your bottle with water, insert the bung, and prop it up with the bricks (upside down now, so that the water shoots downwards). You should have bricks all round the bottom to stop it slipping, and the bottle should not be tilted more than 30 degrees from the vertical (look at a clock face - the rocket should not launch 'before' 11am or 'after' 1pm), preferably pointing slightly into any wind-blowing.

Attach the pump, and go for it. Do not lean over the bottle! You will see the air bubble into the bottle and feel the pressure building up. It will not take as long as the test because there is less space for the air to fit. When the pressure pushes the bung out, it will also push the water out.

Remember Newton? As the water rushes down and out, the bottle whizzes up and away. Rapidly - that's why you didn't lean over it. Water rockets have been known to reach altitudes of 100 metres (300 feet) - they aren't kiddy toys!

Recovering the Water Rocket

Now that it's empty, the bottle is fairly light, so it doesn't need a parachute, but it can still give people underneath a nasty crack if they aren't paying attention. Watch carefully as it falls, just in case a gust of wind carries it away.

Improvements to the Water Rocket

You will have noticed that your bottle tumbled as it flew. Adding fins made of card or cut from another bottle will help it fly truer and further. Try streamlining it with a nose-cone made of card, or carved from polystyrene. Fix all these with duck tape, epoxy or hot-glue. Remember, you are not allowed to have exposed metal on the outside of any amateur rockets flown in the UK or USA (that's the law).

Can you create a recovery system? Parachutes, rotors and fixed or folding wings have all been used to keep them in the air longer.

You will also find that adjusting the amount of water in your rocket will change the range, but I'll leave that up to you to investigate.

Water rockets use air pressure to throw the water out of the rocket, but it doesn't have to be air. Alka-Seltzer (or 'A-S') rockets use gas pressure to throw water out the back, like the water-rocket, but you don't need so much equipment, so much effort, or even so much preparation. The easiest way to find out what we're talking about is to try it. Time for another experiment.

Take an 'Alka-Seltzer' tablet (or any other indigestion remedy with the word 'effervescent' on the packet) and drop it in water. See the fizz? That is carbon dioxide gas (CO2). The gas is produced by a chemical reaction between the solid ingredients of the tablet. Notice how the froth is a lot bigger than the original tablet? If we can trap this large volume of gas, we can create enough pressure to power a rocket.

Time to Build Another Rocket.

As with any experiment involving chemicals or fast-moving parts, safety must be observed. A-S rockets can be fast, so wear safety goggles, which also serve to prevent chemicals being splashed in the eyes. If you know you have an adverse reaction to aspirin (an ingredient of Alka-Seltzer), you should take extra care, or even avoid doing this experiment all together.

These rockets need some, ahem, highly technical equipment:

An Alka-seltzer tablet
A 35mm film canister
Some water
Space

That's it. Really. The rocket is finished. There's nothing else to do except...

Launching the A-S Rocket

A-S rockets are best launched outdoors, as they can go higher than a typical ceiling, but if you have access to a large room with an easily-dried floor (school science lab, church hall, warehouse, etc) then go for it.

Launching an A-S rocket takes quick, nimble fingers. Put a small amount of water in the film canister (about a teaspoon full is a good start). Snap the tablet into four quarters, put on your goggles and get ready for the speedy bit:

Drop-the-tablet-in-the-water, put-the-lid-on-quickly, stand-the-canister-upside-down-on-a-surface-that-doesn't-mind-getting-wet and-stand-back.

The ingredients on the A-S tablet dissolve in the water, and the fizzing starts. CO2 is being generated and the pressure is rising inside the canister. Don't lean over it, because very soon the pressure will be great enough to throw the lid off and the water out backwards, sending the body of the canister flying upwards. There will also be a certain amount of splashing, so don't stand too close!

Alka-Seltzer Rocket Recovery

Now that it's empty, the canister is very light, so it doesn't need a parachute, and won't do any damage on the way down. Watch carefully as it falls, just in case a gust of wind carries it away.

Improvements

> A-S rockets can become the heart of a lot of 'proper' Science:

> What are the ideal quantities of water and tablet to add?

> Will other combinations of chemicals yield the same effect (baking soda and vinegar?)

> Can streamlining improve the tumbling flight of the canister?

> Will other containers act as rockets as well? What about a fizzy pop bottle with a cork in?

Back to Newton again, and an important point: at no point does Newton mention size. He doesn't say 'throw loads of stuff out the back of a big thing to go forwards', he just says 'throw stuff out the back to go forwards'. It doesn't have to be tonnes of liquid hydrogen and oxygen, a matchstick will do. This really is rocket science on the cheap.

Just a Match?

Yes, just a match. The head of a match is a mix of chemicals that act as fuel and oxidiser, allowing the whole thing to burn rapidly and generate a lot of gas. If you can contain this gas and let it our through a small hole, you will get a jet of gas that is fast enough to launch your rocket, as long as you keep the rocket light.

Time to Build Yet Another Rocket

This is important: if you are going to make a rocket, you must be aware of the dangers. You are playing with fire, here, in every sense of the phrase. You will have very hot objects whizzing around the room. This presents a fire risk. If you are not a responsible adult, you must have one present when you attempt matchstick rocketry. You have been warned.

It is strongly advised that you have some form of fire-control to hand. Suitable methods are containers of sand or water, wet cloths or a properly-designed fire blanket or extinguisher. Remember not to use water-based extinguishers near electrical appliances.

Building a rocket isn't as hard as it sounds, but we will need some specialist items:

> Some matches

> Some aluminium kitchen foil

> Two paperclips (one will be a tool to build your rockets, the other becomes the launch-pad).

> You may also need a piece of Blu Tac, modelling clay or sticky-tape to hold your launch-pad down.

> A fire-proof surface to launch from (baking trays are ideal, but ask before you use them).

> Safety goggles are also a very good idea, as matchstick rockets can fly off in unpredictable directions - even in curves or spirals.

Start by straightening out one of the paperclips. With a pair of strong scissors or cheap wire-cutters, snip the head off the match.

Cut a square of kitchen foil, about four or five centimetres square (the exact dimensions you eventually settle on will depend a lot on skill and personal preference.

Look at your foil, and mentally divide it into quarters. Lay the match-head in the centre of the top-left quarter.

Now lay your straightened clip on the foil, one end touching the match-head, the other end passing down the middle of the bottom-left quarter of the foil and sticking out past the edge of the foil. When you remove the clip later, it will leave behind a channel or tube for the gases to travel along.

Carefully fold the left-hand edge of the foil over towards the right, creasing along the line of the paperclip and match-head. Make sure you keep the end of the paperclip touching the match-head, otherwise the gases will not be able to escape.

Fold the foil again, lifting the left-hand edge and creasing along the original edge of the foil. Fold again and again until you run out of foil. You should now have a long rectangle of folded foil, with the lump of the match-head about one quarter of the way along from one end, and the paperclip poking out from the other end.

Gently twist the foil along the length of the paperclip, forming a tube, and on the other side of the match-head, forming a point. Make sure that the pointed end (which will be the front of the rocket) is twisted tightly enough to seal the gases in, and make sure that the foil wrapped around the paperclip (which is now the rocket's nozzle) is a slightly snug fit (it should slide easily on and off the clip). Your rocket is now finished.

Launching Matchstick Rockets

Matchstick rockets are very light, and completely at the mercy of the slightest breeze, so they are definitely an indoor missile. Just be very careful about the flammability of the suroundings. Sofas and matchstick rockets mix a little too well!

Every launch needs a launchpad. Ours is made from the second paperclip. Look at the clip. Did you notice that it is made of four straight sections, joined by curves? Open up the clip slightly so that three of the straight sections form a triangle. Lay the triangle flat on the fire-proof tray, and bend the fourth section up so that it points upwards into the air at about 45�??�?�°. Use the optional equipment to hold the clip to the tray.

Slip the rocket off the straightened paperclip and onto the launchpad paperclip.

Put your goggles on and tie any loose hair back.

Take a second match, light it, and hold the flame under the lump of the rocket that holds the match head. After a few seconds, the heat of the lit match will ignite the match head. The flame and hot gases will (hopefully) rush out of the rocket nozzle, propelling the rocket into the air.

This is the dodgy time, though. Your rocket could shoot metres across the room, fizzle on the pad, or shoot off sideways in a random flight. If you do not use enough foil, the motor (the match head) could burn out through the side. Too much foil, and it will be too heavy to go far.

Recovering the Matchstick Rockets

Let's be honest; many of your matchstick rockets won't need much effort to recover. You will need to be careful, though, as they will be hot. If you need to pick them up quickly, use tweezers, tongs or a clothes peg. If you don't want to squash them, leave them to cool for a couple of minutes. You must watch every flight carefully, as parts of the match-head can fly off in a different direction to the rest of the rocket.

Improving the Matchstick Rocket

There is always room for improvement in matchstick rocketry. Practice is the best way to improve your rockets, but you may also wish to experiment with the actual design;

Change the way you twist the rocket nozzle; leaving the last part flat to act as a tail can improve the flight.

Change the dimensions of the rocket - does it fly best with a longer or shorter nozzle? What about the amount of foil in front of the match-head, or the amount of foil in the whole rocket?

Try altering the fuel supply - can you make a rocket using two match-heads, or with the fuel alone (chipped carefully off the match)? Do different kinds of match make better rocket fuel?

In a rocket, the propellant travels with the projectile.

In a cannon, the propellant stays behind.

So what do you call a projectile that leaves half the propellant behind and takes half with it? I don't know, but it's even easier to make than the previous rocket, and flies well:

You need three matches this time, a strip of foil about 1" by 2", and a bulldog clip.

Lay the foil on the table in front of you, short edge nearest to you.

Lay two of the matches head-to-head on the short edge (the two match deads should be half-way along the edge).

Roll up the foil around the matches, nice and tight.

Stand the bulldog clip up at an angle, and clip one of the matches so that they point upwards at about 45 degrees.

> Remember to be safe, this is still fire, tie your hair back and tuck in loose clothing.

As before, use the extra match to heat the foil and ignite the match heads, and watch your missile fly whole feet down-range...

_{(In the video, I'm using a set of helping hands to hold the match - it proved surprisingly effective.)}

Being safe with Water-rockets

Avoid crowds, pylons, built-up areas and airfields (a bottle sucked into an engine could have fatal consequences).

Don't lean over the rocket.

Don't point it at anybody.

Never launch it more than 30 degrees from the vertical.

Don't launch if winds could carry the bottle out of your chosen safe area.

Being Safe With A-S Rockets.

Avoid areas that don't like getting wet, such as living rooms or anywhere near electrical equipment.

Don't launch in rooms with low ceilings.

Don't lean over the rocket.

Don't point it at anybody.

Being safe With Matchstick Rockets

Avoid crowds and flammable surroundings. Matchstick rocketry and soft furnishings or carpet do not mix well.

Don't lean over the rocket.

Don't point it at anybody.

Do not launch matchstick rockets vertically - you risk getting singed as the gases jet down towards your hand.

Make sure that you are not wearing loose clothing and that long hair is tied back, as these can catch hot rockets and ignite.

Keep your fire-control materials handy.

Run minor burns (for instance, if you pick up a hot rocket too early) under a cold tap for several minutes, then apply burn ointments if required.

Don't limit yourself by what I have written here. Use this as a starter for a personal project:

> Build several rockets to different designs and compare them.

> Challenge friends to rocketry competitions, or enter properly organised events yourself. School laboratories lack carpets, and should be fully equipped with fire extinguishers and first-aid supplies, so make good venues for matchstick rocket ranges. All you need is a friendly science teacher. As many pubs lack carpets, they can be popular locations for matchstick rocket ranges as well. Just remember - alcohol and rockets don't mix, and alcoholic spirits are flammable!

> Are you a Beaver, Cub or Scout? Water and A-R rockets can count towards several different badges, depending how you approach it.

> What about a Science Fair? Imagine the judge's face when you turn up with a whole rocket range in an Altoid tin!

Above all, be safe and have fun - these are real rockets, with real potential for fun and education, as well as the real dangers involved.

Alka Seltza contains two important ingredients: an acid and a carbonate.

The acid is citric acid (the stuff that give citrus fuits their bite), and the carbonate is "bicarb" - sodium hydrogen carbonate. Both of these are solids, and don't react together.

Add water, though, and they dissolve. This gives them the freedom to react, and they produce sodium citrate and carbon dioxide. Carbon dioxide, being a gas, has a much larger volume than the original reactants. Trapping the gas provides the pressure needed to work the A-S rocket.

---

So, why does a matchhead make a good rocket fuel? The reason is that it carries both the fuel and the oxygen required to burn it, and the products are gaseous and are ejected forcibly from the end.

There are two kinds of friction match, the "strike anywhere" match and the safety match.

Consider the "strike anywhere" match. These are manufactured by dipping one end of a bare wooden stick into a fireproofing agent, so that it will not burn too readily. The other end is coated with paraffin, a hydrocarbon. The head of the match contains an oxidising agent, such as potassium chlorate; and a substance that is easily oxidised - usually sulphur. The head also contains a filler of clay; a binding material, such as glue; and dye to give it a distinctive colour. At the very tip is a small amount of phosphorus trisulphide, which decomposes and burns at a low temperature. This ignites the paraffin, which burns more readily because of the presence of the other chemicals. The products of combustion therefore include sulphur dioxide gas and carbon dioxide gas, which occupy very large volumes compared to the solid reactants.