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Rough Science 4 Death Valley: Mike Bullivant's diary: Rocket

Updated Tuesday, 29th August 2006

Powering a rocket with water, Mike is frustrated by the demands of "reality" television.

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Mike tests his rocket Copyrighted  image Icon Copyright: Production team
Mike tests his rocket Copyrighted  image Icon Copyright: Production team
Mike tests his rocket Copyrighted  image Icon Copyright: Production team

Day One

It’s a strange place the 'reality'-TV world. Keen to demonstrate the process of electrolysis, I mistakenly add table salt (sodium chloride) to the water in my electrolysis cell.

The conductivity of water is so low that some ionic compound like this has to be added to allow current to pass through the cell and produce hydrogen and oxygen.

As a result of my mistake, the oxygen formed at the cell’s anode is contaminated with chlorine gas – it smelt like a swimming pool! This would account for the fact that the oxygen wouldn’t re-light a glowing splint (a standard test for the gas).

Strange thing is that, having recognised the problem caused by the sodium chloride, I’m not allowed, on camera, to be seen to be rectifying it by using battery acid (sulphuric acid) in place of sodium chloride.

The “logic” is that the challenge is to power a rocket using water “only”, and that while the viewer will accept me adding salt to the water to get it to conduct, it would be beyond the pale to add sulphuric acid instead.

From a chemist's point of view, this would be the obvious solution to the problem, particularly given the fact that, on camera, just behind my scaled-up electrolytic cell, there are eight or nine car batteries, each containing sulphuric acid. I don't altogether see the logic of what's been decided. As I say, it’s a strange place the 'reality'-TV world.

Day Two

Overnight we agree that it's okay for me to use sodium bicarbonate (baking soda) rather than sulphuric acid, so this morning the race is on to produce some more oxygen and hydrogen to test on camera.

We also have to produce as much hydrogen and oxygen rocket fuel as we can. This proved difficult. The ‘graphite’ electrodes we’ve been using – the ‘lead’ from pencils – were found not to be pure graphite.

We tried the ‘lead’ from different types of pencils, and all of them corroded away after a short time in our electrolytic cell. Luckily, the place that is our workshop is used for car maintenance, and Jonathan (Hare) manages to find a graphite bush on the floor! We can cut this up to make perfect graphite electrodes. Good old J – he saves the day.

We’ve still a problem though, as we only have copper wire to connect the electrolysis cell to our power supply, and under these conditions bare copper will just dissolve away in our cell. We have constantly to strip the ends of the electrode connections and expose some fresh copper to maintain any kind of effective circuit.

We get there though; by 3 pm we have the job done, and we’ve collected lots of one-litre pop bottles full of our rocket fuel; a 2:1 hydrogen:oxygen mixture.

It’s time for a test launch of our hydrogen/oxygen-powered rocket. With a one-litre bottle full of the 2:1 hydrogen:oxygen mixture, we managed to reach a height of about 5m. With two-litre bottles, however, the explosion of the hydrogen/oxygen mixture generates so much heat that it deforms the PET (poly-ethene teraphthalate) from which the bottles are made.

To make matters worse, these larger bottles don't even lift off the launch-pad on ignition. Unfortunately, even though the smaller, one-litre bottles work well on their own, they just don’t have enough thrust to carry the required payload – an egg, a parachute, and a small camera.

Kathy’s water-pressure rocket on the other hand is just perfect. It can generate enough thrust to fire a two-litre bottle to a height of about 10m, even with the payload on board.

By contrast, poor Jonathan’s not had much luck with his steam rocket by the end of this second day. Even if he fails to get his design off the ground by late tomorrow afternoon, we'll still have Kathy’s design to fall back on though.

Day Three

Sure enough, it’s Kathy’s design that works the best out of the three, and it's the one we decide to go with. But what about the payload?

Iain and Ellen have spent the last two days designing a parachute and release mechanism that will allow the egg and camera, once launched, to fall back to the ground without breaking. All that needs to be done now is to knit their parachute and its payload together with the chosen rocket design.

Then it's simply a matter of tweaking things so that the parachute’s released just as the rocket reaches its maximum height.

Fortunately Kathy’s water-pressure rocket is one that can be launched over and over again without too much fussing about. This allows for plenty of trial-and-error launches. After 50 or so of these hilarious test flights, we’re ready to film an attempt at launch and landing.

As things turn out, it couldn’t have worked out more perfectly. On our first filmed attempt, the parachute is released at just the right moment, and the egg falls slowly to the ground … unbroken.

Who said this was Rocket Science! Our combined efforts produce another hard-won success - a rather satisfying ending to this fourth Rough Science series. Here's to Rough Science Five.




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