The rocket diaries
The team
Mike Bullivant's diary about the challenge for the Rocket programme, from the BBC/OU series Rough Science 4
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.
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Content last updated: 19/07/2006
