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By Doug Millard on

Clean Eyes, Clean Rockets

So, what’s the connection between contact lenses and rocket engines? The answer, I probably don’t hear you cry, is hydrogen peroxide and cleanliness.

Blown glass contact lens, 1930s (Science useum/Science & Society)

You see, to clean my newly acquired contacts involves bathing them overnight in a solution of hydrogen peroxide. Peroxide is a pretty powerful chemical agent and disinfects the lenses in 6 hours. If you put your lenses in too soon the still active chemical will turn on your eyeballs and cause them to gush tears like Gordon Ramsay’s head onion peeler. After six hours, though, the peroxide is decomposed and all you are left with is clean and lifeless water.
The lens holder includes a small piece of material (I have yet to identify it) that catalyses the decomposition of the peroxide solution. If it didn’t then the peroxide would remain and, having successfully killed the bugs on your lenses, then do its best to kill the cells of your cornea too. And this is where the rocket engine connection comes in.

The reaction that decomposes the peroxide also produces oxygen – you can see it bubbling off the catalytic material. That same type of reaction, albeit using extremely concentrated hydrogen peroxide, was exploited in the engines of Britain’s Black Arrow space rocket to launch the Prospero satellite into orbit in 1971.

Uprated Black Arrow rocket engine, c. 1970 (Science Museum/Science & Society)

The catalyst used was silver metal gauze and it decomposed the peroxide violently into oxygen and steam, which then ignited kerosene fuel, and so provided thrust to lift the rocket. In fact, earlier rocket engines dispensed with fuel altogether and replied on the thrust of the decomposing peroxide alone.

Oh, and the cleanliness connection? Well, peroxide rocket engines are considered ‘clean’ or green as their exhaust, after all, contains little more than oxygen and steam.