C’mon, People, It’s Just Rocket Science

I am being quickly induced never to look at news coverage of a scientific event ever again. On return from my fluids class this morning, I checked my RSS feeds to find a story on an upcoming scramjet test in Australia, courtesy of the BBC. The first sentence should have warned me that, knowing anything about this subject, I shouldn’t have continued reading:

A new jet engine design able to fly seven times the speed of sound is to be test fired over Australia on Friday.

Well, okay, it’s not totally wrong to say that a Mach 7 engine flies seven times the speed of sound. But it’s the local speed of sound, dammit! But, being an aerospace engineer, something inside me twitches at the thought of being so imprecise. The real pain comes later, when the reporter tries to make a helpful remark about the usefulness of a scramjet engine:

A supersonic combustion ramjet, or scramjet, is mechanically very simple. It has no moving parts and takes all of the oxygen it needs to burn hydrogen fuel from the air. This makes it more efficient than conventional rocket engines as they do not need to carry their own oxygen supply, meaning that any vehicle could potentially carry a larger payload.

First of all, what did they teach you in grade school about pronouns and antecedents? “This makes it more efficient than conventional rocket engines as they do not need to carry their own oxygen supply.” I know that you’re trying to say that scramjet engines don’t carry their own oxygen supply. But, technically, you just told your reader that rocket engines are air-breathing, which, seeing as propulsion devices are classified as either rockets or air-breathing engines, is, well, impossible.

Moreover, when did it become reasonable to compare a rocket to an air-breathing engine in terms of efficiency? They can’t do the same things. Rockets can fly outside of an atmosphere. Air-breathing engines can’t. Rockets tend to be heavier because they have to carry their own oxygen. But, at least in the sense of conventional chemical rockets, they are more powerful. You can lift enormous loads at higher speeds with a chemical rocket than you can even with the most ambitiously imaginative air-breathing engine. In short: you just don’t compare them. They’re apples and oranges. Both are fruit, but you only eat one if you’re wanting Vitamin C.

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