Unfortunately, because rockets need standard hardware like nuts and bolts and because most of the aerospace grade hardware comes from U.S, sources a great deal of the dimensioning on rockets is in English units. The military once tried to dictate the use of metric units and the result was a lot of thing like 2.54 cm bolts.MeteorWayne":2fhmg9tv said:Have no idea, but I suspect like all intelligent lifeforms, they use metric
It is quite true that things are generally easier in the metric system. But it is an unfortunate truth that the English system is firmly entrenched.
Here is one that will drive you crazy. The standard figure of merit for rocket engines and propellant is specific impulse, Isp. It is the single most important number for a rocket motor. Isp is usually quoted in "seconds". What it really is momentum imparted per unit mass of propellant expelled (or thrust divided by the rate of mass expelled). So the units are (force x time / mass ) Now F= ma so the units are mat/m = at = velocity. HOWEVER, in English units this is bastardized to (lbf x seconds /lbm) where lbf is pounds-force and lbm is pounds-mass. Then one "cancels" the lbf in the numerator with lbm in the denominator to arrive at "seconds". Yes, that is really how the units of seconds for Isp come about.
It gets worse. Just when you think you understood F=ma you find that people want to use the units of mass as the lbm, rather than the correct English unit which is the slug. So when you bastardize the units of mass like that you wind up with F = 1/gc *ma where gc is 32.2. And you get to carry this gc thing around . So in English units like that with Isp in seconds in order to get delta velocity in fps from the rocket equation you wind up with
delta vel = gc*Isp*ln(final mass/initial mass)