4 ms·
GP is a nice reverse engineered explanation, but the actual origin of using seconds as a unit is to avoid having to compare metric and imperial units of speed.
by fouronnes3 5y ago
GP is a nice reverse engineered explanation, but the actual origin of using seconds as a unit is to avoid having to compare metric and imperial units of speed. Isp is just exit velocity divided by g and it's conveniently in seconds, a pretty universal unit. And "one pound of thrust" only makes sense when you're in Earth's gravity field with gravity losses. Otherwise it's more precise to use Newtons for thrust.
- jcims 5y agoI use it because even after being an Estes nerd as a kid it was the first explanation that actually made sense to me.
- kbenson 5y ago> conveniently in seconds, a pretty universal unit. Thankfully! Imagine if systems/cultures commonly differed in fundamental measures of time, just as they sometimes do for volume, distance, weight, etc.
- taneq 5y ago> And "one pound of thrust" only makes sense when you're in Earth's gravity field with gravity losses. Ah, but now we're talking about "pounds of force", not 'pounds of mass': https://en.wikipedia.org/wiki/Pound_(force) https://en.wikipedia.org/wiki/Pound_(force)