to expand and clarify on the last question--
the
maximum exhaust velocities are:
Propellant mix - Effective exhaust velocity (m/s)
liquid oxygen/liquid hydrogen - 4462 (
16,063km/h)
liquid oxygen/kerosene (RP-1) - 3510
nitrogen tetroxide/hydrazine - 3369
[
link to en.wikipedia.org]
"The
delta-v needed to achieve low earth orbit starts around 9.4km/s [
33,840km/h]".
[
link to en.wikipedia.org]
So the wheels spin at 30km/h but the car travels at 60km/h???
Rocket science -- like real science but without the pesky facts.
Wheels DON'T spin at MPH -- they spin at RPM. The wheels of a car are in intimate connection with the road.
Now change the scenario; substitute a paddle-wheel boat. The paddle goes SLOWER than the boat.
Now let's change up for a prop-driven boat. What is the link between the propeller speed (in RPM) and the boat's forward speed?
But, alas, the conditions of a rocket are simpler still. What is thrust velocity? It is the velocity at which the propellant leaves the exhaust bell.
Which is itself in motion.Good thing, too. Imagine you were flying an fighter plane moving faster than a speeding bullet. Then you fire your guns. The velocity of the plane is added to the muzzle velocity -- otherwise, fighter pilots would shoot themselves down!
"Wheels DON'T spin at MPH -- they spin at RPM."
Brilliant..and when the the
surface of the tire moves (spins)at the speed of the car, in this example, 30 km/h, the car cannot travel 60 km/h.
The propeller example is utterly irrelevant.
The paddle example is completely incorrect. The paddle wheels circumference moves at or above the speed of the boat, never below. If the paddle went slower, it would have a braking effect on the boat.
As to the bullet, its velocity is
constantly decreasing after being fired and its propulsion is derived from being trapped between the escaping gas and the end of the barrel; there is no propelling force exerted upon the bullet after it leaves the barrel. The bullet is propelled as the exploding gas 'pushes off' the far more massive, speeding aircraft ..and then it (the bullet) immediately begins decelerating.
Unlike a bullet, a rocket is being 'pushed' by its escaping exhaust and can maintain or even increase its velocity (unlike the decelerating bullet)
but this velocity can be no greater than that of its exhaust.
The rocket boys seem to think that just because the decreasing mass associated with the burning fuel allows the rocket to accelerate (gain velocity as opposed to maintaining a constant velocity) that--somehow - this magically allows the rocket to accelerate to
a velocity greater than that of its exhaust-- which is typical NASA nonsense. It can accelerate, but not beyond the velocity of its own exhaust. Acceleration and maximum velocity are apples and oranges.
