Why separate from the SRB? Why not just use SRB all the way? I know you can't stop a SRB but you could only fill them to a certain level (maybe thereby making them shorter if you will say something about that).
Why bother with the extra complexity?
Why bother with the extra complexity?
-
The SRB's have a fairly low "specific impulse", meaning they're actually pretty inefficient--it takes a lot more propellant (by weight) to get a particular change in velocity.
So why use them at all? For one thing, they're relatively inexpensive, and they're easier to store and handle.
Liquid hydrogen (LH2) has a much higher specific impulse, but it's so light that you need a much bigger rocket to store the additional volume of fuel. That's why the Saturn V used kerosene in it's first stage--von Braun decided to trade efficiency for size.
So, you use the SRB to get you moving, and then switch to a higher efficiency fuel when the rocket is already going at a pretty good clip. That way, you don't need as much LH2, and can make the upper stage smaller
So why use them at all? For one thing, they're relatively inexpensive, and they're easier to store and handle.
Liquid hydrogen (LH2) has a much higher specific impulse, but it's so light that you need a much bigger rocket to store the additional volume of fuel. That's why the Saturn V used kerosene in it's first stage--von Braun decided to trade efficiency for size.
So, you use the SRB to get you moving, and then switch to a higher efficiency fuel when the rocket is already going at a pretty good clip. That way, you don't need as much LH2, and can make the upper stage smaller
-
The srb's only have rocket propellant for 2 and a half minutes after that it's just dead weight and would affect performance on the upper stage . Besides it makes no sense in keeping the srb stage attached after it's used and burnt out. Why not use the upper second stage j2x engine for orbit insertion