If you're not flinging your lower stage backward with maximum possible force, then you're missing an opportunity for useful momentum transfer to benefit upper-stage Delta-V.
But why isn't it possible to engineer a vigorous piston effect, above and beyond mere exhaust impingement? Like a gas piston, or a bullet launching from a gun barrel. The idea would be for the separating stages to push away from each other with the highest possible impulse.
Do the newer methods, like the pusher-rod on Falcon 9, offer the highest possible impulse at separation?
Quote from: sanman on 06/24/2017 01:03 pmIf you're not flinging your lower stage backward with maximum possible force, then you're missing an opportunity for useful momentum transfer to benefit upper-stage Delta-V.Wrong. That is not useful Quote from: sanman on 06/24/2017 01:03 pmBut why isn't it possible to engineer a vigorous piston effect, above and beyond mere exhaust impingement? Like a gas piston, or a bullet launching from a gun barrel. The idea would be for the separating stages to push away from each other with the highest possible impulse. wrong. Because 1. the upper stages, full of propellants and payload, are likely heavier than the discarded lower stage. It would a more velocity to the lower stage than the upper stage.
2. The interstage would have to be reinforced to handle the pressure so that it could be harnessed. This would increase mass more than any benefit derived from the impulse. Titan II did every thing it could to release the pressure. That is why Russian vehicles have lattice interstages.
Quote from: sanman on 06/24/2017 01:03 pm Do the newer methods, like the pusher-rod on Falcon 9, offer the highest possible impulse at separation?noThe point is not impulse but to provide separation. The pusher rod is not accelerating the upper stage. It is just pushing it clear. The design does not look at staging as a place to get delta V out of the event, but just to provide clearance from the lower stage.
1. But even that Delta-V for lower stage can be beneficial in the case where lower stage wants to do RTLS (eg. F9R booster) Then the boostback requirement could be reduced.2. Furthermore, why couldn't the mass balance between upper and lower stage be shifted to help momentum exchange favor a higher proportion of Delta-V for upper stage?3. In the winged flyback booster example I gave above, the nose of the booster might already have to be reinforced for re-entry purposes anyway.4. But surely stage separation can accomplish more than just that, can't it?