1. I hadn’t thought about those two modes as being as much of a problem. I’ll think about it and see what I come up with.

2. There are two or more fairly large liquid engines burning from the start, which could be upwards of a million pounds more thrust.
2A. The two SRB solution from the previous post could solve the under power problem with a lot less development cash.

1. I can see how this idea *could* help with longitudinal vibrations. What about lateral and torsional vibrations?

2. IIRC, the SRM is already underpowered. How does adding upper stage mass helps achieve orbital velocity?

I think I understand Eric Collins’ thinking but this ought to work. Thinking out loud the shock absorbers are stiff enough to not respond until receiving greater linear force (from vibration) than normal acceleration would supply, when the 1st stage and 2nd stage main tanks go beyond that level the vibration is absorbed down to an acceptable level by the shock absorbers which are continuously assisted by the above liquid engines providing a pull (any value should help and it must not be too large or the vibration won’t be smoothed out). In other words rocket assisted shock absorbers which should be more responsive in terms of time needed to regain absorption potential and more efficient in relation to their own mass.

This is sort of a reconfiguration of a combination of the active rocket dampening and the shock absorbers that NASA has looked at for Ares I, and also the LAS function. I’m not sure it solves or helps with other issues though.

That’s as far as my brain has got (I might not have understood things correctly and all errors are mine) and it needs a break now ^_^

Having demonstrated considerable ignorance of the SSME, I left that part alone. There would be a minimum allowable mass dictated by the thrust of the SRB. HH was trying to explain that part to me in the last post.

The heating of the drop tank would be a major issue. Whether it would require booming out the engines or adding tank insulation would require considerable thought.

It could be that this idea is so far fetched that most serious commenters are too busy laughing.

The second stage drop tank would make a dandy propellant depot with pumps and handling gear already installed.

As for the quantity of lipstick required for this pig, we need to solve the viscosity problems for a lipstick turbopump, we have a customer.

The engines on every second stage need to be powerful enough to propel the capsule, it’s service module, and the fuel tanks of the stage for a period of time (100+ seconds). John’s innovation is to use the engines to pull rather than push the second stage. The five second supply of fuel in the service module allows the second stage tanks to be dropped in case of emergency while the five seconds of fuel separates the capsule and service module from whatever disaster is occurring below the second stage tank.

As to the plumbing used to pump fuel (and oxidizer) to the engines, think of a drinking straw. The pressure in the second stage tanks (see “gas generator lift pumps” in the diagram) pushes the fuel and oxidizer up the tubes against the direction of acceleration of the rocket.

Your comment about thermal effects of the engines firing against the second stage tanks is a good point. Maybe it will help pressurize the tank? Maybe the effect will turn the second stage tank into something like a plug nozzle?

I doubt any amount of lipstick will save this pig, but the idea seems sound.

Apparently, this idea is not too far fetched… witness the lack of folks commenting on the holes in the concept. As for myself, the only thing I could think of is the thermal interaction of the side mounted engines with the second stage tank. You would either have to have some fairly beefy heat shielding there, or else you would need to cant the engines way out. Either way, you’re talking about a loss of efficiency which may turn out to be non-trivial.