Sea dragon and Big Dumb Booster.

>> There are problems with scaling up engines in fact. The larger the
>> engine gets the more chance there is of 'combustion instability'.
>> This phenomena has killed one or two Russian programs outright, and
>> set back some others. Note the Russians are not noted for their
>> cluelessness in space launch vehicles.

> This is the legendary POGO phenomena. It may be possible to avoid these
> problems with advanced computer modelling techniques. This is something
> that those industrious Russians just did not have. During the early 60's,
> when most of the development was being done, the US didn't have them
> either.

Actually pogo is a somewhat easier issue. Pogo is longitudinal
oscillation of the vehicle. It's caused by interactions between the
acceleration of the vehicle and the hydrostatic pressure of the fuel;
and is fairly well understood, and may well be removable
with computer control.

Combustion stability is usually at a much higher frequency, and need
not be longitudinal. It's mainly a mixing thing within the combustion
chamber; and is far more complex.

> Would it be possible to introduce damping of some kind? Maybe some kind of
> spring damping system? Many previous BDB studies found that combustion
> instabilities were reduced by keeping the feed pressures several atm higher
> than the combustion chamber pressures.

Yes. Combustion instability is to do with mixing patterns that varies in
an oscillating way. Combustion instabilities are improved by higher
pressure, and preburners (i.e. using gases rather than liquids)
helps very greatly.

> Anyway, I'm no rocket scientist. If we manufacture clustered engines by
> the thousand, then we might still retain the cost advantage. The amount of
> R&D that would need to be pumped into a costly new engine development
> program, means that it is probably best if we steer clear of engines that
> might develop POGO problems.
>
> On the other hand, some computer models may allow us to anticipate POGO
> problems and therefor, allow us to design much larger engines.
>
> Tony

civilization?"