Sea dragon and Big Dumb Booster.

On combustion instability... Beale Aerospace claimed that using hydrogen peroxide as an oxidizer basically eliminated the combustion instability problem. Before they went out of business, they had hot-fired an 800,000 pound thrust 2nd stage engine,and planned to build a 3-million pound thrust first stage engine. Their theory was to use singular rather than clustered engines to reduce complexity, and H2O2 allowed them to do that,apparently.

Ron Menich

Ian Woollard

Ian Woollard

>>>>>Non-cryogenic fuels simplify fuel transport, transfer, and storage, so
>>>>>
> Maybe the best solution for a BDB concept, would be a large, re-usable,
> Steel lower stage, fuelled with ordinary diesel and LOX. The stage would be
> fitted with a single, very large pressure fed engine. The engine would be
> inherently simple and robust.

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.

Basically the combustion chamber resonates and sets up some kind of
oscillation with the fuel feeds. The engine frequently fails at that
point. Annoyingly, right before they fail, they apparently can have
greatly improved performance(!) ;-(

The smaller the engine is, the less chance there is of meeting it,
but quite small engines can meet it also; although much more rarely
as they oscillate at higher frequencies which tend to damp out.

Another annoying feature of these instabilities is that they
don't alway's occur and are difficult to test out.

This is one of the reasons that clustered engines are used.

Another advantage of clustered engines is that you need more of them,
but they are all identical, so they can come out cheaper due to buying
them in greater volumes.

Reliability is usually improved with clustered liquids, upto a
point; they rarely fail catastrophically, unlike solids.

> After successful firing and 1st stage separation, a parachute would slow
> the descent of the first stage so that it would splash down several hundred
> Km downrange. The empty fuel tanks would provide enough buoyancy for the
> stage to float. The stage would then be towed back to port and refitted
> with another upper stage. Turn around times could be kept short.

That's not really the BDB idea. The BDB idea is you ditch it in the sea
and buy another one; going for more volume and lowering the cost that
way.

If and when you have enough market to cost reduce the BDB you should be
able to borrow the money as you have a market. One idea is that
reusability is, to a fair extent, antagonistic to reducing launch cost
as it pushes up the costs of the launch vehicle, and probably reduces
performance due to having to make it stronger. A lot of the costs of
a launch vehicle go into the launch facilities and R&D costs;
reusability raises these costs some too.

> Tony

civilization?"