SpaceBanter.com - View Single Post - A kerosene-fueled X-33 as a single stage to orbit vehicle.

**Jeff Findley**

In article , lid
says...

On 15/07/2011 12:30 AM, Jeff Findley wrote:
In , lid
says...

sigh It's not a rocket in airbreathing mode.

It's some ******* engine that does nothing well. It's not as efficient
as a turbofan (likely even a turbojet) aircraft engine when in air-
breathing mode and it's not as efficient as a liquid fueled rocket
engine when operating in pure rocket mode (LOX from internal tanks).

I fail to see how an engine which operates worse than the state of the
art in either mode is better than having two separate stages with two
separate types of engines on each.

All of this silliness is in pursuit of SSTO. Fully reusable TSTO would
be far easier to implement than this because it would require no new
technologies (i.e. fundamentally new engine) to be developed.

It's all about cost per kg payload in orbit. An SSTO, particularly one
that takes off and lands horizontally presents considerable operational
advantages.

Please enumerate the advantages of HTHL over VTVL as they apply to SSTO.
At this point in time, I'm simply not convinced that the advantages are
worth the cost, especially for intact abort scenarios.

While the SABRE engine is more complex than a standard rocket,
complexity is removed in other areas - there's no stage separation, for
example.

Stage separation is an existing technology that's been in place on the
very first orbital launch vehicle. It's at least a fairly well known
quantity, especially if you do your stage separation above the bulk of
the atmosphere.

It also eliminates a whole class of risks associated with
separation, such as collisions between the two parts of the vehicle,
partial separation, etc.

A VTVL SSTO would have the same advantages without the high cost of
SABRE development.

In any case, it's far from clear that a fully reusable TSTO is so easy
to achieve.

Possibly, but so far, no one has tried to build and fly such a vehicle.
It's at least on firmer technological ground than SABRE and Skylon, so
I'd say the chance of success would be much higher for the reusable
TSTO.

Getting Skylon to work in practice may prove more difficult than RE
think. It may prove impossible. But I don't understand the sheer
antagonism towards it evidenced by some in this group. Unless it's a
manifestation of a fear that RE will achieve a disruptive technology.

No, it's mostly the acknowledgment that SABRE is a bleeding edge
technology in much the same way as a hypersonic air breathing engine
(e.g. NASP and more recent technology demonstrators). We've been down
this road more than once, and it's burned us each and every time.

Don't get me wrong, I'd really *like* to see Reaction Engines succeed
and produce a working, economically viable, launch vehicle. I'm just
extremely skeptical due to the inclusion of an engine design which has
never been fully tested *and* has not been successfully integrated into
an actual vehicle.

Aerodynamics is a p.i.t.a. and it will rear its ugly head during the
design phase where the engine is integrated into a *real* vehicle. So
far, I find the "artist's concept" type drawings of Skylon to be lacking
in sufficient aerodynamic detail. In order to provide enough air for
the engines at flight conditions, the engine will need to be *much* more
integrated into the vehicle aerodynamics than current drawings and
renderings suggest.

This should come as no surprise since Reaction Engines is focusing on
building a working engine first. The problem is still that of the
chicken and egg. Without an engine fully integrated into an actual
vehicle, it's awfully hard to test either the engine or the vehicle.
Due to the nature of the engine (and the aerodynamics needed for the
inlet), the two designs are almost inseparable.

Jeff
--
" Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry
Spencer 1/28/2011