In article ,
says...

On 3/6/12 2:27 PM, David Spain wrote:
Justin wrote:
Would it be possible to design something like the XCOR Lynx for level
flight, with a rocket but still have a useable range?
Let's say a normal cruise speed, size and passenger capacity
competitive with a Lear Jet 23, or a Cirrus Vision.


My take on this is that you *could* build one with a longer range, but
it would not be economical to do so because of the added expense of
carrying around all that oxidizer, and certainly not for whatever you
are defining as 'normal cruise speed' for a Lear or a Cirrus.

In other words it would be more expensive to fly than the Lear/Cirrus.
In fact it would aways be more expensive to fly that an air breather. So
unless there was some other distinct advantage (like hypersonic speed),
there would be no point to doing it. SABRE technology excluded here....

Dave



I had to look up SABRE.

Let's bring SABRE into the mix. Would it be possible to desich a rocket
to use the atmospheric O2 when available and then switch to an on board
supply?

In theory, but if you're designing a vehicle for hypersonic cruise, you
could leave off the ability to run off of on board O2 (i.e. rocket
mode).

If you're going completely out of the atmosphere, then you're
essentially talking about flying a suborbital trajectory, similar to an
ICBM. In that case, I'd argue that you'd be better off ditching the
air-breathing mode and use a pure rocket to get above the atmosphere as
quickly as possible to reduce gravity and drag losses.

But the devil is in the details. If SABRE is ever fully developed, the
trajectory of the vehicle would need to be optimized for the actual
specs of the operational engine. In other words, I have little
confidence in a paper vehicle designed to use a paper engine.

Jeff
--
" Ares 1 is a prime example of the fact that NASA just can't get it
up anymore... and when they can, it doesn't stay up long. "
- tinker