You have probably all heard recently about Airbus filing a patent for a
hypersonic aircraft involving turbojets, a rocket engine and ramjets.
Even if in this case the rockets aren’t used for space travel, I still
consider this to be relevant to this newsgroup. Rockets are a space
technology. And if Airbus pulls this off, it means very reliable and
easily reusable rockets. Since these planes would do flights of only a
few hours we can expect them to do say 5 flights per day. So if you have
10 of these planes flying you have about 50 flights per day. You must
have much higher reliability than today's rockets or else your going to
have stories in the newspapers about a rocket failure every other day
and that spells the end of the plane model even if the planes survive
the rocket failures. So developing this plane involves developing very
interesting rocket engines. For these reasons, I think it would be cool
if Airbus, or anyone else, would go forward with this kind of plane.

But I don’t think that their particular plan is the best one. I don’t
think that the ramjet is necessary. If you already have a rocket engine
on board, why not use it a little longer, go a little higher and a
little faster and then glide to near your destination. At that point you
turn on again the turbojets for approach and landing. But that is just
my gut feeling, I would like to know what other people think of that.

Another question I have about such a plane is whether it is feasible to
use the same fuel for the turbojet and the rocket. I see no reasons why
it couldn’t be done. But some times the devil is in the details. If you
use the same fuel that means that if you have a problem with your rocket
engine, you can simply shut it down, dump the oxidizer and have the
pilot open the microphone and say something like: we are sorry but we
will be arriving 8 hours late. This also brings another question. Would
the amount of fuel (fuel only not oxidizer) needed for a flight using a
rocket engine be enough for a flight using the turbojets?

Any thoughts?


Alain Fournier