Soyuz TMA-12 faulty

Jochem Huhmann wrote:
(Derek Lyons) writes:


At the most important moments of successful takeoff and landing the
velocities are the same, being zero. It must, therefore, be possible to
use the jets at the point of liftoff.

The problem isn't that short period when the velocity is zero, but the
rather much longer period when the velocity in nonzero.


The terminal velocity of a blunt vehicle consisting mainly of empty
tanks isn't that high, though. Still, making it work in both cases
wouldn't be exactly easy, I think.

Just to be more precise. It wouldn't be very difficult to make it
work in both cases in the sense that it wouldn't be very difficult
to have the jet engine provide lift in both case. But you don't just
want it to work, you want it to be useful, meaning you want it to
be better than just using the rocket engine that you already have.
I think it is unlikely that it would be worth it to carry a jet engine
all the way to space just so you can have it for a few seconds at
landing. The extra rocket fuel needed to carry it to orbit would
probably be more than what it saves at landing. And if you do build
a rocket landing vertically using a jet engine, you would probably
want to optimize it for landing, if you want to use it for both take off
and landing you might end up making heavier to the point that it again
increases the overall cost. If you are carrying a jet engine at
take off it might very well be wise to use it, but it isn't obvious
to me that it is.

Note that there are some drawbacks in using the rocket engine for
landing also. For landing you need an engine capable of giving about
a 1 g push to the mostly empty rocket. That is much less than a
rocket giving a, let's say, 3 g push to the fully loaded rocket. Deep
throttling of rocket engines have their own complications. But I think
that for the rocket engine case, it is much easier to solve the problem.
You would probably want to have several engines, one of which is
optimized for landing and the other main engines being shutdown at
landing.


Alain Fournier

David Lesher wrote:
Were they from Kansas?





Like Hobbits, Munchkins were far too fond of food to fit through 9" wide
intake openings.
Now you got me started on doing "The Wizard Of Skunk Works" songs:
"Come out, come out, wherever you are, and meet the team that built the
Shooting Star."
"The Northrop "Fang" is not merely dead, it's really most sincerely dead."
"We represent the RCS cross-section team, the RCS cross-section team,
the RCS cross-section team.... and in the name of the RCS cross-section
team...we want you to see our new Have Blue."
"Let the word be quickly spread, that evil old empire is finally dead!"
"Hi-ho, the empire's dead! Which old empire - the Soviet empire! Hi-ho,
the Soviet empire is dead! It's gone where the commies go,
below...below...below...below...straight to hell, that's where they go!
Hi-ho, the USSR is dead!"
"You've always had the power to get back home again; just click those
Hopeless Diamond slippers together and say 'There's no place like
Nellis...there's no place like Nellis'." :-D

Pat

(Derek Lyons) wrote:

:"Reunite Gondwanaland (Mary Shafer)"
:wrote:
:
:On Tue, 10 Jun 2008 17:53:58 GMT, (Derek Lyons)
:wrote:
:
: Rick Jones wrote:
:
: In sci.space.history Alain Fournier wrote:
: Not necessarily. The airflow is reversed between take-off and
: landing.
:
: It is for a plane, but would it be for a VTVL rocket? Wouldn't they
: always be pointing "down?"
:
: For takeoff, the inlets face forward - into the flow. For landing,
: the inlets face aft - against the flow. This make the already
: difficult problem of designing the inlets even more difficult.
:
: Ensuring that the engines recieve sufficient airflow and avoiding
: recirculation during landing will be amusing.
:
:I'm not sure how much of a problem that is. After all, the F-104 has
:two 90° turns in the intake path and it seemed to manage quite well.
:
:As Pat say, this is incorrect.
:
:The F-104 also didn't operate in an environment that promoted
:recirculation.
:

Yep. Reingestion of hot exhaust is a problem for the Harrier (for
example), so I doubt that it would be less of a problem in an
application where the intakes actually face downwards.

However, on the other hand, thrust reversers have been around for a
long time...

--
"The reasonable man adapts himself to the world; the unreasonable
man persists in trying to adapt the world to himself. Therefore,
all progress depends on the unreasonable man."
--George Bernard Shaw