JF Mezei wrote on Sun, 18 Mar 2018
07:19:06 -0400:

On 2018-03-17 02:59, Fred J. McCall wrote:

What are you gibbering about now?


Enterprise was built in another era. No CAD/CAM and no experience in
building a flying rocket.


False. And I note you 'cleverly' removed your original comments.


Enterprise was needed not only use to test
gliding/landing but also to develop/test mounting on the full stack, as
well as firing SRBs to measure vibration.


False. Enterprise was never mated to live SRBs


The knowledge gained from it resulted in a production design
sufficiently different that it wasn't worth retrofitting Enterprise.


False.


BFS, on the other hand tests a fully functioning rocket capable of
taking off and landing. Engines, tanks, software, aerodynamic
controls/paddles, landing gear ad its deployment using real actuators
(Enterprise used explosive bolts) etc. (not sure if it will have side
thrusters for attitude control)


Again, you only need the three sea level engines for all of that. PAY
ATTENTION!!!!!!


Sure, it will lack a payload, crew compartment, ECLSS etc. But from the
rocket point of view, it should be a fairly functional system.


Why would it lack most of those things? If you're going to test
handling and flight, you need the moment arms and CGs to be as close
as possible to the intended final article. You can't add all that
stuff as an afterthought. It's part of dry structure. You can add
engines and heat shield later, since those things are intended to be
removable so they can be refurbished/replaced.


Furthermore, it is an evolution from experience gained from Falcon 9
whereas the Shuttle was truly the "undiscovered Country" since it was
not an evolution from Apollo systems/designs.


Well, not so much. BFR Spaceship is a totally new kind of thing using
totally different engines.



You don't need the vacuum engines to lift off and land. You do need
some if you're planning on going clear to space, but even then you
probably don't need all of them until you start flying heavy cargos.


Montréal got some new Métros about 2 years ago. Previous generation was
designed in early 1970s. Alstom got the contract for the bogies/motors
and went with a fancy pneumatic suspension as well as the tires for our
métro.

All built to fit the existing tunnel dimensions, platform height and
loading gauge.

BUT... during testing, the STM (transit company)discobered that if the
tires blew AND the penumatic suspension lost pressure, a car could sway
enough to rub against tunnel walls in some areas. (previous generation
had spring suspension, so failure of suspension had not been something
they worried about when defining the specs of the vehicle).


BFR Spaceship isn't a subway train.


They may very well make the first BDF launch without vacuum engines. But
this would not validate things very well. If the goal is to validate the
design, and if the vacuum engines are Raptor engines with different
bells, they may want to load them up. (or peruaps load early production
Raptors with vacuum bells to occupy the space and weigfht.


Why?


Prior to launch, they can then test that interaction between engine
bells is within specs in all failure modes, and that a vacuum bell stuck
in the worng orientation won't prevent a launch engine from gaving full
gimball movement. (expecially needed for landing when rapid changes are
needed).


Mayfly, engineers don't just build **** and hope it works. Yes, some
things only come out with full up testing but this is not one of those
things.



If you don't need the heat shield then you don't need the vacuum
engines.


The heat shield is just fancy outside skin. Vacuum engines are mounted
amongst launch/landing engines so ensuring the whole engine "pod" works
even when half the engines are not fired is important.


Do you have any conception at all of how engineering works?


Also, assuming BFS 1,0 does not result in fireworks, the work done to
assemble a more complete vehicle would be of use for its second flight.
(and one would have to do risk management to decide wether to mount good
vacuum engines, or duds from early production but with proper vaccum bells.)


You think they're going to have a lot of 'dud' engines, do you?


And depending on software, I could see a case for needing the vaccum
engines in the event that sea leavel engines fail during landing.
(depending on where in teh cluster those engines are located).


There are 3 sea level engines. You need ONE in order to land.


So just because the grasshoper tests doesn't require vacuum engines on
paper doesn't mean that they won't want to have them on for the test
because integrating as many compotents as possible is a better test.


So you think you know more than Elon Musk about BFR Spaceship, do you?
The things SANE engineers would leave off the vehicle are things that
are intended to be easily removable and replaceable. That's things
like engines and heat shield. It is certainly NOT major structural
components.



I don't know why you're so wrapped around the axle about the
damned tank, since we all know that's done.


Enterprise didn't have fully functioning tanks. Didn't have its real
fuel cells and O2/H2 tanks, didn't have hypergolics. BFS will have fully
functional tanks. So it is far ahead in terms of moving from "idea" to
"product" then Enterprise was.


I repeat - I don't know why you're so wrapped around the axle about
the damned tank, since we all know that's done. You do love removing
your original remarks, don't you?


And this is why advancing first flight is significant because first
flight really needs to have a lot of the final systems finalized.


'Advancing first flight'? What the **** are you talking about now?



No, it was designed as a test article, which is not the same thing.


Test article for something that had never been done before. And with
many changes made as it was being developped (liquid fltyback boosters
abandonned etc).


Again you remove your original comment, WHERE YOU WERE ONCE AGAIN
WRONG. Then you argue with being told you were wrong.


While the payload of BFS (aka: crew compartment for 100 passengers) is
likely going to change a lot from early concepts, the propulsion/tanks
portion as lower structures are likely to be fairly close to final
designs with tweaks over time. (as has happened with Falcon 9).


Why would it 'change a lot'? Static dry structure is the EASY part of
the vehicle.

elide remaining nonsense


--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn