Stacking Starship and Superheavy

In article ,
says...

On 2020-04-05 10:53, Jeff Findley wrote:

Again, I have no idea. But do note the last failure was due to the load
of propellant in the upper tank. Almost all of a launch vehicle's mass
is propellant, so we're talking about *a lot* of mass.

Would "normal practice" call for the rocket to be at least able to stand
on pad, fully stacked but empty tanks, or it is acceptable to require
tanks to be pressurized to support an empty unfueled rocket without cargo?

The exception is tanks required to be pressurized for handling, i.e.
original Atlas.

Originally Starship was to have used transpiration cooling, which meant
it would have to hulls (the tank wall and then an outer wall) separated
by stringers. That would have stiffened the structure. Cite:

https://www.popularmechanics.com/spa...663/elon-musk-
spacex-bfr-stainless-steel/

But since Starship has gone to thermal protection tiles, that's no doubt
changed. Certainly when they're building and stacking Starship it's not
pressurized. That's obvious from the live video feeds of its
construction.

Now whether or not you can stack a Starship, loaded with a payload, on
top of a Super Booster without pressurizing any of the tanks, I don't
know.

With regards to SN3, I know it was almost confirmed lack of pressure on
lower tank did it.

Yes, with the upper tank containing so much liquid nitrogen (which is
what they use for cryogenic testing), the lower tank buckled.

Has there been confirmation this was due to a valve
failure vs testing specs that called for what is now known to be
inadequate pressure?

Starship SN3 failure due to bad commanding. SN4 already under
construction, written by Thomas Burghardt, April 5, 2020
https://www.nasaspaceflight.com/2020...ip-sn3-ground-
flight-testing/

From above:

Elon Musk has since clarified the issue was the result of incorrect
commanding resulting in the loss of pressure, as opposed to any
material issue with the Starship build.

I know Musk has hopes of cutting mucho weight from Starship. Airbus also
did for its A380, but in the end, it needed to be much heavier than
originally hoped for in order to maintain structural integrity.

Initial Starship user's guide says payload to LEO is 100+t. Cite:

https://www.spacex.com/sites/spacex/...s_guide_v1.pdf

With refueling, the idea is that you can place that payload pretty much
anywhere you want including the surface of the moon or Mars.

My concern here is that SpeceX may be caught with pressurization limits
to avoid catastrophic bursts, and having to add structural strength
which would increase weight instead of reducing it.

That's pure speculation on your part.

Both the Spruce Goose and now the A380 proved to be able to fly, but in
the end, the economics didn't make the planes viable. (with COVID19,
the A380 is being retiured earlier than planned by many airlines).

Time will tell what Starship's ultimate payload capability will be, but
100+t is freaking huge. That's at least 5t more than SLS block 1. SLS
block 2 plans on 130t to LEO. But the problem with SLS is that its
upper stage can't be refueled in LEO, so it's payload drops off
precipitously to the moon at only 45t. That's the power of in orbit
refueling.

I have been told here that there hyave been heavy steel rockets in the
past. Is there no l=knowledge left of how they were built, how they
were welded and how much strength thei had with/without pressurized
tanks? I am getting the impression that SpaceX is really strating from
scratch here, toying with various promitive build techniques.

You're welcome to your impression since SpaceX's iterative design
process still seems to elude you.

Jeff
--
All opinions posted by me on Usenet News are mine, and mine alone.
These posts do not reflect the opinions of my family, friends,
employer, or any organization that I am a member of.

On Tuesday, April 14, 2020 at 4:59:54 AM UTC-4, JF Mezei wrote:
On 2020-04-12 15:41, Jeff Findley wrote:

changed. Certainly when they're building and stacking Starship it's not
pressurized. That's obvious from the live video feeds of its
construction.

If am I not mistaken,the current stacking of cylinders has never
progressed to a point where the the cone was put on top. Full height
stacking was only acheived for the PR model used for the press
conference, and that was a structure of beaten up panels welded together.

Considering the size/weight of the cone that is already built, it seems
to be a hefty weight added to those fragiles cylinders below.


Starship SN3 failure due to bad commanding.

Thanks. Strange though that someone would send a command to open a
critical valve during the test when all else would be stable. If this
happened at the end of the test, releasing pressure from wrong valve,
would Musk have tweeted that the test was succesful and it failed with
an error in de-tanking?


Side question:
Also, I heard the lower tank was filled with water with some pressure
added after. (and there was no frost on it). Musk mentioned that steel
is stronger at cryo temperatures.

Is the strength gained at cryo tempoeratures just icing on cake or is it
a significant amount?


Also, another side question:
Considering water is not compressible, would filling a tank to the brim
and closing valve give tank rigidity? Or does the cylinder really
require outward pressure greater than what water can provide to maintain
its shape?





Initial Starship user's guide says payload to LEO is 100+t. Cite:

Wouldn't this be an aspirational tareget at this point since they
haven't yet built anything that goes to Orbit?


With refueling, the idea is that you can place that payload pretty much
anywhere you want including the surface of the moon or Mars.

But commercially, can launching Starship and then waiting for another
rocket to come and refule it be competitive with current crop of
disposable rockets?

That's pure speculation on your part.

Speculation is all that can happen until SpaceX actually builds and
flies a Starship with whatever thermal shielding installed.


Time will tell what Starship's ultimate payload capability will be, but
100+t is freaking huge. That's at least 5t more than SLS block 1. SLS
block 2 plans on 130t to LEO.

SLS has no viable commercial uses. (would it even be allowed as a NASA
rocket?).



You're welcome to your impression since SpaceX's iterative design
process still seems to elude you.

Question stands. If seel rockets have existed before, shouldn't ApaceX'
iterative design have started at a more advanced stage to improve from
existing older steel rockets? I get the impression SpaceX is really
starting from stratch as if steel rockets had never been built/welded
togtether before.

I will only comment on one of your comments: Actually water is compressible but that's irrelevant to the discussion. Water will indeed impart rigidity to a container. Just look at any disposable water bottle as an example.

In article ,
says...

On 2020-04-12 15:41, Jeff Findley wrote:
Starship SN3 failure due to bad commanding.

Thanks. Strange though that someone would send a command to open a
critical valve during the test when all else would be stable. If this
happened at the end of the test, releasing pressure from wrong valve,
would Musk have tweeted that the test was succesful and it failed with
an error in de-tanking?

Obviously some sort of human error. Either the test script/checklist
was wrong or the person executing the test script/checklist did
something wrong.

Side question:
Also, I heard the lower tank was filled with water with some pressure
added after. (and there was no frost on it). Musk mentioned that steel
is stronger at cryo temperatures.

Is the strength gained at cryo tempoeratures just icing on cake or is it
a significant amount?

Significant. But remember, when it's just sitting on the ground, it's
only experiencing one G of acceleration. When it's in flight, it's
experiencing more like 3Gs of acceleration. So flight loads due to
acceleration are obviously about 3x higher than when it's sitting on the
ground.

Also, another side question:
Considering water is not compressible, would filling a tank to the brim
and closing valve give tank rigidity? Or does the cylinder really
require outward pressure greater than what water can provide to maintain
its shape?

Water is not completely incompressible. On a test like this, you'd
likely fill it mostly full with water and then pressurize the volume
that's left with nitrogen or air until the tank is at the desired
pressure. If it was the "drain valve" for the lower tank which was
commanded to open, then all the water would rush out, creating a vacuum
in the tank due to the column pressure of the water (remember how a
barometer works?). That vacuum is what would have caused the tank to
collapse like it did.

Initial Starship user's guide says payload to LEO is 100+t. Cite:

Wouldn't this be an aspirational tareget at this point since they
haven't yet built anything that goes to Orbit?

No. The aspirational target is still 150+t.

With refueling, the idea is that you can place that payload pretty
much anywhere you want including the surface of the moon or Mars.

But commercially, can launching Starship and then waiting for another
rocket to come and refule it be competitive with current crop of
disposable rockets?

Do note that the payload to GTO is 21t without refueling. Falcon
Heavy's GTO payload is 26.7t, so Starship with no refueling is nearly as
capable to GTO as Falcon Heavy. So most payloads would only really need
refueling if it needed to go beyond GTO.

As for refueling, that's why Starship is designed to be rapidly
reusable. This enables multiple refueling flights in a short period of
time. Also, liquid oxygen and liquid methane are relatively easy to
store in orbit (unlike liquid hydrogen which must be kept much colder).
So hopefully boil-off won't be much of an issue.

That's pure speculation on your part.

Speculation is all that can happen until SpaceX actually builds and
flies a Starship with whatever thermal shielding installed.

I'll stick with my own evaluations since I've got an aerospace
engineering degree and enough related knowledge to understand, at least
at a 10,000 ft level, what's going on here.

Time will tell what Starship's ultimate payload capability will be, but
100+t is freaking huge. That's at least 5t more than SLS block 1. SLS
block 2 plans on 130t to LEO.

SLS has no viable commercial uses. (would it even be allowed as a NASA
rocket?).

SLS is a NASA launch vehicle. Every commercial launch vehicle NASA uses
has to be certified by NASA. Falcon 9 and Falcon Heavy are certified by
NASA to carry uncrewed payloads and Falcon 9 is certified to carry crew
(or soon will be since there is a crewed Dragon 2 launch in the works).

You're welcome to your impression since SpaceX's iterative design
process still seems to elude you.

Question stands. If seel rockets have existed before, shouldn't ApaceX'
iterative design have started at a more advanced stage to improve from
existing older steel rockets?

Only if SpaceX were to hire enough engineers with experience actually
designing stainless steel launch vehicles. As far as I know, out of
launch vehicles still flying, only Centaur still uses stainless steel
tanks.

The Centaur Upper Stage Vehicle
Thomas J. Rudman & Kurt L. Austad
Lockheed Martin Space Systems Company
Denver, Colorado USA
https://www.ulalaunch.com/docs/defau...s/the-centaur-
upper-stage-vehicle.pdf

From above:

The Centaur program began in 1958, with its first successful
flight in 1963.

Followed by this blurb about the latest iteration of Centaur which is
still flying today on Atlas V:

The maiden flight of the Atlas V included a Common Centaur
to successfully deploy a commercial satellite on August 21 2002.

So, the last major changes to Centaur were done about 20 years ago. In
that time, how many senior Centaur engineers do you reckon have already
retired?

Knowledge resides mostly in people's heads. Atlas V was designed by
Lockheed Martin Space Systems Company even before the formation of ULA.
Presumably all of the Lockheed Martin engineers who designed the latest
Common Centaur went to ULA, but I have no way to confirm that.

So, how exactly would SpaceX gain such knowledge? It's not like
Lockheed Martin/ULA would publish everything they know on the subject.
They've certainly kept some knowledge proprietary.

I get the impression SpaceX is really
starting from stratch as if steel rockets had never been built/welded
togtether before.

You're welcome to your impression. But, they're clearly not starting
from scratch as stainless steel is a very common material used in
creating pressure vessels (i.e. the oil refining industry, as in Texas).

Jeff
--
All opinions posted by me on Usenet News are mine, and mine alone.
These posts do not reflect the opinions of my family, friends,
employer, or any organization that I am a member of.