View Single Post
  #16  
Old October 2nd 17, 10:58 AM posted to sci.space.policy
Jeff Findley[_6_]
external usenet poster
 
Posts: 2,307
Default NASA is teaming up with Russia to put a new space station near the moon. Here's why.

In article . com,
says...

On 2017-10-01 17:44, Jeff Findley wrote:

Moreover, New Glenn is also, as Bezos repeated Tuesday, "the
smallest orbital rocket Blue Origin will ever build."


Considering the current state of rocket science, once you have the
engines, does designing a rocket to have 3, 5 , 9 or 27 engines make
such a huge difference in terms of how much experience you need?


Once Blue Origin actually flies an orbital launch vehicle then yes it's
possible to reuse the same engines on larger vehicles.

Once BlueOrigin has its first rocket tested, and re-uses same engines,
couldn't it aim for a bigger rocket as the next installment?


But, it is still a lot of work since a larger vehicle is still a new
design even if engines are reused. And beyond the design it often
requires new tooling, new fixtures, new launch facilities, and etc.

Musk explained that they had expected Fancon9 Heavy to use existing
Falcon9 for core and the 2 boosters. Turns out they have to redesign
structures because of different loads (higher payload, + lateral loads
where boosters attach). (This was to explain the delay).


Only for the center lower stage. It has to be different than the
boosters, which are essentially Falcon 9 first stages with nose cones
instead of their own upper stage.

But had they decided at the onset on the need to design the structures
for the Falcon 9 Heavy Loads, wouldn't that design been straightforwards
without needing to push the enelope?


I would, but they'd be carrying around a lot of extra mass which was
completely unnecessary for both Falcon 9 first stages and Falcon Heavy
side boosters.

I can understand building the cryo tanks from carbon fibre for BFR means
developing new techniques and going beyond current state of the art. But
does Falcon 9 Heavy push any such limits or just scale existing tech
within what that tech is capable of?


Carbon fiber tanks will be something new for SpaceX, so it's a risk.
The question is, how big of a risk?

I guess what I am asking is whehther "baby steps" is still needed for
outfits like Blue Origin, or whether state of science allowed bigger
leaps once you have your engines?


Look at history. You can build stages out of existing engines and
tooling. The first stage of Saturn I certainly highlights this. Look a
the engines and the tanks. The downside was that it was quite a bit
heavier and inefficient due to this approach (especially the tanks). A
more efficient design would have used a single F-1 engine and completely
new tanks. But the F-1 wasn't ready and neither was the tooling for
larger tanks. The Saturn I design was done for expediency, not
efficiency. The engineers leading Saturn development were ex-military
missile designers, so "performance uber alles" was kind of the mantra.
This continued, even when it should not have, because Saturn enjoyed
"blank check" style funding due to the Space Race with the U.S.S.R.

But today, "efficiency" isn't the design metric, it's the eventual cost
per pound to orbit that's the design metric. So, if it's cheaper to use
more existing engines on the next design than to have to design and
build new engines, then both Musk and Bezos will do so, even if it
complicates the plumbing, structure, control systems, and etc.

Building new engines has never been especially cheap or quick. What's
more, existing designs don't tend to scale up terribly well, as prior
engine programs have proven. SpaceX is still working on Raptor,
although they've shown videos of it firing on the test stand. Blue
Origin is still working on BE-4, which went "boom" on the test stand, as
these things sometimes do.

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.