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Jeff Bezos' secretive rocket company just revealed its plans to towerover SpaceX



 
 
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  #21  
Old September 14th 16, 07:15 PM posted to sci.space.policy
Fred J. McCall[_3_]
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Default Jeff Bezos' secretive rocket company just revealed its plans to tower over SpaceX

JF Mezei wrote:

On 2016-09-14 01:43, Fred J. McCall wrote:

Look up the specific impulse of LOX/LH2 vs LOX/LNG.


Maybe then someone can explain to me why LNG is better than LH2 for the
second stage.


Any number of reasons. It's easier to handle because it's only mildly
cryogenic. For the stage to have the same performance it would have
to be physically bigger if it was LH2 due to the low density of LH2,
which impacts what the first stage has to lift and LNG is sufficient
to the purpose of the stage. There are no doubt many others.


Since both stages operate in Vacuum, if LH2 performs better in vacuum
than LNG, then why not use LH2 for both Stage 2 and 3 ?


It's got nothing to do with "operating in vacuum". LH2 *always* has a
higher ISP than LNG.


In what way is the second stage different from 3rd ? Dont they both
operate in what is , for all practical purposes, vacuum ?


They have different purposes.



Not necessarily. Remember, we're talking about TWO launchers here;
one is a two stage and the other adds a third 'deep space' stage.
Specific impulse and weight both matter and they tend to matter more
for upper stages.


You brought up von Braun. His Saturn 5 used LH2 for stages 2 and 3.

https://upload.wikimedia.org/wikiped..._schematic.jpg


This contradicts your statement that Saturn 5 was 2 RP-1 stages and LH2
for 3rd stage.


Right. My bad. However, they both had 5 engines, just like the 2nd
and 3rd stage of New Glenn both have one engine. You thought the
latter circumstance just made no sense, so why did the Saturn V make
sense?


One big difference is that for Apollo, they had to make it work at
whatever cost in a very limited amount of time and with little past
experience.

When you look at SpaceX, it is clear that as a business they optimized
the design to have lower costs and mass produce engines. They learned
from previous rockets in history. SpaceX started small and scaled up
instead of making one hunking big rocket from the get go.


SpaceX started 'bigger' than Blue Origin did.


This is why I am a bit weary of some company with little experience in
rockets starting off with a very large rocket.


Uh, where did you get the idea that Blue Origin has "little experience
in rockets"? They succeeded in having a first stage (of their New
Shepard launcher) land before SpaceX did and have reused such a stage
where (so far) SpaceX has not.


--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn
  #22  
Old September 15th 16, 02:54 AM posted to sci.space.policy
Fred J. McCall[_3_]
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Default Jeff Bezos' secretive rocket company just revealed its plans to tower over SpaceX

JF Mezei wrote:

On 2016-09-14 14:15, Fred J. McCall wrote:

Uh, where did you get the idea that Blue Origin has "little experience
in rockets"? They succeeded in having a first stage (of their New
Shepard launcher) land before SpaceX did and have reused such a stage
where (so far) SpaceX has not.


As I understand, New Sheperd is in the same class as Branson's joy rides
in Virgin Galactic. It goes up and falls back down.


It's a rocket, is it not? It's smaller than Falcon 1, is it not?
First you complain that Blue Origin didn't 'start small' like SpaceX
and now you're complaining that they started TOO small?


OK, so I read up a little.


You know, it would be really nice if you did that BEFORE you started
posting...


BE-3 is an engine they have already designed,
but they need to make the vacuum version. If they mass produce BE-3 for
the joy-ride business, I guess it isn't so bad if they use them for 3rd
stage now and then (and apparently being considered for the ULA Vulcan
upper stage).


You should recognize that Vulcan with new engines is even more of a
paper rocket than New Glenn. You should also note that it uses BE-4
on its first stage and BE-3 on its third stage, very like New Glenn.


But then, why not use BE-3 on second stage and make bigger tanks when
needed ?


You mean other than the small detail that you'd need something like 5
BE-3 engines to replace that single BE-4 on the second stage? And
you'd need much larger tanks just to get the same performance (which
screws up New Glenn 2-stage)? And now you're carrying all that excess
tankage and engines you didn't need if you'd actually staged onto your
deep space mission?

BE-3 thrust - 110,000 lbf
BE-4 thrust - 540,000 lbf


Or better yet, could they attach extra tanks to Stage 2, and
stage 2 could ditch them once empty to reduce weight ?


That's almost always a losing proposition. You almost always get
better performance if you ditch all the structure (including the
engine package) and use a smaller, lighter engine package on the upper
stage. Note that there are rockets (vague recollection) that cut the
middle ground and ditch tanks plus SOME of the engines when they
'stage' (which just seems unnecessarily complicated to me).


Also, with current materials technology, do LOX / LH2 tanks weight
considerably less than in Saturn 5 days or still roughly the same ?


They CAN be lighter, but aren't necessarily. Lighter tanks are more
expensive. The idea these days is to cut cost rather than go for
performance over all.


I recall I think DC-X experimenting with composite tanks but as with
most nasa projects, got cancelled before they could get it to work. I
note that SpaceX uses Aluminium-Lithium compiosite for its
structures/tanks. I take it that composite tanks aren't ready for prime
time yet?


DC-X needed that sort of thing because it was developing SSTO
technology and if you wanted ANY payload you needed to pretty
aggressively cut weight, no matter what it cost.


--
"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
  #23  
Old September 15th 16, 12:54 PM posted to sci.space.policy
Fred J. McCall[_3_]
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Default Jeff Bezos' secretive rocket company just revealed its plans to tower over SpaceX

JF Mezei wrote:

On 2016-09-14 21:54, Fred J. McCall wrote:

BE-3 thrust - 110,000 lbf
BE-4 thrust - 540,000 lbf


Ok thanks. I had not seen those numbers, puts things in perspective.

What is the weight of each engine ? is there a massive difference of
same order of magnitude as their thrust ?


Looking around, I don't find anyone giving weights of the engines. You
know, you could look as easily as anyone else and pretty much everyone
is going to have to try to look it up.

It is of interest, though, that the Blue Origin BE-4 looks very like a
SpaceX Raptor engine. Same fuel/oxidizer and very close to the same
thrust.


They CAN be lighter, but aren't necessarily. Lighter tanks are more
expensive. The idea these days is to cut cost rather than go for
performance over all.


OK, so basically, if I read correctly, since the Saturn 5 days,
advancements in materials have not made significant dents in tank weights.


Unless you're willing to pay for it.


Do LNG, RP-1 and LH2 tanks all have similar weight for same volume or
does LH2 need thicker/heavier walls for instance ?


I would assume that the more cryogenic the fuel is the heavier the
tank structure has to be, both for insulation and pressure containment
purposes.


Is it correct to state that LH2 needs more volume, but weights less than
RP1 to get same delta-V ? I asusme the "weights less" really means that
the fuel weights much less, but since it needs bigger tank, the combo of
fuel/tank weights just "less" ?


You need to look at what is called the bulk density of the
fuel/oxidizer mix and the ISP both to get an idea of just what the
difference in tank size needs to be to get equivalent total
performance. Values in the following table should let you figure it
out.

http://yarchive.net/space/rocket/fuels/fuel_table.html

ISP for RP-1 and LNG are about the same, but the bulk density of
LNG/LOG is only about 80% that of RP-1. So LNG rockets need tanks
over 20% larger than an RP-1 rocket. Based on bulk density, LH2/LOX
bulk density is like 35% that of RP-1, so if they had the same ISP I'd
need almost 3x as much tankage for an LH2 stage. However, LH2 has a
large ISP advantage, so to get the same total performance the LH2
rocket really only needs tanks about 2.3 times as large as RP-1.


--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn
  #24  
Old September 16th 16, 02:06 AM posted to sci.space.policy
Alain Fournier[_3_]
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Default Jeff Bezos' secretive rocket company just revealed its plans totower over SpaceX

On Sep/15/2016 at 2:22 PM, JF Mezei wrote :
On 2016-09-15 07:54, Fred J. McCall wrote:

need almost 3x as much tankage for an LH2 stage. However, LH2 has a
large ISP advantage, so to get the same total performance the LH2
rocket really only needs tanks about 2.3 times as large as RP-1.



Assuming for sake of discussion that engines are the same weight:

Is it correct to assume that for same delta-V, the weight of LH2+
bigger tank will still be less than weight of RP-1+tank ?

(aka: weight of lighter fuel more than compensates for heavier tank?)


Yes that that is correct.

The assumption that the engines are the same weight isn't too bad once
you are in orbit or nearly in orbit (for upper stages) because you can
use smaller engines and let them burn longer. But for the for the first
stage, since you need much more thrust, that assumption does not hold.


Alain Fournier

  #26  
Old September 17th 16, 03:00 AM posted to sci.space.policy
Fred J. McCall[_3_]
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Default Jeff Bezos' secretive rocket company just revealed its plans to tower over SpaceX

JF Mezei wrote:

On 2016-09-15 07:54, Fred J. McCall wrote:

need almost 3x as much tankage for an LH2 stage. However, LH2 has a
large ISP advantage, so to get the same total performance the LH2
rocket really only needs tanks about 2.3 times as large as RP-1.



Assuming for sake of discussion that engines are the same weight:

Is it correct to assume that for same delta-V, the weight of LH2+
bigger tank will still be less than weight of RP-1+tank ?

(aka: weight of lighter fuel more than compensates for heavier tank?)


Rocket performance is based on MASS of fuel, not volume.


--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn
  #27  
Old September 17th 16, 03:03 AM posted to sci.space.policy
Fred J. McCall[_3_]
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Posts: 10,018
Default Jeff Bezos' secretive rocket company just revealed its plans to tower over SpaceX

William Mook wrote:

On Wednesday, September 14, 2016 at 10:14:45 PM UTC+12, Jeff Findley wrote:
In article ,
says...

Rob wrote:

wrote:

"The largest of the two new rockets, called the "New Glenn 3-stage," is an
enormous 23 feet in diameter (about half the length of a school bus), 313 feet
tall (close to the height of the Apollo moon rockets), and will spew out 3.85
million pounds of thrust ? about half as powerful as NASA's Saturn V launcher.

Size in feet and weight in pounds? Is it designed in the 19th century?


It's designed someplace that's actually capable of doing it. Real
aeronautical engineers work in feet, pounds, and Rankine.


LOL. I'll take working in SI units over imperial units any day.

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.


SI Rules!


Then you should avoid airplanes entirely. Fuel is measured in pounds,
altitude is measured in feet, and distance is measured in nautical
miles. The only place that did it differently was the old Soviet
Bloc.


--
"Ignorance is preferable to error, and he is less remote from the
truth who believes nothing than he who believes what is wrong."
-- Thomas Jefferson
  #28  
Old September 17th 16, 06:34 AM posted to sci.space.policy
William Mook[_2_]
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Posts: 3,840
Default Jeff Bezos' secretive rocket company just revealed its plans totower over SpaceX

On Saturday, September 17, 2016 at 2:03:15 PM UTC+12, Fred J. McCall wrote:
William Mook wrote:

On Wednesday, September 14, 2016 at 10:14:45 PM UTC+12, Jeff Findley wrote:
In article ,
says...

Rob wrote:

wrote:

"The largest of the two new rockets, called the "New Glenn 3-stage," is an
enormous 23 feet in diameter (about half the length of a school bus), 313 feet
tall (close to the height of the Apollo moon rockets), and will spew out 3.85
million pounds of thrust ? about half as powerful as NASA's Saturn V launcher.

Size in feet and weight in pounds? Is it designed in the 19th century?


It's designed someplace that's actually capable of doing it. Real
aeronautical engineers work in feet, pounds, and Rankine.

LOL. I'll take working in SI units over imperial units any day.

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.


SI Rules!


Then you should avoid airplanes entirely. Fuel is measured in pounds,
altitude is measured in feet, and distance is measured in nautical
miles. The only place that did it differently was the old Soviet
Bloc.


--
"Ignorance is preferable to error, and he is less remote from the
truth who believes nothing than he who believes what is wrong."
-- Thomas Jefferson


Outside the US SI units are generally used (kg, meters, kilometers)
  #29  
Old September 17th 16, 09:07 AM posted to sci.space.policy
Rob[_8_]
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Posts: 57
Default Jeff Bezos' secretive rocket company just revealed its plans totower over SpaceX

Fred J McCall wrote:
Then you should avoid airplanes entirely. Fuel is measured in pounds,
altitude is measured in feet, and distance is measured in nautical
miles. The only place that did it differently was the old Soviet
Bloc.


That is not correct. Outside the US, jet fuel is widely measured
in kilograms. A wellknown near-accident in Canada was caused by
the fact that the crew ordered a number of kilograms of fuel and
got delivered that number of pounds, as the switchover from pounds
to kilograms had been made shortly before.
  #30  
Old September 18th 16, 10:17 AM posted to sci.space.policy
Sylvia Else
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Posts: 1,063
Default Jeff Bezos' secretive rocket company just revealed its plans totower over SpaceX

On 17/09/2016 12:03 PM, Fred J. McCall wrote:
William Mook wrote:

On Wednesday, September 14, 2016 at 10:14:45 PM UTC+12, Jeff Findley wrote:
In article ,
says...

Rob wrote:

wrote:

"The largest of the two new rockets, called the "New Glenn 3-stage," is an
enormous 23 feet in diameter (about half the length of a school bus), 313 feet
tall (close to the height of the Apollo moon rockets), and will spew out 3.85
million pounds of thrust ? about half as powerful as NASA's Saturn V launcher.

Size in feet and weight in pounds? Is it designed in the 19th century?


It's designed someplace that's actually capable of doing it. Real
aeronautical engineers work in feet, pounds, and Rankine.

LOL. I'll take working in SI units over imperial units any day.

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.


SI Rules!


Then you should avoid airplanes entirely. Fuel is measured in pounds,
altitude is measured in feet, and distance is measured in nautical
miles. The only place that did it differently was the old Soviet
Bloc.


And visibility is measure in statute miles.

Oh, and cloud cover is measured in eighths of the sky.

Sylvia.
 




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