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



 
 
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  #11  
Old September 13th 16, 09:09 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 2016-09-12 13:14, wrote:

http://www.techinsider.io/blue-origi...rockets-2016-9


Is there commercial demand for such a heavy lifter?


It only lifts 70% of what Falcon Heavy will lift.


Or are its hopes
pinned on governmentds funding the assembly of a large mars expedition
ship, at which point a heavy lifter can be of use to bring the large
modules with fewer flights?


It's physically big, but it doesn't have the lift capacity for that
sort of thing.


Secondly, what is the advantage of having a 3rd stage as oppposed to
making a bigger tank for 2nd stage for longer burn with same delta-V ?


More stages means you're lifting less parasitic structure weight.


Since both second and 3rd stages are single engine, I don't see much of
an advantage of having 3 stages since you end up pushing one extra
engine and all extra weight to orbit.


You shed the parasitic mass of the second stage on the way up. By
your logic, we could just build one big stage. Why have a second one?


If LOX/LH2 is so much more efficient than LOX/LNG, why not make second
stage LOX/LH2 ?


LOX/LNG is only mildly cryogenic and thus easier to handle. Note that
the SpaceX Raptor engine currently in development will also be a
LOX/methane engine.


Seems to me like they could produce their 2 variants by simply making
one with larger tanks for second stage. (or even 2 tanks of each on
second stage if having smaller tanks has advantages over single very
large tank).


Ask yourself why we don't just build single stage rockets. The
reasoning is the same.


--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn
  #12  
Old September 13th 16, 09:29 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 2016-09-12 22:52, Brian T. wrote:

You don't lug the extra drymass of the larger stage on missions that
don't need it.


How feasable is it to make 2 versions of the second stage ? One with
elongated tanks, and one with normal tanks ?


It's feasible but you'd lose performance.


Would building longer tanks be the equivalent of boeing building 787s of
different lengths? Just add "plugs" that make the fuselage longer and
styrenghten a few stringers in strategic places ?


No, it's not the same. More stages means less parasitic mass carried
along. Why do you think we don't just build them with one really big
stage?


It seems to me that buidling 2 versions of stage 2 with just more fuel
capacity as the difference would be far more simpler and cost effective
than building 2 totally different stages with different engines, fuel,
tank designs etc.


Big performance hit.


And finally, this "Glen-3" project. How much of a pipe dreamn is it ?
does it have credibility or is this just a press release for vapourware
that has little chance of being built ?


So far it's ALL a pipe dream, since they don't have engines yet.

I'm not sure what niche they're aiming at with these, given that they
won't be flying until after Falcon Heavy is available. Unless they
are significantly cheaper, I don't see how they compete wedging
themselves between Falcon 9 and Falcon Heavy.


--
"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
  #13  
Old September 13th 16, 09:38 AM posted to sci.space.policy
William Mook[_2_]
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Default Jeff Bezos' secretive rocket company just revealed its plans totower over SpaceX

On Tuesday, September 13, 2016 at 2:52:27 PM UTC+12, Brian T. wrote:
On Mon, 12 Sep 2016 17:26:25 -0400, JF Mezei
wrote:

On 2016-09-12 13:14, wrote:

http://www.techinsider.io/blue-origi...rockets-2016-9



Is there commercial demand for such a heavy lifter?


There will be, now that there are two (maybe three, but I suspect
Falcon Heavy will eventually be replaced by variants of SpaceX's BFR.)
Comsats are about to get a lot bigger.



More powerful and greater numbers.


Or are its hopes
pinned on governmentds funding the assembly of a large mars expedition
ship, at which point a heavy lifter can be of use to bring the large
modules with fewer flights?


It looks like SpaceX (Mars) and Blue Origin (Orbital Tourism, strong
hints about Lunar Tourism with their talk of New Armstrong) will be
their own core customers. They'll pick up commercial contracts along
the way just due to their price points, and will likely establish new
markets. Space Solar Power just became much more realistic (although
it will still need oil to spike again.)


Space tourism is doable with highly reusable vehicles. The history of comsats are one to one (telstar) then one to many (Sirius satellite radio, satellite TV) and many to many (wireless global hotspot). Teledesic and Iridium were the first forays into that field. Limitations and cost of access to space limited their success. SpaceX and Blue Origin changes that. At stake? $1.7 trillion per year telecom market.

Thin film concentrating optics with high intensity highly efficient thin disk lasers, in conjunction with holographic laser tracking - make 22 megawatt per ton power satellites possible. At $10 million per ton, 50 to 60 ton satellites attain over 1 GW at a cost LESS than coal fired power. This gives access to $5 trillion + primary energy markets. This is the big enchilada.

Secondly, what is the advantage of having a 3rd stage as oppposed to
making a bigger tank for 2nd stage for longer burn with same delta-V ?


Let's say you have a 3.5 km/sec exhaust speed and a total delta vee requirement of 9.2 km/sec when you include gravity and air drag losses. Then you need to have 92.78% propellant on take off. With a 4.22% structure fraction you're left with 3.00% payload. So, for a given payload on orbit, say 60 tonnes, you need a rocket that's 60 tonnes divided by 0.03 or 2,000 tonnes take off weight!

Now let's say you have the same 3.5 km/sec exhaust speed, but you divide the rocket into two stages that achieve 4.6 km/sec each stage for the same total 9.2 km/sec. Then you need to have 73.14% propellant on take off in each stage. With a 4.22% structure fraction, you're left with 22.64% payload on each stage. 5.12% of the take off weight ends up on orbit. So, dividing into 0.0512 60 tonnes obtains 1,170 tonnes take off weight. A SMALLER VEHICLE!

Now, let's say you have the same 3.5 km/sec exhaust speed, but you divide the rocket into three stages that achieve 3.1 km/sec each stage for the same total 9.2 km/sec Then you need to have 58.76% propellant on each stage. With 4.22% structure fraction this leaves 37.02% payload fraction for each stage. Over three stages that's 5.23% of take off weight ends up on orbit. 1,145 tonnes take off weight - a yet smaller vehicle.

Looked at differently, if the 1,170 tonne 2 stage vehicle is equipped with a third stage, it puts up 61.1 tonnes instead of 60.0 tonnes - details count - slight improvements in propellant density, thrust, and so forth - can eke out 2, 3, 4 or 5 extra metric tons to LEO - structure fractions drop slightly - propellant increase slightly, acceleration is adjusted slightly, thrust increased slightly, etc.

You don't lug the extra drymass of the larger stage on missions that
don't need it.


The more stages the more of the take off mass ends up in orbit as shown.

The third stage might also have other uses in the
future (lunar tug? orbital tanker?) He might plan on recovering Stage
2 in New Glenn Mk.II.



The BE-3 is a LOX LH2 engine - that is ideally suited for a fourth kick stage for lunar operations as described in another post.

Since both second and 3rd stages are single engine, I don't see much of
an advantage of having 3 stages since you end up pushing one extra
engine and all extra weight to orbit.


The more stages the more fraction of take off weight ends up in orbit. This is basic rocket science. Displacing a portion of the 60 tonnes with propellant mass - extends range dramatically.


If LOX/LH2 is so much more efficient than LOX/LNG, why not make second
stage LOX/LH2 ?


Because of the cost of LOX/LH2 versus LOX/LNG. Because of the logistics. Because of the complexity. Best used in a fourth kick stage to push 20 tonnes beyond LEO to the moon or Mars.

It would have to be bigger/heavier.


Not really. The more stages the better, especially if structure fraction is high.

To show this lets do a calculation with a really big structure fraction. Consider a two stage and three stage rocket with a 10% structure fraction and a 3.5 km/sec exhaust speed.

TWO STAGE

Ve = 3.5 km/sec, Vf = 9.2 / 2 = 4.6 km/sec
u = 1 - 1 / exp(4.6/3.5) = 0.74133
p= 1 - 0.74133 - 0.1 = 0.16867 per stage --
0.16867^2 = 0.02448 --
60/ 0.02448 = 2,109.1 tonnes

take off weight.

THREE STAGE

Ve = 3.5 km/sec, Vf = 9.2 / 3 = 3.067 km/sec
u = 1 - 1 / exp(3.067/3.5) = 0.58364
p = 1 - 0.58364 - 0.1 = 0.31636 per stage ---
0.31635^3 = 0.10008

A 60 ton to orbit three stage vehicle masses only 600 tonnes at take off. A two stage to orbit vehicle masses 2,109.1 tonnes. A one stage vehicle can't make it to orbit - with this huge structure fraction!

Now the interesting detail is this - 2,109.1 tonnes take off weight translates to 210.9 tonnes payload on orbit - BECAUSE OF THE THIRD STAGE! See?

Bezos might (probably does?) also
have Stage 2 reusability in mind for down the road, so he's saving
mass for that application.


FULL REUSABILITY is the goal- that's a definite.

Brian


Seven BE-4 engines have 3.85 million pounds of thrust. Taking off at 1.28 gees - the same as the Saturn V - actual calculations involve calculus of variations solution - but 1.28 gees is a good first approximation of optimal take off acceleration - 1.28 gees means that the weight of the vehicle at take off is 3.00 million pounds of weight. A TWO stage version of this vehicle lifts 2.45% of its take off weight into LEO - which is 73,500 pounds! A THREE stage version of this vehicle lifts 10.00% of its take off weight into LEO - which is 300,000 pounds!

You start with one stage - and fly it. Then you go to two stage and fly it.. Then you add a third stage.


  #14  
Old September 13th 16, 04:23 PM posted to sci.space.policy
Brian T.
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Default Jeff Bezos' secretive rocket company just revealed its plans to tower over SpaceX

On Tue, 13 Sep 2016 01:09:42 -0700, Fred J. McCall
wrote:

It only lifts 70% of what Falcon Heavy will lift.


70% of what? FH Fully Expendable or FH outboards to LZ-1 and core to
barge?

And really, that 70% is based on extrapolation from the sizes/thrust
given. We're not that sure of them yet. BO probably isn't yet, either.
I've seen 40 tons, 50 tons, and even 60 tons estimates in just the
last 24 hours.

We're not really sure what FH will truly be capable of, either.

Brian
  #15  
Old September 13th 16, 05:46 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

Brian T. wrote:

On Tue, 13 Sep 2016 01:09:42 -0700, Fred J. McCall
wrote:

It only lifts 70% of what Falcon Heavy will lift.


70% of what? FH Fully Expendable or FH outboards to LZ-1 and core to
barge?


Whichever you like IF you assume the same mode of operation for both
rockets. They're speculative numbers at best.


And really, that 70% is based on extrapolation from the sizes/thrust
given. We're not that sure of them yet. BO probably isn't yet, either.
I've seen 40 tons, 50 tons, and even 60 tons estimates in just the
last 24 hours.


Fair enough, but you've got a rocket with significantly bigger
structure (and thus significantly higher parasitic mass) and
significantly less thrust.

Yes, performance for these is speculative, since they don't even have
the engines through testing yet. It's still three years out. However,
we know that a rocket using LNG for fuel needs about 20% more tankage
to get the same total impulse when compared to RP-1 because the bulk
density of LNG/LOX is only around 80% that of RP-1/LOX. And we've got
pretty reliable thrust numbers at this point.

So they're sort of stuck with the bigger structure if they want
equivalent burn times. And they're stuck with lifting that bigger
second stage as well.


We're not really sure what FH will truly be capable of, either.


Uh, we're pretty sure of those numbers, since SpaceX has published
them and development of Falcon Heavy is pretty far along. The engines
are existing engines with lots of flight experience. We even know
pricing for Falcon Heavy.


--
"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
  #16  
Old September 14th 16, 05:16 AM posted to sci.space.policy
William Mook[_2_]
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Default Jeff Bezos' secretive rocket company just revealed its plans totower over SpaceX

This is a preliminary estimate of stage weights - based on what has been publicly released

Stage Total------- Stage Wgt- Propellant
1------ 3,080,000.0 2,002,000.0 1,767,920.0
2------ 1,078,000.0 700,700.0 618,772.0
3------ 377,300.0 245,245.0 216,570.2
Payload 132,055.0 132,055.0

Here's the acceleration with 7 engines on the first stage, 1 engine on the second stage, and 1 engine on the third stage, all at full blast (but recall they can be throttled back from 550,000 lbf to 20,000 lbf!)

G-start G-end
1.250 3.571
0.510 1.458
1.458 4.165

Here's the radial acceleration due to centripetal force of a rocket moving at the terminal velocities each is capable of;

Speed Loss Net--- Gee- Net
2.800 0.865 1.935 0.063 0.937
6.000 1.295 4.705 0.371 0.629
9.200 1.295 7.905 1.048 -0.048

So, the acceleration of the first stage starts at 1.25 gees straight up and ends up at 3.571 gees largely horizontal! Of course these can be throttled back to maintain a reasonable maximum - say 2.000 gees. At first stage burn out the ship is moving at 1.9 km/sec and centripetal acceleration is 0.63 gees and 0.937 gees is pulling back. The second stage starts out at 0.5 gees but rises to 1.458 gees at second stage burn out. At that time the ship is moving at 4.7 km/sec and centripetal acceleration reduces gee loading to 0.63 gees! Now, to counteract that gravity pull, the rocket is pointed up 25.5 degrees - as it continues to accelerate horizontally at altitude. The third stage fires horizontally, and if its not throttled back itends up at over four gees! However, throttling again saves the day, limiting the load to two gee.

So, these engines are perfectly well suited for this mission. A second engine might be useful in the second stage, but isn't strictly necessary, since the ascent trajectory is chosen to allow for the turning of the rocket in such a way as to minimise gravity losses. This is the gravity turn trajectory all space launch vehicles follow - for minimum propellant use and maximum efficiency.

http://www.space.com/images/i/000/03...atellit-11.jpg



  #17  
Old September 14th 16, 05:20 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 2016-09-13 04:09, Fred J. McCall wrote:

More stages means you're lifting less parasitic structure weight.

You shed the parasitic mass of the second stage on the way up. By
your logic, we could just build one big stage. Why have a second one?


First stage: many heavy engines and lots of fuel needed to get the thing
going.

I can understand if stage 1 had sayd 9 engines, stage two had 3 and
stage 3 had 1.


Well, no, you apparently don't understand it at all. The number of
engines per stage is essentially irrelevant and has nothing to do with
whether staging makes sense or not. The relevant numbers are dry mass
dropped with a stage (all structure, including tanks and engines) plus
the additional mass to 'stretch' the tanks vs the additional mass
required to make the new stage (engines, tanks). Plus you need to
take into account optimization of an engine for specific altitudes;
stage 1 engines will be less efficient at the altitude range where
stage 2 will burn, etc.

Saturn V Stage 1 and Stage 2 both had 5 engines.


With each release of a stage, you reduce the number of engine mass you
need to accelerate for the next step.


You're also dropping tank and structure weight that you no longer need
to carry along.


But for Glen-3, both stages 2 and 3 have 1 engine.


But they are not the same engine and do not burn the same fuel. Stage
3 has the same purpose as the third stage on a Saturn V and doesn't
increase payload to LEO at all. It's intended for longer range
missions.

remove silly assumptions

Engineers don't design staging schemes in ways to make them fail. Your
assumed numbers indicate your stages are designed by someone who is
not very bright.


--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn
  #18  
Old September 14th 16, 05:48 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

The first stage of the Glenn 3

2,002,000.0 pounds - stage weight
234,080.0 pounds - structure
1,767,920.0 pounds - propellant
1,403,400.4 pounds - LOX
364,519.6 pounds - LNG

Could be clusted into a three element launcher, or a seven element launcher..

A three element launcher, with the second stage of the Glenn 3

700,700.0 pounds - stage weight
618,772.0 pounds - propellant weight
81,928.0 pounds - structure

This Glenn 3 heavy can put up 278,000 pounds into LEO! It masses 7.02 million pounds at lift off and produces 11.55 million pounds of thrust!

The Glenn 3 Super is a seven element system puts 555,000 lbs into LEO. It masses 14.65 million pounds at lift off and produces 26.95 million pounds of thrust at lift off!

This lifts 4.16x the payload of the original inline Glenn 3 and puts 67 passengers and 13 crew members into Low Lunar Orbit and returns them to Earth. The passengers and crew use rocket belts to land on the moon and return to the orbiting ship - landing and taking off three times each - providing a really compelling lunar exploration adventure!


  #19  
Old September 14th 16, 06:43 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

JF Mezei wrote:

On 2016-09-14 00:20, Fred J. McCall wrote:

whether staging makes sense or not. The relevant numbers are dry mass
dropped with a stage (all structure, including tanks and engines) plus
the additional mass to 'stretch' the tanks vs the additional mass
required to make the new stage (engines, tanks).


You are conveniently forgetting dry mass that needs to be
lifted/accelerated from ground to the point where a stage's engines are
started.


You are conveniently making **** up, since I'm doing no such thing.


So Stage 3 is dead weight from liftoff until its engine is lighted up.


True, but what's your point?


If Stage 2 with bigger tanks ends up weighting less than normal Stage 2
+ Stage 3, then you gain much efficiency between liftoff and the spot
where Stage 3 would have separated.


Yes, if an idiot designs the staging scheme this can certainly happen.


Yeah, the Stage3 with big (half empty) tanks may not be as light and
efficient as stage 3, but this cost MAY be less than the advantages of
carryting less mass from the ground.


It MAY be, but only if an idiot designs the staging scheme.


Since both stage 2 and 3 will operate in vacuum, I am somewhat perplexed
that one would consider one engine to be better suited for the job in
vaccuum than the other.


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


If the LH2/LOX BE3 engine is better in vacuum, then logically shouldn't
it also be used on stage 2 ?


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.


I am always weary of announcements that appear more as PR exercises than
something which was conceived by engineers after having played with the
numbers to optimize a design. This smells more of Blue Origins wanting
to keep a foot in each BE-4 and BE-3 doors by announcing this virtual
design. In other words, a design that is more driven by business
relationships than by engineering optimizations.


I'm sorry, but I don't think you'd recognize "engineering
optimizations" if they bit you on the ass. Saturn V was two LOX/RP-1
stages and a third 'deep space' stage with LOX/LH2. They didn't need
to maximize ISP for the two lower stages that got them to LEO. They
did need to maximize ISP for that 'deep space' stage because otherwise
it would be too heavy to get the total impulse they needed. Your
position here seems to be that everyone starting with Werner von Braun
got it wrong and that you know better.

You don't.


--
"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
 




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