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 Post subject: Re: Stratolaunch 6 engine, dual hull jet
PostPosted: 01 Jun 2017, 16:45 
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Dumb question........ why do you need two fuselages?


The best place for the cargo is close to centers of weight and list. Putting a fuselage to one side allows that and gets the fuselage away from any blast from the rocket. A second fuselage restores balance?

Ashley


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 Post subject: Re: Stratolaunch 6 engine, dual hull jet
PostPosted: 01 Jun 2017, 18:42 
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Air launch buys you several things, the ability to launch to any orbit optimally, you are not tied to a specific launch location/physical range.

For the same rocket it will perform better at higher altitude, you can have bigger expansion cone on the first stage and less air drag.

This is a bigger issue for small rockets than large ones.
This is a bigger issue for solid propulsion rockets than liquid. (typically higher initial accelerations, more penalized by air drag)

This aircraft will only ever launch small rockets, never anything as big as a Falcon 9.

My issues is that any company that can build to the mass fraction and performance necessary for the 2nd, or 3rd stage, will find building a big dumb first stage an easy exercise. In contract to making the rocket structure strong enough to hang it horizontally from the CG fully loaded. This project never made any sense to me.

Wings don't belong on a system for an orbital rocket. Suboribtal like space ship one, or virgin galactic it makes sense. On the other hand an orbital rocket spends such a small part of its performance budget in the atmosphere that air launch is a net negative.


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 Post subject: Re: Stratolaunch 6 engine, dual hull jet
PostPosted: 01 Jun 2017, 20:16 
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 Post subject: Re: Stratolaunch 6 engine, dual hull jet
PostPosted: 02 Jun 2017, 06:43 
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plenty of justification for a heavy lift orbital injection system, do you honestly think one of musk's rockets will be able to cheaply place anything over 5 tons into orbit?

not a chance, they just recently had to forgo the recovery of the booster to get a 13,380 lb payload into orbit, which added great expense- and this setup can lift how much?


Can I just quickly point out that 13,380 lb is in fact more than 5 tons, and that was to geosynchronous orbit, the hardest to get to.


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 Post subject: Re: Stratolaunch 6 engine, dual hull jet
PostPosted: 02 Jun 2017, 15:26 
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Can I just quickly point out that 13,380 lb is in fact more than 5 tons, and that was to geosynchronous orbit, the hardest to get to.


you can but it wasn't cheap, and their business model does not support ongoing use of the rockets in a disposable fashion, it's centered around the reuse


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 Post subject: Re: Stratolaunch 6 engine, dual hull jet
PostPosted: 02 Jun 2017, 15:29 
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Username Protected wrote:

Can I just quickly point out that 13,380 lb is in fact more than 5 tons, and that was to geosynchronous orbit, the hardest to get to.


you can but it wasn't cheap, and their business model does not support ongoing use of the rockets in a disposable fashion, it's centered around the reuse

care to share the number that you saw on their invoice for the launch ?

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 Post subject: Re: Stratolaunch 6 engine, dual hull jet
PostPosted: 02 Jun 2017, 17:28 
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>> You and me, Us, will have a chance to go to space for a reasonable price in our lifetimes.

Most likely, in an urn...


Yes, cremation is the ultimate cost-saving measure for space travel.


Launching Urns into outer space... now that's a business idea!

"Spend eternity in interstellar bliss"

Or maybe "Fry and fly"
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 Post subject: Re: Stratolaunch 6 engine, dual hull jet
PostPosted: 02 Jun 2017, 17:32 
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care to share the number that you saw on their invoice for the launch ?


it's in literally every form of communication SpaceX has released, that they can only sustain their profitability with a reusable booster rocket

this mission was covered in great detail, and the risks to both parties were known, the logical takeaway here is, the falcon9 was not designed to continually launch 13,000lb objects into orbit, an air launch mission, as is being advertised, could handle that

if someone says I can't afford a wife, but I can afford an escort- do you need to see receipts to understand their point?


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 Post subject: Re: Stratolaunch 6 engine, dual hull jet
PostPosted: 02 Jun 2017, 19:10 
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The large plane will only launch payloads smaller than a Falcon 9.

Note that at this time all of the groups doing active public design for a rocket to hang under this beast have folded.

Spacex's solution of a reusable 1st stage makes far more sense.
This is also blueorigin's approach for an orbital launcher, reusable first stage.


At this time the largest orbital payload that is currently planned to be launched from this monster aircraft is 443 Kg.

All significant loads on a rocket are axial, unless you add a very significant strongback to the aircraft this requires that the rockets hang from their middle.

What most people don't realize is how much of a rocket is fuel.
The Ratio of weights for a fully fueled orbital stage full/vs empty is approximately the same as the ratio of weights of a 2L soda bottle full/vs empty.

The minimum change (DV) in velocity to get something to orbit is about 8000 m/sec.

The rocket equation for a single stage is:

DV=g*isp*ln(mi/mf)

is 9.81m/sec, isp is the impuse efficency of the rocket engine, mi is mass initial, mf is mass final assuming that all the difference in mass between mi and mf is spewed out the back at the velocity (g*isp). This value mi/mf is called the mass fraction.


Raising the launch altitude improves your initial ISP from 309 to maybe 340.
But that benefit only lasts to your first staging point. The 2nd,3rd stages will all have vacuum optimized rocket engines.

The real cost for airlaunch comes in the mf part of the equation.
The final empty mass of the vehicle must be larger to support the torsional loads from hanging the rocket by its middle. Notice in watching launch preparations most western rockets (F9 is an exception) are stacked vertically on the launcher. They are not strong enough to be assembled horizontally and raised to vertical.

The F9 does this by being attached to a large strongback that provides the strength to make the vehicle rigid while its being raised to vertical.

The Russians do something very similar with the soyuz.


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 Post subject: Re: Stratolaunch 6 engine, dual hull jet
PostPosted: 02 Jun 2017, 19:15 
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I'm not smart enough to participate in this thread.
:oops:

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 Post subject: Re: Stratolaunch 6 engine, dual hull jet
PostPosted: 02 Jun 2017, 20:22 
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I'm not smart enough to participate in this thread.
:oops:
Come on, Chip - it's not rocket science. :whistle:


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 Post subject: Re: Stratolaunch 6 engine, dual hull jet
PostPosted: 03 Jun 2017, 00:18 
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Great information, here. I have been hoping that a "space/rocket" forum would be started at some point.

RM

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 Post subject: Re: Stratolaunch 6 engine, dual hull jet
PostPosted: 03 Jun 2017, 07:18 
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Username Protected wrote:
The large plane will only launch payloads smaller than a Falcon 9.

Note that at this time all of the groups doing active public design for a rocket to hang under this beast have folded.

Spacex's solution of a reusable 1st stage makes far more sense.
This is also blueorigin's approach for an orbital launcher, reusable first stage.


At this time the largest orbital payload that is currently planned to be launched from this monster aircraft is 443 Kg.

All significant loads on a rocket are axial, unless you add a very significant strongback to the aircraft this requires that the rockets hang from their middle.

What most people don't realize is how much of a rocket is fuel.
The Ratio of weights for a fully fueled orbital stage full/vs empty is approximately the same as the ratio of weights of a 2L soda bottle full/vs empty.

The minimum change (DV) in velocity to get something to orbit is about 8000 m/sec.

The rocket equation for a single stage is:

DV=g*isp*ln(mi/mf)

is 9.81m/sec, isp is the impuse efficency of the rocket engine, mi is mass initial, mf is mass final assuming that all the difference in mass between mi and mf is spewed out the back at the velocity (g*isp). This value mi/mf is called the mass fraction.


Raising the launch altitude improves your initial ISP from 309 to maybe 340.
But that benefit only lasts to your first staging point. The 2nd,3rd stages will all have vacuum optimized rocket engines.

The real cost for airlaunch comes in the mf part of the equation.
The final empty mass of the vehicle must be larger to support the torsional loads from hanging the rocket by its middle. Notice in watching launch preparations most western rockets (F9 is an exception) are stacked vertically on the launcher. They are not strong enough to be assembled horizontally and raised to vertical.

The F9 does this by being attached to a large strongback that provides the strength to make the vehicle rigid while its being raised to vertical.

The Russians do something very similar with the soyuz.


Paul,

Roughly at what altitude does "air" launch become viable? (If ever).

Tim


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 Post subject: Re: Stratolaunch 6 engine, dual hull jet
PostPosted: 04 Jun 2017, 06:20 
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>Roughly at what altitude does "air" launch become viable? (If ever).

If you are doing suborbital flights like the original spaceship one or virgin galactic, or the proposed (now mothballed) XCor vehicle then the air launch has significant gains.

For an orbital vehicle I would say never. The only advantage is flexible launch position when trying to hit exact orbital targets.


Lets define some things... people confuse space and orbit.

Space is defined as any altitude above the von karmen line. ~333000 ft..
IF you go straight up to 330000 ft then you be in space.
If you do this straight up then you will fall straight back down.



Orbit is going fast enough to keep right on falling but you are going so fast you continuously miss the planet...
Attachment:
Newton_Cannon.png


If the air drag would not cause you to burn up from the insane speed (17,500 mph)
you could be in orbit at zero altitude.

The real requirement to get into orbit is horizontal speed, not vertical travel.
The real reason orbital rockets go straight up at launch is to get out of the atmosphere so they can start their horizontal acceleration without the air drag.

From an energy imparted to the payload in orbit requires 25 times more energy be imparted to the payload than putting the payload into "Space" straight up.


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 Post subject: Re: Stratolaunch 6 engine, dual hull jet
PostPosted: 04 Jun 2017, 08:53 
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Paul,

So what you are saying is that whole "Space elevator" is a pipe dream :D
Seeing the cannon on the image you posted reminds me of a magnetic rail cannon on a mountainside to launch satellites which was proposed on one those go fund me type sites. It was rather funny.....

Interesting, I never knew the horizontal thrust was such a major factor. I knew it existed, but never considered the magnitude of the numbers involved.

Tim


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