Stratolaunch: General Company and Development Updates and Discussions

[deltaV]

JATO bottles?

If you're going to propel the aircraft using rocket engines you might as well use the rocket engines you already have, i.e. the ones on the Falcon 5 like stage. That would work nicely most of the time, but when things get exciting you'd risk losing the aircraft and its pilots. Allen and Rutan have apparently decided that risk isn't worth taking.

Another option would be using low bypass afterburning F100 fighter engines instead of high bypass turbofans to improve thrust to weight. I'm guessing they rejected this option because an aircraft with around twenty F100 engines would not be cheap. The reduced fuel efficiency would also hurt range and make it harder to use the launch aircraft for cargo transport.

[starsilk]

JATO bottles?

If you're going to propel the aircraft using rocket engines you might as well use the rocket engines you already have, i.e. the ones on the Falcon 5 like stage. That would work nicely most of the time, but when things get exciting you'd risk losing the aircraft and its pilots. Allen and Rutan have apparently decided that risk isn't worth taking.

Another option would be using low bypass afterburning F100 fighter engines instead of high bypass turbofans to improve thrust to weight. I'm guessing they rejected this option because an aircraft with around twenty F100 engines would not be cheap. The reduced fuel efficiency would also hurt range and make it harder to use the launch aircraft for cargo transport.

JATO are solids, so you're pretty much guaranteed they'll work reliably, minimal risk of ignition failures etc... and if things do go wrong they could be dropped without losing a large, expensive rocket and its payload.

it would be a (relatively) cheap, simple way of adding 'afterburners' to the plane for the pull up maneuver.

[simonbp]

Paul Allen has a bigger boat than I, however.

And most countries' navies, for that matter...

[Nomadd]

JATO bottles?

If you're going to propel the aircraft using rocket engines you might as well use the rocket engines you already have, i.e. the ones on the Falcon 5 like stage. That would work nicely most of the time, but when things get exciting you'd risk losing the aircraft and its pilots. Allen and Rutan have apparently decided that risk isn't worth taking.

Another option would be using low bypass afterburning F100 fighter engines instead of high bypass turbofans to improve thrust to weight. I'm guessing they rejected this option because an aircraft with around twenty F100 engines would not be cheap. The reduced fuel efficiency would also hurt range and make it harder to use the launch aircraft for cargo transport.

JATO are solids, so you're pretty much guaranteed they'll work reliably, minimal risk of ignition failures etc... and if things do go wrong they could be dropped without losing a large, expensive rocket and its payload.

it would be a (relatively) cheap, simple way of adding 'afterburners' to the plane for the pull up maneuver.

JATO doesn't mean solid. It's a generic term that could be any type of motor. The Messerschmitt used peroxide ones. The US navy experimented with liquids for a while.
 But, I think the whole topic might be off base anyhow. Airliners only use what, 50% of their thrust at cruising altitude? I might be off, but I had the idea that thrust for airliner engines at 35,000 ft was something like half what they could do at sea level, meaning that if the Stratolauncher was crusing at 50% throttle like an airliner, they'd be at around 100,00 lb and could add another 100,000 lb of thrust just by pushing the throttles forward.
 Or, if the fuselages had O2 tanks, they could just shove two Merlins up their twin butts. That would be something to see.

 Not sure if "747 engines" means 45,000 lb or 66,000 lb. They've grown quite a bit in 40 years.

[sanman]

Furthermore, JATO/RATO are aircraft-related technologies, which would likely make them cheaper than pure dedicated spaceflight-specific technologies. The problems should be framed in terms of economics, and not merely physics alone.

[ArbitraryConstant]

I thought this Systems Engineering talk by our excellent antonioe (a member here) was pertinent:
He goes on to talk about the advantages of airlaunch, etc.

He's an excellent speaker, he does a great job of explaining the trades. I think I understand more of the stratolaunch approach now.

[starsilk]

JATO bottles?

If you're going to propel the aircraft using rocket engines you might as well use the rocket engines you already have, i.e. the ones on the Falcon 5 like stage. That would work nicely most of the time, but when things get exciting you'd risk losing the aircraft and its pilots. Allen and Rutan have apparently decided that risk isn't worth taking.

Another option would be using low bypass afterburning F100 fighter engines instead of high bypass turbofans to improve thrust to weight. I'm guessing they rejected this option because an aircraft with around twenty F100 engines would not be cheap. The reduced fuel efficiency would also hurt range and make it harder to use the launch aircraft for cargo transport.

JATO are solids, so you're pretty much guaranteed they'll work reliably, minimal risk of ignition failures etc... and if things do go wrong they could be dropped without losing a large, expensive rocket and its payload.

it would be a (relatively) cheap, simple way of adding 'afterburners' to the plane for the pull up maneuver.

JATO doesn't mean solid. It's a generic term that could be any type of motor. The Messerschmitt used peroxide ones. The US navy experimented with liquids for a while.

yeah, generic term. all the 'in service' ones were solid I think though.

[360-180]

[Robotbeat]

Here's a comparison with the largest satellites in orbit, the MENTOR (or "Advanced Orion") SIGINT GSO satellites launched by NRO (there are now about 4 or 5 of these guys up there). They are pretty big, with the main reflector being perhaps over 100m (330ft) in diameter:
http://en.wikipedia.org/wiki/Mentor_(satellite)

[RanulfC]

JATO bottles?

JATO are solids, so you're pretty much guaranteed they'll work reliably, minimal risk of ignition failures etc... and if things do go wrong they could be dropped without losing a large, expensive rocket and its payload.

it would be a (relatively) cheap, simple way of adding 'afterburners' to the plane for the pull up maneuver.

Note here, IF you use JATO/RATO ("Jet" or "Rocket" which was/is used interchangably for this type of motor) your airframe has to be strengthened and reinforced. Both to handle the thrust loads AND transfer those loads through the whole airframe. Military aircraft (and some civilian versions there-of) are the ONLY airframes built this way and they are normally only used for certain situations.

Yes for the most part modern JETOs are solid rockets, they however are NOT cheap as they are made in limited numbers and availability is questionable. They are not "easy" ways to add extra thrust as noted the airframe will have to be substationally beefed-up to take the thrust.

Lastly, consider that you would already HAVE a set of rocket engines strapped to the airframe, and if you built it to take those loads already the fact that you can test your LV engines prior to release is a very, very big plus. (As is the ability to get to a high gamma angle)

But, I think the whole topic might be off base anyhow. Airliners only use what, 50% of their thrust at cruising altitude? I might be off, but I had the idea that thrust for airliner engines at 35,000 ft was something like half what they could do at sea level, meaning that if the Stratolauncher was crusing at 50% throttle like an airliner, they'd be at around 100,00 lb and could add another 100,000 lb of thrust just by pushing the throttles forward.
 Or, if the fuselages had O2 tanks, they could just shove two Merlins up their twin butts. That would be something to see.

 Not sure if "747 engines" means 45,000 lb or 66,000 lb. They've grown quite a bit in 40 years.

This paper does a good bit of explaining on that subject:
http://home.anadolu.edu.tr/~mcavcar/common/Jetengine.pdf

High-bypass turbofans (such as on the 747 and most modern airliners) move the majority of their air (thrust) with the fan element rather than the jet element. Since air density decreases with altitude, the available thrust of the engine decreases also. As figure 4 shows if your engine has 2000lbs of thrust available at 5000ft, at 35,000ft it would have a little under 800lbs of thrust available. Since you need to have a thrust to weight ratior of over 1.0 when performing the pitch-up manuver (to avoid stalling) you can easily see that just turbofans themselves would be unable to produce the needed thrust.

Randy

[Lee Jay]

Since you need to have a thrust to weight ratior of over 1.0 when performing the pitch-up manuver (to avoid stalling)...

No you don't.  You carry energy in the form of inertia.  This is why even gliders can do vertical maneuvers.

[RanulfC]

Furthermore, JATO/RATO are aircraft-related technologies, which would likely make them cheaper than pure dedicated spaceflight-specific technologies. The problems should be framed in terms of economics, and not merely physics alone.

While it's true that problems should be framed in more than just "physics" terms there are many other terms of which economics is only one

JATO/RATO systems ARE "aircraft-related" technology but they ARE also "rocket/space" systems related, and fall under the economics of a "niche" market, low production rates, and operational/safety concerns.

Randy

[RanulfC]

Since you need to have a thrust to weight ratior of over 1.0 when performing the pitch-up manuver (to avoid stalling)...

No you don't.  You carry energy in the form of inertia.  This is why even gliders can do vertical maneuvers.

True, I just didn't want to get into that much detail

Vertical maneuvers bleed energy at a VERY fast rate that's why you don't see gliders performing "zoom-climb" manuevers

Without a form of thrust capable of equaling the force of gravity you can't maintain the required angle for more than a few seconds before your wings stall. This is "worse" for a heavily loaded aircraft, especially at high altitude.

Ugh, now that I think of it the problem gets worse once you release the rocket! If you were using the rockets motors to both check them out and to provide the needed thrust for the "zoom" you lose that as soon as you release AND what lift you have it now pushing you to a HIGHER Angle-of-Attack!

Without the mass of the LV you should be able to use the engines an controls to "push-over" back to nose level while retaining control, but if you had an on-board high-thrust device (have to be liquid rockets as solids don't throttle well and you'd have to constantly throttle the thrust over the whole manuever) to get you through it would be much easier.

Anyway you look at it the flight is going to be 'exciting' but as noted this is all pretty much speculation because of what we don't know combined with some extrapolation from what we do know....

Still, it's fun ain't it?

Randy

[go4mars]

What are the limiting factors for diminishing returns with (technically and unrelated to the market)? 

Could a "stratolauncher" be made to carry a million pound rocket?  3 million?  8 million? 

[Ben the Space Brit]

What are the limiting factors for diminishing returns with (technically and unrelated to the market)? 

Could a "stratolauncher" be made to carry a million pound rocket?  3 million?  8 million? 

Ultimately, it is the point where the carrier aircraft and related infrastructure (loading hanger, fuelling and safety facilities and also runway) become more expensive to develop and run than a VL rocket first stage, pad and infrastructure.

[neilh]

What are current rates like for the air transport of cargo? I'm wondering about ways for the Stratolaunch carrier to make money when not being used for launch, a little like how the Zero-G aircraft gets used for cargo flights.

[robertross]

What are current rates like for the air  of cargo? I'm wondering about ways for the Stratolaunch carrier to make money when not being used for launch, a little like how the Zero-G aircraft gets used for cargo flights.

http://en.wikipedia.org/wiki/Antonov_An-225

"An example of the cost of shipping cargo by An-225 was €266,000 for flying a chimney duct from Denmark to Kazakhstan in 2008.[22]"
22: http://www.steelcon.com/fileadmin/user_upload/pdf/News/Steelcon__News_GB.pdf

and (as a ref):
"In May 2011 Antonov CEO is reported to have said that the completion of a second An-225 Mriya transport aircraft with a carrying capacity of 250 tons requires at least $300 million, but if the financing is provided, its completion could be achieved in three years.[9]"
9: http://www.ukrainianjournal.com/index.php?w=article&id=12454

[Rocket Science]

What are the limiting factors for diminishing returns with (technically and unrelated to the market)? 

Could a "stratolauncher" be made to carry a million pound rocket?  3 million?  8 million? 

Ultimately, it is the point where the carrier aircraft and related infrastructure (loading hanger, fuelling and safety facilities and also runway) become more expensive to develop and run than a VL rocket first stage, pad and infrastructure.

Agree Ben, that's why I think my Flyback Falcon makes more sense. But, hey that's just me...

Robert

[Norm38]

Is a "zoom" maneuver really needed?  The Crossbow paper says the main requirement for the carrier is to hit the gamma angle, and ensure the rocket remains above 10km after the drop.  The carrier will already be going Mach 0.85 and can't go any faster as the separation needs to be subsonic.  So all that is needed is extra starting altitude and a pitch up maneuver, but not any real acceleration.

The Crossbow paper also says the thrust for pitch up can come basically for "free" from the rocket itself.  If the first stage engines are started at low thrust for checkout prior to the drop (and they need to be), then the position of the rocket below the carrier's CG will cause the carrier to pitch up naturally.

The rocket then throttles up immediately after the drop and accelerates forward while the carier climbs up and banks away.

[RanulfC]

Is a "zoom" maneuver really needed?  The Crossbow paper says the main requirement for the carrier is to hit the gamma angle, and ensure the rocket remains above 10km after the drop.  The carrier will already be going Mach 0.85 and can't go any faster as the separation needs to be subsonic.  So all that is needed is extra starting altitude and a pitch up maneuver, but not any real acceleration.

The Crossbow paper also says the thrust for pitch up can come basically for "free" from the rocket itself.  If the first stage engines are started at low thrust for checkout prior to the drop (and they need to be), then the position of the rocket below the carrier's CG will cause the carrier to pitch up naturally.

The rocket then throttles up immediately after the drop and accelerates forward while the carier climbs up and banks away.

Well you "kinda" answered your own question Norm38, as the "zoom" (pitch-up) IS required in one form or another to get the rocket to the proper gamma for release.

The rocket itself could be used, though as far as I know rockets don't start out at "low-throttle" but would have to be throttled back after they fire. Not really an overall "issue" if you design for it.

Of course at this point I need to mention that you don't HAVE to change the AoA of the carrier aircraft at all given a system like the AirLaunch trapeze-and-lanyard drop method:
http://www.airlaunchllc.com/AIAA-2008-7835-176.pdf

Other papers here:
http://www.airlaunchllc.com/TechPapers.html#

Which is why "I" personally am leaning towards StratoLaunch planning on igniting the rocket prior to seperation. Otherwise they are planning on spending a lot of money on both the aircraft and rocket without having any way to verify engine operability prior to release, and in which case Airlaunch's business plan beats the economic pants off them despite having the "worlds-biggest-aircraft"!

If Gary-et-al can come up with a way to check-fire the engines on their concept, (and I fully imagine there ARE ways) then despite the 'brain-power' and 'depth-of-money' invested in StratoLaunch I'm of the opinion that AirLaunch can and will end up eating these guys lunch...

Randy