Stratolaunch: General Company and Development Updates and Discussions

[yg1968]

Yet some consider that the Stratolaunch may be overbuilt for this new world of smaller-scale satellites.

Is this really true? Cubesats are a different market from regular sats. I was under the impression (from Jim among others) that GEO sats aren't getting any smaller. They are getting bigger if anything.

[Kabloona]

I'm a bit surprised they went for such a wide space between the fuselages, to date air launch space vehicles have modest wingspans, and even something of over 200 tons launch mass wouldn't have a wingspan of more than 20 meters if it's a delta wing.

It looks like they basically just scaled up White Knight Two in planform until they got an overall wingspan with enough area to lift both fuselages (plus engines, fuel, etc) and the amount of payload they wanted to carry.

Once you've established an overall wingspan, spacing the fuselages closer together increases the span of the outboard wing sections, and thus the bending stresses near the wing roots. Looks to me like the fuselages are probably spaced in such a way as to minimize bending stresses, with the result that the overall span is divided roughly into thirds.

If that is their design rationale, then the spacing between fuselages is less about the wingspan of whatever rocket it carries and more about optimizing the structural design of the aircraft itself.

[catdlr]

Paul Allen vs. Elon Musk: a different approach to satellite launches

source: http://www.csmonitor.com/Technology/2016/0620/Paul-Allen-vs.-Elon-Musk-a-different-approach-to-satellite-launches

[Comga]

Paul Allen vs. Elon Musk: a different approach to satellite launches

source: http://www.csmonitor.com/Technology/2016/0620/Paul-Allen-vs.-Elon-Musk-a-different-approach-to-satellite-launches

This is the same information-free story we have been hearing upthread, and for a few years.

They do add some imagined competition to sensationalize it.  Allen vs Musk.  Musk vs Bezos.  Pshaw!  None of their companies are going after the same markets.

It still seems highly unlikely that the proffered story for Stratolaunch the real one. 

[Zed_Noir]

Looks like the width of the wheel tracks is a little over the wingspan of White Knight Two, so around 45 meters, 60 meters wide runways are not uncommon.

I'm a bit surprised they went for such a wide space between the fuselages, to date air launch space vehicles have modest wingspans, and even something of over 200 tons launch mass wouldn't have a wingspan of more than 20 meters if it's a delta wing.

IMO your delta wing design have poor landing handling characteristics. And more importantly, where will you put the 6 turbofan engines required along with the landing gears and fuel tankage?

Oops. got to remember to avoid posting before coffee.

edit to add: The Turbofans, landing gear requirements and fuel tankage for the carrier aircraft dictates a big aircraft footprint.

[kch]

Looks like the width of the wheel tracks is a little over the wingspan of White Knight Two, so around 45 meters, 60 meters wide runways are not uncommon.

I'm a bit surprised they went for such a wide space between the fuselages, to date air launch space vehicles have modest wingspans, and even something of over 200 tons launch mass wouldn't have a wingspan of more than 20 meters if it's a delta wing.

IMO your delta wing design have poor landing handling characteristics. And more importantly, where will you put the 6 turbofan engines required along with the landing gears and fuel tankage?

* Delta wing works fine for Pegasus.
* Turbofan engines -- even 6 of 'em! -- won't get you to orbit.
* Don't need landing gear for something that isn't going to land.
* Solids are a much better fit for air launch than liquids.

Anything else? 

[Robotbeat]

Looks like the width of the wheel tracks is a little over the wingspan of White Knight Two, so around 45 meters, 60 meters wide runways are not uncommon.

I'm a bit surprised they went for such a wide space between the fuselages, to date air launch space vehicles have modest wingspans, and even something of over 200 tons launch mass wouldn't have a wingspan of more than 20 meters if it's a delta wing.

IMO your delta wing design have poor landing handling characteristics. And more importantly, where will you put the 6 turbofan engines required along with the landing gears and fuel tankage?

* Delta wing works fine for Pegasus.
* Turbofan engines -- even 6 of 'em! -- won't get you to orbit.
* Don't need landing gear for something that isn't going to land.
* Solids are a much better fit for air launch than liquids.

Anything else? 

I disagree about the solids.

Solids are great for ground-launch because they generate a stupendous amount of thrust. But they have poor mass fraction and low Isp. Both these things mean that you need to carry a MUCH heavier rocket for the same payload to orbit as you could for a pump-fed hydrolox-based rocket. And airlaunch is ultimately limited by the weight of the rocket you're carrying. So if you're stuck with solids, you mass to orbit will be like half of what it would be for liquids.

Yes, there's a lot more complication with boil-off, but if you solve that engineering challenge, then high-Isp and low dry mass liquids are MUCH better for air-launch.

[TrevorMonty]

In case of aborted launch could Stratolauncher land with LV still attached?. Also would they want to land with fully fuelled LV.

NB a lot aircraft max landing weight is considerably less than their takeoff weight.

[Kabloona]

Yes, there's a lot more complication with boil-off, but if you solve that engineering challenge, then high-Isp and low dry mass liquids are MUCH better for air-launch.

It's not just boiloff. For liquid systems you need much more GSE, which makes ground ops more difficult, time consuming, and expensive. Liquids are never going to be as easy to handle as solids, so anyone making these choices is still going to be left with the basic performance vs ground ops tradeoffs.

Also, it's worth noting that liquid system performance will suffer a mass fraction hit because of the need to strengthen the tanks for bending loads during captive carry (as compared to a similar ground-launched vehicle), whereas solids composite cases are more suited to taking those bending loads because they're already quite beefy to handle the chamber pressure. Yes, a liquid air-launched vehicle should outperform a solid, but the advantage is somewhat reduced by the need for stronger tanks.

[Alf Fass]

Looks like the width of the wheel tracks is a little over the wingspan of White Knight Two, so around 45 meters, 60 meters wide runways are not uncommon.

I'm a bit surprised they went for such a wide space between the fuselages, to date air launch space vehicles have modest wingspans, and even something of over 200 tons launch mass wouldn't have a wingspan of more than 20 meters if it's a delta wing.

IMO your delta wing design have poor landing handling characteristics. And more importantly, where will you put the 6 turbofan engines required along with the landing gears and fuel tankage?

Oops. got to remember to avoid posting before coffee.

edit to add: The Turbofans, landing gear requirements and fuel tankage for the carrier aircraft dictates a big aircraft footprint.

I think you've interpreted me as arguing for a delta wing on the carrier aircraft, whereas I'm actually talking about one on the rocket (as is seen on Pegasus).

[Alf Fass]

With regard to the distance between the two fuselages, on the ground the weight of the whole is carried on the landing gear, the weight of the 220 ton rocket is carried by the mid wing across a span to ~45 meters, so that section of the wing will need quite a bit of strength. On the other hand when in flight the weigth is carried by the wings, so having more wing area above the rocket makes more sense. I suppose the best compromise would be to have a narrower span between the fuselages but more wing area over the rocket through having a deeper wing.

If we were to start with a clean slate probably the best configuration would be to have a shallow but strong center fuselage that could support the entire length of the rocket with multiple attachment points, thus reducing the bending loads the rocket would need to endure, and minimizing the structural weight of the carrier, with the landing gear housed in a pair of wing nacelles no wider apart than is necessary to accommodate the rocket and any wings that it might be equipped with.

[ChrisWilson68]

If we were to start with a clean slate probably the best configuration would be to have a shallow but strong center fuselage that could support the entire length of the rocket with multiple attachment points, thus reducing the bending loads the rocket would need to endure, and minimizing the structural weight of the carrier, with the landing gear housed in a pair of wing nacelles no wider apart than is necessary to accommodate the rocket and any wings that it might be equipped with.

Stratolaunch did start with a clean slate, and they came to a different conclusion than you did.

[Alf Fass]

If we were to start with a clean slate probably the best configuration would be to have a shallow but strong center fuselage that could support the entire length of the rocket with multiple attachment points, thus reducing the bending loads the rocket would need to endure, and minimizing the structural weight of the carrier, with the landing gear housed in a pair of wing nacelles no wider apart than is necessary to accommodate the rocket and any wings that it might be equipped with.

Stratolaunch did start with a clean slate, and they came to a different conclusion than you did.

Not really, their original intent was to use most of the original fuselages to save the amount of new structure, when they found that not feasible (probably either from weight problems or from adapting a low wing fuselage to a high wing design) they just carried on with the two fuselage design by building new fuselages, also there was probably a bias to follow the layout of the White Knight two design that Scaled Composites had already built.

[Fan Boi]

With a liquid rocket: The moment it is released from the carrier aircraft it will decelerate, which will cause the liquid to move away from the tank exits. Won't it be difficult to prime the plumbing and pumps with the liquid at the top of the tanks?

[RonM]

If we were to start with a clean slate probably the best configuration would be to have a shallow but strong center fuselage that could support the entire length of the rocket with multiple attachment points, thus reducing the bending loads the rocket would need to endure, and minimizing the structural weight of the carrier, with the landing gear housed in a pair of wing nacelles no wider apart than is necessary to accommodate the rocket and any wings that it might be equipped with.

Stratolaunch did start with a clean slate, and they came to a different conclusion than you did.

Not really, their original intent was to use most of the original fuselages to save the amount of new structure, when they found that not feasible (probably either from weight problems or from adapting a low wing fuselage to a high wing design) they just carried on with the two fuselage design by building new fuselages, also there was probably a bias to follow the layout of the White Knight two design that Scaled Composites had already built.

I'm pretty sure Scaled Composites have engineers on their staff and they have more information than we do about the design choices they made.

With all the work that went into the current design, after deciding not to use most of the original fuselages it would not have been a good idea to start over again with a new design.

[punder]

Prediction: the Stratolaunch carrier will end up a specialized cargo transport along the lines of Super Guppy and Beluga. With a dash of Sikorsky Skycrane thrown in.

Mixing airplanes and rockets just introduces too many complications and compromises. The glaring difference between VG and BO should provide enough evidence of that.

Just yelling my piece from the peanut gallery...

[TrevorMonty]

This plane would be ideal for launching XS1 vehicles. The extra structural strength required for air launch may be a benefit for a RLV, performance gains from air launch should overcome any weight gains.

[yg1968]

SN also has an article:
http://spacenews.com/stratolaunch-seeks-launch-partners-as-aircraft-nears-completion/

[simonbp]

Prediction: the Stratolaunch carrier will end up a specialized cargo transport along the lines of Super Guppy and Beluga. With a dash of Sikorsky Skycrane thrown in.

Mixing airplanes and rockets just introduces too many complications and compromises. The glaring difference between VG and BO should provide enough evidence of that.

Just yelling my piece from the peanut gallery...

Probably.

IMHO, Allen is continuing with the project not because of space launch, but point-to-point passenger suborbital. An LH2/LOX single-stage vehicle launched from Roc would make a nice quick trans-pacific vehicle.

[Robotbeat]

It's a prestige project. That's why Allen hasn't cancelled it.