Will StratoLaunch Fly?

[magnemoe]

On 13.10.2016 at 6:20 AM, Northstar1989 said:

Nibb, I must remind you that the Delta-V necessary to reach a given speed and altitude and the speed you travel at that altutude are two entirely different things.  It takes well over 2000 m/s to reach Mach 3 and 24 km altitude.  You also can efficiently use vacuum-optimized rocket nozzles at 24 km, which drastically increases your ISP...

 

See below:

The problem with air-launch really isn't that it doesn't make sense from a ohysics perspective.  It's that to really get the most out of it, you need an expensive-to-develop plane uniquely built for high altitude flight with a very heavy payload...  The R&D costs are what get you...

Besides, if you're trying to get the most out of a plane, why stop at air-launch?  It makes a lot more sense to just build a spaceplane that dolphins out of the atmosphere, and release a heavy upper-stage on a suborbital trajectory at a couple km/s of speed.  This way, you eliminate the need for a first stage entirely, while not needing to design a spaceplane that can get all the way to orbit (the difficulties, of soaceplane design increase exponentially the more Delta-V it needs to carry- and the wings/ airbreathing engines don't provide any benefit once you're high enough you need to swap to rocket propulsion, they're just deadweight, and at that point Lift/Drag is likely to end up below 1...)

Of course, at that point you're probably just better off with a reusable launch stage, ala Falcon 9, unless you're using something like Microwave Beamed Power which is very limited in takeoff-thrust (and since Escape Dynamics went under, MBP probably won't happen for at least 40 years...)

 

Regards,

Northstar

You could get more of an effect if you went high supersonic as in mach 3, however releasing an large payload at high supersonic speed is hard. 
Now if you get up to mach 6-8 you can release out of atmosphere, benefit is that its easier to release and you probably don't need an fairing, if you do very lightweight one should do.

Problem is that building an large hypersonic plane is expensive compared to building an reusable first stage. 
 

[Northstar1989]

On 10/14/2016 at 4:22 PM, magnemoe said:

You could get more of an effect if you went high supersonic as in mach 3, however releasing an large payload at high supersonic speed is hard. 
Now if you get up to mach 6-8 you can release out of atmosphere, benefit is that its easier to release and you probably don't need an fairing, if you do very lightweight one should do.
 

If you dolphin, no amount of speed is an issue.  What I'm suggesting is basically exactly what you suggested- speeding up to Mach 6-8 and then releasing out of the atmosphere.  You can't exit the atmo ar Mach 6 through a steady climb- you have to dolphin higher than your sustainable cruise altitude to get there...

On 10/14/2016 at 4:22 PM, magnemoe said:

Problem is that building an large hypersonic plane is expensive compared to building an reusable first stage. 
 

It is expensive, but it can easily be 100% reusable if you can fly the plane back to the runway.  So it's really not that expensive to build once you amortize out all the launches, and thanks to lift/drag and the use of airbreathing engines it's much more energy-efficient than using a rocket first stage to reach a similar release trajectory...

That being said, the R&D costs would be astronomical.  So it's one of those things that wouldn't really be economical unless we adopted Microwave Beamed Power for spacecraft propulsion (the most important benefit it provides is that it's a compact and lightweight way to provide massive amounts of electricity to spacecraft to run electric/ion engines, at power-levels normally only associated with chemical rockets...) or developed compact, lightweight fusion reactors qualified for spacecraft propulsion usage (the most promising such tech is open-cycle reactions that harness the energy of fusion directly to heat working mass, as they avoid the need to develop energy-positive fusion electrical generators...)  Conceivably, you could use such tech to develop thermal turbojets that operate very well even at very high internal airspeeds- and thus generate usable thrust at much higher speeds and lower pressures than any existing jet engines... (Look up Project Pluto.  What I'm talking is a nuclear ramjet- except a fusion one- which would produce far less thrust at sea level, but operate up to incredibly high airspeeds and low pressures due to the very high temperature of the heat source...)

 

Regards,

Northstar

Edited August 29, 2017 by Northstar1989
Spelling

[todofwar]

2 hours ago, Northstar1989 said:

If you dolphin, no amount of speed is an issue.  What I'm suggesting is basically exactly what you suggested- speeding up to Mach 6-8 and then releasing out of the atmosphere.  You can't exit the atmo ar Mach 6 through a steady climb- you have to dolphin higher than your sustainable cruise altitude to get there...

It is expensive, but it can easily be 100% reusable if you can fly the plane back to thecl runway.  So it's really not that expensive to build once you amortize out all the launches, and thanks to lift/drag and the use of airbreathing engines it's much more energy-efficient than using a rocket first stage to reach a similar release trajectory...

That being said, the R&D costs would be astronomical.  So it's one of those things that wouldn't really be economical unless we adopted Microwave Beamed Power for spacecraft propulsion (the most important benefit it provides is thst it's a compact and lightweight way to provide massive amounts of electricity to spacecraft to run electric/ion engines, at power-levels normally only associated with chemical rockets...) or developed com0act, lightweight fusion reactors qualufied for spacecraft propulsion usage (the most promising such tech is open-cycle reactions that harness the energy of fusion directly to heat working mass, as they avoid the need to develop energy-positive fusion electrical generators...  Conceivably, you could use such tech to develop thermal turbojets that operate very well even at very high internal airspeeds- and thus generate usable thrust at much higher speeds and lower pressures than any existing jet engines... (Look up Project Pluto.  What I'm talking is a nuclear ramject- except a fusion one- which would produce far less thrust at sea level, but operate up to incredibly high airspeeds and low pressures due to the very high temperature of the heatsource...)

 

Regards,

Northstar

The problem I see with dolphining  (my new favorite verb) is the extreme g forces you would experience as you pull up, as well as the aerodynamic forces as you try to steer at hypersonic speeds. If you make the turn to slow you stall too deep, too fast you get ripped apart.

[Northstar1989]

On 10/15/2016 at 1:46 AM, todofwar said:

The problem I see with dolphining  (my new favorite verb) is the extreme g forces you would experience as you pull up, as well as the aerodynamic forces as you try to steer at hypersonic speeds. If you make the turn to slow you stall too deep, too fast you get ripped apart.

It's tricky, absolutely.  But you have a much larger margin for error on a plane with low wing-loading (you can turn more sharply without ripping the wings off, as your angle of attack more closely follows your prograde vector), so the key to doing this effectively would be to develop a really *long* spaceplane that's basically a flying-wing (so you can have low wing loading but still have high wing-sweep).  This also lends itself well to hypersonic deployment, since a plane with lower wing-loading flies higher at the same speed (and thus flies in lower dynamic pressure).

I've always been a fan of designing planes to have really low wing-loading, but in this case it makes a lot of sense.  Larger wings mean the plane masses more- so its stability is less likely to be adversely affected by the deployment of a given size rocket- and planes with lower wingloading have an easier time dolphining above their max cruising altitude and deploying their payload in a stall, yet still safely recovering afterwards (as lower wing-loading also means lower stall-speed).

Finally, since the spaceplane would, at best, only be suborbital (if it even crossed the Karman Line at all), it wouldn't have to worry about hauling those huge wings all the way to orbit, or indeed spending much of the flight profile at all at altitudes where wings would only be deadweight.  The rocket in the cargo bay, meanwhile, would reap all the benefits of a higher deployment (thus enabling use of more fuel-efficient engines) without having to worry about extra mass...

Honestly, I think the biggest problems with Stratolaunch previously were that they deployed a small solid rocket at a comparatively low altitude and speed, and with a small payload.

Solid rockets are best for use in the lower atmosphere due to their high exhaust pressure (which suffers less from ambient pressure) and actually detract from aerodynamic stability due to concentrating mass at the wrong end.  Stratolaunch should have used a liquid rocket (probably KeroLOX as it is least cryogenic) for its higher ISP, which would have meant a lower wing-loading on the plane due to a lighter rocket.

Launching at a low altitude and speed were a mistake, meanwhile, because they detracted from the benefits of an air-launch.  If they were going through all the trouble of designing their rocket to launch from a plane, they shouldn't have utilized a modified commercial subsonic plane (I can see that they did this to try and save on R&D, but it ultimately limited them to a very small rocket, which still proved quite complicated and expensive to air-launch, but derived very little benefit from the modified commercial plane's comparatively low cruising speed/altitude).

Instead they should have raised the capital to design their own plane, and made it BIG (so it could carry a larger rocket), with huge wings and engines/shape optimized for hypersonic flight at very high altitudes...  Sure, it would have been much more expensive to design and build in the first place, but it was the only way they were ever going to get their ongoing costs low enough to turn a real profit vs. conventional launches...

None of it may matter too much now, as SpaceX and the British Skylon project (a true, orbital spaceplane- which could just as easily be modified to fly a suborbital trajectory and leave circularization for the cargo in order to carry a heavier payload on each flight) have rendered StratoLaunch largely irrelevant anyways.  But it's nice to dream about what *COULD* have happened if only they had been a little more daring and ambitious in their plans...

 

Regards,

Northstar

 

Edited August 29, 2017 by Northstar1989
Spelling

[Kryten]

Since this is the closest thing we have to a general stratolaunch thread; 

 

[magnemoe]

On 15.10.2016 at 4:19 PM, Northstar1989 said:

It's tricky, absolutely.  But you have a much larger margin for error on a plane with low wing-loading (you can turn more sharply without ripping the wings off, as your angle of attack more closely follows your prograde vector), so the key to doing this effectively would be to develop a really *long* spaceplane that's basically a flying-wing (so you can have low wing loading but still have high wing-sweep).  This also lends itself well to hypersonic deployment, since a plane with lower wing-loading flies higher at the same speed (and thus flies in lower dynamic pressure).

I've always been a fan of designing planes to have really low wing-loading, but in this case it makes a lot of sense.  Larger wings mean the plane masses more- so its stability is less likely to be adversely affected by the deployment of a given size rocket- and planes with lower wingloading have an easier time dolphining above their max cruising altitude and deploying their payload in a stall, yet still safely recovering afterwards (as lower wing-loading also means lower stall-speed).

Finally, since the spaceplane would, at best, only be suborbital (if it even crossed the Karman Line at all), it wouldn't have to worry about hauling those huge wings all the way to orbit, or indeed spending much of the flight profile at all at altitudes where wings would only be deadweight.  The rocket in the cargo bay, meanwhile, would reap all the benefits of a higher deployment (thus enabling use of more fuel-efficient engines) without having to worry about extra mass...

Honestly, I think the biggest problems with Stratolaunch previously were that they deployed a small solid rocket at a comparatively low altitude and speed, and with a small payload.

Solid rockets are best for use in the lower atmosphere due to their high exhaust pressure (which suffers less from ambient presdure) and actually detract from aerodynamic stability due to concentrating mass at the wrong end.  Stratolaunch should have used a liquid rocket (probably KeroLOX as it is least cryogenic) for its higher ISP, which would have meant a lower wing-loading on the plane due to a lighter rocket.

Launching at a low altitude and speed were a mistake, meanwhile, because they detracted from the benefits of an air-launch.  If they were going through all the trouble of designing their rocket to launch from a plane, they shouldn't have utilized a modified commercial subsonic plane (I can see that they did this to try and save on R&D, but it ultimately limited them to a very small rocket, which still proved quite complicated and expensive to air-launch, but derived very little benefit from the modified commercial plane's comparatively low cruising speed/altitude).

Instead they should have raised the capital to design their own plane, and made it BIG (so it could carry a larger rocket), with huge wings and engines/shape optimized for hypersonic flight at very high altitudes...  Sure, it would have been much more expensive to design and build in the first place, but it was the only way they were ever going to get their ongoing costs low enough to turn a real profit vs. conventional launches...

None of it may matter too much now, as SpaceX and the British Skylon project (a true, orbital spaceplane- which could just as easily be modified to fly a suborbital trajectory and leave circularization for the cargo in order to carry a heavier payload on each flight) have rendered StratoLaunch largely irrelevant anyways.  But it's nice to dream about what *COULD* have happened if only they had been a little more daring and ambitious in their plans...

 

Regards,

Northstar

 

An skylon could carry more cargo to orbit if it went suborbital and used an upper stage. 
An suborbital only skylon would be useful in its own, perhaps as an version 0.9.
Much less heat issues than reentry, you could go for an far scaled down version, you might need an larger cargo hold as you can use h2/O2 on upper stage too. 
an upper stage dropped in space would not need an fairing, 

You could do this without the skylon engines even but with less performance, use jets to mach 3 rocket to mach 6, release payload in space. 
 

[insert_name]

6 hours ago, Kryten said:

Since this is the closest thing we have to a general stratolaunch thread; 

 

how complete is this? it looks like some control surfaces are missing but other than that it looks okay. however we don't know what they've put inside it yet.

[monophonic]

5 hours ago, insert_name said:

how complete is this? it looks like some control surfaces are missing but other than that it looks okay. however we don't know what they've put inside it yet.

I don't think the control surfaces are actually missing. Just without hydraulic power they are hanging down and thus mostly invisible from this angle.

Oh, and it should be pretty complete given that they are about to test putting fuel in it. You need not only the fuel tanks and lines but their control systems in place too if you are to do many meaningful tests with them.

[kerbiloid]

_{Looks like ailerons are absent, but maybe for such juggernaut the outer flaps are used like flaperons instead.}

They are.

Anyway, this empty space between two semi-planes frighten me.

Spoiler

They need more struts in between. Like here.

 

Edited June 1, 2017 by kerbiloid

[FltEng]

While I am a (former) Flight Engineer and not an aerospace engineer, I can't see the design of "Roc" being feasible. I have no doubt that people more knowledgeable than myself (and those who think they are) will comment on this, but I would think there will be an extreme amount of stress on the "wing" between the two fuselages. And the Roc will fly like, well… a rock!

 

[Nibb31]

There is probably a reason they didn't attach the horizontal stabilizers. Maybe it caused some sort of aerodynamic turbulence that messed with the payload. Maybe they need some degree of flexibility between the two fuselages and attaching them would have caused extra stress and cracks.

I know it looks sketchy, but they aren't stupid. The central wing section must have been designed to support the entire load.

The economics are all wrong though.

[Zayne Kerman]

yes

yes it will.

Edited June 5, 2017 by Zayne Kerman
"more syle"

[wumpus]

On 6/4/2017 at 10:20 PM, Zayne Kerman said:

yes

Ok, I expect it will fly.  Now the real question is if it will ever launch a real spacecraft or find any other worthwhile mission?

[Northstar1989]

On 6/4/2017 at 6:15 AM, Nibb31 said:

There is probably a reason they didn't attach the horizontal stabilizers. Maybe it caused some sort of aerodynamic turbulence that messed with the payload. Maybe they need some degree of flexibility between the two fuselages and attaching them would have caused extra stress and cracks.

I know it looks sketchy, but they aren't stupid. The central wing section must have been designed to support the entire load.

The economics are all wrong though.

They're cutting corners (and probably short on funding).  I don't trust it.  They could have at least run some struts between the two semi-planes, if not actually attached the horizontal stabilizers.  I don't buy into the whole "aerodynamic turbulence" hand-waving either.  Specifically *what* issues would connecting the tailplanes have caused?  It would have just basically become a giant P-38 at that point, which didn't have the kind of major turbulence issues you are alluding to (although the connected tailplane WAS a giant hazard when bailing-out of a damaged fighter, and cost many pilots their lives...)  I'd be more likely to buy that they were concerned over the payload hitting the tailplane than anything else...

 

Regards,

Northstar

Edited August 29, 2017 by Northstar1989

[YNM]

It is indeed looks impossible. But AFAIK planes aren't a rigid thing - too rigid and it's less likely to fly well. I guess they're basing their aerodynamic model off the WhiteKnight.

Edited August 29, 2017 by YNM

[mikegarrison]

Carbon fiber is impressive stuff. We tend to judge things like strength based on steel, but carbon fiber can be quite a bit stronger. If anything, I bet the center section is overdesigned.

5 hours ago, Northstar1989 said:

They're cutting corners (and probably short on funding).  I don't trust it.  They could have at least run some struts between the two semi-planes, if not actually attached the horizontal stabilizers.  I don't buy into the whole "aerodynamic turbulence" hand-waving either.  Specifically *what* issues would connecting the tailplanes have caused?  It would have just basically become a giant P-38 at that point, which didn't have the kind of major turbulence issues you are alluding to (although the connected tailplane WAS a giant hazard when bailing-out of a damaged fighter, and cost many pilots their lives...)  I'd be more likely to buy that they were concerned over the payload hitting the tailplane than anything else...

Flutter is tricky.

[Racescort666]

The whole aircraft is mostly carbon fiber right? Maybe they wanted the fuselages to be as similar as possible to save money on tooling? You have to build tools for CFRP parts and it was probably cheaper to build the tools smaller and double up on the number of parts.

It could be that the aerodynamics work for separate horizontal stabilizers and for one large one but manufacturing would drive to a design with more common parts. If the aerodynamics are negligible in the face of manufacturing costs, it's an easy decision.

[wumpus]

7 hours ago, mikegarrison said:

Carbon fiber is impressive stuff. We tend to judge things like strength based on steel, but carbon fiber can be quite a bit stronger. If anything, I bet the center section is overdesigned.

Flutter is tricky.

My understanding is that this plane is expected to fly pretty slow, much slower (probably half of) the 747 it is based on.  I suspect this has more to do with flutter avoidance than engine power.  They are probably using multiple strategies to avoid flutter, but I certainly wouldn't want to be on the first flight (more thanks to corners cut than any one thing).

Does anyone know the hours on the engines?  That is, if stratolaunch goes bankrupt, can we be nearly certain that the engines will be pillaged and the rest of the craft thrown away (although someone could buy it and attach even older engines).  At this point, I doubt that anyone would take the plane for free.  The cost of developing a rocket for it is just too high (and there is no point for multiple pegasus launches, that couldn't be taken seriously).

[mikegarrison]

15 hours ago, wumpus said:

My understanding is that this plane is expected to fly pretty slow, much slower (probably half of) the 747 it is based on.  I suspect this has more to do with flutter avoidance than engine power.  They are probably using multiple strategies to avoid flutter, but I certainly wouldn't want to be on the first flight (more thanks to corners cut than any one thing).

Does anyone know the hours on the engines?  That is, if stratolaunch goes bankrupt, can we be nearly certain that the engines will be pillaged and the rest of the craft thrown away (although someone could buy it and attach even older engines).  At this point, I doubt that anyone would take the plane for free.  The cost of developing a rocket for it is just too high (and there is no point for multiple pegasus launches, that couldn't be taken seriously).

That plane is in no way "based on" a 747. Not structurally, not aerodynamically, not in any way except that it reuses some old 747 engines.

Also, I'm not certain, but I'm pretty sure the market value of old PW4056s is quite low. Many of the planes they were designed to be used with are almost completely out of service. I found asking prices on the internet for an entire 747, with four PW4056s, for under $10M. That's to buy the whole plane.

Edited August 30, 2017 by mikegarrison

[wumpus]

7 hours ago, mikegarrison said:

That plane is in no way "based on" a 747. Not structurally, not aerodynamically, not in any way except that it reuses some old 747 engines.

Odd, that was the original plan.  I'm guessing that there isn't a realistic way to tie two 747s together like that.

[YNM]

1 hour ago, wumpus said:

Odd, that was the original plan.  I'm guessing that there isn't a realistic way to tie two 747s together like that.

If my sight can be believed I read that they only move the "control" systems (computers, cables, piping, the lot). There's no way for structural things to be just moved that way - the same as in the fact that a "kit car" isn't going to be as believably strong as a purposefully designed car, or you don't quite see one bridge being fixed by parts from other bridges.

Edited August 30, 2017 by YNM

[mikegarrison]

On 8/30/2017 at 7:51 AM, YNM said:

If my sight can be believed I read that they only move the "control" systems (computers, cables, piping, the lot). There's no way for structural things to be just moved that way - the same as in the fact that a "kit car" isn't going to be as believably strong as a purposefully designed car, or you don't quite see one bridge being fixed by parts from other bridges.

It would not be surprising if many of the propulsion control systems are also taken from a 747. Those are often very integrated with the engines. Although keep in mind that PW4056 engines are also used on 767s, so they are, to some extent, designed to be plugged into different airplanes.

But there is nothing common for aerodynamics between a swept-wing 747 and a straight-wing Stratolauncher. Nor is there any commonality between a plastic, nearly rectangular high-wing fuselage and a double-radius aluminum low-wing fuselage. In fact, I would guess that unlike the 747, the Stratolaunch fuselage is unpressurized.

[YNM]

2 hours ago, mikegarrison said:

But there is nothing common for aerodynamics between a swept-wing 747 and a straight-wing Stratolauncher. Nor is there any commonality between a plastic, nearly rectangular high-wing fuselage and a double-radius aluminum low-wing fuselage. In fact, I would guess that unlike the 747, the Stratolaunch fuselage is unpressurized.

At least they could tweak the settings such that it's as responsive (or not as responsive) as the 747. Or the pilot can just compensate. No way that any of the actual control surfaces are ported wholly, at most it's only the actuators or somesuch. I mean, they got two whole aircraft, why would they just use the engines...

It's not exactly plastic either, haha. You know how much Airbus love them.

[mikegarrison]

53 minutes ago, YNM said:

It's not exactly plastic either, haha. You know how much Airbus love them.

I just assumed it was CFRP, because Scaled Composites built it.

According to the Wikipedia article on it, they also used landing gear and some other systems from the 747. That makes sense I guess -- landing gear for such a large plane is extremely expensive and they already had some they could adapt. But IMO, that's not at all the same as saying the airplane "is based on" the 747. I guess that's a semantic argument, however.

[YNM]

3 hours ago, mikegarrison said:

I just assumed it was CFRP, because Scaled Composites built it.

Well, FRP isn't called "plastic" apparently in what I'm learning 

Yeah, they're maximizing the usage of the old 747 on this plane. Surely not the fuselage etc, more likely the actuators or hydraulics or gears, computers etc.

Edited September 2, 2017 by YNM