Stratolaunch: General Company and Development Updates and Discussions

[apace]

Why does everybody talk about recovery?  They explicitly say they are not doing it.

Looking into it later they told, but not start with it. So the question will be, why they think, their concept of a 3 stage launch system is cheaper than a 2 stage rocket. Hope it works, but I cannot belive it.

[mr. mark]

Is the SpaceX rocket and Dragon capsule subcontracted for Stratolaunch or licenced for use in this system? I was wondering if Spacex retains ownership of their portion of the vehicle such as the Dragon spacecraft.

[Jim]

I think they've got a good shot to make a real difference here, and am looking forward to seeing more details coming out.

that is the real question.  It is technical feasibly but economic.

Also, it is all on Allen; Rutan and Musk have no skin in the game.  As far as they are concerned, why not? they have nothing to lose.

[Jim]

Is the SpaceX rocket and Dragon capsule subcontracted for Stratolaunch

Read the documents

[Prober]

Compare with this design
Svitiaz

http://www.yuzhnoye.com/index.php?id=30&path=Aerospace Technology/Launch Vehicles/Svitiaz/Svitiaz_e&lang=en

[jongoff]

Why does everybody talk about recovery?  They explicitly say they are not doing it.

Well, they said that they hadn't ruled it out of the trades, but weren't currently planning on it.  I think air-launch actually makes recovery/reuse a *ton* easier (see the link MP99 provided above to my article on the idea from several years ago), but I agree that at this juncture they're not pitching this as a reusable system at all.  I hope they change their mind, but would understand if they didn't.

~Jon

[jongoff]

I think they've got a good shot to make a real difference here, and am looking forward to seeing more details coming out.

that is the real question.  It is technical feasibly but economic.

Also, it is all on Allen; Rutan and Musk have no skin in the game.  As far as they are concerned, why not? they have nothing to lose.

While I think Allen expects to make a profit on this, he also may be willing to take a much higher risk than other investors.  That's the one nicest things about a philantrocapital setup--is that you're not facing the same economics that other capitalist ventures typically face.  The personal, non-economic interests of the philantrocapitalist matter a lot.  If Allen were say, willing to write-off the startup costs as "sunk costs", I'm just about positive he could make a good profit from there.  The bigger challenge will be making sure it's a profit without him mentally writing off the initial investment.

That make any sense?

~Jon

[iamlucky13]

You'd be adding another half million pounds of thrust to an aircraft designed to take 2/3 that. That would also exert a very large torque about a single point on the wings, risk the aircraft taking debris from any engine failures, and have to deal with the plume.

And all of those are ones that can be mitigated easily if designed in from the start.  As a bonus, doing such a rocket assisted zoom climb (or gamma maneuver) saves you a lot of delta-V in gravity losses, eliminates the need for the Pegasus wing, and reduces the bending moments on the rocket stages allowing you to have lighter structures.

Plus the whole making sure you don't drop a fully-loaded rocket till you know its engines are working properly.

Well, yes, they can be mitigated, but building the wing to take that kind of torque doesn't help with keeping aircraft mass down, and I'm not sure you can ever really be confident you won't have an uncontained engine failure.

As for delta-V, you'd lose about 9.8 m/s for each second between release and ignition, right?

I'm not sure you gain reduced bending moments. I assume that little wing doesn't generate anywhere near 1 G of lift, but the rocket has to take over 1 G in lateral loads while being carried.

I'm also not sure about mitigating plume affects. We're talking about 1000+ pounds per second of a 3000 m/s exhaust stream at several thousand degrees potentially impinging on an aluminum and composite airframe.

I also didn't previously consider acoustic effects.

I understand your arguments, but to me it looks like it's risking a few hundred million dollars in payload versus risking the aircrew and a one-off aircraft that is likely worth more than most payloads, plus leaves your business dead in the water for a couple years while you build a replacement.

As far as bending the velocity vector upwards, the video animation shows a pitch up maneuver before release. That should be possible simply using the aircraft's momentum.

[simonbp]

Well, they said that they hadn't ruled it out of the trades, but weren't currently planning on it.

And, for what it's worth, vertical landing the much shorter/lighter Falcon 4/5 would be a heck of lot easier than the very long Falcon 9 first stage. So, even if it's not used operationally, Stratolaunch could be a good test platform for SpaceX's recovery development (a kind of Grasshopper 2).

[Jason1701]

Did they say if the plane will be aluminum or composite?

[jongoff]

Ian,

It's more complicated than that. 

Just do a quick thought experiment.

You drop the vehicle and light the engine 3 seconds later.  That means the engine has just under 30m/s of downward velocity at ignition.

Say your rocket stage has a T/W ratio of 1.4:1 (which is actually really high for a liquid rocket).  That means that your net upward acceleraiton is 4m/s^2.  Which means you end up taking 7.5s to null out the initial downward velocity.  But in that time, you've taken about 75s of gravity losses in addition to your 30m/s of downward velocity drop.

There are papers going into the physics of all this, but the short answer is that you need your velocity vector at the point the rocket leaves the aircraft under powered flight to be pointed at a fairly steep angle to get the most out of an air launch.  Otherwise you end up losing back most of the delta-V benefit from the air launch.

The small pull-up they showed in the video will help a little, but not as much as a full-up zoom climb.


That said, you don't *need* to do things this way, and I doubt that it makes sense for Stratolaunch to take that much development risk on.  I was just pointing out that if you wanted to use the rocket-assisted zoom-climb (and there are some real benefits), these problems can be solved, and in fact several groups have previously investigated the concept and felt it was workable. 

~Jon

You'd be adding another half million pounds of thrust to an aircraft designed to take 2/3 that. That would also exert a very large torque about a single point on the wings, risk the aircraft taking debris from any engine failures, and have to deal with the plume.

And all of those are ones that can be mitigated easily if designed in from the start.  As a bonus, doing such a rocket assisted zoom climb (or gamma maneuver) saves you a lot of delta-V in gravity losses, eliminates the need for the Pegasus wing, and reduces the bending moments on the rocket stages allowing you to have lighter structures.

Plus the whole making sure you don't drop a fully-loaded rocket till you know its engines are working properly.

Well, yes, they can be mitigated, but building the wing to take that kind of torque doesn't help with keeping aircraft mass down, and I'm not sure you can ever really be confident you won't have an uncontained engine failure.

As for delta-V, you'd lose about 9.8 m/s for each second between release and ignition, right?

I'm not sure you gain reduced bending moments. I assume that little wing doesn't generate anywhere near 1 G of lift, but the rocket has to take over 1 G in lateral loads while being carried.

I'm also not sure about mitigating plume affects. We're talking about 1000+ pounds per second of a 3000 m/s exhaust stream at several thousand degrees potentially impinging on an aluminum and composite airframe.

I also didn't previously consider acoustic effects.

I understand your arguments, but to me it looks like it's risking a few hundred million dollars in payload versus risking the aircrew and a one-off aircraft that is likely worth more than most payloads, plus leaves your business dead in the water for a couple years while you build a replacement.

As far as bending the velocity vector upwards, the video animation shows a pitch up maneuver before release. That should be possible simply using the aircraft's momentum.

[jongoff]

Did they say if the plane will be aluminum or composite?

I can't remember if they explicitly said it, but come on, this is Scaled *Composites* we're talking about.  :-)

~Jon

[iamlucky13]

Yeah, I have to agree that it's always impressive as hell to see someone like Mr Allen with the balls to put several hundred $M on the line for something that people are so ready to nay-say. 

Because my posts have probably come across as critical, I want to clarify that I don't intend to be a naysayer.

I suppose part of my nature as an engineer is to naturally think about the technical challenges of a project like this.

So even though I agree this project is technically feasible, and I'm in fact quite excited by the prospect of seeing this system fly, I'm most interested in talking about the things that make this endeavor difficult, (and in comparing different ideas about how best to approach this, like our discussion about pre-release ignition).

On the flip side, those difficult aspects are also the things that will earn Allen and his team huge amounts of respect if they succeed.

[Rocket Science]

Did they say if the plane will be aluminum or composite?

Does Rutan ever bend metal?

[Jim]

As far as real concerns, mine is ex MSFC and the Huntsville area involvement in this project.  They don't and wont understand the Scaled and Spacex culture and I see a clash in the future

[Jason1701]

Did they say if the plane will be aluminum or composite?

Does Rutan ever bend metal?

They did say they were acquiring some 747s. Perhaps the fuselages will be aluminum and the wings will be composite.

[AS-503]

Most of my thinking has already been elaborated by others on this forum, but....

Jim actually cracked a joke (a good one too), about Griffin putting an SRB on it.

It is a good day......

[jongoff]

As far as real concerns, mine is ex MSFC and the Huntsville area involvement in this project.  They don't and wont understand the Scaled and Spacex culture and I see a clash in the future

Well, one thing to remember is that the part of Dynetics most likely involved in this is going to be the old Orion Propulsion guys.  While Dynetics is run by a lot of the old Ares-I people, the former Orion group is led by Tim Pickens--who helped with the SS1 propulsion system, and also built his daughter a hybrid rocket powered bike...I think at least that part of Dynetics isn't goint to have any problem interfacing with the SpaceX/Scaled people... :-)

[Rocket Science]

Did they say if the plane will be aluminum or composite?

Does Rutan ever bend metal?

They did say they were acquiring some 747s. Perhaps the fuselages will be aluminum and the wings will be composite.

I could see by the pics and video the forward fuselage and cockpit, engines, gear and other mechanical systems. It would be a departure for him to do other than composite… But hey, its early days!

[iamlucky13]

Say your rocket stage has a T/W ratio of 1.4:1 (which is actually really high for a liquid rocket).  That means that your net upward acceleraiton is 4m/s^2.  Which means you end up taking 7.5s to null out the initial downward velocity.  But in that time, you've taken about 75s of gravity losses in addition to your 30m/s of downward velocity drop.

There are papers going into the physics of all this, but the short answer is that you need your velocity vector at the point the rocket leaves the aircraft under powered flight to be pointed at a fairly steep angle to get the most out of an air launch.  Otherwise you end up losing back most of the delta-V benefit from the air launch.

Good point, and in fact 3 seconds is probably even being conservative, especially when you add in the time it takes to throttle up. I want to make three additional points, and then I think we've covered the pros and cons of igniting before release pretty well.

1.) You're definitely losing a non-trivial amount of delta-V, but not actually most of it. You start out with about 200 m/s of horizontal velocity and an elevation advantage equivalent to another 400-450 m/s. As a very rough ballpark, I'd say a nozzle sized for the launch altitude might gain you another couple hundred m/s.

2.) With your rocket attached to your plane, the thrust/weight ratio drops significantly. That doesn't eliminate the benefit you describe, but it does reduce it.

3.) As I understand it, starting delta-V isn't really the biggest benefit of air launch anyways. Rather, it's the ability to chose your launch location to best suit your orbit and safety constraints, and to avoid some of the weather-related factors.

I might add in relation to the launch location benefit, they probably aren't staring at costs to achieve that radically different from what Sea Launch faced, so I'd be remiss in not recognizing another venture that had been successful in doing something radically different from the norm with a launch vehicle even bigger than what Stratolaunch is attempting.