Stratolaunch: General Company and Development Updates and Discussions

[john smith 19]

Agreed. I'm also rather partial to SpaceX's argument that orbital-capable aircraft are almost always more tradeoffs and wasted mass than they're worth, unless you desperately require huge cross range glide capabilities.

I'd be very wary of the "wasted mass" argument from a company that's planning to go to orbit then "waste" 5 more launches launches to reload it's tanks.
And has put wings on its US as that turns out to be the only way to get orbital recovery at scale.

Consider what they say, then consider what they're doing.

Another massive issue here is that Roc at best counts as maybe a quarter of a first stage (based on air density at 0 v. 35000 feet). Black Ice would basically have to be SSTO to work. The Shuttle stack was two stages and ~2000 metric tons fueled, whereas Black Ice would have to be less than 230t. Shuttle had a payload fraction of 1.5% (orbiter excluded) and VentureStar had a theoretical payload fraction of 2%, so something around 2.5% could probably be expected from an airlaunched SSTOish spaceplane. 5 tons to LEO isn't horrible...

Unless of course you had an engine that could deliver an Isp over say 3000secs, even for part of the trajectory.

Still a massive engineering hurdle with many unknowns, but I'm a fair bit less skeptical after spitballing some rough estimates. Doesn't hurt to have the support of a multibillionaire.

True.

[envy887]

Well, RL-10s have terrible sea level performance and excellent vacuum performance, so being able to launch at high altitude might make them feasible as main propulsion. Maybe enough to do SSTO reusable.

RL-10 produces 10 tonnes-force of thrust in vacuum and only about 8 tonnes-force at 10 km. They would need 28 of them to both get a TWR of 1 at the airdrop and max out the mass capabilities of the aircraft. Any reasonable number of RL-10 would be too small a vehicle to get much mass to orbit in one stage.

It would need RS-25, J2X, Vulcain 2, or something similar. Or it could possibly be done with Raptor, though being mass-constrained by the carrier aircraft really hurts methalox.

[john smith 19]

The T/W ratio is too anemic. People tend to overestimate the need for isp efficiency in a deep gravity well (with atmosphere to boot). It is not as important as most think for getting to LEO.

Getting to LEO can be done with Solids, as Scout and the Japanese Mu (which achieved sample return for an asteroid. A phenomenal achievement given the capability of the LV).

Reusable return from orbit turns out to need higher Isp as SX discovered.

High Isp makes everything else a lot easier.

[GWH]

Something like the X-33/Venture Star would seem plausible. 2.5x the size of X-33 would fit the lift off limits of Stratolaunch.

[JAFO]

Dream Chaser Cargo is black right now. Maybe???


What would it take to make DC StratoLaunch launchable?

[Prettz]

What would it take to make DC StratoLaunch launchable?

A rocket to put it on.

[Elmar Moelzer]

Maybe they are planning on benefiting from the "fallout" of the XS-1 project? Some of these designs (or derivates) might fit the requirements for an air launched "SSTO".

[Lars-J]

The T/W ratio is too anemic. People tend to overestimate the need for isp efficiency in a deep gravity well (with atmosphere to boot). It is not as important as most think for getting to LEO.

Getting to LEO can be done with Solids, as Scout and the Japanese Mu (which achieved sample return for an asteroid. A phenomenal achievement given the capability of the LV).

Reusable return from orbit turns out to need higher Isp as SX discovered.

High Isp makes everything else a lot easier.

All other things being equal, of course! But the same goes for anything else. (low weight is better than high weight, high thrust is better that low thrust, a high throttle range is better than low throttle range, cheaper is better than expensive, and the list goes on and on...)

But in the real world, you have to make engineering compromises to actually step out of theory into reality. Which is where an unhealthy focus on high Isp leads you down bad decision trees. How is that high Isp approach working out for a fully reusable system?

[Archibald]

LH2 is a lure, a huge red herring that fooled many people for decades. For SSTOs the big gain in specific impulse is exactly cancelled by the very low density and big, unaerodynamic tanks.
At the end of the day the SSTO insane propellant mass fraction doesn't change much: 92% for LH2, 95% for LOX/kerosene or storables.

By contrast nothing beat LH2 for upper stages. There it rules supreme.

[envy887]

LH2 is a lure, a huge red herring that fooled many people for decades. For SSTOs the big gain in specific impulse is exactly cancelled by the very low density and big, unaerodynamic tanks.
At the end of the day the SSTO insane propellant mass fraction doesn't change much: 92% for LH2, 95% for LOX/kerosene or storables.

By contrast nothing beat LH2 for upper stages. There it rules supreme.

A spaceplane dropped by a carrier aircraft is an upper stage. LH2/LOX is the only propellant that makes sense for that appliation.

You don't need anything exotic to get from 10 km to LEO and then land in one piece.

[vaporcobra]

LH2 is a lure, a huge red herring that fooled many people for decades. For SSTOs the big gain in specific impulse is exactly cancelled by the very low density and big, unaerodynamic tanks.
At the end of the day the SSTO insane propellant mass fraction doesn't change much: 92% for LH2, 95% for LOX/kerosene or storables.

By contrast nothing beat LH2 for upper stages. There it rules supreme.

A spaceplane dropped by a carrier aircraft is an upper stage. LH2/LOX is the only propellant that makes sense for that appliation.

You don't need anything exotic to get from 10 km to LEO and then land in one piece.

If you want it to be worth the effort and even vaguely competitive with the reusable rockets that will be flying in the 2020s, you sure do need to go a bit beyond what is the status quo today. This is coupled with the fact that any modern spaceplane effort VERY SPECIFICALLY cannot copy the Shuttle if it ever hopes to have any success. I'll be interested to see what they lean towards.

[Lars-J]

LH2 is a lure, a huge red herring that fooled many people for decades. For SSTOs the big gain in specific impulse is exactly cancelled by the very low density and big, unaerodynamic tanks.
At the end of the day the SSTO insane propellant mass fraction doesn't change much: 92% for LH2, 95% for LOX/kerosene or storables.

By contrast nothing beat LH2 for upper stages. There it rules supreme.

A spaceplane dropped by a carrier aircraft is an upper stage. LH2/LOX is the only propellant that makes sense for that appliation.

You don't need anything exotic to get from 10 km to LEO and then land in one piece.

I think you may be exaggerating the difference between a ground launch, and one from Stratolaunch. :-) You are nowhere even close to the place where "LH2/LOX is the only propellant that makes sense". Not even in the ballpark.

Even if you said that LH2/LOX is the only propellant that makes sense for upper stages, you would be wrong. And they stage *above the atmosphere*, whereas Stratolaunch would release its rocket deep in the atmosphere.

Get away from the "Isp uber alles" approach, for your own sake. Your post makes it seem like you stepped out of a time machine from 20+ years ago.

[brickmack]

There was an earlier announcement that they bought some RL10s, is that still relevant? This could be the propulsion for the "Black Ice" shuttle project. Since these engines are expensive but reliable and efficient they're a good choice for a reusable vehicle.

As others have said, too small for main engines. Also, we know Stratolaunch is doing some engine development of their own (they've got an SAA with NASA for it). Plus, those engines were bought back when Thunderbolt/Pegasus II was still a thing, so it implies nothing about this.

They could still be useful as secondary engines though. Use a high-TWR engine for initial boost, then cut it and burn the RL10s the rest of the way to orbit, for any on-orbit maneuvers, and deorbit. Adds a bit of mass, but potentially tens of seconds ISP gain for the vacuum phases of flight, and it'd mean the main engine only needs to ignite once per flight. Teledyne Brown's similar concept went with 1 RS-25 and 6 RL10s for basically the same reasons, and some other spaceplanes have proposed roughly the same configuration.

But if they're doing their own engine development anyway, I don't think it makes a lot of sense to outsource RL10. Expander cycle engines are dead simple, they could almost certainly develop their own for a tiny fraction the cost of the main engine

[meekGee]

How can you consider a subsonic jetliner as a first stage?  Or even a fraction of one?

It will be going all of 200 m/s, about 10% of what real first stages deliver.  Altitude is also about 10%.

You trade one set of logistical difficulties for another, but otherwise, there's no fundamental difference from ground launch.

 

[envy887]

LH2 is a lure, a huge red herring that fooled many people for decades. For SSTOs the big gain in specific impulse is exactly cancelled by the very low density and big, unaerodynamic tanks.
At the end of the day the SSTO insane propellant mass fraction doesn't change much: 92% for LH2, 95% for LOX/kerosene or storables.

By contrast nothing beat LH2 for upper stages. There it rules supreme.

A spaceplane dropped by a carrier aircraft is an upper stage. LH2/LOX is the only propellant that makes sense for that appliation.

You don't need anything exotic to get from 10 km to LEO and then land in one piece.

I think you may be exaggerating the difference between a ground launch, and one from Stratolaunch. :-) You are nowhere even close to the place where "LH2/LOX is the only propellant that makes sense". Not even in the ballpark.

Even if you said that LH2/LOX is the only propellant that makes sense for upper stages, you would be wrong. And they stage *above the atmosphere*, whereas Stratolaunch would release its rocket deep in the atmosphere.

Get away from the "Isp uber alles" approach, for your own sake. Your post makes it seem like you stepped out of a time machine from 20+ years ago.

The Stratolaunch carrier aircraft can only lift a vehicle of ~230 t gross mass. Hydrolox is the only viable propellant that can make it to orbit with any reasonable payload, without dropping anything, and with that starting mass constraint from a subsonic airdrop, and with mass margins for a return and landing.

If you try it with kerolox or methalox you will get half the payload or less, because of the hard constraint of starting mass. If you have the option to throw more mass and thrust at the system, or refuel, then hydrocarbons are better. But for a one-shot mass-constrained system LH2 is better.

[envy887]

How can you consider a subsonic jetliner as a first stage?  Or even a fraction of one?

It will be going all of 200 m/s, about 10% of what real first stages deliver.  Altitude is also about 10%.

You trade one set of logistical difficulties for another, but otherwise, there's no fundamental difference from ground launch.

Starting ISP and thrust is substantially better compared to ground launch, and you can run expansion ratios out to 80-120:1 with moderate chamber pressure and decent ISP. More like 150:1 with a high pressure engine.

E.g. with SSME you could run the nozzle out to 120:1 and get an average ISP of ~455 instead of ~425 from a SL launch at 70:1.

[raketa]

Every day astronaut has good point:
Do you like to take off with a rocket full of kerosene and oxygen? You save maybe 30% fuel of the first stage, but you are in danger to kill your airplane crew any moment of you hour fly, not sure, it is acceptable.
If fuel of rocket will more benign, I will be ok to revisit this approach.

[john smith 19]

A spaceplane dropped by a carrier aircraft is an upper stage. LH2/LOX is the only propellant that makes sense for that appliation.

You don't need anything exotic to get from 10 km to LEO and then land in one piece.

That's pushing it quite a bit. Less than 1 Mach number and 6% to a 200Km orbit is more like a "Launch Assist" device.

Dream Chaser Cargo is black right now. Maybe???


What would it take to make DC StratoLaunch launchable?

Most of the thrust of an Atlas 551 IIRC. The design itself has no launch capability.

Something like the X-33/Venture Star would seem plausible. 2.5x the size of X-33 would fit the lift off limits of Stratolaunch.

Why?

NASA spent $1.5Bn+ on that (supposedly) M15 vehicle and got nothing, although I'm sure LM stockholders got a nice dividend.
Even the linear aerospike engine was only needed because of the lifting body shape, which turned out to be just more bid candy (along with the absurd amount they promised to pay if the supposed "V*" vehicle ever got built) to win a contract LM management had zero desire to see fly.

AFAIK the nearest to a vehicle that might go in this direction would have been the XCOR Lynx, given it was
a)Designed for HTO b)Liquid rocket powered (with highly reusable rockets) c)Planned to have an expendable US for small payloads
Which could make the basis of a first generation spaceplane, moving up to a full space capable vehicle without needing a US.

[GWH]

Something like the X-33/Venture Star would seem plausible. 2.5x the size of X-33 would fit the lift off limits of Stratolaunch.

Why?

Not the X-33/Venturestar exactly, just a design that resembles it somewhat as a starting point. Namely a lifting body hydrolox based vehicle. Although maybe a big cheese wedge isn't the way to go given the limited width available on stratolaunch.
Was also thinking an aerospike would be ideal, but envy887's posts suggest that the benefits of aerospike may be somewhat diminished vs a higher expansion ratio vehicle.

[john smith 19]

All other things being equal, of course! But the same goes for anything else. (low weight is better than high weight, high thrust is better that low thrust, a high throttle range is better than low throttle range, cheaper is better than expensive, and the list goes on and on...)

Rather a pointless list of facts.

But in the real world, you have to make engineering compromises to actually step out of theory into reality.

Correct, that's when you find out that your plan to make an upper stage returnable from orbit (with the materials you have available) can't be made to work, for example.

Which is where an unhealthy focus on high Isp leads you down bad decision trees. How is that high Isp approach working out for a fully reusable system?

It depends what you mean by "High Isp" Methalox is "high" Isp compared to Kerolox and SX don't believe they can do full reusability without it.

Or do you know something SX don't?

But by air breathing standards all existing rocket propellants are "low" Isp. 380secs (roughly the SSME at takeoff)? Try 3000+ secs for an air breathing system.

That's what made the entire commercial aviation business possible, in the same way that the mass efficiency of a cylinder for propellant storage (as long as the weight is distributed in the right way, and that distribution does not change very much of course) makes a VTO rocket (just about) possible. Air breathing's 50+% mass fraction lets you build robust HTOL structures where most of it is not propellant with operating lives in 10s of 1000s of hours, while a rockets 5-8% mass fraction and VTO mode just about let it take off in the first place.