Stratolaunch: General Company and Development Updates and Discussions

[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.

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.

The benefit of somewhat higher ISP during first stage flight is not something fundamental...  It's part of the trade-offs.

If you're treating the space plane as a second stage ("almost SSTO") then the back side of the trade-off is that your carry large tanks and wings (and associated heat shield) to orbit.

The whole rocket ships vs. space planes argument is playing out these days. There are many space plane designs, and so far, they've all either died in the hangar or on the drafting table, or were non competitive.

I am glad that space planes are given a fair chance.  I am not a fan of the concept, but would hate for then to disappear just due to lack of trying.



ABCD: Always Be Counting Down

[Lars-J]

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?

I was comparing it to HydroLox or nothing sentiment. When someone states it is necessary for the concept to work, that is the textbook case "unhealthy focus on high Isp". (as Envy887 stated: "LH2/LOX is the only propellant that makes sense for that appliation")

[john smith 19]

I was comparing it to HydroLox or nothing sentiment. When someone states is is necessary for the concept to work, that is the textbook case "unhealthy focus on high Isp". (as Envy887 stated: "LH2/LOX is the only propellant that makes sense for that appliation")

As always it depends on the design and what the fuel is used for.  There's usually a shedload of assumptions behind such a comment.

Assuming all are correct, and required, it could be true. 

[EDIT And in fact he specifies what some of them are

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.

Emphasis mine.
Which sounds pragmatic, not dogmatic, to me.  ]

If they are not, or not required then no it may not be true.

[john smith 19]

The whole rocket ships vs. space planes argument is playing out these days. There are many space plane designs, and so far, they've all either died in the hangar or on the drafting table, or were non competitive.

I am glad that space planes are given a fair chance.  I am not a fan of the concept, but would hate for then to disappear just due to lack of trying.

They won't.  I guarantee at least one of them is going to be flying by the mid to late 2020's.

[DreamyPickle]

X-33 had a 20m wingspan and weighed 130 tons. Stratolaunch can carry 230 tons so X-33 would only need to be scaled up 175% or up to a ~25meter wingspan (multiply 20 by sqrt3(1.75)). I don't know if they published more detailed payload size limits but by measuring pixels over the plane's outline I get ~35 meters between the twin fuselages so the enlarged X-33 would fit with room to spare.

The low thrust of RL-10 might indeed be a problem but it doesn't actually need T/W>1. Since it's launched from another aircraft it will start generating lift right away and only needs the engine to accelerate.

[GWH]

Well they J2-X is just sitting around...

[Robotbeat]

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.

The T/W ratio is too anemic.

Y'all are wrong. RL-10 is sufficient. In fact, it was even baselined for SSTO from the ground with DC-Y.

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...

11 tons.

And only about 8 tonnes-force at 10 km.

Better than that.

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.

So what, Falcon Heavy had 27. But regardless, they don't actually have to max out the mass capability. In fact, they probably don't want to. You have more room for a better launch angle instead of the straight drop that Pegasus does (which necessitates really heavy wings). rocketrepreneur talks about this "gamma maneuver" in his blog post: http://selenianboondocks.com/2015/05/boomerang-air-launched-tsto-rlv-concept-part-i/

Any reasonable

Ahem, that is pretty subjective in a world where SpaceX seriously proposed a 42 engine ITS.

number of RL-10 would be too small a vehicle to get much mass to orbit in one stage....

"Much mass" is also subjective. Not everything needs to be F9 class.


DC-Y baselined 16 RL-10s from the ground. From the air would be far more optimal (given the low chamber pressure), especially if combined with Jon Goff's gamma maneuver.

RL-10 remains a pretty awesome engine, and with air launch would work fine for SSTO.

The key is to not need that really expensive Pegasus pull-up maneuver. If they can implement the Gamma maneuver, then air launch looks much better performance-wise than it otherwise would.

[Robotbeat]

Heck, RL-10 already does an extendable nozzle...

[envy887]

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?

I was comparing it to HydroLox or nothing sentiment. When someone states it is necessary for the concept to work, that is the textbook case "unhealthy focus on high Isp". (as Envy887 stated: "LH2/LOX is the only propellant that makes sense for that appliation")

Hydrogen seems to be working fine for Blue's fully reusable system.

Airdrop to orbit is an awful long ways for a small methalox stage to go. I'll grant that 1-2 tonne payloads are probably feasible with Raptor, but currently flying LH2 tech could do the 6-8 tonnes that I think would be needed for passengers.

I don't see the point of a fully reusable vehicle unless it can support passengers.

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.

The T/W ratio is too anemic.

Y'all are wrong. RL-10 is sufficient. In fact, it was even baselined for SSTO from the ground with DC-Y.

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...

11 tons.

And only about 8 tonnes-force at 10 km.

Better than that.

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.

So what, Falcon Heavy had 27. But regardless, they don't actually have to max out the mass capability. In fact, they probably don't want to. You have more room for a better launch angle instead of the straight drop that Pegasus does (which necessitates really heavy wings). rocketrepreneur talks about this "gamma maneuver" in his blog post: http://selenianboondocks.com/2015/05/boomerang-air-launched-tsto-rlv-concept-part-i/

Any reasonable

Ahem, that is pretty subjective in a world where SpaceX seriously proposed a 42 engine ITS.

number of RL-10 would be too small a vehicle to get much mass to orbit in one stage....

"Much mass" is also subjective. Not everything needs to be F9 class.


DC-Y baselined 16 RL-10s from the ground. From the air would be far more optimal (given the low chamber pressure), especially if combined with Jon Goff's gamma maneuver.

RL-10 remains a pretty awesome engine, and with air launch would work fine for SSTO.

The key is to not need that really expensive Pegasus pull-up maneuver. If they can implement the Gamma maneuver, then air launch looks much better performance-wise than it otherwise would.

Ok, lets cluster 21 RL-10A-4-2 behind a Ariane 5 EPC, with 187 t gross mass for tanks and engines. At an average of 455 sec ISP it gets to orbit with 25 tonnes IMLEO. The tanks and engines are 16 tonnes, so we have 8 tonnes for TPS, landing gear, wings, and payload accommodations, and for payload.

[jongoff]

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.

I don't think LOX/LH2 is the only way to go, but I also don't think it's crazy for airlaunch, where you're severely GTOW constrained. While people like to point out that Isp isn't everything and LOX/Kero SSTOs aren't really that much harder than LOX/LH2 SSTOs, the payload fraction (payload to GTOW) is going to be a lot worse for the LOX/Kero SSTO case, and with air launch you can't just grow the rocket's GTOW to compensate like you can with ground launch.

Of course, if I was going to do an air-launched LOX/LH2 SSTO, I'd probably cheat like crazy by investing in my hobby horse TAN (of the variable mixture ratio variety), to help with the propellant bulk density and engine T/W ratio issues. I think you could get a properly-TANed RL-10 up into the 100klbf class without going too munchkin on things, so you'd only need ~7 of them. And I'd be seriously tempted to see if you could do some sort of gamma maneuver while you're at it. Airlaunching without a proper gamma maneuver just feels like a waste. Without it airlaunch saves you a couple hundred m/s of gravity/drag losses. With it, it can save as much as 1000m/s of losses.

~Jon

[Rocket Surgeon]

Ha!

I think I know why it's called 'Black Ice'

Carbon Composite Construction (Black) and Cryogenic Fuel/Engines (Ice)

Would make sense if it's going to be an almost SSTO.

Nice!

[Lars-J]

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.

I don't think LOX/LH2 is the only way to go, but I also don't think it's crazy for airlaunch, where you're severely GTOW constrained. While people like to point out that Isp isn't everything and LOX/Kero SSTOs aren't really that much harder than LOX/LH2 SSTOs, the payload fraction (payload to GTOW) is going to be a lot worse for the LOX/Kero SSTO case, and with air launch you can't just grow the rocket's GTOW to compensate like you can with ground launch.

Since no one as been able to create an SSTO of either kind, I would say that the edge one has over the other is far more hypothetical rather than certain.

In retrospect the decades old industry infatuation LOX/LH2 was based more on "they must know what they are doing so we must do the same" rather than hard data and experience, and this "SSTOs must be LOX/LH2" I see as just a fading echo of that.

[GWH]

Ha!

I think I know why it's called 'Black Ice'

Carbon Composite Construction (Black) and Cryogenic Fuel/Engines (Ice)

Would make sense if it's going to be an almost SSTO.

Nice!

Hopefully its that, not named after a transportation hazard that kills 100's every year 

[john smith 19]

I don't think LOX/LH2 is the only way to go, but I also don't think it's crazy for airlaunch, where you're severely GTOW constrained. While people like to point out that Isp isn't everything and LOX/Kero SSTOs aren't really that much harder than LOX/LH2 SSTOs, the payload fraction (payload to GTOW) is going to be a lot worse for the LOX/Kero SSTO case, and with air launch you can't just grow the rocket's GTOW to compensate like you can with ground launch.

And of course when people say "SSTO" they are usually implying Vertical Takeoff SSTO, where thrust must exceed GTOW. Historically the Teledyne Firebee II supersonic drone broke the sound barrier with a TWR of 0.5.  Aerodynamic lift can help a lot. The question is can it help enough to do HTOL SSTO?

Of course, if I was going to do an air-launched LOX/LH2 SSTO, I'd probably cheat like crazy by investing in my hobby horse TAN (of the variable mixture ratio variety), to help with the propellant bulk density and engine T/W ratio issues. I think you could get a properly-TANed RL-10 up into the 100klbf class without going too munchkin on things, so you'd only need ~7 of them. And I'd be seriously tempted to see if you could do some sort of gamma maneuver while you're at it. Airlaunching without a proper gamma maneuver just feels like a waste. Without it airlaunch saves you a couple hundred m/s of gravity/drag losses. With it, it can save as much as 1000m/s of losses.

~Jon

With a job as tough as SSTO it's simply foolish not  to use any tactic that you can take in design which improves your chances of success. Propellant pre cooling would be another tactic (something the X33 did manage to demonstrate for LH2 quite well).  Likewise as many degrees as possible above horizontal would be good too.

[meekGee]

The whole rocket ships vs. space planes argument is playing out these days. There are many space plane designs, and so far, they've all either died in the hangar or on the drafting table, or were non competitive.

I am glad that space planes are given a fair chance.  I am not a fan of the concept, but would hate for then to disappear just due to lack of trying.

They won't.  I guarantee at least one of them is going to be flying by the mid to late 2020's.

Flying, maybe.  Competitive? We'll see.

But not for lack of trying, that's the main deal.

Between VG, XCor, VO, dreamchaser, spaceplane, stratolaunch, skylon - we'll see every combination of LV that has a flight portion to it, with every type of propulsion.

So we'll see.


------
ABCD: Always Be Counting Down

[Elmar Moelzer]

Good points on both sides of the hydrolox vs other propellants argument.
Gary Hudson and other designers of SSTOs always emphasize the importance of mass fraction for SSTOs over Isp. Elon Musk made a similar comment on Twitter when people brought up the higher Isp of the hydrolox upper stages on ULA LVs.
So, I think there is a lot of valid evidence that mass fraction will help a lot and kerolox systems like the F9 and FH have demonstrated very impressive mass fractions. We have yet to see how well Methalox will perform in comparison when BFS/BFR starts flying. We already know the mass fractions for proposed hydrolox SSTOs.
From my personal understanding of things, it looks pretty even among all three. You gain some, you lose some. I would not dare to say that hydrolox is the _only_ option. It certainly does sound feasible, though.
Regarding the _linear_ aerospike engine for the X-33, I remember that it was necessary to be _linear_ because of the shape of the X-33. A more traditionally shaped aerospike or plug should be a lot easier to develop and would probably perform better. Of course high chamber pressures help too.
Whoever is going to develop that "space plane" certainly have their work cut out for them. I don't believe that this is something we can expect to see in the near term.

[Archibald]

There had been a 2009 paper that explored TAN further and they got very impressive results for SSTOs and TSTOs.

https://arc.aiaa.org/doi/abs/10.2514/6.2009-4983

The author is Melvin Bulman from Aerojet. Thrust Augmented Nozzle is kind of his pet project

It is a shame no progress was made for the last decade.

If somebody is interested I have this paper on my HD...

[Darkseraph]

There would be some really neat advantages to an air-launched hydrolox spaceplane. The nozzles can be optimized for high altitude compared to ground launch. The ISP is obviously very high without increasing the GTOW too much and the Roc has a serious constraint in what mass it can carry. For aerodynamic recovery, the extra volume required for hydrolox is actually a good thing on the way down due to an overall lower ballistic coefficient. This is an extraordinarily exciting development, far more so that the previous plan of flying pegasus rockets. Stratolaunch have Jeff Thornberg working on their propulsion whose previous experience was on SpaceX's Raptor and NASA's J2X. I can't wait to see what their concept for a spaceplane booster looks like. Reusable rockets have been slowly moving towards incorporating more aerodynamic features for recovery from the current design of the BFR to the control surfaces on New Glenn and at the extreme end XS-1. Rapid access to space without weather or launch time constraints would be transformation, even if the payload capacity is relatively small.

On a little side note :

I hope ISP Uber Alles isn't just replaced with SpaceX Uber Alles. All propulsion solutions should be examined on their own merits and specific context. SpaceX not using hydrolox engines doesn't mean these aren't a valid solution numerous use cases. Blue Origin plans to use them for many different applications. ULA plans to do phenomenal work with ACES/XEUS.  Just a few years ago the common wisdom was that SHLVs were totally unnecessary and EELVs with depots could it all cheaper... until SpaceX announced they planned to do one! Suddenly no size of Mars rocket was too small!

[Robotbeat]

SSTO isn’t impossible. There are multiple ways to achieve it. If someone wants to use airlaunch, though, the case for hydrogen (provided you solve storage issues or can top off from the carrier plane), is better than it is for ground launch.

Expendable SSTO is SUPER easy. FH side booster could do it. Even the original Atlas rocket (over half a century old) was pretty close to it and could do it if fitted with modern engines.

[Elmar Moelzer]

So, I did some calculations for a SSTO based on the Falcon9 upper stage mass ratios. I used that because I had the most solid data for it. I hope others will do similar with other structure/engine/propellant combinations:
Assumptions:
I went ahead and doubled the GLOW for the Falcon 9 upper stage, which results in roughly 222 tons of mass.
I assume a dry mass 13 tons. This assumes 3 MVacs attached to two F9 US oxygen tanks and two F9 US RP1 tanks for a total of 8.5 tons, leaving about 4.5 tons for wing/lifting body, additional support structure, TPS and landing gear.
It may be possible to shave some weight of this by combining the two sets of tanks, but we are having the thing hang horizontally before launch so the extra structure may be needed.
A crew compartment (or capsule) for 3 people with 3 tons gross weight (or an equivalent other payload) seems reasonably doable based on the weight of Dragon or the Apollo command module (we don't need TPS, thrusters, etc).
So the total dry weight plus payload would be 16 tons.
I made the assumption that the MVac can operate at full Isp/thrust at the release altitude. That may not be the case, but I am not sure how much I would have to subtract for that, since I don't know enough about Roc and the proposed launch parameters.
MVac Isp according to SpaceX: 348
T/W ratio at liftoff is 1.5
Entering these assumptions into Strout's DeltaV calculator I get a DeltaV of about 9096.51 m/s.
I am not sure how much Delta V the Roc will provide in the end, but maybe 150 m/s?  So close to 9250 m/s total DeltaV.
With a moderately reduced Isp of 330, I still get a Delta V of 8626 m/s, adding the 150 m/s from Roc, it may just be enough to get back from orbit too...
Please feel free to correct any mistakes I might have made.