Stratolaunch was not built to launch 1,000 lb satellites either.
Speed isn’t the only part of that equation. 35K feet of altitude. Think about it.
May not be SSTO, but it won’t be 3STO, either.
Except for the difference in aeroelastic drag due to the reduced density of air at 30+ kft and sea level, the altitude is virtually meaningless. Low Earth Orbit is between 200 nmi and 1200 nmi (about 1200 kft and 7300 kft) so 30 kft is between 2.5% and 0.4% of the orbital altitude, but the critical component of making orbit is the orbital speed, not altitude. If you lofted a satellite up to LEO altitude without any forward velocity it would just fall back down to Earth. Basically, an object in orbit is going “forward” so quickly that it continually falls above the horizon, and if it doesn’t have enough forward speed it will fall “under” the horizon, e.g. into the ground.
Stranger
Actually, it’s not just a tooling issue. It’s an existing pieces issue. I found this on wikipedia:
Which is bloody brilliant, actually. They had to buy two 747s to get the engines and landing gear they needed, so why not use both windshields while you’ve got them.
I look at it and think “rather than conventional tails on both fuselages, why not a single horizontal stabilizer connecting the two tail booms?” But I imagine they have their reasons.
Interesting. I was struck while reading the article with the launch plane’s fuel capacity, 250,000 pounds. If they just wanted to take off, climb to altitude, launch, and land, it doesn’t seem like they’d need nearly that much. I thought maybe they were planning ferry flights, too; fly the carrier aircraft and payload down to South America (to be near the equator), refuel, do the launch flight, bring the carrier aircraft home. But your description adds a lot. The range is apparently 1,200 nm on launch flights; maybe that’s to fly out to sea, turn to whatever launch course they want, and come back.
Wikipedia also says it needs a 12,000 ft runway to take off. I wonder if they have one specific base planned, or if they’ll be using multiple launch sites.
The launch facility also needs someplace to perform vehicle final integration and payload processing/integration, which requires someplace sufficiently near the flightline that meets quantity distance (QD) requirements for the solid propellants (which are technically explosives) and standoff distances for any toxic or caustic liquid propellants. So that seriously limits the locations where the plane could be sited. I would guess that Stratolaunch plans to operate out exclusively out of the Mojave Air and Space Port for the foreseeable future. All of the other suitable sites I can think of are military stations and grounds (CCAFS, VAFB, NTTR, YPG) which would require expensive leasing costs and siting requirements.
Stranger
Those are not 747 windows. I suspect they reused a lot of the flight deck electronics and instruments, but the airframe appears to be all original.
The oricinal Pegasus II design had three stages. The cryogenic third stage proved untenable and was replaced by two solid stages, for a total of four stages.
The Pegasus II program seemed to fall apart and they now plan on launching the Pegasus XL, which has three solid stages and an optional fourth liquid stage. Stratolaunch definitely isn’t saving anything with regard to staging here.
A 1 kg object in LEO has about 32 MJ of kinetic energy and 4 MJ of gravitational potential energy. A 1 kg object at 10 km and 250 m/s has 0.03 MJ of kinetic energy and 0.1 MJ of potential energy.
This is a little unfair since I’m comparing the payload vs. the whole launch vehicle, but nevertheless you can see that the boost you get from the plane is negligible.
About the biggest performance-related improvement (as compared to logistics) I can think of is that you can size your engine nozzle to be more efficient than it would be at sea level. It’s not totally negligible, but again not something that will remove a whole stage.
Note: Orbital Sciences Corporation (now Orbital ATK after its merger with the former ATK, previously Alliant Technologies, Concordant Technologies, Morton-Thiokol, Thiokol Propulsion, et cetera, which also produces the solid propellant motors for the Pegasus) has been flying the Pegasus XL since the mid-'Nineties, and has flown the XL exclusively since 2002. The XL is just a stretched version of the Pegasus using the Orion 50SXL and Orion 50XL as the first and second stages instead of the Orion 50S and Orion 50 on the original Pegasus.
The original Statolaunch booster stages were actually going to be an adaptation of the Falcon 9, but the requirements for air launch posed too much reduction in payload capacity and substantial modifications to the SpaceX design. (How that wasn’t apparent at the beginning is beyond me.) Orbital did some conceptual work and even mockups of the Pegasus II, but no flight articles were ever constructed and it was eventually judged to be economically unfavorable.
The advantage of being able to optimize the expansion ratio of the nozzle to higher altitude conditions and thereby avoid losses in underexpanded flow is an advantage of a few percent, which is significant, but not one that by itself justifies the complexity of features for air launch. Altitude compensating nozzles are sometimes used (almost exclusively deployable exit cone extensions) to improve performance in near vacuum or to keep the pre-operating form within a reasonable package size, but true altitude compensation in the form of aeospike, plug, modular plug, and other types of nozzles could be used in theory to achieve similar performance improvements across ranges of altitude. That they have not is largely a materials science and heat management issue.
Stranger
There’s a short Wiki article on it. It would have had four first-stage engines.
The whole idea of air-launching a LOX rocket (aside: it bugs me that I can’t say “cryogenic” here even though LOX is cryogenic, since “cryo” in rocketry is reserved for LH2) always seemed nuts to me. Stable liquids are one thing, but the ground support you need for LOX rockets is immense, and they wanted to put all of that on a plane? Crazy. It’s one of those fractally complex things, where the simplest of subproblems breaks apart into innumerable sub-subproblems upon closer inspection. Just thinking about ice buildup alone makes my head spin.
Agreed; air launch really begs for operational simplicity, and the potential for adverse interactions, both environmental and modal, between the carrier and a liquid propellant launch vehicle would seem to be too significant to warrant the rather modest advantages. The advantage of optimal azimuth could be better obtained by at-sea launch (either from a towed barge or actually from a semi-submerged buoyant platform, which has been done) and the drag effects from sea level launch versus altitude launch are readily compensated by adding more propellant, which is just a scaling problem. Stratolaunch in general doesn’t seem economically viable; even Orbital has had a tough time making the case for the much smaller Pegasus (its cost per kilogram payload is actually unfavorable compared to larger vehicles but it offers the advantage of getting the payload to a specific orbit for a few tens of millions versus complicated rideshare agreements or a hundred million plus for a larger dedicated vehicle) and was not the market disrupting technology originally envisioned, but it was the first successful fully commercial orbital rocket launch system and the first air launched orbital delivery system.
Stranger
A plane that size would be a big gas user.
So they’ve rolled it out of the hanger. Have they actually flown it yet?
The Boeing 747s that transported the space shuttle were never a launch platform. They were just for transportation and aerodynamic testing of the shuttle. The only shuttle ever released from the back of a 747 in flight was OVO-101, The Enterprise, which was never flown to space, just glided in from atmosphere to prove the orbiter could land on its own.
Enjoy,
Steven
Nice update. The biggest thing this demonstrates is that they’ve not yet abandoned the project.
As our experts Stranger and Dr. Strangelove have said, this project seems fun but pointless.
I wonder how much , like the YAL-1 747-based anti-ICBM laser, it’s an example of a reasonably good idea that took so long in the development that progress elsewhere in the industry eclipsed it. And it took way too long for the sponsoring organization to wake up and smell the now-stale coffee and pull the plug on what had long ago become a pointless white elephant.
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I know your comment was a few months ago but I can’t resist.
It’s easy to get an M1 above the U-2 altitude record. Just drop it from higher than that. M1s are very safe vehicles. They fly like a safe, they climb like a safe, and most of all they land like a safe. 
Paul Allen must have a tiny penis!
Well, unlike most of the rest of us, his penis is *much *smaller than his wallet. So he naturally wants to transfer some of that excess size to where it’ll do more good. 
I’d probably do the same thing if I had either of those problems. 
I wonder if they’ll turn the platform into a superheavy transport craft when it proves to be uneconomic for space launch.
It would not be unheard of–the Antonov An-225 is a (nearly) unique craft used for particularly large and heavy loads that can’t be handled any other way.
The Stratolaunch could be even better at this task: it has a higher payload, and the underslung cargo attachment means it could handle extremely awkward (long, wide, whatever) loads.
One problem is that there just aren’t many airports it can land at. Even a 60 m runway width is probably too close for comfort, and those are only at the largest airports. It also needs a 3700 m length.
Another possible problem is that it might not be able to land with the maximum weight. It’s entirely possible that the maximum loads were only intended for the liquid-fueled version where they expected to dump the propellant in case of launch abort. But I really don’t know.
Hell, I’d cut mine off for his money!
I agree with your concerns. It probably can’t be used (much) as an outsized lift machine. It’s special-purpose enough that the compromises they made building it preclude more versatile applications. As you suggest, max landing weight is probably a significant limitation.
As to the extra-long runways, that’d be for takeoff at max weight in a hot place like Mohave. For lesser missions runway lengths would be more ordinary. Which of course is no help for the extra width required, both of the runway and of the surrounding airport taxiways and parking area.
The big challenge to my eye is that the payload is carried outside in the breeze. So unless the thing was already a complete aerostructure, it’d have to be enclosed in some sort of cargo pod.
So now they need to design, certificate, and build a pod. And develop loading / unloading tools for it. Whatever size/shape they design it for, anything that doesn’t fit won’t fly. The one thing that’s generally true of outsized cargo is that it’s a weird and inconvenient shape.
By carefully designing their pod to be a different envelope than the An-225, they might capture all the traffic it can’t carry. e.g. they design for something shorter but fatter than An-225 can hold. But how much traffic like that is there?
In all, I see a single purpose white elephant. It might yet discover a use in space launch for something other than Pegasus XL, but I’m skeptical. It will be cool to see flying, if only for the early test program. IMO soon enough it, like the YAL-1 & XB-70 before it, will be recognized as the dead end they truly were/are.
Agreed. At first, I thought the suspended aspect would be a boon. But the reality is that even the most awkward of equipment is usually designed to sit on the ground somehow, and that’s where the hard attachment points are going to be. So the pod pretty much has to be a plane fuselage in and of itself, with a sturdy floor to strap the cargo to, a way to split the whole thing open for loading, etc.
Expensive, and as you say is still only going to capture the stuff that the An-225 can’t fit (since it’s the more convenient craft for other reasons). Still–they are clearly building the thing. They have to be considering other uses, since even if the launch business is successful, it’s still going to be sitting idle 95% of the time.