Stratolaunch Takes Flight
Scaled Composites Flies World’s Largest Wingspan Aircraft, SpaceRef Business (With video)
“Scaled Composites, LLC made aviation history today with the flight of the largest wingspan aircraft. During this initial flight, the team tested out specific handling qualities to validate the design.”
I wish them the very best of luck on executing a great idea. Space X may have too great a lead, however. I do hope they can fit in with their exciting program.
Never be afraid to cancel a bad project.
Too true. Fancy plane, but what’s the point of building a system for air launch that requires a special runway and has a very limited range of flight? The only reason to even do an air launch is to be able to fly out of any airport and launch over the sea and above the bad weather. Just another odd Burt Rutan design.
I liked your proposal way back, for doing in-air fueling of dry rocket stages carried up on planes. I know that the maximum weight in flight is higher than the Maximum Take-Off Weight, but I can’t find any good information on what the maximum weight at full flight would be for a large jet plane.
On rocket-planes. The HTOL-carrier-thing is also the first stage. It carries a second stage that separates above the atmosphere at a normal 80-120km staging.
Honestly, in normal operation, it’s around the same as the max take-off weight, because you pick an altitude at which you nearly max out your engine RPM for a given payload. (The higher you go, the thinner the air, the lower the drag, the more fuel efficient the engines are for the same fan-RPM.)
But with a rocket-plane/carrier/thing, you can stay lower and slower during fuelling, with correspondingly higher maximum payload, because it’s not the height and speed that matters when you light the rockets. It’s the flexibility combined with reusability. (Assuming the concept could be made to work, of course.) The concept isn’t about gaining speed/height from “airbreathing”.
(Although it’s not trivial either. A VTO uses something like a third of its fuel gaining the first km/s speed and 5km height, and more than half of that in the first 300m/s. Getting a “free” 250-270m/s isn’t going to hurt when you are carrying so much extra dry-mass.)
When it comes to the mid-air fueling of rocket planes, it’s also worth noting that landing gear and the mechanical structures related to supporting the aircraft’s weight while on the ground are not trivial. If memory serves, it adds up to a few percent of the takeoff weight. For a fully fueled rocket plane (orbital or suborbital capable) that’s a sizable fraction of the non-tank dry mass. That can eat up the useful payload mass. Taking off with near-empty tanks and mid-air fueling avoids that problem.
That seems like it would be a lot more complicated and heavy, since you’d need to have both jet engines and rocket engines on the same rocket plane stage. Although I suppose you could use the same fuel for both – RP-1 (or even just JP-5) gets pretty good ISP when burned with either liquid oxygen or high-test hydrogen peroxide (and the latter has the advantage of being non-cryogenic). Use some of the fuel to take off in air-breathing jet engines, then after you’ve transferred your oxidizer and additional fuel fire up the rockets and use the same fuel with the oxidizer in the rocket engines.
IIRC that was a proposed mode for a Shuttle successor at one point, although it wouldn’t have been as good because of the lack of in-air fueling. Getting slightly more speculative, it would be highly useful to have if you ever build a rotating skyhook to lift up cargo.
Putting your heavy stuff on the first-stage has less impact on payload. Anything that adds to the second stage takes away from payload kg for kg. But anything added to the first stage (loosely speaking, rule-of-thumb-within-narrow-ranges, YMMV) takes away the same percentage of payload. For ex, add 5 tonnes to the upper stage and that’s 100% of your payload gone. Add five tonnes to the first stage and that only reduces payload by 20%. (Number pulled out of my nethers.)
So if you’re going to try for something clever and sneaky, you’re better off trying it on the first stage.
This concept is based around the Black Horse SSTO proposal. With the added observation that SSTO’s are stupid. Just stick a conventional upper-stage on it and your whole design becomes easier. Fatter margins, bigger payload, easier re-entry, etc etc.
That’s the concern that leads people to ask, “Hmm, I wonder if we could combine them into rocket-jet hybrid engines?” (Answer: No. No you can’t. Stop it.)
You do gain from launching at altitude and speed. Not much, but rocket equation favours still improvements in that first minute. IMO, that won’t be enough to balance out the increase in dry-mass of the first stage. But I believe the other advantages should make up for it.
No, if it were that easy we’d have either an SSTO space plane reliably using scramjet engines, or a viable SABRE.
I’m more divided on whether you’d use hydrogen peroxide or liquid oxygen as the oxidizer. Storing and transferring liquid oxygen mid-flight would be much more of a pain, but going with peroxide means you probably also have to commit to using that as the oxidizer on the second stage (or have entirely separate planes to transfer it).
The original Black Horse proposal was hydrogen peroxide (for an SSTO!), but that makes little sense to me. We transfer LOx all the time. Doing from an aerial refuelling tanker would be a neat trick, but IMO having fully unmanned refuelling tankers will be a bigger task (but one that should have DoD interest. So hardly a single-purpose development for the vendor.)
Why does it need fully uncrewed refueling tankers? The cost of pilots isn’t going to be that huge compared to the overall cost of the launch.
Safety. It doesn’t need it, but it’s a basic precaution, whether it’s LOx or peroxide.
(And I don’t think it’ll lower costs at all. As I said, it’s a big cost to develop. The saving grace is that autonomous aerial refuelling is a potentially valuable military product. It also won’t lower operational costs, since there’ll be a remote monitoring pilot or at least a systems engineer crew.)
If memory serves, the idea of using hydrogen peroxide instead of liquid oxygen wasn’t about the propellent transfer. The Black Horse idea was all about reducing the dead (non-payload) mass of a single stage to orbit rocket plane. Virtually all the dry mass is wings, tanks, and mechanical structure (like landing gear.) So even a modest reduction in any of those elements can mean a massive increase in useful payload to orbit.
In the case of the oxidizer, hydrogen peroxide is 27% denser than oxygen at its boiling point. That alone cuts the mass of the fuel tank by almost 20%. The fact that you don’t need any insulation around the tank make for even greater savings. (Note that SpaceX has found that supercooling oxygen is worth it, and that only increases density by about 10%.)
I guess they are imagining filling a niche for medium-scale payloads? I have been wondering about this project, since it seems like Orbital/Pegasus never really hit a whole lot of business. They’ve been doing air-launches for 20 years. I assume this is designed for something bigger than the Pegasus.
That’s part of the problem, it was designed to carry a larger rocket but so far all attempts to come up with one have been a dead end. They were in discussions with SpaceX and Orbital, when that went nowhere they started plans to build their own launcher, but that project was cancelled after Paul Allen died.
Doesn’t it have a kind of Rube Goldberg feel to it?
It’s hard to believe that Rutan would design a “Spruce Goose” knowingly or unknowingly. I would certainly like to hear him comment on Stratolaunch now that it’s flown.
In the long run, it may not be any more useful. But at least it’s flown further and higher than the Spruce Goose. (Which was the previous record holder for largest wingspan aircraft to get off the ground.)
You probably are aware of debates about whether the Spruce Goose could have actually flown, with many believing that it could have never gotten out of ground effect. A few years ago a university in Wales tried it out in a flight simulator and found that it was definitely flyable. Although not entirely stable, they found that if you didn’t keep the wings level it could go into a spiral.
The next question for Stratolaunch is how long can it hold out without any customers. Hughes reportedly keep his plane in flying condition for many years, even having the engines fired up occasionally to keep them in running condition. But he was a billionaire who could afford such hobbies, Stratolaunch no longer has such a benefactor.
Stratolaunch can in theory launch three Pegasus at a time but I don’t see that happening, but maybe they will find some customers to launch a single Pegasus. I wonder what a single Pegasus launch will cost on Stratolaunch compared to the L-1011. Maybe not much difference. Now that Grumman owns Orbital I wouldn’t be surprised if they will gladly pass the torch to Stratolaunch, then they can retire the L-1011 but still have customers for Pegasus. Assuming there are any.
I agree about the idea of launching three Pegasus. That’s possibly useful for a small constellation, where all three spacecraft belong to the same customer. But that’s a really small niche market. For multiple customers, they’d see schedule delays because one of the three delivered late, conflicting requirements for inclination, local time of launch, etc.
That’s what Arianespace learned from dual launches with the Ariane 5. Multi-spacecraft launches do work for some applications (CubeSats, some technology demonstrations, etc.), but mostly when the spacecraft involved have generic interfaces and don’t really care about what orbit they get into, as long as it’s in orbit.
The problem is of course the lack of a launch vehicle that is designed to take advantage of the Stratolaunch lift capacity. Because weight is limiting a liquid propellant launch vehicle, i.e. something along the lines of the X-34, would provide higher performance than a solid fueled vehicle like the Pegasus. Unfortunately no development funding appears in sight.
Wow, cool.
I did not think they were this close.
I recall the pricing needs some work, but it’s a huge, beautiful bird.
Whether or not they ever get to drop & light a rocket from it, the aero-technology of this giant Siamese could help the development of very-heavy lift aircraft (more than the Antonov). I’ve read of dual-fuselage concepts* that may carry cargo in them or in a module between them. However, I’m real iffy on the utility of such a thing flying passengers, despite its mutated lineage from the 747 (which is still surviving nicely as a cargo hauler)
* – Personally, I’m more enamored with the idea of a mega-flying wing (where you’d load cargo throughout the whole span)!