IANARS but this plane should give the remaining stage(s) four advantages:
1. +230m/s orbital velocity [1]
2. +9km launch altitude [1]
3. can launch in more weather conditions
4. 1st stage can abort mid-launch without loss of payload.
Of these, the most important is the increase in launch altitude, because that means stage 2 launches in air of greatly decreased density, leading to the following efficiencies:
A. a vacuum-optimized nozzle can be used, increasing engine performance
B. less aerodynamic/drag energy losses
C. max Q should be lower, allowing full throttle usage, reducing mass needed for structural elements, and reducing vibration stresses on payload
The primary advantage of airplane launch is that you can fly to into a launch window for an orbital rendezvous. Otherwise you'd have to wait for the target's orbit to be just right w/respect to the launch site, or do a long orbit matching process.
This is very useful if say you want to very quickly and quietly launch something towards another satellite.
People are making comparisons with the Spruce Goose, but the Glomar Explorer may be a better analogy.
The largest downside is the rocket needs to be strong in more than one direction which adds a lot of weight. Sub Mach 1 first stage will save a little net weight but significantly less than you might diets assume.
Sure, but the strength it needs to have in the additional "hanging horizontal" orientation is only 1g -- much less than the many-g strength that all rockets need to have along their thrust axis. It adds some weight, but not enough to ruin the other benefits.
It would be potentially suitable for a larger payload akin to the X-37B. This would be handy if the intent isn't destruction, but rather interference or even retrieval. https://en.wikipedia.org/wiki/Boeing_X-37
Ha also by Howard Hughes... ah I was obsessed with this guy for a while... I realize it's a movie but The Aviator is a favorite... Katherine Hepburn/Howard Golf scene haha
edit: CIA and kursk submarine, was it the kursk doesn't sound like the right time
edit: nope Kursk is 141, K-129 is the one they wanted (Glomar Explorer)
I like the jet-rotor tip helicopter too
edit: haha yeah beast (photo of the helicopter with massive rotors spinning I think at 88rpms)
I haven't actually seen anyone mention it, but it shouldn't be much more risky than taking off fully-fueled. That said, landing with the rocket still on board might break some fuel-balancing assumptions.
That's the fuel the plane takes off with. I don't know how much this beast uses, but those six engines must be burning quite a lot of it. Also, the landing gears seem to be very robust.
The A340-600 has four engines, not six. But the point is still true with, say, a Boeing 787. Here are the figures for the 787-9: maximum takeoff weight: 560,000 lb; maximum landing weight: 425,000 lb [1]. In case of an emergency the pilot has to get rid of fuel before landing if the airliner is above maximum landing weight.
We don't know Roc's maximum landing weight but abort is possible if the maximum landing weight is more than weight of the whole craft plus its cargo minus the fuel. I assume it takes of with a lot of fuel because it has potentially 1.5x time fuel consumption of an old 747.
Fundamentally, landing speeds are lower than takeoff speeds. To travel at the same (low) speed and rate of descent with more weight means getting more lift at the same speed. That is done by increasing angle of attack or adding flaps. There is a limit to both.
Scaled Composites built it. It should work. Although Rutan has retired, the company goes on. It's interesting that they didn't connect the tails, like the old Lockheed P-38, but there's probably some good reason for that.
Launching a Pegasus XL has to be just a demo. That's normally launched by dropping it from an old Lockheed L-1011; it doesn't need this monster. They need something bigger to launch. There was a contract with Pegasus for a "Pegasus II", but that didn't work out. The "Dream Chaser" mini-shuttle is a possibility, if that ever gets built.
The 747 engines are probably used. There are lots of retired 747s around, many at the Mojave boneyard. Great aircraft, but a fuel hog by current standards.
>The 747 engines are probably used. There are lots of retired 747s around, many at the Mojave boneyard. Great aircraft, but a fuel hog by current standards.
>The crew’s flight deck is literally that of a 747.
>Allen bought two used jumbo jets formerly flown by United Airlines and cannibalized them for parts that account for about half the empty weight of the Roc.
>So although the shell of the cockpit and all the rest of the plane’s body is new — hand-built by Scaled Composites from carbon fiber composites — various key pieces and systems, including avionics, hydraulics and fuel subsystems, are salvaged 747 parts. BAE Systems was subcontracted to disassemble the 747 and install its systems on the Roc.
>The cockpit seats look old and used because they are. The seats as well as the controls the crew will manipulate and the windows they’ll look out of all came from the 747s.
>So did the plane’s six Pratt & Whitney engines, which are already refurbished, cleaned, wrapped and set aside in a corner, ready to hang on the airframe when it’s finished.
That's absolutely how I would've done it. Way cheaper to make a monster hybrid of two used 747s than to try to make a one-off custom airplane from scratch. Sure, it won't be as efficient at its job as if it were purpose-built, but you'd never get all of that R&D money back.
The market would have to be really large (like way larger than the current global launch market) to justify it though. The conjoined twin 747s are gonna be good enough for any payload that they can carry.
The Seattle Times article says that the Vulcan rocket will have a mass of 375 tons. (Probably US tons?) Assume it's got the same payload fraction as a Soyuz, about 2.5%, which means it can put 9.4 tons into orbit. (A Falcon 9 can put 22 metric tons into orbit)
According to some comment on stack exchange, the world collectively orbited 255 tons of stuff in 2007. Assuming every payload can be launched on a Vulcan rocket, (Which they can't) and assuming a generous turnaround time of one week, (Allen says it should be faster than that) then it would take only a single plane 27 weeks to satisfy the launch needs of the entire world. You could double the amount of stuff launched, and still only need one plane.
There's probably not going to be a lot of airframes to spread development costs across.
Either that, or we will launch a lot more stuff, 9 tons at a time.
The biggest thing going against it is it's not clear this scheme can drive the costs down enough to double or triple the launched mass per year. There is a limited number of things we can do in space. A significant part of the cost of any single probe is the launch.
If we can reduce launch costs enough (maybe making the booster reusable) and through building a standard probe with pluggable sensors, drive down the building costs, we could have dozens of probes going places we currently can't afford to go. We spend enormous effort in shaving off every single gram from anything that goes to space. If going to space gets cheaper, we can spend a lot less time shaving probes and more time probing.
This is being blown out of proportion. Vulcan's Stratolauncher is not the future of launch; if this thing ever manages to leave the ground (with a payload), I doubt it will host more than five-to-seven launches throughout its lifetime, and that's a generous estimate.
This vehicle is going to be incredibly expensive, compared to both other air launch options and dedicated smallsat options. Although this can change, the current plan is for Stratolaunch to use OATK's Pegasus-XL payload, which provides an indicator for cost. Pegasus-XL launches are incredibly expensive ($337.3K per kg). Now, this is due to a variety of reasons (the L-1011's incredibly high maintenance costs, OATK's expensive labor structure, low launch cadence). Vulcan will bear similar costs--the inefficient OATK overhead tied to Pegasus-XL, Stratolauncher is a one-of-a-kind aircraft and increasing maintenance costs (despite using 747 engines). Due to significant development delays, the company has yet to develop or execute a customer strategy. Depending on how much more PA pumps into it, the company will not be price competitive in the market.
For comparison, other small launchers charge ~$25K/kg-$41K/kg (e.g., Rocket Lab, Virgin, Arianespace), and most of these will be able to launch US payloads. Virgin's comparable airlauncher delivers slightly less mass (15 kg less), but is priced at ~$40K/kg. Virgin is already a leg up as it has engaged commercial, civil govt., and mil-govt. customers.
Lastly, it's worth noting that this vehicle still has significant work to be done--look at the wings in the picture.
you seem to know a lot, any chance we could talk about this topic, would love to hear more of your thoughts on the topic? I don't see an address to contact you.
This is awesome but a little bit scary. Interesting that they didn't physically connect the tail wings at all, I wonder what stresses and torques the main wing will endure under maneuvering or turbulence. I assume all the control surfaces are computer controlled to synchronize and minimize that, but from the perspective of an ignorant observer, looks a little fragile.
Clearly Allen and his team did the necessary engineering work, but I'm not sure the GlobalFlyer is a good example. It had a single mid-mounted engine, and had a gross, fully loaded weight of 22,000lbs. This thing has 70,000+ lbs of engines alone. The torque has to be absolutely colossal.
Again, I know that much smarter people did the math, but from the eye check this does not look like a tenable design.
I agree. There are so many forces at such incredible potential levels of torque that the center wing must be almost entirely full of structural elements... and those probably pass through to the outer wings.
Imagine differing oscillations of pitch or yaw from each fuselage happening at the same time... and at just the right/wrong frequency for the connecting structure.
I'm sure I'm just overly paranoid, but often we find out long after something is built that some "little possibility" was overlooked.
>Imagine differing oscillations of pitch or yaw from each fuselage happening at the same time... and at just the right/wrong frequency for the connecting structure.
Exactly. I expect they have real-time computer control of all control services that quickly adapt the relative attitude of both fuselages to prevent over-stressing the wing, but what about "rogue waves" of turbulence hitting each fuselage differently. What's the safety factor on both the adaptive controls and, as a backup, the structural integrity of the wing?
Almost every aircraft Burt Rutan has built is a breakthrough. Mostly asking questions that other designers weren't, like does a twin need to be symmetric.
twin tail booms have a long history.
e.g p38 with twin engines.
Burt Rutan's key realization was that the connected skinny horizontal tail doesn't really add much torsional stiffness and it's easy to obtain the required stiffness with the wing center box.
Scaled Composites has some secret CFRP processes of construction which non Americans are not allowed to know about under ITAR regulations, so i cannot tell you haha.
Well, proven at small scale. I'm sure the new bigger one will work fine too under most anticipated conditions, but I wonder what its structural safety factor is.
I'm sorry, I know it has been mentioned a billion times already, but can someone make a browser plugin that converts everything on a website to normal SI units? As a non-american I have no idea how big this aircaft is or how much it can lift - sure I can look up conversions(I have) but it would be awesome if there was an automatic website conversion option.
Agree, but just to throw it out there - nautical miles are actually an SI derived unit. It was originally defined as a minute (1/60 of a degree) of latitude, which doesn't convert exactly to km since it is not a constant measure. Although now it has been defined as the mean value.
I'd be surprised if a unit-converter plugin didn't exist already, but it should definitely preserve the original measures since the units do have contextual significance. e.g. nautical miles in navigation
I second the request. I had an unit conversion extension once, but it would slow the whole browser down to a crawl when it activated on a large and complex page, like Facebook or GMail. So I'm looking for something smarter / more efficient.
It seems like air launch doesn't buy you a whole lot, but it turns out that a small win on delta-v can result in a fairly big win on payload. This might seem counter-intuitive, but you have to remember that in orbital class rockets, payload is only 5% or so of total mass at take-off.
It's a small win on delta V, a small win on gravity losses, and a small win on Isp (due to atmospheric pressure). The delta V and Isp wins are exponentially related to stage mass fraction so they actually become very big wins.
It's a bit like having a very small first stage that gets you out of the thickest air, with a little speed and altitude.
The Falcon 9, by comparison, uses the first stage to get many times higher, but spends a huge amount of it's fuel during that first part of takeoff. For smaller launches, the plane-drop seems a much better idea.
Except Musk and Branson who've been doing this before it was the cool new thing- it feels the newcomers are just doing it for legacy. Having hospitals and colleges named after you isn't special enough anymore. Space is the new frontier for ego battles.
I'm confused as to what this thing can accomplish. It can probably fly very high, but I assume it can't fly very fast (relative to orbital speed), and I thought the overwhelming majority of the delta-V to get something into orbit was for forward momentum and that just launching from higher up wouldn't help much.
Clearly there's something I'm missing here (or they wouldn't have built it), can anyone fill me in?
>Atmospheric and gravity drag associated with launch typically adds 1.3–1.8 km/s to the launch vehicle delta-v required to reach normal LEO orbital velocity of around 7.8 km/s (28,080 km/h).
So it'll help. Also significant is the ability to base out of an airport and launch closer to the equator.
Right. Reducing the delta-v by a constant amount reduces the fuel requirements by a specific percentage. The correct thing to measure delta-v savings to isn't the launch requirements, but rocket exhaust speed. That is, if your rocket exhaust speed is 1 km/s, saving a km/s of delta-v will reduce your fuel requirements by a factor of 2.718
The majority of the horizontal delta-V is produced in the second stage. The job of the first stage is to a large extent just to lift the second stage out of the densest part of the atmosphere, to minimize drag for the second stage. A plane can do the same thing, and possibly more cheaply in certain scenarios (well, that has to be Allen's plan anyway).
Keep in mind that it's not just a matter of getting the second stage up high, but giving it enough vertical velocity so that it can reach orbital speed before it falls back into the atmosphere. If you could magically drop the second stage off at its separation altitude but with zero vertical speed, it wouldn't be able to reach orbit. An airplane won't provide much vertical speed, if any, so it's not really doing the same job. Still, just letting the rocket start up high is a big advantage.
Is it really that dramatic a difference? I suppose it must be, if they're building it, but it's strange that no one has done this before if it really helps.
It is a pretty big difference. In vacuum you want a huge nozzle to extract as much energy as possible from the engine's exhaust. In atmosphere, there's a limit to how large the nozzle can be before the exhaust flow separates from the sides and you get asymmetric thrust or worse. Since the nozzle can only be optimized for one particular altitude, that means that rockets which launch from sea level spend a good portion of their ascent with a smaller nozzle than they'd like to have. By launching from high altitude they can be significantly more efficient.
As others noted, this has been done before, but it's not too common. I think that's mainly because rockets need to be really, really big to get a decent-sized payload to orbit. Launching from an aircraft would let them be a bit smaller, but they still need to be huge. Pegasus (the one currently in use) is a small rocket and can only orbit a small payload. This plane is designed to carry about 500,000lbs of rocket. For comparison, a fully loaded Falcon 9 is about 1.2 million pounds, and that's only a medium-sized rocket when it comes to orbital launchers.
Amusing aside: in the 1970s, the US Air Force tested the feasibility of air-launching ICBMs. The test was carried out by loading a Minuteman ICBM into a C-5 Galaxy transport, flying it over the ocean, and then essentially shoving the missile out the back door and lighting it up. In this case, the advantage wasn't efficiency or payload, but rather the ability to move ICBMs around to make it more difficult to destroy them in a first strike. They decided it wasn't worth all the trouble in the end.
Virgin Galactic's White Knight is a very similar aircraft. It was used to launch SpaceshipOne which one the x prize. The article doesn't mention it but this new plane is the logical extension of the White Knight.
They have been doing it all along, just in reverse. Those heat shields glowing red hot and ablating away is pretty dramatic. That is pushing very thin air at (sub?) orbital delta-V
Not really that much less gravity, certainly not enough to notice, let alone have a difference to a rocket launch. Gravity varies as 1/R^2 where R in this case is distance from the earth, so it's the difference between that at ~6380 km and ~6400 km (for a 20 km altitude) which is not much - you have to be well into space, at over 1000 km up, before gravity drops to less than 7 km/s^2 for instance.
For anyone unclear on why launching a rocket from a plane isn't as great of an idea as it sounds like it would be, this is an excellent explanation: https://what-if.xkcd.com/58/
This is pretty cool but to be honest I don't expect it to be very advantageous.
The big advantage of airlaunch is the Isp improvement from launching at altitude. Since the rocket equation is exponential with respect to the ratio of delta V and Isp improving Isp even a little has big effects, and reducing delta V even a little does too.
But the big advantage of ordinary vertical launch rockets is that it's fairly straightforward to just make them bigger. The Saturn V was able to launch Skylab with a 6.6 meter diameter. And rockets could easily be scaled up to launch even larger diameter payloads. That's pretty difficult with something like Stratolaunch. Even with basically the largest aircraft ever made it still has a pretty small payload mass and fairing size.
One other cool thing about stratolaunch is that it has the ability to launch out of a lot more locations since it doesn't depend on a launch pad and tower. However, I suspect that's not going to be of huge importance.
I'd like to see what they can do with this technology but I suspect it'll be underwhelming.
Since the Orbital ATK Pegasus already exists and already has a customised plane it launches from, can we assume launching Pegasus is just phase 1 for this plane? If that's all it's going to do there would be no point. So presumably this has capabilities the current Pegasus launch plane doesn't have, and eventually we'll see it launching something like a Pegasus XL Plus? Do we have any indication how big a rocket this thing can carry?
Also, I wonder how this compares in capability to the XS-1 currently under development, which will be a vertically launched first stage rocket that can fly back for a runway landing.
Edit: just found the link below from last year on Space.com.
This is a very good idea. In rocketry, air is your enemy. At the speeds rockets move it causes enormous heat/mechanical stress on the rocket, drag energy losses, and it messes with the flow of matter out the back of the engine that provides your thrust.
With a jet engine, air is your friend, because it is the matter you spit out the back of the engine. And at the much smaller speeds of an airplane, mechanical and thermal stresses are much smaller.
Rockets require cryogenic fuels, workers and large launch complexes. In contrast, Everest is a mere 9km and the first stage of a rocket will take it to something along the lines of 100km at 2000m/s. It is much easier just to throw more fuel in the first stage (or move to the equator) than try and relocate around the relatively smooth surface of Earth.
Florida's air is humid and dense. You get lots of heat gain from that. The density itself matters. Condensation is a huge source of heat. Freezing is another huge source of heat. So you boil off cryogenics and maybe worse. We lost a space shuttle due to a chunk of ice hitting the wing. Falcon 9 rockets need unusually cold filler; if it warms then it expands and won't even fit in the rocket. It probably pours out and gets drained away, the alternative being a rupture.
The USA would do better launching from near Tuscon, Arizona. It's decently high up and dry, which helps keep the cryogenic content cold. We used to do this in fact, before the Mexican embassy complained about defective rockets crashing in Mexico. We chose to move to Florida instead of making a liability payment deal with Mexico.
I think it's mainly that the difficulty of building infrastructure up there, and hauling rockets and payloads up every time you launch, isn't worth the benefits. If you could magick a launch pad and rocket to the top of Mount Everest and launch it from there, you'd get a small but decent performance improvement.
I imagine it's a mix of mountainous terrain making it hard to transport launch vehicles to the top and most mountains aren't next to the sea (so the payload would have to travel over land, raising the stakes of an unplanned early failure).
Those are not mutually exclusive, you could build one on some plateau in the andes near the equator. But I guess the economics still don't work out for that.
> Dumb question: why don't they launch rockets from the tops of mountains?
Not a dumb question at all. It would actually give you some non-trivial advantage - but altitude matters considerably less than speed when trying to achieve orbit.
Starting a mile higher would allow you to avoid the densest parts of atmosphere, giving you less air resistance and helping with the Max Q, or maximum dynamic pressure (rockets sometimes need to reduce their engine output until they have cleared the denser atmospheric layers, or they would break up due to air resistance stresses).
This does unfortunately not outweigh the cost and complication of moving your launch site on top of a mountain. If you're really after every scrap of advantage, moving your launch site closer to the equator is way better than moving it up (until you already have it at the equator, that is).
The low pressure lets them get away with toroidal tanks, pressure fed booster engines, and a relatively large faring. Or at least that's the plan, they haven't launched anything close to orbital class yet.
The point isn't to get higher up, the point is to get out of the damn atmosphere so you can use wider bells, lower chamber pressure, and lighter weight tankage.
Because doing stuff from the tops of mountains is very difficult. The logistical complexity and cost of doing something from the top of a mountain swamp out the comparatively small advantages.
Also, the best places to launch from are near the equator where there is a large body of water Eastward. And there are very few mountains in such spots.
Altitude is much less important than velocity.* The extra altitude you'd get from launching from a top of a mountain would not be worth the expense of having to lug the rocket up there in the first place.
Every time you get some altitude, you also get a minuscule amount of velocity because the Earth is rotating. A space elevator gets you so much mind blowing altitude that you'll also get all the velocity you need.
The article doesn't mention SpaceX, I wonder what's the difference in energy and cost for launching (and landing) the relative stage 1s. Does anyone have an idea on that?
At separation, Falcon 9 first stage is doing about 2500 meters/second and is at about 70km altitude. The two connected 747s flying in formation don't get that fast (or that high, but horizontal velocity is much more important).
The Falcon 9 first stage releases stage 2 at around 6-10 times the height and 10x the speed.
That said, remember that the difficulty of elevating yourself above a given height is much worse the lower you are. Using a plane-drop means skipping the very worst parts of the launch. The air is so much thinner.
There's other advantages though. Launch windows get much easier, as the plane can fly in any direction, and stay at a given heading a bit longer.
I feel overcome by the Dianne Kruger effect, to an extent I don't remember feeling any time recently. I'm becoming more and more interested in news about rocketry (due to SpaceX of course) but I'm still a full on space-pleb. I see something like this and my intuition screams "Woah! Of course! Why don't other rocket companies do this? What's wrong with them?!"
But the rational part of my brain kicks in and slaps me down for being so arrogant. It feels humbling to be reminded how stupid one can be.
The traditional rocket companies have no interest in reducing launch costs. Now they're looking like fools for letting SpaceX patent critical tech they could have developed 20 years ago.
SpaceX doesn't patent anything[0]. Tesla does file for patents, but has basically made all their patents free to use for all[1]. Seems like Musk is just not a fan of the patent regime.
Yeah, but if they'd gotten the patents then they could profit off them (i.e. rent-seeking). Elon Musk getting the patents removes those revenue streams.
I don't know. Honestly, I feel hit by D-K myself here, because until today I was convinced that launching a rocket from an airplane is a huge expense compared to the very small benefit it can bring. But this thread made me seriously reevaluate this assumption.
The worst thing is, I can't even remember where I have learned that plane-launched rockets make little sense.
The Dunning-Kruger effect: The idea that people of low skill or knowledge about something don't know how much they don't know and thus think they're much better at it then they actually are.
They could always use a chase car like they do with the U-2 Dragon Lady because of its ridiculous wing span. This wouldn't help you avoid watching it, though.
youtu.be/W2tnCDBkIoI
That pilot is an artist. Such a narrow gear stance on such a huge wingspan and he lands it perfectly. Wonder how many times it went wrong versus how many times it worked.
There's only one flight deck and it in the right-hand fuselage. I was at a recent friends and family day at Scaled Composites and was able to see and touch this amazing plane.
Both fuselages seem to have identical windows. Is that just so they can use the same tooling for both, or is there something else in the left fuselage? Passenger/observer seating, maybe?
The fuselages are used 747s that were repurposed. They have identical windows because of the design of a typical 747, not anything purpose-specific to this mission.
It's literally just two cannibalized used 747s attached together, with a minimum number of necessary modifications made (which doesn't include changing the cockpits or forward sections of fuselage).
This might be a dumb question, but it looks like there are two cockpits on this plane. I imagine the plane is drive by wire, so it doesn't matter where you are on the plane. Why do they have two?
Extending my question further, why does this plane have a cockpit at all? Isn't this something you could remotely pilot, especially to mitigate the potential risk of being at 30k feet with thousands of kilos of RP-1 or similar?
They just bought two used 747s and stuck them together. Way more work to remove the cockpits than just leave them intact on their individual airframes.
Hell, for all we know, this could be remotely piloted.
The really interesting question - does the modest increase in initial velocity and altitude with a boost out of the lower atmosphere make it practical to build a Single Stage To Orbit rocket? If they can, then it's an impressive achievement. If not, then it doesn't really seem worth the trouble.
The altitude boost is certainly not worth the work. The velocity from the plane is small but since fuel requirements go up exponentially with necessary velocity every bit helps.
More important than that is that the rocket doesn't have to punch through as dense of an atmosphere when getting up to speed. That means you don't have to reinforce the rocket as much since it's maximum dynamic pressure (maxQ) is lower giving you a better mass ratio and it means that you're not losing as much delta-v to air resistance but that's only another 100 m/s or so for a decently sized rocket like the one being launched here.
But more importantly you can design your engines so that they don't have to work at higher atmospheric pressures.
A Merlin engine with a bell designed for taking off from sea level has a trust at sea level of 845 kN but a thrust in Vacuum of 914 kN all while burning the same amount of fuel. And a Merlin with a nozzle sized for vacuum use can go up to 934 kN when firing in vacuum, again for the same fuel flow rate.
While having fewer stages sounds simpler and easier, that's not necessarily a major cost. Having a big and powerful 1st stage is a major cost so this should allow either a cheaper 1st stage or a heavier payload.
The article claims that it hold's the record for largest wingspan, which is 385ft. It then goes on to say that this blows away the previous record of 65ft. I don't know what the largest wingspan is, but I thought B-52s had a wingspan of 185ft? Error in the article?
Really interesting thing is the flat walls on the fuselages. They were done that way for ease of construction, and are not pressurized containers therefore don't suffer from stress singularities at the corners.
I wonder if they considered a half-loop launch, toss bombing style. That way they could dump the wing, perhaps at a price of higher strength requirements.
I'm confused by this. I don't know if Paul Allen is a Huey Lewis fan. What I do know is that he's a big Jimi Hendrix fan.
Allen basically built a museum to (mostly) Hendrix. It's since been re-purposed somewhat, and Wikipedia doesn't have much of the history. But originally the museum was mostly Hendrix. Here are links to a few early articles that make it clearer:
1. +230m/s orbital velocity [1]
2. +9km launch altitude [1]
3. can launch in more weather conditions
4. 1st stage can abort mid-launch without loss of payload.
Of these, the most important is the increase in launch altitude, because that means stage 2 launches in air of greatly decreased density, leading to the following efficiencies:
A. a vacuum-optimized nozzle can be used, increasing engine performance
B. less aerodynamic/drag energy losses
C. max Q should be lower, allowing full throttle usage, reducing mass needed for structural elements, and reducing vibration stresses on payload
[1] http://dailym.ai/2soH6FD
P.S. Thank you KSP for teaching me this stuff! :D
Bonus: video of pegasus air launched rocket: https://www.youtube.com/watch?v=jz_5hnIw2jc