In California, giant Stratolaunch jet flies for first time

https://techxplore.com/news/2019-04-california-giant-stratolaunch-jet-flies.html

by lelf • 7 years ago

165 131 7 years ago

tyingq3• 7 years ago

I'm curious what the emergency landing options are for this thing. It looks like there would be limited places it could land with that wingspan and landing gear spread.

Edit: Curious, not critical. Maybe it can land in a lot of places, just reacting to the size.

degobah• 7 years ago

Since its purpose is to launch rockets, I assume it lands where it takes off, and might never stray far away.

tyingq3• 7 years ago

That's the sort of thing I'm interested in. Like, for example...how far away are you once you get this huge thing high enough to launch.

I'm not trying to criticize it, I'm just curious how dangerous a typical mission will be.

inamberclad2• 7 years ago

They're going to move it all over the world (or at least, over the latitude range) in order to get into the most optimal launch position.

base6982• 7 years ago

Was there for this flight yesterday, and with someone who worked on the project.

Most runways are too narrow for both the wingspan and wheel span. It is quite limited in areas it can land and take off.

bronco21016• 7 years ago

With an option to jettison the payload I would imagine it can land relatively short. The majority of stopping distance is related to having enough rubber on pavement and keeping brakes cool enough. Stopping energy required changes dramatically as weight is reduced as it’s less energy required to stop and a slower touchdown speed.

I’m not sure how the dimensions of the aircraft affect its ability to use other airports though and exiting a shorter runway after repair can also present a major challenge.

salawat• 7 years ago

Me too. I have serious questions in regards to maximum landing weight, will or won't the payload have to be jettisoned, and whether there will be propellant restrictions.

Imagine an emergency scenario where a high payload of hydrazine/NTO/UDMH/MMH has to be dumped at low altitude to recover the plane "safely".

With a traditional vehicle you at least will never have an incentive to take your launch vehicle anywhere where down range includes a low altitude intersect with a population center.

This on the other hand... Oof. This brings an entirely new dimension to Range Safety. I can see the lesson having to be relearned the hard way if we aren't careful. Not saying it isn't worth it, but man, those postmortem would not be fun.

Would be a hell of a thing to see go off without a hitch though.

yonkshi• 7 years ago

This is such a cool concept, I really wish these guys would succeed. Though last time I heard they gave up developing their own rocket (as a second stage to space). Anyone who's in the loop, does Stratolaunch currently have any potential rockets lined up?

exochrono• 7 years ago

Article states that they're going to use Northrop Grumman's Pegasus XL.

kryptiskt• 7 years ago

They have been contracted to launch Pegasus XL rockets.

not_a_terrorist2• 7 years ago

They abandonned all development activity of their own rockets, shortly after Allen's death.

shereadsthenews• 7 years ago

The concept is indeed good, which is why people have been air-launching Pegasus rockets for decades. I’m actually not sure what the new thing is with this aircraft. Just that it can launch three rockets per flight?

eismcc3• 7 years ago

How did they prevent the two fuselages from torquing the wing apart? Seems like keeping both “sub-planes” from ripping the middle wing apart would be challenging.

hliyan• 7 years ago

This was my first thought as well. But then I remembered that modern twin-engine commercial jets can fly with one engine down in an emergency. Not an aircraft engineer, but I suspect the structure is strong enough to handle normal torques during turning.

PopePompus• 7 years ago

Heavy turbulence might be exciting, though.

base6982• 7 years ago

The complications with flying a twin engine during a single engine failure have more to do with flight characteristics than structural.

Ie, does the rudder have enough authority to stop a spin or does the engine provide enough thrust to maintain level flight.

CarVac• 7 years ago

Active control systems, presumably.

vpribish• 7 years ago

the center wing structure is strong

rootusrootus• 7 years ago

One of my favorite airplane-related videos is one from the old days during 747 development, where they bent the wing until it broke. Turns out it is extremely strong.

Note: I did a search for that old video and came up with a more recent 777 video instead. Still interesting to see how far they have to bend it before it will break. https://www.youtube.com/watch?v=WRf395ioJRY

danaliv• 7 years ago

I’m not sure I follow. Unless they did something bananas with the design (which I admit is entirely possible given who designed it), the lift from the wings is transmitted to the rest of the aircraft through a spanwise spar(s). The fuselages hang off of the spar. What forces would rip that apart?

eismcc3• 7 years ago

I would expect the forces go both ways. The fuselages have their own forces on the wings and since they are essentially sub-planes I’d imagine the forces could both strong and un coordinated - eg one trying to go one way while the other tries to go the other way. I’m sure under normal circumstances, computers keep everything aligned, but wondering about stressful situations.

sfifs2• 7 years ago

I'm puzzled by what added benefit being 10km up in the air and going at 300-400kmph gives over regular rocket launches since speed and altitude are a very small fraction of what's required to orbit.

The article says it will be less affected by weather windows but (1) would a normal LEO commercial launch be so highly time bound to find this of value? (2) if weather was bad for a rocket launch on surface, would you fly a heavily laden giant plane into it?

Leads me to wonder if the real customers of this is the military who do value very short turnaround launches.

alex_anglin• 7 years ago

It's probably a more enjoyable launch experience for passengers.

mikeash4• 7 years ago

The amount of rocket you need to reach a given speed is exponential with respect to that speed: https://en.m.wikipedia.org/wiki/Tsiolkovsky_rocket_equation

Shaving off a small amount of speed can have a large payoff. This is why most launch sites are near(ish) the equator.

simonh3• 7 years ago

That's not actually a very big effect compared to mid latitudes. The main reason to launch near the equator is because a lot of payloads go into equatorial orbits and plane changes are expensive.

From the equator you can go into any orbit equally easily (because you just wait for the earth to rotate until you’re on the desired orbital plane), but the only way to go into an equatorial orbit without a plane change is from the equator.

wl• 7 years ago

Rockets waste a lot of fuel punching through the atmosphere at lower altitudes.

khuey• 7 years ago

You get to skip the densest part of the atmosphere, and you get to use an air-breathing jet engine (instead of a rocket engine that carries its own oxidizer) to get up there.

knowaveragejoe• 7 years ago

I thought speed was one of the most crucial elements of achieving orbit. Granted the extra 3-400kmph you mention is basically negligible for that.

dgudkov• 7 years ago

From Wikipedia [1]:

"40,000 feet (12,000 m) is only about 4% of a low earth orbital altitude, and the subsonic aircraft reaches only about 3% of orbital velocity, yet by delivering the launch vehicle to this speed and altitude, the reusable aircraft replaces a costly first-stage booster."

[1] https://en.wikipedia.org/wiki/Pegasus_(rocket)

simonh3• 7 years ago

It could replace an extremely weak, low capability first stage. In comparison the F9 first stage throws the second stage up to an altitude of 65km at 2km/s, or 26% of orbital velocity. So this air launch approach only achieves about one fifth as much as an F9 first stage.

jpindar• 7 years ago

Planes can fly above (some) bad weather.

ilaksh• 7 years ago

One of the biggest challenges for acheiving orbit is the dense atmosphere near the ground. Takes much much more fuel to go the same speed than it does when higher. It is dramatically less dense and then goes away as you get higher.

Gravityloss5• 7 years ago

A rocket engine nozzle produces thrust only for the part where the pressure is greater than atmospheric pressure. (Makes sense, right?)

Launching at lower ambient pressure (greater altitude) makes the engine work better. It gives more thrust for the same fuel flow (higher ISP). You can also make the nozzle bigger, getting even more thrust and ISP.

This is a significant advantage AFAIK. Also, AFAIK, if your rocket engine is low-tech, you will likely have low chamber pressure, meaning the nozzle is small. The beneficial effect is proportionally larger then.

ThenAsNow12• 7 years ago

A rocket engine nozzle produces thrust only for the part where the pressure is greater than atmospheric pressure.

A rocket engine produces thrust when its chamber pressure exceeds ambient pressure, which is trivially true for any rocket engine. The flow coming out of the nozzle can have lower pressure at the exit plane than ambient and still make plenty of thrust. This is called "overexpanded" flow, and is the regime that produces shock diamonds in rocket and afterburning jet engine plumes at low altitudes.

Reduced to quasi-1D form, thrust is given by:

  T = mdot*(delta V) + (p_e - p_a)*A_e

Where mdot is mass flow coming from the nozzle, delta V is change of velocity of that efflux with respect to the vehicle reference frame (in a rocket, it is just exit velocity, in an airbreathing system, you have to take into account the incoming momentum), p_e is static pressure at the exit plane, p_a is ambient pressure, and A_e is the area of the exit plane.

In an overexpanded scenario, p_e < p_a , but the majority of thrust is coming from the momentum change term, which is the one containing mdot.

Nozzle performance is optimal when pressure at the exit plane matches the ambient pressure. This is when the exhaust velocity is maximized and the pressure thrust term vanishes. It can be shown (undergraduate aeropropulsion course homework) that you get more thrust from ideal expansion than from pressure thrust (underexpanded regime).

The point you are trying to make is that an air-launched system allows the rocket to start with a higher area ratio than if it were ground-launched. In the ground-launched scenario, a large nozzle area ratio will suffer overexpansion losses and how large you can go will also be limited by structural implications from the internal nozzle separation that will occur with gross overexpansion.

While this is all true, the reality is that the additional rocket performance you can get from a larger nozzle area ratio is not that compelling in light of building, operating, and maintaining an entire air-launch aircraft platform. You're better off putting that money into incrementally larger propellant tanks due to the lower mission-averaged Isp associated with the ground-launched vehicle.

jcims3• 7 years ago

Pegasus launches occur at closer to 900km/h.

It takes a Falcon 9 about a minute and roughly 150,000kg of propellant to get to 10km altitude, at which point it's going to be travelling closer to 1200km/h. If you can move that part of the mission to a carrier, you can substantially reduce the size and fuel capacity of the stage or maybe even entirely skip a staging operation (edit: not skip, carrier becomes first stage, thanks DenisM!).

Back to the Falcon 9 at mid-first stage, from 10km to stage separation you're running on motors that had to be built to operate at sea level. This means that they are 'underexpanded' for operating at 10km altitude and are therefore not as efficient as they could be. If you know your engines will always start off at 10km, you can build bigger expansion nozzles and improve the overall efficiency.

DenisM2• 7 years ago

You’re not skipping staging, your carrier is your (reuseable) first stage.

ccozan2• 7 years ago

I wonder, why isn't possible an engine that can use air ( for oxigen ) then later use/switch another oxidant, when the air oxigen level drops?

edit: just found this https://en.wikipedia.org/wiki/SABRE_(rocket_engine). Seems that there is a solution.

ThenAsNow12• 7 years ago

The real answer, which is somewhat saddening given the immense amount of effort put into Stratolaunch, is that air-launch, when all is accounted for, has negligible benefits from a performance perspective when you are deploying expendable stages.

AIAA paper 2004-872 "Air Launching Earth-to-Orbit Vehicles: Delta V gains from Launch Conditions and Vehicle Aerodynamics" gives a decent and readable treatment of this scenario.

The advantages air-launch inarguably has are letting you pick the location and azimuth at which the high-performance launch vehicle stage begins its run as opposed to being constrained by your launch site and populations under the launch vehicle trajectory. If those are your most important metrics, air-launch may "win". If you are releasing a reusable stage from the air-launch platform, that could also be a unique value proposition as you could do a downrange landing of the stage (reserve no propellants for boost-back) to any desired site. SpaceX accomplishes this with a landing barge for their system.

By virtually any other measures, air launch from a subsonic platform does not make engineering sense over a ground-launched system. DARPA's ALASA program explored air-launch from an F-15, and was struggling to get ~100 lbs. to orbit. Even if you use a "big" supersonic platform like a B-1, by the time you take into account the volume associated with a launch vehicle, you quickly realize that at absolute best, you are talking a low supersonic staging Mach number. It would require a new high-thrust aircraft platform if you wanted a supersonic air-drop. And regardless of staging speed, if the flight path angle ("gamma") at release is too low, the deltaV advantage significantly diminishes (I recall the cited paper above shows this).

Consider the following issues:

* The Strato carrier aircraft is (unless even more megadollars are spent) is one-of-a-kind. If anything happens to it, no paying customer will be able to launch.

* Any stage stack that is launched from the carrier aircraft has to be rated for manned safety. This is its own expensive undertaking that autonomous ground-launched systems do not have to contend with. This is in addition to any public safety issues associated with population overflight (to be fair, air-launch may be able to diminish those concerns, but compliance with the former is much more onerous than the latter).

* The carrier aircraft presents very significant structural and volumetric constraints to the launch vehicle. The rumored lift capability is in the neighborhood of 500 klbs. For something like a hydrogen-fueled launch stack, you can do some rough sizing and realize that geometry will constrain you faster than mass. Don't forget to include flexible body effects, as that will be very significant with this airframe.

There is definitely an engineering accomplishment in the flight of this aircraft. However, unless Strato does something that they can uniquely do, or they lose money hand-over-fist on each launch (Pegasus is very expensive already, and I think SpaceNews reported that Strato shut down their own internal launch vehicle development efforts), they cannot be commercially-competitive. That launch point and azimuth control has to be critical, or air-drop just doesn't make sense.

As much as Burt Rutan has to be admired for his ability to think creatively, Stratolaunch was an insufficiently vetted architecture sold to an enthusiast billionaire who was probably delighted with the result of their SpaceShip One collaboration. And yet you see that in SS1, Scaled basically designed a one-off experimental vehicle architecture that fared very poorly when it was scaled into what was intended to be a sustainably-operated commercial system. Strato is another example of this kind of mindset.

tropo• 7 years ago

Launches are very often cancelled due to weather, and launch windows are usually limited due to the physical location of the launch pad.

Stratolaunch solves both those problems.

curtis2• 7 years ago

There's three advantages you get from air launch. One is that your first stage rocket engines can use nozzles that are optimized for vacuum or close to vacuum resulting in better performance through the entire first stage burn. (The RS-68 used on the Delta-IV, for example, has a sea-level ISP of 365s and a vacuum ISP of 420s, which is a pretty substantial difference.[1])

The second is that a launch aircraft at 30,000 or 40,000 feet is providing not just forward velocity but has also allowed the first stage to avoid some gravity loss (to accelerate at 1G at launch you need 2Gs of thrust). It's also allowed the first stage to side-step a major portion of the aerodynamic resistance.

Finally, an air-launched system is not as strongly constrained to specific launch windows. When targeting a specific orbit, you don't have to wait for a specific launch window at the primary launch site (the airfield), you can simply wait until one is relatively nearby and fly to it. This might be a big operational advantage even when it's not a big performance advantage since you can launch your aircraft when you have decent weather over the airfield and the fly to a more ideal spot to launch the rocket. If the radius of the loaded launch airplane is wide enough, this could be a very big advantage.

Even if you add all of these effects up, it's still a pretty small fraction of the 9,000 m/s of delta-v or so that you need to reach orbit. But keep in mind that rockets only deliver a few percent of their launch mass to orbit. A relatively small reduction in the delta-v needed to reach orbit might result in big gains in payload into orbit. In extreme cases, maybe it could double it.

The biggest disadvantage of air launch is that you are seriously constrained in the maximum size of the rocket. The Stratolaunch aircraft can carry about 230 metric tons of payload, whereas a Falcon Heavy weighs in at something like 1,400 metric tons[2].

[1] http://www.astronautix.com/r/rs-68.html

[2] https://en.wikipedia.org/wiki/Falcon_Heavy

ethagknight• 7 years ago

Comparing stratolauncher payload to Falcon Heavy’s gross weight at takeoff is not really a helpful comparison. FH has a 60 metric tons to LEO max payload, roughly 5% of its total weight. I’m sure someone has done the calcs on the theoretical potential of the Stratolauncher, but it looks like a Pegasus can get 1000 lbs to LEO at a total weight of 40,000 lbs, so same 5% ratio. Seems to be in the same ballpark, and Stratolauncher (would?) use a fraction of the resources.

newnewpdro2• 7 years ago

I think it's just a matter of needing less fuel, which saves weight, further lowering fuel requirements. So it just makes launches cost less.

Using the rocket to get off the launchpad is wasteful. It's basically the wrong tool for the first stage but the simplicity of the approach is nice.

dweekly• 7 years ago

Scott Manley walks through why this isn't helpful yet since they have nothing useful to launch in delightful detail (complete with Kerbal simulations): https://youtu.be/yw84qJIGZeo

jessriedel• 7 years ago

That's not a good summary. Yes, the plane is not very valuable in the short term (~4 years) because the only viable existing air-launched rocket is the pegasus, which is old and can be more cheaply launched on the smaller planes for which it was designed. But as Manley emphasizes, the whole stratolaunch plan is predicated on developing a new air-launched rocket, and we just don't know what the specs on that will be.

ThenAsNow12• 7 years ago

the whole stratolaunch plan is predicated on developing a new air-launched rocket, and we just don't know what the specs on that will be

Neither will Stratolaunch, any time soon:

https://spacenews.com/stratolaunch-abandons-launch-vehicle-p...

craftyguy4• 7 years ago

What an embarrassingly (for him) short sighted 'walk through'. Just having more capability to perform ariel launches will encourage companies to make vehicles. The likely reason nothing exists today is because there really aren't any options today..

vkou3• 7 years ago

Who is going to pay for companies to develop these vehicles?

Developing and certifying a new rocket is an incredibly expensive affair. What are the cost savings this promises, compared to SpaceX?

adventured• 7 years ago

I know there's a lot of skepticism about whether the plane has any likely long-term use and whether it can be successful commercially at all. I find it spellbinding to watch it fly. I'm so glad Paul Allen funded its creation.

theseadroid• 7 years ago

I wonder why this type of specific purpose airplane needs human in the cockpit? Why can't it be remote controlled?

craftyguy4• 7 years ago

I suspect this huge, complex aircraft with it's very expensive, highly explosive cargo isn't as straight forward as flying a drone.

klhugo• 7 years ago

Does anyone have a cost comparison between different launch systems?

ourmandave• 7 years ago

If they're launching Pegasus XLs I wonder if they're on Northup Grumman's future acquisitions radar.

Their competition, Virgin Orbit has it's own subsidiary Vox Space that makes the launch vehicle.

tyingq3• 7 years ago

It looks like intended rocket has changed a few times:

https://en.wikipedia.org/wiki/Stratolaunch_Systems#Launch_ro...

But did eventually settle to the Pegasus XL: https://spacenews.com/stratolaunch-abandons-launch-vehicle-p...

avmich2• 7 years ago

There are several advantages for airplanes as first stages. Less air drag on the higher altitude and more efficient engines, as they are optimized for smaller external air pressure. The speed of aircraft adds to the speed of the rocket. Another plus is that with aircraft you don't need to build a launch pad, the rocket is just released in mid-air. Yet another benefit is that aircraft can fly to a more preferable point for the launch - for example, the point where it is convenient to drop the first stage of the rocket, or the point closer to the equator so the satellite won't need to spend as much fuel to change the orbital plane. The airplane first stage can potentially fly to very different launch point, in many different countries, which can make logistics simpler. Those advantages all add up economically.

duxup2• 7 years ago

I hadn't thought of the fixed launch pad situation.

Do they expend a lot of energy / cost moving a satellite from where a fixed launch pad might easily place the satellite vs it's proffered orbit?

myself2482• 7 years ago

Mostly they have to pick their launch site so the flight path, headed into the right orbital plane, doesn't pass over populated areas. It would be rude to drop boosters and stages on people. https://history.nasa.gov/EP-165/p25.htm

inamberclad2• 7 years ago

I asked the engineers a while back, and they said the biggest gain was in potential energy that the rocket no longer has to make up.

ThenAsNow12• 7 years ago

I've a detailed comment that addresses several of the points you're making at https://news.ycombinator.com/item?id=19660163

Is it true, strictly speaking, that you may use less propellant in the expendable stage due to air-drop? Sure. Although to be clear when talking about engine efficiency, it's really about being able to run a larger area ratio nozzle and getting a higher mission-averaged Isp. But ultimately when you consider all the "puts and takes" in launch system economics, those considerations are small potatoes (price out bulk LO2, and your choice of fuel). People (even university professors make this mistake) get so focused on minimizing propellant use that they fail to realize that complexity and dry weight are orders of magnitude more important.

The only serious advantages to air-launch are the logistical ones you noted. Also note that for U.S.-based systems, the idea that you will be able to fly down to equatorial latitudes requires you have the range to carry the laden launch system (and top-off to contend with LOX boil-off) pretty far. Strato certainly doesn't have these kinds of legs. Virgin will probably be able to get more out of their system, but it's not going to scale significantly higher.

nbadg2• 7 years ago

I agree that for traditional launch systems it doesn't make that much sense -- particularly in light of the recent development of reusable (or at least, partially reusable) rockets.

That being said, I think the math changes somewhat for smaller launchers. The smaller the rocket, the worse the losses to the atmosphere get, and the more advantageous it is to escape atmospheric resistance in the soupy low atmosphere. So I think where air-launch systems could really shine, is by enabling low-cost launch of very small payloads.

I am, however, not entirely convinced that a sufficient market for those kinds of dedicated launch services will emerge (as opposed to hitching a ride in spare fairing space of a separate launch). I could see this going either way; as much as I'd like to see easier space access for eg. university-funded nanosats, I'm not sure the timing will be right for something like Stratolaunch, because the new private aerospace (SpaceX, Blue Origin, etc) is focused so intensely on pushing down the cost of larger-scale rocketry, to a point where that same market would be better served by bulk launches using some kind of standardized dispenser.

Retric2• 7 years ago

Fuel is almost irrelevant from a money perspective. However, two rockets both cost the same to build and one needs less fuel to orbit that directly translates into more payload to orbit. It’s a question of mass not money.

Alternatively, you can spend that budget on something else like a ‘single stage’ to orbit system which more directly lowers costs. This is more useful for tiny cargo like an anti satilite weapon system where getting even a few pounds into the right orbit works.

As to long term costs, having already built the aircraft that becomes a sunk cost. It might have been a poor choice, but it represents actually value before you can get satilite stock orbit. Which then allows a company to raise more money on better terms.

afterburner• 7 years ago

Another plus is that with aircraft you don't need to build a launch pad

That one doesn't seem like an advantage, a launch pad is much cheaper than the world's largest really odd-looking and unique airplane.

avmich2• 7 years ago

Yes, but for a launcher you may want to have several launchpads for different kinds of missions, say GEO and SSO launches. Strato can serve them all. And if something happens to launch pad after rocket ignition, you have to rebuild the pad, while with Strato if you released the rocket and flew away, rocket problems don't affect the plane.

razster• 7 years ago

They’re going to need to tighten up the landing. After touch down and braking, it was swing left and right. Seems kinda worrying

hawski• 7 years ago

How does a rocket deal with those side stresses while it's attached to the airplane? AFAIK rockets generally do not deal well with sideways forces, because a rocket is a giant can.

mirimir2• 7 years ago

It's clear that solid-fuel rockets are OK with sideways forces, because they're transported that way. The can may be weak (except re internal pressure, obviously) but the fuel/oxidizer is ~like rubbery plastic.

It's also clear that liquid-fuel rockets are OK with sideways forces, before they're loaded with fuel and oxidizer. Because they're so light. But once they've been loaded, they're very fragile re sideways forces.

I've watched lots of rocket-failure video. A ~common scenario is loss of attitude control, for whatever reason, followed by crumpling and fireball.

So I don't see how this thing could launch liquid-fuel rockets. Unless it could fly straight up, for long enough to transfer fuel and oxidizer. That'd be insane.

gaze• 7 years ago

Isn't it amazing how you can tell a Burt Rutan design just by looking at it?

netman21• 7 years ago

Is anyone looking at catapults yet? Seems that would be a great technology to pour billions into. Maybe that is why Musk is proposing Hyperloop? Get the engineering done for high speed trains, then scale it up. Way up.

The Startram project estimated $60 billion for a catapult that could launch people. http://www.startram.com/

jccalhoun• 7 years ago

I know people have talked about this for a long time. There must be a logistical reason for it.

DenisM2• 7 years ago

How much acceleration can you endure? 3g is typical for a rocket launch, 9g is almost deadly. Accelerating to 6000mps at 3g will require 6000^2/(23g) = 600 kilometers of track, and it will take 200 seconds. That's a huge track, which has to be exactly linear or the payload will destroy it.

Then there is also the fact that the payload will be exiting the catapult at the sea-level, thus facing the full atmosphere at 6000mps. Which is to say the payload will be instantly incinerated unless some kind of magic is invented akin to supercavitation. By contrast rockets do not even reach supersonic 300mps until 10k altitude, thus never encounter this sort of problem. Maybe you could build this 600km track thing in the Himalaya, but that much and that high in the mountains isn't going to be cheap.

You can tell I though a lot about the same thing that you did. :)

bufferoverflow• 7 years ago

As soon as we figure out how to build 100+ km tall structures.

rdiddly2• 7 years ago

Kind of a threadbare article. Not a word on why dual fuselages are desirable? Why it needs to have the world's longest wingspan? Like I'm supposed to just know all that from my aeronautics background? What if I flunked that course?

asteli• 7 years ago

You need a large space open to attach the rocket to, and it has to be at the center of lift. You can't have one fuselage and put the rocket to the side, because then the balance would change drastically when you add the rocket, and you can't put the rocket under/in the fuselage because it's very large.

rdiddly2• 7 years ago

Thanks... it's the simple things!

blunte• 7 years ago

I hope that center wrong is unbelievably strong to handle the tortional forces that two separate horizontal stabilizers on lengthy lever arms might exhibit in acute turbulence.

godson_drafty• 7 years ago

That flimsy tail design bothered me as well. Even if the center wing and wing roots are incredibly strong, there's little reason to place them under stresses that could be alleviated with a single-stabilizer tail design, as other commenters have pointed out. The fact that they did not do this suggests this aircraft is designed to launch millions in contributions into the designers' pockets, and not so much rockets into space.

lstodd• 7 years ago

I wonder how fast it would disintegrate in a case of asymmetric stabilizer runoff.

orbital-decay• 7 years ago

I guess this thing has a pretty sophisticated control system to keep it stable, similar to modern combat aircraft. I also wonder if they have any fuel dumping procedures for an aborted launch; landing with a non-empty launch vehicle still on board seems quite scary.

perilunar• 7 years ago

Why didn't they just mount the tailplanes higher and join them? (e.g. like the OV-10 Bronco tail)

dredmorbius2• 7 years ago

I get the distinct impression Stratolaunch wasn't happy with the post-landing roll:

https://youtube.com/watch?v=ZBj3FCdYS80

(At 3m20s.)

jdsully• 7 years ago

I think its just fighting a bit of crosswind.

ridgeguy• 7 years ago

I agree.

It was crabbed a few degrees to its left while aligned with the runway (3:24 - 3:33 in GP's video). That would indicate crosswind from the aircraft's left.

dredmorbius2• 7 years ago

The edit cut away immediately, to onlooker shots. It's an interesting flight phase, and pretty clearly one Stratolaunch did not care to feature.

Several other onlookers did catch the roll, and the aircraft slewed markedly, with several cameramen commenting on this.

m3at• 7 years ago

As cool as it looks, this airplane seems promised to go the way of the Hercules H4: fly once then stay in a museum forever. This recent podcast from mainenginecutoff speaks about Stratolaunch [1]

[1] https://mainenginecutoff.com/podcast/108

bacon_waffle2• 7 years ago

I hope they take inspiration from these folks and do a simultaneous takeoff with a smaller plane, in opposite directions:

https://youtu.be/R5P70XtI4zQ?t=39

In California, giant Stratolaunch jet flies for first time

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