In California, giant Stratolaunch jet flies for first time
techxplore.com
techxplore.com
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?
Will likely no longer be an issue once the new chinese spaceport in the south fully comes online.
The uncontrolled versions, less entertaining.
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.
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.
Do you have any analysis you can point to to substantiate this? I suspect any such analysis is heavily predicated on assumptions, such as whether or not the small launcher is designed around existing engines/motors.
I don't think there is a compelling case to be made that operating an air-launch carrier aircraft in addition to the costs associated with the remaining rocket stages works out economically^.
Orbital was not able to get compelling economics out of Pegasus. To be fair, they were doubly-hamstrung by their use of a carrier aircraft airframe operated by vanishingly few (L-1011) as well as the Pegasus using expensive solid rocket motors (here's another non-intuitive reality of rockets - solid motors are very expensive unless you buy in bulk).
^The most compelling test of economic viability of air-launch for small systems will come with Virgin Orbit/VOX space that is using a carrier aircraft airframe which is still in significant commercial use (quite a few 747 air freighters) as well as modern-yet-relatively low complexity LOX/RP liquid rocket propulsion. And if they want to say double their payload capability, they will not be able to do that with the 747. Maybe at the extremely low-end, GOLauncher will also be similar.
Unfortunately I don't, no. I thought about running such an analysis as part of my grad studies (this was quite a while ago; I've switched careers since then) but I didn't get much farther than filling up a napkin before I decided I was already stretched too thin in my coursework.
Ultimately the premise is based on cubed-vs-squared relationships in rocketry (both in terms of aerodynamic forces and structural ones, though through a neat trick of math the mass of your fuel tanks actually scales linearly with their volume [1]). Like most other things in engineering, there are also economies of scale at play (for example, avionics mass consumes a smaller mass fraction of larger rockets), but my hunch -- and this is, as you say, fairly unsubstantiated -- is that the aerodynamic effects alone are sufficient. Cubed-vs-squared in aerodynamics is really just incredibly punishing. At 35kft (Stratolaunch's altitude) it's not as good as at 100kft or so (like you might expect with a weather balloon), but it's still a pretty big difference [2] -- basically allowing you to halve the radius of your rocket compared to an equivalent aero loss at sea level.
To take this to a really absurd level, I can imagine a 100kg rocket -- large by amateur model rocket standards, but beyond tiny compared to consumer rocketry -- with sufficient mass ratio to make it to orbit in a vacuum, but I can't possibly imagine the same rocket making it from the earth's surface.
[1] https://en.wikipedia.org/wiki/Pressure_vessel#Design
[2] https://www.engineeringtoolbox.com/standard-atmosphere-d_604...
No such thing. A "reusable" rocket means you waste capacity carrying fuel for the return trip, and so raise the costs.
It's not like you can refuel the rocket once you get where you're going.
This is the reason why nobody uses "reusable" rockets today, not tech. (The tech was available back in the '60s.)
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.
The way you state this is insufficiently constrained as to make the comparison I think you are trying to make. I think what you are trying to suggest that is that if two launch systems have the same per-launch recurring costs and the same gross mass the one that has higher payload mass fraction is better. Well, I can't disagree with the rocket equation.
If you are trying to relate this back to air-launch, my point is that for equivalent technology levels (meaning the same propulsion system other than nozzle area ratio, tankage with similar structural efficiency, etc.), the benefits you get in terms of recurring cost per unit mass from air-launch (by reducing rocket propellant consumed and dry mass of expended hardware) pale in comparison to the operating economics of having to additionally operate the air-launch platform. In other words, the recurring cost per unit mass to orbit, for the equivalent mass class, will be higher for air-launch than ground launch. And that doesn't even take into account the non-recurring costs associated with the air platform and need to amortize them.
> Alternatively, you can spend that budget on something else like a ‘single stage’ to orbit system which more directly lowers costs.
I'm not even sure where "directly lowers costs" applies in the SSTO case. I'm guessing you mean the case of a fully-reusable SSTO vehicle? At the end of the day, your per-fligt costs will reflect the need to amortize the non-recurring costs you've incurred. SSTO systems will tend to very high non-recurring costs, and the extreme sensitivity to dry mass means you will pay more per pound of dry mass for an SSTO vehicle than a multistage vehicle. The only people that think SSTO with today's technology will lower costs are the ones still hoping for the VentureStar to become operational.
> 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.
I'm not sure what you're trying to say here. If Strato can find a net cashflow-positive way to use their carrier aircraft, great. I think it's unlikely their launch economics will beat other systems in the marketplace so it won't win on pure cost short of Strato taking a loss on launches. However, in terms of launch, they may get some business if a customer really needs the logistical flexibility mentioned in the root post of this thread.
That’s likely true, but depends on how many launches you do. An air launch platform could likely handle multiple launches per day, but finding customers for thousands of launches per year is not going to happen.
> I'm not even sure where "directly lowers costs" applies in the SSTO case.
I am very specifically talking about a non reusable, anti satilite weapon. You can find several such weapons launched from aircraft. In that specific case using far more fuel and a larger rocket is potentially worth it to have dramatically fewer moving parts. Actual designs may be multi staged to increase capabilities to reach geostationary satilites etc, but it’s far less nessisary for LEO.
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.
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.
Solid motor casings are inherently quite stiff, to deal with combustion pressures. There would be less attachment/carriage hardware mass penalty than with liquids.
Bottom line, there is nothing inherent to Stratolaunch that makes it incapable of launching liquids, and even with the additional structural mass penalty, it's entirely possible for Strato to have lower cost per unit of mass to orbit via a liquid rocket stack than with solids (likely, in fact).
But it strikes me that one could get a sense by looking at LPG and LOX truck tanks.
For LPG tanks, I found one source:[0]
Material: 16MnR
Yield strength (Mpa): 345
Permissible stress (Mpa): 170
Comparison: The wall thickness is ... 10-14mm.
0) https://www.anstertrailer.com/lng-lpg-tank-trailer-guide/
1) https://www.popularmechanics.com/space/rockets/a25953663/elo...
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.
Shaving off a small amount of speed can have a large payoff. This is why most launch sites are near(ish) the equator.
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.
You can’t really get into any orbit equally easy when launching from the equator. The higher the inclination, the more delta v you need. For example, the Shuttle lost several thousand pounds of payload capacity when launching to the ISS compared to what it would have been able to carry to the Space Station Freedom, which would have been at an inclination matching KSC’s latitude. It’s just that the penalty is vastly worse for launching into a low-inclination orbit from high latitudes (thus why we didn’t tell the Russians to suck it and deal with an inclination better suited to KSC).
Vaguely related, Baikonur is an interesting example of political issues. It's at 45.6 degrees latitude, but the minimum inclination it can reach is 51.6 degrees, because anything less would involve dropping boosters on China, and China is not enthusiastic about the idea.
"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."
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.
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
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.
> A rocket engine nozzle produces thrust only for the part where the pressure is greater than atmospheric pressure.
This is trivial at best and wrong at worst. When you say "the pressure", what do you mean? If chamber pressure, this is trivial and also not relevant to air launch vs. other modalities. If you mean pressure at the nozzle exit, the statement is false. Most of what I wrote above addressed why the latter is false.
Take some small patch of the nozzle surface. If the pressure inside is bigger than outside, that area contributes to thrust. If the pressure inside is smaller than outside, then it contributes negative thrust.
Curious to hear if you think that is wrong.
You can construct some pathological cases, like a very small thruster that is highly overexpanded to get the rate of momentum change term at or below the magnitude of the pressure contribution, but that doesn't represent a practical rocket engine (maybe more like a Reaction Control System thruster fired at ambient conditions).
I suspect your notion of thrust may be based just on the pressure contribution and is missing the rate of momentum change term, which will be significantly larger than the pressure term in launch system rocket engines.
"A rocket engine nozzle produces thrust only for the part where the pressure is greater than atmospheric pressure"
With the word "part" I meant "patch of the nozzle surface".
Then you went on to talk how I'm wrong and talked about the chamber and the nozzle exit area etc. All irrelevant.
I guess it was a misunderstanding but it felt quite uncharitable.
> "A rocket engine nozzle produces thrust only for the part where the pressure is greater than atmospheric pressure"
> Then you went on to talk how I'm wrong and talked about the chamber and the nozzle exit area etc. All irrelevant.
Your statement is just plain incorrect (or being charitable, misleading) as written. When the velocity of the exhaust flow is > 0, even if the pressure in some section of the nozzle is below ambient, the nozzle (including the section below ambient pressure) is accelerating the flow, so every element of the nozzle's net contribution to thrust is always > 0.
At the end, I think you are talking about overexpansion losses, but short of pathological cases, in a rocket engine the overexpansion losses will not outweigh the rate of momentum change term.
Edit: To add further, the overexpanded nozzle is producing less thrust than the ideally expanded nozzle. But the overexpanded section is still producing positive thrust, it's just less than what you would have if the nozzle had ended earlier. It's not like that section has reversed sign in terms of thrust production.
Let's break it down, it will be interesting to see which part do you disagree with?
1. Optimum expansion ratio has exhaust at ambient pressure. (we agree on this)
2. Adding more nozzle, going to overexpansion, reduces total thrust. We can call the expanded part of the nozzle the "nozzle extension". If this wasn't true, then part 1 wouldn't be true (optimum). (we agree on this)
3. The pressure in the nozzle extension, as experienced by the inside nozzle wall, is lesser than ambient. (my claim, that you disagree with)
4. Sampling some area of the nozzle extension, it constitutes negative thrust. (my claim, you also disagree with this)
5. If the overexpanded nozzle extension contributed positive thrust (like you claim), one could just keep on adding more nozzle and get more and more thrust. (Until flow separation.)
6. In vacuum one can add a lot of nozzle (because ambient pressure is zero) to get more and more thrust for the same fuel amount - until one hits mass or size constraints, or condensation or chemical effects too?
It doesn't really matter if the exhaust is accelerated by the nozzle extension or not. If the sum of total pressure points inwards, then when integrating over the nozzle extension area, force points downwards. This is because the momentum given by the exhaust is not the only force acting on the nozzle.
Most likely the gas is just too rarefied so the total pressure it exerts is less than ambient. Even if it gets accelerated (momentum, yay), it's not enough to overcome the pressure on the other side of the nozzle wall.
I'm interested in hearing why I would be wrong.
We agree on #3 actually. Disagree with the "nozzle extension" terminology on #2, for reasons that should be explained below.
Next, let me admit a significant error in my parent to your post. I wrote:
> When the velocity of the exhaust flow is > 0, even if the pressure in some section of the nozzle is below ambient, the nozzle (including the section below ambient pressure) is accelerating the flow, so every element of the nozzle's net contribution to thrust is always > 0.
The "so every element of the nozzle's net contribution to thrust is always > 0" portion of the sentence is just wrong. It is certainly possible for a segment of nozzle to be accelerating the flow and still have a net negative contribution to thrust based on the pressure component. Indeed as you correctly suggest, this is the overall mechanism by which overexpansion losses arise. Very basic error on my part.
The two roots of my disagreement with your sentence are a) the simplistic relationship stated between pressure in the nozzle vs. ambient pressure being the sole arbiter of thrust production or not, and b) the ambiguous nature of the words "produces thrust". With regard to b), I believe we agree that it is both possible to participate in thrust production and also have a net negative contribution. I prefer something like the latter phraseology so things are unambiguous. As you have proceeded to parse out the specifics of what you meant, you have also clarified your words.
Regarding point a), thinking of the nozzle in a quasi 1D sense obscures the fact that the gasdynamics are at least 2D, and flow is not just being expanded in the nozzle, in anything other than a fixed conical nozzle, it's also being turned. Let's say I design an ideal bell nozzle by a standard method such as Rao's. At the end of the nozzle, when the ambient pressure is matched to the design value, the flow has zero angularity. Now let's run that same nozzle at a higher ambient pressure, same chamber conditions. If I just cut off the nozzle to a uniform length at the point where the internal pressure at the nozzle surface matches the ambient pressure, there will be > 0 angularity. Correspondingly, the pressure is not uniform across the cut-off exit plane. It's not axiomatically the case that continuing the nozzle some finite distance along its original contour, where these loss mechanisms are mitigated even though the internal surface pressure on that segment is below ambient, will produce less thrust.
What is happening mentally is the misleading equivalence between this "cut off nozzle" and an equivalent area ratio nozzle that is designed to terminate at the same nozzle surface pressure. These are actually two different contours, which quasi 1D gasdynamic theory does not distinguish. If the flow was always uniform axially while expanding (not possible), then the simple criterion you stated (part of nozzle below ambient pressure does not make a net contribution to thrust) would be true. But while it is not necessarily way off (specifics depend on several variables), this is just too simple a criterion to be correct. This is why for the purposes of this specific discussion, I think your "nozzle extension" way of thinking about the problem is misleading and should be avoided.
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.
The power would be different (energy is used up much faster in the 3 second case)
The specific impulse of a Merlin engine is on the order of 280s at sea level. The specific impulse of the PW4000's in Stratolaunch is closer to 10,000s. Now the Stratolaunch 'cheats' a little by not carrying onboard oxidizer, but that's almost three orders of magnitude more efficient.
Put another way, the Falcon 9 and Boeing 747 carry about the same amount of fuel onboard. However, that same fuel can push a Boeing 747 for 16+ hours while the Falcon 9 burns it in ~2.5 minutes.
edit: just found this https://en.wikipedia.org/wiki/SABRE_(rocket_engine). Seems that there is a solution.
By contrast, internet businesses return or bust in that timeframe.
It does appear that we don't have a great funding mechanism that is expecting long-term returns vs short term. Past the 10 year expected payoff mark, there's debt, and there's grants. VC is a possible solution, but, there is very little willingness to stretch funds out past 10 years, since the 10 year mark is kind of a benchmark that is marketed to investors in the funds. When you are playing with other people's money, 10 years is already a really long time.
It's also hard to crowdsource a space venture. Government's funds such as DARPA's or billionaire's such as Elon Musk's or Bezos's, or Paul Allen's in this case, make more sense. So our best bet to advance science is to have science friendly government in place. That or inspire rich people to be interested in science.
As an exception, there are segments that receive substantial investment, such as small rocket launch. Many many companies emerged in recent years such as Rocket Lab, Firefly, Relativity, Vector, Astra. Investors clearly see the market in near term for small satellites.
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.
Stratolaunch solves both those problems.
While that's all true of air-launch, saying "Stratolaunch solves both those problems" is overstating the case. Right now, the only stages they have after their air carrier "Stage 0" are economically uncompetitive Pegasus XLs, and it's not clear what the weather capability is of their carrier aircraft.
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].
I'd personally like to see Stratolaunch succeed, but without a dedicated rocket designed to exploit its scale, that's going to be hard. I think Rocket Lab's Electron rocket (a small rocket and a relatively small payload fraction on top of that) would likely benefit greatly from air-launch. On the other hand launching one from the Stratolaunch would be complete overkill, unless you stuck 5 or 6 of them on a rotary launcher or something. An aircraft like Virgin Galactic's White Knight Two would be a much better match for Electron.
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.
Neither will Stratolaunch, any time soon:
https://spacenews.com/stratolaunch-abandons-launch-vehicle-p...
Developing and certifying a new rocket is an incredibly expensive affair. What are the cost savings this promises, compared to SpaceX?
VCs and other investors who see a company that wants to build these vehicles for cheaper launches? I don't really understand the point you are trying to make. Yes, it's expensive to build X, but usually $Y motivates people/companies to invest in the initial costs to cover building X because the payoff, $Y, will be greater than the cost. The news here is that the initial cost is potentially MUCH lower because now they can use this airplane as a stage 1 and not have to develop their own.
So, a currently non-existant SpaceX 'competitor' that wants to hitch itself to the success or failure of Stratolaunch?
That's an incredibly sketchy business to build. You'll be sinking a billion or five dollars before you have any hope of seeing a cent of revenue, and then having an unknown probability of discovering that reusable rockets will eat your financial launch.
Right now, $X is measured in the billions, $Y is anywhere between 0 and billions, and there's a %Z chance (Which is probably over 50%) that your complement product (Stratolaunch) will die before you get a cent of revenue.
Ie, does the rudder have enough authority to stop a spin or does the engine provide enough thrust to maintain level flight.
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
https://youtube.com/watch?v=ZBj3FCdYS80
(At 3m20s.)
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.
Several other onlookers did catch the roll, and the aircraft slewed markedly, with several cameramen commenting on this.
Their competition, Virgin Orbit has it's own subsidiary Vox Space that makes the launch vehicle.
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...
The Startram project estimated $60 billion for a catapult that could launch people. http://www.startram.com/
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. :)
Edit: Curious, not critical. Maybe it can land in a lot of places, just reacting to the size.
I'm not trying to criticize it, I'm just curious how dangerous a typical mission will be.
It can climb in a circle so that it's never far from its base.
I think clearly payload launch is the risky part. What are the kinds of launch failures? Rocket engine failure can be uncontained and spectacular.
Most runways are too narrow for both the wingspan and wheel span. It is quite limited in areas it can land and take off.
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.
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.