Air Launching vs SpacePlanes

[iamzac]

Which of these two solutions do you think is the most economical for sending small to medium payloads to the low earth orbit?

I think that in the near future air launching seems a better solution because:

-You don't have to carry jet engines, big wings and other stuff you need for low altitude flying into space

-Can be done (and it is already done) with current technology. There are no spaceplanes yet, Skylon will probably be the first one

-The technology is much simpler and probably cheaper

-The mothership can be used for other tasks such as general cargo carrying, testing new plane designs, ...

With supersonic launchers this system will become more efficient.

But a (hyper)supersonic mothership would be more expensive and it will be harder to use for general cargo carrying because of the price so this would be a step between current solutions and future spaceplanes.

In the future, as newer technologies are developed such as lighter and stronger materials and reliable hybrid engines like SABRE SSTO spaceplanes will probably be the best solution.

And for heavy payloads rockets remain the only solution.

Here is an interesting article about air launching.

An article about Soar, a supersonic launcher,

which will launch 6,120 kg (13,500 pounds) to LEO.

In KSP it is difficult to simulate proper air launches because after a certain distance one of the two ships will be deleted.

Here are some of my models to air launch in KSP.

[Nibb31]

As you have noted, air launch already exists. It's nothing more than a reusable first stage that gives you a small boost in dV. You still need a full size expendable rocket to perform the rest of the orbital acceleration.

An aircraft costs much more to build, design, and maintain, especially if it's very specialized and can only be used for a couple of launches per month. A dedicated expendable 1st stage will provide a much bigger boost for cheaper.

You need to design the rocket to be suspended under the carrier, which means that it has to be strengthened for lateral loads as well as longitudinal loads. This means a heavier structure and a heavier rocket, which means less payload.

It's also not very scaleable. Stratolaunch is working on a carrier aircraft that will be the biggest aircraft ever built, yet it will have quite a small payload capacity. To carry something like a fully fueled Falcon 9, you would need a plane so big that there are no runways that could handle it. Basically, you need to build a whole new reinforced airstrip with both aircraft facilities and rocket fueling facilities.

And then there's a whole slew of safety problems. If your engine fails to start, you lose the rocket. If you abort the launch, you need to land the carrier with a fully fueled rocket attached underneath. And of course, there's the whole complexity and chain of failure modes related to the separation of a big rocket.

Now, as a first stage, yes, it's reusable. However, a plane still sucks as a first stage compared to, for example, an SRB both in terms of performance, cost, and safety.

In terms of economy, safety, and performance, air launch is a non starter. The only advantage is flexibility: you can launch at any time to any orbit, which could be of interest for DoD payloads. For commercial payloads, there isn't much point.

Edited June 21, 2014 by Nibb31

[Dwayne_Knight]

As you have noted, air launch already exists. It's nothing more than a reusable first stage that gives you a small boost in dV. You still need a full size expendable rocket to perform the rest of the orbital acceleration.

An aircraft costs much more to build, design, and maintain, especially if it's very specialized and can only be used for a couple of launches per month. A dedicated expendable 1st stage will provide a much bigger boost for cheaper.

You need to design the rocket to be suspended under the carrier, which means that it has to be strengthened for lateral loads as well as longitudinal loads. This means a heavier structure and a heavier rocket, which means less payload.

It's also not very scaleable. Stratolaunch is working on a carrier aircraft that will be the biggest aircraft ever built, yet it will have quite a small payload capacity. To carry something like a fully fueled Falcon 9, you would need a plane so big that there are no runways that could handle it. Basically, you need to build a whole new reinforced airstrip with both aircraft facilities and rocket fueling facilities.

And then there's a whole slew of safety problems. If your engine fails to start, you lose the rocket. If you abort the launch, you need to land the carrier with a fully fueled rocket attached underneath. And of course, there's the whole complexity and chain of failure modes related to the separation of a big rocket.

Now, as a first stage, yes, it's reusable. However, a plane still sucks as a first stage compared to, for example, an SRB both in terms of performance, cost, and safety.

In terms of economy, safety, and performance, air launch is a non starter. The only advantage is flexibility: you can launch at any time to any orbit, which could be of interest for DoD payloads. For commercial payloads, there isn't much point.

I was thinking a fanjet and long thin wings can get you altitude efficiently, and a jet engine can get you the first fraction of your delta V in atmosphere efficiently. I'm just guessing one platform can't get you both so easily.

Have you guess seen any proposals for jet engine first stages? I've seen one before but it seemed questionable at best.

[DaveofDefeat]

Atmospheric drag is only a small fraction of your total delta-v cost, for air launched platforms to be viable you need to gain speed, more speed than any plane is capable of right now and that's without a rocket strapped underneath it. Going up 10km in altitude ultimately saves you little in fuel compared to a normal launch and only adds complexity.

[Dkmdlb]

If you abort the launch, you need to land the carrier with a fully fueled rocket attached underneath.

It's actually probably worse than that: if you abort the launch, you need to dump the entire rocket into the ocean before landing.

[PakledHostage]

I recall that we had a similar discussion about 10 months ago. At that time, I did a "back of the envelope" calculation of the amount if delta-V that you'd save by launching from an airplane. The result was less than a 10% savings (i.e. you could save at most about 800 m/s out of over 9000 m/s if you didn't consider the requirement for an air launched rocket to be stronger in bending than one that is launched vertically, or for it to have other additional complexities that would negatively impact performance and available payload.)

I was able to find the thread here: SpaceshipTwo Second Powered Flight

[cpast]

The biggest advantage of it is flexibility - with small payloads (i.e. Pegasus), you can use a normal aircraft, and can launch from almost any airfield (at least, military ones and decent-size civil airports), fly above weather, not need a reinforced launch pad, and even launch places where there's no infrastructure at all (you just fly over there and launch).

[Nibb31]

I was thinking a fanjet and long thin wings can get you altitude efficiently, and a jet engine can get you the first fraction of your delta V in atmosphere efficiently. I'm just guessing one platform can't get you both so easily.

Have you guess seen any proposals for jet engine first stages? I've seen one before but it seemed questionable at best.

Yes, you get a "first fraction" of dV of less than 1000m/s out of the 9000m/s that you need to reach orbital speed. It's peanuts compared to any conventional rocket first stage that usually provides 3 to 5000 m/s, which means that you still need a full size expendable multi-stage rocket.

You might gain 2000 or 3000km/h if you go supersonic, but good luck building an ultra-specialized supersonic carrier that is 4x the size of a 747, as well as finding a place to land the damn thing safely and figuring out the complications of separating a 500 ton rocket in a supersonic airflow.

It's a non-starter, economically and technically.

Edited June 22, 2014 by Nibb31

[iamzac]

Interesting information, although I was already convinced that rockets are better for heavy payloads, I was only wondering about spaceplanes vs air launches since both use the same idea: launching like a plane using jet engines but one takes those engines into space while the other leaves them.

[LethalDose]

It seems like the savings from the air launcher (Uses less fuel & resuable) could be worthwhile if you were launching small payloads frequently. And your orbital stage can still be reusable. Virgin Galactic's SpaceShipTwo is an fully resuable, air-launched space craft. I guess you could call it spaceplane, but since it's staged, I don't feel like the descriptor really fits. Others may have different opinions.

Again, for small payloads, e.g. passengers, IMO fully resuable, air-launched spacecraft very well may have a place in future space travel.

Edit: Aaaaaannd apparently SS2 is still only sub-orbital... So nerts to that theory. Maybe it's still feasible.

Edited June 22, 2014 by LethalDose

[kujuman]

One of the things the article you linked mentioned was that the Israelis are looking at using F-15s to air launch 100kg payloads. For light military payloads (I have no idea what these would be...maybe anti satellite / ABM launchers?), this seems to make sense. Rapid deployment and avoidance of weather seem like useful attributes of air launch. Also, I'd expect air launches can be done more "stealthy" than ground launches.

I'm curious as to the delta-V savings one would expect for certain orbits, eg, trying to launch equatorial payloads when your closest launch facility is 25 deg north or south of the equator, since a plane could possibly fly to the equator before launching.

Compared to a space plane, some staging is always a good thing. I just don't see how you get around that with a space plane with modern propulsion.

Edited June 22, 2014 by kujuman

[R0cketC0der]

While air launching only has a minor advantage in delta-V, it has a few other advantages. For example, a nozzle designed for air pressure ~15-20km would have a significantly higher vacuum ISP than one designed for sea level pressure.

Also, because most planes can fly long distances before returning, you can launch into any inclination you want, not just the ones equal or higher than that of the launch site(inclination changes often cost multiple thousand m/s of delta-V in real life, so it is pretty inefficient to correct you inclination after getting to orbit).

[Kryten]

One of the things the article you linked mentioned was that the Israelis are looking at using F-15s to air launch 100kg payloads. For light military payloads (I have no idea what these would be...maybe anti satellite / ABM launchers?), this seems to make sense.

The US tried this approach in the 50s with the NOTSNIK program, but the payloads were under 10kg. I don't see how you could do 100kg with anything that could feasibly fit on such a small aircraft.

[kujuman]

The US tried this approach in the 50s with the NOTSNIK program, but the payloads were under 10kg. I don't see how you could do 100kg with anything that could feasibly fit on such a small aircraft.[emphasis added]

I imagine that was due to 1) the purpose of the NOTSNIK program being a tech demonstrator rather than a fully developed program and 2) perhaps the mass of hardware had been significantly reduced by improved electronics (lower mass avionics make a bigger impact on low payload masses).

If we take the nominal payload fraction of a ground-based launcher as .05, then a 100kg payload would require a 1900kg launcher (total start mass 2000kg). This is well within the capabilities of the F-15 (total lift, whether any individual hardpoint can carry that I don't know).

For an idea of how big the F-15 is, its max take-off weight is 81,000lbs (for the strike eagle variant); the Falcon 1 massed 85,000lbs.

Edited June 23, 2014 by kujuman

[Nibb31]

Interesting information, although I was already convinced that rockets are better for heavy payloads, I was only wondering about spaceplanes vs air launches since both use the same idea: launching like a plane using jet engines but one takes those engines into space while the other leaves them.

Well, there is no such thing as an SSTO spaceplane, and there won't be before many many years. It is simply not feasible economically.

(and don't get me started on Skylon, there are already plenty of Skylon threads in the forum where we've explained why it won't happen. Let's not start another one.)

[magnemoe]

I imagine that was due to 1) the purpose of the NOTSNIK program being a tech demonstrator rather than a fully developed program and 2) perhaps the mass of hardware had been significantly reduced by improved electronics (lower mass avionics make a bigger impact on low payload masses).

If we take the nominal payload fraction of a ground-based launcher as .05, then a 100kg payload would require a 1900kg launcher (total start mass 2000kg). This is well within the capabilities of the F-15 (total lift, whether any individual hardpoint can carry that I don't know).

For an idea of how big the F-15 is, its max take-off weight is 81,000lbs (for the strike eagle variant); the Falcon 1 massed 85,000lbs.

F15 payload has also been significantly increased from the first versions.

Note that the F15 also has some other features you don't get then using an bomber or cargo plane as first stage, you can probably get up to mach 2 and the edge of atmosphere then releasing.

Israel also has an obvious problem with launch profile so using an F15 let them travel west over the sea, refuel and launch.

[78stonewobble]

http://en.wikipedia.org/wiki/ASM-135_ASAT

F-15 launched anti satelite weapon. If you guys were curious. It's not a whole lotta payload, but apparently enough for that purpose.

[SargeRho]

ASAT missiles typically aren't orbital rockets though.

[Aghanim]

Well, there is no such thing as an SSTO spaceplane, and there won't be before many many years. It is simply not feasible economically.

(and don't get me started on Skylon, there are already plenty of Skylon threads in the forum where we've explained why it won't happen. Let's not start another one.)

Your link doesn't work...

[Nibb31]

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