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I understand that the Space Technology Mission Directorate's Game Changing Development program https://gameon.nasa.gov/ has a broad scope and is not necessarily focused on immediate payoff. Exploration of ideas and concepts to the experimental stage can be beneficial in many ways - both direct and indirect.

Can someone help me understand at least the potential benefits of the towed glider air launch concept with a nice, concise summary? In what situation would it be attractive and/or competitive.

I've looked at several discussions, but better "carry efficiency" doesn't speak to me. Can this put one or a group of cubesats in LEO at a lower cost per cube (or per kilogram) than other current or likely near-future launch services? Or perhaps is easier to get to the desired latitude for a better choice of inclination or altitude?

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Air launching has been around for awhile, see the Pegasus rocket system as an example. The White Knight is another system. The main goal of much rocket development is cost reduction, and air launching is a way to reduce the size and complexity of a rocket by using an airplane to get it part of the way. So far all the aircraft used for air launch have been manned (B52s and L1011s).

Manned aircraft have to have a certain size and complexity in order to provide a pressure vessel and support systems for the squishy organics inside. This extra complexity and size adds significant design and build cost. Manned aircraft need much more certification because of the safety aspects, adding to the design and build cost. Bigger aircraft need more fuel, bigger engines, etc adding to the build and running costs. This proposal uses advances in pilotless aircraft to reduce the size and complexity of the launch platform by making it unmanned and unpowered (except for a small rocket engine). It essentially outsources the design, certification, and build of the manned, powered aspect to a 3rd party. You don't need an astronaut or test pilot to fly the towing airplane because it's commercial off the shelf - some extra training and similation would certainly be required but not to the level that someone flying the White Knight would need. Because there's no people in the lifter-glider if something goes wrong the towing aircraft can just cut it loose over the sea. The rocket could explode and the tow would simply fly away. A small rocket on the lifter-glider would boost the glider into a better drop angle for the rocket and get it clear after the drop, which would be harder to accomplish on a manned airplane. All these aspects mean you could possibly reduce the price of high-altitude launch.

The term "game changer" is often over-used, often to get more budget. Whether it is appropriate to this proposal is opinion-based. I see potential to this proposal, at the same time there's a lot that would have to go right with it. Towing a big glider with a rocket on it using a big jet is a bit different from towing a sailplane behind a super-cub! The towing airplane might require significant modifications to handle the stresses, and that could make the proposal much less financially attractive. I personally think this is worth investigation but I'm not dancing a jig just yet.

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  • $\begingroup$ I think the Towed Glider Air-Launch System is an alternative to unmanned rockets launched from the surface - which is how it's almost always done. Could you limit your discussion to that please? $\endgroup$ – uhoh Sep 5 '16 at 11:57
  • $\begingroup$ It's an alternative to manned air-launched rocket systems @uhoh, that's exactly what my answer is about. $\endgroup$ – GdD Sep 5 '16 at 12:10
  • $\begingroup$ Oh... wow... OK now I understand. So manned air-launch has been the alternative in waiting for quite some time. This is now the alternative to the alternative or 2nd generation alternative or alt-alternative technology. OK, it might be helpful if you add a sentence at the beginning pointing that out for readers like me. Thanks! $\endgroup$ – uhoh Sep 5 '16 at 12:18
  • $\begingroup$ Air launching of rockets to orbit is nothing new really, it's been around for awhile. B-52s and L1011s have been used for it, maybe other airplanes as well. I'll clarify that. $\endgroup$ – GdD Sep 5 '16 at 12:26
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    $\begingroup$ It has taken off to a certain extent, there's a limit on the size of the payload which makes it an applicable technology for small spacecraft to LEO. $\endgroup$ – GdD Sep 5 '16 at 12:52
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Rockets burn a huge percent of their fuel at the first few kilometers of lift off before they get to 10-12 kilometer altitude.

Airplanes can reach the same altitudes much more efficiently and deploy the rocket.
The difference and advantage of towed glider as opposed to direct deployment of rocket from under the wings as has been the conventional way, is safety and capacity of lifting heavier rockets.
Because the rocked weight is not carried by the towing plane more weight and larger mass can be carried, and safety because of introduction of an unmanned vehicle which would play a safer role in case of catastrophic abortion of mission and providing more recovery options.

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  • $\begingroup$ So if I reduce this even farther - the airplane's wings need only produce enough lift for the plane itself, not the weight of the rocket. There is now a second set of wings producing lift supporting the weight of the rocket during the towed segment. I'm not sure if the glilder wings provide any further lift when the glider's rocket engages at a pitch-up of 70 degrees, but they are obviously necessary to bring the glider safely to Earth for re-use. The pilot safety aspect is of course important for the launch supplier, but not necessarily for the payload owner who is mostly cost oriented. $\endgroup$ – uhoh Sep 6 '16 at 1:35
  • $\begingroup$ Oh, and the glider can pitch to near-vertical before the rocket is ignited, while in conventional air launch the rocket must spend propellant reorienting itself from horizontal to vertical using its own thrust. $\endgroup$ – uhoh Sep 6 '16 at 1:49

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