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There are working systems based on aircraft and balloons which can launch satellites into orbit with the help of a rocket booster. All of these are fairly small payloads. Are there any studies of the feasibility of launching humans into orbit with a balloon or airplane as the first stage?

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    $\begingroup$ Possible duplicate of Could it be possible to launch a rocket from a balloon? $\endgroup$ – DarkDust Nov 25 '19 at 13:50
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    $\begingroup$ My question has an emphasis on getting humans to orbit. As I linked to in the question, I've seen launch systems based on aircraft and balloons for satellites. I'd like to know some details about larger payloads including humans. $\endgroup$ – Kaushik Ghose Nov 25 '19 at 13:59
  • $\begingroup$ How much money do you have? Do you just want to launch a person in essentially a "survival capsule" which will dock with a space station? The technology is easy; the cost and the "value added" over other human-rated launch systems are not. $\endgroup$ – Carl Witthoft Nov 25 '19 at 15:35
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    $\begingroup$ “Many novel launch schemes need some amount of help from rockets. What kills a lot of them is doing a tradeoff study of just enlarging the rocket part and getting rid of the non-rocket part. Surprisingly often, that works out to be better and cheaper.” — Henry Spencer $\endgroup$ – Russell Borogove Nov 26 '19 at 1:10
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    $\begingroup$ Mandatory xkcd reference. "The reason it's hard to get to orbit isn't that space is high up. It's hard to get to orbit because you have to go so fast." $\endgroup$ – vsz Nov 26 '19 at 5:37
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The MAKS design was supposed to do this.

enter image description here

There is much additional info about MAKS in the answers to this question and their sources: Seeking concept art or photo of MAKS on carrier plane

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Trying to do some estimates: First, we have Space Ship Two/White Knight Two which is designed for suborbital space flights carrying humans so suborbital flight is in the foreseeable future. Orbital flight would be a different matter.

Doing some back-of-the envelope calculations to guess the weight of an orbital version, I'll start by comparing the suborbital Mercury-Redstone at a weight of 30,000 kg, while the Mercury-Atlas weighed about 118,000 kg.

For comparison, SpaceShipOne has a loaded mass of 3600 kg and an empty mass of 1200 kg (surprisingly close to that of the Mercury capsule at 1050 kg empty) so if we assume that the 4x weight difference holds today an orbital rocket would be a minimum of 15,000 kg.

This is a total guess and sounds extremely low, especially since SpaceShipOne reached 112 km altitude, while Mecury-Redstone 3 reached 187 km, but I'll use it anyway.

15,000 kg would be at the edge of the capability of White Knight Two (17,000 kg), and close to the limit of Orbital Science's Stargazer (23,000 kg). For another data point, Virgin Orbit's Cosmic Girl 747 lists a max payload of 200 kg (possibly later up to 400 kg), which is well below our estimated payload of 1000 kg.

So I would call it potentially feasible, but whether it would be cheaper than a Falcon-based approach is not clear.

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  • $\begingroup$ This doesn't include the delta-v savings you get from launching at altitude with some initial velocity, does it? I think they're not very big, but probably not negligible $\endgroup$ – llama Nov 25 '19 at 22:34
  • $\begingroup$ Ah, the wikipedia page quotes Musk saying you get about a 5% payload increase (but also quotes him saying you can just make the first stage of a rocket 5% bigger to do the same thing, which I believe ignores the tyranny of the rocket equation?) en.wikipedia.org/wiki/Air_launch_to_orbit#Disadvantages $\endgroup$ – llama Nov 25 '19 at 22:40
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    $\begingroup$ @llama No, the exponential part of the tyranny happens when you try to scale up the delta-v, not the payload. Payload mass is approximately linearly related to launch mass — there are some nonlinear scale effects but they’re not related to the rocket equation. $\endgroup$ – Russell Borogove Nov 26 '19 at 1:13
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UK's Bristol Spaceplanes has the Space Cab concept -- although the carier airplane has both Jet engines and rocket engines.

UK's HOTOL concept included a manned module (complete with bubble canopy).

After Rolls-Royce pulled out of engine development, Interim HOTOL was considered -- which would have been launched from the back of a Antonov An-225. I don't know if it would have had the capacity for a manned module though.

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