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High altitude rocket assembly

Use dirigibles for forward staging of rocket stages
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Small rockets have been hoisted by balloons and launched since the 1950’s (actually 1949, link). It’s a good way to avoid burning expensive fuel to punch through the thicker air at ground level. Disadvantages are size limitations and the fact that balloons aren’t steerable, limiting launch opportunities.

I propose a fleet of unmanned, remotely controlled heavy lift dirigibles. Each will loft a solid-fuel rocket booster to high altitude (and one will lift a payload module rather than a booster*), where they will be snapped together to make a much larger booster. Once assembled, the heavy lifters drop it and get out of the way for it to fire.

---
* Tip of the hat to [Lurch] for pointing out that I forgot to mention the payload in the original writeup.

a1, Nov 12 2021

Rockoon https://en.wikipedia.org/wiki/Rockoon
[a1, Nov 12 2021]

Low-tech space entry vehicle Low-tech_20space_20...mountains_20needed)
[Skewed, Nov 12 2021]

Max Q in a rocket launch https://en.wikipedi..._in_a_rocket_launch
What you can stop worrying about with a high altitude launch [a1, Nov 12 2021]

The handle broke off! https://www.history...on-landing-accident
Bad design, by definition [a1, Nov 12 2021]

Aerojet 260 series http://www.astronautix.com/a/aj-260.html
largest monolithic solid rocket motors ever tested. [a1, Nov 14 2021]

[link]






       Should be pretty spectacular. Too bad those boosters couldn't also have a payload attached to them.
lurch, Nov 12 2021
  

       // Too bad those boosters couldn't also have a payload attached to them. //   

       Y'know, I originally did specify a payload module hoisted by its own dirigible. Don't recall why I took it out, but I'll put it back. Thanks!
a1, Nov 12 2021
  

       Ah, note that was with a wink & I couldn't decide where to start...   

       Note there's nothing impossible about this; it's just that all of the myriad obvious problems are surrounded and outnumbered by non- obvious problems.   

       Starting at the end, //get out of the way// -- dirigibles are renowned for their modesty of acceleration. If you have power available to quickly move your launch platform, it would be advantageous to use it adding downrange velocity for your rocket. Then make your separation maneuver by decelerating. (Get the whole thing in a jet stream, add a few kph.)   

       Backing up a notch, // drop it // 9.8 meters per second per second of acceleration in the wrong direction at a point where your engines aren't even running yet, and when you do get them started up, they'll be at their worst efficiency & effectiveness of the whole flight. When they dropped the X-15 from the B-52, it was a loss in potential energy, but it was compensated by the fact that they were moving forward at 500 miles per hour, and the free-fall traded for even more airspeed, which translated to aerodynamic lift, which was useful. Not so much for an SRB.   

       Backing up one more, // they will be snapped together //... well, let's pair that with //generally aren't steerable// and then imagine how the tolerances for assembly are going to work out.   

       It sounds *expensive*.
lurch, Nov 12 2021
  

       I would handle most of your concerns about the drop & ignition sequence by repositioning all the tethers* in a ring somewhere above the assembly's center of gravity - so it'll be pointed "nose up" and all the dirigibles are off at a safe** distance. Picture them arrayed in really big a circle around the thing. On ignition or in the few seconds it takes to build up enough thrust for the thing to go up, the dirigibles cut loose and hopefully get out of the way.   

       Or they DON'T get out of the way. I assumed they would be unmanned - so perhaps they be considered expendable. Certainly would allow for a cheaper construction spec. And if they're filled with hydrogen instead of helium for the extra 8% of lift, they could put on an even more spectacular show.   

       And as for EXPENSIVE (dismissive wave of the hand). Hey, this IS rocket science after all. With possible flaming dirigibles! Isn't that show worth the money?   

       ---
* repositioning tether: After the whole rocket is assembled, separate aerial drones fly out and one at a time pluck a tether from its original lift point to the designated point for launching.
  

       ** for some acceptably defined value of "safe."
a1, Nov 12 2021
  

       //
Backing up one more, // they will be snapped together //
let's pair that with //generally aren't steerable//
... tolerances for assembly //
//
  

       Dirigibles ARE steerable by definition, which is why I specified them over ordinary weather balloons used in the earliest rockoon experiments. I concede assembly will probably be more complicated that simply "snapping them together" but the interstage rings would be attached before lift and designed to make that easier. Nobody should have to go out on a tightrope with a wrench.   

       I mean, not unless you're volunteering.
a1, Nov 12 2021
  

       We have 'some' elements of prior art here I think [link], elsewhere too I'm sure
Skewed, Nov 12 2021
  

       [Skewed] THANKS! Great link and discussion of underlying concepts. The only new thing in mine is mid-air assembly of the multi-stage rocket.
a1, Nov 12 2021
  

       A single large airship in the form of an elliptical toroid, with the launch occurring through the center seems like a better solution than assembling mid-air.   

       Of course, as with most rockoon solutions, simply getting up to ~60km (current highest proposed airship launch design) doesn't help that much. The reduction in air density is a plus, but you've still got another ~1940km vertical to go, and that's less of an issue than getting up to orbital velocity. 100km suborbital requires ~1.4km/s delta V. LEO requires 9-10.
MechE, Nov 12 2021
  

       // 60km ... doesn't help that much. The reduction in air density is a plus //   

       Although you say it doesn't help "that much," I think you may be underestimating the value. At 60km you're practically in a vacuum, no need to streamline your launch vehicle or even worry about aerodynamic heating or buffeting as you go supersonic. That's a huge saving in weight and structural costs. Even at a more modest 20KM, air resistance would be low enough to only require a very lightweight fairing to survive max Q (link).   

       That's true of any high-altitude launch, not just my halfbaked version.
a1, Nov 12 2021
  

       //Dirigibles ARE steerable by definition//   

       Crackly radio voices 60 km up:   

       "How do you steer this thing?"
"Use the definition!"
"I tried that, the handle broke off!"
pertinax, Nov 12 2021
  

       // the handle broke off! //   

       [pertinax], do you know the Apollo 11 circuit breaker story? (Link)
a1, Nov 12 2021
  

       That was definitely not my fault. I have an alibi.
pertinax, Nov 13 2021
  

       //get out of the way//
They will be getting out of the way; they've just been released from a heavy payload, so they will be going UP.
Alternatively, use hydrogen. Small initial thruster on the rocket accelerates enough to replace the lift from the balloons, whose hydrogen is then pumped INTO the rocket as fuel. Remaining parts (pumps, framework etc) the release & parachute home as rocket fires main engines.
neutrinos_shadow, Nov 14 2021
  

       [neutrinos_shadow] - good point about where the dirigibles go when they cut loose. But they can’t pump fuel into the rocket, the original spec is for solid fuel boosters.
a1, Nov 14 2021
  
      
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