Yes, yes, for every action there is an equal and opposite reaction. But, if the launch platform also had engines that launched at the same time as the rocket, they could counter the downward thrust. also, rocket propulsion in the atmosphere actually uses the atmosphere as if it were an opposing force. Put a rocket horizontally on a clothes line and set it off and it will move forward yet the only opposing force it has is the air itself. Additionally, the rockets initially force is so quick and the rockets weight so light that the mass of the platform would not instantly drop at an equivalent speed of the total upward force of the rocket, even without counter propulsion. Some speed would be knocked off that it would have on the ground, but not a significant amount as to cause the platform to drop instead of the rocket lifting off. Float a foil covered Styrofoam platform of say 4'x4' in a pond of water with a rocket on it and the rocket will launch but the platform won't sink because the rocket is aerodynamic while the pressure required to submerse the Styrofoam is significantly greater than the brief thrust coming from the model rocket.

In short, I think it could be done with a triangular platform of ultra lightweight material like balsa with three balloons attacked, one to each corner, and the tops of the balloons attached together such that the move as one. The rocket could be put at the center of the triangle and launched from the space between the balloons. Additional thrust could be put into the rocket and not lost to the platform by attaching a second identical rocket at the center point underneath the platform that fired at the same time, thereby countering some of the lost thrust do to the brief platform descent.

Gunfighter makes a good point. That's how the X planes were launched. Drop then ignite a rocket built into them.

Why drop it, and why use a platform? Why not suspend the nose of the rocket from the balloon, then when the rocket ignites, it could slash right through the flimsy balloon? Or, are weather balloons to rugged to permit this? This design already points the rocket upward, and would not need to overcome the loss of energy from being dropped.

What gases do the weather balloons use to float? Are the ignitable? Will the alter and possible cause the engines not to fire? I don't know enough about model rocketry to answer that.

Weather balloons use either helium or hydrogen, with the latter being more popular due to its lower cost.

Don't know if a weather balloon could lift a 78,000 pound (Minutemen family) rocket. I would drop it out of the back of a cargo plane with a parachute and launch as soon as the plane is clear, just to prove the concept of airborne launches. The only problem is that cargo airplanes generally have fairly low service ceilings, especially when carrying cargo and especially compared to business jets or military jets, and even some commercial jets. Sure, it will go to 30,000 easy enough, but 50,000 would be a much better altitude for a launch.

A helium balloon large enough to lift a rocket worth launching from an airborne platform would be cost-prohibitive and would take a while to ascend (hydrogen ascends faster than helium if I remember my high school science classes correctly)

I suppose the rocket could punch through a hydrogen balloon without sparking anything (a titanium nosecone punching through a synthetic plastic-based hydrogen balloon shouldn't cause an explosion, right?)

Well there you go. Piercing through a giant hydrogen balloon would potentially cause the balloon to explode when the flames from the rocket reached the hydrogen destroying the rocket that pierced it and ending that flight a little too soon.

I'm trying to think of a practical way SYnapse could actually do it. Something affordable. Cargo planes and decommissioned rockets don't fit that bill. But a balsa platform with a model rocket and three weather balloons tied together does.

Atmospheric pressure drops off pretty fast, faster than you might think. For example, I read somewhere that a pilot at 40,000 feet who loses cabin pressure and can't find an oxygen mask has somewhere in the ballpark of 6 seconds of useful consciousness.

I'm no rocket scientist (pun intended) but I would assume that two equal rockets launched from 0 feet and 30,000 feet respectively would have drastically different performance due to the air pressure difference alone.

Would not the rockets themselves burning trigger a hydrogen explosion?

@ Draugnar

Oh shit. Female blonde moment for Gunfighter. I forgot about the rocket exhaust lol.

But if the rocket is moving, could it simply outrun the burning hydrogen? A brief exposure to burning hydrogen gas wouldn't endanger the rocket, right?

And yes, Hydrogen being the lightest of all the elements has a mass about 1/4th that of helium.

The rocket wouldn't be moving fast enough relative to the exploding hydrogen to escape it. It has mass and the thrust is still accelerating that mass where as the hydrogen is a chemical reaction travelling from atom to atom, molecule to molecule, much faster than the rocket's momentum mere moments after launch.

Would a combined balloon/rocket system be feasible, SYnapse? Although it probably wouldn't be worth the effort. Even the beefiest model rocket would only give you a few thousand more feet, and there might be issues with the rocket itself. It's a rocket, of course, so lack of air wouldn't be an issue, but temperature might be. Will the average model rocket function at -100 degrees Fahrenheit below zero?

Yeah, but it would still be a relatively brief burn. Would it jeopardize a metal-skinned rocket?

Also, could the rocket briefly drop away from the balloon under a stabilizing parachute, a small charge destroys the balloon, then the rocket fires?

Model rockets aren't metal skinned. too heavy for their engines. They are paper on balsa. Even some of the larger ones that cease being model rockets are paper mache. Seriously, do you not simply google this stuff before making assumptions? I know next to nothing about model rocketry and yet google has told me so much for this thread.

Now, assuming you could pop the balloon before the flame reached it, it might do OK, but the explosion is going to send a shock wave down towards the rocket (it goes out in all directions) and I don't know what effect that might have on the rocket's orientation.

The skin could be made fireproof so an explosion would not affect the rocket. However, I think Gunfighter has a good point. How much weight can a weather balloon lift. Can it haul up a powerful enough rocket to lift more than a few thousand feet? Some model rockets can go 50,000 feet, or higher, but I don't know how heavy they are.

Multiple weather balloons bring back the possibility even with a super lightweight launch platform.

One thing to remember about the explosion isn't just the flame, but the pressure. The center of the explosion is extremely high and violent pressure and expanding outward is a shockwave that can disrupt the orientation and even damage the rocket. think about the glass and shrapnel when a gas line explodes in a building...

A lightweight launch platform with a series of rocket engines underneath providing additional lift to the balloons then a multi stage rocket launched from it should get a capsule with a green army man into space.

What I would like to see is complete escape velocity reached so that the green army man continue on his way until he ran into something else out there like a meteor or (and wouldn't it be cool to say you put a [green army] man on) the moon.

Presumably, in a balloon the hydrogen will be relatively pure, unlike a gas leak in a house where there is a mixture of oxygen and gas. I'm not sure, but I think this would cause the combustion of the balloon to be relatively slow, and not really an explosion. I remember a science experiment where we harvested hydrogen into a test tube and ignited it. The igniting part was not part of the experiment, and was not done under the supervision of the teacher. :-) But it did not explode, it just burned extremely rapidly. I don't know if it would react the same way in a large balloon though.

The balloon being under pressure would burst when pierced, though. That would be a shockwave all its own. I'd just rather stick with a known entity (no explosive decompression or chemical heat and pressure reaction).

But if the balloon's decompression could be controlled and directed to provide upward momentum for the rocket...

You might be right. The decompression might be a bigger influence than the effect of the burning hydrogen.

And for an example of a hydrogen balloon burning, one need only look at the Hindenburg.

@Draug, @Gunfighter, @Devonian: See the link I posted earlier:- www.theregister.co.uk/Wrap/lohan/. These guys are serious, they even built a barometric temperature controlled chamber to test fire their rocket motors at the temperatures and pressures it would experience at a height of 100,000 feet - the first attempts failed (and yes, I know there's lots of double entendres in the story titles, that's just something you have to put up with The Register's Special Projects Bureau).

Using hydrogen instead of helium in the balloon may well give increased lift, but the chances that you'd kill yourself before the balloon left the ground are high. You'd also have to find some way to *safely* get the hydrogen to the launch site and into the balloon.

If the balloon caught fire, it wouldn't burn fast enough to count as an explosion, look how (relatively) slowly the Hindenburg burned (http://www.youtube.com/watch?v=F54rqDh2mWA).

I'm a fan of the rocket+ballon idea; plus you don't need to go straight up; most orbital/sub-orbital flights don't.

So the question is, where do you want to go. Into space? That's a kind vague one, Draug's 'escape velocity' is nice, but may be much harder (and less useful*) than into orbit. Especially an orbit which is going to decay for later retrieval.

Lets assume you hang the rocket at roughly a 45° angle, and launch from 2-3 meters below the balloon (hanging from some string) We should be able to avoid destroying the balloon. (though getting the balloon to return to earth should also be possible, perhaps with data recording of the rocket launch)

The two/three balloons suggested could also give a better shape... The question is whether the rocket will spin out of control. And that's something which i think is a problem with all of the above plans. You can't use rifling, and you don't have a stable platform to launch from. (so you've got whatever wind, and vibrations from the balloon(s) to counter - nevermind shock-waves from a decompressing balloon)

Still, i suspect stabilising fins will help even out most problems once you can get up to velocity. Obviously a rifle/cannon would help as a launch 'platform' - but a paper rocket isn't going to enjoy this launch...

*if you can't get data back from your rocket then you can't actually say where it went. Though that's a seperate issue i guess.

Can I just say what a great thread? Not a single politically based insult yet....

You gave us something wonderful and fun to thinly about, SY.

Think not thinly - stupid autocomplete.