The Model Rocket and the Weather Balloon

[The Jedi Master]

I'm curious--if you attached a model rocket to a weather balloon, let the balloon go up, detached it just before it popped, and fired the rocket engine, would the rocket leave the atmosphere? If it would, I would certainly start saving up for weather balloons and model rockets!

[Brotoro]

Weather balloons can go about 40 kilometers. Typical model rockets go less than a mile (although you could probably double that with a rocket near the high end of the impulse range that defines "model rocket"). The rocket will do better starting from higher altitude, but not better enough to get it into space, I suspect.

[Budgie]

Plus, if it did... how would you know?

[LaydeeDem]

Plus, if it did... how would you know?

You can stick equipment on to model rockets.

[Rockhem]

Because of such low atmosphere densities the engines may be able take the rocket further.

[N3X15]

People have tried this, with mixed results.

On the one hand, you're way the heck up there and have a head start.

On the other: 100mph+ winds and the balloon itself make it difficult to keep the rocket pointed up. There's also the issue of if the rarefied air will allow the rocket motor to ignite. Balloons can't carry much weight, so liquid rockets are out of the question. Oh, and control: Radio tends to be a PITA at those altitudes.

[K^2]

On the other: 100mph+ winds and the balloon itself make it difficult to keep the rocket pointed up.

Balloon is moving with the wind, so it doesn't matter how fast the wind is. Rocket can point straight up and experience no relative wind on start. This isn't a problem at all in itself. You can get shears, especially since the balloon tends to stop near the layer boundary, but this is just a matter of checking high altitude weather before launch.

There's also the issue of if the rarefied air will allow the rocket motor to ignite.

Also not a problem. Rocket motors have their own oxidizer, whether you are talking about cheap black powder hobby motors or the high end APCP or hybrid motor. So they can operate and be started in vacuum without any problems.

Balloons can't carry much weight

That's the main limitation, honestly. People have successfully built "amateur" rockets that climb to the edge of atmosphere, and these are not small rockets. If you want your rocket to add more than a couple of km, the balloon needed to lift it would be enormous. At that point, it's easier and cheaper to just build a much larger rocket that goes even higher.

[nhnifong]

Anyone know the function that relates lifting gas volume, density, payload mass, and atmosphere density?

I'd like to take a shot at figuring how big a balloon you need to get a pegasus rocket to 40km

[kujuman]

Anyone know the function that relates lifting gas volume, density, payload mass, and atmosphere density?

I'd like to take a shot at figuring how big a balloon you need to get a pegasus rocket to 40km

Just use buoyancy. So apparent mass = weight - weight of displaced fluid. Setting apparent mass = 0 (neutral buoyancy) means weight of displaced fluid will equal the weight of the total airship.

If the density of air at 40km = 1g/L a 10L balloon will lift 10g to 40km. (total mass of the balloon is 10g, not the payload)

If the density of your lifting gas at 40km is .7g/L then you displace 10g of air with a 10L balloon but you also are lifting 7g of lifting gas, leaving you with a payload volume of 3g

Edited July 2, 2013 by kujuman
ps this might all be wrong. I am not a smart man.

[Unistrut]

Unless there's a whole level of "cheap hobby motor" I have not experienced, even the solid ones from the hobby store have their own oxidizer. Might need to make sure the igniter would still work, but if you got the motor lit it would go just fine. I even had one travel underwater for a short period without trouble. I mean aside from the "my rocket is in the pool and not the sky" trouble.

[Errol]

I thought the idea of "rockoons" was tried by the US a few times back in world war II. First few attempts failed due to suspected icing of the motor during balloon ascent causing the motors to fail to ignite. Supposedly they had these cans of orange juice they heated up in warm water and tied to the igniter with towels, to ad thermal mass. The third attempt, with added orange juice thermal mass did ignite, but I do not remember if it had instruments to report status back with.

I hope I didn't just dream that up, because it sounds so cheesy....

[mardlamock]

If you got a propellant mass ratio of 4:1 you could almost cross the karman line, you'd have to launch from around 30k meters for it to be even remotely possible though. A high powered rocket without much added stuff (a light parachute and camera) could do it.

this rocket would probably make it into space. Edited February 18, 2015 by mardlamock

[linkxsc]

Well, if you spent the money for a big balloon rig like what they used for whatshisface to make his high altitude skydive, you could get a fairly sizeable rocket up there... but would probably still be quite limited in max altitude. I think some of the larger rockets Ive built have scraped up to a half mile or so (before i started getting angry letters) if you were to line a real stack of motors up in a way so that they'll stage themselves, you might pull off a few km above your launch altitude. 10km would be some real wishful thinking, but probably not impossible. Cost if this mission would be quite high also. By some point, you might just consider buying some old Sidewinders or Atolls off some military, and use those as your engines (The AIM 9 has a 7-8 mi range for some of its early models, that you could probably buy for a couple grand in the middle east, would probably put you on some watchlists though.)

Unless there's a whole level of "cheap hobby motor" I have not experienced, even the solid ones from the hobby store have their own oxidizer. Might need to make sure the igniter would still work, but if you got the motor lit it would go just fine. I even had one travel underwater for a short period without trouble. I mean aside from the "my rocket is in the pool and not the sky" trouble.

Curious, how well did it go underwater (or was it like you launched it from underwater to the air?)

[Errol]

What if you hosted up some sort of small air-breathing drone space-plane type thing? It could save all it's fuel for the first few portion of the flight at least...

I'd like to note here, I've never even launched a model rocket, all my experience comes from KSP, scott manley and wikipedia.

[BagelRabbit]

At the risk of sounding like a nut-job, I'm working on a project like this right now in my (very limited) spare time.

My first prototype is already being assembled in my basement. It's a pretty standard minimum-diameter rocket, a descendant of the one that I used to get over a mile high on a commercially-available H motor. Here's the original craft, called the HyPr. (The reason for the big cone on the back was to properly accommodate the motor, by the way; I'm not going to need as similar cone for this project though, nor will I need the stand-off for that little launch lug tube you can see at the top.)

I should mention that this rocket, and the rocket I'm currently building, are both 29mm in diameter: only a bit more than an inch.

Even though the HyPr was lost because of a lack of a transmitter, I'm pretty sure that this guy broke the mile mark because it did not shred on the way up. (Top speed came out to something like Mach 1.3.)

It wouldn't be too difficult to carry a rocket like this up on a weather balloon: the parts so far weigh a little more than a pound and a half, and the final rocket will be below two pounds.

So, I'm planning another rocket of the same diameter, meant for travelling up to 95,000 feet on a balloon before being launched. According to my good-quality rocket simulation program (it's called Rocksim, maybe you've heard of it), the rocket I'm building would reach 31,400 feet above the balloon at its apogee, taking it up into the lower stratopause. The rocket would go from near-zero to Mach 1 in less than a second. Hooray for an almost complete lack of drag! I've got most of the equipment needed, though I'm still lacking a really small tracker that can get a range of maybe 30 miles... maybe someone here can help

I'm planning to do a test in about three months, in which I take the rocket up to about 10,000 feet AGL with balloon before firing it to about 18,000 feet AGL. It will be nice to see if everything works. After that, I'll probably go for 130k feet if there's no serious problems with the first flight.

I've given this a fair deal of thought, and I know what I'm doing. Please don't look at me that way.

At any rate, I'll have to overcome a heck of a load of obstacles to get this to work, but it's worth a try.

-Upsilon

[EDIT: Holy necro, Batman! Although I suppose this topic is still relevant, so there's no real reason to shut it down.]

Edited February 18, 2015 by UpsilonAerospace

[Errol]

How do you plan to cut the rope and ignite the engine?

[YNM]

Shoot it ? Or maybe wait for it to blurps away... ?

Anyway, was just going to post this link. Granted it's on some silly ideas but I guess the calculations might still be useable.

[wumpus]

It looks like the register (tech rurmour website) has been working on an amature project on this very topic. Note that baloon has gone over 100,000' (not sure about payload beyond a small figurine), so it seems to be a bit more than a standard weather baloon. One thing I remember is that their first [few?] attempts with ignition failed. Off-the-shelf rocket ignitors simply didn't raise the temperature enough when your rocket is at something like 40 below.

http://www.theregister.co.uk/science/lohan/

[BagelRabbit]

How do you plan to cut the rope and ignite the engine?

I don't plan to cut the rope. Rather, the rope will be very long (30 feet), which will mean that if the rocket is fired at a slight angle from vertical (less than ten degrees), it will miss the balloon entirely. Trigonometry for the win!

(Oh, and this longer rope will also dampen any back-and-forth movement caused by wind, which is nice if you need the rocket to be pointed upwards when launching. )

As for igniting the engine, the biggest issue is not the extreme cold, but rather the lack of pressure: even with their small amount of oxidizer, conventional igniters simply won't work at very low pressures. The current fix I have for this involves sealing the motor so that it is airtight with hot glue (which will melt almost instantly after ignition), and using a special e-match igniter augmented with plenty of pyrogen. It will be very worrisome putting a dab of hot glue in the nozzle of a live motor, but I'm chalking this up to 'a risk that I've gotta take, and one that isn't too bad as long as I don't do anything stupid.'

[Errol]

Will the rope and balloon not cause massive drag? It needs to release from that doesn't it? Do you have an altitude trigger, or are you going to do it remotely? I would think that any sort of time delay would be too unpredictable.

I'm sorry if it seems like I'm asking a lot of questions, I'm super interested in this. I had a dream about launching rockets horizontally from way up in the atmosphere after having hoisted it there with a blimp. Obviously the math wont allow such a feat, but that dream led me to this:

http://en.wikipedia.org/wiki/Rockoon

Which is pretty neato.

Edited February 20, 2015 by Errol

[BagelRabbit]

Will the rope and balloon not cause massive drag? It needs to release from that doesn't it? Do you have an altitude trigger, or are you going to do it remotely? I would think that any sort of time delay would be too unpredictable.

I'm sorry if it seems like I'm asking a lot of questions, I'm super interested in this. I had a dream about launching rockets horizontally from way up in the atmosphere after having hoisted it there with a blimp. Obviously the math wont allow such a feat, but that dream led me to this:

http://en.wikipedia.org/wiki/Rockoon

Which is pretty neato.

Oh, that's what you mean.

The rocket will be mounted on a three-foot rail, at a seven-degree-from-vertical angle. The rail will be attached to a 'gondola' containing a power source to ignite the motor, cameras, weather monitors, and a radio link with the ground. Hopefully, this will allow for limited live telemetry, as well as the ability to send a signal to fire the rocket. Once the rocket fires, it will leave the rail and speed away from the gondola, which will still be attached to the balloon. The gondola will ride the balloon up until it pops, and then descend on a parachute. The rocket, however, will descend freely and land in a different spot.

Fortunately, the gondola would be capable of carrying both a more committed tracking system and a radio control capable of launching the rocket. The rocket itself would have some pretty bare-bones equipment: just a modest tracking system and a dual-deploy rocket altimeter. That's really it.

Oh, and I should also mention that I'm probably going to place a decal of Jeb at minimum, and actually fly a tiny clay model of him if at all possible. (The Shapeways model might be better for the gondola, as it's far too large for the rocket.)

[Errol]

Having never flown a model rocket, but played TONS of this game (including TONS of faffing about with roverdude's sounding rockets mod) that is honestly the coolest thing I have ever heard of. I cannot wait to see that footage if you upload it somewhere. Anything about this project if it isn't secret, this is wickedly neat.

[wumpus]

If you got a propellant mass ratio of 4:1 you could almost cross the karman line, you'd have to launch from around 30k meters for it to be even remotely possible though. A high powered rocket without much added stuff (a light parachute and camera) could do it.

this rocket would probably make it into space.

Mass ratios sounds like it comes down to staging. Of course, I'd assume that the first stage (the balloon) is pretty fixed. And if ignition is one of the bigger problems, each stage just multiplies that (unless you are using some sort of self-staging model rockets).