Balloon Launch Discussion

wow that's a great idea i bet a bunch of university research projects or student groups would like to have access to a relatively inexpensive balloon setup. i imagine you can buy them for high altitude atmospheric research but if i had to guess i'd think they'd be overpriced...

Wait until you guy's see this next payload!
The Project was really cheap Rob in the sprit of the N-Prize it Cost us a Balloon and some Helium and a 35$ camera and we recovered that so by N-Prize rules it cost us right at $85 I'm dissapointed we could have made it $38 if we used my Hydrogen genarator and some scrap Alum. pistons from our free source. The rest was scrounged from what we had and free stuff including the tracking software. Oh, one more thing if we had a source for polyethylene we could have made our own balloon and that would reduce it to $3 for Sodium Hydroxide and we could probably find a source for that too.

Monroe

This next payload might mak a nice kit?

Guys,

I have been researching balloons and how to make them, and I happily ran across the web site to the NASA Columbia Scientific Balloon Facility:

http://www.csbf.nasa.gov/balloons.html

I pretty much already knew all that about balloons, but the facility itself is in Palestine, TX. I'll call and see if I can talk to someone knowledgeable about balloon manufacturing details. It might even be worth a field trip to take a site visit. Overall we just need a way to cut gores accurately from thin polyethylene, and heat-seal the edges together. I know there have to be some tricks involved with the welding, because as you start joining the seam the shape becomes non-flat and is going to start curling. Plus the plastic is slick, and how do you hold it accurately? How do you join the final seam to close the balloon? Perhaps it's done like clothing, where you do the seams on the outside and turn it all inside out? How the heck would you turn a massive balloon inside out? No, nevermind, on a balloon you could leave all the seams showing and it wouldn't matter anyway. And how do you pack a balloon for transportation? Hopefully the NASA guys can answer some of those questions, and even better would be to see it done. After all, our tax dollars pay their salaries.

Stew

Do go for that! That would defiantly be a field trip we would make. I hope you can find more information, we are defiantly going to have to make balloons in the near term. Besides that some shape experimentation may be in order. A cylinder shape would be easier to make with straight seams only the ends would be difficult. They can rise standing on end laterally and go horizontal as they fill at lower pressure. We need to figure out what thickness for what size and determine weights. We may need a special valve to control pressure at altitude.

Monroe

The NASA site mentions .8 mil polyethylene. I've used .5 mil drop cloth and it's pretty fragile, 1 mil is sturdier. I don't know what they use for the suspension lines. I calculated the stresses on the plastic near the suspension lines and even with .5 mil it looks like the plastic can support pretty thin lines, like monofilament fishing line for small sizes. Something thicker will probably be necessary for larger balloons, perhaps tubular nylon. At any rate, the envelope isn't going to weight very much at all.

We may be able to double seal the seams and incorperate the support lines in the seams? Make the seal lay in the support line and then seal again? That way we can trim the excess poly right up to the second seal without to much worry about causing a leak as well?

Monroe

Stew
At some point we will need a gas flow meter. I wonder if we could (or should?) modify a standard Natural Gas flow meter to measure the exact amout of gas going into our balloons? Or is there something better/cheaper? A standard meter may be to slow I guess we could use a regular ball type (welding) flow meter and just do a calculation for time to fill at that CFM?

Monroe

Monroe,

You and I think so much alike in an engineering sense it's almost scary. I had already thought of the possibility of incorporating the support lines in the seams, and it seems like a good idea. I'm still trying to think about how to make a seam-sealing apparatus, no really good ideas yet. I'm hoping to learn from the NASA guys. I had thought about the necessity to measure the gas and I think it can be avoided. Using a zero-pressure balloon design, you just overfill it and it vents the excess as it climbs anyway. However, I did some research on the aluminum/lye reaction and it may have a couple of side effects we will need to deal with. One is the powdered aluminum oxide you typically get. I understand experimenters usually bubble the evolved gas through water to remove this. If we do that we'll get hydrogen saturated with water vapor at the temperature of the water tank, or close to it. That's going to add density to the hydrogen and cause condensation on the inside of the envelope as it cools during ascent. Condensation will drop through the vent hole at the bottom, but once it starts to freeze at altitude we're stuck with the mass of that water and I imagine it will be a problem. We're going to need either a desiccant bed or a refrigeration system to remove the residual water vapor from the hydrogen.

Stew

I like the refrigerant method. The reaction get's plenty hot as well. A dry ice methanol coolant pumped through a condenser like device would be pretty ez to use in the field. I could rig a dual evaporator system on our truck and use that to refrigerate the gas too. I'll look into that. Hummm that is interesting? Yep I could make that work. Suburban’s and some vans have dual evaporators. I could rig a system that would switch evaporators and make a "suitcase" for the secondary evaporator that sits outside the truck on the ground. I found some information on the gore patterns I want to try making a small one I just need the poly film and the mono line I have a little hand sealer I can use for the experiment. Did you say "drop cloth" like from home depot?

Monroe

I’m not a team member, but you might find this interesting.

For a living I am an IT Manager at a company that does a lot of shrink wrapping. To do this we take a roll of thin flat plastic fold it in half and then weld it into a tube. The weld is very clean and tested to be nearly as strong as the rest of the plastic. It is made by taking the folded plastic and running it between two sets of belts (think tank treads facing each other) which hold the plastic. Between those is an angled rod heated to a precise temperature. The plastic gets fed between the belts which holds each side and then against the shallowly angled rod which welds and cuts the plastic. I can send pictures or give you machine specs so you can find diagrams on the internet.

The problem I’m trying to solve is to make it mobile as it would be impossible to feed the plastic in, so the machine needs to be mobile and track along the edge of a premade form to create the balloon. My present best guess is to layout the plastic on a form and then have the welder ride model train tracks along the curve needed.

MisterQED
Team Daedalus

That's excellent information, QED. If you had a link or some pictures that'd be even better, I'm having a little trouble visualizing the exact arrangement. I was imagining some kind of heated rollers, but I was concerned about how to keep the plastic from sticking to the rollers. Also, I know precise temperature control will be important. I considered cannibalizing a laser printer for the fuser assembly, which applies both heat and pressure to thin sheets of material, but fusers operate at about 350F, whereas I'm pretty sure we need in the 220-240F range, so it'd be necessary to regulate the heater. A variac might also work, if I had one....

Monroe: yes, good old LDPE plastic sheeting, commonly sold cheaply in large sheets as painter's drop cloth. 1 mil is probably what we want, although it might be worth experimenting with the 0.5 mil too. It's not UV resistant, so especially with the UV flux at altitude it won't last more than a few days, but that should be more than plenty unless we want to build long-duration balloons. Greenhouse suppliers sell UV-resistant stuff, but usually in greater thicknesses. I can't wait to start building balloons, I'm hoping your basic bag sealer will let us get started before we build a better rig. Just a few bucks of drop cloth should let us build a fairly large balloon. So the cost equation looks like this: a few bucks of plastic drop cloth + a few bucks of fishing line + some scrap aluminum and lye = significant payloads to the upper atmosphere! Perfect for rocket scientists on a budget.

About the water issue, the evaporator will have to be very cold to do what we need, essentially it will need to chill the gas down to the lowest temperature we expect at altitude to avoid condensation. That probably puts it out of the realm of freon and into the realm of dry ice, although the freon might make a good first stage cooler and condense most of the water out as liquid, since all it will do at -70 or so is turn into frost.

Stew

Here is the exact machine we have with lots of pictures and a movie:
http://www.spsgm.com/
Patent 7281362
Sadly that patent isn't on Google.

MisterQED
Team Daedalus

Great! I looked at the video and was able to learn a lot. I also looked up the patent and finally found a patent site that had the pictures as well as the text for free. It looks like a very well designed machine, and even better I learned some significant points about sealing plastic. Mainly, temperature, pressure, and time are the key variables. This machine is interesting in that it also cuts as well as seals, which isn't necessarily something we're trying to do. I then thought about how to make a small version of something like this (hopefully without infringing on their patent, although it's not like we're trying to make or sell such a device for profit). Your track idea sounded interesting, you should be able to get a precise curve that way. I had been thinking about a stationary machine that you run the sheeting through, but with a curved edge that has its own set of difficulties.

However, it turns out there's an easy solution, at least for small scale. Hmmm, what household appliance is designed for applying heat and pressure... a clothes iron! I started experimenting and rapidly discovered that the plastic film sticks instantly and near-permanently to the surface of a hot iron. Not so good. Easily reaches melting temperatures even on the lowest heat setting though, probably significantly too hot in fact. Then I grabbed a sheet of paper I had nearby and used it as a shield, folding the paper around the edge of the folded-over plastic sheet. This worked beautifully, and I experimented with the time a bit. It takes only about 4 seconds to bond the plastic to itself, and the bond is plenty strong. The surrounding sheeting tears before the bond itself does when you pull on it. This leaves about a 1 inch wide seam, but that could be trimmed down. It should also be a snap to put the suspension line inside the seam before sealing it, although hopefully the line would have a higher melting point than LDPE (nylon does, in fact) and wouldn't get damaged appreciably by the very brief heat. Getting the paper away from the plastic cleanly is slightly problematic, but it appeared to work better if you let it cool completely than when warm. Presto- instant balloons, as easy as your iron and ironing board. Of course, working with many square feet of balloon material is going to get awkward, but it should be possible to build pretty good size balloons this way. Next step, cut out some gore patterns and try doing whole seams.

Stew

Stew
I think we both like the idea of making balloons and I believe thats a good thing. Thanks QED for the link and it dosen't mater what team your on or not we all need the help. This little device has a wire over a block and some type of material (non-stick? it looks like some type of cloth) over the wire and its maybe 1/2" it's a clam shell type device. Run's off two AA battery's I put my finger in there and clamped down and sure enough it get's plenty hot!

Monroe

We use an Actaris 400A flow meter. It's mainly used for natural gas, but it's rated for Helium as well. It's a bit bulky, however is a lot cheaper than a conventional Helium flow meters. New ones go for about $500, (Helium flow meters with a high enough flow rates start around $2600).

The calibration chart that comes with it is worthless so you will need to do it yourself. It's an easy process and will need to be done once a year. It's a great way to train the team on the meter.

Used ones are a poor option. You can get then cheap, but you will always be chasing leaks and will need to recalibrate it all the time.

You will need to make a set of fittings to attach it to your helium regulator. We brazen all of ours then cover then with an JB Weld coating.

Metering your helium is the only way to go. You can nail you climb rates and peak altitudes. It also makes the whole fill process a lot easier.

John
JP Aerospace
www.jpaerospace.com