How to build a high altitude solar balloon

This balloon can deliver a 2 lb payload to 72,000 ft (22 km) and fly for as long as the sun shines.  It can be hand launched by two people without the aid of electricity and lift gas.  The envelope is built from cheap, easy to find materials.  Total construction time is 4-6 hours for a team of two.

It’s best to find a large area, such as a gym, for building the envelope.  Take care to not damage the plastic – I recommend taking your shoes off so that you can step on the balloon material without ripping it.  When it comes time to darken the envelope, I highly recommend *not* doing it somewhere where lots of charcoal dust will cause a problem.  We recently did it in a parking deck, which meant that spills were no big deal and also kept the wind from blowing the balloon around.


-400 x 12 foot sheet of 0.33 mil plastic sheeting (sold as “light duty paint dropcloth” at hardware stores)

-Several rolls of heavy duty clear packing tape, such as these on Amazon.


-Permanent marker

-Tape measure

-Heavy duty string or cord (I use parachute cord)

-Air float charcoal, at least 1 lb

Building the envelope:

This is where you cut the plastic into the required shape, tape it together into a balloon, and check it for holes.  Click here to see a time lapse of this process.

Step 1: Cut the plastic sheeting into five 30 ft sections.  This is around the 10 second mark in the video above.

Step 2: Unfold them until you have five 30 x 12 rectangular sheets of plastic.  This is around the 15 second mark in the video above.

Step 3.  Fold each sheet once across the longer section and once across the shorter section.  Now you have five 15 x 6 ft sections.  This is between the 15 and 25 second mark in the video.

Step 4.  Lay the five sheets on top of each other, all facing the same way.  Find the corner that forms the center of the original sheet (this is where the fold seams all meet each other).  That corner is in the video around the 28 second mark, next to the guy in the blue shirt.  We spend

Step 5.  Consider the corner described in the previous point as the origin, the long part of the sheets as the X axis, and the short part of the sheets as the Y axis, draw the following points using a permanent marker (units in inches):


0 72

18 71

36 68

54 64

72 58

90 51

108 42

126 33

144 22

162 11

180 0

These points describe a half gore pattern, which is how we turn two dimensional objects (plastic sheets) into a 3 dimensional object (a spherical balloon).  Here, it happens to be a sine curve.  This is from the 40 to the 50 second mark in the time lapse.

Step 6:  Carefully insure that all sheets in the stack are lined up with each other (from about 28 to 40 seconds in the video).  Then, using a pair of scissors, carefully cut along the curved line defined by the points drawn on the top sheet (50-52 second mark).

Step 7: Unfold the sheets; you should have 5 diamond shaped ones.  These are gores, and they form the envelope of the balloon.  The other, roughly triangular pieces of plastic are trash (52-54 second mark).

Step 8:  Tape one edge of the first gore to one edge of the second gore using packing tape.  The seam should be centered in the tape, with no gaps between successive pieces of tape.  We have one person hold the two sheets together and the other tape them together, see photo below:


Taping the gores together.  If you have more people, you can have multiple teams going at once!  Photo by Mary Lide Parker, UNC Research Communications.

Step 9.  Add the next three gores successively, to make an ever larger sheet of plastic.  Finally, tape the two ends of the sheet together: you’ve now made a ball a little more than 19 feet across (the envelope of the balloon!)  This process takes up from the 1 minute to about the 2 minute mark in the video.

Step 10:  Find one of the two “poles” of the balloon (where the taped seams all meet).  Cut the pole off to make a hole about 5 feet across.  This will become the bottom of the balloon, and allow you to fill it with air.  We do this at 2:14 in the video.

Step 11:  Carefully tow the balloon back and forth, holding the hole open.  It will begin to fill with air.  This is from 2:15 to 2:17.


Filling the balloon with air prior to checking for holes.  Photo credit: Mary Lide Parker, UNC Research Communications.

Step 12:  At this point, it should be pretty clear whether or not you built the balloon correctly.  If everything looks good, send a brave soul inside to check the envelope for holes (gaps in seam tape are the most common culprits).  Someone on the outside can fix the holes as they are found.  Be careful, of course, since the air supply in there is finite.  This is from 2:18 to 2:36 in the video.


Checking each seam for holes.  Photo credit: Mary Lide Parker, UNC Research Communications.

Step 13:  Deflate and pack the balloon.  Start from the pole opposite the hole, and slowly push air towards the open end of the balloon.  Don’t go too fast or you’ll pop sections of the balloon.  It’s pretty simple to then stuff the balloon into a big garbage bag for storage.  This is from 2:37 to the end of the video.

Rigging the balloon:

The open hole on one side of the balloon is very weak and susceptible to tearing.  Also, it does not provide any means of attaching a payload.  Thus, we need to reinforce it and provide a way to attach our equipment.

A simple way to do this is to run some tape around the bottom, poke some holes in the tape, attach some string, and tie your payload on.  Our first versions had this system, but it was not ideal; in fact it is probably why we had an “unscheduled rapid disassembly” at 72,000 ft last May.

A much better way is to tie a length of strong cord (parachute cord, for example) into a loop slightly larger than the opening of the balloon.  Pull the opening through the loop, fold it around the loop, and tape the edge of the opening to the outer envelope of the balloon.  This provides a very strong lining system for the bottom.  A payload can be attached by tying guy lines onto the cord loop.  I believe the best place for these guy lines is right at each seam, since the seam tape provides a means of distributing the load along a relatively strong portion of the envelope.  The photo below shows one edge of the balloon with the parachute cord folded in, as well as one payload attachment string.


Darkening the envelope:

This is the most fun part (besides launching).  Find a place that is protected from the wind but will allow you to make a big mess.  As mentioned earlier in the post, an indoor parking deck is ideal.

Unpack the balloon and lay it out on the ground. Throw a generous quantity of air float charcoal into the open end, and shake it all the way through the balloon.  The charcoal is so fine it will coat the interior of the balloon, changing it from white to dirty gray.


Midway through darkening our solar balloon.

Then, wait for good weather conditions:


Two solar balloons and their payloads in storage.


The launch procedure is simple: tow the balloon back and forth until it fills with air, attach the payload, let the whole thing heat up for a bit, and off it goes.   Here’s a video of us doing it.  Simple, right?  No.

Actually, launching solar balloons is hard.  It’s a lot harder than helium balloons, since ground conditions are much more restrictive.  With this in mind:

An ideal day for solar ballooning has clear skies and calm ground winds.  This is actually pretty rare, and you may have to wait several weeks for an opening.  If you start to get impatient, keep in mind that even winds barely strong enough to move leaves can make handling a 20 foot tall balloon very dicey.  Early mornings (just after dawn) are best.

An ideal site for a launch is a large open field, where slowly rising balloons will not get caught in trees, power lines, etc.  An alternative is a parking lot between tall buildings, since wind tends to go around them.  This is risky, though, since the balloon can still hit and potentially snag on them.

Finally, if you are planning on recovering your payload, realize that the balloon will fly until the sun sets.  This means that even a 10 mph wind can carry the balloon 120 miles, assuming 12 hours at float.  Many times, the winds in the upper troposphere/lower stratosphere are much stronger.  Careful consideration of the wind profile from 0 to 100,000 ft above sea level is thus imperative before attempting a full day flight with payload recovery.

Happy ballooning!


How to build and launch candle balloons

Birthday candle powered hot air balloons are a lot of fun. Sure, you can buy kits on Amazon. But there’s nothing better than building the balloon yourself and watching it drift off into the night sky, finally burning out miles away and thousands of feet in the air. This post provides an equipment list and instructions for making the candle balloons in the video below:

Equipment List:

0.31 mil clear plastic paint dropcloth (get it at Home Depot or any large hardware store)

one pack of birthday candles

another spare candle

drinking straws

scotch tape

paper clip or sewing needle

clothes iron


How to Build the Balloon:

1.  Cut a 6 x 6 ft (~2 x 2 m) square of drop cloth.

2.  Fold it in half lengthwise.

Folded over piece of plastic ready to be sealed with an iron.

Folded over piece of plastic ready to be sealed with an iron.

3.  Seal the top and side by melting them together using the iron.  Leave the bottom open.  It may take a bit of adjusting to get the iron hot enough to weld the plastic together but not so much that it melts.  If you’ve not done this before, I suggest practising on a spare piece of plastic.  Once you’re done with the balloon, it will form a cylinder 6 ft high and about  2 ft in diameter.

4.  Make a frame to hold the candles by taping straws together to make a “+”sign.  Disassemble the paper clip to make a pin (or just grab a sewing pin).  Push the pin through the centre of the frame.  This pin will hold the candles onto the frame.


5.  Make a double row of birthday candles (or just take the back off the pack of candles, leaving them lined up in a convenient package).  Drip wax from the spare candle onto the rows of birthday candles to bind them together.  This pack of candles is your heat source.  I call it an “engine” out of habit.


6.  Attach the frame to the balloon (I usually poke holes through the plastic, then tape the frame to the bottom of the balloon on the outside).  Stick the engine on the pin.  The balloon is ready to fly!

Launching the Balloon

Call a friend and wait until the winds are very light.  In general, the best policy is to make sure that the wind is imperceptible and that it is not disturbing leaves on trees.  Go to a wide open area without nearby houses or isolated trees.  I’ve lost more balloons than I care to count in trees – and nearly hitting a house is almost as nerve wracking as explaining to the owner why his house burned down.  Thankfully, I have not had that experience!

Have one person hold the balloon up and another lay on the ground.  Light the candles, being sure to keep the plastic off the flames.  The balloon should reach neutral buoyancy in about thirty seconds.  Gently release the balloon when it is positively buoyant.  Do not try to fight the wind – if it starts blowing, walk with the wind to avoid it pushing plastic onto the flames or collapsing the balloon entirely.

Having hot wax dripped onto your jacket's just part of the experience!

Having hot wax dripped onto your jacket’s just part of the experience!

Safety and Legal Considerations

There are county level regulations in some parts of the USA that prohibit candle balloons.  The FAA regulation on unmanned free balloons permits the operation of balloons with payloads less than 4 pounds without restriction, but there is a catch-all clause stating that the balloon must not jeopardize health and safety.  So if the balloon starts a forest fire, burns down a house, or even causes a public disturbance, then you are liable.

I have had the police called on me once.  The homeowner who placed the call thought we were committing arson.  Once I explained what we were doing, the officers were perfectly fine with it, but they did point out that they’d be getting in contact if there were any house fires that night.  Our very first launch started a small fire when the balloon got stuck in the tree and the engine fell onto the ground.  I have seen another, poorly constructed balloon land in a parking lot when the frame fell apart.  Also speaking from personal experience – never, ever use the kind of candles that don’t blow out!  They keep going all the way down.

The take home message:  use common sense.  Launch after rain or snow.  Consider where the balloon may land if something goes wrong.  Remember that most people who see these have no idea what these balloons are, and they tend to assume the worst.  In any case, treat the balloons like fireworks, and you’ll have no problems.

10 ft diameter solar balloon launch

A few weeks ago some fellow grad students and I successfully launched a 10′ spherical solar balloon from southern Chapel Hill, North Carolina.  It carried 3 messages in bottles and presumably landed in the ocean, a week before superstorm Sandy.

I will describe how I made the balloon at the bottom of the post.

I had a couple of objectives for this launch.  First, I wanted to test an interior radiator design.  I suspended a black Nordstrom Rack dress cover (courtesy of my wife) inside the envelope, with the idea that it would absorb sunlight and radiate heat directly into the balloon.  This solves the problem of using a black plastic (or darkened) outer envelope, where a lot of the solar radiation is lost to the outside of the balloon.  Here’s a picture of the balloon with the radiator inside:

Unfortunately, the balloon did not sustain lift with the radiator suspended inside.  I think the surface area was too small to heat up the balloon.  It was also hazy right around dawn, so perhaps the solar flux was not high enough.  Either way, since my Ph. D. advisor was among my audience, I decided I needed to make sure this thing flew.  To that end I did my traditional charcoal dust balloon darkening technique (see the video above and also my post here).   That worked a lot better:

Originally I had 10 bottles that I wanted to lift (recovered from our unsuccessful launch a few weeks before, see the rather amusing photos here).  However, the balloon didn’t have enough lift, so I ended up removing 7 bottles and only lifting three.  Still, the balloon crept upwards and right over a soccer game, whereupon both teams stopped the game and ran to the fence to watch it drift overhead:

Unfortunately the balloon was not tracked, so I have no idea where it went.  I hope it landed in the ocean, and that the messages in the bottles were deployed.  If they were, then they probably got some serious mileage because Hurricane Sandy tore up the ocean barely a week later.  Either that, or the balloon is stuck in some pine tree in Virginia.  Since I have not gotten any replies from my bottles, I really can’t say at this point!

How I made the balloon:
Supplies: 0.31 mil paint dropcloth (from Home Depot), airfloat charcoal powder (, also can get from pyrotechnic supply shops/websites), string, paper bag, bottles, scotch tape, duct tape, clothes iron, hair dryer

First, I cut a spherical gore pattern from the paint dropcloth (find a pattern here).  Then, I used a clothes iron to weld the plastic gores together.  By adjusting the heat of the iron, you can find a “sweet spot” where the two pieces of plastic melt together without burning through.  Make sure the iron does not have water in it for this step.  Once you’re done, patch any holes with scotch tape.

Once the balloon envelope was complete, I cut about a 6″ hole in the bottom, reinforced it with duct tape, and tied a string to one side for the payload.  I actually recommend making a hoop of tubing to keep the bottom open as opposed to tying  a string to one side so that the balloon is more balanced-but I was in a hurry.  I attached a paper bag to the other end of the string and tossed the bottles inside.  My idea is that the paper bag hits the water, becomes waterlogged, and sinks: the bottles then float out the top and drift off.

On launch day, I filled the balloon with air using a hair dryer, then added about a quarter cup of airfloat charcoal to darken the envelope, rolling the balloon over and over to distribute it (see the beginning of the video). Then I put the hair dryer on high heat and injected hot air into the balloon.  After a few minutes of holding on to make sure it was well heated, I let it go.  I had to jettison 7 of my 10 bottles, but eventually it lifted off with three bottles on board, heading East.  That was the last we saw of it!

First Message in a Bottle found from Solar Balloon!

A couple of weeks ago I posted about my launch of a large solar balloon, called “Jake III”, from Norwood, Massachusetts.  Jake III was carrying nine messages in a bottle held together (and to the balloon) with a melted sugar seal.  I had the messages in bottles idea when I realized that prevailing winds should carry the balloon over the Atlantic.  The sugar seal was designed to dissolve on contact with seawater; the idea being that each bottle would drift off on its own.

Well apparently it worked!

At 6 AM this morning, a man walking his dog on Humarock Beach in Scituate, Massachusetts, found one of the bottles.  It was my wife’s bottle, in fact, and he emailed her this morning.  The bottle came ashore after a week of exceptionally high tides and stormy weather (his deck was damaged by waves). 

Although I was hoping for a little more distance than Scituate, I am very happy that someone found a bottle.  This means both that Jake III did land in the ocean (since it wasn’t tracked, I wasn’t positive that it had) and that the sugar seal successfully detached the bottles from the balloon and each other.

Jake III was likely in the air for at least 12 hours, so I’m at a bit of a loss to explain why the bottle was found so close to the launch site.  I have a couple of ideas:

a) The payload fell off somewhere over Massachusetts Bay.

b) The entire balloon went down.  Maybe the patchy high clouds did it in, or part of it ripped open.

c) It wasn’t very windy, so the balloon didn’t go very far.

d) The balloon went over 60,000 ft high, where the winds were predicted to be going east-to-west (so it went out over the ocean, then came back towards land)

e) The balloon landed hundreds of miles northeast, and the near shore southern current off New England and the recent nor’easter pushed it all the way back to Massachusetts.


I can eliminate c) pretty easily.  Even in a 10 mph wind, the balloon would have flown 120 miles (90 miles offshore).  Plus there was an 80 mph jet stream that day.

a) is possible.  I’m not sure how melted sugar stands up to loads.  I doubt b) happened though.  It takes a lot to rip a balloon suspended in air (major wind shear).  Plus if it had come down just offshore we’d probably have picked it up with our tracker.

d) would be awesome, but there’s no way to know.  Plus it seems improbable that the balloon would come right back at us.

This leaves e).  According to current maps and how the winds probably were this week, I’m pretty sure e) is the answer.  The jet stream was going to the northeast on launch day, so the balloon probably came down off of Labrador, and the ocean current brought the bottles back to Massachusetts.  I was hoping to make it to the Gulf Stream, but that looked unlikely even before the bottle was found since the winds were not due east.


Here’s to hoping for more bottles, this time a bit further afield!

Jake III – The successful launch of a 20 ft solar balloon

Jake III Solar Balloon Launch!

Last Friday (May 18th, 2012), my coworkers and I successfully launched a 20 ft diameter solar balloon from Norwood, Massachusetts (42.173073,-71.213297)..  It had an Android cellphone on board with the free Instamapper app for tracking purposes.  It also had a group of 9 messages sealed in bottles, since I expected the balloon to land in the Atlantic Ocean.  These bottles were attached to the balloon using a caramel seal (a toilet paper tube filled with melted sugar), which should have dissolved when it hit the water, allowing the bottles to drift off into the current.

What is a solar balloon, you ask?  It is a hot air balloon heated by the sun.  That means it requires no fuel; the sun heats up the air inside the balloon, and the whole thing lifts off.  I will describe how I constructed Jake III later on in this blog post, for other good websites check here and here.  The design that inspired Jake III is here.

Below is a photo of Jake III heating up before launch:


Launch sequence:

After I finished making Jake III, we had two weeks of cloudy, windy weather.  Go figure.  But we finally got a four day stretch of clear, calm weather.  My coworker Josh Simpson and I picked last Friday because the weather report said 0 mph winds at 6:00 AM.  We sent word out to our coworkers, and got quite a group together considering we were meeting at 5:30 AM.

After scoping out the winds (very gentle and from the southwest), we taped the Android right to the bottom of the balloon and laid it out on a couple of tarps.  I tossed charcoal powder inside the balloon to darken the clear plastic fabric, and Jason Chrzanowski fired up his leaf blower for inflation.

After inflating the balloon about halfway, we gave it about 20 minutes or so to heat up.  I was concerned because I have never actually launched a solar balloon before, but after a while it was clear that the air inside was heating up.  We added a bit more air and soon the balloon began to rise.

Jake III starts to become buoyant:


Once the balloon started to rise, all the charcoal powder tumbled out.  This means that you should really add the charcoal powder prior to launch (we were hoping the leaf blower would distribute it but that didn’t pan out).  Still, part of the balloon was dark.

The balloon ascended to the end of the 30′ string I had attached to the payload, and we began to walk it out into the park.  After a couple of minutes more, the balloon had gained enough lift to pick up the payload.  I let it go and walked beside it for a while, and it slowly gained elevation.  It narrowly missed a light pole, and kept going up and up.

Here’s Jake III flying under its own power:


We watched it drift south for a while, drift back north, and then finally catch some higher winds and take off to the southeast.  Our tracker was able to locate it until it got up to 9,000 ft, after which time it was above cell phone reception.  When we last heard from it, it was rising 300 ft per minute, moving at 18 mph to the southeast.  We expect that it caught the jet stream (80-100 mph that day) and was taken far out to sea, where it landed after sunset.  But we’ll never know for sure unless someone finds a bottle and writes us back.

Here’s Jake III in flight:


How I built Jake III:

Cost:  around $50.


9 x 400 ft roll of 0.31 mil clear painter’s drop cloth (get it at Home Depot for about $25)

Make sure it is 0.31 mil.  This is the thinnest plastic you can buy.  It is comparable to the fabrics used for scientific balloon launches.  Do not try to use trash bags-you will spend weeks ironing them together, and the balloon will be weaker anyway.

1 Jar of Artist’s Charcoal Powder (got it off of




Duct Tape

Scotch Tape

Small plastic tubing

Clothes iron

We also used a smartphone for tracking, but it didn’t work as well as we’d hoped because it only tracked below 9,000 ft.  If you do opt for a smartphone, use the app I mention at the beginning of the post and make sure you use a phone on the website’s list.  Not every smartphone will work.  My coworker James Roehrig’s android was up for renewal, so he sacrificed his old phone to our balloon.  Obviously we got the phone for free, so I didn’t include it in the cost, but I believe you can get one that will work for around $50.

Construction of the Balloon Envelope:

Instead of using the tetroon designs that are common on the Internet, I made a spherical balloon by cutting gores from the plastic I bought.  You can use a gore pattern for a parachute (for example here); since a parachute is a half sphere.

If you are making a 20′ balloon, you’ll probably need help, and you’ll need a large space, like a gym (one gore for a 20′ balloon is around 33 ft long).  I recommend cutting each length of plastic from the drop cloth sheet and folding it twice; once lengthwise and once crosswise, then laying each folded sheet on top of each other.  Then draw the gore pattern on the top sheet and make a single cut.  I ended up with 7 gores that I could just unfold into their final shape using this method.

Next, you have to weld the gores together.  You can do this in a smaller space as long as you keep all your pieces of plastic organized.

I use a regular clothes iron to weld plastic.  You will need to practice and adjust the iron settings before the plastic will weld correctly.  Too hot, and the plastic will melt together and stick to the iron; plus the seam is very weak.  Too cold and it won’t stick at all.  Just right, and the two pieces of plastic will hold even when you pull pretty hard.  One piece of advice:  make sure you’re on a hard floor.  Carpet and ironing don’t mix.  Take the water out of the iron and use the iron edge rather than the middle.

A lot of people apparently use tape to attach the gores together.  This is probably faster but weighs a lot more. Also tape can make a huge mess if it comes undone and gets snarled in the rest of the balloon.

When you’ve ironed the final gores together, weld the two edges of the giant sheet of plastic you’ve made together, and now you have a truly massive bag-your balloon.  Try not to trap any air because it makes the balloon a lot harder to store.

Finally, cut a circular hole in one part of the balloon for the air intake.  I recommend doing this at one of the poles, where all the gores meet up.  This is a natural weak spot, so using it removes one place where the balloon could rip open.

I reinforce this opening by making a
loop of tubing, pulling the balloon fabric through, and folding it back on the outside of the balloon, then duct taping it on the outside and the inside.  This gives the opening enough strength to hold a substantial payload without ripping.

Here’s a picture of the opening (in the red duct tape).  The balloon is packed and ready to go!


Making the payload:

A payload can be anything you want, but you absolutely need weight on the bottom to keep the balloon opening pointing down, so that the hot air is trapped in the bag above it.  For Jake III, I probably could have put a pound or two and it would have been fine.  I am not sure what the maximum payload I could have lifted is, but I expect I probably could have gotten around 10 lbs off the ground.  Of course, the bigger the payload, the lower the final altitude is.  Also, the FAA regulates payloads above 4 pounds, read the regs here and make sure you understand them.

However, since I was planning to launch it into the ocean, I thought it would be neat to have my coworkers and their children write messages in bottles (my wife and I contributed some too) and fly them on the balloon, so that when it landed they would drift off and be found someday.  To this end I developed a payload release mechanism that (I hope) did the trick.  I tied a string to a cardboard toilet paper tube for the balloon attachment, and then draped another string loosely inside the same tube for the bottle attachment.  I then filled the whole thing with melted sugar and let it harden.  My thought is that the water dissolves the sugar, and the bottles float off.  This is based on how underwater seismographs are deployed.  Of course, I won’t know if it worked or not unless at least two bottles are found unattached to each other!  Here’s a photo of the payload setup:


Making the balloon dark:

I used artist’s charcoal powder to coat the inside of the plastic.  Jake III wasn’t too dark because I did it on launch day, but a prototype I did worked really well when I spent 10 minutes or so flapping the powder inside before I dumped it back out.  The prototype was 10′ in diameter and easily picked up a 2 pound bucket.

Launch day:

Obviously it has to be sunny, otherwise the balloon won’t heat up and fly.  But there also has to be absolutely no wind.  Wind ruins your day in a hurry.  First, it makes it harder to inflate the balloon because the wind just pushes the air out again.  Second, solar balloons take along time to climb out of tree range.  The more wind, the more chance the whole thing flies into a tree.

If leaves are rustling, there is too much wind.  Go back to sleep.

Also, you need a good inflation method.  A leaf blower works great, especially a gas powered backpack mounted one like we used.  Exhaust from vacuums work also, but the exhaust tends to be hot so your balloon might take off pretty quick.  Hair dryers are great for smaller solar balloons but it would take a very long time to inflate a Jake III sized balloon with one.  It took 10 or 15 minutes of continuous leaf blower action, and a leaf blower moves a lot of air even on idle (we didn’t crank it because I didn’t want to pop the balloon).

Make sure you are in a big open space, and that you are at the most upwind portion of it.  Even when you can’t feel any wind, the wind is going at about walking pace.  You’ll need the space for the thing to take off.

Inflate, wait for it to heat up, let it go, and enjoy the show!

Note: although these objects are legal when subject to the regs I linked to earlier, do realize that you are liable for injuries or destruction caused by something you launch.  Keep it away from airports.  I even notified the local airport so they could give pilots a heads up.  Also, secure the payload so that it doesn’t drop off from 20,000 ft and put a hole through someone’s car.  Finally, what goes up must come down; spare a thought to what the balloon might land on.  That’s why I chose the Atlantic Ocean.