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.

Materials:

-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.

-Scissors

-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):

X Y

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:

bowman_solarballoon_06.jpg

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.

bowman_solarballoon_08.jpg

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.

bowman_solarballoon_12.jpg

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.

IMG_1001.JPG

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.

IMG_0871.JPG

Midway through darkening our solar balloon.

Then, wait for good weather conditions:

CkJ1x7MVAAEathy.jpg:large.jpeg

Two solar balloons and their payloads in storage.

Launching:

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!

Advertisements

Anyone seen a red lunch box with cameras attached?

Catastrophe!  Yesterday, while launching a hydrogen balloon in Chapel Hill, North Carolina, our satellite tracker fell out of the payload.  The camera box, however, cheerfully continued its ascent into the wild blue yonder.  The result?  There is a red lunch box with three cameras in it somewhere in North Carolina.

Detailed description of payload as it will appear on the ground:

Shreds of mylar and a balloon nozzle, followed by a 40′ string, then a plastic parachute (may look like a plastic bag from far away).  Another length of string approximately 10′ long, followed by a red lunch box with “Solar Balloon Payload” and my phone number written on it.  The lunch box has three cameras, one pointing down, one pointing out the side, and a smaller one pointing up.  A milk jug with a sticker saying “Soleil Multimedia” may also still be attached.

The projected landing zone was in north/northwest Harnett County.  I believe that is reasonably accurate.  So our payload, with spectacular footage, is somewhere out there.  I want it back.

Here’s a couple of potential flight trajectories:

Trajectory 1

Trajectory 2

Trajectory 3

If you have any information or know anyone in the region who might be able to help, please contact us.

Jake VI – Successful Test of Cutdown

I’m happy to announce that we had a major success last weekend.  My friend launched a weather balloon carrying a GPS and an Arduino computer programmed to cut the cable on the balloon at 20,000 m (~66,000 ft).  This launch, designated Jake 6, carried out its mission perfectly.  The payload separated from the balloon 20 kilometres above the snow-covered Minnesota landscape, then parachuted down for a safe landing in a tree.  The descent was a little scary as we watched our payload parallel, then cross the Mississippi River!  We knew it was about to land, and it would have been a very poor ending to the day to have it splash down in the brutally cold water.

Click here for a video of the flight!  A good photo taken from the air is below:

IMG_2182

What went right:

-Successful cutdown at 20 kilometers.

-Detailed GPS data of the flight

What went wrong:

-The GPS did not get a fix until about 10 kilometers above the ground, which means we lost some data on the ascent

-The camera was accidentally programmed to take RAW format images, which means it ran out of memory at around 10 kilometres.  Still got some cool pics though!

-Our faithful parachute had to be left behind in the tree, despite my friend’s valiant recovery of the payload box

 

17 Miles above New Mexico – A High Altitude Balloon Flight into Near Space

I’m back after a brief intermission to tell you how to do one of the neatest things I have ever done-flying a camera on a weather balloon into the mid stratosphere, where the sky is black and the horizon is curved.

We are definitely not the first people to do this; in fact it seems like every other day I hear about some high schooler launching a balloon into near space.  But when it comes down to it, who cares how many times it’s been done?  The pictures are spectacular:

Image

A YouTube video with the photo sequence and some cool music:

Want the individual pictures?  Have the entire photo set!

Note:  the photos are released under the Creative Commons with Attribution license.  If you display the photos for anything other than home use, please caption them with “Courtesy of Bovine Aerospace”.

How to do this yourself

The goal is to get a camera really, really high.  You could use rockets, of course, but they are hard to build, very regulated, and have a tendency to explode.  There is an easier way, however-just use a really big balloon.  Here are the things that have to happen for this to work:

1.  You need to lift the camera and protect it during flight.

2.  The camera needs to either record video or take photos every so often.  We did the latter.

3.  The balloon needs to release the camera so you can get it back.

4.  You need to be able to track the camera so you can find it again.

5.  You need to slow the camera on the descent so it doesn’t smash itself into smithereens.

6.  Last but definitely not least, the camera needs to land in the appropriate place (i.e. not water, rough terrain, or a military base).  We had some issues with this…

Materials:

weather balloon

camera

SPOT tracker

GPS cell phone

styrofoam cooler

string

tubing

ripstop fabric

helium tank

zipties

hand warmers

Lifting the camera

We used a Canon A530 camera (around $30 used on Amazon) and we used the CHDK package to make it take a picture every 10 seconds.  If you are not a programmer, either buy a camera that you can set to take a picture every so often or use a video camera.

We bought a Styrofoam cooler to protect the camera, and we threw in some hand warmers to keep it warm (it gets cold up there…like -90 F).  We also had the tracking system in the cooler (more on that later).

We used a 600 gram weather balloon from Kaymont to lift the cooler.  You can fill the balloon with hydrogen or helium.  We used helium.  It’s available from welding supply shops (you can buy 200 cubic feet for around $80, we used about half of that).  Hydrogen is cheaper and will give you slightly more lift but it is harder to find and also extremely flammable.

Here we are with our balloon, parachute, and instrument package:

Once the balloon reaches a certain height (75,000 to 90,000 ft, for our balloon), it pops and the styrofoam cooler starts its descent.

Tracking

You must track your balloon in order to get it back.  Otherwise, unless you are extremely lucky and find your camera or someone else finds it and mails it to you, your camera will disappear into the sky and never be heard from again.

There are a couple of ways to track your camera.  If you have good cell phone coverage where you expect the balloon to land (see section below on landing prediction), you can use a GPS enabled smart phone with the free Instamapper app.  However, if you are concerned that the balloon might land in a place with poor cell reception, use the SPOT tracker.  We used both Instamapper and SPOT.  The cell phone never answered on the way down, so if we hadn’t had the SPOT we would never have gotten our photos back.

If you are into HAM radio, you could also use radio telemetry.  I think there are websites that describe how to do this but I have no personal experience with it.

The Landing

A styrofoam cooler that falls 17 miles will hit the ground pretty hard.  We found this out on the first launch we tried (we think the parachute failed…we never found the camera).  So it is very important to slow your falling camera down with a well made parachute.  You can buy parachutes online, but my friend and his girlfriend ended up making ours out of ripstop nylon.   Here’s a picture of the parachute:

You can use this online calculator to design a parachute that will work for you.  I believe that you want your camera to land at less than 15 mph.  After our first failure I was very conservative and designed ours to land at 6 mph. As I recall the cooler was undamaged (and styrofoam is pretty fragile!).

If you decide to design your own parachute, you can use this website to make a sewing or taping pattern.  I also have a python script that will generate half sphere gores, and when I post it I’ll add the link here.

A couple of parachute construction notes:

Make sure that the parachute is a long way below the balloon.  That’s because the shreds of material created when the balloon bursts can get tangled in the parachute and prevent it from opening…bad news for your 17 mile fall.  Also, put in a spreader (a circle of tubing) near the parachute to make sure it is slightly open, so that when the balloon pops and the whole thing starts to fall, the parachute can open.  Here’s a photo of the balloon in flight; note how far the parachute is from the balloon:

Predicting Where the Balloon Will Go

Balloon flight prediction depends on weather prediction.  If the weather prediction is accurate, then this website will give you a very good idea of where your balloon will end up.  If the weather prediction is not accurate…good luck.  In our case, a snowstorm had just passed, and the jet stream was swinging north.  Since the winds were changing direction so quickly, our balloon actually landed 50 miles south of where we predicted.  That’s why it ended up in the mountains, and that’s why it took a 3 day hike to get it back.

A Final Note on Legality

What we did was legal under FAA regulations.  However, it is your responsibility to ensure that whatever you do is legal.   Find the regulations here.  If you are not sure, contact your regional FAA office.