A "Typical" balloon mission/Answers to Frequently Asked Questions

Some thoughts on building, flying, and recovering high-altitude balloons.




Our group didn't have the luxury of working with another balloon group to "learn the ropes". We started by reading materials available on the web put out by the government and other groups. Some we'd like to recommend are: There are many others, check AMSAT's Balloon Page for more.

Here's our contribution to the cause:


While there's not really a "typical" mission (every one is different in some way), there is a general pattern and flow to how our group goes about doing balloon flights. Here's a rundown of the way things usually go:

Planning meeting:

Every mission starts with the group getting together and brainstorming about what the next mission should be, what it should do, and how we are going to do it. The idea behind brainstorming is that you don't squash other people's ideas or discuss them, you just keep a list of everything everybody throws out. This can lead to some very creative ideas, and people feed off each other's creative energy. When the brainstorming is over, then is the time to go back over the list and discuss things like complexity, cost, time to prepare, weight, etc. At the end of two or three hours, we have the basic idea of the mission hammered out, and have decided who is going to be responsible for what elements of assembly, testing, etc.

Procurement:

The next phase is getting the materials together that will go into building the gondola. If you can't find people who own needed equipment (or don't want to risk it on a balloon flight), it's time to get your checkbook out. Hamfests are an excellent place to buy needed equipment like radios, connectors, cables, etc. Some things you just have to buy (balloons, helium, batteries, film, etc). Some things you will only need to buy once (i.e. pressure regulator, filling hose, filling adapter), so their cost is not recurring. Don't forget little details! I forgot to bring a single hoseclamp on one mission, and we nearly had to scratch it at the last moment (luckily the guy who owned the land we were launching from had one). Making a checklist of all needed materials and parts is a very good idea!!

Construction:

Now we can finally get started building. The biggest enemy of balloon work (other than bad weather) is weight. The lighter you can make the gondola, the better. Don't get all wrapped up in shaving fractions of a gram off the payload, but make alterations when it will actually count. For instance, we take the lithium battery packs we buy from surplus apart and build our own flight packs. This reduces the number of cells and saves a lot of weight. If you're flying 35mm (or other) cameras, remember that plastic cameras are not only cheaper than metal bodied ones, they weigh a lot less (and they self-insulate better against the extreme cold at high altitude). For building the gondola, we usually stick with pink foam insulation sheeting which is available at building supply centers for a very reasonable price. Foam is lightweight, easy to work with simple tools, strong, insulates well, absorbs impact during landing to help protect your equipment, and floats in water. To make attachments, you can use silicone adhesive (like 'liquid nails'), duct tape, hot glue (although it can cause the foam to melt), or mechanical connections like string or sishkabob skewers. It's a good idea to keep your building materials bright and easy to see. This not only helps locate the package on the ground or in a tree or bushes, but it also helps pilots see and avoid the thing. Some of our group dislikes the pink foam (not a very manly color I guess), and have painted or covered some payloads in fluorescent orange or red/ yellow colors. You can also use mylar sheeting to cover the box, which helps reflect heat and give the box a cool, 'spacecraft' look.
Keeping things neat and organized while building is a very good idea. It makes troubleshooting later a lot easier. It's a good idea to take photographs of the process too, to document things and in case you lose the gondola, you at least have something to remember it by :).
We try to keep our gondolas modular in design. This makes it a lot easier to build future gondolas. For instance, we mounted our main flight microcontroller and power regulators in a box with interface and programming connectors on the outside. We don't have to worry as much about damaging it that way.
Anchor components! We lost two cameras on one mission because we forgot to put in two simple string tethers. The payload splashed down in a lake, an access door sprung off, and the cameras went in the drink, never to be found. The rest of the components were held in by tape, terminal strips, and hotglue and were not ejected.
As for making the box super-insulated, don't worry too much about it. A few air leaks are inevitable, and some of our gondolas have had huge gaps in them and didn't freeze anything. Some groups even reported overheating problems with their equipment since even though it's really cold up high, the air is so thin it acts like a vacuum thermos bottle and kept in all the heat.
During building, the group keeps an eye on the targeted launch date decided on during the planning meeting. If things go slower than expected, we can push the date back at this point and make sure everyone knows (communication with all team members is vital all throughout a balloon mission).
Things we try to include on every flight:
Some things like radar reflectors and parachutes are required by the FAA. Be sure to read the FAR 101 regulations and stick to them! You can get creative, however. One very serviceable parachute was made from a broken golf umbrella rescued from a dumpster. We pressed in some grommets and discarded the frame, and the 'chute worked well for several flights. Our radar reflector was made from some discarded poster board, aluminum foil, and hotglue.
Lithium primary batteries. These work better in the cold and have the best power-to-weight ratio of all available suitable cells. Our cameras use alkaline cells, since we don't like to modify the cameras any more than necessary (the lithiums are too big to fit, and are the wrong voltage in any case). One caveat: lithium cells have very low internal resistance. This means that, when shorted out, they can dump a tremendous amount of current through a system and easily start a fire. When building new battery packs with lithium cells, always include fuses in them! Putting the fuses in the packs themselves makes them safe even if the wires get pulled out and jumbled around in a rough landing.
GPS/APRS tracking. Our early balloons were tracked by directional antennas. This can be a real pain, let me tell you! We almost feel like we're cheating using GPS, but with the cost of the gear, it's the only way to go these days.
Audio beeper. This is a speaker hooked to the flight computer. The computer beeps it when it's not doing anything else. This lets us know the computer is running. It also helped us find one gondola that was stuck in a tree. Remember, DF and GPS will only get you so close, and if the package is in a tree or bush, you might walk right past it.
Sign on outside of gondola identifying it as a harmless radio experiment and giving details on how to contact us to return it. Our first gondola to be recovered had only one sign, and that ended up sitting face-down in the grass. The rancher who found it couldn't see the sign and thought the package might be a bomb. Two of her hired men wanted to get their guns and shoot it (I'm not kidding). Luckily our chasers happened on the scene in time and rescued the gondola. We now put two signs on our gondolas.

Testing:

Usually, a lot of testing has gone on during construction, but it is a good idea to get the whole shebang running to check for things like interference problems and improper wiring. Anything designed and built by more than one person will always need to be checked. This is also the phase where the finishing touches are put on the flight software. Things like when the cutdown mechanism will be triggered and when photographs should be taken are put in now.
If equipment doesn't work on the ground, it sure as heck won't work at 90,000 feet. Low power transmitters that have limited range on the ground will have much larger range when airborne. When you get everything working, it's time to load the flight batteries to make sure you don't have a dead or weak cell (it can happen), and put your new camera batteries through a tester before putting them in for the same reason. I've seen one dead alkaline and two weak lithium cells in just over a year of balloon work, either one of which could have caused big problems had they not been caught on the ground.

Weather check, FAA:

We try to keep an eye on the weather all the time as we progress toward launch day. There are all kinds of excellent data available on the web in terms of ground and upper-air forecasts. The weather has to be good for a balloon launch: the FAA won't let you launch into more than 50% clouds, and trying to launch in a wind higher than 15 mph is not a task for the faint of heart (we have a rather amusing tape of our group filling a balloon in a gusty 20 mph wind. I'm desperately holding on to the filling adapter, which has pulled me over onto my back, and the balloon is trying to gobble up the balloon minders and battering them mercilessly. It's funny to watch now, but it was a real pain at the time, and I'm still amazed the balloon didn't burst).
If the weather for launch day looks good, and we haven't done so already, it's time to file the NOTAM with the FAA. We try to get the NOTAMs filed 3 days in advance, check the FAR 101's for required lead-time. (The FAA says 6 to 24 hours in advance of flight time, but may be more flexible if they're not busy). We are lucky enough to have a member of our group who is an air traffic controller. We just email our flight info to him and he files the paperwork for us. If you don't know any FAA folk personally, just get the phone number of your local FAA flight service station and they'll tell you what to do. If we have two possible launch days and the decision is to be made the morning of the launch, we file two NOTAMS, one for each possible launch window. When we know which window will be used, we cancel the unused one. NOTAMS need to be canceled at least a half hour before they become active (one hour or more is better).

Launch day:

Woo hoo! It's time to have some fun. But first, it is imperative to look after the details. Two launches were put in jeopardy when your author forgot a hose clamp and a nylon cable tie at inopportune times. Now we have a standard kit we bring on each launch. It includes:

Other needed things:
Our electronics guy usually brings extra tools and a multimeter in case he has to do last-minute troubleshooting. Chasers need to look after their own gear. Some includes:
Everyone is encouraged to fill their fuel tanks before going out to launch. Balloons can move very fast when they get into the jetstream, and while you can't disobey the speed limit to chase them, you will waste time stopping to fill up on gas. We do a last-minute weather check before heading out to the launch site. It is very important to not get caught up in 'go fever' at this point. If the weather is not good, we don't launch. It can be stressful with a bunch of people waiting on you to make the call, but it's important to make the right one. If we do cancel, we call the FAA to cancel the NOTAM, then call the hams and chasers to let them know we're postponing.
If the weather ok, it's go-time. We find a suitable location at the launch site for filling. This can be just about any relatively flat surface with no nearby obstructions that might damage a balloon (trees, powerlines, etc). We have on two occasions done our filling indoors in a farm shed with a very tall garage door. This works very slick, but care has to be taken when removing the filled balloon to the outdoors for launch not to bump it on anything. One note here, we always use helium for our balloons. This costs us about $40 extra per launch, but eliminates the risk of fire or explosion. If you use hydrogen, don't fill your balloon indoors! As long as it doesn't pop, you're fine, but if it does, the hydrogen would mix with the air inside the building and the possibility of explosion and fire are substantial. If you use hydrogen, always fill outdoors!!
We spread the plastic tarp out to protect the balloon from the ground. The helium tank is carried from the vehicle to the tarp and laid on its side at one edge. You should always lay your tank down before unscrewing the safety cap. The biggest risk of handling high-pressure inert gas is having the valve break off if the tank falls over. The tank then becomes an unguided rocket with about 1000 pounds of thrust and will do an unbelievable amount of damage to anything in its way. The safety cap prevents this, so leave it on until you have the tank laid down and braced, if necessary (to keep it from rolling. Use sandbags, rocks, wooden doorstops, or whatever is handy). If you're using hydrogen, make sure at this point that everyone knows there is no smoking from now until the balloon is released! With the tank secure and the cap off, the tank valve is then opened just a bit then quickly shut. This blows out any crud that might be in the valve and keeps it from being forced into the regulator. We then get the regulator out of the 'balloon bag' (duffle bag that carries all our filling equipment. You can't be too organized!) and attach it to the cylinder. Our regulator has a big wheel that allows us to attach it without a wrench, but we still bring one in case the cylinder cap is stubborn. With regulator securely in place, hose and adapter attached, and adapter valve shut, we open the tank valve fully and check the pressure. It should be between 1800 and 2200 psi.
Now the balloon is removed from its protective plastic bag and laid out along the tarp. All handling of the balloon is done by people wearing gloves. Things like watches and hats with sharp stuff on them are removed to protect the balloon. The balloon nozzle is slipped over the filling adapter and is secured in place with the hose clamp (we've now tethered the hose clamp to the adapter with some string so we always know it's there when we need it). The valve on the adapter is opened slightly, and when we're assured the gas is flowing into the balloon properly and the balloon isn't sticking to itself, the valve is opened fully. The water ballast jugs are then tied to the filling adapter body to keep the balloon in place should the pneumatic quick-connector come loose.
Balloon filling with our rig takes about 30 minutes. While this is going on, others are preparing the gondola. Cameras are loaded with film, tested, and installed. Various payload electronics are activated, and the main computer and transmitter switched on. GPS and APRS are tested, as well as the audio beeper.
Another group prepares the tether. The tether from the balloon to the cutdown device is made from cotton string. Its' relatively weak breaking strength keeps the FAA happy. The other end attaches to the metal ring on the cutdown device. The ring is loaded into the device and the device is locked down. The cutdown device is mounted in the center of our parachute, and uses the 'chute as part of the suspension train. At the bottom of the parachute shroud lines we attach the radar reflector, strobe (where applicable), and one end of a bungee loop. The other end of the bungee loop is attached to the top of the gondola via its connection harness. The bungee serves as a strain relief should the balloon encounter strong horizontal wind shear conditions (it keeps the tether from breaking). The cutdown device is plugged into the flight computer.
While the balloon is being filled, one balloon handler sits on the ground holding the filling adapter. If there's any wind at all, another group of handlers with cotton gloves in place stand around the balloon and hold it upright, so it doesn't bounce on the ground and damage itself.
By this time the gas should be in the balloon. Most of our flights have used all the gas in the cylinder. This gave us at least two or more pounds of positive lift (balloon lift minus payload weight), and assured a rapid ascent and relatively low burst altitude. This helps keep the landing site a manageable distance away, as well as getting us above 60,000 feet as quickly as possible (above FL600 airspace is not controlled). When the tank gauge reads zero, it's time to seal the balloon and attach it to the train. (Note: if you don't want to use all the gas, you should use a calibrated ballast weight. If your payload is 6 pounds, and you want one pound of positive lift, fill a plastic jug with 7 pounds of water and tie it to the filling adapter. When the balloon starts to lift the jug off the ground, you have the lift you want.) One balloon handler squeezes the nozzle just at the base of the balloon tight, and folds it along its' length. This keeps the nozzle tube the same length, but reduces it from a tube to a string of rubber 'cord' about the diameter of your little finger. While the first guy holds this, a second handler wraps a nylon cable tie around it and cinches it down, sealing off the nozzle. We tried string for our first mission, but cable ties work a LOT better, you just have to be careful not to poke the balloon with them. When the first tie is in place, a second one is added about three inches below it, near the filling adapter. The balloon end of the suspension tether is tied to the nozzle at a point between the two cable ties. Now it's time for the exciting part. The hose clamp is loosened with a screwdriver while the first two handlers keep a firm grip on to the nozzle. With the filling adapter is disconnected, The nozzle is folded over width-wise, so that the two ties are next to each other and the nozzle forms a U-shaped section, with the tether tied to the bottom. We then attach a third cable tie to clamp the top of this 'U' together, which makes the tether captive.
One last check is made of the gondola to be sure everything is turned on. THIS IS VERY IMPORTANT. We use bare bits of wire, twisted together and taped for our switches. While this sounds low-tech, there are several good reasons for it: a switch that is 'off' looks remarkably like one that is 'on', exposed switches can easily be bumped 'off' if the package bounces along the ground or off a tree or powerline, and at the end of the mission, when the gondola parachutes to the ground, it would be a darn shame if the power switch got bumped 'off' and the chasers couldn't find it. If you do use switches, put them in a protected place, or do like we do and use stone-age ones that can take all kinds of abuse.
While the gondola is double-checked, others scan the skies for low-flying aircraft, or a change in cloud cover that would prevent us from launching. If everything's ok, one balloon handler starts easing up the balloon by going hand-over-hand on the tether. It's very important for this person to have gloves on, not only to protect the balloon, but to protect themselves from rope burns if a gust of wind grabs the balloon. Two other handlers hold the parachute and gondola ready. When all the train has been let out, the gondola handler lets the gondola go, and if everything is cool, the balloon floats up and away.

Post launch:

At this point there's usually cheering, some hams let other hams know the balloon has been launched, the chasers who came to the launch jump in their vehicles and go charging off after the balloon (others wait downrange), and the launch crew goes into post launch phase.
The first thing that needs to be done is to call the FAA (1-800-WXBRIEF (1-800-992-7433), press option to speak to a briefer (usually '1').) on the cell phone and let them know the balloon has been launched. We may need to tell them again where we're launching from, when we expect the balloon to go through flight level 600 (60,000 feet), and the predicted landing area. They know all this stuff already, they're just making sure we're all taking about the same NOTAM. If we need to, we also cancel the backup date NOTAM at this time. If the chase controller is not within radio range, we call them on the cell phone as well to let them know it's showtime.
Then the site needs to be cleaned up. We shut the cylinder valve and remove the regulator. The cap is reinstalled (there is no risk now, but if you don't put the cap back on and the tank falls, the valve could still be damaged). The cylinder is hauled back to the car. The regulator, hose, and adapter are all stowed in the balloon kit bag. Any bits of trash are picked up and tossed in the bag or a handy pocket (don't litter!). The tarp is folded up and returned to the car. One last check is made for anything that needs to be collected, and we head back to town. The responsibility for the balloon has been handed off to the chase controller.
The launch crew then usually grabs some breakfast and heads to chase control to watch the fun.

Chase control:

In our earlier missions, we attempted to use a mobile chase controller in one of the chase vehicles. This lead to all sorts of confusion as soon as he went out of repeater range, and the chasers sometime lost contact. While a fixed controller doesn't get to go out and mix it up in the field, we've found that it works better if the controller is in one spot, with both radio and phone connections at the ready. A fixed control point also allows us to have all the maps, internet, and other resources we need (as well as a high-power transceiver and an antenna mounted high-up off the ground). Now, there are times when a chase needs to hand off control to another control point (either fixed or mobile), like when there are hardware failures or the chase teams go out of range. You should have provisions to do this easily during the chase.
Chasing with GPS/APRS is one sweet deal (when it works): you watch the APRS program plot out where the balloon is and where it's headed, and relay this to the chasers (who often times have the same info on their mobile terminals). The chasers try to get ahead of the balloon and predict where the gondola will fall.
Chase control also communicates with hams who are not chasing, but monitoring from their own fixed or mobile locations. Seeing who can hear our signal and work the balloon repeater helps map the coverage we're getting with the balloon. The controller has to keep good logs so that these hams can get their QSL cards and proper recognition.

Mobile chasers:

Mobile chasers do (in my opinion) the hard part. They try to keep close enough to the balloon to get an idea of where it lands, and actually recover the payload. All manner of hardships they can run into: poison ivy, bugs, swamps, lakes, private property, all must be dealt with properly and carefully.
Some chasers are equipped with APRS workstations, but most just use plain old roadmaps and a radio and coordinate with chase control and the other chasers. For safety, most work in groups of two or more chasers per vehicle: one to drive, one to work the radio and navigate. Most carry hand GPS units to get their exact location so they can zero in on where the balloon is last heard from. From there, they hunt using traditional 'foxhunting' techniques to find the gondola.
Oh, and one other note: chasing will take you on some less- traveled roads, so this is not the time to drive the vintage Caddie, a 4WD pickup works a lot better in mud.

Fixed chasers:

Fixed chasers differ from other hams participating in the project in that they often have directional gear and weak-signal capability. Anyone can participate, of course, and I'm not saying someone who only has an HT and APRS station set up to record the packets isn't a fixed chaser, I guess the only real distinction is fixed chasers are committed to following the flight from beginning to end, while other participating hams come and go as they please.
Fixed guys have saved us more than once when a package went down and we couldn't find it. They also coordinate through chase control to keep everyone apprised of what the balloon is doing.

Post recovery:

If everything goes well the gondola will descend into a nice, easy-to-access area and be recovered by the chasers. For most of our missions (1200g balloon, full tank of gas, 6 to 10 pound gondola) this is about 2 to 2.5 hours after launch. Now the chasers let chase control know the package is recovered, take some pictures/tape of the recovery, switch off the electronics, and head on back to chase central. It's important to let everyone involved with the project know the package is found. Again communication is essential. Nothing frustrates people more than to search for something that's already been found and no one bothered to tell them.
While the chasers drive back to town, the tracking data is saved at chase control, and the logs are printed off in prep for sending out QSLs.
When the chasers return, they meet up with the rest of the group either at chase control at the University or at one of the members' homes. We inspect the payload for damage, take group photos for the website, and disassemble the package to extract experiments and the cameras. The experiments are handed off to the people responsible for them, while one or two folks rewind the cameras and extract the film, then head to a competent local one-hour photo processing lab. We then usually head out to the home of one of the group (if we aren't already there), fire up the grill, and get ready to party a bit. The after-mission social is an enjoyable and much- needed time to wind down, swap stories, and just have a good time. One hour or so later the pics are retrieved and brought to the party, to be oo'd and ah'd over by all involved. One set is kept together to be scanned and placed on the website, while the other is circulated among all present.
Balloon day can get rather long, even when things go right. Sometimes we've had packages lost and recovered days later by locals. It's always a good idea to have contact info printed on the gondola so people can find you if they run across it. A reward will help ($50 to $100 is what we offer, depending on what hardware is on the gondola).
Final work on the mission involves updating the website, mailing out QSL cards, recognizing the contributions of the chasers and other helpers, and following up on the science payloads. All this will stimulate ideas for future missions.