You saw the pictures online, the video on your local news or the commercial on the television. Whatever spurred it on, you want to launch a weather balloon to near-space - for the photos, video or just to do it. It can be a daunting and difficult looking task at the outset. I'm here to tell you that with a little work, a little research and a bit of luck you can certainly launch a balloon payload to ~100,000 feet and recover it! Read on for more information on how to get pictures like this:
Overview
The basic idea is to launch a weather balloon carrying a box with a payload of a camera, sensors and most importantly, a tracking system so you can chase it down and recover everything when it's over. The balloon is filled with lighter-than-air gas to 5-6 feet in diameter on the ground. As it rises, the gas inside expands as the external pressure drops until the balloon is 20-30+ feet in diameter, generally around 100,000 feet altitude, at which point it bursts apart and the payload falls back to earth. Of course, this makes the balloons one-time use.
It's a great hobby and I encourage anyone with interest to pursue even a simple launch, they're a lot of fun to put together and follow through with!
While this is a fairly extensive guide, it's by no means exhaustive. Please use it as a starting point and do your own research. If you have any questions, don't hesitate to ask me, a mailing list, IRC, or any other resource you find. We're a nerdy bunch, but friendly to be sure. Don't be afraid to ask questions!
Sections
- Is This Even Legal?
- The Balloon
- The Gas
- Recovery System (parachute)
- The Payload Container
- Tracking System - Easy Way Out
- Tracking System - The Hard (but awesome) Way
- Weather Sensors
- Batteries
- Media
- Miscellany
Is This Even Legal?
Great first question. The answer is: yes, completely! But of course there's some fine print.
If you happen to be in the US, we're dealing with "unmanned free balloons" according to the FAA as per the Federal Aviation Regulations. These are covered under FAR part 101, which I highly encourage you to at least glance over before thinking about a launch. The EOSS guys have a great version with annotations as well. The important part is subpart 1, the applicability of the regulations. If you don't meet any specifications in that section, you are considered exempt and need no waivers or announcements for launch. The gist of it says that you can't:
- Have a balloon larger than 6 feet in diameter
- Have a combined payload weighing more than 12 pounds
- Have a single payload section weighing more than 6 pounds
There are other, more subtle things to note here, so please read through the entire set of regulations. It's really not that bad, I promise.
In addition, balloons should not travel through Class B, C, D or E Airspace). Think of the airspace like an upside-down tiered wedding cake with each upper level a bit larger than the one lower. Each layer is like a disc that has a different floor and ceiling you can't enter through. Look up the airspace for your nearest major airport to be sure you won't enter their airspace; maps are available online or in paper form at a local pilot center.
If you are planning a larger launch or have other extenuating circumstances, please contact the FAA's regional ballooning coordinator for your area. They will be able to give you more information or set you up with a waiver application. For the vast majority of launches, this is unnecessary.
If you have any questions or concerns, please get in touch with a local Air Traffic Controller - the ATC will assist you in your situation locally and answer any questions you might have. If you are located in more dense urban areas or near an airport, you might be required to notify the ATC before launch regardless of your payload.
If you are outside the US, please look up your local regulations.
Above all, please do your research and be aware - let's keep this hobby safe and sane!
The Balloon
In the US, weather balloons are used by the National Weather Service, each with what are called radiosondes attached to them. They are used to model and predict weather patters, and are generally launched twice daily, every single day from over 100 locations all over the US. If you do some quick math, you'll note that there are over 73,000 launches annually just across North America. If you're worried about the safety of the launch, let this allay your fears just a tad - though please be aware and safe!
Purchasing a New Balloon
The best source for new balloons is Kaymont. They manufacture them for the NWS among others, and are very good quality. They are starting to cater more to the one-off hobbyist orders, and even have a section on their Web site for them now.
Many people find surplus balloons on eBay and the like, but I can't vouch for them. Most of them are fine and work brilliantly, but there are no guarantees. Most latex balloons do have a shelf life of a year or two at most before they start to degrade, so be wary of exceptionally old balloons. I personally opt to spend the extra money for the peace of mind that the envelope will not burst prematurely, plus it's nice to know the design specifications beforehand.
Balloon Sizes
Balloons are categorized based on their weight. The most popular sizes are between 800 and 1500 grams. Each has different properties and behaves differently, but your first balloon should be 1000 or 1200 gram unless you know you want something different. A 1000g balloon will lift a few pounds to ~90,000 feet quite readily, and is completely sufficient for most launches.
Filling
TODO:
The Gas
In order for the balloon to rise at all, it needs to be filled with a lighter than air gas. Traditionally, helium is used as it is completely inert and fairly safe if handled properly - I highly recommend helium for your first launch.
The other option is Hydrogen. Many folks prefer hydrogen, as in practice it is slightly less dense than helium and provides greater lift. In addition, it is much cheaper than helium, sometimes less than a third the cost. Naturally, there is a drawback, and it's a doozy: it's highly flammable. Extreme caution must be used when working with hydrogen, especially during filling, as a stray spark could set the whole thing ablaze. Again, I highly recommend helium for your launch.
Working with helium isn't nearly as dangerous. As with any compressed gas, care needs to be taken while transporting and working with the tank, but the risk of an explosion or fire is minimal.
Recovery System (Parachute)
After the balloon bursts, the payload will start falling to the ground. In the upper atmosphere there is little air to resist the falling, and it can reach speeds well over a hundred miles per hour. As it falls closer to earth, it will need something to slow it down on the descent so it doesn't make a small crater on impact.
I use a four foot parachute from The Rocketman. There are many places online to find simple nylon parachutes, including ebay and surplus stores, but again I prefer to buy new so I know the expected properties of what I'm working with. Parachute selection isn't totally crucial, just make sure you get an adequate sized chute for your payload mass.
The main considerations when selecting a chute is the descent rate. It's good (and fun!) to do a "drop test" from the top of a building