Preparing for Balloon Launch
The purpose of this tutorial will be to outline the tools and equipment necessary to launch the balloon in addition to the RFD900 GPS tracker. This section will also review the rules and best operating procedures for launching a balloon.
Overview of Physical Equipment and FAA regulations
Before discussing the equipment I use on my balloons it is important to ensure that we review the FAA requirements to ensure that no rules are infringed upon. It is important to note that once the balloon is launched it is out of our control. Therefore it is important to have equipment like parachutes to prevent injury to the public. Additionally, this equipment will also ensure that the data collected near space is returned safely to the ground. Before continuing this tutorial read this document from the Global Space Balloon Challenge. This source describes the rules and regulations created by the FAA which pertain to balloons. While reading this document be sure to note the importance of not creating hazards or damage to other people and their property. Also, note the benefits of having a light payload. Lighter payloads are much less restricted and are exempt from the rules that govern larger balloons. For this reason, the weight will be one of the greatest considerations while choosing equipment for the balloon
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Now let us get started, after reading the article attached above I was determined to meet the provisions of subpart D which exempt balloons under four pounds with a weight/size ration of more than three ounces per square inch. To do this required careful planning before purchasing the necessary equipment for the balloon. Before going into detail, I want to give a quick overview of the various components needed for the balloon
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Balloon
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Parachute
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Rope
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Batteries
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Tracking System
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Secondary Tracking System
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Enclosure
Balloon
The balloon is what is needed to lift the payload off the ground and into the sky. Typically balloons are sold by their weight. For my first two flights, I used a 600 and 800-gram balloon respectively. The benefit of larger balloons is that they typically will reach higher altitudes before popping, assuming the same payload. For my first two flights and the foreseeable future, I get my balloons from a website known as Scientific Sales inc. This company provides balloons in a variety of sizes and I have always received my orders quickly and have been impressed with the quality of balloons. One important note is that if you are not going to launch your balloon immediately ensure that you store the balloon in a dark place as sunlight can compromise the strength of the balloon, leading it to pop earlier. Another important note is to always fill your balloon up with helium never use hydrogen as it is very flammable and can be deadly.
Parachute
The next component necessary for a balloon is the parachute. Note that as with the balloon the larger our payload the larger the parachute needed. So far I have only needed to purchase one parachute since all my payloads have been close to the same size. I like to buy my parachutes from a company known as RocketMan Parachutes. The great thing about RocketMan is that on all of their parachutes they list the expected vertical speed of the payload for a given weight. Typically when choosing a parachute it is ideal for the payload to stay at speeds around 5 m/s. For both of my launches, I used a 5-foot parachute. Also, do not buy the biggest parachute you can otherwise your balloon could drift much farther on the winds.
Rope
The rope is pretty simple, I chose to purchase the nylon rope used for parachutes cords. You do not want the rope to be too thick it, ideally, it would have a diameter of at must around 5mm to 1cm. I would also suggest purchasing a rope that is brightly colored. This goes for anything listed in this tutorial. More brightly colored objects are easier to see meaning they will be easier to find and will also be less likely to cause an accident with an aircraft.
Batteries
Batteries are very important as they are vital in allowing you to recover your payload. Always buy batteries that have a large enough capacity to power the balloon for the entirety of the flight and then some. My favorite brand of battery packs is Anker, for my flights I use a 13000 and 10000 mAH battery pack. Note you can convert from mAH to wH using the output voltage of the battery and the mAH of the pack using an online calculator like the one here. Also, note that it is important to ensure that the battery can easily be connected to the other balloon components. I like the Anker batteries because they use USB ports to easily connect to the various components of the balloon. Additionally since these batteries output 5v they can be plugged directly into the Arduino, STM boards, etc without fear of damaging these components
Tracking System
Of course it is important to have a tracking system for use with the balloon, but since most of my other tutorials pertain to this subject I will not discuss it here.
Secondary Tracking System
For redundancy, it is useful to include a second tracking system in the event of primary system failure. Many people use various hiking GPS trackers which are commercially available. Additionally, some people opt to use their phones. One caveat of this is that at lunch and while above 20,000 feet all phones must be in airplane mode. To get around this on some Android phones the airplane mode can be timed to turn on and off at specific times. Unfortunately, all my old phones were iPhones which cannot turn airplane mode on and off by themselves. To get around this I just turned the phone off and then used a servo to turn it back on after it was below 20,000 feet on the return trip. Below is a video of the servo turning the iPhone screen on and off by hitting the lock button.
Enclosure
Finally, the last piece that is needed for the balloon is the enclosure. I chose to use a simple Styrofoam cooler, because it was light weight and would insulate the balloon components from the cold temperatures outside. The size of cooler you need will be determined by the size of your payload but I would suggest getting the smallest cooler possible for your payload. Also ensure that you get a thicker Styrofoam. It should ideally be at least 1-2 inches thick. Once you have all of your components I would suggest distributing them so that the center of mass of the payload is near the center of the box. This way your payload will not be leaning one way or the other. I would also usggest getting a metallic spray paint to paint your box, and make it more reflective.
Pre-flight
Once you are ready to launch your balloon, please be patient you do not want to lose your balloon by launching it on a windy day just because you are antsy. In addition to this also go to the website here to predict where the balloon will land.
To the left is a screenshot from the program accessed through the link. In the box to the bottom right of the screen your launch location should be input along with the expected ascent rate in m/s and your expected burst altitude. All of this can be calculated using the Burst Calculator which is also located in the right lower menu. You will need to calculate the weight of your balloon prior to this. This can be done by either measuring the assembled balloon using a scale or by using datasheets to find the weight of each separate component. Finally, the descent rate will be predicted by the weight of your balloon and size of your parachute. Be sure to note that the Burst Calculator will output the volume of helium you will need when purchasing a canister of helium.
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To buy the helium I would suggest, searching for helium providers in your area. There will probably be a welding supply store or equivalent that will be able to provide the necessary gas.
Now that everything is situated in the enclosure and the balloon and parachute are ready how is it all attached together? To do this I first purchased a U-Bolt like the one shown below.
Note that the U bolt in the left picture was inserted into the lid of the Styrofoam cooler so that the rope could be tied to the lid. As a precaution, I also used superglue on all of the knots to ensure they did not come undone. Next I tapped the lid of the Styrofoam cooler down with duct tape and then tied it with string. It is important to have multiple layers of protection not only to ensure the balloon's success but also the safety of others. After that the parachute will have a loop which can be used to tie the parachute to the payload; attach this loop to the payload. Once the parachute is attached to the payload we need to connect the parachute to the balloon. Before we can tie the parachute to the balloon it is time to fill the balloon up with helium. To do this I simply placed the opening of the balloon over the gas cylinder and let it fill up. There are much better methods of doing this, which can be found online.
To the right is an image of my family and friends filling the balloon up with helium. Once the balloon was filled we tied the string to it and released the balloon. While the balloon was in flight I used my software to track it and we were ultimately able to recover the balloon.
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To see the fully assembled balloon look at the image below.
