Brownwood News – (TRICKHAM, TEXAS) On May 2, 2020, three college friends used their extra time at home due to the COVID-19 quarantine to design, plan, build and launch a weather balloon from Trickham to 90,000 feet above Brown County. The photos they captured are amazing! This is the story of Joseph Kenrick, Justin Kilb and Matthew Rehberg.
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Introduction
Where do you begin with a story like this? Two weeks prior to the launch when the project started, four years ago when the idea was first expressed, or 20 years ago when the dreams of working in Space first arose? We’ll start the story seven years ago when the three of us met. We all went to university at the Colorado School of Mines in Golden, Colorado and played on the Men’s Club Volleyball team. It was on the court and in our roles as club President (Joseph), Treasurer (Matthew), and Risk Manager (Justin) where we learned to work together as a team and feed off each other’s strengths. As our friendship and curiosity grew together, our goals became more and more ambitious. It started with small Arduino projects to automate things around the house, which then later transitioned into building model rockets and eventually competing in a Mar’s Drilling contest with NASA. The skills required for this project were being developed individually and had yet to come together to accomplish a single goal. The idea of sending a camera to space was discussed during our time in University, but time was limited due to school and Volleyball. Justin and Joseph received their degree in Petroleum Engineering, and Matt received his degree in Chemical Engineering. Although our fields do not exactly line up with the application of sending a camera to space, engineering is a tool, no matter the application. Our relatively diverse backgrounds to each other brought unique perspectives towards a converging idea and life goal. This idea has been growing within us, even beyond this project, and it was not until a couple years later when stuck at home during our weekends due to the COVID Quarantine that we found ourselves with the time needed for such a project. Joseph was in California at the time, where he lives and works, and Justin and Matt were in Texas. We began to put the pieces together for the project through the power of online video chat and collaborative online environments. The first, and obvious question we had to ask was, so how do we send something to space? Let’s start with the mechanics.
Ascent
There are several ways to send something up to 90,000 ft. The cheapest and easiest way is certainly via a weather balloon. Weather balloons come in many different sizes, which ultimately provide different maximum altitudes. We decided to go with a Kaymont 600 gram weather balloon to achieve the intended altitude of 90,000 ft. This balloon near the surface of Earth is about 5.4 ft in diameter when filled. Weather balloons are made of a very sensitive Latex material designed to expand as they rise in the atmosphere. The balloon will rise and expand, fueled by the decreasing atmospheric pressure as you move away from the surface, until it ultimately expands to a point that the strength of the Latex can no longer hold, and the balloon pops. All handling of the balloon had to be done with Latex gloves as the oils from your hands can create irregularities on the surface of the balloon and thus create a point of weakness. This ultimately means the balloon will not go as high. Next question is, what do you fill the balloon with? Hydrogen? It’s the lightest stable element and will give us the lift needed to get to space. It’s also in abundance and consequently, cheap. It is, however, very flammable and dangerous to work with (think Hindenburg). The much safer option is the second lightest element, Helium. Being a noble gas, it does not react with other elements. The problem we initially faced, however, was the United States is in a national shortage of Helium, so it was very difficult to find it in a high enough quantity and purity needed for the project. We eventually found a supplier and decided to go with Helium. So how much Helium do you need? Let’s start with the concept of lift. If you have a force acting downwards (with gravity) on an object, in order for that object to float it needs to have an equal and opposite force acting on it (upwards against gravity). If you have more force acting against gravity than you do with gravity you get a net lift. The more the net lift, the faster the object moves in the direction of that net lift. In rough terms, the density of air is a little more than 1.2 grams per liter, and Helium is a little less than 0.2 grams per liter. That means for every liter of Helium you have, you get 1 gram of net lift upwards. Thus, to just suspend a 4 pound payload (roughly 1,800 grams) and the 600 gram balloon in the air, we would need 1800g + 600g = 2,400 grams of lift = 2,400 liters of Helium, or 85 cubic ft. So, in order to get the balloon to move upwards, we need more than 85 cubic ft to create a net lift in the upwards direction. How much more?
Distance Traveled = Initial Velocity * Time + ½ * Acceleration * 〖Time〗^2
We wanted a roughly 2.5 hr ascent to prevent the balloon from traveling too far in the jet stream, and the goal was 90,000 ft. Plugging those values into the equation above yields an average desired acceleration of 8 ft per minute squared or 0.0006773 meters per second squared. The acceleration changes throughout the flight due to the varying atmospheric conditions, but the rough average will suffice for estimations.
Force divided by acceleration equals mass, and we want the net lift in mass, as we already have the correlation from net lift in mass to volume of Helium, we need to find the net force on the balloon.
Volume of Balloon = 〖(0.82 m radius of balloon)〗^3* 4/3 * π = 〖2.33m〗^3
Force Downwards = Weight of Payload + Weight of Helium =
〖2.33m〗^3* 〖0.152kg/m〗^3 * 〖9.81m/s〗^2 + 2.4kg payload * 〖9.81m/s〗^2 = 27.025N
Force Upwards = Volume of Balloon *〖9.81m/s〗^2* 〖1.18kg/m〗^3 = 27.0254N
Net Force / Acceleration = Net Lift in Mass = 0.0004N / 〖0.0006773m/s〗^2 = 408 grams
= 15 cubic ft of Helium
So a total of 85 + 15 = 100 cubic ft of Helium.
The process to determine exactly how much Helium you need is a bit iterative and there are several online calculators to help cross check your numbers. In general, though, the more Helium you have, the more net lift and thus faster acceleration and shorter flight time, which means less horizontal distance traveled from where you launched. This is helpful, however, with more Helium the balloon will actually pop at a lower altitude since it is starting with a larger volume it will reach it’s bursting volume sooner. Technically, you could have a net lift of just a few grams, and it will get much higher than 90,000 ft, but the ascent time will be many hours, if not days, and by then the balloon could have traveled hundreds to thousands of miles away. With our planned amount of payload and helium, we expected an average ascent rate of about 3 meters per second. We have what we need to go up, now what about getting back down?
Descent
After some research we found and purchased a specialized weather parachute online. The parachute was scheduled to arrive the day before launch, but unfortunately it was sent to the wrong address. As a result, we created our own parachute with a bedsheet. The diameter of the parachute, during tension, is very important as this influences the volume of air the parachute will interact with during its descent back to Earth. In general, a larger diameter parachute will interact with more air molecules, thus slowing the falling speed. Although a slower falling speed is beneficial to the preservation of the payload as it collides with earth, it can also increase the distance the payload travels on its descent back to earth.
In addition to selecting the correct diameter of parachute, we were cognizant of the fact that a cloth material with a high permeability to air would increase the descent speed. In other words, if air molecules can easily slip through the parachute fabric, then the parachute will face less resistance during its descent and increase the velocity that it falls. A simple analogy to this concept would involve a parachute with large holes in it.
Photo Left: Testing the Parachute and Riggings
Another key element to the parachute was assuring that each rope attached to the parachute was equal in length. Any variation in rope length could lead to an imbalanced parachute. This could increase the parachute’s tendency to glide, drastically increasing the distance the payload travels as it descends back to earth. We reinforced the parachute with additional fabric at each rope attachment point. This being said, we did not reinforce these attachment points like you would for a human skydiving parachute. When a human skydiver deploys their parachute, they’re usually traveling at terminal velocity. This sudden jolt places an enormous amount of stress on the parachute. In contrast, the parachute we launched begins to deploy slightly under maximum altitude as it’s direction of movement transitions from up to down. Therefore, when the parachute opens, the payload is traveling much slower than a skydiver, which places less stress on the parachute. Furthermore, U.S. skydivers typically deploy their parachutes around 13,000 ft which is drastically lower than the altitude at which our parachute began to deploy. At 90,000 ft, the density of air molecules is much less than it would be at 13,000 ft. This non-linear distribution of increasing air density from high to low altitude creates a relatively gentle onset of force felt by the parachute. The final design of our parachute had a diameter of roughly 4.5 ft, providing a descent rate of about 5 meters per second.
Trajectory
We have the vertical components of this journey figured out now, what about the horizontal component? As mentioned, if there is too little Helium, or if the parachute is uneven, the payload can glide quite a far distance. With that in mind, the location of the launch is key. An open area around the launch for uninterrupted take off, and a relatively open area with minimal water, airports, cities, and restricted airspace for miles around is required. We ultimately decided to launch from local legend Pat McClatchy’s 3Mac Ranch just North of Trickham, Texas. The abundance of farmland provided miles of uninterrupted air space and high visibility landing. With the information we now have, we can use trajectory forecast calculators found online to start to get an idea of the balloon’s path, and ultimately determine the best day for a launch. The prediction is only accurate a few days before launch as it takes weather forecasts into consideration and becomes more accurate closer to launch. Initial forecasts showed our payload landing 150 miles to the East, past Waco. As the launch day approached, however, the wind died down and the forecast only predicted a 40 mile distance, landing near Zephyr, which we deemed acceptable.
Initial Trajectory Projection (Purple) and Launch Day Trajectory Projection (Green)
Payload and Testing
We’ve mentioned our payload is 2,400 grams, but what does that entail? For starters, the camera. Redundancy is key – trust us. We used two cameras for the first launch, and 3 for the second launch. Yes, we launched twice. We used a GoPro 7, GoPro 2, and added a Motorola x4 phone for the second launch, which also happened to be Matt’s phone. One facing out to the side and one facing down. We cut molds out for the GoPro’s to allow just the lens to show. The box that the molds were cut into was made of styrofoam. Styrofoam is a light weight, impact resistant, shape-able, and thermally insulated material that makes for the perfect payload box. Battery packs for each GoPro is a crucial element for ensuring the cameras have enough life for the length of the journey. We were also interested in gathering data throughout the journey, so we added two Arduinos programmed to read and write data to SD Cards from a temperature sensor, barometer for pressure, and a 9 degrees of freedom orientation sensor. The Arduinos also required a power source. Tallying the weight up, including the weight of the parachute and rope to tie it all together, it started to narrow in on 1,800 grams, plus the 600 gram weather balloon, made 2,400 grams.
We used the two battery powered Arduino boards to measure and record conditions during the ascent and the descent of the balloon. A gyroscope was used to measure the speed of rotation around three axes. This type of data helps to determine the orientation of the payload. An accelerometer was used to measure acceleration in three axes. Acceleration can be used to determine the G-forces experienced by the payload. The final sensor used to help determine orientation of the payload was a magnetometer. A magnetometer measures the direction, strength or relative change of a magnetic field. A compass utilizes this type of data to determine Earth’s magnetic field. In addition to the payload’s orientation in space, we included a temperature and pressure sensor. Both of these sensors were selectively chosen for their ability to measure in extreme conditions. We were expecting to encounter temperatures as low as -70 ℉. Interestingly, the coldest temperatures are not experienced at 100,000 ft, but rather at ~ 40,000 ft to 60,000 ft. This is because the stratosphere undergoes what is referred to as temperature inversion. This is when short wave ultraviolet rays react with oxygen to continuously form ozone with heat as a byproduct.
Photo: Balloon, Parachute, and Payload
At 100,000 ft, the pressure is about 1% of pressure at sea level. The pressure at this altitude is so low that you would not have to heat water to boil it. So how do we get our payload and its constituents to survive in these conditions?
Temperature is a difficult subject to understand. Everyone knows the output of measuring temperature, some number describing how “hot” or “cold” something feels. Temperature is a measurement of the thermal energy contained within a substance. Cold substances have a low amount of thermal energy. This energy will always flow from high to low. As you press your finger against an ice cube you feel the flow of your finger’s thermal energy being transferred to the ice cube.
Anyone who has been outside with a phone in temperatures below 0 ℉ has experienced our primary problem of battery performance degradation. The lithium ion batteries powering the GoPros, cell phone, and Arduinos are nothing more than a contained chemical reaction. All chemical reactions need a certain amount of energy to take place. You can put two logs in a fireplace but unless there is enough heat to start the combustion reaction, nothing will occur. The same principles apply to our batteries. The temperature our GoPro’s battery face will begin to halt, if not stop, the chemical reactions providing electricity. This is great in theory, but how is our battery performance going to be in actuality? We decided to run some tests to find out:
Test #1: Put the GoPro directly in the freezer (-10 ℃ )
The battery lasted 15 minutes before it shut off.
The flow of thermal energy is commonly referred to as heat transfer. Remembering the flow is always from hot to cold, the GoPro transfers its energy directly to the low energy gas molecules surrounding it.
Test #2: Put the GoPro in a styrofoam box, then inside the freezer
The battery life improved to 60 minutes. Styrofoam is an insulator, meaning it doesn’t allow thermal energy to flow easily through it. This is what makes it a great coffee cup material. The GoPro now transfers heat to the surrounding gas within the styrofoam box which then slowly transfers heat to the surrounding freezer.
Test #3: GoPro attached to an external battery pack, in a styrofoam box inside the freezer
The battery lasted 200 minutes. The GoPro battery itself is 1,100 mAh. The external battery pack’s capacity is 2,200 mAh. This test allowed us to calculate how big of a battery pack we were going to need to power the GoPros. Given that we were planning to get to 90,000 ft at an ascent rate of 3 m/s, then descend at 5 m/s, we calculated a total flight time of (roughly) 4 hours or 240 minutes.
240 flight_minutes x (2,200 mAh)/(200 minutes) x 2 GoPros x 2 safety factor ≈10,000 mAh
We applied the safety factor because our testing was only done at 0 ℃ while the known conditions were going to be far more severe (we later tested in -78 ℃ with Dry Ice but had to buy the battery pack several weeks prior due to shipping times). The engineer in us wanted a more definitive answer to the question “will our batteries work at -70 ℉? To answer this question, we took an analytical approach.
Test #4: GoPro with a temperature sensor directly on it, in a styrofoam box, inside the fridge (0 ℃ )
The GoPro during this test was pressed into an exact cutout of its shape within the styrofoam box. As mentioned previously, styrofoam has a high resistance to thermal energy flow. We can assume the heat loss from the GoPro to the styrofoam can be ignored. This allows us to assume that all of the heat loss from the GoPro will be to the outside (fridge) environment. In a steady state environment, the flat line in the graph above, the generation of heat within our system is equal to zero. The form of heat transfer from the GoPro to the fridge is via convection. The rate of convective heat loss is a function of the area exposed (GoPro base surface area), the heat transfer coefficient (can be assumed), and the change in temperature between the two objects. We are now able to model how much heat the battery is putting out.
Q_(Batttery )+ Q_(Loss )= Q_Generation
Q_Battery=Ah(ΔT)
Test #5: GoPro with a temperature sensor and handwarmer directly on it, in a styrofoam box, inside the fridge (0 ℃ )
A handwarmer provides a new heat source to the system. However, the heat output of the battery does not change. This yield the following equations:
Q_(Battery )+ Q_(Loss )+Q_Handwarmer= Q_Generation
Q_Handwarmer=Ah(ΔT_2)- Ah(ΔT_1)
ΔT_1=21C-0C,ΔT_2=41C-0C,A=0.00202〖 m〗^2,h≈20W/m^2 K
Q_Handwarmer=2.02 W
We can now calculate approximately what the steady state temperature of the GoPro will be at the atmospheric conditions expected.
Q_(Battery )+Ah(T_(Steady State)-T_Atmospheric)+n_Handwarmer×Q_Handwarmer=0
Little did we know how this equation would come to ruin us…
There are two other battery dilemmas we faced that are worth noting. Arduino’s require a very low amperage to run (50-250 mA) and most commercial battery packs are not made for these conditions. The electronic devices battery packs are intended for (phones, headphones, laptop…) will begin to limit the amperage they draw as the battery nears a complete charge. The battery pack takes this as a signal to turn off, avoiding overcharging issues. We had to purchase (actually we had one for personal Arduino use) a specialty battery pack to provide power to the Arduinos. This could have been accomplished with 4AA batteries (6 V in series) but the Arduino takes 5 V supply. This difference would be emitted as waste heat by the Arduino voltage regulator. The capacity of the AA batteries was also far less than the battery pack we had available.
The second battery dilemma was for the GPS, which was mounted on the exterior of the styrofoam payload and there was no option for us to insulate the GPS from the harsh atmospheric conditions (more on this below). Luckily, Energizer has a “Ultimate Lithium” battery that is made to perform at low temperatures. However, our concerns were not subdued as the graphs on the Energizer website did not go down to-50℃. We tested the systems in dry ice conditions to further simulate the conditions at altitude. All systems passed the dry ice testing, both GoPros filmed for 5+ hours, the Arduino’s wrote to the SD cards, and the GPS continued flashing throughout.
Photo Left: Arduino and Box Testing at Temperature
Global Positioning System (GPS)
Almost ready for launch. We have the ascent, the descent, what we’re sending up, the flight path, and we’ve tested each component. Now how do we find it? The flight trajectory predictor will give you the general area, but it can be plus or minus a few miles upon landing, so you cannot rely on that. Using cell tower-based positioning devices, such as your phone, is risky (and also illegal for the phone, Matt’s was on Airplane mode). If your payload lands in a place with no cell service, you’re out of luck. That leaves satellite-based positioning systems, otherwise known as GPS. We used a Spot Gen 3 GPS that required an account with a monthly subscription. Word of advice, don’t overlook the GPS. If you can’t find your payload once it’s landed, it’ll all be for nothing. The GPS worked great for low altitudes, but gives out around 20,000 ft as the satellites can longer track it above that point. Fortunately, the GPS will come back into service when it gets back below 20,000 ft so you can begin tracking it again. It’s a stressful couple of hours waiting for it to come back. Although the altitude was spotty, requiring us to frequently run flight calculations to confirm readings, the X-Y coordinates were very accurate, we found. The GPS has to be mounted to the top of the box on the outside in order to provide uninterrupted signal to the satellites, so temperature performance batteries are important for the GPS. The first landing went straight through an industrial wind farm, missing the windmills and fortunately landed just off the road where we could quickly grab it. As we will get into later, the flight ended up being a total bust, so we launched again, and the second landing ended up in a local’s yard near the train tracks in South East Zephyr. Both times we were able to walk straight to it.
Federal Aviation Administration (FAA)
Is all this legal anyway? Yes, Jerry, it is. Provided you follow some regulations. The FAA has rules regarding what an amateur can send towards space. However, the regulations apply to something that “carries a payload package that weighs more than four pounds and has a weight/size ratio of more than three ounces per square inch on any surface of the package, determined by dividing the total weight in ounces of the payload package by the area in square inches of its smallest surface.”
We are not law experts. The website containing the regulations is here (https://www.ecfr.gov/cgi-bin/text-idx?rgn=div5&node=14:2.0.1.3.15). We contacted the FAA FSDO station responsible for our launch zone via email and phone, as well as a few other FAA FSDO stations within Texas several weeks before the launch. No one we spoke with minded what we were doing. We continued communication leading up to launch.
Launch Day
6:00 am May 2nd, 2020, Trickham Texas. We’ve done our designing, planning, testing and retesting, built the launch procedure- It’s time. The three of us cool, calm, and collected contain our nerves and excitement and execute the procedure to near perfection. Camera’s and Arduino’s plugged in, the box is sealed, the knots are tied, and the balloon is filled. We release with a semblance of hope and excitement as we watch it quickly ascend out of view. We watch the GPS for the first 30 minutes of the flight, and everything seems to be working as expected. The altitude ascends to 30,000 ft, then the next reading gives an altitude of 1500 ft – our altitude. We run the calculations to see what the velocity would even have to be in order for it to fall that fast. The velocity came out to exactly terminal velocity. Catastrophic failure. And then a ping. 4,000 ft, what? Remember, the altitude is spotty. All is good, and we’re well on our way to space! The GPS goes out of range shortly after this and we go into 2 hours of radio silence. We start to head to the projected landing spot, and as we near the GPS comes back into service. We drive around backroads for a while trying to predict where it’s going and meet it upon descent. An ambitious goal we quickly found out. 30 minutes later the payload is down, and we eventually find it along the road. We check the instruments, and everything is off. Everything. We looked at the footage and data, and everything turned off 10 minutes into the flight. How is this even possible? It couldn’t have been the extreme cold, because it hadn’t reached max altitude by then. Did they run out of battery somehow? No, they were fully charged. What about our hand warmer positions? We did place them awfully close to the batteries, maybe we overheated? This is the fickle beauty that is science. You can seemingly do everything right, and everything can still go wrong. Murphy’s law. So, what do you do? This is our dream. Do we give up? No, we develop a hypothesis, adapt, and run it back. Don’t get me wrong, there was nearly an hour of absolute silence upon the discovery of failure, but we bought two balloons and enough Helium for this reason. We rushed back to the launch site, making adjustments along the way, charged up the devices again, and prepared for a second launch. This time we decided to scrape the Arduinos and sensors and add another camera to increase our chances of getting that one photo this was all for.
2:00 pm May 2nd, 2020, Trickham Texas. Things are different this time. It’s not a quiet, beautiful morning anymore. It’s a blusterous, hot day. Conditions less than ideal, we decided to push through. We start to fill the second balloon with Helium, and the task quickly becomes daunting. The wind is pushing the balloon all over the place, and if it touches the ground, it could pop, and we’re done. We need two people holding the balloon up at all times, leaving one person to rotate and get all the equipment ready, tie all the knots, and take the measurements. Stress was high and shoulders were burning from holding up this 6 ft balloon for 45 minutes, but we got it ready with a little less finesse this time round. We sent the balloon off in an act of desperation and the waiting game began again.
Fast forward 2 hours and we find ourselves waiting on a back road staring up in the sky, searching. We get a ping, and the balloon is on the projected trajectory. We followed it as far as we could until it landed, and we came up on a local’s home. We approached the door and shared our story with the gentleman who answered. He allowed us to proceed through his property to the train tracks to find the payload and even very graciously offered for us to take his off road 4-wheeler to get through the rough.
Photo: Second Launch Struggles
As we approached the tracks we could hear a train in the distance. Fueled by the excitement of finding the payload and not knowing if it was on the track itself, it turned into an all-out sprint towards the payload. We found it hanging in the side of a tree just a few feet from the track and grabbed it just as the train approached. It was difficult to tell if the equipment was still running from the outside of the box in the light. We headed back to the house and thanked the family and were on our way. We drove just a short distance down the road to open the box and see what was inside. Two of the cameras were off and one had an overheating symbol on it. Not a good sign. Checked the first two. Both turned off early. All down to the last camera that overheated. Well, I think you can figure out what happened…
The Figure that needs no explanation
The process we follow, the cycle we ride.
Conclusion
Why did we do this you may be asking? Was it just for that one photo? On the surface we would say yes, and even if that was all it was about, we would still do it all over again. We have the memories of the trials and tribulations that will stay with us forever. We can remember the moments of struggle and pure exhaustion of holding the balloon up, knowing if we dropped the balloon all would be lost. These memories fill us with joy and pride, and nothing else can match that feeling, but these are just memories. What about a valued tangible idea or purpose that we can take with us in the future? For three curious and ambitious engineers in this world, we are just trying to find significance to our lives in this fragile planet, just like everyone else. We all have different means to get there, and we find that our own wisdom and courage is what can bring life meaning. As Carl Sagan so eloquently puts it, “if we crave some cosmic purpose, then let us find ourselves a worthy goal.” The goal here is not just sending a balloon to space but is a steppingstone to something much bigger. Space, and the evolution of humankind through Space Resources. The Colorado School of Mines has opened the first, and currently only, Space Resources program in the world, led by Angel Abbud-Madrid, and we plan to start this program and evolve our careers into this new and world- nay solar system changing field.
Matt, Joseph, Justin
