At the top of the list for a high altitude balloon is the balloon. For this first flight, the choice is a Kaymont 350g latex balloon. These balloons are sold by the weight of the balloon itself, not by diameter or lifting capacity, because those things vary by the amount of helium or hydrogen added to the balloon.
In this picture are both 350g and 1000g Kaymont balloons along with a 1m Rocketman chute designed for high altitude balloon launches. How a balloon performs in flight is a balancing act of payload size, the amount of helium, and the balloon size. Add a lot of helium to a small balloon, and it can generate a lot of lift, but burst at a low altitude. Add too little helium to a large balloon, and you can end up with the dreaded “floater” — a balloon that never ascends high enough to pop, and just drifts along tens of thousands of feet in the air. That’s a great situation if you’re doing research and have some way to radio your results to the ground. A terrible result if you ever want to get your payload back.
Fortunately, a number of sites have tools to help you calculate what you can expect from a combination of balloon, payload, and helium. For example, KOSMOS 1 is using a 350g balloon, and I happen to know the payload weighs in around 850g (more on that later). So, based on what the pages at Launch with Us and High Altitude Science predict,
I should be looking at a 24k altitude for balloon burst if I add around 60 cubic feet of helium (and yes, there are always going to be awkward mixes of units in this series). What does that mean for critical questions like how far the balloon will travel and where it would land if I carried through on my initial plan to launch from the softball field at a nearby community college? Fortunately, there are web sites to help with those questions as well.
The CUSF Flight predictor and the ASTRA High Altitude Balloon flight planner both use a combination of those balloon performance calculations, launch locations, and weather data to provide a predicted path of travel for your balloon. This includes the altitude where it will pop, and the location where it should land.
If I were to launch this afternoon, into the howling snowstorm and colliding fronts, my balloon should travel a path to the northeast. Which is seriously bad. Not only would this path take the balloon into the controlled airspace of St. Louis Lambert field, it would pass almost directly over the airport at Columbia, IL and actually wander uncomfortably close to Scott Air Force Base. But trust me, this is a very unusual result. On most days, the balloon would travel resolutely southeast. Typical flight paths would tend toward the state park just visible at the bottom right corner of this map, with a landing near Benton, IL. So I could not fly (and would not want to) from my nearby site today, but on most days it would take a path that was pretty much across semi-rural area. Which is what I want.
So, what about the payload? Here’s a labeled version of the top picture, for better reference.
Consider this table like NASA’s Vehicle Assembly Building. Just … smaller. It’s where all the components of KOSMOS 1 are being slotted together.
In the bottom right is a bit of black foam board topped by the flight computer. In KOSMOS 1, the flight computer is really nothing but a glorified data logger. It has a GPS module, a sensor for barometric pressure and temperature, and drive to write data on a tiny micro-SD card. The whole thing is built an arduino knockoff which, despite costing just $12 and being about the size of a deck of cards, is still massive overkill for what it’s doing here. The flight com is considerably neatened from last week, but still something of a mess. Part of that is because I decided to leave the GPS components on long leads so that I put the antenna outside the enclosure.
The flight computer for KOSMOS 2 is already taking shape, and it’s going to be quite a different shape. In the bottom left of this image you can see an Arduino mega, which is the basis for flight com 1, and an Arduino nano, which is going to be the core of flight com 2. It is … smaller. Uses less power, as well. Both of those are good things when mass is at a premium. If all works out, Flight Com 3 will actually use a printed circuit board and be smaller still — but I’m just learning the free version of the Eagle PCB designer tool so … prototype boards will do for now.
Because I still don’t have the APRS chip I needed for my Arduino (which I had to order from England) and I still haven’t wandered in to take my test for a lowest-common-denominator ham radio license (amateur radio technician) , there will be no live radio broadcast from KOSMOS 1. Instead, the nose of the craft will be capped with a SPOT Trace tracker, which is essentially a single-purpose satellite phone that updates its position every few minutes. At $100, plus $10 a month for service, it also happens to be the most expensive item in the whole program.
Backing up the SPOT tracker is a cheaper tracker from Spytech. It’s cheaper because it communicates over vanilla cell networks, so isn’t much good for anything until the payload is on the ground. This is genuinely there in the role that on many balloons is played by “old Android phone, pitched in the box.”
The intention is to have KOSMOS 1 launch with three cameras — 2 on the sides, 1 pointing down. If you look right above the two trackers in the image above, you’ll see three tiny black boxes. One is a Polaroid Cube cam. Another is a Vouo spy cube. The bigger object above the other two is a still small, and absolutely generic ‘XtremePro Action Cam. The biggest reason for going with these three is — that were already here. The Polaroid was something my wife used in her classroom. The Vouo was purchased for another rocket project several years ago. The ‘XtremePro was a gift from my son.
Unfortunately, that gift camera looks as if it will need to be replaced. In testing over the last week, the Cube ran 106 minutes on a single charge, the ‘XtremePro made it 50 minutes, and the tiny Vouo did just 46 minutes before pooping out. However, further testing showed that the Cube and the Vouo would both record while charging. Attaching them to a $6 power bank from Dollar General allowed them to record for more than 4 hours. In fact, they didn’t stop because batteries ran out. They stopped because they filled a 32g SD card with video.
With total flight time expected to be on the order of three hours, the ‘XtremePro may be out of the running. In fact, I have splurged a whole $34 for a refurbished edition of another camera, so there are still components on the way.
Yes, my friends, that is a Styrofoam minnow bucket. I obtained four of these beauties from the local farm supply store for the extravagant price of $2 apiece. Why did I not use one of the rectangular foam boxes already stacked in the basement from our time trying one of those home food delivery services? Because I thought this looked more like a space capsule, that’s why.
One thing that’s really not clear here is that there will be three “floors” inside the bucket, er, capsule. Right behind the beauteous KOSMOS 1 outer shell you might make out a $1 sheet of foam board. Just in front of the container is a scattering of white things I’ve printed out of my little 3D printer. These items include a lot of plastic rings to reinforce points on the bucket, so that when attaching things like the line to the parachute, the foam doesn’t just rip through. These reinforcements will be paired with zip ties to lock the cameras, computer, and power blocks in place.
They’ll also be used, in classic IKEA bookshelf fashion, to fix two additional floors in the capsule. With the SPOT on the nose, the Spytec tracker will be on the top floor directly below it (testing this week has demonstrated that the foam doesn’t really seem to impede the GPS signal). The next floor down will have the power blocks. Finally, on the ground floor (or bucket lid, if you insist) will be the flight computer and a printed bracket to hold the down-facing camera.
It didn’t make the picture, but I discovered this week that my local Dollar General Store (supplier of all things worth buying) has keychain power supplies for the princely sum of $6. They’re rated at 1250ma, which is on the puny end. But they are rather puny. And light. In test this week, they not only drove the cameras to their limits, but powered the flight computer for 3 hours, 46 minutes. So this is the chosen product for KOSMOS 1. There will be four of these mounted on foam board on the ‘second floor’ of the capsule.
Sir not appearing in this picture
Not yet arrived is the radar reflector. Which is really just a bit of cardboard covered in foil. It’s something I could definitely make, but seeing that this is the first flight, I decided to order one and use it as a model for making more.
Oh, and Sir Appearing In This Picture But Not In This Flight would be the rocket bits in the background. You can see a nosecone that i printed up along with a few more printed parts and some plain vanilla Estes BT-55 body tube.
And that’s … I think that’s it. I’m assembling, touching up the code on the flight computer, conducting tests, and hoping for good weather in the next couple of weeks. When the signs look right, I’ll call Party City for a two-day rental of a helium tank. Which at this point looks as if it will run me around $250.
I’m sure I left out Many Things I promised to talk about last week. So remind me.