Over the holidays, I let it be known that I was challenging the heavens, and carefully following FAA regulations, to create my own private space program. Of course, my space program is pretty modest. More of a space-ish program, since the goal is really to launch a series of high altitude balloons that will burst at altitudes above 100,000 feet. Later models of these balloons will attempt to launch a “rockoon” — a small, balloon-lofted rocket. But neither the balloons nor the rocket are likely to come anywhere near the 100 kilometer “Karman Line” that supposedly marks the boundary between Earth and not-so-much Earth.
The Karman line was named after Theodore von Kármán, who set that boundary by looking for the point where craft could no longer be controlled by aerodynamic forces. It’s a line that makes sense for determining how you steer your spaceship, but may not make as much sense in determining “space” in a more meaningful sense.
The X-2 rocket plane reached an altitude of 126,000 feet in 1955. At that altitude, it was above all but less than 1 percent of the atmosphere. It was dark. There were stars. You could see the curve of the planet. For most of us, that might seem pretty much space. However, 98 percent of the lift on the vehicle was still generated by aerodynamic forces. so Kármán put that definitely in the realm of not-space. The Air Force, back in the same era, set a fairly arbitrary boundary for space at 50 miles. That’s an altitude that was reached by several pilots in the X-15 program, and they were promptly awarded astronaut wings. Here. Look at this.
So when Virgin Galactic recently got the VSS Unity up to 82 kilometers, they celebrated reaching space in the sense that they would have earned astronaut wings under NASA’s rules, but critics denied that they had reached space because they fell short of the magical Karman Line. By the way, that X-15 on its record flight was above all about 1/2,000,000 of the atmosphere. That’s definitely space by most standards. And yet those satellites that dare dip as low as 160km don’t remain there long, since there’s still enough drag at that altitude to bring them screaming home.
In any case, see that bottom line? The one way down at the bottom of the graphic. That’s where I’m aiming. Now, let’s go see how to get there.
Okay then. I’m not expecting to cross the Karman Line, or to earn astronaut wings. Instead, I’m aiming at the “hey, that’s pretty good” line, which in this case is defined by 100,000’ elevation. Like all the other lines short of orbit, that’s an arbitrary value, but it has one big advantage — I think I can get there.
And I’m making progress. Take a look at that picture at the top of the article. That represents about $100 worth of electronics scattered with near maximum entropy across my nice white standing desk. Let’s take a look at some of it in more detail.
The biggest object near the center top of this image is an Arduino Mega. It’s a larger version of the Arduino micro-controller, chosen because it was both cheap and large enough for my aged eyes to see (with the help of reading glasses). If you know anything about electronics, then you’ll know what what I have here is known by the technical term of “unholy mess.” However, I haven’t tried to do electronics since transistors were something you bought one at a time, so I’m feeling pretty good about my accomplishment here.
That object hanging off the Arduino on the lower right is a catalex micro-SD drive. The chip pinned to a small board just below the Arduino is a ublox GPS module. The blue thing left is an elegoo temperature and humidity sensor. Below the GPS chip, and still unconnected to anything, is a barometric pressure sensor. There are also a couple of resistors and LED lights, positioned to light up when the GPS is successfully picking of satellites and when the SD drive is successfully writing data.
Paired with all this hardware is some software I’ve cobbled together from examples. Fortunately, I already knew C, so this part is probably the easier end of the equation for me. Right now, this concoction will successfully detect GPS satellites. Once a second, it writes a record into a file on the micro-SD drive that contains time, date, latitude, longitude, elevation, the number of GPS satellites spotted, direction, heading, temperature, and humidity. I want to get the barometric pressure sensor wired up as a backup to the GPS altitude value, just in case the GPS cuts out at high altitude — which can happen.
Over the next week, I intend to get that barometric sensor wired up and add a few more LEDs to track possible issues. Then, after some testing, I will carry the whole thing around to the other side of the basement for some quality time with the soldering iron. Hopefully, the end result will be considerably smaller and neater than the mess in the image.
If you’re wondering what all of this costs, the Ardunio mega is about $10. The GPS component is the most expensive bit, this one cost me $18. The rest of the pieces were under $2 a pop — though in some cases, I had to buy a stack of them. So if you need a spare micro-SD drive or barometric sensor, let me know.
What’s not in here is the APRS radio. The only available chip seems to come from a supplier in the UK, and it’s not going to arrive for some time. So I’m going to go ahead on the first flight without the APRS, trusting to a SPOT satellite unit to let me track down the payload after it hits the ground.
Next week, I’ll hopefully be showing the completed flight computer, the balloon, the parachute, cameras, the SPOT, and progress on the payload container. I’ll also show some sites and tools for calculating how a balloon will behave in flight and just where it might land.
Then, rather than have a tethered balloon test next week, I think I’m going to hold off one more week and, if all is going well, conduct free flight #1. Stay tuned.