We’re over 80% of the way to our $10,000 funding goal, and there’s only 3 days left. Thanks for all the amazing support so far, you guys are really rather awesome. Now we need your help to push us over the top! If you haven’t donated, please consider doing so now, and please forward our request to all the engineering and space geeks in your life. Help support your local space program!
What Your Money Funds #2: “DxWiFi: Connecting to your laptop, from space”
During our rocket’s flight, we want live data from the sensors on the rocket, especially the video cameras. So how do you talk to a rocket that goes into space? If you thought “radio!” then you’d be absolutely right. But not the usual “space” radio — there are no high power, specialized radios here. One thing that makes PSAS special is that we use a different kind of radio for rockets — we use WiFi, the same WiFi that you use to connect your laptop to the Interwebs.
Wait, what? My WiFi can’t even reach my basement, how do you use it to reach a rocket?
We totally have the same problem with our laptops. WiFi range is just terrible. That’s because it’s meant to be very, very low power, both so that it doesn’t drain your laptop batteries, and also to not interfere with people who are kilometers away.
Solution #1: Turn it up to 11!
To get the range we need, we do something special: we take a test! It’s called the “amateur radio license exam”, and it gives us an “amateur radio license” from the FCC. You have probably heard this referred to as “ham radio”. Under the amateur license, we’re legally allowed to take the WiFi “channel 1” signal, which has a frequency of 2.400 to 2.420 GHz, and amplify the heck out of it. We call this “DxWiFi”, where “DX” means distance in ham radio speak. As hams, we can take the original signal, which is about a milliwatt, and amplify it to as much as 5 watts! 5 watts at 2.4 GHz is uncomfortably close to a microwave oven, however, so we only end up going to 1 Watt (as it turns out, that’s all we need).
Green = bi-directional 2.4 GHz amplifier, red = USB WiFi adapter
Solution #2: Focus, focus, focus
Your laptop spews out its WiFi radio signals in all directions. It has to, because your laptop doesn’t know where your router is, and your laptop’s location changes all the time. But this is really inefficient — it would be much better if you could focus the radio waves, like a flashlight. We can totally do this with the right kind of antennas.
On the ground, it’s easy. We use a very focused antenna called a “helical” antenna. We don’t want a big antenna, so we use a particularly weird kind called a “stubbed helical” with a “semi-parabolic” reflector behind it. We mounted this helical antenna on the “TrackMaster 2000”, a shoulder mounted receive antenna that is manually pointed at the rocket. It has a beam width of 20 degrees, so it’s pretty easy to point. Eventually, though, we’ll automate it with computers and motors.
Erin showing off the stylishly high-tech (and highly focused) wearable Trackmaster 3000
On the rocket, we have a much harder problem, because pointy things that stick out of the rocket tend to rip off at Mach 2. And we can’t just put it inside our rocket, because our rockets are made out of carbon fiber, which is conductive and thus blocks radio waves. So what do we do? We do the same thing the professionals do: use conformal, wraparound patch antennas. Except instead of costing $18,000 each (trust us, we asked), we built our own out of circuit boards and Python scripts for about $200 each. We went to NW EMC (THANKS NW EMC!) to test our antennas, and it turns out they even work well.
Left: Our 3 cylindrical patch antennas. Right: Testing the antennas at NW EMC
Will this crazy thing really work?
Yes! We even tried it. On a plane! To Mt St Helens! Back in January we put our Even Bigger Antennas on the top of Rocky Butte in Portland, pointing north. Then a friend of ours flew her plane from Troutdale north past Mt St Helens, with a small version of our DxWiFi system and a GPS, spewing GPS coordinates. We got packets from over 125 km away!
Left: Rocky Butte. Right: Airplane!
Above: GPS data received from the plane by the Rocky Butte receiver. That’s a WiFi connection past Mt St Helens!
With your help, we’ll bring the DxWiFi system to the next level. We just began collaborating with a team of students from PCC with a high-altitude weather balloon project. They’ll fly a small system to over 100,000 ft, and we’ll try to communicate with it from the ground. We’ll start with 100 km, and work our way up to 500 km. 500 km is all the way from Mt Hood to Boise, Idaho! And if we reach 500 km, you’ll have helped break the world record for WiFi links. And helped prove that we can use WiFi to not only reach space, but even communicate with satellites in Low Earth Orbit (LEO). That’s pretty good for a small donation.
Thanks for your support!