I got out and launched some more rockets. Although it doesn’t exactly compare apples to apples, you can see on the image to the right that things either went very wrong with my initial iPhone launch or the GPS data I’m getting is screwed up.

The black line is a flight with the red iPhone rocket but instead of an iPhone I flew a standard altimeter (a PerfectFlite MAWD). The red line is the prediction from RockSim for that flight. You can see it matches almost exactly.

The green line is the plot of the GPS data from the iPhone and the yellow line is the prediction for that flight. You can see it doesn’t match at all.

One would be tempted to think that the time stamps on the GPS data is just stretched out or something, because it would look a lot more normal if you compressed it so it had a faster climb at the beginning and a descent rate like the other flight. But I just checked again and on the video it is a 74 second flight. That is 20 seconds longer than it should have been.

Thus, the only theory that makes sense to me is that the motor burned slow and long. From the video I tried to determine the velocity and acceleration of the launch and it matches the GPS data within uncertainties. So I think the GPS data is good and the problem was with the motor.

As a rocketry dork aside, I was using the Copperhead igniters when I launched the iPhone and I used the FirstFire igniters the 2nd time. I think the Copperheads did not work correctly or I used them incorrectly, because one other flight seemed to have a weird start with them.

I tried to fly both the iPhone and the PerfectFlite altimeter at the same time but I couldn’t get them both to fit in the payload bay. That is the next test I need to to.

We also have a few new things over at Slacker Astronomy.

And did you check out my iPhone app, Bubbler? GIVE ME $0.99 NOW!!!!!

Spread a little too thin sometimes…

Finally, here is video of the 3 launches of my iPhone. The first one is the failed launch due to a motor failure. The 2nd is the one where I got all the data that I’ve posted. The 3rd one I got almost no data but the motor performed better as the flight seemed much more normal.

Sorry Elton! Don’t sue me, but I couldn’t think of a more appropriate song.

iPhone Rocket Launch and Interview (from MobileOrchard.com) from Mobile Orchard on Vimeo.

I’ve been meaning to put my video stuff together but have had some technical difficulties. I’ll get that finished up soon!

If anyone from Apple should stumble upon this: I want to be Apple’s Official Rocketeer! Make it happen, Steve.

This is kind of a cool plot using only the GPS data:

Here is a plot of the first few seconds of the launch from the accelerometer:

You can see that the data peaks at 3g when I was expecting 12g. The acceleration heads back up from negative territory quicker that predicted as well. The prediction is from RASAero.

Here’s the whole flight from the accelerometer:

The red line at 1 at t < 0 the phone is sitting upright in the rocket before launch. Most of the acceleration is in the Y axis at launch but some is in Z as the rocket leans over into the wind. The ejection charge, in theory, goes off at 15 seconds or so but at 22 seconds the accelerometer goes nuts and by 27 seconds the iphone is now inverted, hanging upside down from the parachute. The data dies for some unknown reason when it hits the ground at t=74s.

I need to look for rotation in the X and Z axes with Fourier or something.

The reasons were obvious: the iPhone has a 3D accelerometer in it, as well as GPS, including altitude, network access and a really great development environment (Xcode).

So my goal was to write a program for the iPhone that would log all of the data inside the phone for later retrieval. At the same time I would send out the GPS position over the network to my web server to act as a rocket finder in case it got lost. I had just lost 3 rockets so that was big on my mind. I didn’t want to send my iPhone into a corn field or the middle of the woods and not be able to retrieve it.

So that’s what I did. I wrote the code, built the rocket and launched it! It was one of the most fun geek/dork projects I’ve ever worked on. Let me add that there is nothing very special about this on either the iPhone dev side or the model rocketry side. People do far more interesting things in both regimes. But, as far as I know, no one has ever launched an iPhone in a model rocket. I did it, I didn’t blow up my iPhone in the process, and I got some nice data to play with.

This is only the prelude — more to come!

In the past when Apple had popular product launches you could walk in the store on Day 1 and buy it. Now Apple has joined the ranks of companies so stupid they let supply limit their sales rather than demand. There is a phrase for this: bad planning.