Linux-Powered Amateur Rocket Goes USB
In summer 2005, I stood on a sandy hill a couple miles east of Bend, Oregon. Through my binoculars, I could see people scattered in a distant ring around our 12-foot amateur rocket, waiting to take pictures when it launched. A mile away, I could see the tents and cars at ground control.
I was part of a recovery team for the Portland State Aerospace Society (PSAS). PSAS is a completely open-source aerospace engineering group. You can take our open-source software and open hardware designs from our Web site (see Resources) and make your own rocket. Our long-term goal is to guide our rocket into space actively and put a cube satellite into orbit.
That summer day, we weren't going into orbit; we were just testing our latest rocket. Our rocket would launch, deploy its parachute at about 18,000 feet above the ground, and then drift safely to the ground, all the while spewing sensor data over our 802.11 wireless telemetry link. Once the rocket had landed, the recovery teams would use the GPS coordinates to find the rocket.
Over my 2-meter ham radio, I could hear Andrew Greenberg (PSAS's self-proclaimed “benevolent dictator”) warning the bystanders at the launch site that the rocket motor was about to go live. The DTMF tones to arm the rocket followed.
“...3...2...1. We have liftoff!” The ground crew could see the streaming video from the rocket showing the ground become farther and farther away. The Java RocketView software displayed the rocket's sensor data: GPS coordinates, acceleration, rotation, pressure and the state of all the rocket's subsystems. Everything looked good.
I watched the rocket get smaller and smaller as it shot into the sky. The Linux flight computer on board the rocket would evaluate all the sensor data and decide when to deploy the parachute. The parachute needed to be deployed in the five-second window when the rocket reached its peak altitude (apogee), slowed down and started to fall downward.
At ground control, the crew watched the flight computer decide to deploy the drogue shoot. Everyone cheered, because the hard part of the flight was over. Or so we thought.
Five seconds later, the flight computer figured out that the rocket was still falling. It tried to deploy the main parachute, but it was still accelerating, as if the parachutes hadn't deployed. Something was wrong. Andrew frantically began to send the DTMF tones to the rocket for an emergency parachute deployment. The flight computer reported seeing the DTMF tones, but the rocket continued to plummet toward the ground.
Thirteen seconds later, the link to the flight computer was dead. The last known speed was more than 500mph, with a GPS reading about 1,000 feet off the ground. The depressed ground crew relayed the last-known latitude and longitude from RocketView.
Dave Allen, my fellow recovery team member, was eager to get to the rocket first. Dave and I got as close to the GPS coordinates as we could using the road and a four-wheel drive. Then we started hiking through the desert.
Finally, I spotted a glint of metal in the middle of a scrub brush. About a foot of rocket was sticking out of the ground. If we didn't have the GPS coordinates, it would have been impossible to find.
PSAS members showed up and we began to dig the rocket out. Our 12-foot rocket had been compressed into a three-foot piece of twisted metal. The electronics were dust and bits of broken silicon. Amazingly, Baker, our sock monkey survived. He was a little squished, and his helmet was ripped, but he would fly another day.