Ohohia - The Pacific-Crossing Attempt

Here are a few of articles about the success of the TAM5 model aircraft across the Atlantic:
From the B.B.C.
From the AMA - this story may roll off the page in time.
AZCentral.com
globeandmail.com
Sun-Sentinel.com

I was thinking about Ohohia today and realized there is a considerable degree of probability that the plane will wind up in the Pacific Ocean. In the event this were to occur, it would be nice if there was some possibility of recovering it - or at least tracking it for a while until it finally dies.

By design, the electronics payload will be sealed in a watertight canister to ensure two things:
1) That the plane will remain afloat if it goes into the ocean.
2) That the electronics will survive a dip in the sea.

The canister will also provide a stable environment for the electronics, making it easier to maintain stable calibration settings for certain sensors. At least in theory.

So here is a complete wish list of components and sensors that I would like to have on the aircraft. This is not a realistic list, but will merely serve as a starting point. It will be pared down to necessity, but hopefully with room for at least one or two "luxury" items.

Component List:

• IMU (required)


• GPS (required)


• RC4 (required)


• Telemetry data & command transceiver (possible digital image transmission as well)


• Tiny video camera with video frame capture


• Engine exhaust temperature sensor


• Engine RPM sensor


• Alternator voltage output


• Compass heading


• Altimeter


• Air speed sensor


• 6-point minimal LED lighting for nighttime navigation


• XENON strobe for visual indication


• Internal canister temperature sensor


• External temperature sensor


• Electronic fuel mixture adjustment (micro servo?)


• Fuel level sensor


• Battery level/condition sensor


• Battery charge/discharge indicator


• Internal moisture sensor


• External moisture sensor


• Supplemental solar cell

I want the on-board system to be able to detect problems and report them in the event something goes wrong. If the mission fails, I want to know why. Being able to transmit an image from the airplane's perspective could provide much useful information as well. Therefore, I would like to position the camera somewhere where I can at least see the prop. Also, although there is no guarantee that the aircraft would remain upright if it went down, it would be nice if it could continue to take pictures even after it goes down (if it goes down).

By having separate sensors to detect engine RPM, engine exhaust and alternator voltage, the system can distinguish between sensor failure and a critical failure. If the RPM goes to zero, but the exhaust temperature remains up and the alternator is putting out power, we know the RPM sensor was lost and the engine is still running. Similarly, if any one sensor dies, good reading from the remaining two sensors will indicate this. If all three drop, then it is pretty certain that the engine has quit running. At that point, the system can take a quick picture (for verification) and transmit it back to home base before it goes down.

The idea of having a small solar panel is so that if the plane did go down, the system would detect this and go into a sleep mode, shutting down all systems. The solar panel could soak up some energy from the sun during the day, either putting it into the batteries, or charging up a small super capacitor, to maintain or extend the life of the on-board systems. The system would then periodically (like once every two or four hours during
daylight hours) fire up the telemetry systems to collect GPS info and other sensor data and transmit it before going back to sleep.

Perhaps during these telemetry bursts, it could activate the data receiver for a couple minutes, waiting for commands from home base. If it hears nothing, it goes back to sleep to recharge. Otherwise, I could send it a command to take a picture, turn on the XENON strobe, activate the homing beacon, or whatever, before telling it to go back to sleep. Maybe even give it a schedule for future telemetry bursts.

There wouldn't be enough power in the batteries to keep the main processor running, continuously, so this complicates things a bit. Although, I don't know what SBCs are around these days that have standby features that could put it in a minimal power mode that might fit the bill. But since I have a VERY limited budget, I may have to resort to using a microcontroller to control the power of the main board. But this adds another potential point of failure that makes me very nervous. For now, this whole idea is on the wish list and is not critical to the mission. But it is fun to think about. I feel like I'm planning a NASA mission. I want to be able to communicate with my probe!

I figure the moisture sensors will be useful for two reasons: 1) to determine if the airplane is flying through some rain, and 2) to determine if the airship is taking on water (if it has gone down).

I expect to have a useful Flash or Java interface on a web site during the flight so that people can tune in and see the latest telemetry and images.

Well, more later as I think of it. Too many distractions right now.