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LOHAN serves up Raspberry Pi sensorgasmotry

Inside our spaceplane mission's fruity electronics

The Low Orbit Helium Assisted Navigator (LOHAN) team is battling away on several fronts ahead of next month's launch of the Vulture 2 spaceplane, and while there's still plenty of work to do, we do at least have the mission electronics fit for duty.

Click here for a bigger version of the LOHAN graphicOur recent test flight of the Special Project Electronic Altitude Release System (SPEARS) control board proved successful, demonstrating that we can indeed get a rocket motor igniter to go pop at a predetermined altitude.

While SPEARS was quietly going about its business, it was the Raspberry Pi tracker/camera rig aboard our Covert High Altitude Vehicle (CHAV) aircraft which delivered the most entertainment.

This "PiCam" set-up is the work of hydrogen head honcho Dave Akerman, and is an evolution of his tried-and-trusted Pi tracker which had already delivered live Slow Scan Digital Video (SSDV) images from aloft via a webcam.

Naturally, as soon the diminutive PiCam became available, Dave had that off to the stratosphere, with similarly impressive results.

Here's the Pi before insertion into the CHAV's fuselage. The PiCam is in the nose, and you can just see the ribbon cable for that coming out of the back of the aircraft's nose podule:

The CHAV aircraft and the Raspberry Pi rig before assembly

Dave explained: "As usual it has a Radiometrix NTX2 radio transmitter and UBlox GPS receiver, (both from fellow LOHAN team member Anthony Stirks's HAB Supplies), and the camera, all connected to a model A Pi.

"An addition for this flight was a 9-axis IMU (Interial Measurement Unit), which the Pi used to measure and log accelerometer, gyro and compass data as well as temperatures and pressure."

In the event, the tracker proved a tight fit, due largely to the batteries (Energizer Ultimate Lithiums - the high-altitude power source of choice).

Putting the Pi into the CHAV

Putting the Pi into the CHAV

The Pi installed the CHAV's fuselage

Dave said: "We used six AA cells through a switched-mode regulator. The cells were chosen less for their capacity and more for the weight they would bring to the nose of the aircraft. For the flight time we had, just four AAAs would have been enough, but wouldn't have brought the centre-of-gravity far enough forward for flight."

The only physical modification from Dave's previous flights was to use an extended 300mm CSI ("Camera Serial Interface, disappointingly," Dave noted) cable. This was to allow connection of the PiCam to the board before fitting the CHAV node podule to the fuselage.

Regarding software, Dave said: "It was pretty much as on previous flights, except for the logging of all that extra data. The other change was for it to switch the camera to video mode when descending through 2,000 metres, to capture the landing, before switching back to images again. Also, the software was set to send small images at low altitudes and larger images at higher altitudes (above 3,000 metres)."

With the tracker installed, we grabbed a couple of fetching snaps of our plucky Playmonaut and the CHAV's Pi nose artwork:

The CHAV nose podule, with the Playmonaut and Picam

The Raspberry Pi logo on the CHAV nose podule

And the results from the PiCam? We'll get to that in a bit, but first we should raise a well-deserved pint to Anthony Stirk and his miniature PAVA trackers.

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