Raspberry Crusoe: how a Pi got lost at sea

The tale of the little HAB that could and its three-month journey from Portslade Aldridge Community Academy in the UK to the coast of Denmark.

High-altitude ballooning

Some of you may be familiar with Raspberry Pi being used as the flight computer, or tracker, of high-altitude balloon (HAB) payloads. For those who aren’t, high-altitude ballooning is a relatively simple activity (at least in principle) where a tracker is attached to a large weather balloon which is then released into the atmosphere. While the HAB ascends, the tracker takes pictures and data readings the whole time. Eventually (around 30km up) the balloon bursts, leaving the payload free to descend and be recovered. For a better explanation, I’m handing over to the students of UTC Oxfordshire:


Over the past few years, we’ve seen schools and their students explore the possibilities that high-altitude ballooning offers, and back in 2015 and 2016 we ran Skycademy. The programme was simple enough: get a bunch of educators together in the same space, show them how to launch a balloon flight, and then send them back to their students to try and repeat what they’ve learned. Since the first Skycademy event, a number of participants have carried out launches, and we are extremely proud of each and every one of them.

The case of the vanishing PACA HAB

Not every launch has been a 100% success though. There are many things that can and do go wrong during HAB flights, and watching each launch from the comfort of our office can be a nerve-wracking experience. We had such an experience back in July 2017, during the launch performed by Skycademy graduate and Raspberry Pi Certified Educator Dave Hartley and his students from Portslade Aldridge Community Academy (PACA).

Dave and his team had been working on their payload for some time, and were awaiting suitable weather conditions. Early one Wednesday in July, everything aligned: they had a narrow window of good weather and so set their launch plan in motion. Soon they had assembled the payload in the school grounds and all was ready for the launch.

Just before 11:00, they’d completed their final checks and released their payload into the atmosphere. Over the course of 64 minutes, the HAB steadily rose to an altitude of 25647m, where it captured some amazing pictures before the balloon burst and a rapid descent began.

Soon after the payload began to descend, the team noticed something worrying: their predicted descent path took the payload dangerously far south — it was threatening to land in the sea. As the payload continued to lose altitude, their calculated results kept shifting, alternately predicting a landing on the ground or out to sea. Eventually it became clear that the payload would narrowly overshoot the land, and it finally landed about 2 km out to sea.

Portslade Aldridge Community Academy Skycademy Raspberry Pi High Altitude Ballooning

The path of the balloon

It’s not uncommon for a HAB payload to get lost. There are many ways this can happen, particularly in a narrow country with a prevailing easterly wind like the UK. Payloads can get lost at sea, land somewhere inaccessible, or simply run out of power before they are located and retrieved. So normally, this would be the end of the story for the PACA students — even if the team had had a speedboat to hand, their payload was surely lost for good.

A message from Denmark

However, this is not the end of our story! A couple of months later, I arrived at work and saw this tweet from a colleague:

Good Samaritan Henning Hansen had found a Raspberry Pi washed up on a remote beach in Denmark! While walking a stretch of coast to collect plastic debris for an environmental monitoring project, he came across something unusual near the shore at 55°04’53.0″N and 8°38’46.9″E.

This of course piqued my interest, and we began to investigate the image he had shared on Facebook.

Portslade Aldridge Community Academy Skycademy Raspberry Pi High Altitude Ballooning

Inspecting the photo closely, we noticed a small asset label — the kind of label that, over a year earlier, we’d stuck to each and every bit of Skycademy field kit. We excitedly claimed the kit on behalf of Dave and his students, and contacted Henning to arrange the recovery of the payload. He told us it must have been carried ashore with the tide some time between 21 and 27 September, and probably on 21 September, since that day had the highest tide over the period. This meant the payload must have spent over two months at sea!

From the photo we could tell that the Raspberry Pi had suffered significant corrosion, having been exposed to salt water for so long, and so we felt pessimistic about the chances that there would be any recoverable data on it. However, Henning said that he’d been able to read some files from the FAT partition of the SD card, so all hope was not lost.

After a few weeks and a number of complications around dispatch and delivery (thank you, Henning, for your infinite patience!), Helen collected the HAB from a local Post Office.

Portslade Aldridge Community Academy Skycademy Raspberry Pi High Altitude Ballooning


We set about trying to read the data from the SD card, and eventually became disheartened: despite several attempts, we were unable to read its contents.

In a last-ditch effort, we gave the SD card to Jonathan, one of our engineers, who initially laughed at the prospect of recovering any data from it. But ten minutes later, he returned with news of success!

Since then, we’ve been able to reunite the payload with the PACA launch team, and the students sent us the perfect message to end this story:

Portslade Aldridge Community Academy Skycademy Raspberry Pi High Altitude Ballooning


Shannon Spurling avatar

Awesome! I want to launch one of these. I guess the moral of the story is, make it sea worthy!

Dave Akerman avatar

I recommend an address/phone/email, laminated so keep the water out. Also, take a photo of the label with the camera that’s flying, so there’s a copy on the SD card.

Of course the main recommendation is to choose the flight path carefully and make sure that the balloon is inflated enough, so there’s no risk of it overshooting and landing at sea.


the hatter avatar

Not actually legal to ‘make it seaworthy’, as it happens. International law says that if it lands on the sea, you should make sure that if it’s not recovered quickly, then it should sink (to avoid being a hazard to shipping or wildlife). Not that a small traditional HAB polystyrene box poses much of a hazard but at a minimum, the cable connecting the balloon and capsule, left floating near the surface, could foul a small propellor. So unless you actually have boats at hand and are anticipating a sea recovery, at best your accidental litter may with luck be washed up, found, recognised and returned.

That said, if you’re putting your effort into sealing vulnerable parts and making sure contact information remains visible, that’d be valuable whether your project is lost for a while on land or at sea, and is a better use of your time than trying to engineer buoyancy.

Heston avatar

Ha ha great story and gave me a chuckle for the day. Everything came together for this one from the efforts and determination of many good people. Perfect example of the Pi community I’ve come to known. So don’t give up hope!

Peter D avatar

What did Jonathan the Engineer do to recover the data on the SD card?

Joseph Alway avatar

I’m guessing he used something like Recuva or ddrescue. Though, maybe Jonathan the Engineer will provide details? :-)

jdb avatar

I used cocktail sticks, isopropyl alcohol, a binocular microscope, and a £5 SD card reader.

Modern micro-SD cards are completely encapsulated in epoxy, so they are in theory completely waterproof. The same can’t be said for the exposed contacts, on which rust had adhered to and the edges of the gold fingers had started to corrode.

After I scrubbed those off, I simply put the card in a microSD reader and DD’d the whole disk into a disk image and stored it somewhere safe. The first rule of amateur data recovery is to assume that if you have a working device at present, it may suddenly decide to not work at any point in the future – so copying the data to a known good storage device is the first priority.

After that, it was simply a case of mounting the disk image as a loopback filesystem and copying the relevant subdirectories. ext4 is reasonably tolerant of power failures so even though the power died as the payload got dunked in the sea, most of the pictures were recoverable.

AndrewS avatar

What a fantastic story! The modern equivalent of “message in a bottle” :-)

Vikas Kashyap avatar

wow incredible story and gave me a laugh for the day. Everything met up for this one from the endeavors and assurance of numerous great individuals. Culminate case of the Pi people group I’ve come to known. So don’t surrender trust!

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