I promised I’d tell you if this deployment became un-boring. Well, it did.
At around 10:00 p.m. last Saturday, as I was crawling into bed, the horribly annoying text tone I reserve especially for glider mission aborts came blaring from my phone. A glider had aborted its mission for a device error, meaning that the glider was having an issue with one of its critical systems. The glider had only been deployed for four days.
My fantasy of sleep slowly drifted away.
The glider’s oil pump had stopped and taken itself out of service. The oil pump is indeed a critical system – the glider uses it to adjust its oil volume to change its buoyancy for diving and climbing. When the glider is preparing to dive, it retracts its oil as far into itself as possible, which makes the nose of the glider heavy so that it angles down. It also confines the mass of the glider to a smaller volume, which makes it more dense, and the glider dives. When the glider gets to the depth we specified, it reverses that process. It pumps its oil as far out into the nose as possible, which makes the nose lighter so that it angles up. It also spreads the mass of the glider over a bigger volume, which makes the glider less dense, and the glider climbs back to the surface.
Pretty cool, right? It is, as long as the pump is working. But the pump stopped when the glider was around 240 meters under the surface during a deep dive. The glider was able to restart its pump, surface, and let us know there was a problem.
We’ve seen device errors before. In our experience, they’ve meant that the glider just had a little glitch. Re-starting the mission usually takes care of the problem.
So that’s what I did. I restarted the mission and went to bed. I am not a night owl, even on Saturdays.
Five hours later, at 3 a.m., my phone screamed at me again to alert me to another mission abort. But this abort was much, much worse than the first one. This time, when I opened my laptop, I saw this message:
PROGRAM STARTED WIRE BURNING
My heart sank, right along with our glider.
The pump had failed again right around 240 meters, but this time, it didn’t restart itself. This time, the glider just began sinking.
And sinking, and sinking, and sinking.
Fortunately, once the glider passed a certain depth (1,005 meters, or almost 3,300 feet), it ejected its emergency weight (that’s what “wire burning” means). Ejecting the weight made the glider positively buoyant and it came back up to the surface. Unfortunately, because gliders have to be properly ballasted, or weighted, in order to dive and climb, this glider was unable to dive anymore because it was too light after it ejected its weight. We had to try to find a ship in the area to recover it.
We got lucky. The science and tourism communities in Antarctica recognize that research is crucial for understanding how the Antarctic ecosystem is changing as the environment changes. So when we sent out a call for any ship in the area to rescue our glider, we got an overwhelming response from people wanting to help. The glider was recovered by a nearby tour ship 12 hours after it aborted its mission, and it’s now back in Punta Arenas, Chile, awaiting shipping back to our lab. Even though the glider was only deployed for four days, it still collected valuable data that we are eager to review.
The preliminary cause of the pump failure was a mechanical issue deep in the pump assembly, but we won’t be able to confirm the cause until we get the glider back. This issue would not have been apparent to us during any of our pre-deployment checks.
We still have one glider deployed, and that glider is still having a perfectly boring deployment.