Elon Musk tweeted on Saturday that a team of SpaceX engineers is hours away from completing work on a "tiny kid-sized submarine" that could be used to extract 12 teenagers and preteens who are stranded with their soccer coach in a flooded cave in Thailand. Musk has had a team of engineers working on the problem for the last couple of days and has been keeping the world updated on the work via Twitter.

On Thursday night, Musk tweeted about an idea to use an inflatable nylon tube to help the kids escape. By Friday afternoon, Musk's thinking had evolved. He tweeted that his team was working on building "double-layer Kevlar pressure pods with Teflon coating to slip by rocks." A mid-day tweet on Saturday provided another update:

Got more great feedback from Thailand. Primary path is basically a tiny, kid-size submarine using the liquid oxygen transfer tube of Falcon rocket as hull. Light enough to be carried by 2 divers, small enough to get through narrow gaps. Extremely robust. — Elon Musk (@elonmusk) July 7, 2018

And this isn't just a theory: Musk says that his team is building the contraption now. "Construction complete in about 8 hours, then 17 hour flight to Thailand," Musk tweeted just before noon, California time.

We haven't seen any reaction from Thai authorities to this idea yet, but it could provide a solution to the deadly dilemma facing Thai rescuers. Much of the path out of the cave is flooded, and in places the cave gets as narrow as 70cm. A route that narrow is a big challenge for even the most experienced cave divers—indeed, one diver died ferrying oxygen tanks to the boys earlier this week. Some of the boys don't even know how to swim, and so it might not be possible to provide them with the training necessary to swim out, even with professional help.

Yet waiting may also not be an option. The oxygen level in the boys' location has been dropping. On top of that, Thailand is just entering its rainy season. With heavy rains expected in the coming days, there's a danger that the water level could rise, drowning the group.

The kind of tiny submarine Musk is describing could allow professional divers to bring the boys out without requiring the boys to do anything more than lay still. It would still be a harrowing and claustrophobic experience, but—if everything works as Musk describes—it could be much less dangerous than conventional scuba diving, where a panicking teenager could lead to the death of the teen himself as well as his professional scuba guides.

At the same time, Musk says he's continuing to work on his earlier idea: an "inflatable tube with airlocks" that could be inflated inside the submerged portions of the tube, creating a tunnel the kids could crawl through. In a Friday evening tweet he described this option as "less likely to work, given tricky contours, but great if it does."

Update: In a follow-up tweet, Musk describes some features of the rescue pod.

4 handles/hitch points on front & 4 on rear. 2 air tank connections on front & 2 on rear, allowing 1 to 4 tanks simultaneously connected, all recessed for impact protection w secondary cap seal if leak develops. — Elon Musk (@elonmusk) July 7, 2018

And when someone asked if it had been "Confirmed to maneuver through even the most narrow passages," he answered "yes."