The next frontier is under your feet

Welcome “subterra”

In today’s Diary:

• Nature’s steam engine switches on

• Robot otters will deliver your food

• Where nuclear waste disappears forever

• The chokepoint no one’s guarding

• A submarine for solid rock

Hey Rational Optimist,

Humans have walked on the Moon and sent a spacecraft 3 billion miles “up,” past Pluto.

Yet the furthest “down” we’ve ever gotten is just 7 miles.

In 1970 Soviet scientists started drilling a hole the width of a dinner plate. They drilled for 19 years and only got 0.2% of the way to the Earth’s core. The rock down there hit 180°C, hot enough to turn metal to mush, so the hole kept squeezing shut around the drill.

The Kola Superdeep Borehole is now a rusted steel cap welded shut in the Arctic.

A frontier can sit quiet for decades. The signal it’s time to pay attention is when many smart people start tackling it from different angles. That’s what’s happening underground today.

A new wave of American entrepreneurs is pulling clean power straight from the planet’s heat… lifting sinking cities out of the mud… delivering coffee through underground pipes… and driving beneath the traffic.

Deep underground, an endless furnace burns hotter than the surface of the sun.

Almost every power plant today, be it nuclear, coal, or gas, is just an elaborate way to boil water into steam. That steam spins turbines and voilà, electricity.

Geothermal is nature’s steam engine. Drill holes into hot underground rocks. Pump water down. Use the hot water or steam to spin turbines and generate power.

Iceland gets around 30% of its power from geothermal, thanks to its boiling mud pits and steam vents. Yet geothermal provides only 0.4% of America’s power today.

Why so little? That heat is typically trapped miles down behind layers of impenetrable rock.

A handful of companies are now devising new ways to tap into the underground furnace.

Fervo Energy is performing precision surgery on the Earth’s crust.

It took the fracking playbook and applied it to geothermal power.

Picture two wells side by side. The first drops about two miles straight down, then bends and runs sideways through the hot granite. Cold water goes down, absorbs the heat, and the second well carries the steam back up.

Google is buying Fervo’s power to feed its AI warehouses. Fervo also signed the largest geothermal power deal ever with Southern California Edison to power 350,000 homes.

Fervo’s flagship plant in Beaver County, Utah, will start sending power to the grid late this year.

Quaise Energy wants to drill deeper than we’ve ever gone before.

Born in MIT’s nuclear fusion lab, Quaise is chasing “superhot” rock where temperatures hit 400°C.

To reach those depths you must drill miles past the point where ordinary drills fail. So Quaise ditched the steel and instead melts rock using millimeter waves, the same technology used to heat plasma inside a fusion reactor.

The “laser” vaporizes granite like a blowtorch through ice:

Source: Quaise

Last summer Quaise fired that beam clean through 100 meters of solid granite. Its goal is to have its first geothermal plant up and running by 2028.

If I had to bet on a geothermal horse, Quaise gets my money. I think it shatters the Soviets’ Kola depth record before this decade is out.

I’m visiting one of Quaise’s test sites outside Austin this week and will tell you all about it.

Imagine a home ATM for anything you want.

You wake up, tap a “cappuccino” button, and walk downstairs. You slide open a drawer in your lobby. Steam hits your face as you open the lid. A few minutes earlier, that coffee was prepared by a barista across the neighborhood.

Impossible? Only for now. Austin startup Pipedream Labs is building a network of underground tunnels for its “Otter” delivery robots to zip through at 60 mph.

Pipedream lays a pipe about two feet wide made of the same tough plastic we use for water mains. Inside, its Otter robots carry a grocery sack that fits more than 95% of the items you typically order from Walmart.

Your order surfaces through a “Portal” on the street that works like a vending machine.

It’s crazy we still have humans driving 3,000-pound cars delivering 1-pound burritos. If Pipedream succeeds it can help unclog our roads. Founder Garrett McCurrach’s goal is to deliver anything in under 10 minutes.

Pipedream’s test site in Peachtree Corners, Georgia, is running food from a restaurant to customers in under 15 seconds. Now it’s working to lay 40 miles of pipe and open 100 Portals in Austin.

Two-foot pipes are fine for moving groceries. But to move people you need a much bigger hole. And how we dig those today makes no sense whatsoever.

We use a half-billion-dollar machine once… and leave it underground to rust.

A traditional tunnel-boring machine costs hundreds of millions of dollars. And after it finishes digging, operators steer it into a side chamber and bury it forever. Seriously!

The Boring Company is doing for tunnels what SpaceX did for rockets: make them reusable so costs fall and learning curves kick in.

Boring Co.’s giant digger, Prufrock, chews forward and builds the tunnel behind it, laying concrete rings as it goes. I got to stand inside one of these rings on a recent trip to Bastrop with ROS cofounders Dan Steinhart and Matt Ridley:

Prufrock can dig for roughly $12 million to $15 million per mile, versus traditional tunnel borers that can cost over $1 billion per mile. It can also bore holes in months that usually take years.

Walk into the Las Vegas Convention Center, and you’ll find a Boring Co. station. You hail a ride, a Tesla pulls up, and it glides you through a one-way tunnel straight to your stop.

The Vegas Loop has 11 stations and has transported more than 4 million riders. Once fully built it’ll be 68 miles of tunnel that can carry you anywhere in the city in under 8 minutes.

The Boring Co. just broke ground on its next project, the Dubai Loop. It’s also digging a tunnel in Nashville that will take you from downtown to the airport in less than 10 minutes.

After two hours touring the Boring Co. last fall, I walked away thinking this might be the next trillion-dollar company.

I’m looking forward to visiting its HQ in Bastrop again soon!

300 million people will face routine coastal flooding by 2050…

And up to now, the best idea anyone has had is… building walls.

A young founder in Berkeley looked at the problem and said, “What if we raise the ground instead?”

Terranova raises land with a material made of wood chips, the same mulch at your local playground. It blends them with water into a slurry and pumps it 40 to 60 feet underground. The land above rises inch by inch, at 2-millimeter precision.

Two robots work the job site. Atlas, a car-sized rover, crawls into position. Prometheus, the injection pod, bolts onto Atlas and delivers the mixture underground.

A third unit, Ark, sits in a shipping container at the edge of the site, blending the slurry and running the fleet over Starlink.

Terranova is the definition of rational optimism. Sea-level rise has always been a “fate” problem: You either build very expensive walls (New York will spend over $100 billion on sea walls) … or you flee.

Terranova is pioneering a third way that doesn’t cost billions of dollars. As founder Laurence Allen told me on a recent ROS podcast episode, it will make sinking cities a problem our grandkids read about in history class.

Glowing green goo, oozing out of a rusting barrel…

That’s what most people picture when they hear nuclear waste.

The reality is all the atomic waste America produced in 60 years would fit on a single football field stacked less than 10 yards high. Right now that waste sits safely in concrete casks at about 80 sites across nearly 40 states.

But nobody wants to babysit radioactive goo. The better option is to bury it underground like Finland is about to do.

Finland built a cave 430 meters down where spent fuel goes into copper canisters. The canisters then go into the ancient rock built to hold them for 100,000 years.

Deep Isolation is bringing that technology to America.

I chatted with CEO Rod Baltzer, who walked me through how it works. First, drill a borehole about the width of a pizza box. The hole stretches up to three miles down, then curves sideways like an L-shaped straw. Slide a sealed corrosion-proof canister to the bottom and you’re done.

In January 2026 Deep Isolation broke ground on a full-scale demo in Cameron, Texas.

If you can lower a canister of waste down a borehole… why not lower a reactor?

That’s what its sister company Deep Fission is doing.

A normal nuclear plant spends a fortune on a giant steel-and-concrete dome to contain the reactor. Deep Fission deletes that step by dropping a small reactor a mile down a borehole, turning the ground into the containment.

Sounds like a gimmick, but it was picked for the Department of Energy’s reactor pilot program. Deep Fission is drilling its first test wells in Parsons, Kansas, as I write… and it just went public to fund the build.

For all of history, war has had four domains...

Land, sea, air, and space. Traysar founder Yadin Soffer says there’s a fifth domain beneath your feet, which he calls “subterra.”

Before the submarine, naval warfare happened entirely on the surface. Then one machine learned to move underwater and war at sea was never the same. Traysar wants to do that for subterra.

Soffer is Israeli. Traysar is his answer to the October 7 attacks. One of his co-founders spent his army years in the IDF unit whose job was hunting and destroying Hamas’s tunnels by hand.

In Gaza, Hamas built an estimated 500 kilometers of tunnels... basically an entire subterranean city! And in Ukraine the skies are so thick with attack drones the surface has become a no-man’s land. Both sides are digging tunnels and moving underground.

Traysar is building two machines to crack open subterra. The first is an autonomous robot that crawls into an enemy’s tunnels, maps them in pitch dark, and clears them.

The second is a high-speed burrowing machine that drills its own path through rock to reach a buried target from below. It’s basically a torpedo that can move through solid ground, built to hit the bunkers even a 30,000-pound bomb can’t.

Traysar’s engineers come straight from SpaceX and The Boring Company. Traysar’s big breakthrough is boring without excavation—no mountain of dirt to haul away—in a rig small enough to fit on a truck.

Soffer told me building subterra machines is…

“Harder than rocket science.”

With a rocket, you know the forces you’re fighting. The physics is the same every launch. Underground, the rock changes foot by foot, and you’re flying blind.

The real unlock, he says, is the sensing: reading the geology ahead so the machine can steer through it. Today when you bomb a tunnel, you often can’t even tell whether you destroyed it!

To Traysar the Earth’s crust is “the new strategic chokepoint.” More than 10,000 known facilities are already buried around the world, and almost nothing in the U.S. defense budget is aimed at them. Traysar is the first company actually building the machines to fight there. I’m hoping to meet the team soon.

I’m confident the winners in this new subterranean arena will be startups like Traysar. Unlike on land or in the air, nobody has a 50-year head start underground. The edge will go to whoever’s fastest and most willing to build the strange new thing.

Why is the subterranean domain suddenly opening?

Around 2010 a handful of Texans figured out how to pull oil and gas out of solid shale. “Fracking” worked so well America now pumps more oil than Saudi Arabia!

These engineers invented steerable drills, high-pressure pumps and fiber-optic sensors that “listen” to rock. This turned underground from a luck business into an engineering challenge.

Next came robots. The same self-driving brains we built for cars are what allow Pipedream to run couriers through a pipe… Terranova to drive a 12,000-pound digger from a phone… and Traysar to map an enemy tunnel.

The companies in today’s Diary are just the opening act. The real subterranean fortunes are yet to be made.

And remember your #1 job as a rational optimist: Make sure to share our content to help us bring more rational optimists into the fold.

—Stephen McBride

P.S.: The most important part of opening a new frontier is keeping it open.

We’ve had the technology to fly much faster for decades. Yet 53 years ago, Washington banned supersonic flight over land because a vocal minority complained about the sonic booms.

Last week the FAA moved to scrap the ban, clearing the runway for a new wave of startups to go supersonic. There’s just one catch: You still can’t make a sonic boom. As we covered in our Deep Dive on supersonic flight, “boomless” supersonic flight is exactly what Blake Scholl’s Boom Supersonic is perfecting.

Crack that, and the sky finally loses its speed limit.