Every day, thousands of people take the Tube from the north to the south of London or the Channel Tunnel to cross the English Channel. These routes are only possible because of something very important: tunnels that are underwater. But how does someone build something so amazing?

The shield for tunneling
Before French-British engineer Marc Isambard Brunel got an idea from nature in 1818, no one knew how to build an underwater tunnel. After seeing how the shell plates of a shipworm let it cut through wood, Brunel took that idea and made the tunneling shield bigger.

In this case, it was a huge, rectangular mold made of cast iron. The walls had shutter openings that were opened one at a time so that miners could dig into the soft ground outside. The shield was then moved forward with screw jacks, and the process started all over again. In the newly carved area behind, a protective “shell” of bricks was built around the tunnel.

Because of this, the first tunnel under the water was built under the River Thames in London. It was finished in 1842. In later tunnels under the Thames, the air in front of the shield was pressed down to try to stop flooding while the tunnels were being built.

Today, tunneling shields are still used. They are round and usually made of steel, which is also used to make the support rings for the tunnel. Modern versions also use hydraulic jacks to move the shield forward. There is a door in front of the shield that can be used when it’s not moving. Shields also have a protective hood on them for the people who go out to work there.

Machines that dig tunnels
Of course, digging through soft ground is one thing, but boring through rock under the water is something completely different. In this case, tunnel boring machines (TBMs), which were used to build the Channel Tunnel, changed the rules of the game dramatically.

The tunneling shield and the TMB both do the same thing, but the TMB uses a mechanical spinning cutting head to dig through the rock in front of it instead of people. It does this by putting stress on the rock, which breaks it up. There is no need for people to move the broken rock out of the way because it is taken back on a conveyor belt.

There are eleven TMBs that were used to dig the three 56.3-kilometer (35-mile) long tunnels. Some parts of the tunnels are 45 meters (148 feet) below the surface of the water.

Tunnels with immersed tubes
In the first two methods, the tunnel walls are built as the work is done, but there is another way to do it. Immersed tube tunneling is another method. W.J. Wilgus, an American engineer, was the one who created it.

With this method, the tunnel is built somewhere else first, with several sections already built, while a trench is dug into the riverbed or seabed where the tunnel will go. The pieces are then floated to the spot and sunk into place. The water is then drained from them, and dirt from the excavation is put on top of the tunnel to bury it and make the bed level again.

The International Space Station (ISS) has had a busy week. First, a spacewalk had to be called off because coolant water got everywhere in the airlock. The astronauts then had to take cover in the spaceship they were in because there was a report of potentially dangerous space junk coming toward them.

The pieces were made when an old satellite broke apart. Resurs-P1 was a Russian commercial Earth observation satellite that was used until 2021, when it was turned off because some of its equipment stopped working. It wasn’t meant to deorbit, so it just kept going around in a circle about 355 kilometers (221 miles) above our heads. It would have burned up and lost altitude in the end, but on Wednesday, something else happened.

LeoLabs, a company that tracks satellites, says that the satellite broke into more than 100 pieces that can be tracked. The ISS is farther away than their orbit; it is between 413 and 422 kilometers (257 and 262 miles) high. Even so, some of the debris could still hit the ISS, so the astronauts were told to stay inside as a safety measure.

LeoLabs has detected a debris-generating event in Low Earth Orbit.

Early indications are that a non-operational Russian spacecraft, Resurs P1 (SATNO 39186), released a number of fragments between 13:05 UTC 26 June and 00:51 UTC 27 June.

— LeoLabs (@LeoLabs_Space) June 27, 2024

Starting around 8:45 p.m. EDT on Wednesday, June 26, NASA told crews on the space station to take cover in their own spacecraft as a standard safety measure after learning that a satellite had broken up near the station earlier that day. NASA wrote in a blog post that Mission Control kept an eye on the path of the debris and after about an hour, the crew was told they could leave their spacecraft and normal operations returned to the station.

LeoLabs said Thursday afternoon that they were tracking at least 180 pieces of debris, and they expect that number to go up. The sudden breaking apart of the satellite is still not clear, but LeoLabs hopes to be able to figure it out.

Update: We are now tracking at least 180 fragments resulting from this event.

We expect this number to increase in the coming days. We are actively analyzing the debris cloud to characterize it, identify a potential cause, and estimate the impact.

More details to follow. https://t.co/tp3GC9Ti5s

— LeoLabs (@LeoLabs_Space) June 27, 2024

It’s possible that Resurs-P1 was hit by another piece of space junk, which caused a swarm of debris. The object Resurs-P1 is not small; it’s about the size of a van. A van that is going 5 miles per second (8 km/h). It’s very fast, so even a small thing hitting it would do a lot of damage.

A collision of space junk is a big problem because it could cause the Kessler Syndrome, which is a chain reaction of debris that blocks access to a certain orbital region. A lot of people want satellites to have a plan for deorbiting right now to avoid this kind of thing.

People have been interested in the Antikythera mechanism for more than 120 years, and new research has shed more light on this amazing machine in recent years. The pieces that are still there show that it was probably used to figure out things like eclipses and where the planets were in the sky. With some statistical methods that are often used in gravitational wave research, astronomers from the University of Glasgow have found more proof that it is linked to the Moon.

Professor Graham Woan and Dr. Joseph Bayley each used a different method after an interesting X-ray analysis of the object was done years ago. Some people don’t know how many holes are in one of the rings, which is thought to be a calendar. There is only a small piece of the ring left, and it’s hard to say for sure what it is because it spent 2,000 years underwater.

Based on the X-ray data, Woan and Bayley used bayesian statistics to determine how many holes there were in the rings. The most likely number was either 354 or 355 holes, they found. Around 354 days make up a lunar calendar. Based on the research, this number is 100 times more likely than 360 holes, which is what the Egyptian solar calendar has. This means that a 365-hole ring, which would be like a real solar year, is very unlikely.

“Towards the end of last year, a colleague showed me data that YouTuber Chris Budiselic had collected. Budiselic was trying to make a copy of the calendar ring and was looking into ways to find out how many holes it had,” Professor Woan said in a statement. “I thought it was an interesting problem that I might be able to solve in a new way over the Christmas break, so I started using some statistical methods to find the answer.”

The Markov Chain Monte Carlo and nested sampling methods were used. These are common ways to figure out how likely one result is given incomplete data. These techniques lead us to believe that the whole ring was 77.1 millimeters across and had either 354 or 355 holes spaced 0.028 millimeters apart.

“Previous research had suggested that the calendar ring probably followed the lunar calendar, but the two methods we used in this project make it much more likely that this was the case,” Dr. Bayley said. “It’s made me appreciate the Antikythera mechanism and the work and care that Greek craftsmen put into making it even more. To punch the holes so precisely, they would have needed to be measured very accurately and punched with a very steady hand.”

The study has been written up in The Horological Journal.