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On Monday, the two halves of HS2's Wendover "green tunnel" in Buckinghamshire were joined. A green tunnel is a box built in a trench and then buried, so the land on top can be landscaped again. This one hides the high-speed line for 1.4 km.

It is made from 2,740 precast concrete segments that form an "M" shape, with separate bores for northbound and southbound trains. The team built it in two halves. That let digging, building and backfilling go on at the same time. Next come the tunnel entrances, the fit-out and the backfill on top.

After about 20 years of planning, trams reached the TU Delft campus in the Netherlands on 5 October. The 2.5 km extension cost €93m and has six stops, four of them on campus.

The problem was the labs. Trams vibrate and their power supply makes magnetic fields, which can spoil sensitive experiments. The trams turned out worse on both counts than expected. So engineers set the rails in concrete slabs on rubber, to soak up vibration. They also ran the power cables close together between the rails, not overhead, to cut the magnetic field. Even so, trams run only on weekdays from 07:00 to 19:00.

ITER is an international fusion experiment being built in southern France. Its core is a vacuum chamber shaped like a hollow doughnut, where hydrogen will be heated into a plasma. The chamber comes in nine sections. The last one arrived on 2 October, after more than 16 years of work by European manufacturers. Five sections were made in Europe and four in Korea.

Assembled, the chamber will be 19.4 m across, 11.4 m high and weigh about 5,200 tonnes. Every major part of the core machine is now on site. The timeline is still long: research starts in 2034, and fusion fuel isn't due until 2039.

Offshore wind farms have little space for batteries on their platforms. UK firm Verlume has built one that sits on the seabed instead. Its Orah system stores 500 kWh. Its 10-tonne enclosure is 7.2 m long and was squeezed in a pressure chamber in Aberdeen to prove it survives deep water.

It is the largest vessel ever tested at that centre. The full system weighs 85 tonnes. It will go to OranjeWind, a wind farm in the Dutch North Sea. The companies say it will be the first seabed battery at an offshore wind farm that can help keep the grid stable. The planned depth and start date haven't been published.

Last week we reported that AI data centres want to feed their racks at 800 V DC (direct current). The catch is stepping that down towards the roughly 1 V that chips use. Just reaching 6 V normally takes two converters: 800 V to about 50 V, then 50 V to 6 V.

Navitas and Microchip have shown a design that does it in one step. It uses 16 gallium nitride (GaN) transistors, which switch faster and waste less energy than silicon. They switch a million times a second, which lets the other parts shrink. The companies claim up to 96% peak efficiency, and say the unit is about 20% thinner than a phone. It is a reference design for other firms to copy, not a product yet.

DARPA, the US military's research agency, is testing whether any quantum computer could do useful work by 2033. On 7 October it moved four companies to the final stage: Atom Computing, Diraq, IBM and IonQ. They join Microsoft and PsiQuantum, making six.

Both IonQ and Diraq say their deals are worth up to $300m. Diraq builds qubits (quantum bits) in silicon, on the same 300 mm wafers used for normal chips. Among those that did not go through was the UK's Quantum Motion.

Making cement normally means heating limestone in a kiln to about 1,450 °C. That releases a lot of carbon dioxide. Concrete accounts for about 7.5% of the CO₂ humans emit, and the cement is almost 90% of that, Cambridge researchers say.

Their idea, now run by start-up Reclinker, skips the kiln. Steelmakers already add lime to their electric arc furnaces to clean the molten steel. Reclinker replaces that lime with old cement paste recovered from demolished concrete. It comes out of the furnace as new cement clinker. "Thousands of tonnes" have been made at a Cardiff steelworks. This week Reclinker raised £10m. It claims a 50% cut in emissions at first, at the same cost as normal cement. Those are company figures.

Perovskites are cheap crystals that turn sunlight into electricity well in small lab cells. They usually do worse as panels get bigger. Engineers at UNSW in Sydney, with Chinese manufacturer UtmoLight, have made a 30 × 30 cm panel with a certified efficiency of 23.5%. That beats the previous record by 0.6 percentage points.

The trick was removing a nickel-oxide layer. The team hasn't published how long the panel lasts, which is perovskites' big weakness. The next target is a full-size 2.8 m² panel at 18–19%.

Low orbit is filling up with dead satellites and spent rocket stages. Before anyone can clear them up, they need to know how each one is tumbling. NASA's SSPICY mission (Small Spacecraft Propulsion and Inspection Capability) will find out. It uses Otter, a spacecraft "about the size of a washing machine" built by Starfish Space, which launched on 1 October.

From early 2027 it will fly within a few hundred metres (NASA says "hundreds of yards") of up to four dead US objects. It will measure their spin, which way they face and what state their surfaces are in, without touching them. Cameras and software steer it on its own. Its electric thrusters sit on a robotic arm that can point them.

Themis is a test rocket meant to teach Europe how to land and reuse boosters. At Esrange in northern Sweden, ArianeGroup filled it with liquid nitrogen at about −200 °C, to check how it copes with the cold without using real fuel. The European Space Agency (ESA) reported the test on 7 October.

The test also tried out robots that will find the rocket after landing, connect to it and drain leftover fuel. A rehearsal with real liquid oxygen and methane comes next, then an engine firing. The first hop will rise up to 100 m and try to land upright.

Robot hands normally hang from an arm. Researchers at ETH Zurich unbolted one and taught it to walk on its fingertips. It carries an 80 g backpack holding a battery, motion sensor and a small Raspberry Pi computer.

It crawled over 14 different surfaces at an average 9 cm a second. When tipped over, it flipped itself upright in 21 of 25 tries. It also pushed a 41 g cube to targets up to 40 cm away, 15 times in a row. The paper is a preprint, so it hasn't been peer-reviewed yet.

Avoiding something that moves is hard when you don't know where it's going. MIT's planner, called SANDO, needs only one fact about each moving obstacle: its top speed. It surrounds the obstacle with a bubble that grows by that speed over time. Then it plans a path that stays outside every bubble. The guarantee holds only if no obstacle goes faster than its stated top speed.

In 12 real flights, drones using only their own sensors and computers avoided every moving obstacle. The work is in IEEE Transactions on Robotics.

About 1 in 100 babies is born with a heart defect. Children who need a new valve outgrow it, which can mean repeated open-heart surgery. On 1 October, the US Food and Drug Administration (FDA) approved a valve designed to avoid that. It is the Autus valve, made by Edwards Lifesciences.

It goes in at about 13 mm wide. Later, doctors can stretch it to as much as 22 mm with a balloon pushed through a blood vessel. Its flaps are made of polymer, not animal tissue, a first for an FDA-approved valve. In a trial of 62 children, there were no deaths or strokes. Three valve frames cracked, but none caused symptoms. Patients will be followed for 10 years.

In 2017, students in MIT's product-design class 2.009 built a wristband for people with tremors. It vibrates to stimulate stretch sensors in the wrist. That project is now Encora Therapeutics. Its band was cleared by the FDA in February, and MIT told its story this month.

In a 2024 trial of 47 people with essential tremor, a common shaking disorder, over 70% improved. In home use, 78% reported a benefit after 90 days. Some wear it 12 to 14 hours a day.