On 15 April 1988, a modified Tupolev Tu-154 airliner took off from Moscow's Zhukovsky airfield with one of its three engines running on liquid hydrogen. It climbed to altitude, flew a circuit, and landed without incident. The aircraft was designated Tu-155, and it was — for a brief, extraordinary moment — the most advanced propulsion experiment in aviation history.

Thirty-eight years later, as Airbus, Boeing, and a constellation of startups race to develop hydrogen-powered commercial aircraft, the Tu-155 remains the only full-size airliner ever to have flown on hydrogen fuel. The Soviet Union got there first. Then it collapsed, and the project died with it.

The Cryogenic Engine

The Tu-155 programme began in 1980 under the direction of the Tupolev Design Bureau, with the goal of proving that cryogenic fuels — liquid hydrogen (LH2) and later liquefied natural gas (LNG) — could power a commercial airliner. The host aircraft was a standard Tu-154B, the Soviet Union's workhorse medium-range airliner, with the starboard (No. 3) engine replaced by a modified Kuznetsov NK-88 turbofan designed to burn hydrogen.

The engineering challenges were formidable. Liquid hydrogen must be stored at -253°C — just 20 degrees above absolute zero. The fuel tank, installed in the rear fuselage where passenger seats would normally sit, was a vacuum-insulated cryogenic vessel weighing over a tonne empty. The fuel delivery system required entirely new pumps, valves, and seals capable of handling a fluid that boils at room temperature and leaks through almost any material. The combustion chamber of the NK-88 was redesigned to handle hydrogen's dramatically different flame characteristics: hydrogen burns hotter, faster, and with an almost invisible flame.

Despite these obstacles, the Tu-155 flew successfully. A total of five flights were conducted on liquid hydrogen in April 1988, followed by more than 100 flights on liquefied natural gas (LNG) between 1989 and 1990. The LNG flights were operationally significant: the aircraft flew routes from Moscow to Bratislava, Hannover, and Nice, demonstrating that cryogenic fuel could sustain a normal commercial flight profile.

Why Hydrogen?

The Soviet interest in hydrogen was driven by energy security rather than environmental concern. The USSR's vast natural gas reserves made LNG an attractive alternative to kerosene, which required oil refining capacity that the Soviet economy struggled to maintain. Hydrogen, producible by electrolysis from water using nuclear-generated electricity, offered an even more strategically independent fuel source.

But the physics of hydrogen also offered genuine performance advantages. Hydrogen has roughly 2.8 times the energy per kilogram of kerosene. An aircraft burning hydrogen produces only water vapour as exhaust — no CO2, no particulates, no sulphur compounds. In an era when climate change was not yet a political priority, these characteristics were noted by Soviet engineers as long-term benefits worth pursuing.

The catch — and it is a significant one — is density. Liquid hydrogen has roughly one-quarter the energy per litre of kerosene. To carry the same total energy, a hydrogen aircraft needs fuel tanks four times larger by volume. This is why the Tu-155's hydrogen tank consumed a large section of the passenger cabin, and why every modern hydrogen aircraft concept — from Airbus's ZEROe to startups like ZeroAvia and Universal Hydrogen — wrestles with the same fundamental trade-off between fuel weight and fuel volume.

The Tu-156: The Airliner That Never Was

Encouraged by the Tu-155's success, Tupolev proposed the Tu-156 — a purpose-built hydrogen/LNG-powered airliner based on the Tu-204 airframe, with all three engines converted to cryogenic fuel and redesigned integral fuel tanks. The Tu-156 was intended to enter service in the mid-1990s, carrying up to 164 passengers on medium-range routes.

It never left the drawing board. The collapse of the Soviet Union in 1991 ended state funding for almost every advanced aviation programme. The cryogenic fuel infrastructure that would have been needed — hydrogen liquefaction plants at airports, insulated refuelling systems, safety protocols — was never built. The Tu-155 prototype was grounded, eventually parked at the Gromov Flight Research Institute, and largely forgotten.

The Modern Echo

Nearly four decades later, the aviation industry has rediscovered what Soviet engineers already proved: hydrogen can fly. Airbus has committed to entering a hydrogen-powered airliner into service by 2035 under its ZEROe programme. Rolls-Royce and easyJet successfully ground-tested a hydrogen-burning AE 2100-A turboprop engine in 2022. ZeroAvia is flight-testing hydrogen fuel cell powertrains on modified Dornier 228 commuter aircraft.

Every one of these programmes faces the same challenges the Tu-155 team solved in the 1980s: cryogenic storage, fuel delivery, combustion dynamics, and the brutal volumetric penalty of liquid hydrogen. The difference is that in 2026, the motivation is not energy security but climate survival — and the engineering tools available (computational fluid dynamics, advanced composites, solid-state hydrogen storage) are a generation beyond what Tupolev's team had.

The Tu-155 is often cited in modern hydrogen aviation literature, but rarely given the credit it deserves. It was not a concept study. It was not a subscale demonstrator. It was a full-size, three-engine airliner that flew on hydrogen and proved the concept worked — thirty-eight years before anyone else managed to do the same.

The prototype still sits at Zhukovsky, weathered and largely ignored. If Airbus succeeds with ZEROe in 2035, the engineers who made it work might want to visit Moscow and pay their respects. The Soviet Union got there first.

Sources: Tupolev Design Bureau archives, Aviation Week, Flight International, Royal Aeronautical Society