RD-0124

The RD-0124 is a Russian rocket engine that fires high above the ground, giving spacecraft their final push toward orbit. Small, efficient, and clever in its design, it helped modernize one of the most-used rockets in the world.

Quick facts

• Designation: RD-0124 (also known by the Russian index 14D23)
• Maker: KBKhA, in Voronezh, Russia
• Propellants (the fuel and oxidizer it burns): liquid oxygen and RG-1 kerosene, a refined rocket-grade form of kerosene
• Cycle: oxidizer-rich staged combustion (explained below)
• Thrust in vacuum: 294.3 kilonewtons, about 30 tonnes-force — the pushing power it produces
• Specific impulse in vacuum: about 359 seconds — a measure of fuel efficiency
• Chamber pressure: roughly 15.5 to 15.7 megapascals — how hard the burning gases press inside
• Layout: four small steerable combustion chambers driven by one turbopump
• Burn time: about 270 seconds on Soyuz; about 424 seconds for the RD-0124A on Angara
• Dry mass: about 572 kg (548 kg for the RD-0124A variant)
• First flight: 27 December 2006, on Soyuz-2.1b

What it is and how it works

The RD-0124 is a liquid-propellant upper-stage engine, meaning it runs on liquids rather than solid fuel and lights only after a rocket is already high and fast. It burns liquid oxygen with RG-1 kerosene to produce thrust.

Its efficiency comes from a “closed” staged-combustion cycle. Here is the idea in plain terms. A small chamber called a preburner first burns most of the oxygen with a little kerosene to make a stream of hot, oxygen-rich gas. That gas spins a turbine, which drives the turbopumps that force propellant into the engine at high pressure. The trick is what happens next: instead of dumping that gas overboard, the engine routes it into the main chambers and burns it with the remaining kerosene. Almost nothing is wasted, so efficiency rises. Think of it like a wood stove that captures its own smoke and burns it again for extra heat, rather than letting it escape up the chimney.

Before it burns, the kerosene first flows through cooling channels wrapped around the chambers and nozzles, carrying away heat so the metal does not melt. And rather than one large nozzle, the RD-0124 uses four small combustion chambers. Each one can gimbal, meaning it swivels to point the thrust slightly off-center, which steers the rocket during the burn.

Why it matters

The RD-0124 modernized Russia’s workhorse Soyuz rocket and made the newer Angara family possible. It replaced the 1960s-era RD-0110, an older engine that used a simpler “open” cycle and threw away some gas. By switching to a closed cycle, the RD-0124 pushed upper-stage specific impulse up to about 359 seconds — among the highest of any kerosene engine ever flown. That gain let Soyuz-2 carry roughly 950 kg more payload to orbit, making the Soyuz-2.1b far more capable for satellites, science probes, and cargo, and giving Angara a proven, efficient upper stage.

Where it is used and notable examples

• Soyuz-2.1b: the RD-0124 powers the Block I third stage of this widely used Russian launcher.
• Soyuz-2.1v: a light-lift Soyuz variant using the RD-0124 on its Block I upper stage.
• Angara A5 and Angara 1.2: use the RD-0124A version on the URM-2 upper stage, with a longer burn of about 424 seconds.
• RD-0110: the older gas-generator engine that the RD-0124 replaced on Soyuz upper stages.
• RD-0124MS: an announced derivative built from two twin-chamber blocks (four chambers in all), producing about 588 kilonewtons, planned for the future Soyuz-5 rocket.

A hard-won design

The four-chamber layout, inherited from the RD-0110, lets a small upper-stage engine reach high pressure while steering itself, avoiding the need for separate steering thrusters. The oxidizer-rich staged-combustion cycle is very efficient but difficult to build, because hot, high-pressure oxygen-rich gas is fiercely corrosive to metal — a technology Soviet and Russian engineers at bureaus like KBKhA mastered well ahead of the West. Tight funding after the Soviet era slowed the work: ground tests began in 1996, the first flight came in 2006, and full certification arrived only in May 2011, after 225 test firings totaling about 55,000 seconds.