Rhenium is a refractory metal used in aerospace applications. Melting point: 3,186 °C. Tensile strength: 1,070 MPa.
Some of the most important parts of a spacecraft never leave their final orbit, and a few of them are made from one of the rarest metals on Earth. Rhenium is the quiet workhorse inside the small engines that nudge satellites and deep-space probes to exactly where they need to be.
Quick facts
- Element: Rhenium, chemical symbol Re, atomic number 75, atomic weight about 186.21.
- Melting point: around 3,186°C (3,459 K) — one of the highest of any element. It boils at about 5,630°C.
- Density: about 21.0 grams per cubic centimeter, among the densest of all elements (only platinum, iridium, and osmium are heavier for their size).
- Rarity: roughly 1 part per billion in Earth’s crust — one of the rarest stable elements. It is pulled out mostly as a byproduct of mining molybdenum and copper.
- Strength when hot: it keeps useful mechanical strength above about 2,200°C, and unusually, it stays ductile (bendable rather than brittle) even when very cold.
What it is and how it works
Rhenium is a silvery, ultra-rare metal prized for one trait above all: it stays solid and strong at temperatures that would melt or soften almost anything else. That makes it ideal for a rocket thruster’s combustion chamber — the container where fuel and oxidizer burn to make hot gas and thrust.
Small engines used in space usually can’t carry the extra plumbing of regenerative cooling (pumping cold propellant through the walls to carry heat away). Instead they are radiation-cooled: the chamber simply glows red- or white-hot and radiates its heat away into space, the way a stovetop element glows and gives off warmth. That only works if the wall can stay strong while glowing, which is exactly rhenium’s gift — it holds together above 2,200°C where most metals fail.
Rhenium has one weakness: in the oxygen-rich exhaust at those temperatures it oxidizes (corrodes) badly. The fix is to line the inside of the chamber with a thin layer of iridium, a platinum-group metal that resists oxidation and acts as a shield between the corrosive gases and the rhenium. These chambers are typically made by electroforming — chemically depositing iridium and then rhenium layer by layer onto a form (a process such as EL-Form) to grow a seamless, iridium-lined rhenium chamber.
Why it matters
In space, an engine’s value comes down to how efficiently it uses its limited, hard-to-resupply propellant. That efficiency is measured as specific impulse — roughly, how much push you get per kilogram of propellant burned. By raising the temperature an engine can survive, iridium-coated rhenium chambers run hotter and burn more completely, giving about 20 seconds more specific impulse than the older niobium (also called columbium) chambers they replaced. For an in-space engine, that is a large gain.
Those extra seconds add up to real outcomes: a satellite can carry more revenue-generating payload, or reach its final orbit with fuel to spare; a deep-space probe can reach a target it otherwise couldn’t. Because these engines run on room-temperature-storable propellants (nitrogen tetroxide and monomethylhydrazine) and need no separate igniter, they have become the standard workhorses for satellite orbit-raising and spacecraft maneuvering. The trade-offs are real — rhenium is among the rarest and most expensive metals on Earth, it is dense, it needs the iridium liner, and the chambers are costly to build — but for high-value missions the performance payoff justifies it.
Where it is used and notable examples
- Aerojet Rocketdyne HiPAT (R-4D-15): a roughly 445-newton iridium/rhenium bipropellant engine that performs apogee insertion and orbit-raising for many commercial communications satellites. Aerojet announced its 100th geosynchronous-satellite apogee insertion using the HiPAT.
- NASA/Aerojet AMBR (Advanced Materials Bipropellant Rocket): developed with NASA Glenn Research Center, with an iridium-coated rhenium chamber (electroformed by Plasma Processes Inc.). It set a storable-propellant efficiency record and demonstrated operation above 4,000°F.
- R-4D engine family heritage: variants of the R-4D — the lineage behind the iridium/rhenium HiPAT — have flown on NASA’s Cassini mission to Saturn and on the ESA ATV and JAXA HTV International Space Station resupply vehicles.
- Geostationary communications satellites: iridium/rhenium apogee thrusters are the standard way to circularize and raise these satellites from their transfer orbit into their final geostationary slots.
- Jet-engine turbine blades (an earthbound cousin): rhenium-bearing nickel single-crystal superalloys, such as those with about 6% rhenium in engines on the F-22 and F-35, use the very same high-temperature strength. In fact, jet-engine superalloys consume roughly 70% of the world’s rhenium — which keeps it scarce and pricey for space.
Re 99.99%+
| DENSITY | 21 kg/m³ |
| TENSILE STRENGTH | 1,070 MPa |
| YIELD STRENGTH | 290 MPa |
| STRENGTH-TO-WEIGHT | 50903.9 kN·m/kg |
| MELTING POINT | 3,186 °C |
| MAX SERVICE TEMPERATURE | 2,000 °C |
| THERMAL CONDUCTIVITY | 47.9 W/m·K |
| THERMAL EXPANSION | 6.2 µm/m·K |
| CATEGORY | Refractory Metal |
| DESIGNATIONS | ASTM B616 |
| MANUFACTURER | Molymet / Rhenium Alloys |
| DENSITY | 21 kg/m³ |
| TENSILE STRENGTH | 1,070 MPa |
| YIELD STRENGTH | 290 MPa |
| MELTING POINT | 3,186 °C |
| MAX SERVICE TEMP | 2,000 °C |
| THERMAL CONDUCTIVITY | 47.9 W/m·K |
| THERMAL EXPANSION | 6.2 µm/m·K |
| CORROSION RESISTANCE | Excellent |
| WELDABILITY | Fair |
| MACHINABILITY | Poor |
| COST RATING | Extremely High |
