Before 2015, rockets were disposable. After launch, they burned up or crashed into the ocean. That changed when SpaceX landed the first Falcon 9 booster back on Earth. But landing was only half the battle. The real challenge? Flying it again. And again. And again. Today, some Falcon 9 boosters have flown more than 20 times. How? It’s not magic. It’s materials science.

Why Reusable Rockets Need Better Materials

A rocket doesn’t just fly once-it survives extreme heat, freezing cold, violent vibrations, and crushing pressure, all within minutes. Then it does it all over again. Each flight subjects the booster to temperatures from -185°C in the fuel tanks to over 3,000°C during reentry. That’s a 3,200-degree swing in under an hour. Metals expand, contract, crack, oxidize, and fatigue. One tiny flaw can mean a failed landing-or worse.

The goal isn’t just to survive one flight. It’s to survive 20, 30, even 50, with minimal repairs. That’s why SpaceX and others stopped using traditional aerospace alloys and started building rockets like they build smartphones: with upgrades after every use.

The Metal That Made Reusability Possible

Early rockets used aluminum alloys-light, but weak under heat. Falcon 9’s first stage switched to 2195 aluminum-lithium, a high-strength alloy that’s 10% lighter than traditional aluminum and handles stress better. But aluminum melts at just 660°C. Reentry heat? That’s a problem.

Enter stainless steel. Starship, SpaceX’s next-gen rocket, is made mostly of 301 and 304L stainless steel. At first, engineers laughed. Steel is heavy. But it has a melting point of 1,425°C-more than double aluminum’s. It stays strong at cryogenic temperatures. It doesn’t need complex heat shields. And it’s cheap. You can weld it with robots. You can repair it on the launchpad. That’s the secret: reusability isn’t about being the lightest-it’s about being the most repairable.

Engine Parts That Can Take the Heat

The real battlefield is inside the engine. The Merlin engine on Falcon 9 burns fuel at 3,000°C. The Raptor engine on Starship? Even hotter, with pressures over 300 bar. That’s more than 3,000 times atmospheric pressure. No ordinary metal survives that.

Enter Inconel 718 and Inconel X-750. These nickel-based superalloys are used in jet engines and nuclear reactors. They keep their strength even when glowing red-hot. They resist oxidation. They handle thermal cycling-rapid heating and cooling-better than anything else. SpaceX uses them in turbine blades, combustion chambers, and fuel pumps.

But there’s a catch: Inconel is hard to machine. That’s where 3D printing changed everything. SpaceX’s Raptor engine is over 80% 3D-printed. Instead of welding dozens of parts together, they print one piece. Fewer welds mean fewer failure points. A single turbopump housing that once had 100 welds now has maybe 5. And those 5 are stronger because they’re fused as one solid structure.

The Heat Shield That Doesn’t Burn Out

Reentry is brutal. The bottom of the booster hits plasma hotter than lava. Traditional heat shields used on capsules like Apollo were designed to burn away. That’s fine for one-time use. Not for a rocket that flies 20 times.

SpaceX’s solution? A combination of ablative materials and thermal barrier coatings. The Octaweb structure-where the engines attach to the booster-is covered in a special ceramic-based coating that slowly erodes, carrying heat away. After each flight, technicians inspect it with borescopes and touch up damaged spots with laser cladding. This repair technique adds a thin layer of new material to worn areas, extending life by 3 to 5 more flights.

NASA’s GRCop-42, a copper-chromium-niobium alloy, is used in combustion chambers where heat transfer matters most. It conducts heat 100°C better than the old NARloy-Z copper alloy. That means less stress on surrounding parts. Less stress = longer life.

Why Some Engines Last Longer Than Others

Not all rocket engines are built the same. Falcon 9’s Merlin engine uses a gas-generator cycle. It’s less efficient but gentler on parts. That’s why it’s flown 20 times with little more than a fluid flush and a visual check.

Raptor and Blue Origin’s BE-4 use staged combustion cycles. They’re more powerful and efficient, but they’re brutal on materials. Raptor runs at 300+ bar pressure. BE-4 burns oxygen-rich fuel, which eats away at metal like acid. Oxygen can cause metal fires inside the engine-a real risk NASA documented decades ago.

To fight this, engineers are developing new oxygen-compatible coatings. MIT’s Thomas Cordero says these coatings could reduce metal fire risk by 60% and let turbomachinery survive 20+ flights. That’s critical for Starship, which needs to fly dozens of times to make Mars missions affordable.

How They Know When Something’s About to Fail

You can’t just guess when a part is worn out. That’s how rockets explode.

Today, every booster undergoes a detailed post-flight inspection. Borescopes peer inside the combustion chamber. Thermal imaging finds hidden cracks. Eddy current tests detect micro-fractures in welds. Pressure tests check for leaks in fuel lines. All of this used to take weeks. Now? SpaceX does it in under 20 days.

One former SpaceX engineer on Reddit said post-flight checks for routine flights now take less than 24 hours. The key? Modularity. Instead of replacing an entire engine, they swap out just the turbine blade or the fuel injector. That cuts repair time by 40%.

Still, the biggest headache? The heat shield. As one maintenance specialist noted, plasma erosion around the engine bell is the most time-consuming fix. Every time a booster lands, that area takes a beating. It’s like the exhaust pipe on a race car-always the first to wear out.

The Future: 50 Flights and Beyond

The goal isn’t 20 flights. It’s 50. Then 100. That’s what lunar bases and Mars colonies will need.

NASA’s Advanced Materials Project is funding research into ceramic matrix composites that can handle 1,800°C for long periods. These materials could replace metal parts entirely in the hottest zones of the engine. They’re lighter. They’re tougher. And they don’t oxidize.

ASTM, the global materials standards body, is preparing a new standard-F42.90.05-set to release in mid-2024. It will define how to test materials for reuse. No more guesswork. No more proprietary secrets. Just science.

The numbers speak for themselves. In 2017, only 3% of orbital launches used reusable rockets. In 2023, it was 41%. By 2035, Euroconsult predicts 85% will be reusable. That’s not just a trend. It’s a transformation.

What This Means for the Future of Space

Reusable rockets aren’t just cheaper. They’re more reliable. SpaceX’s mission success rate jumped from 80% in 2015 to 98% in 2023-not because they launched more rockets, but because they flew the same ones more often. Each flight gives engineers more data. Each landing teaches them something new.

Satellite companies like Starlink now launch hundreds of satellites per year-every one on a reused booster. NASA’s $2.9 billion contract with SpaceX for the Starship lunar lander was awarded specifically because Starship is fully reusable. No other company could offer that.

Materials science didn’t just make reusability possible. It made space affordable. And that’s the real breakthrough.