Translated from the German original. Read the original in German.
Reusable launch vehicles and their technical challenges
For reusable launch vehicles (RLVs) to succeed commercially, as many components as possible – especially the technologically demanding and expensive ones – must achieve a high rate of reuse.
That requires new design principles and an entirely different approach to risk management. Whereas expendable launch vehicles (ELVs) are designed around a single successful launch, RLV components must work reliably over many launches, re-entries and landings – across their entire service life cycle.
🔩Structural loads
Reuse means repeated load cycles during launch, re-entry and landing. The structures must withstand changing loads – g-forces, aerodynamic pressure peaks, vibration and oscillation – many times over without damage. That demands more intensive testing and more durable materials, which initially drive up development costs but make lower costs per flight possible in the long run.
🔥Thermal loads
Re-entry is the hottest phase of any mission. While ELVs often use simple, single-use ablative heat shields, RLVs must survive extreme thermal cycles. Their thermal protection must not degrade, and it has to be easy to maintain and quick to repair.
For interplanetary missions in particular, this is an enormous challenge. Imagine a crewed Mars landing with the 52-metre-tall Starship: replacing heat-shield tiles on Mars would hardly be practicable – and yet they must provide reliable protection on the return flight and during re-entry at around 40,000 km/h. Surface temperatures can reach up to 2,500 °C.
🚀 The engines
An ELV’s engines are designed for a single flight: ignited once, run until burnout.
On an RLV, by contrast, they must be restartable, durable, maintainable and reliable over many cycles. That calls for new approaches to design, cooling, choice of materials and quality assurance.
One example is SpaceX’s Raptor engines: they are designed for dozens of flights and ignitions – a paradigm shift compared with classic single-use engines. Even during a single mission, the Super Heavy stage fires several times: at launch, for the boostback burn, for the re-entry burn and finally for landing.
Longevity and reusability are not a luxury but the prerequisite for interplanetary spaceflight. Without them, launches remain expensive, rare and technically limited. Only when launch vehicles, engines and thermal protection systems survive many flights does spaceflight become scalable – as routine as aviation is today. Only true reusability will make it possible to transport people and materials regularly between Earth, the Moon and Mars – not as the exception, but as routine.
