Getting to another world is hard. Getting down onto it in one piece is harder. A lander is a spacecraft designed to descend through an atmosphere or fire retrorockets in vacuum, then settle onto the surface and operate there.

Designs vary by destination. Mars landers use heat shields, parachutes, and retro-rockets because the planet has a thin atmosphere. Moon landers rely entirely on engines since there is no air to slow them. Some landers carry rovers, others stay fixed and run experiments in place.

Key subsystems

• Descent engine and propellant tanks
• Landing legs or crushable structures
• Guidance and hazard avoidance sensors
• Power, communication, and thermal control

The final seconds are the most dangerous. Dust kicked up by engine exhaust can blind sensors, and uneven terrain can tip a lander onto its side. Engineers rehearse descent profiles for years before launch.