Why did Elon Musk state that departures to Mars can only occur every two years?

Elon Musk, the founder of SpaceX, has stated that departures to Mars can only occur every two years because of the alignment of Earth and Mars. When Earth and Mars are closest to each other in their orbits around the Sun, it is the ideal time for a spacecraft to make the journey from Earth to Mars. This alignment happens approximately every 26 months, which is why departures to Mars can only occur every two years.

Musk has stated that this is one of the biggest challenges facing SpaceX's plan to colonize Mars. The company's goal is to establish a self-sustaining city on Mars, but this can only be achieved by sending multiple spacecraft to the planet over a period of several years.

Despite this challenge, SpaceX is working on developing the technology to make the journey to Mars possible. The company has already made significant progress with its reusable rocket technology, which has reduced the cost of spaceflight and made it more accessible. SpaceX is also developing a spacecraft called Starship, which is designed to carry humans and cargo to Mars and other destinations in the Solar System.