SpaceX's Starship rocket exploded again. Elon Musk's Mars dreams remain grounded, for now.

• SpaceX launched Starship and its Super Heavy booster toward space for the second time on Saturday.
• The rocket exploded again, but this time it came within seconds of a successful launch.
• Elon Musk wants Starship to settle Mars. NASA wants it to put astronauts on the moon. But it has to fly first.

SpaceX's Starship mega-rocket has failed to complete a launch to space for the second time.

Seven months after its first explosive test flight, Starship climbed higher than ever, within seconds of success on Saturday morning before it suddenly disappeared and SpaceX lost communications. 

At about 7:02 a.m. Central Time, the booster's array of 33 Raptor engines roared to life and heaved it into the skies above SpaceX's new orbital launchpad in Boca Chica, Texas.

Starship successfully separated from its booster, nailing the maneuver that turned it into a giant fireball last time it flew. This time, the booster exploded as it tumbled back to Earth, but no matter — Starship was still climbing to the heavens.

About six minutes later, however, Starship needed to shut off its engines so that it could coast around the planet. Instead, it stopped sending signals back to the ground.

After a few tense shots of SpaceX CEO Elon Musk speaking with others in what appeared to be the Starship control room, the livestream hosts unceremoniously announced that Starship had met the same explosive fate as its booster — a "rapid unscheduled disassembly."

It's unclear what caused the failure, or how high Starship got before exploding.

Sitting atop its stainless steel Super Heavy booster, Starship stands nearly 400 feet tall. Super Heavy's Raptor engines can produce roughly 16 million pounds of thrust. If Starship had reached space on Saturday, it would have been the largest and most powerful launch system to ever do so. 

Elon Musk's biggest plans hinge on SpaceX's most explosive rocket

Starship is the cornerstone of Elon Musk's grandest plans. He and SpaceX both say the Starship-Super Heavy launch system will one day spit next-generation Starlink internet satellites into orbit, ferry passengers anywhere on Earth in an hour or less, and carry 100 people at a time to Mars to build the first settlement there.

Musk isn't the only one counting on the shiny new launch system. Billionaire Yusaku Maezawa has already booked a trip around the moon aboard Starship. NASA has contracted SpaceX to turn the spacecraft into a lunar lander to put astronauts on the moon's surface again, for the first time since 1972.

All those ambitions rest on Starship's power, yes, but also on its promise of being fully reusable. Starship and its Super Heavy booster are both designed to land themselves safely back on Earth after flight, so that they can be recycled and relaunched another day.

That full reusability should slash the cost of heaving each ton of cargo past Earth's atmosphere and into space — savings that will be crucial for the hundreds of high-powered launches Musk anticipates for building the first city on the red planet.

However, Starship has become famous for its explosions. On several smaller-scale test flights, prototypes of the spaceship have ended in flames through a thrilling variety of explosions and crashes.

SpaceX's explosions aren't necessarily failure in Musk's eyes

The complete Starship-Super Heavy system first attempted to reach space in April. It ended up exploding in a fireball, after Starship and the Super Heavy booster failed to separate at a critical moment of the flight, when the booster had finished pushing Starship through the skies and the spaceship was supposed to continue toward orbit on its own.

The April launch also blasted a giant hole in its launchpad, initiating a volcano-like eruption that rained debris down on towns five miles away.

These exploding Starships are not necessarily failures in Musk's eyes. Unlike NASA or legacy aerospace firms, SpaceX's testing philosophy is to build it, fly it, fix any problems that arise, and fly it again. That's allowed the company to move quickly compared to its competitors.

It's not easy, though. To address the problems of the April flight, SpaceX installed a new system for the separation phase of flight, added a water deluge system to the launchpad to counteract the engines' heat, and reinforced the launchpad with steel.

It took seven months to make all those adjustments, regain regulatory approval for flight, and prepare to launch Starship a second time.

Now that Saturday's launch has likely revealed even more issues, it's not clear how long it will be before Starship can fly again.