Side-by-side photos show 4 major changes made to SpaceX's Starship rocket system after its first launch ended in an explosion

• SpaceX's Starship mega-rocket is "ready to launch" again, CEO Elon Musk said. 
• On its first test flight, the mega-rocket exploded four minutes after liftoff.
• SpaceX made four major changes to help it reach orbit for the first time.

SpaceX made crucial upgrades to its Starship launch system since the rocket last exploded, and it's about to test them out.

The new features, some of which are huge installations visible in photos, could help the world's largest and most powerful rocket finally reach orbit.

The stakes are high. CEO Elon Musk is counting on Starship to establish a human settlement on Mars. The company has also received billions of dollars from NASA to put humans back on the moon for the first time in more than 50 years.

The company has been racing to improve its flagship rocket's flaws ahead of its next launch. On its first attempt, Starship blew up mid-air around three minutes after launch. It blasted a crater through its launchpad that sprayed debris over the area, some of which reportedly rained down on a small town about 5 miles away. 

More than a thousand changes have been made to the rocket since and it is now "ready to launch" again Musk recently said. 

Here are four of the biggest modifications to the rocket, explained by a former SpaceX mission director. 

1. SpaceX added a vent between the rocket and the booster to try a risky new maneuver

SpaceX has added a vent between the two stages of its rocket. This is evidence of a bold change for its next flight: hot staging. 

SpaceX's enormous Starship mega-rocket is made of two stages: the Starship spaceship and its booster, the Super Heavy booster.

The booster generates an immense amount of thrust, heaving the entire system off the ground and through the thickest parts of Earth's atmosphere. The spaceship then separates from the booster miles above the ground to fly off on its own.

Typically, on traditional rockets "the main engines on the booster stage come to a stop, then the second stage lights up after it's been separated," Abhi Tripathi, a former mission director for SpaceX's Dragon spaceship, told Insider.

But for Starship's next launch, the spaceship will start igniting its engines "while still essentially connected" to its booster, said Tripathi, who is now Director of Mission Operations at the University of California's Berkeley's Space Sciences Laboratory.

That's why Starship added the vents — and heavy-duty heat shields — to the top of the booster, so the flames can escape and the rocket doesn't "just blow itself up," Musk told journalist Ashlee Vance in a live interview on X in June.

The upside of this approach is that it gives the spaceship a small but significant boost, increasing the rocket's payload by about 10%, Musk told Vance.

The tradeoff is that hot staging might put the booster at more risk from the flames, a counter-intuitive move for a company that aims to reuse its booster, Tripathi said.

So why did SpaceX decide to take the potential risk? Engineers may have decided it was worth it for better performance, Tripathi said.

2. New protection against booster damage

To the casual observer, the first Starship test flight was going amazingly well until the rocket suddenly burst into flames. But there were clues that something was going wrong long before the explosion.

The live stream of the flight included a diagram of the rocket's 33 raptor engines. This showed two engines dying during the flight, and a third flickered off and on, on top of three that were off from the get-go.

A few engine failures during a flight is no big deal — Starship is so powerful, it could still make it to orbit with less than full thrust, said Tripathi.

But it was a symptom that something was going awry in the booster. A statement later published by SpaceX later explained that a fuel leak inside the booster had caused fires. Because of this, SpaceX lost communication with the rocket's primary flight computer "and, ultimately, control of the vehicle," per the statement.

"If something cascades from the engine to knock out the smarts of your rocket, that's not good," said Tripathi.  

The bigger picture here is that SpaceX probably underestimated the shielding needed to bolster its rocket from the power of its own engines, Tripathi said.

To address this, SpaceX has likely had to add more protection to the components in the booster, Tripathi said. The company said it was adding more systems to control fires onboard.

All of this adds weight, which may have contributed to the decision to move to hot staging, per Tripathi. 

3. A safer self-destruct system?

Wild cheers let off by SpaceX engineers fell to worried hushes at around 2 minutes 45 into the test flight. 

The rocket was due to have separated from its booster, but it had clearly failed. For about a minute, it tumbled out of control, before it burst into a huge fireball.

But that explosion didn't happen immediately, and that is a big problem. 

Starship is fitted with a self-destruct system, which automatically detects when something is going wrong. That system — called the Autonomous Flight Safety System (AFSS) — did set off explosives in the rocket, but only after an "unexpected delay," SpaceX said in a statement on September 8. 

This means the AFSS system did not work as it should have, a matter that would have been taken very seriously by the FAA.

SpaceX is not allowed to share much about the improvements for security reasons, Tripathi said. But the company has confirmed it has "enhanced and requalified the AFSS to improve system reliability."

4.  A 'gigantic upside-down shower head' on the launchpad

During its April launch, the rocket blasted through its launchpad, sending fragments of concrete and other debris flying around the launch site in Boca Chica, Texas.

The debris was spread across 385 acres, including some state park land, and the launch also ignited a 3.5-acre fire in a state park to the south, Bloomberg previously reported. 

This angered local environmental groups who filed a lawsuit against the FAA over their oversight of the launch. 

The problem, Tripathi said, is that SpaceX hasn't built a flame diverter at Boca Chica. A flame diverter is made up of a series of huge tunnels typically built under launchpads to direct flames hundreds of yards away.

It's not immediately clear why this hasn't been done, but it could have to do with the fact Starbase is located near a nature reserve, said Tripathi.

Instead, for Starship's maiden test flight, SpaceX decided to see if they could absorb the force of the flames with a thick concrete launchpad alone.

"As we all saw, that calculation did not go right," said Tripathi. 

Ahead of the next launch, SpaceX has decided to tweak its approach by adding what Musk called a "water-cooled steel sandwich" to the pad, he told Vance in June.

The pad has now been fitted with two thick steel plates along with a water deluge system — essentially a "gigantic upside-down shower head" Musk told Vance.

"It's going to basically blast water upwards while the rocket is over the pad to counteract the massive amount of heat from the booster," he told Vance.

The launchpad has also been reinforced with 35,300 cubic feet of high-strength concrete,

This approach has raised concerns of its own, as the water used to cool the pad could constitute "industrial process water" which is tightly regulated in the US, CNBC previously reported.

The Texas Commission on Environmental Quality (TCEQ) told CNBC that SpaceX had not applied for permits to regulate that water, adding there was "no determination" made as to whether the activity violated environmental laws

The FAA has given the all-clear, but will Starship fly?

Over four months after the first launch, the FAA has said it is ready to allow SpaceX to fly again.

A mishap investigation launched after April's aborted test flight — standard procedure when a flight doesn't go to plan — has now been closed, and SpaceX has likely already made the changes the agency required, Tripathi said. 

Acting Administrator Polly Trottenberg told reporters Wednesday the FAA is "optimistic" a launch license could be issued "sometime next month," per Reuters.

Still, Starship isn't orbit-bound yet.

The FAA will still need to review the changes made to the Starship launch system before it can grant a new license. This includes an environmental review of the new launchpad system, the administration told Insider in an email. 

The lawsuit raised against the FAA's handling of Starship's environmental review could also cause delays. This case "has the potential to delay launches, but only if we bring a motion for an injunction, which we have not done yet," Jared M. Margolis, a Senior Attorney for Center for Biological Diversity, one of the plaintiffs in the case against the FAA, told Insider.

Correction: September 19, 2023 — An earlier version of this article misstated the reason that Tripathi thinks SpaceX switched to hot staging. He thinks the company may have done it for performance gains, not necessarily because new booster reinforcements made Super Heavy heavier.