Elon Musk’s success criteria for Starship test flight: “Don’t blow up the launch pad”

SpaceX’s fully fueled Starship and Super Heavy booster during the first launch attempt Monday, April 17. Credit: SpaceX

Elon Musk, SpaceX’s founder and CEO, did his best to set low expectations heading into the first test flight of the gargantuan Super Heavy booster and Starship rocket this week.

“I would consider anything that does not result in the destruction of the launch mount itself … to be a win,” Musk said Sunday night in a Twitter Spaces meeting with his subscribers.

SpaceX’s first try to launch the first full-scale test flight of the Starship rocket from Texas was cut short April 17 by a frozen valve in the pressurization system for the launch vehicle’s first stage.

The SpaceX launch team fully loaded roughly 10 million pounds of methane and liquid oxygen propellant into the nearly 400-foot-tall (120-meter) rocket Monday. But after the valve problem cropped up, the launch attempt effectively became another countdown dress rehearsal. The countdown continued until T-40 seconds, when SpaceX stopped the clock and began procedures to drain the rocket’s voluminous propellant tanks.

SpaceX technicians spent the last couple of days working around the bottom of the Super Heavy booster, using mobile lifts and booms to reach different parts of the nearly 30-foot-diameter (9-meter-wide) rocket. Ground teams also installed scaffolding to access the rocket’s 33 Raptor engines on the bottom of the Super Heavy booster.

In preparation for the next countdown, more than 100 tanker trucks were expected to deliver fresh liquid nitrogen, liquid oxygen, and methane to the SpaceX launch site, called Starbase. The nitrogen is used to chill the propellants to super-cold temperatures before they are pumped into the rocket.

The Super Heavy booster’s 33 engines will generate more than 16 million pounds of thrust at full throttle, making the Super Heavy and Starship vehicle the most powerful rocket in history, with about twice the thrust of NASA’s Saturn 5 moon rocket from the Apollo program and the more recent Space Launch System moon rocket for the Artemis program.

There’s a good chance something goes wrong before the test flight reaches its full 90-minute duration, according to Musk.

“I guess I’d like to just set expectations low,” Musk said Sunday. “If we get far enough away from the launch pad before something goes wrong, I would consider that to be a success. Just don’t blow up the launch pad.”

The Super Heavy will also surpass the thrust of the Soviet Union’s N1 launch vehicle, which had 30 engines with 10 million pounds of thrust. The N1, however, never reached space on any of its four test flights between 1969 and 1972.

“It’s worth bearing in mind that the Russian N1 rocket, which is the closest comparison to Starship, had a string of failures and never reached orbit,” Musk said. “And that was when the Soviet Union was at peak rocket capability with the “A” team, with maximum stick, maximum carrot, meaning you will be Hero of the Soviet Union if you succeeded, or off to the Gulag if you don’t. So maximum motivation, the A-plus team, and they still failed. It’s worth keeping that in perspective.”

SpaceX’s behemoth stainless steel launch vehicle towers over the coastal wetlands and brush country of South Texas, just a few miles north of the Mexican border. The Super Heavy booster has grid fins and chines, or small aerodynamic protuberances, to help the rocket during descent back to Earth for recovery and reuse.

A controlled water landing of the Super Heavy booster in the Gulf of Mexico is a goal for the upcoming test flight, now set to blast off during a 62-minute launch window opening at 8:28 a.m. CDT (9:28 a.m. EDT; 1328 UTC) Thursday.

A view of the 33 Raptor engines on SpaceX’s Super Heavy booster. Credit: SpaceX

Above Super Heavy sits the Starship vehicle itself, with articulating fins and heat shield tiles to protect the rocket’s metallic structure from the scorching temperatures of re-entry back through the atmosphere.

For the first integrated test flight of this new rocket, the Starship is just a prototype without any operational payloads to deploy into space. In fact, even if everything goes according to plan, the Starship will not reach orbital velocity, and will instead re-enter and impact the Pacific Ocean north of Hawaii after nearly one full lap around the Earth.

SpaceX eventually wants to recover and reuse both stages of the Starship rocket. The company has an ambition to eventually perform daily launches of this giant rocket, with launch facilities in Texas and Florida either operational or under construction.

Commercial satellites, such as those for SpaceX’s own Starlink internet network, could be among the first payloads to fly on Starship. NASA also has a contract with SpaceX to develop a derivative of the Starship rocket as a human-rated lander for the Artemis moon program. That will require SpaceX to test novel and untried technology for in-orbit refueling.

SpaceX says the first attempt to launch a Starship into space is, first and foremost, a learning exercise. SpaceX is in the final stages of assembling new Super Heavy boosters and Starships in Texas for more test launches in the coming months, assuming the Starbase launch pad is not significantly damaged on this week’s test flight.

“It may take us a few kicks of the can here before we reach orbit, and then beyond reaching orbit, we’ve got to bring the booster back and land,” Musk said. “We’ve got to bring the ship back and land. And in order for the reusability to be rapid, it’s got to land where it took off because transporting this gigantic beast around is extremely difficult.”

Musk said he thinks SpaceX can have the Super Heavy and Starship rockets recoverable and rapidly reusable in two or three years. The company wants to eventually retire the Falcon rocket family and Dragon spacecraft in favor of Super Heavy and Starship, although Falcon and Dragon are expected to remain in service launching crews and cargo the space station until the late 2020s.

“This is really kind of the sort of first step in a very long journey that will require many, many flights,” Musk said Monday. “For those that have followed the history of Falcon 9, and Falcon 1 actually, and our attempts at reusability, I think it might have been close to 20 attempts before we actually recovered a stage. And then it took many more flights before we had reusability that was meaningful, where we didn’t have to rebuild the whole rocket.”

After clearing its nearly 500-foot-tall launch pad tower, Super Heavy and Starship will steer on a trajectory east from Starbase over the Gulf of Mexico. The rocket will surpass the speed of sound and maximum aerodynamic pressure in less than a minute, when Starship will endure the harshest structural loads of its ascent into space.

Musk said SpaceX retrofitted the first flight-ready Super Heavy booster, called Booster 7, with shielding to protect its engines from failures of nearby engines.

“This is very important because if you have 33 engines and if any one of them goes wrong, it’s like having a box of grenades, really big grenades,” Musk said.

“It’s both blast shielding and heat shielding at the base of Booster 7 because we realized that the initial shielding that we had was just way too weak,” Musk said. “We’ve taken Booster 7 apart and put it back together again so many times, it is an artisanal rocket … So we just want it to take off and move on to Booster 9 (the next flight-worthy Super Heavy booster).”

The 33 engines on the Super Heavy booster will shut off nearly three minutes into the flight, allowing the booster stage to drop away from the Starship upper stage. Then the Raptor engines on the Starship vehicle will ignite, firing for the first time in the airless void of space to begin a planned six-and-a-half minute burn to accelerate to a speed close to orbital velocity.

Starship’s orbit is expected to be elliptical, or elongated in shape, with a high point, or apogee, nearly 150 miles (250 kilometers) above Earth and a low point, or perigee, at an altitude inside of Earth’s atmosphere.

After separating from the Starship vehicle about three minutes after liftoff, the Super Heavy booster will reignite some of its 33 engines to cancel out its downrange velocity for a “boost-back” burn. Falling toward the Gulf of Mexico, the rocket will be programmed to light a subset of its engines again just before reaching the sea to slow for a controlled splashdown.

Both stages of the Starship vehicle use an autogenous pressurization system in which heated oxygen and methane is routed back into the propellant tanks in a gaseous state to supply pressure, ensuring the liquid oxidizer and fuel smoothly flows into the Raptor engines. Musk said Sunday night that one challenge in the Starship design is making sure the pressurization gases do not get cold enough to liquify in the tanks.

The Starship vehicle will coast around the world, flying over the Straits of Florida, the Atlantic Ocean, Africa, the Indian Ocean, Indonesia, and the Pacific before a scorching re-entry into the atmosphere north of Hawaii. SpaceX hopes to gather data during the ship’s re-entry, but the Starship vehicle will not perform any propulsive landing maneuvers, and therefore won’t be recovered intact.

Both stages of the Starship launch vehicle are designed to be fully reusable, a step forward from SpaceX’s partially reusable Falcon 9 and Falcon Heavy rockets, which require brand new upper stages on each flight.

SpaceX’s concept for recovering the Super Heavy booster involves catching it with articulating “chopstick” arms on the launch tower. The Starship will also use its engines to return through the atmosphere and land back on Earth, or reach the surfaces of other planetary bodies like the moon or Mars. The first Starship orbital test flight, however, will not include any recovery and reuse attempts.

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Follow Stephen Clark on Twitter: @StephenClark1.