A key moment will come 2 minutes and 41 seconds into the next Starship test flight.

Enlarge / SpaceX’s second Starship rocket stands a few feet taller than the first iteration of the full-size vehicle.

SpaceX will have answers to some burning questions in the first three minutes of the next Starship test flight. Did the upgrades to the Starship launch pad in Texas hold up to the rocket’s powerful thrust? Are the rocket’s Raptor engines more reliable than they were on the first Starship test flight in April? And did the rocket’s Super Heavy booster safely separate from the Starship upper stage?

The answers to these questions will show how quickly SpaceX can move forward with everything else it wants to do with Starship. These next steps include launching Starlink Internet satellites, which will expedite the network’s ability to directly connect with consumer cell phones. SpaceX needs to test in-orbit refueling for Starship flights to the Moon for NASA, and engineers want to demonstrate recovering Starship’s giant booster and upper stage, necessary steps to make the rocket fully reusable.

But first, the rocket needs to make it into space. That didn’t happen during Starship’s first full-scale test flight on April 20, but SpaceX learned a lot from that mission. Engineers learned they needed to beef up the launch mount, which took a beating from the Super Heavy booster as it generated more than 15 million pounds of thrust from its methane-fueled Raptor engines.

The upgraded launch pad includes a water-cooled steel plate underneath the pedestal that the Starship rocket sits on during the countdown. SpaceX believes this water deluge design will better handle the heat and acoustic energy from the Super Heavy booster during liftoff. When Starship took off in April, it blasted away concrete chunks from the launch and sent car-size pieces of debris into the surrounding wetlands. That’s something SpaceX wants to avoid this time.

Six of the 33 Raptor engines on the Super Heavy booster failed before liftoff or in flight on the April test launch. Propellant leaks and fires in the booster’s engine compartment eventually severed connection with the rocket’s primary flight computer, and the vehicle lost control a little more than two minutes into the flight. It reached an altitude of around 128,000 feet (39 kilometers), then exploded when a self-destruct mechanism finally engaged about four minutes after liftoff. Debris from the rocket rained down over the Gulf of Mexico.

Although SpaceX first revealed the rocket that became Starship seven years ago, the program is still very much in an experimental phase. Engineers are continually iterating on the design, finding problems, then fixing and testing them. So the second full-scale Starship test launch is, first and foremost, a learning exercise. But let’s face it—some outcomes are better than others.

What does SpaceX need to prove?

The second Starship test flight could happen as soon as next week, perhaps as early as Monday morning, from SpaceX’s launch base near Brownsville, Texas. The final thing standing in the way of a launch attempt is an environmental review by the Federal Aviation Administration and the US Fish and Wildlife Service.

Once that review is complete, which could happen this week, SpaceX will receive its FAA launch license. Technicians will install pyrotechnic charges on the Starship rocket to complete the arming of its flight termination system, the destruct mechanism needed to blow up the vehicle if it veers off course.

Then SpaceX will stack the Starship upper stage on top of the Super Heavy booster to create the fully formed, nearly 400-foot-tall (120-meter) launch vehicle, the largest rocket ever built. On launch morning, SpaceX teams will load more than 10 million pounds of methane and liquid oxygen into the two-stage rocket.

Then it’s go time. If all looks good, computers will issue the command to light the 33 Raptor engines clustered at the bottom of the booster. After a final health check, the automated countdown sequencer will give the green light for liftoff.

Enlarge / A discolored plume of exhaust was visible beneath the Super Heavy booster’s Raptor engines on the Starship rocket’s April 20 test flight, a likely indication of a propellant leak or fire in the engine compartment.

Elon Musk, SpaceX’s founder and CEO, said before the April 20 launch that a successful test flight would mean the rocket didn’t blow up on the launch pad. This time, SpaceX hopes to make it a little further. Ideally, the flight will go into space and reach full duration, a 90-minute trip around the world that will end with a reentry and splashdown of the Starship upper stage in the Pacific Ocean northwest of Hawaii.

Let’s call that a stretch goal. If that’s how the flight ends, you’ll probably hear the hollering all the way from South Texas. It would mean nearly everything worked on the humongous Starship rocket, including all or nearly all of the engines on the booster and upper stage, a daring new method of separating its booster from the upper stage, a brand-new steering system design, the Starship’s ceramic heat shield tiles to protect it during reentry, and complex guidance, navigation, and control algorithms.

It would unlock the next steps in SpaceX’s Starship program. Perhaps SpaceX could meet Musk’s goal of launching Starlink satellites on Starship toward the end of next year. Maybe SpaceX can start demonstrating refueling Starship in orbit, a major milestone for NASA’s Artemis program, which will rely on getting Starship to the Moon to serve as a landing craft for astronauts traveling to the lunar surface.

In June, Musk predicted that there’s a roughly 60 percent chance that Starship will make it to near orbital velocity on the second test flight. The rocket won’t quite attain the speed necessary to reach a stable orbit around Earth, so if it makes it that far, Starship will fall back into the atmosphere over the Pacific Ocean about 90 minutes after launch.

At the other end of the spectrum, let’s assume Starship blows up before clearing the launch pad. That would probably set back the privately run rocket program by at least six months. It took nearly that long for SpaceX to repair the extensive damage, but not destruction, at the launch pad following the April 20 test flight. It might even prompt more scrutiny from regulatory agencies, throwing another wrench into SpaceX’s schedule.

It seems to me that getting through the first three minutes of flight would be enough to show that SpaceX is on the right path with Starship. A successful flight up to that point would mean that SpaceX has mitigated the problems that caused fuel leaks and fires in the engine bay on the April test flight. It would likely also mean that SpaceX has improved the reliability of its Raptor engines and that the rocket’s new electric thrust vector controls, used to gimbal or pivot the Raptors for steering in flight, worked like a charm.

The hot new thing

Heading east from the Texas Gulf Coast, the Super Heavy booster will accelerate the rocket to several times the speed of sound. About two minutes and 39 seconds after launch, the booster will start preparing for separation from the Starship upper stage.

This will happen high above the Gulf of Mexico in the rarefied air of the upper atmosphere. And SpaceX isn’t using the tried-and-true approach to staging it uses on the Falcon 9 rocket, which shuts down its booster engines before detaching from the upper stage, using pneumatic pushers to separate the two main elements of the vehicle. The Falcon 9 then fires its upper stage engine to accelerate and climb into orbit.

In June, Musk revealed a “late-breaking change” to the Starship design. The modification is pretty significant. Instead of separating the lower and upper parts of the rocket without any engines firing, Starship’s upper stage engines will light while the booster is still attached.

This is called a “hot staging” technique. Russian rockets, like the venerable Soyuz, have employed the hot staging technique for decades, but it’s not used on any modern US launch vehicle. On the upcoming test flight, most of the Super Heavy’s 33 engines will shut down two minutes and 39 seconds into the launch, according to a timeline released by SpaceX. Hot staging comes two seconds later with the simultaneous ignition of the Starship upper stage and jettison of the Super Heavy booster.


The hot staging technique has risks, but SpaceX engineers believe they have mitigated them. “Obviously, that results in kind of blasting the booster, so you’ve got to protect the top of the boost stage from getting incinerated by the upper stage engines,” Musk said, adding that the design change would add a roughly 10 percent improvement to the Starship rocket’s payload capacity, which already amounted to more than 100 metric tons to low-Earth orbit.

Engineers have added shielding to protect the top of the stainless steel booster from the engine blast. SpaceX wants to recover and reuse the booster numerous times once Starship is fully operational, so it’s important to reduce damage from stage separation. SpaceX has added a metallic vented ring between the Super Heavy booster and Starship upper stage, a new element that will allow super-heated engine exhaust from the upper stage engines to escape the closed volume between the stages.

Enlarge / The “hot staging ring” installed on top of the Super Heavy booster.

Musk said hot staging is one of more than 1,000 tweaks, upgrades, and modifications to the rocket since the April test flight. Some of the changes were already in the works for the second Starship launch before April, including electric thrust vector controls to replace the hydraulic steering system used on the first Starship test flight.

This next Starship flight will use “Raptor 2” engines similar to the ones flown in April. SpaceX is working on an upgraded “Raptor 3” design to address reliability.

SpaceX has strengthened shielding around the booster’s 33 Raptor engines to protect them from explosions of nearby engines. This is intended to reduce the risk of one engine failure taking out another on the climb into space. Future Raptor engines will have an improved fuel manifold design with fewer leak paths, but for the second Starship flight, technicians have tried to address this concern by torquing bolts tighter on the manifolds.

The Super Heavy booster assigned to the upcoming flight, called Booster 9, also has an expanded fire suppression system to reduce the risk of engine bay fires.

Musk described hot staging as the riskiest part of the second Starship launch. “If the engines light and the ship doesn’t blow itself up during stage separation, then I think we’ve got a decent chance of reaching orbit,” he said last month in remarks at the International Astronautical Congress.

There are six Raptor engines on the Starship upper stage, three with larger nozzles optimized for firing in the vacuum of space and three standard Raptors suited for operating in the atmosphere. SpaceX hasn’t ignited a Raptor engine in space before, so officials are eager to see how the Starship upper stage performs. If all goes well, Starship will fire its upper stage engines for nearly six minutes as it speeds across the Gulf of Mexico toward the Straits of Florida.

At the same time, the Super Heavy booster will attempt a controlled soft splashdown in the ocean just off the Texas coast, validating parts of SpaceX’s plan to land the booster back on its launch pad on future Starship flights.

This will be a can’t-miss event for anyone interested in rockets or space exploration. There are, not surprisingly, higher expectations going into the second Starship test flight than there were back in April. NASA, which has more than $4 billion in contracts to use Starship for Moon landings, will watch closely as the Starship’s second Orbital Flight Test thunders away from Boca Chica Beach.

“I hope everybody is cheering on OFT-2 when it’s time to go because we need that to be successful to get us that much further down the road,” said Jim Free, the NASA official who oversees the Artemis lunar program, in remarks last month.

For NASA, success probably means any outcome that allows SpaceX to move toward the next phase of Starship testing—namely, orbital refueling—sometime over the next year or two. That would keep alive hopes to land Starship on the Moon with astronauts by the late 2020s, which seems realistic even if NASA’s official schedule of 2025 is no longer feasible.

SpaceX’s Starship program is rich in hardware, and the company’s workforce moves fast. There are numerous rockets in various stages of production in South Texas. If the second Starship doesn’t make it to orbit, more vehicles are waiting to fly.

But there are many more hurdles to jump before Starship can start deploying Starlink satellites or flying to the Moon for NASA, the two most significant near-term objectives for the rocket. Clearing just a few of those hurdles later this month would be cause for celebration at SpaceX.


[08 Nov 2023] If the next Starship makes it through staging, you can call that a win
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