SpaceX will launch several upgrades for the second launch of its massive Starship large-scale rocket. These improvements include a major change in how the two rocket stages are separated, propulsion system improvements, and a reinforced launch pad in South Texas that should withstand blasting from 33 main engines.
“There are an awful lot of changes between the last spacecraft flight and this one, more than a thousand,” said Elon Musk, founder and CEO of SpaceX. “So I think the probability that this next flight will be successful, and get into orbit, is much higher than the previous flight. Maybe as high as 60 percent. It depends on how well we do in the separation phase.”
Musk outlined some of the modifications to the Starship rocket in a discussion on Twitter Spaces on Saturday with journalist Ashley Vance. He said the next Starship rocket and upgrades to the launch pad at the Starbase facility in South Texas should be ready for the next test flight in about six weeks. “This is the best we know right now,” Musk said.
The Starship is designed to be fully reusable, and SpaceX plans to use it to fly satellites into orbit, build refueling tankers and fuel depots, and eventually ferry cargo and crew to the Moon and Mars. SpaceX’s long-term goal is to replace the Falcon 9 rocket and Dragon crew capsule with a privately funded Starship.
SpaceX officials were pleased with the outcome of the Starship’s first full test flight on April 20, which reached an altitude of about 24 miles (38 kilometers) before spinning out of control after multiple engine failures and the loss of the rocket’s guidance system. The test flight broke the record for the largest and most powerful rocket ever launched—394 feet (120 meters) high and propelled by nearly 15 million pounds of methane-fueled Raptor engines.
The missile is divided into two parts. A booster stage called the Super Heavy with 33 Raptor engines is designed to power the craft through Earth’s atmosphere, then an upper stage with six engines—known simply as a Starship—takes over to accelerate to orbital speed. On operational missions, the Starship’s upper stage can serve as a pusher carrier, payload carrier, or crew compartment.
One of the most significant changes SpaceX has made to the Starship’s design is the separation of the booster from the upper stage, an event that occurs about three minutes after liftoff. The Starship test flight in April did not reach the separation stage.
“We’ve made a kind of late change that’s really significant to the way phase separation works, which is to use what’s called ‘hot staging,’ where we light the engines of the upper stage, or ship, while the first stage, or boost stage, The engines are still running.”
Russian rockets, such as the venerable Soyuz, have used hot-staging technology for decades, but it has not been used on any modern American launch vehicle. Rockets usually shut off their booster engines for a few seconds before discarding the first stage and lighting the upper stage engine.
Musk said SpaceX will shut down most of the Super Heavy booster engines, then fire the engines in the Starship’s upper stage one at a time. The result of the change is that it increases the Starship’s payload-lifting capacity, which already stands at over 100 metric tons in low Earth orbit. But that means engineers must add armor to the top of the stainless steel booster, which SpaceX wants to recover and reuse multiple times.
“Obviously, that kind of blows out the booster, so you have to protect the top of the booster stage from getting burned by the upper stage engines,” Musk said, adding that the design change would add about a 10 percent improvement to the payload capacity of the Starship rocket.
Separating the rocket stages from the booster motors that are already shut down results in a loss of thrust. As the rocket continues to climb temporarily, the Earth’s gravitational pull begins to reduce its speed.
“So you want the ship’s engines to start before the booster engines completely shut off,” Musk said.
Musk said SpaceX is adding an extension to the top of the Super Heavy booster with vents to allow superheated gas from the upper stage engines to flow safely out of the rocket structure “and not just blow itself up.” “This is the most dangerous thing, I think, for the next trip.”
Several of the 33 Raptor engines on the Super Heavy booster either failed to ignite or lost power during the April 20th test launch. Musk said the Starship’s first test flight used a “hodgepodge” of engines built and tested over a year.
For the Starship’s second test flight, SpaceX teams are adjusting manifolds on the Raptor engines that direct hot, methane-rich gas toward each engine’s combustion chamber to mix with the oxygen-rich gas. The earlier design was prone to leaks, as hot gas could escape through the bolt holes used to attach the manifold to the engine. Engineers will introduce an improved manifold design and add more torque to the bolts to address the concern about high-heated gas leakage.
In previous comments, Musk outlined several other upgrades to debut on the spacecraft’s next test flight. This includes electric thrust vector controls to replace the hydraulic steering system used in the April 20 launch, along with a stronger shield around each of the Raptor 33’s boosted engines to protect them from nearby engine explosions, a measure intended to reduce the chance of cascading failure.
One of the most visible areas of work at the Starbase launch site is pouring nearly 1,000 cubic meters of steel-reinforced concrete under the base of the launch pad, where the Starship and its Super Heavy support stand stand before liftoff. During launch in April, the powerful blast from the rocket’s Raptor engines tore a hole in the concrete slab below the launch pad, hurling chunks of material thousands of feet from the pad.
SpaceX will install two thick steel panels over the new layer of reinforced concrete, with channels routed through them to allow water to flow through and release the top.
“Think of it like a giant, upside down shower head,” Musk said. “You’re basically going to push the water up while the rocket is on top of the platform to counteract the massive amount of heat from the booster.”
The Starship’s upcoming test flight plan will also have the rocket remaining on the platform for a shorter period of time, reducing the chance of damage. “We’re actually going to overdo it with the steel and concrete sandwich,” Musk said. “This should leave the base of the pillow in a much better shape than last time.”
Dumping water on a launch pad is not a new concept. SpaceX uses water to dampen acoustic energy on its Falcon 9 launch pads in Florida and California, but managers decided not to use a similar setup at the Starship launch pad in Texas.
“Hindsight is 20/20,” Musk said. “Yes, of course, we are sorry.”
When asked about the most difficult remaining technical challenge for the Starship program, Musk demurred. He said the purpose of the Starship test flights is to “solve the unknowns” about the missile, many of which can’t be fixed until engineers collect data from the actual launch.
One topic Musk did not discuss during his Twitter Spaces chat was a review of the Starship rocket’s flight termination system, which took longer than expected to destroy the craft after it deviated from a previously planned flight path in April. The demolition system works by detonating pyrotechnic canisters to fragment the missile’s fuel tanks and is supposed to cause the vehicle to quickly disintegrate before it threatens populated areas.
The FAA, the regulatory agency tasked with ensuring that missile launches do not endanger the public, will need to review any changes to the destruction regime.
The Starship’s April test flight did not threaten any public areas, but Musk said in remarks shortly after the April 20 test flight that it may take more time to “rehabilitate” the flight termination system than to solve other problems in SpaceX’s schedule before. The next spacecraft launch.
Musk acknowledged on Saturday that it may not be up to SpaceX when the next Starship test launch happens. “There are a lot of variables here that are out of our control.”
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