Starship Sails Through Hot-Staging Separation Before Vehicles Are Lost

Starship IFT-2

Credit: SpaceX

BOCA CHICA, Texas—A Starship-Super Heavy vehicle lifted off from SpaceX’s privately owned spaceport on the shores of the Gulf of Mexico on Nov. 18, with all 33 of its first-stage Raptor engines burning as it headed into a second integrated flight test (IFT-2) of the most powerful rocket ever built.

With a deep and powerful roar, the 397-ft. Starship-Super Heavy transport slowly rose from its Boca Chica, Texas, launch mount at 8 a.m. EST (7 a.m. local time) with the primary goal of demonstrating a new first-stage separation system designed following the short-lived IFT-1 on April 20.

For the first time, all 33 of the Super Heavy’s methane-burning Raptor engines ignited and remained firing during ascent, with most shutting down as planned 2 min. 39 sec. after launch. The new hot-staging system was designed to leave three engines burning as the Starship upper stage’s six Raptor engines ignited, a technique designed to boost Starship’s payload capacity by 10%.

Super Heavy then separated and unexpectedly broke apart. If it had remained intact, SpaceX had planned to test the Super Heavy landing system with a boost-back burn, followed by a tail-first descent into the Gulf of Mexico.

Super Heavy’s early demise was upstaged by the steady, six-engine firing of Starship, which was aiming for a looping, suborbital trajectory and a soft landing in the Pacific Ocean north of Hawaii about 80 min. after launch.

However, toward the end of the 6-min. burn, SpaceX reported that Starship’s automated flight termination system had triggered, ending IFT-2.

“Ultimately we had an incredibly successful day,” mission commentator Kate Tice said. “Even though we had a rapid, unscheduled disassembly of both the Super Heavy booster and the ship, we got so much data and that will all help us improve for the next flight.”

The Starship-Super Heavy IFT-2 began at 7 a.m., the opening of an abbreviated, 20-min. window. The launch had been delayed one day for replacement of an actuator in a Super Heavy grid fin, used for aerodynamic control during re-entry.

The Super Heavy first stage is the most powerful rocket in history, capable of producing 16.5 million lb. of thrust at liftoff—twice as much as NASA’s Space Launch System rocket and the Apollo-era Saturn V. Both the Super Heavy and the Starship upper stage are designed to be reflown with little servicing between missions.

SpaceX’s first Starship integrated flight test on April 20 ended 4 min. after liftoff after the Super Heavy booster and Starship upper stage failed to separate following multiple engine failures during ascent and the loss of the rocket’s steering system.

The launch also destroyed Super Heavy’s concrete launch mount, which was rebuilt and upgraded with a water-cooled, steel flame deflector. The powerful water-deluge system is designed to mitigate acoustic energy and vibration from the booster ignition.

Company founder, CEO and Chief Technology Officer Elon Musk said the launchpad repairs were among more than 1,000 upgrades and improvements made for IFT-2, including a more robust electronic steering system to gimbal the engine nozzles and a revamped automated flight termination system. The self-destruct system, intended to ensure a failing rocket does not impact populated areas, was used during IFT-1, with some delay.

In addition to vehicle and ground support fixes, SpaceX addressed 63 FAA-mandated corrections to improve flight safety and performance.

SpaceX says all the work was completed in mid-September and the company waited two more months for the FAA to complete its review and issue a launch license. The authorization to proceed with the flight, which was granted on Nov. 15, applies only to IFT-2.

The review included consultations with the U.S. Fish and Wildlife Service and a written evaluation of the 2022 Programmatic Environmental Assessment. The FAA concluded there were no significant environmental changes.

Musk said in October that Starship had  a decent chance of reaching orbit on its second try, with the riskiest part of the mission being stage separation.

Hot-staging, which is used by the Russians, is intended to increase the vehicle’s performance and simplify the first-stage separation system. “We’re trying to move to a passive stage-sep [separation] system where you don’t have pushers, essentially, to try to eliminate parts. There’s no interstage, like Falcon 9 has,” Musk told reporters during a program update in October.

“In hot-staging, we throttle down and shut down most of the booster engines, then we light the Starship engines. It’s one of the most efficient ways to do stage separation,” he said.  “I’d say that’s the riskiest part of the flight.”

The Starship-Super Heavy stack included a 20,000-lb. “forward heat shield interstage”—a hot-staging ring—with vents for the Starship’s six Raptor engines.

SpaceX is looking to begin operational Starship missions next year, starting with flights to deploy the company’s next-generation Starlink broadband satellites into low Earth orbit. SpaceX would use those Starlink missions to refine techniques and technologies needed to safely reenter and land the Starship upper stage.

SpaceX has been regularly reusing Falcon 9 first stages—the upper stages on the Falcon 9 are not recovered—with the fleet leader completing 18 flights. The latest target is to get to 20 flights per booster, says Bill Gerstenmaier, the company’s vice president of build and flight reliability.

Irene Klotz

Irene Klotz is Senior Space Editor for Aviation Week, based in Cape Canaveral. Before joining Aviation Week in 2017, Irene spent 25 years as a wire service reporter covering human and robotic spaceflight, commercial space, astronomy, science and technology for Reuters and United Press International.


1 Comment
SpaceX quote: "rapid, unscheduled disassembly". Well! While one must salute SpaxeX with its progress and previous amazing achievements, their language remains controversial. Failure apparently is not in their vocabulary. .Certainly, their approach is very different from that seen elsewhere, with their "learn from failure" attitude. But one cannot easily forget that application for the manned moon landing project is fast approaching. For those of us that remember the (few) SATURN 5 trials, (SA501 and 502) the difference to STARSHIP is striking. But then, NASA was government run, and a private enterprise like SpaceX can likely better accept failures if they eventually lead to full success. Jens Hoeg, Herlev, Denmark