Accelerating Starshipby Jeff Foust
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| “Really the point of today’s test is to try to get as much data as we can so we can inform the next iteration of the design of Starship, work those things into flight test number four, and new objectives there that will eventually get us that glorious rapid reusable future that we so badly want,” said Bharadvaj. |
The second flight, in November, made it through staging, only to suffer separate failures of the Super Heavy booster on its descent back to the Gulf of Mexico and the Starship on the final phases of its ascent (see “Starship flies again”, The Space Review, November 20, 2023). SpaceX CEO Elon Musk said in January that the Starship upper stage caught fire when venting excess liquid oxygen late in the burn. “If it had a payload,” he said at a company event at Boca Chica, “it would have made it to orbit because the reason that it actually didn’t quite make it to orbit was we vented the liquid oxygen, and the liquid oxygen ultimately led to a fire and an explosion.”
SpaceX later explained that it carried excess liquid oxygen “to gather data representative of future payload deploy missions and needed to be disposed of prior to reentry to meet required propellant mass targets at splashdown.” In that same statement, SpaceX said the Super Heavy booster had a blocked liquid oxygen line to its Raptor engines during its boostback maneuver “that eventually resulted in one engine failing in a way that resulted in loss of the vehicle.”
Those issues, certainly, would be addressed for the third flight, alternatively called Integrated Flight Test (IFT) 3, Orbital Flight Test (OFT) 3, or simply Flight 3. The question was how much further the flight would get.
“We have some really ambitious goals for today’s test, but really the point of today’s test is to try to get as much data as we can so we can inform the next iteration of the design of Starship, work those things into flight test number four, and new objectives there that will eventually get us that glorious rapid reusable future that we so badly want,” said Siva Bharadvaj, one of the host of SpaceX’s webcast of the launch, just a few minutes before launch.
The rocket got off the ground without incident: a clean countdown, with the only delay caused by ships (shrimpers, SpaceX president Gwynne Shotwell later said) in restricted waters offshore. Two minutes and 45 seconds after liftoff, the vehicle successfully completed “hot staging,” where the Starship upper stage ignited its engines while still attached to Super Heavy, a move designed to increase performance by avoiding any gap in thrust.
As Super Heavy descended towards the Gulf of Mexico, Starship continued its ascent. Eight and a half minutes after liftoff, Starship shut down its six Raptor engines, having reached a speed of neatly 26,500 kilometers per hour. “Nominal orbit insertion,” launch controllers said.
Strictly speaking, Starship was not in orbit. The vehicle was flying a suborbital trajectory, but one that was different from that planned for the first two flights, which would have had Starship splash down near Hawaii 90 minutes after liftoff. This flight was going on a higher trajectory that would bring it down over a stretch of the Indian Ocean about 65 minutes after liftoff. The change in trajectory, the company said, would allow it to carry out additional tests, in particular a brief relight of Starship’s engines, without jeopardizing public safety.
| “Congrats to SpaceX on a successful test flight! Starship has soared into the heavens,” said NASA administrator Bill Nelson. |
Other tests included opening the vehicle’s slot-shaped payload bay doors, dubbed “Pez” doors like the candy because they are designed for the ejection of Starlink satellites, one or two at a time. Another test planed for the in-space phase of the flight was a propellant transfer demonstration, where liquid oxygen would be transferred from one tank inside Starship into another, a step towards vehicle-to-vehicle propellant transfer needed for Starship to go to the Moon and beyond.
During this phase of the flight, SpaceX provided live video of Starship coasting above the atmosphere, slowly rolling, set to, of all things, elevator music. All seemed to be going well until the planned Raptor engine relight, which did not take place a scheduled about 40 minutes after liftoff. The engine burn was not needed to return to Earth, the company emphasized, and the company later said the engine burn was called off “due to vehicle roll rates during coast.”
That roll became a bigger concern as the vehicle began reentry about five minutes later. Some tiles could be seen coming off the vehicle as it approached the upper atmosphere at nearly 27,000 kilometers per hour. Remarkably, a camera mounted on a flap continued to send high-definition video via SpaceX’s Starlink satellites as Starship plunged deeper into the atmosphere and the vehicle was enveloped in plasma.
“This is the first time that we’re getting to collect this reentry data and understand how these 18,000 hexagonal heat shield tiles are working together to protect the belly of Starship,” said SpaceX’s Kate Tice on the webcast. The rolling, though, suggested that parts of the vehicle not protected by those tiles were also being exposed to the heat of reentry.
Finally, about 49 minutes and 30 seconds after liftoff, video and other telemetry was lost from Starship as it descended through an altitude of 65 kilometers. Fifteen minutes later, around the time that Starship was planned to splash down in the Indian Ocean, SpaceX declared that Ship 28, the company’s designation for the vehicle, was lost.
As for Super Heavy, the booster was descending towards what SpaceX called a “soft splashdown” in the Gulf of Mexico. But the vehicle appeared to lose some control in the final few kilometers of its descent. “Super Heavy successfully lit several engines for its first ever landing burn before the vehicle experienced a RUD,” SpaceX later said, using its terminology for “rapid unscheduled disassembly” or explosion. “The booster’s flight concluded at approximately 462 meters in altitude and just under seven minutes into the mission.”
“To make it that far, to demonstrate the controlled reentry up to that point is pretty darn good,” Bharadvaj said shortly after the Super Heavy booster was lost. “That’s something we can learn for the next one.”
 Starship returned live video of its reentry even as it was enveloped in plasma. (credit: SpaceX) |
Picking up the pace
Flight 3 did not achieve all its stated objectives, but clearly went further than the previous two flights. That was enough for SpaceX to declare the mission a success: “HUGE congratulations to the entire team for this incredible day,” Shotwell posted shortly after the end of the mission.
NASA, whose interest in Starship is nearly as high as SpaceX’s, agreed. “Congrats to SpaceX on a successful test flight! Starship has soared into the heavens,” Bill Nelson, NASA administrator, said.
That interest is from the $4 billion in contracts it awarded to SpaceX to develop lunar lander versions of Starship for its Human Landing System (HLS) program. That lander is currently scheduled to take NASA astronauts to the lunar surface for the first time since Apollo 17 on the Artemis 3 mission in late 2026. (An uncrewed demonstration, using the same architecture, is projected for late 2025.)
“With each flight test, SpaceX attempts increasingly ambitious objectives for Starship to learn as much as possible for future mission systems development,” Lisa Watson-Morgan, NASA’s HLS program manager, said in a NASA statement after the launch, noting the flight “allows both NASA and SpaceX to gather crucial data needed for the continued development of Starship HLS.”
| “I’m very excited about the fact that we’ve got four sets of Starships and Super Heavies basically already built at Starbase, ready to go for the next flights,” said SpaceX’s Cummings. |
That included the propellant transfer test that took place while Starship coasted above the atmosphere. That test was part of a NASA “Tipping Point” technology demonstration award to SpaceX, and the agency said it was working with SpaceX to review the data collected, including how the propellant moved between tanks in microgravity conditions and how the vehicle could settle the propellant into the destination tank to ensure a smooth flow into the Raptor engines.
“Storing and transferring cryogenic propellant in orbit has never been attempted on this scale before,” said Jeremy Kenny, manager of NASA’s Cryogenic Fluid Management Portfolio, in a statement. “But this is a game-changing technology that must be developed and matured for science and exploration missions at the Moon, Mars, and those that will venture even deeper into our solar system.”
It is also, of course, a critical technology for SpaceX, since Starship’s HLS design relies on refueling in orbit in order to go to the Moon. How many launches is not clear: a SpaceX official said in January that the company expected “ten-ish” refueling launches for a Starship HLS mission (see “Twenty years of chasing the Moon”, The Space Review, January 15, 2024), while NASA officials last fall suggested the number was closer to 20. The Aerospace Safety Advisory Panel, in its annual report in January, pegged the number at “approximately 15.”
Even if the number of refueling flights comes in the lower end of that range, it will nonetheless require a drastic shift in Starship operations by SpaceX, launching vehicles in quick succession to minimize propellant boiloff in orbit. That will, in turn, make reusability a necessity.
SpaceX is preparing to accelerate flights. Even before Flight 3, Musk said that a fourth flight could take place “shortly thereafter” as the company stockpiles ships and boosters.
“I’m very excited about the fact that we’ve got four sets of Starships and Super Heavies basically already built at Starbase, ready to go for the next flights,” Nick Cummings, senior director of program development at SpaceX, said at the FAA Commercial Space Transportation Conference in February.
That will require support from the FAA, which said it would require SpaceX to perform a mishap investigation after last week’s flight before allowing additional launches, just as it did after the first and second flights.
At the conference, Kelvin Coleman, FAA associate administrator for commercial space transportation, said approvals for subsequent launches would depend on exactly what happened with Flight 3, but added he was aware of SpaceX’s interest in increasing flight rates. “They’re looking at a pretty aggressive launch schedule this year,” he said, with “at least nine” launches proposed for 2024. “We’ll work with them to get them back going as soon as they can.”
The concept of nine or more Starship launches this year is, on one hand, remarkable given the sheer scale of the vehicle. However, it’s also a reminder, like a Starship accelerating towards space, of how much faster SpaceX has to go to meet its own expectations as well as those of NASA.
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