Starliner spacecraft returns safely to Earth without astronauts

By Lee Billings

After three agonizing months in space, an orbital mission originally scheduled to last little more than a week ended with a parachute-braked, airbag-cushioned autonomous landing shortly after midnight EDT at NASA’s White Sands Space Harbor in New Mexico.

Starliner — the Boeing-built spacecraft that launched a troubled test flight to the International Space Station (ISS) in June — is finally back on Earth. The same cannot be said for its crew, however: NASA astronauts Butch Wilmore and Suni Williams are remaining aboard the ISS. Last month, space agency officials decided, for safety reasons, to instead fly them home in February 2025 on a tried-and-tested Dragon spacecraft built and operated by Boeing’s spaceflight rival SpaceX. To accommodate this change, two other NASA astronauts, Zena Cardman and Stephanie Wilson, had to be pulled from SpaceX’s next scheduled Dragon flight to the ISS: the Crew 9 mission, scheduled to launch later this month. That leaves two spots open for Wilmore and Williams when Dragon returns to Earth next February.

In search of the dragon

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The successful landing – the Starliner’s third – means Boeing’s program has survived and can fly another day, but much of what happens next is still uncertain.

That test flight was supposed to be the final leg of certifying the Starliner’s readiness for annual flights to the ISS with astronauts. But if the spacecraft doesn’t return with its crew, NASA could require additional test flights before granting that certification — at Boeing’s expense. When the space agency selected Boeing and SpaceX to develop crewed spacecraft in 2014, both companies signed “fixed-price contracts” under which they, not NASA, would pay for cost overruns. In addition, payments from NASA would be contingent on each company hitting certain set milestones. The space agency provided SpaceX with a total of $2.6 billion — and Boeing with $4.2 billion. SpaceX flew its first crewed Dragon to the ISS in May 2020 and has been fulfilling its contractual obligations to NASA ever since. In contrast, Boeing’s Starliner program has been plagued by technical missteps and delays, and quarterly reports from late June showed the company has lost $1.6 billion on the endeavor so far.

At a press conference last month announcing the switch to Dragon as the return vehicle for Wilmore and Williams, NASA Administrator Bill Nelson expressed “100 percent” confidence that Starliner would fly crews again and mentioned that he had recently spoken with Boeing’s new CEO, Kelly Ortberg. “He expressed to me his intention to continue working on the issues once Starliner has safely returned,” Nelson said.

It’s still unclear how and when Starliner will return to crewed flight — and what assurances other spacefaring nations that partner with NASA on the ISS might require before letting their own personnel fly on Boeing’s vehicle. But this much is certain: The company is running out of time to meet its commitments to NASA. The space agency intends to leave the ISS in 2031 — and recently announced that it has contracted SpaceX to do so using a heavily modified Dragon rocket.

The long farewell

Wilmore and Williams closed the Starliner hatch at 1:29 p.m. EDT on Thursday to prepare for the unmanned launch. The vehicle – nicknamed Calypso— undocked from the ISS at 6:04 p.m. EDT on Friday, leaving the astronauts behind as the ISS flew over central China. Moments after undocking, the spacecraft performed a “breakout burn,” a dozen bursts of its auxiliary engines to maneuver itself away from the ISS and avoid colliding with the orbital habitat. Calypso When the space shuttle had shrunk to a point that was barely visible through the ISS’s viewing windows, Williams radioed a simple, almost wistful message to flight control: “It’s on its way home.”

Over the next few hours, the probe underwent a series of diagnostic tests while traveling 56 miles from the ISS. At 11:17 p.m. EDT Calypso began the “deorbit burn,” using auxiliary engines to orient itself while the more powerful main engines fired to propel it through our planet’s atmosphere. During this descent, another burst of auxiliary engines ensured that CalypsoThe empty crew module separated from the service module, which burned up at high altitude as planned.

The fiery end of the service module, necessary to expose a heat shield for Starliner’s return home, was a fundamental obstacle to fixing the spacecraft’s most worrisome mishaps. This disposable module contains 28 auxiliary engines, five of which failed during Starliner’s approach and rendezvous with the ISS on June 6. It was also here that Starliner repeatedly experienced several small leaks of helium, an inert gas used to push fuel through the thrusters. But since the faulty hardware was destined for mid-air destruction rather than recovery and study, the only option was to analyze it remotely and gather as much data as possible in hopes of finding causes – and remedies – before the service module burned up in Earth’s skies.

In the doghouse

Based on these remote investigations, as well as ground-based tests of identical engines, NASA and Boeing engineers attributed the failure of the service module’s five engines to overheating during operation. The service module’s auxiliary engines are mounted in four propulsion capsules, called “doghouses.” Researchers found that these retain more heat than expected when the engines fire, exacerbating the problem. The overheating likely caused Teflon seals to swell and restrict fuel flow, ultimately leading to the failures. In the worst case scenario, such malfunctions could lead to catastrophes, such as the Starliner colliding with the ISS and breaking through the ISS, or tumbling and disintegrating during atmospheric re-entry in a fireball.

Although engineers had identified the likely cause of the engine problems, uncertainties still remained. For example, four of the Starliner’s five failed engines were later repaired — but no one could explain exactly how. In discussions with NASA, Boeing officials nevertheless argued that it was safe to fly the two astronauts home on the spacecraft — an important goal that, if not met, would likely require another budget-busting crewed test flight. But because there was no way to thoroughly examine the engines in orbit to ensure their performance, NASA ultimately felt it was safer to send the Starliner back without Wilmore and Williams.

During the last briefing on the issue, there was “some tension in the room,” Steve Stich, program manager for NASA’s Commercial Crew Program, acknowledged in a pre-flight press conference on Wednesday. “Boeing believed in the model they had developed that tried to predict the degradation of the engines for the rest of the flight… The NASA team looked at the model and saw some limitations, and it really became a question of, ‘Do we have confidence in the engines — and how well can we predict their degradation — from undocking to the deorbit burn?’ And (we) couldn’t get comfortable with that.”

Nevertheless, Stich reiterated during the press conference on Wednesday: “We have confidence in the vehicle … We have had two good (unmanned) landings with Starliner so far and are expecting another one on Friday.”

With that seemingly flawless (but not exactly triumphant) reentry and landing now in the books, Boeing is expected to redouble its efforts to recover from its spaceflight setbacks and restore the Starliner’s tarnished reputation. Whether NASA – or anyone else – can be expected to have any faith in that effort is another question entirely, however.